Structural Slab Repair Crystal Lake

Structural Slab Repair Crystal Lake

Sidewalk Leveling Experts

Let's dive into how the Smart Lift System raises your concrete with its innovative process. With Smart Lift, you're not just getting a quick fix; you're investing in a solution that's designed to last. Imagine a driveway in Crystal Lake, sunken and cracked, posing a tripping hazard and diminishing the property's curb appeal. Read more about Structural Slab Repair Crystal Lake here Learn more about Structural Slab Repair Crystal Lake here Our customer service is second to none, with a responsive team ready to answer any questions and address any concerns. You're looking at a starting point that's competitive within the Crystal Lake market, ensuring you get top-notch service without breaking the bank.
With systems like Smart Lift, you're not just raising concrete; you're precisely adjusting it to the millimeter, ensuring a perfect fit and prolonged stability. Whether it's through our website or a quick phone call, we're here to listen. This efficiency saves you time and, importantly, money. Trusted concrete raising experts are now offering long-lasting solutions tailored to your needs.
Safety concerns from tripping hazards have significantly diminished, bringing peace of mind to families and visitors. Learn more about Smart Lift System® Concrete Repair in Crystal Lake, Illinois here. They use high-grade materials and cutting-edge techniques to deliver durable, long-lasting results. They've mastered the polyurethane injection technique, ensuring your concrete not only looks new but also lasts longer. Reviews and testimonials can be a goldmine of information, revealing not just the quality of work but also the company's reliability and customer service.
That's where Acme's Smart Lift System comes in, offering a smart, efficient solution. Acme Concrete's solution directly targets these issues, significantly reducing the risk of falls and injuries. How much does it cost to bring your concrete back to life with Acme Concrete's services? If you're ready to elevate your property's safety and aesthetics, starting with us is a seamless process. Concrete Driveway Maintenance Concrete Patching Services

It's simpler than you think. You'll enhance the safety and appearance of your property while avoiding the higher costs associated with neglecting these issues. This traditional technique involves pumping a mixture of water, soil, and cement beneath settled concrete to raise it. They use state-of-the-art equipment and the latest techniques to ensure the job is done right the first time. So, it's not just smart; it's a strategic move for any business looking to optimize their operations and presentation.

They've literally raised the bar for home services,' he admits with a chuckle. It's also lightweight, reducing the risk of further sinking, and it's water-resistant, which guards against the very erosion that caused the problem. By choosing to repair rather than replace, you're not just avoiding the immediate higher costs of new concrete, but you're also dodging the associated demolition and disposal fees. By leveraging advanced materials and precision lifting techniques, they're able to address the root cause of the issue-soil instability-without the mess.

Concrete Raising Experts



    You might feel overwhelmed, thinking about the complexity and expense of fixing these issues. Imagine concrete raising methods that not only repair but also enhance the longevity and durability of your structures. You'll experience real-time, accurate diagnostics of your concrete issues, allowing for more personalized and cost-effective solutions. And let's not overlook the aesthetic aspect; repaired sidewalks and driveways enhance your home's overall appearance, potentially boosting its value.

    Polyurethane foam is highly resilient and capable of withstanding substantial loads, ensuring a long-lasting solution to your sunken concrete problems. Early detection can mean simpler, more cost-effective repairs. The integration of digital tools and IoT (Internet of Things) into concrete raising will enable real-time monitoring of conditions, predicting potential issues before they become problems. You won't have to worry about frequent repairs or maintenance.

    Citations and other links

    Sidewalk Repair Crystal Lake

    It's not merely about the visual appeal; it's a safety concern too. But don't let the cost deter you. Building on their commitment to quality and efficiency, Acme Concrete Raising & Repair employs innovative repair techniques to ensure your walkways aren't only safer but also aesthetically pleasing. Next, consider a backyard patio that's seen better days, with slabs that have shifted and settled over time.

    Imagine stepping outside to see your once uneven concrete now perfectly level, all without the hassle and expense of a complete replacement. You'll find that Acme's approach isn't just about injecting material beneath the surface. Quick Concrete Lifting Service This not only helps in lowering your carbon footprint but also aligns with modern standards for eco-conscious construction and repair.

    You should also monitor for any new cracks or signs of settling.

    Concrete Preservation

    1. Polyurethane Foam Injection
    2. Polyurethane Concrete Lifting
    3. Concrete Joint Sealing
    4. Driveway Leveling Crystal Lake
    5. Sunken Concrete
    6. Concrete Slab Stabilization
    7. Concrete Leveling
    8. Affordable Concrete Raising
    9. Crystal Lake Mudjacking Company
    10. Sinking Slab Correction
    11. Concrete Foundation Settlement
    12. Concrete Lifting Near Me
    13. Cracked Driveway Repair
    14. Sidewalk Leveling Experts
    15. Slab Leveling Solutions
    16. Garage Floor Lifting
    17. Sunken Walkway Fix
    18. Concrete Lifting
    19. Eco-Friendly Concrete Lifting
    20. Local Concrete Leveling Services
    During this meeting, they'll assess the current state of your walkways, listen to your concerns, and discuss the most effective solutions tailored to your specific needs. Trip Hazard Removal The system uses a specially formulated material that's both strong and eco-friendly, avoiding the need for chemical-laden solutions or the excessive waste often associated with older methods.

