Concrete Raising Services in Crystal Lake

Concrete Raising Services in Crystal Lake

Garage Floor Lifting

The root of the problem often lies beneath the surface. In most cases, the area is ready to use the same day. Building on the remarkable revitalization of Crystal Lake's concrete landscapes, let's explore how Acme Concrete's polyurethane raising technique has directly benefited our clients through their success stories.

Sunken Concrete

  1. Interior Floor Lifting
  2. Polyurethane Foam Injection
  3. Basement Floor Lifting
  4. Concrete Raising Reviews
  5. Settled Concrete Solutions
  6. Slab Leveling Solutions
  7. Sidewalk Leveling
  8. Void Filling
  9. Porch Leveling
  10. Concrete Pressure Grouting
  11. Concrete Driveway Maintenance
  12. Concrete Contractors Crystal Lake
  13. Crystal Lake Mudjacking Company
  14. Quick Concrete Lifting Service
  15. Crystal Lake Foundation Contractors
  16. Concrete Crack Repair
  17. Fast Concrete Repair
  18. Uneven Concrete Repair
  19. Sunken Walkway Fix
With every repair, they're not just fixing a crack or leveling a slab; they're enhancing the visual harmony of the surroundings. Learn more about Affordable Sidewalk and Driveway Lifting in Crystal Lake, IL here. Learn more about Concrete Raising Services in Crystal Lake here
After the initial meeting, they'll devise a plan that's specifically designed for your situation. You've seen the process, now let's dive into the real-life results that have truly made a difference. The materials used are heavier and can contribute to further soil erosion and settling.
It's a two-part compound that, when mixed, expands rapidly to fill voids and raise concrete with precision. The material is also resistant to water, which is crucial.

Concrete Sinking

  1. Foam Injection Contractors
  2. Driveway Leveling Crystal Lake
  3. Foundation Leveling Services
  4. Concrete Preservation
  5. Eco-Friendly Concrete Lifting
  6. Sidewalk Trip Hazard Fix
  7. Fast Dry Concrete Lifting
  8. Structural Concrete Repair
  9. Concrete Pressure Injection
  10. Sustainable Concrete Repair
  11. Sidewalk Leveling Experts
  12. Driveway Void Repair
  13. Soil Erosion Under Slab
  14. Crystal Lake IL Contractors
  15. Crystal Lake Home Services
  16. Subgrade Stabilization
  17. Sinking Slab Correction
  18. Pool Deck Repair
  19. Concrete Floor Leveling Contractors
Acme Concrete's approach not only saves you time and money but also spares you the hassle of extensive construction work. Driveway Repair
To truly appreciate the impact of our concrete raising services, let's explore some transformative before and after project showcases. Acme's Smart Lift System offers a revolutionary approach to fixing sinking concrete by targeting the underlying issues without major disruption to your property. Beyond enhancing beauty, ensuring your safety is our top priority when it comes to walkway repairs and maintenance.

You might wonder about the longevity and effectiveness of this method. Embarking on your journey with Acme Concrete for repairs starts with a simple, straightforward process. Rest assured, concrete raising is a durable repair technique that's been used successfully for decades. Plus, by maintaining the integrity of your concrete, you're ultimately preserving the value of your home. Tell us about the concrete issues you're facing, and we'll schedule a convenient time to come out and inspect your property.

First, you'll need to get in touch with their team. Imagine you're walking through your neighborhood in Crystal Lake, admiring the serene views, when suddenly you trip over a raised slab of concrete. When you choose Acme Concrete's solution, you're not just fixing uneven slabs; you're also revitalizing the look of your sidewalks, driveways, and patios. Mudjacking They appreciated not only the high-quality work but also the way our team took the time to explain the process, ensuring they understood every step.

When the support vanishes, concrete slabs begin to sink, leading to uneven surfaces. What's more, the Smart Lift System is remarkably efficient. With Acme Concrete Raising & Repair, you're not just getting a service provider; you're gaining a partner who cares about the safety and aesthetics of your walkways. What you're left with isn't just leveled concrete but a restored foundation that's ready for immediate use.

Imagine walking up your driveway without the fear of tripping over a raised edge, or watching your kids play on the sidewalk knowing they're less likely to take a nasty fall. The environmental footprint of concrete raising methods is a critical consideration for both consumers and professionals in the industry.

Sunken Concrete

  • Concrete Repair Estimate Crystal Lake
  • Interior Floor Lifting
  • Polyurethane Foam Injection
  • Basement Floor Lifting
  • Concrete Raising Reviews
  • Settled Concrete Solutions
  • Slab Leveling Solutions
  • Sidewalk Leveling
  • Void Filling
  • Porch Leveling
  • Concrete Pressure Grouting
  • Concrete Driveway Maintenance
  • Concrete Contractors Crystal Lake
  • Crystal Lake Mudjacking Company
  • Quick Concrete Lifting Service
  • Crystal Lake Foundation Contractors
  • Concrete Crack Repair
  • Fast Concrete Repair
There's also the undeniable appeal of improved safety and curb appeal. Another case involves a municipal sidewalk that had become uneven due to years of soil erosion underneath. Concrete Sinking

Citations and other links

Sidewalk Lifting Crystal Lake

This project didn't just improve the aesthetic and functionality of the area; it also demonstrated the cost-efficiency and minimal disruption of using advanced techniques over old methods. Acme Concrete's introduction of polyurethane power into Crystal Lake's concrete raising services might just be the game-changer you're seeking. So, why should you keep an eye on this development? It's also water-resistant, which prevents future erosion and soil destabilization underneath the concrete.

Garage Floor Lifting

  • Garage Floor Lifting
  • Local Concrete Repair Crystal Lake
  • Polyjacking Services
  • Residential Driveway Leveling
  • Leveling Concrete Slabs
  • Foundation Repair
  • Mudjacking
  • Concrete Sinking
  • Concrete Lifting Specialists
  • Garage Slab Settlement
  • Driveway Repair
  • Garage Apron Repair
  • Cracked Driveway Repair
  • Sunken Concrete
  • Concrete Raising Cost Estimate
  • Concrete Floor Repair
Diving into how the Smart Lift system revolutionizes concrete repair, you'll find its process both innovative and straightforward.
The system uses a polyurethane foam, which is more durable and stable than the materials used in traditional concrete raising methods. This leaves voids under the concrete, and without support, the concrete slabs begin to sink. You're not just getting a cost-effective solution; you're also choosing a path that's kinder to our planet. This means you'll have a proactive approach to maintenance, saving time, money, and hassle in the long run.
When you choose them, you're not just fixing the present; you're investing in the future of your property. Read more about Concrete Raising Services in Crystal Lake here As we explore the intricate workings of the Smart Lift System and share real-life success stories, you'll see why this could mark the future of concrete raising, making you reconsider everything you thought you knew about maintaining solid foundations. Our reviews speak volumes, with clients praising our professionalism, punctuality, and the outstanding quality of our work. Sunken Concrete With our state-of-the-art techniques, we lift and stabilize your concrete to eliminate hazards, creating a smooth, level surface.
But how does this system work, and what makes it stand out from traditional methods? Unlike traditional methods that often involve digging up and replacing entire sections, Acme's system focuses on precision lifting and stabilization. The precision of the injection process allows us to control the lift and avoid further damage to the slab. Water often undermines concrete by washing away the soil underneath or causing freeze-thaw cycles that lead to cracks and sinking.

Sidewalk Lifting Crystal Lake
Concrete Raising and Leveling Company Crystal Lake

Concrete Raising and Leveling Company Crystal Lake

It's a win-win situation where safety meets aesthetics. First, you'll need to get in touch. To combat the pervasive issue of sinking concrete, Acme Concrete has developed a cutting-edge solution that's both efficient and long-lasting. Understanding the process of polyurethane raising begins with drilling small, strategically placed holes into the sunken concrete.

You can walk on your driveway or patio almost immediately after the job is done. The precision control of the injection process allows for meticulous adjustments, ensuring a level finish. Acme's Smart Lift System fixed it over a weekend, and we were back to business without any downtime.

By embracing an innovative approach, they not only address the common challenge of settling concrete but also offer a solution that stands out for its durability and efficiency. You're at the forefront of witnessing an industry evolution, where technological innovations and eco-friendly solutions are becoming the norm. They not only provide a lightweight solution but also resist erosion better than their predecessors. Concrete Lifting Specialists Local Concrete Repair Crystal Lake

With Acme, you're getting more than a quick fix. It's not just about fixing the problem; it's about preventing future issues. Plus, the material's lightweight nature means less burden on the soil, reducing the risk of future settlement.

Cement Stabilization Crystal Lake

You can contact them through their website or give them a call to schedule a consultation. This method involves injecting a high-density foam under the concrete slab, which then expands and lifts the slab back to its original level. You'll find that polyurethane offers a lightweight solution, which means less stress on the underlying soil and a reduced chance of resettlement. Polyurethane concrete raising, also known as foam lifting, utilizes a lightweight, durable material that requires fewer and smaller injection holes in the concrete.

