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Polyurethane Resins are a broad family of polymers obtained from the reaction of polyols with isocyanates and carrying the urethane linkage (–NH–CO–O–) in their chain. They do not describe a single chemical; the term covers liquid, dispersion, granule and solid systems produced from polyester or polyether polyols, aromatic or aliphatic isocyanates, and according to the form of use. They are widely used in paints, adhesives, synthetic leather, footwear and elastomers because hardness, flexibility and abrasion resistance can be adjusted.
Urethane resin, in two-component systems, crosslinks at room temperature when the polyol component and the isocyanate hardener are mixed, and forms a hard, chemical-resistant film. It is used as paint and varnish on wood, metal and plastic surfaces, and as a protective layer in floor and pipe coatings. Aliphatic isocyanate-based types keep their color and gloss outdoors, while aromatic types offer an economical solution for interior and primer applications.
Water-based polyurethane dispersion is a form of use preferred in textiles, leather, wood coating, packaging lamination and glass fiber sizing thanks to its low solvent emission. Thermoplastic polyurethane and moisture-curing prepolymers are other members of the family; in selection, the polyol type, isocyanate type, solids content, NCO content and the manufacturer’s documents should be evaluated together. These products can be supplied from ATAMAN KİMYA; for technical information and requests, contacting ATAMAN KİMYA is recommended.
WHAT ARE POLYURETHANE RESINS?
Polyurethane Resins cover polymers formed when polyols carrying two or more hydroxyl groups react with compounds containing two or more isocyanate groups. The urethane linkage formed in the reaction is the basic unit of the polymer and repeats along the chain.
In terms of chemical class, the name does not denote a single substance but a product family whose structure varies with the choice of raw materials. The properties of the family are determined by the polyol type, the isocyanate type and the ratio of chain extenders and crosslinkers.
The raw materials can be combined in a single step, an NCO-terminated prepolymer can be prepared first and then chain-extended, or the prepolymer can be dispersed in water to obtain a dispersion. Commercial products are offered as liquid solutions, water-based dispersions, granules and reactive hot melts.
Fully cured polyurethane is a tough, flexible material that contains no free isocyanate. Uncured resin, prepolymers and hardeners, on the other hand, may carry isocyanate and therefore call for separate safety measures.
COMMON PRODUCT AND CHEMICAL NAMES OF POLYURETHANE RESINS:
Polyurethane
Polyurethane resin
Polyurethane resin (alternative form)
Urethane resin
Urethane resin (alternative form)
Polyurethane polymer
Polyurethane paint resin
Polyurethane coating resin
Polyurethane varnish resin
Polyurethane adhesive resin
One-component polyurethane resin
Two-component polyurethane resin
Moisture-curing polyurethane
Solvent-based polyurethane resin
Solvent-free polyurethane resin
Water-based polyurethane resin
Polyurethane dispersion
Aqueous polyurethane dispersion
Polyurethane emulsion
Thermoplastic polyurethane
Polyurethane elastomer
Polyester polyurethane
Polyether polyurethane
Aliphatic polyurethane resin
Aromatic polyurethane resin
Isocyanate prepolymer
Polyurethane prepolymer
Polyurethane synthetic leather resin
Polyurethane casting resin
Polyurethane hot melt resin
Trade names depend on the manufacturer. In polyurethane paint systems the Desmophen polyols and Desmodur isocyanates are seen, in water-based dispersions the Baybond, Alberdingk Pur and Hydran series, in thermoplastic types Desmopan, and in hot melt adhesives the Technomelt PUR series.