    You're also looking at a minimal disruption to your daily life. It's a win-win for your property and the planet. Basement Floor Lifting However, Acme Concrete's approach turns this on its head.

    Sidewalk Repair Crystal Lake
    Concrete Raising Crystal Lake

    Concrete Raising Crystal Lake

    You won't be waiting around for days to see results. The foam expands, filling voids and raising the concrete to its original level. This means no odd color patches or visible signs of intervention. With their innovative polyurethane foam injection method, they're miles ahead of the traditional mudjacking techniques that others still cling to. Opting for Acme Concrete's services ensures you benefit from leading-edge repair techniques and unparalleled customer service.

    They use a state-of-the-art polyurethane foam injection technique. There's minimal disruption to your property, and you can walk on the repaired surface almost immediately. Water infiltration, freeze-thaw cycles, and chemical exposure (like salt in winter) can accelerate the aging process. Don't hesitate to ask for before-and-after photos of previous projects.

    They don't just repair concrete; they restore your peace of mind, proving time and again why they're the top choice in Crystal Lake. You won't have to wait days for the area to be usable; in most cases, it's ready within hours.

    Commercial Concrete Services

    1. Sidewalk Leveling Experts
    2. Void Filling
    3. Concrete Crack Injection
    4. Void Filling
    5. Concrete Crack Injection
    6. Void Filling
    7. Concrete Crack Injection
    8. Void Filling
    9. Concrete Crack Injection
    10. Void Filling
    11. Concrete Crack Injection
    12. Void Filling
    13. Concrete Crack Injection
    14. Void Filling
    15. Concrete Crack Injection
    16. Void Filling
    Tripping on an uneven surface can result in injuries, and water seeping through cracks can undermine the foundation of structures, making them unsafe. Garage Slab Settlement They offer ongoing maintenance advice, showing you how to care for your concrete to maximize its durability.

    As we peel back the layers of this essential service, you'll discover the intricate process and the benefits it holds for your home. This system isn't about patchwork that screams “repair”; it's about a seamless integration that makes your concrete appear as good as new. You'll be amazed at how quickly and quietly the process unfolds, often in mere hours. Acme's technicians are trained to spot the unique challenges each site presents, from soil composition to the extent of the damage, tailoring their application method to address these issues head-on.

    Affordable Concrete Lifting Crystal Lake IL

    When you choose Acme Concrete's advanced repair system for your sidewalks and driveways, you're making a decision that benefits everyone around you. It's also waterproof, which prevents future erosion and soil destabilization under the slab. To inject the mixture, large holes are drilled into the slab. Void Filling The beauty of this system is its precision and efficiency. Addressing these issues isn't just about patching up a few cracks.

    It's perfect for a wide range of commercial applications, from warehouse floors to parking lots, sidewalks, and more. They're not just about fixing your concrete; they're committed to offering solutions that last. This precision means you're not left with a patchwork of repairs but a seamlessly restored sidewalk or driveway. But here's the good news: Acme Concrete has developed a range of repair techniques that not only save you money but also extend the life of your concrete surfaces.

    By choosing concrete raising, you're also opting for a quicker fix. Furthermore, the aesthetic improvement your property undergoes can inspire others to take similar actions, creating a ripple effect of enhancements throughout your area. Moreover, Acme Concrete values your time and property. One standout technique they use is polyurethane foam injection, a method far superior to traditional mudjacking.

    Hearing directly from satisfied customers offers the best insight into the quality and impact of our concrete raising services. You're not just investing in a temporary fix, but a durable solution that brings peace of mind. This approach not only saves you money but also time, as repair work is typically completed much faster than full replacements. The materials used are designed to last, ensuring you won't be revisiting the same issues anytime soon.

    Affordable Concrete Lifting Crystal Lake IL
    Cement Driveway Repair Crystal Lake
    Cement Driveway Repair Crystal Lake

    It's not just about aesthetics; it's a matter of safety, too. You'll benefit from quicker, cleaner, and more precise applications, minimizing disruption to your daily life. Commercial Concrete Services During the inspection, we'll assess the extent of the damage and determine the best course of action. Plus, the drilled holes are then filled and sealed, leaving your concrete looking as good as new.