Polyjacking Services

  • Sunken Walkway Fix
  • Backyard Patio Repair
  • Concrete Surface Repair
  • Concrete Settling
  • Slab Foundation Repair
  • Concrete Leveling
  • Local Concrete Leveling Services
  • Concrete Joint Sealing
  • Foam Jacking
  • Concrete Resurfacing
  • Foam Injection Contractors
  • Driveway Leveling Crystal Lake
  • Foundation Leveling Services
  • Concrete Preservation
  • Eco-Friendly Concrete Lifting


Moreover, the Smart Lift system enhances the safety and aesthetics of your property, potentially increasing its value. Don't worry if you're not exactly sure what's wrong; they're experts at diagnosing issues just from your descriptions and images. Polyjacking Services This durability translates into fewer repairs and replacements down the line.

Many homeowners face the challenge of aging concrete, which can significantly impact the safety and aesthetics of their property. Here's how we do it:First, we'll inspect your property to understand the extent of the damage. You'll see immediate cost savings, as this innovative approach is designed to repair rather than replace your sidewalks and driveways.

With Acme Concrete's advanced repair system, you're not just fixing a problem. Navigating the world of home maintenance can feel like sailing through a stormy sea, especially when you're facing the sinking ship scenario of settling concrete. They serve as a testament to the innovative solutions available today that address the root causes of concrete settlement without the drawbacks of outdated mudjacking.

Cement Stabilization Crystal Lake
Cement Repair Services Crystal Lake
Cement Repair Services Crystal Lake

Trust us to keep your walkways safe, ensuring peace of mind for you and your community. The root cause is often the soil beneath the concrete. This project not only enhanced the property's curb appeal but also increased its overall value.

Garage Slab Settlement

  • Concrete Raising Reviews
  • Settled Concrete Solutions
  • Slab Leveling Solutions
  • Sidewalk Leveling
  • Void Filling
  • Porch Leveling
  • Concrete Pressure Grouting
  • Concrete Driveway Maintenance
  • Concrete Contractors Crystal Lake
  • Crystal Lake Mudjacking Company
  • Quick Concrete Lifting Service
  • Crystal Lake Foundation Contractors
  • Concrete Crack Repair
  • Fast Concrete Repair
  • Uneven Concrete Repair
Acme Concrete recommends consulting with them for the best sealant options tailored to your specific repair work. This proactive approach means you're investing in the longevity of your home's concrete surfaces, which can improve your property's overall value.

It's a solution that not only saves you time and money but also extends the life of your concrete surfaces without compromising on quality or safety. Stay with us as we uncover the layers of this groundbreaking approach, exploring its key features, benefits, and how it could transform your property maintenance strategy. Having explored the challenges of aging concrete, let's now look at how Acme Concrete's innovative repairs offer a sustainable solution for Crystal Lake homeowners. This process not only corrects uneven concrete surfaces but also prevents the potential trip hazards they pose.

There's no need for heavy machinery trampling your garden or disrupting your daily life for days on end. You can do this through their website or by giving them a quick call. You'll find that these advancements aren't just about lifting concrete more efficiently; they're also about doing it smarter, with less impact on the environment and more durable results. Stick around to uncover why choosing the right experts could be the best decision you make for your home's future.

This step is crucial for tailoring our approach to your specific needs. The precision of the Smart Lift system means less mess and less time spent on repairs, letting you get back to your daily life faster. Foundation Repair Repairing instead of replacing means less waste heading to the landfill. They pride themselves on transparent pricing, so expect a detailed quote with no hidden fees.

Driveway Slab Leveling Crystal Lake

Lastly, Acme hasn't skimped on durability. Imagine your driveway has just been transformed from a cracked and uneven surface to a smooth, level expanse, all thanks to Acme Concrete's innovative approach to polyurethane concrete raising in Crystal Lake. Unlike the traditional method, which often uses materials that can be harsh on the environment, Acme's approach is designed with sustainability in mind. By choosing to repair rather than replace, you're opting for a more affordable approach. We believe in transparency, so we'll provide you with a detailed quote that outlines the costs involved.
The process is precise, allowing for targeted lifting that repairs your concrete without the need for replacement. Polyurethane foam is a lightweight, durable substance that's injected beneath concrete slabs to lift and level them. Understanding the root causes of concrete deterioration is key to addressing the issue effectively. You're not just getting a service; you're gaining a partner who values your satisfaction above all.
Now that you understand the benefits of concrete raising for your Crystal Lake home, let's explore why our team is the top choice in delivering these services. Acme Concrete Raising & Repair emphasizes the importance of regular inspections to catch and address minor issues before they escalate. From the initial consultation to the final inspection, they're with you every step of the way, ensuring your questions are answered and your concerns are addressed. This can exacerbate the initial problem, leading to a vicious cycle of repairs.

Garage Apron Repair

  • Precision Concrete Leveling
  • Chicagoland Concrete Solutions
  • Illinois Concrete Repair
  • Concrete Raising Contractors
  • Concrete Leveling Companies
  • Concrete Foundation Settlement
  • Trip Hazard Removal
  • Polyurethane Concrete Lifting
  • No-Dig Concrete Repair
  • Concrete Waterproofing
  • Concrete Raising Experts
  • Residential Concrete Services
  • Affordable Slab Lifting Crystal Lake
  • Affordable Concrete Raising
  • Concrete Lifting
  • Concrete Repair Estimate Crystal Lake

It's not magic-it's our expertise in action.

Garage Slab Settlement

  1. Fix Uneven Driveway Crystal Lake
  2. Crystal Lake Concrete Experts
  3. Patio Leveling
  4. Slabjacking
  5. Soil Stabilization
  6. Concrete Expansion Joint Repair
  7. Level Concrete Surfaces
  8. Helical Piers
  9. Driveway Settling Solutions
  10. Concrete Crack Injection
  11. Commercial Concrete Services
  12. Concrete Patching Services
  13. Concrete Grinding
  14. Concrete Void Filling
  15. Curb Lifting
  16. Precision Concrete Leveling
  17. Chicagoland Concrete Solutions
  18. Illinois Concrete Repair
Acme's solution not only restored these areas to their original condition but also ensured they were more durable against future erosion. Unlike mudjacking, which uses a heavier, messier slurry, Acme's polyurethane solution is lightweight and causes minimal disruption to the surrounding area. With its blend of cutting-edge technology and user-friendly features, Acme's system not only promises to raise the bar but also to redefine it.

Explore Concrete Raising Services in Crystal Lake here
Driveway Slab Leveling Crystal Lake
Polyurethane synthesis: the urethane groups −NH−(C=O)−O− link the molecular units, resulting in a polymer consisting of an alternating chain of two monomers.
A kitchen sponge made of polyurethane foam

Polyurethane (/ËŒpÉ’liˈjÊŠÉ™rəˌθeɪn, -jʊəˈrÉ›θeɪn/;[1] often abbreviated PUR and PU) is a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane does not refer to a single type of polymer but a group of polymers. Unlike polyethylene and polystyrene, polyurethanes can be produced from a wide range of starting materials, resulting in various polymers within the same group. This chemical variety produces polyurethanes with different chemical structures leading to many different applications. These include rigid and flexible foams, and coatings, adhesives, electrical potting compounds, and fibers such as spandex and polyurethane laminate (PUL). Foams are the largest application accounting for 67% of all polyurethane produced in 2016.[2]

A polyurethane is typically produced by reacting a polymeric isocyanate with a polyol.[3] Since a polyurethane contains two types of monomers, which polymerize one after the other, they are classed as alternating copolymers. Both the isocyanates and polyols used to make a polyurethane contain two or more functional groups per molecule.

Global production in 2019 was 25 million metric tonnes,[4] accounting for about 6% of all polymers produced in that year.

History

[edit]
Otto Bayer in 1952 demonstrating his creation

Otto Bayer and his coworkers at IG Farben in Leverkusen, Germany, first made polyurethanes in 1937.[5][6] The new polymers had some advantages over existing plastics that were made by polymerizing olefins or by polycondensation, and were not covered by patents obtained by Wallace Carothers on polyesters.[7] Early work focused on the production of fibers and flexible foams and PUs were applied on a limited scale as aircraft coating during World War II.[7] Polyisocyanates became commercially available in 1952, and production of flexible polyurethane foam began in 1954 by combining toluene diisocyanate (TDI) and polyester polyols. These materials were also used to produce rigid foams, gum rubber, and elastomers. Linear fibers were produced from hexamethylene diisocyanate (HDI) and 1,4-Butanediol (BDO).

DuPont introduced polyethers, specifically poly(tetramethylene ether) glycol, in 1956. BASF and Dow Chemical introduced polyalkylene glycols in 1957. Polyether polyols were cheaper, easier to handle and more water-resistant than polyester polyols. Union Carbide and Mobay, a U.S. Monsanto/Bayer joint venture, also began making polyurethane chemicals.[7] In 1960 more than 45,000 metric tons of flexible polyurethane foams were produced. The availability of chlorofluoroalkane blowing agents, inexpensive polyether polyols, and methylene diphenyl diisocyanate (MDI) allowed polyurethane rigid foams to be used as high-performance insulation materials. In 1967, urethane-modified polyisocyanurate rigid foams were introduced, offering even better thermal stability and flammability resistance. During the 1960s, automotive interior safety components, such as instrument and door panels, were produced by back-filling thermoplastic skins with semi-rigid foam.