CAS NO, EC / EINECS NO AND CHEMICAL IDENTIFICATION OF POLYURETHANE RESINS
Product name: Polyurethane Resins
Common abbreviation: PU; PUD for water-based types, TPU for thermoplastic types
Chemical name: Polyurethane (polyaddition polymer of polyols with di- or polyisocyanates)
INCI name: There is no single INCI name for the resin itself; some special cosmetic-grade polyurethanes are registered under numbered names such as Polyurethane-34 and Polyurethane-35
CAS No: There is no single CAS number; 9009-54-5 is frequently seen in sources for general polyurethane, while products carry different numbers depending on composition
EC / EINECS No: Since polymers are not listed in EINECS, no single number is given for the resin; the raw materials have their own numbers
Molecular formula: There is no fixed formula; the general repeating unit is shown as –[O–R′–O–CO–NH–R–NH–CO]n–
Molecular weight: Varies by product type; manufacturer data report an equivalent weight of approximately 340–935 g/mol for polyester polyols and approximately 315 g/mol for a TDI-based polyisocyanate
Chemical class: Polymer, polyaddition polymer containing the urethane linkage
Main functions: Film former, binder, adhesive, elastomer matrix, protective coating
SUBFAMILIES OF POLYURETHANE RESINS
Polyurethane Resins should be evaluated not as a single product but as a whole made up of subfamilies with different properties. Below, five main subfamilies are summarized with their chemical structures, typical properties and fields of use.
The values given are example product data published by the manufacturers concerned and general literature ranges. The technical data sheet of each product should be taken as the basis.
1. POLYESTER POLYOL-BASED POLYURETHANE RESINS
Polyester polyol-based resins are formed by the reaction of hydroxyl-terminated polyesters, obtained by the condensation of acids such as adipic acid or phthalic anhydride with glycols, with isocyanate. They provide high tensile and tear strength.
Because ester groups are polar, strong interactions form between the chains. This structure is the source of mechanical strength; the same linkages are also open to hydrolysis under water and heat.
Semi-crystalline polyesters give the best resistance to oils, grease, fuels and hydrocarbon solvents. A high melting point, high acidity and a broad molecular weight distribution, on the other hand, can affect processing and catalyst behavior; residual esterification catalysts accelerate hydrolysis.
Hydrolysis resistance can be increased through the structure of the polyol. In one comparison the polyol was heated with 10 percent water at 90 °C for up to 12 hours and the acid formed was measured; 2-methyl-1,3-propanediol adipate showed the highest resistance, and mixtures of this glycol with butanediol or hexanediol also gave better results than butanediol adipate.
The methyl group in branched glycols shields the ester linkage sterically; neopentyl glycol adipate gives a similar level of resistance. Caprolactone- and polycarbonate-based polyols are also more stable than standard adipate and phthalate polyesters.
Carbodiimide-based stabilizers slow degradation by binding the acids formed by hydrolysis; an additive at about 1 percent has been found effective, but it has been reported that it does not prevent degradation completely.
Example manufacturer data, Desmophen 1200: Slightly branched polyester polyol; hydroxyl content 4.7–5.3 percent; viscosity 16,000–31,000 mPa·s (23 °C); acid number at most 4 mg KOH/g; water content at most 0.1 percent; equivalent weight approximately 340 g/mol.
Example manufacturer data, Desmophen 1800: Slightly branched polyester polyol; hydroxyl content 1.73–1.91 percent (hydroxyl number 57–63 mg KOH/g); viscosity 19,000–24,000 mPa·s; equivalent weight approximately 935 g/mol.
Polyester-based polyurethanes are superior in friction and sliding abrasion; hydrolysis that starts at the surface, however, lowers long-term abrasion resistance. This structure is preferred in parts such as gears, seals and belts working in oily and fuel-contaminated environments.
A polyol of low equivalent weight gives a hard and chemical-resistant film, while a polyol of high equivalent weight gives a flexible one. It has been reported that Desmophen 1200 is used with the Desmodur L hardener in metal, wood and plastic coatings, and Desmophen 1800 in flexible coatings on rubber and plastics.
Main fields of use:
• Paints for metal, wood and plastic
• Flexible coatings applied to rubber and plastics
• Adhesive and lamination systems
• Elastomer parts requiring high tear and cut resistance
Strengths:
• High tensile, tear and flex fatigue strength
• Good resistance to oils and solvents, resistance to sliding abrasion
• Retention of properties at high temperature
Limitations:
• Susceptibility to hydrolysis under continuous water, steam and humid conditions
• Lagging behind polyethers in low-temperature flexibility
• Need for protection from moisture because of being slightly hygroscopic
It is stored in the original sealed container at 0–30 °C, and the stated properties are valid for 9 months from shipment. In quality control, the hydroxyl number (ASTM D4274), acid number, water content and viscosity are monitored.