    Sidewalk Leveling Experts

    1. Slabjacking
    2. Void Filling
    3. Patio Leveling
    4. Sidewalk Leveling
    5. Local Concrete Repair Crystal Lake
    6. Mudjacking
    7. Concrete Raising Contractors
    8. Garage Apron Repair
    9. Residential Driveway Leveling
    10. Curb Lifting
    11. Concrete Pressure Injection
    12. Sidewalk Trip Hazard Fix
    13. Precision Concrete Leveling
    14. Helical Piers
    15. Fix Uneven Driveway Crystal Lake




    Quick Concrete Lifting Service

    • Concrete Grinding
    • Leveling Concrete Slabs
    • Concrete Settling
    • No-Dig Concrete Repair
    • Concrete Raising Reviews
    • Driveway Repair
    • Slabjacking
    • Void Filling
    • Patio Leveling
    • Sidewalk Leveling
    • Local Concrete Repair Crystal Lake
    • Mudjacking
    • Concrete Raising Contractors
    • Garage Apron Repair
    • Residential Driveway Leveling
    • Curb Lifting
    Concrete Floor Leveling Crystal Lake

    They're not just fixing the problem temporarily; they're providing a long-term solution that'll save you money and hassle down the line. While effective, mudjacking is messy, requires larger holes, and the materials can take a while to settle and harden. In most cases, the repair is completed within a few hours, and you can walk or drive on the surface almost immediately after. Concrete Waterproofing Moreover, precision is getting a significant boost. Here's how it works: small holes are drilled into the affected concrete, through which a high-density foam is injected.

    Basement Floor Lifting

    • Concrete Crack Repair
    • Concrete Expansion Joint Repair
    • Crystal Lake Home Services
    • Concrete Void Filling
    • Crystal Lake Concrete Experts
    • Concrete Grinding
    • Leveling Concrete Slabs
    • Concrete Settling
    • No-Dig Concrete Repair
    • Concrete Raising Reviews
    • Driveway Repair
    • Slabjacking
    • Void Filling
    • Patio Leveling
    • Sidewalk Leveling
    • Local Concrete Repair Crystal Lake
    • Mudjacking
    • Concrete Raising Contractors
    • Garage Apron Repair

    Polyurethane foam cures quickly, usually within minutes, allowing you to use the repaired area almost immediately. Polyurethane foam, already known for its efficiency, is getting greener, reducing its carbon footprint without compromising on quality. As we look toward the horizon, it's clear that the future of concrete raising holds exciting advancements and possibilities for our community.

    Chicagoland Concrete Solutions

    1. Concrete Support Injection
    2. Concrete Floor Leveling Contractors
    3. Interior Floor Lifting
    4. Structural Concrete Repair
    5. Concrete Surface Repair
    6. Concrete Resurfacing
    7. Concrete Raising Cost Estimate
    8. Concrete Sinking
    9. Crystal Lake Foundation Contractors
    10. Soil Stabilization
    11. Affordable Slab Lifting Crystal Lake
    12. Illinois Concrete Repair
    13. Uneven Concrete Repair
    14. Sunken Step Repair
    15. Garage Slab Settlement
    16. Chicagoland Concrete Solutions
    17. Concrete Driveway Maintenance
    18. Concrete Preservation
    19. Commercial Concrete Services
    20. Basement Floor Lifting
    Essentially, it boils down to the ground beneath it.
    Understanding our concrete raising process from start to finish will give you peace of mind as we work on your property. The homeowner, initially skeptical, opted for the latest polyurethane foam injection method over traditional mudjacking. Not only does it save you money, but it also significantly reduces the time involved in making your concrete surfaces safe and appealing again. Acme's techniques, such as concrete raising, are designed to be less invasive and less expensive than full walkway replacements.

    Concrete Waterproofing

    1. Concrete Patching Services
    2. Concrete Repair Estimate Crystal Lake
    3. Quick Concrete Lifting Service
    4. Trip Hazard Removal
    5. Concrete Leveling Companies
    6. Garage Slab Settlement
    7. Chicagoland Concrete Solutions
    8. Concrete Driveway Maintenance
    9. Concrete Preservation
    10. Commercial Concrete Services
    11. Basement Floor Lifting
    12. Water-Resistant Foam Injection
    13. Concrete Waterproofing
    14. Concrete Raising Experts
    15. Driveway Settling Solutions
    16. Soil Erosion Under Slab
    17. Driveway Void Repair
    18. Sustainable Concrete Repair

    After exploring the ease of installation and low maintenance of Acme's Smart Lift System, let's hear directly from those who've experienced its benefits firsthand. They understand the importance of your time and aim to get the job done quickly without sacrificing quality. Understanding this, it becomes clear why a durable solution to lifting settled concrete is necessary. This method is also environmentally friendly; it reduces the need for new concrete production and minimizes waste, aligning with sustainable practices.

    Explore Structural Slab Repair Crystal Lake here

    Chicagoland Concrete Solutions

    • Crystal Lake IL Contractors
    • Polyurethane Foam Injection
    • Polyurethane Concrete Lifting
    • Concrete Joint Sealing
    • Driveway Leveling Crystal Lake
    • Sunken Concrete
    • Concrete Slab Stabilization
    • Concrete Leveling
    • Affordable Concrete Raising
    • Crystal Lake Mudjacking Company
    • Sinking Slab Correction
    • Concrete Foundation Settlement
    • Concrete Lifting Near Me
    • Cracked Driveway Repair
    • Sidewalk Leveling Experts
    • Slab Leveling Solutions
    Concrete Floor 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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    [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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    9. ^ n ≥ 2
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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