In 1969, Bayer exhibited an all-plastic car in Düsseldorf, Germany. Parts of this car, such as the fascia and body panels, were manufactured using a new process called reaction injection molding (RIM), in which the reactants were mixed and then injected into a mold. The addition of fillers, such as milled glass, mica, and processed mineral fibers, gave rise to reinforced RIM (RRIM), which provided improvements in flexural modulus (stiffness), reduction in coefficient of thermal expansion and better thermal stability. This technology was used to make the first plastic-body automobile in the United States, the Pontiac Fiero, in 1983. Further increases in stiffness were obtained by incorporating pre-placed glass mats into the RIM mold cavity, also known broadly as resin injection molding, or structural RIM.

Starting in the early 1980s, water-blown microcellular flexible foams were used to mold gaskets for automotive panels and air-filter seals, replacing PVC polymers. Polyurethane foams are used in many automotive applications including seating, head and arm rests, and headliners.

Polyurethane foam (including foam rubber) is sometimes made using small amounts of blowing agents to give less dense foam, better cushioning/energy absorption or thermal insulation. In the early 1990s, because of their impact on ozone depletion, the Montreal Protocol restricted the use of many chlorine-containing blowing agents, such as trichlorofluoromethane (CFC-11). By the late 1990s, blowing agents such as carbon dioxide, pentane, 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1,1,3,3-pentafluoropropane (HFC-245fa) were widely used in North America and the EU, although chlorinated blowing agents remained in use in many developing countries. Later, HFC-134a was also banned due to high ODP and GWP readings, and HFC-141B was introduced in early 2000s as an alternate blowing agent in developing nations.[8]

Chemistry

[edit]

Polyurethanes are produced by reacting diisocyanates with polyols,[9][10][11][12][13][14] often in the presence of a catalyst, or upon exposure to ultraviolet radiation.[15] Common catalysts include tertiary amines, such as DABCO, DMDEE, or metallic soaps, such as dibutyltin dilaurate. The stoichiometry of the starting materials must be carefully controlled as excess isocyanate can trimerise, leading to the formation of rigid polyisocyanurates. The polymer usually has a highly crosslinked molecular structure, resulting in a thermosetting material which does not melt on heating; although some thermoplastic polyurethanes are also produced.

 
Carbon dioxide gas and urea links formed by reacting water and isocyanate

The most common application of polyurethane is as solid foams, which requires the presence of a gas, or blowing agent, during the polymerization step. This is commonly achieved by adding small amounts of water, which reacts with isocyanates to form CO2 gas and an amine, via an unstable carbamic acid group. The amine produced can also react with isocyanates to form urea groups, and as such the polymer will contain both these and urethane linkers. The urea is not very soluble in the reaction mixture and tends to form separate "hard segment" phases consisting mostly of polyurea. The concentration and organization of these polyurea phases can have a significant impact on the properties of the foam.[16]

The type of foam produced can be controlled by regulating the amount of blowing agent and also by the addition of various surfactants which change the rheology of the polymerising mixture. Foams can be either "closed-cell", where most of the original bubbles or cells remain intact, or "open-cell", where the bubbles have broken but the edges of the bubbles are stiff enough to retain their shape, in extreme cases reticulated foams can be formed. Open-cell foams feel soft and allow air to flow through, so they are comfortable when used in seat cushions or mattresses. Closed-cell foams are used as rigid thermal insulation. High-density microcellular foams can be formed without the addition of blowing agents by mechanically frothing the polyol prior to use. These are tough elastomeric materials used in covering car steering wheels or shoe soles.

The properties of a polyurethane are greatly influenced by the types of isocyanates and polyols used to make it. Long, flexible segments, contributed by the polyol, give soft, elastic polymer. High amounts of crosslinking give tough or rigid polymers. Long chains and low crosslinking give a polymer that is very stretchy, short chains with many crosslinks produce a hard polymer while long chains and intermediate crosslinking give a polymer useful for making foam. The choices available for the isocyanates and polyols, in addition to other additives and processing conditions allow polyurethanes to have the very wide range of properties that make them such widely used polymers.

Raw materials

[edit]

The main ingredients to make a polyurethane are di- and tri-isocyanates and polyols. Other materials are added to aid processing the polymer or to modify the properties of the polymer. PU foam formulation sometimes have water added too.

Isocyanates

[edit]

Isocyanates used to make polyurethane have two or more isocyanate groups on each molecule. The most commonly used isocyanates are the aromatic diisocyanates, toluene diisocyanate (TDI) and methylene diphenyl diisocyanate, (MDI). These aromatic isocyanates are more reactive than aliphatic isocyanates.

TDI and MDI are generally less expensive and more reactive than other isocyanates. Industrial grade TDI and MDI are mixtures of isomers and MDI often contains polymeric materials. They are used to make flexible foam (for example slabstock foam for mattresses or molded foams for car seats),[17] rigid foam (for example insulating foam in refrigerators) elastomers (shoe soles, for example), and so on. The isocyanates may be modified by partially reacting them with polyols or introducing some other materials to reduce volatility (and hence toxicity) of the isocyanates, decrease their freezing points to make handling easier or to improve the properties of the final polymers.

MDI isomers and polymer
MDI isomers and polymer

Aliphatic and cycloaliphatic isocyanates are used in smaller quantities, most often in coatings and other applications where color and transparency are important since polyurethanes made with aromatic isocyanates tend to darken on exposure to light.[page needed][18] The most important aliphatic and cycloaliphatic isocyanates are 1,6-hexamethylene diisocyanate (HDI), 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate, IPDI), and 4,4′-diisocyanato dicyclohexylmethane (H12MDI or hydrogenated MDI). Other more specialized isocyanates include Tetramethylxylylene diisocyanate (TMXDI).

Polyols

[edit]

Polyols are polymers in their own right and have on average two or more hydroxyl groups per molecule. They can be converted to polyether polyols by co-polymerizing ethylene oxide and propylene oxide with a suitable polyol precursor.[19] Polyester polyols are made by the polycondensation of multifunctional carboxylic acids and polyhydroxyl compounds. They can be further classified according to their end use. Higher molecular weight polyols (molecular weights from 2,000 to 10,000) are used to make more flexible polyurethanes while lower molecular weight polyols make more rigid products.

Polyols for flexible applications use low functionality initiators such as dipropylene glycol (f = 2), glycerine (f = 3), or a sorbitol/water solution (f = 2.75).[20] Polyols for rigid applications use higher functionality initiators such as sucrose (f = 8), sorbitol (f = 6), toluenediamine (f = 4), and Mannich bases (f = 4). Propylene oxide and/or ethylene oxide is added to the initiators until the desired molecular weight is achieved. The order of addition and the amounts of each oxide affect many polyol properties, such as compatibility, water-solubility, and reactivity. Polyols made with only propylene oxide are terminated with secondary hydroxyl groups and are less reactive than polyols capped with ethylene oxide, which contain primary hydroxyl groups. Incorporating carbon dioxide into the polyol structure is being researched by multiple companies.

Graft polyols (also called filled polyols or polymer polyols) contain finely dispersed styrene–acrylonitrile, acrylonitrile, or polyurea (PHD) polymer solids chemically grafted to a high molecular weight polyether backbone. They are used to increase the load-bearing properties of low-density high-resiliency (HR) foam, as well as add toughness to microcellular foams and cast elastomers. Initiators such as ethylenediamine and triethanolamine are used to make low molecular weight rigid foam polyols that have built-in catalytic activity due to the presence of nitrogen atoms in the backbone. A special class of polyether polyols, poly(tetramethylene ether) glycols, which are made by polymerizing tetrahydrofuran, are used in high performance coating, wetting and elastomer applications.

Conventional polyester polyols are based on virgin raw materials and are manufactured by the direct polyesterification of high-purity diacids and glycols, such as adipic acid and 1,4-butanediol. Polyester polyols are usually more expensive and more viscous than polyether polyols, but they make polyurethanes with better solvent, abrasion, and cut resistance. Other polyester polyols are based on reclaimed raw materials. They are manufactured by transesterification (glycolysis) of recycled poly(ethyleneterephthalate) (PET) or dimethylterephthalate (DMT) distillation bottoms with glycols such as diethylene glycol. These low molecular weight, aromatic polyester polyols are used in rigid foam, and bring low cost and excellent flammability characteristics to polyisocyanurate (PIR) boardstock and polyurethane spray foam insulation.

Specialty polyols include polycarbonate polyols, polycaprolactone polyols, polybutadiene polyols, and polysulfide polyols. The materials are used in elastomer, sealant, and adhesive applications that require superior weatherability, and resistance to chemical and environmental attack. Natural oil polyols derived from castor oil and other vegetable oils are used to make elastomers, flexible bunstock, and flexible molded foam.

Co-polymerizing chlorotrifluoroethylene or tetrafluoroethylene with vinyl ethers containing hydroxyalkyl vinyl ether produces fluorinated (FEVE) polyols. Two-component fluorinated polyurethanes prepared by reacting FEVE fluorinated polyols with polyisocyanate have been used to make ambient cure paints and coatings. Since fluorinated polyurethanes contain a high percentage of fluorine–carbon bonds, which are the strongest bonds among all chemical bonds, fluorinated polyurethanes exhibit resistance to UV, acids, alkali, salts, chemicals, solvents, weathering, corrosion, fungi and microbial attack. These have been used for high performance coatings and paints.[21]

Phosphorus-containing polyols are available that become chemically bonded to the polyurethane matrix for the use as flame retardants. This covalent linkage prevents migration and leaching of the organophosphorus compound.

Bio-derived materials

[edit]

Interest in sustainable "green" products raised interest in polyols derived from vegetable oils,[22][23][24] fatty acids,[25] lignin, sorbitol,[26] etc. These are mostly contributing to polyol part. There are attempts made to prepare isocyanate part using bio-derived material. However, as far as commercialization is concern, polyol part is more targeted being easy and required in more quantity than isocyanate part. Various oils used in the preparation polyols for polyurethanes include soybean oil, cottonseed oil, neem seed oil, algae oil,[27][28] and castor oil. Vegetable oils are functionalized in various ways and modified to polyetheramides, polyethers, alkyds, etc. Renewable sources used to prepare polyols may be fatty acids or dimer fatty acids.[29] Some biobased and isocyanate-free polyurethanes exploit the reaction between polyamines and cyclic carbonates to produce polyhydroxyurethanes.[30]

Chain extenders and cross linkers

[edit]

Chain extenders (f = 2) and cross linkers (f ≥ 3) are low molecular weight hydroxyl and amine terminated compounds that play an important role in the polymer morphology of polyurethane fibers, elastomers, adhesives, and certain integral skin and microcellular foams.

The elastomeric properties of these materials are derived from the phase separation of the hard and soft copolymer segments of the polymer, such that the urethane hard segment domains serve as cross-links between the amorphous polyether (or polyester) soft segment domains. This phase separation occurs because the mainly nonpolar, low melting soft segments are incompatible with the polar, high melting hard segments. The soft segments, which are formed from high molecular weight polyols, are mobile and are normally present in coiled formation, while the hard segments, which are formed from the isocyanate and chain extenders, are stiff and immobile. As the hard segments are covalently coupled to the soft segments, they inhibit plastic flow of the polymer chains, thus creating elastomeric resiliency. Upon mechanical deformation, a portion of the soft segments are stressed by uncoiling, and the hard segments become aligned in the stress direction. This reorientation of the hard segments and consequent powerful hydrogen bonding contributes to high tensile strength, elongation, and tear resistance values.[12][31][32][33][34] The choice of chain extender also determines flexural, heat, and chemical resistance properties.

The most important chain extenders are ethylene glycol, 1,4-butanediol (1,4-BDO or BDO), 1,6-hexanediol, cyclohexane dimethanol and hydroquinone bis(2-hydroxyethyl) ether (HQEE). All of these glycols form polyurethanes that phase separate well and form well defined hard segment domains, and are melt processable. They are all suitable for thermoplastic polyurethanes with the exception of ethylene glycol, since its derived bis-phenyl urethane undergoes unfavorable degradation at high hard segment levels.[10] Diethanolamine and triethanolamine are used in flex molded foams to build firmness and add catalytic activity. Diethyltoluenediamine is used extensively in RIM, and in polyurethane and polyurea elastomer formulations.

Table of chain extenders and cross linkers[35]
Compound type Molecule Mol.
mass
Density
(g/cm3)
Melting
pt (°C)
Boiling
pt (°C)
Hydroxyl compounds – difunctional molecules Ethylene glycol 62.1 1.110 −13.4 197.4
Diethylene glycol 106.1 1.111 −8.7 245.5
Triethylene glycol 150.2 1.120 −7.2 287.8
Tetraethylene glycol 194.2 1.123 −9.4 325.6
Propylene glycol 76.1 1.032 Supercools 187.4
Dipropylene glycol 134.2 1.022 Supercools 232.2
Tripropylene glycol 192.3 1.110 Supercools 265.1
1,3-Propanediol 76.1 1.060 −28 210
1,3-Butanediol 92.1 1.005 207.5
1,4-Butanediol 92.1 1.017 20.1 235
Neopentyl glycol 104.2 130 206
1,6-Hexanediol 118.2 1.017 43 250
1,4-Cyclohexanedimethanol
HQEE
Ethanolamine 61.1 1.018 10.3 170
Diethanolamine 105.1 1.097 28 271
Methyldiethanolamine 119.1 1.043 −21 242
Phenyldiethanolamine 181.2 58 228
Hydroxyl compounds – trifunctional molecules Glycerol 92.1 1.261 18.0 290
Trimethylolpropane
1,2,6-Hexanetriol
Triethanolamine 149.2 1.124 21
Hydroxyl compounds – tetrafunctional molecules Pentaerythritol 136.2 260.5
N,N,N′,N′-Tetrakis
(2-hydroxypropyl)
ethylenediamine
Amine compounds – difunctional molecules Diethyltoluenediamine 178.3 1.022 308
Dimethylthiotoluenediamine 214.0 1.208

Catalysts

[edit]

Polyurethane catalysts can be classified into two broad categories, basic and acidic amine. Tertiary amine catalysts function by enhancing the nucleophilicity of the diol component. Alkyl tin carboxylates, oxides and mercaptides oxides function as mild Lewis acids in accelerating the formation of polyurethane. As bases, traditional amine catalysts include triethylenediamine (TEDA, also called DABCO, 1,4-diazabicyclo[2.2.2]octane), dimethylcyclohexylamine (DMCHA), dimethylethanolamine (DMEA), Dimethylaminoethoxyethanol and bis-(2-dimethylaminoethyl)ether, a blowing catalyst also called A-99. A typical Lewis acidic catalyst is dibutyltin dilaurate. The process is highly sensitive to the nature of the catalyst and is also known to be autocatalytic.[36]

Another class of catalysts was published in a study in May 2024. In this study, polyurethane synthesis was investigated in the presence of acid catalysts, namely dimethylphosphite (DMHP), methanesulfonic acid (MSA), and trifluoromethanesulfonic acid (TFMSA). The thermodynamic profile was examined and described in detail through computational tools, showing that TFMSA had the best catalytic properties. The study aimed to open the door to a new class of catalysts.[37]

Factors affecting catalyst selection include balancing three reactions: urethane (polyol+isocyanate, or gel) formation, the urea (water+isocyanate, or "blow") formation, or the isocyanate trimerization reaction (e.g., using potassium acetate, to form isocyanurate rings). A variety of specialized catalysts have been developed.[38][39][40]

Surfactants

[edit]

Surfactants are used to modify the characteristics of both foam and non-foam polyurethane polymers. They take the form of polydimethylsiloxane-polyoxyalkylene block copolymers, silicone oils, nonylphenol ethoxylates, and other organic compounds. In foams, they are used to emulsify the liquid components, regulate cell size, and stabilize the cell structure to prevent collapse and sub-surface voids.[41] In non-foam applications they are used as air release and antifoaming agents, as wetting agents, and are used to eliminate surface defects such as pin holes, orange peel, and sink marks.

Production

[edit]

Polyurethanes are produced by mixing two or more liquid streams. The polyol stream contains catalysts, surfactants, blowing agents (when making polyurethane foam insulation) and so on. The two components are referred to as a polyurethane system, or simply a system. The isocyanate is commonly referred to in North America as the 'A-side' or just the 'iso'. The blend of polyols and other additives is commonly referred to as the 'B-side' or as the 'poly'.[citation needed] This mixture might also be called a 'resin' or 'resin blend'. In Europe the meanings for 'A-side' and 'B-side' are reversed.[citation needed] Resin blend additives may include chain extenders, cross linkers, surfactants, flame retardants, blowing agents, pigments, and fillers. Polyurethane can be made in a variety of densities and hardnesses by varying the isocyanate, polyol or additives.

Health and safety

[edit]

Fully reacted polyurethane polymer is chemically inert.[42] No exposure limits have been established in the U.S. by OSHA (Occupational Safety and Health Administration) or ACGIH (American Conference of Governmental Industrial Hygienists). It is not regulated by OSHA for carcinogenicity.

Open-flame test. Top: untreated polyurethane foam burns vigorously. Bottom: with fire-retardant treatment.

Polyurethanes are combustible.[43] Decomposition from fire can produce significant amounts of carbon monoxide and hydrogen cyanide, in addition to nitrogen oxides, isocyanates, and other toxic products.[44] Due to the flammability of the material, it has to be treated with flame retardants (at least in case of furniture), almost all of which are considered harmful.[45][46] California later issued Technical Bulletin 117 2013 which allowed most polyurethane foam to pass flammability tests without the use of flame retardants. Green Science Policy Institute states: "Although the new standard can be met without flame retardants, it does NOT ban their use. Consumers who wish to reduce household exposure to flame retardants can look for a TB117-2013 tag on furniture, and verify with retailers that products do not contain flame retardants."[47]

Liquid resin blends and isocyanates may contain hazardous or regulated components. Isocyanates are known skin and respiratory sensitizers. Additionally, amines, glycols, and phosphate present in spray polyurethane foams present risks.[48]

Exposure to chemicals that may be emitted during or after application of polyurethane spray foam (such as isocyanates) are harmful to human health and therefore special precautions are required during and after this process.[49]

In the United States, additional health and safety information can be found through organizations such as the Polyurethane Manufacturers Association (PMA) and the Center for the Polyurethanes Industry (CPI), as well as from polyurethane system and raw material manufacturers. Regulatory information can be found in the Code of Federal Regulations Title 21 (Food and Drugs) and Title 40 (Protection of the Environment). In Europe, health and safety information is available from ISOPA,[50] the European Diisocyanate and Polyol Producers Association.

Manufacturing

[edit]

The methods of manufacturing polyurethane finished goods range from small, hand pour piece-part operations to large, high-volume bunstock and boardstock production lines. Regardless of the end-product, the manufacturing principle is the same: to meter the liquid isocyanate and resin blend at a specified stoichiometric ratio, mix them together until a homogeneous blend is obtained, dispense the reacting liquid into a mold or on to a surface, wait until it cures, then demold the finished part.

Dispensing equipment

[edit]

Although the capital outlay can be high, it is desirable to use a meter-mix or dispense unit for even low-volume production operations that require a steady output of finished parts. Dispense equipment consists of material holding (day) tanks, metering pumps, a mix head, and a control unit. Often, a conditioning or heater–chiller unit is added to control material temperature in order to improve mix efficiency, cure rate, and to reduce process variability. Choice of dispense equipment components depends on shot size, throughput, material characteristics such as viscosity and filler content, and process control. Material day tanks may be single to hundreds of gallons in size and may be supplied directly from drums, IBCs (intermediate bulk containers, such as caged IBC totes), or bulk storage tanks. They may incorporate level sensors, conditioning jackets, and mixers. Pumps can be sized to meter in single grams per second up to hundreds of pounds per minute. They can be rotary, gear, or piston pumps, or can be specially hardened lance pumps to meter liquids containing highly abrasive fillers such as chopped or hammer-milled glass fiber and wollastonite.[citation needed]

The pumps can drive low-pressure (10 to 30 bar, 1 to 3 MPa) or high-pressure (125 to 250 bar, 12.5 to 25.0 MPa) dispense systems. Mix heads can be simple static mix tubes, rotary-element mixers, low-pressure dynamic mixers, or high-pressure hydraulically actuated direct impingement mixers. Control units may have basic on/off and dispense/stop switches, and analogue pressure and temperature gauges, or may be computer-controlled with flow meters to electronically calibrate mix ratio, digital temperature and level sensors, and a full suite of statistical process control software. Add-ons to dispense equipment include nucleation or gas injection units, and third or fourth stream capability for adding pigments or metering in supplemental additive packages.

Tooling

[edit]

Distinct from pour-in-place, bun and boardstock, and coating applications, the production of piece parts requires tooling to contain and form the reacting liquid. The choice of mold-making material is dependent on the expected number of uses to end-of-life (EOL), molding pressure, flexibility, and heat transfer characteristics.

RTV silicone is used for tooling that has an EOL in the thousands of parts. It is typically used for molding rigid foam parts, where the ability to stretch and peel the mold around undercuts is needed. The heat transfer characteristic of RTV silicone tooling is poor. High-performance, flexible polyurethane elastomers are also used in this way.

Epoxy, metal-filled epoxy, and metal-coated epoxy is used for tooling that has an EOL in the tens of thousands of parts. It is typically used for molding flexible foam cushions and seating, integral skin and microcellular foam padding, and shallow-draft RIM bezels and fascia. The heat transfer characteristic of epoxy tooling is fair; the heat transfer characteristic of metal-filled and metal-coated epoxy is good. Copper tubing can be incorporated into the body of the tool, allowing hot water to circulate and heat the mold surface.

Aluminum is used for tooling that has an EOL in the hundreds of thousands of parts. It is typically used for molding microcellular foam gasketing and cast elastomer parts, and is milled or extruded into shape.

Mirror-finish stainless steel is used for tooling that imparts a glossy appearance to the finished part. The heat transfer characteristic of metal tooling is excellent.

Finally, molded or milled polypropylene is used to create low-volume tooling for molded gasket applications. Instead of many expensive metal molds, low-cost plastic tooling can be formed from a single metal master, which also allows greater design flexibility. The heat transfer characteristic of polypropylene tooling is poor, which must be taken into consideration during the formulation process.

Applications

[edit]

In 2007, the global consumption of polyurethane raw materials was above 12 million metric tons, and the average annual growth rate was about 5%.[51] Revenues generated with PUR on the global market are expected to rise to approximately US$75 billion by 2022.[52] As they are such an important class of materials, research is constantly taking place and papers published.[53]

Degradation and environmental fate

[edit]

Effects of visible light

[edit]
Polyurethane foam made with an aromatic isocyanate, which has been exposed to UV light. Readily apparent is the discoloration that occurs over time.

Polyurethanes, especially those made using aromatic isocyanates, contain chromophores that interact with light. This is of particular interest in the area of polyurethane coatings, where light stability is a critical factor and is the main reason that aliphatic isocyanates are used in making polyurethane coatings. When PU foam, which is made using aromatic isocyanates, is exposed to visible light, it discolors, turning from off-white to yellow to reddish brown. It has been generally accepted that apart from yellowing, visible light has little effect on foam properties.[54][55] This is especially the case if the yellowing happens on the outer portions of a large foam, as the deterioration of properties in the outer portion has little effect on the overall bulk properties of the foam itself.

It has been reported that exposure to visible light can affect the variability of some physical property test results.[56]

Higher-energy UV radiation promotes chemical reactions in foam, some of which are detrimental to the foam structure.[57]

Hydrolysis and biodegradation

[edit]

Polyurethanes may degrade due to hydrolysis. This is a common problem with shoes left in a closet, and reacting with moisture in the air.[58]

Microbial degradation of polyurethane is believed to be due to the action of esterase, urethanase, hydrolase and protease enzymes.[59] The process is slow as most microbes have difficulty moving beyond the surface of the polymer. Susceptibility to fungi is higher due to their release of extracellular enzymes, which are better able to permeate the polymer matrix. Two species of the Ecuadorian fungus Pestalotiopsis are capable of biodegrading polyurethane in aerobic and anaerobic conditions such as found at the bottom of landfills.[60][61] Degradation of polyurethane items at museums has been reported.[62] Polyester-type polyurethanes are more easily biodegraded by fungus than polyether-type.[63]

See also

[edit]
  • Botanol, a material with higher plant-based content
  • Passive fire protection
  • Penetrant (mechanical, electrical, or structural)
  • Polyaspartic
  • Polyurethane dispersion
  • Thermoplastic polyurethanes
  • Thermoset polymer matrix

References

[edit]
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  53. ^ Jakhmola, Swati; Das, Sonalee; Dutta, Kingshuk (2023-10-31). "Emerging research trends in the field of polyurethane and its nanocomposites: Chemistry, Synthesis, Characterization, Application in coatings and Future perspectives". Journal of Coatings Technology and Research. 21 (1): 137–172. doi:10.1007/s11998-023-00841-z. ISSN 1935-3804. S2CID 264908475.
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  57. ^ Newman, Christopher R.; Forciniti, Daniel (2001). "Modeling the Ultraviolet Photodegradation of Rigid Polyurethane Foams". Industrial & Engineering Chemistry Research. 40 (15): 3346–52. doi:10.1021/ie0009738.
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[edit]
  • Center for the Polyurethanes Industry: information for EH&S issues related to polyurethanes developments
  • Polyurethane synthesis, Polymer Science Learning Center, University of Southern Mississippi
  • Polyurethane Foam Association: Industry information, educational materials and resources related to flexible polyurethane foam
  • PU Europe: European PU insulation industry association (formerly BING): European voice for the national trade associations representing the polyurethane insulation industry
  • ISOPA: European Diisocyanate & Polyol Producers Association: ISOPA represents the manufacturers in Europe of aromatic diisocyanates and polyols

 

Polyurethane synthesis: the urethane groups −NH−(C=O)−O− link the molecular units, resulting in a polymer consisting of an alternating chain of two monomers.
A kitchen sponge made of polyurethane foam

Polyurethane (/ËŒpÉ’liˈjÊŠÉ™rəˌθeɪn, -jʊəˈrÉ›θeɪn/;[1] often abbreviated PUR and PU) is a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane does not refer to a single type of polymer but a group of polymers. Unlike polyethylene and polystyrene, polyurethanes can be produced from a wide range of starting materials, resulting in various polymers within the same group. This chemical variety produces polyurethanes with different chemical structures leading to many different applications. These include rigid and flexible foams, and coatings, adhesives, electrical potting compounds, and fibers such as spandex and polyurethane laminate (PUL). Foams are the largest application accounting for 67% of all polyurethane produced in 2016.[2]

A polyurethane is typically produced by reacting a polymeric isocyanate with a polyol.[3] Since a polyurethane contains two types of monomers, which polymerize one after the other, they are classed as alternating copolymers. Both the isocyanates and polyols used to make a polyurethane contain two or more functional groups per molecule.

Global production in 2019 was 25 million metric tonnes,[4] accounting for about 6% of all polymers produced in that year.

History

[edit]
Otto Bayer in 1952 demonstrating his creation

Otto Bayer and his coworkers at IG Farben in Leverkusen, Germany, first made polyurethanes in 1937.[5][6] The new polymers had some advantages over existing plastics that were made by polymerizing olefins or by polycondensation, and were not covered by patents obtained by Wallace Carothers on polyesters.[7] Early work focused on the production of fibers and flexible foams and PUs were applied on a limited scale as aircraft coating during World War II.[7] Polyisocyanates became commercially available in 1952, and production of flexible polyurethane foam began in 1954 by combining toluene diisocyanate (TDI) and polyester polyols. These materials were also used to produce rigid foams, gum rubber, and elastomers. Linear fibers were produced from hexamethylene diisocyanate (HDI) and 1,4-Butanediol (BDO).

DuPont introduced polyethers, specifically poly(tetramethylene ether) glycol, in 1956. BASF and Dow Chemical introduced polyalkylene glycols in 1957. Polyether polyols were cheaper, easier to handle and more water-resistant than polyester polyols. Union Carbide and Mobay, a U.S. Monsanto/Bayer joint venture, also began making polyurethane chemicals.[7] In 1960 more than 45,000 metric tons of flexible polyurethane foams were produced. The availability of chlorofluoroalkane blowing agents, inexpensive polyether polyols, and methylene diphenyl diisocyanate (MDI) allowed polyurethane rigid foams to be used as high-performance insulation materials. In 1967, urethane-modified polyisocyanurate rigid foams were introduced, offering even better thermal stability and flammability resistance. During the 1960s, automotive interior safety components, such as instrument and door panels, were produced by back-filling thermoplastic skins with semi-rigid foam.

In 1969, Bayer exhibited an all-plastic car in Düsseldorf, Germany. Parts of this car, such as the fascia and body panels, were manufactured using a new process called reaction injection molding (RIM), in which the reactants were mixed and then injected into a mold. The addition of fillers, such as milled glass, mica, and processed mineral fibers, gave rise to reinforced RIM (RRIM), which provided improvements in flexural modulus (stiffness), reduction in coefficient of thermal expansion and better thermal stability. This technology was used to make the first plastic-body automobile in the United States, the Pontiac Fiero, in 1983. Further increases in stiffness were obtained by incorporating pre-placed glass mats into the RIM mold cavity, also known broadly as resin injection molding, or structural RIM.

Starting in the early 1980s, water-blown microcellular flexible foams were used to mold gaskets for automotive panels and air-filter seals, replacing PVC polymers. Polyurethane foams are used in many automotive applications including seating, head and arm rests, and headliners.

Polyurethane foam (including foam rubber) is sometimes made using small amounts of blowing agents to give less dense foam, better cushioning/energy absorption or thermal insulation. In the early 1990s, because of their impact on ozone depletion, the Montreal Protocol restricted the use of many chlorine-containing blowing agents, such as trichlorofluoromethane (CFC-11). By the late 1990s, blowing agents such as carbon dioxide, pentane, 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1,1,3,3-pentafluoropropane (HFC-245fa) were widely used in North America and the EU, although chlorinated blowing agents remained in use in many developing countries. Later, HFC-134a was also banned due to high ODP and GWP readings, and HFC-141B was introduced in early 2000s as an alternate blowing agent in developing nations.[8]

Chemistry

[edit]

Polyurethanes are produced by reacting diisocyanates with polyols,[9][10][11][12][13][14] often in the presence of a catalyst, or upon exposure to ultraviolet radiation.[15] Common catalysts include tertiary amines, such as DABCO, DMDEE, or metallic soaps, such as dibutyltin dilaurate. The stoichiometry of the starting materials must be carefully controlled as excess isocyanate can trimerise, leading to the formation of rigid polyisocyanurates. The polymer usually has a highly crosslinked molecular structure, resulting in a thermosetting material which does not melt on heating; although some thermoplastic polyurethanes are also produced.

 
Carbon dioxide gas and urea links formed by reacting water and isocyanate

The most common application of polyurethane is as solid foams, which requires the presence of a gas, or blowing agent, during the polymerization step. This is commonly achieved by adding small amounts of water, which reacts with isocyanates to form CO2 gas and an amine, via an unstable carbamic acid group. The amine produced can also react with isocyanates to form urea groups, and as such the polymer will contain both these and urethane linkers. The urea is not very soluble in the reaction mixture and tends to form separate "hard segment" phases consisting mostly of polyurea. The concentration and organization of these polyurea phases can have a significant impact on the properties of the foam.[16]

The type of foam produced can be controlled by regulating the amount of blowing agent and also by the addition of various surfactants which change the rheology of the polymerising mixture. Foams can be either "closed-cell", where most of the original bubbles or cells remain intact, or "open-cell", where the bubbles have broken but the edges of the bubbles are stiff enough to retain their shape, in extreme cases reticulated foams can be formed. Open-cell foams feel soft and allow air to flow through, so they are comfortable when used in seat cushions or mattresses. Closed-cell foams are used as rigid thermal insulation. High-density microcellular foams can be formed without the addition of blowing agents by mechanically frothing the polyol prior to use. These are tough elastomeric materials used in covering car steering wheels or shoe soles.

The properties of a polyurethane are greatly influenced by the types of isocyanates and polyols used to make it. Long, flexible segments, contributed by the polyol, give soft, elastic polymer. High amounts of crosslinking give tough or rigid polymers. Long chains and low crosslinking give a polymer that is very stretchy, short chains with many crosslinks produce a hard polymer while long chains and intermediate crosslinking give a polymer useful for making foam. The choices available for the isocyanates and polyols, in addition to other additives and processing conditions allow polyurethanes to have the very wide range of properties that make them such widely used polymers.

Raw materials

[edit]

The main ingredients to make a polyurethane are di- and tri-isocyanates and polyols. Other materials are added to aid processing the polymer or to modify the properties of the polymer. PU foam formulation sometimes have water added too.

Isocyanates

[edit]

Isocyanates used to make polyurethane have two or more isocyanate groups on each molecule. The most commonly used isocyanates are the aromatic diisocyanates, toluene diisocyanate (TDI) and methylene diphenyl diisocyanate, (MDI). These aromatic isocyanates are more reactive than aliphatic isocyanates.

TDI and MDI are generally less expensive and more reactive than other isocyanates. Industrial grade TDI and MDI are mixtures of isomers and MDI often contains polymeric materials. They are used to make flexible foam (for example slabstock foam for mattresses or molded foams for car seats),[17] rigid foam (for example insulating foam in refrigerators) elastomers (shoe soles, for example), and so on. The isocyanates may be modified by partially reacting them with polyols or introducing some other materials to reduce volatility (and hence toxicity) of the isocyanates, decrease their freezing points to make handling easier or to improve the properties of the final polymers.

MDI isomers and polymer
MDI isomers and polymer

Aliphatic and cycloaliphatic isocyanates are used in smaller quantities, most often in coatings and other applications where color and transparency are important since polyurethanes made with aromatic isocyanates tend to darken on exposure to light.[page needed][18] The most important aliphatic and cycloaliphatic isocyanates are 1,6-hexamethylene diisocyanate (HDI), 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate, IPDI), and 4,4′-diisocyanato dicyclohexylmethane (H12MDI or hydrogenated MDI). Other more specialized isocyanates include Tetramethylxylylene diisocyanate (TMXDI).

Polyols

[edit]

Polyols are polymers in their own right and have on average two or more hydroxyl groups per molecule. They can be converted to polyether polyols by co-polymerizing ethylene oxide and propylene oxide with a suitable polyol precursor.[19] Polyester polyols are made by the polycondensation of multifunctional carboxylic acids and polyhydroxyl compounds. They can be further classified according to their end use. Higher molecular weight polyols (molecular weights from 2,000 to 10,000) are used to make more flexible polyurethanes while lower molecular weight polyols make more rigid products.

Polyols for flexible applications use low functionality initiators such as dipropylene glycol (f = 2), glycerine (f = 3), or a sorbitol/water solution (f = 2.75).[20] Polyols for rigid applications use higher functionality initiators such as sucrose (f = 8), sorbitol (f = 6), toluenediamine (f = 4), and Mannich bases (f = 4). Propylene oxide and/or ethylene oxide is added to the initiators until the desired molecular weight is achieved. The order of addition and the amounts of each oxide affect many polyol properties, such as compatibility, water-solubility, and reactivity. Polyols made with only propylene oxide are terminated with secondary hydroxyl groups and are less reactive than polyols capped with ethylene oxide, which contain primary hydroxyl groups. Incorporating carbon dioxide into the polyol structure is being researched by multiple companies.

Graft polyols (also called filled polyols or polymer polyols) contain finely dispersed styrene–acrylonitrile, acrylonitrile, or polyurea (PHD) polymer solids chemically grafted to a high molecular weight polyether backbone. They are used to increase the load-bearing properties of low-density high-resiliency (HR) foam, as well as add toughness to microcellular foams and cast elastomers. Initiators such as ethylenediamine and triethanolamine are used to make low molecular weight rigid foam polyols that have built-in catalytic activity due to the presence of nitrogen atoms in the backbone. A special class of polyether polyols, poly(tetramethylene ether) glycols, which are made by polymerizing tetrahydrofuran, are used in high performance coating, wetting and elastomer applications.

Conventional polyester polyols are based on virgin raw materials and are manufactured by the direct polyesterification of high-purity diacids and glycols, such as adipic acid and 1,4-butanediol. Polyester polyols are usually more expensive and more viscous than polyether polyols, but they make polyurethanes with better solvent, abrasion, and cut resistance. Other polyester polyols are based on reclaimed raw materials. They are manufactured by transesterification (glycolysis) of recycled poly(ethyleneterephthalate) (PET) or dimethylterephthalate (DMT) distillation bottoms with glycols such as diethylene glycol. These low molecular weight, aromatic polyester polyols are used in rigid foam, and bring low cost and excellent flammability characteristics to polyisocyanurate (PIR) boardstock and polyurethane spray foam insulation.

Specialty polyols include polycarbonate polyols, polycaprolactone polyols, polybutadiene polyols, and polysulfide polyols. The materials are used in elastomer, sealant, and adhesive applications that require superior weatherability, and resistance to chemical and environmental attack. Natural oil polyols derived from castor oil and other vegetable oils are used to make elastomers, flexible bunstock, and flexible molded foam.

Co-polymerizing chlorotrifluoroethylene or tetrafluoroethylene with vinyl ethers containing hydroxyalkyl vinyl ether produces fluorinated (FEVE) polyols. Two-component fluorinated polyurethanes prepared by reacting FEVE fluorinated polyols with polyisocyanate have been used to make ambient cure paints and coatings. Since fluorinated polyurethanes contain a high percentage of fluorine–carbon bonds, which are the strongest bonds among all chemical bonds, fluorinated polyurethanes exhibit resistance to UV, acids, alkali, salts, chemicals, solvents, weathering, corrosion, fungi and microbial attack. These have been used for high performance coatings and paints.[21]

Phosphorus-containing polyols are available that become chemically bonded to the polyurethane matrix for the use as flame retardants. This covalent linkage prevents migration and leaching of the organophosphorus compound.

Bio-derived materials

[edit]

Interest in sustainable "green" products raised interest in polyols derived from vegetable oils,[22][23][24] fatty acids,[25] lignin, sorbitol,[26] etc. These are mostly contributing to polyol part. There are attempts made to prepare isocyanate part using bio-derived material. However, as far as commercialization is concern, polyol part is more targeted being easy and required in more quantity than isocyanate part. Various oils used in the preparation polyols for polyurethanes include soybean oil, cottonseed oil, neem seed oil, algae oil,[27][28] and castor oil. Vegetable oils are functionalized in various ways and modified to polyetheramides, polyethers, alkyds, etc. Renewable sources used to prepare polyols may be fatty acids or dimer fatty acids.[29] Some biobased and isocyanate-free polyurethanes exploit the reaction between polyamines and cyclic carbonates to produce polyhydroxyurethanes.[30]

Chain extenders and cross linkers

[edit]

Chain extenders (f = 2) and cross linkers (f ≥ 3) are low molecular weight hydroxyl and amine terminated compounds that play an important role in the polymer morphology of polyurethane fibers, elastomers, adhesives, and certain integral skin and microcellular foams.

The elastomeric properties of these materials are derived from the phase separation of the hard and soft copolymer segments of the polymer, such that the urethane hard segment domains serve as cross-links between the amorphous polyether (or polyester) soft segment domains. This phase separation occurs because the mainly nonpolar, low melting soft segments are incompatible with the polar, high melting hard segments. The soft segments, which are formed from high molecular weight polyols, are mobile and are normally present in coiled formation, while the hard segments, which are formed from the isocyanate and chain extenders, are stiff and immobile. As the hard segments are covalently coupled to the soft segments, they inhibit plastic flow of the polymer chains, thus creating elastomeric resiliency. Upon mechanical deformation, a portion of the soft segments are stressed by uncoiling, and the hard segments become aligned in the stress direction. This reorientation of the hard segments and consequent powerful hydrogen bonding contributes to high tensile strength, elongation, and tear resistance values.[12][31][32][33][34] The choice of chain extender also determines flexural, heat, and chemical resistance properties.

The most important chain extenders are ethylene glycol, 1,4-butanediol (1,4-BDO or BDO), 1,6-hexanediol, cyclohexane dimethanol and hydroquinone bis(2-hydroxyethyl) ether (HQEE). All of these glycols form polyurethanes that phase separate well and form well defined hard segment domains, and are melt processable. They are all suitable for thermoplastic polyurethanes with the exception of ethylene glycol, since its derived bis-phenyl urethane undergoes unfavorable degradation at high hard segment levels.[10] Diethanolamine and triethanolamine are used in flex molded foams to build firmness and add catalytic activity. Diethyltoluenediamine is used extensively in RIM, and in polyurethane and polyurea elastomer formulations.

Table of chain extenders and cross linkers[35]
Compound type Molecule Mol.
mass
Density
(g/cm3)
Melting
pt (°C)
Boiling
pt (°C)
Hydroxyl compounds – difunctional molecules Ethylene glycol 62.1 1.110 −13.4 197.4
Diethylene glycol 106.1 1.111 −8.7 245.5
Triethylene glycol 150.2 1.120 −7.2 287.8
Tetraethylene glycol 194.2 1.123 −9.4 325.6
Propylene glycol 76.1 1.032 Supercools 187.4
Dipropylene glycol 134.2 1.022 Supercools 232.2
Tripropylene glycol 192.3 1.110 Supercools 265.1
1,3-Propanediol 76.1 1.060 −28 210
1,3-Butanediol 92.1 1.005 207.5
1,4-Butanediol 92.1 1.017 20.1 235
Neopentyl glycol 104.2 130 206
1,6-Hexanediol 118.2 1.017 43 250
1,4-Cyclohexanedimethanol
HQEE
Ethanolamine 61.1 1.018 10.3 170
Diethanolamine 105.1 1.097 28 271
Methyldiethanolamine 119.1 1.043 −21 242
Phenyldiethanolamine 181.2 58 228
Hydroxyl compounds – trifunctional molecules Glycerol 92.1 1.261 18.0 290
Trimethylolpropane
1,2,6-Hexanetriol
Triethanolamine 149.2 1.124 21
Hydroxyl compounds – tetrafunctional molecules Pentaerythritol 136.2 260.5
N,N,N′,N′-Tetrakis
(2-hydroxypropyl)
ethylenediamine
Amine compounds – difunctional molecules Diethyltoluenediamine 178.3 1.022 308
Dimethylthiotoluenediamine 214.0 1.208

Catalysts

[edit]

Polyurethane catalysts can be classified into two broad categories, basic and acidic amine. Tertiary amine catalysts function by enhancing the nucleophilicity of the diol component. Alkyl tin carboxylates, oxides and mercaptides oxides function as mild Lewis acids in accelerating the formation of polyurethane. As bases, traditional amine catalysts include triethylenediamine (TEDA, also called DABCO, 1,4-diazabicyclo[2.2.2]octane), dimethylcyclohexylamine (DMCHA), dimethylethanolamine (DMEA), Dimethylaminoethoxyethanol and bis-(2-dimethylaminoethyl)ether, a blowing catalyst also called A-99. A typical Lewis acidic catalyst is dibutyltin dilaurate. The process is highly sensitive to the nature of the catalyst and is also known to be autocatalytic.[36]

Another class of catalysts was published in a study in May 2024. In this study, polyurethane synthesis was investigated in the presence of acid catalysts, namely dimethylphosphite (DMHP), methanesulfonic acid (MSA), and trifluoromethanesulfonic acid (TFMSA). The thermodynamic profile was examined and described in detail through computational tools, showing that TFMSA had the best catalytic properties. The study aimed to open the door to a new class of catalysts.[37]

Factors affecting catalyst selection include balancing three reactions: urethane (polyol+isocyanate, or gel) formation, the urea (water+isocyanate, or "blow") formation, or the isocyanate trimerization reaction (e.g., using potassium acetate, to form isocyanurate rings). A variety of specialized catalysts have been developed.[38][39][40]

Surfactants

[edit]

Surfactants are used to modify the characteristics of both foam and non-foam polyurethane polymers. They take the form of polydimethylsiloxane-polyoxyalkylene block copolymers, silicone oils, nonylphenol ethoxylates, and other organic compounds. In foams, they are used to emulsify the liquid components, regulate cell size, and stabilize the cell structure to prevent collapse and sub-surface voids.[41] In non-foam applications they are used as air release and antifoaming agents, as wetting agents, and are used to eliminate surface defects such as pin holes, orange peel, and sink marks.

Production

[edit]

Polyurethanes are produced by mixing two or more liquid streams. The polyol stream contains catalysts, surfactants, blowing agents (when making polyurethane foam insulation) and so on. The two components are referred to as a polyurethane system, or simply a system. The isocyanate is commonly referred to in North America as the 'A-side' or just the 'iso'. The blend of polyols and other additives is commonly referred to as the 'B-side' or as the 'poly'.[citation needed] This mixture might also be called a 'resin' or 'resin blend'. In Europe the meanings for 'A-side' and 'B-side' are reversed.[citation needed] Resin blend additives may include chain extenders, cross linkers, surfactants, flame retardants, blowing agents, pigments, and fillers. Polyurethane can be made in a variety of densities and hardnesses by varying the isocyanate, polyol or additives.

Health and safety

[edit]

Fully reacted polyurethane polymer is chemically inert.[42] No exposure limits have been established in the U.S. by OSHA (Occupational Safety and Health Administration) or ACGIH (American Conference of Governmental Industrial Hygienists). It is not regulated by OSHA for carcinogenicity.

Open-flame test. Top: untreated polyurethane foam burns vigorously. Bottom: with fire-retardant treatment.

Polyurethanes are combustible.[43] Decomposition from fire can produce significant amounts of carbon monoxide and hydrogen cyanide, in addition to nitrogen oxides, isocyanates, and other toxic products.[44] Due to the flammability of the material, it has to be treated with flame retardants (at least in case of furniture), almost all of which are considered harmful.[45][46] California later issued Technical Bulletin 117 2013 which allowed most polyurethane foam to pass flammability tests without the use of flame retardants. Green Science Policy Institute states: "Although the new standard can be met without flame retardants, it does NOT ban their use. Consumers who wish to reduce household exposure to flame retardants can look for a TB117-2013 tag on furniture, and verify with retailers that products do not contain flame retardants."[47]

Liquid resin blends and isocyanates may contain hazardous or regulated components. Isocyanates are known skin and respiratory sensitizers. Additionally, amines, glycols, and phosphate present in spray polyurethane foams present risks.[48]

Exposure to chemicals that may be emitted during or after application of polyurethane spray foam (such as isocyanates) are harmful to human health and therefore special precautions are required during and after this process.[49]

In the United States, additional health and safety information can be found through organizations such as the Polyurethane Manufacturers Association (PMA) and the Center for the Polyurethanes Industry (CPI), as well as from polyurethane system and raw material manufacturers. Regulatory information can be found in the Code of Federal Regulations Title 21 (Food and Drugs) and Title 40 (Protection of the Environment). In Europe, health and safety information is available from ISOPA,[50] the European Diisocyanate and Polyol Producers Association.

Manufacturing

[edit]

The methods of manufacturing polyurethane finished goods range from small, hand pour piece-part operations to large, high-volume bunstock and boardstock production lines. Regardless of the end-product, the manufacturing principle is the same: to meter the liquid isocyanate and resin blend at a specified stoichiometric ratio, mix them together until a homogeneous blend is obtained, dispense the reacting liquid into a mold or on to a surface, wait until it cures, then demold the finished part.

Dispensing equipment

[edit]

Although the capital outlay can be high, it is desirable to use a meter-mix or dispense unit for even low-volume production operations that require a steady output of finished parts. Dispense equipment consists of material holding (day) tanks, metering pumps, a mix head, and a control unit. Often, a conditioning or heater–chiller unit is added to control material temperature in order to improve mix efficiency, cure rate, and to reduce process variability. Choice of dispense equipment components depends on shot size, throughput, material characteristics such as viscosity and filler content, and process control. Material day tanks may be single to hundreds of gallons in size and may be supplied directly from drums, IBCs (intermediate bulk containers, such as caged IBC totes), or bulk storage tanks. They may incorporate level sensors, conditioning jackets, and mixers. Pumps can be sized to meter in single grams per second up to hundreds of pounds per minute. They can be rotary, gear, or piston pumps, or can be specially hardened lance pumps to meter liquids containing highly abrasive fillers such as chopped or hammer-milled glass fiber and wollastonite.[citation needed]

The pumps can drive low-pressure (10 to 30 bar, 1 to 3 MPa) or high-pressure (125 to 250 bar, 12.5 to 25.0 MPa) dispense systems. Mix heads can be simple static mix tubes, rotary-element mixers, low-pressure dynamic mixers, or high-pressure hydraulically actuated direct impingement mixers. Control units may have basic on/off and dispense/stop switches, and analogue pressure and temperature gauges, or may be computer-controlled with flow meters to electronically calibrate mix ratio, digital temperature and level sensors, and a full suite of statistical process control software. Add-ons to dispense equipment include nucleation or gas injection units, and third or fourth stream capability for adding pigments or metering in supplemental additive packages.

Tooling

[edit]

Distinct from pour-in-place, bun and boardstock, and coating applications, the production of piece parts requires tooling to contain and form the reacting liquid. The choice of mold-making material is dependent on the expected number of uses to end-of-life (EOL), molding pressure, flexibility, and heat transfer characteristics.

RTV silicone is used for tooling that has an EOL in the thousands of parts. It is typically used for molding rigid foam parts, where the ability to stretch and peel the mold around undercuts is needed. The heat transfer characteristic of RTV silicone tooling is poor. High-performance, flexible polyurethane elastomers are also used in this way.

Epoxy, metal-filled epoxy, and metal-coated epoxy is used for tooling that has an EOL in the tens of thousands of parts. It is typically used for molding flexible foam cushions and seating, integral skin and microcellular foam padding, and shallow-draft RIM bezels and fascia. The heat transfer characteristic of epoxy tooling is fair; the heat transfer characteristic of metal-filled and metal-coated epoxy is good. Copper tubing can be incorporated into the body of the tool, allowing hot water to circulate and heat the mold surface.

Aluminum is used for tooling that has an EOL in the hundreds of thousands of parts. It is typically used for molding microcellular foam gasketing and cast elastomer parts, and is milled or extruded into shape.

Mirror-finish stainless steel is used for tooling that imparts a glossy appearance to the finished part. The heat transfer characteristic of metal tooling is excellent.

Finally, molded or milled polypropylene is used to create low-volume tooling for molded gasket applications. Instead of many expensive metal molds, low-cost plastic tooling can be formed from a single metal master, which also allows greater design flexibility. The heat transfer characteristic of polypropylene tooling is poor, which must be taken into consideration during the formulation process.

Applications

[edit]

In 2007, the global consumption of polyurethane raw materials was above 12 million metric tons, and the average annual growth rate was about 5%.[51] Revenues generated with PUR on the global market are expected to rise to approximately US$75 billion by 2022.[52] As they are such an important class of materials, research is constantly taking place and papers published.[53]

Degradation and environmental fate

[edit]

Effects of visible light

[edit]
Polyurethane foam made with an aromatic isocyanate, which has been exposed to UV light. Readily apparent is the discoloration that occurs over time.

Polyurethanes, especially those made using aromatic isocyanates, contain chromophores that interact with light. This is of particular interest in the area of polyurethane coatings, where light stability is a critical factor and is the main reason that aliphatic isocyanates are used in making polyurethane coatings. When PU foam, which is made using aromatic isocyanates, is exposed to visible light, it discolors, turning from off-white to yellow to reddish brown. It has been generally accepted that apart from yellowing, visible light has little effect on foam properties.[54][55] This is especially the case if the yellowing happens on the outer portions of a large foam, as the deterioration of properties in the outer portion has little effect on the overall bulk properties of the foam itself.

It has been reported that exposure to visible light can affect the variability of some physical property test results.[56]

Higher-energy UV radiation promotes chemical reactions in foam, some of which are detrimental to the foam structure.[57]

Hydrolysis and biodegradation

[edit]

Polyurethanes may degrade due to hydrolysis. This is a common problem with shoes left in a closet, and reacting with moisture in the air.[58]

Microbial degradation of polyurethane is believed to be due to the action of esterase, urethanase, hydrolase and protease enzymes.[59] The process is slow as most microbes have difficulty moving beyond the surface of the polymer. Susceptibility to fungi is higher due to their release of extracellular enzymes, which are better able to permeate the polymer matrix. Two species of the Ecuadorian fungus Pestalotiopsis are capable of biodegrading polyurethane in aerobic and anaerobic conditions such as found at the bottom of landfills.[60][61] Degradation of polyurethane items at museums has been reported.[62] Polyester-type polyurethanes are more easily biodegraded by fungus than polyether-type.[63]

See also

[edit]
  • Botanol, a material with higher plant-based content
  • Passive fire protection
  • Penetrant (mechanical, electrical, or structural)
  • Polyaspartic
  • Polyurethane dispersion
  • Thermoplastic polyurethanes
  • Thermoset polymer matrix

References

[edit]
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  3. ^ "Polyurethane". American Chemistry Council. Retrieved 2022-09-19.
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  8. ^ Feske, Bert (October 2004). "The Use of Saytex RB-9130/9170 Low Viscosity Brominated Flame Retardant Polyols in HFC-245fa and High Water Formulations" (PDF). Polyurethanes Expo 2004. Las Vegas, NV: Alliance for the Polyurethane Industry Technical Conference. p. 309. Retrieved 2007-08-01.
  9. ^ n ≥ 2
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  20. ^ EP 0755955, Hager, Stanley L.; Knight, James E. & Helma, Gregory F. et al., "Polyether polyols suitable for flexible polyurethane foam prepared by co-initiation of aqueous solutions of solid polyhydroxyl initiators", published 1997-01-29, assigned to ARCO Chemical Technology 
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[edit]
  • Center for the Polyurethanes Industry: information for EH&S issues related to polyurethanes developments
  • Polyurethane synthesis, Polymer Science Learning Center, University of Southern Mississippi
  • Polyurethane Foam Association: Industry information, educational materials and resources related to flexible polyurethane foam
  • PU Europe: European PU insulation industry association (formerly BING): European voice for the national trade associations representing the polyurethane insulation industry
  • ISOPA: European Diisocyanate & Polyol Producers Association: ISOPA represents the manufacturers in Europe of aromatic diisocyanates and polyols