2. POLYETHER POLYOL-BASED POLYURETHANE RESINS
Polyether polyol-based resins are produced with polyols based on polypropylene glycol and polytetramethylene ether glycol derived from monomers such as propylene oxide or tetrahydrofuran. Polyethers make up about 80–90 percent of the polyols used today.
The ether linkage is resistant to hydrolysis and keeps the chain flexible. For this reason polyether-based systems are preferred in humid, wet and water-immersed environments, and also at low temperatures.
Polytetramethylene ether glycol (CAS 25190-06-1) is a fully difunctional polyol with low acidity and a narrow molecular weight distribution, and is used in high-performance elastomers thanks to its low viscosity and consistent production. Its tendency to crystallize under strain gives high mechanical strength.
Polypropylene glycol (CAS 25322-69-4) is a more economical option; its structure contains a small amount of monofunctional components and less reactive secondary hydroxyl groups, and the molecular weight that can be reached is lower. Its mechanical properties are lower than those of polytetramethylene ether glycol.
Low molecular weight grades of polytetramethylene ether glycol melt below room temperature, while high molecular weight grades melt slightly above room temperature. This may create a need for heating during storage and dosing.
The property of a polyol is expressed by the hydroxyl number (mg KOH/g). As molecular weight increases, the hydroxyl number falls. In polyol control, functionality, molecular weight distribution, equivalent weight, water content, reactivity, viscosity, color and acid number are also monitored.
The choice of isocyanate varies with the use; toluene diisocyanate is common in flexible foams and coatings, and diphenylmethane diisocyanate in rigid foams and elastomers. Amine-terminated polyether polyols and, to a lesser extent, polycarbonate polyols are also used.
Polyether-based thermoplastic polyurethanes stay flexible down to about –60 °C, whereas for polyester-based types this value is about –40 °C. Continuous service temperature is reported as about 100 °C for polyester and about 90 °C for polyether.
Typical properties:
• Very good resistance to hydrolysis
• Low glass transition temperature and flexibility at low temperature
• High rebound (resilience) and low heat build-up
• Good resistance to microbial degradation
Main fields of use:
• Flexible foams and cushioning materials, furniture and automotive seats
• Dynamic elastomer parts such as wheels, belts, hoses and pipes
• Underwater, cold storage and medical tubing applications
• Foams and elastomers in the footwear, construction and heating-cooling sectors
Strengths:
• Stability in wet and humid environments
• Flexibility at low temperature
• Impingement abrasion resistance
Limitations:
• Lower resistance to oils, fuels and solvents than polyesters
• Susceptibility to thermo-oxidative degradation in polypropylene glycol-based systems
• Polypropylene glycol-based types lagging behind in tensile and tear strength
Selection note: The choice between polyether and polyester polyol depends on the working environment. In wet and cold environments polyether stands out, in oily and hot environments polyester. In some products the two structures are used together.
3. WATER-BASED POLYURETHANE DISPERSIONS
Water-based polyurethane dispersions are low-viscosity, milky-looking liquids obtained by dispersing polymer particles in water. During drying the water evaporates, the particles coalesce and a continuous film forms.
The ionic groups bound to the chain as an internal emulsifier keep the particles in water. The common route is to use dimethylolpropionic acid (CAS 4767-03-7) and neutralize the carboxyl groups with an amine such as triethylamine; nonionic stabilization with polyethylene oxide segments is also applied.
In production an NCO-terminated prepolymer is prepared first, then dispersed in water and chain-extended. In the literature, an example has been reported in which a prepolymer brought down to 2.6 percent NCO in about 2.5 hours at 80 °C was dispersed in water at 40 °C to give a dispersion of pH 6.5.
General ranges: 30–50 percent solids by weight (more than 50 percent is also obtained with a continuous extruder method); viscosity 50–500 mPa·s; particle size 50–2000 nm; carboxyl content about 0.3–1.2 meq/g; film tensile strength 10–50 MPa; elongation at break 200–800 percent.
Particle size affects performance. Small particles of 200–300 nm penetrate porous surfaces, while large particles of 1000–2000 nm increase abrasion resistance in the surface layer; bimodal distributions are also used.
Manufacturers also offer special dispersion grades for synthetic leather, metal coating, film primer and ink binder, together with high-solids water-based resins. Some dispersions can be diluted with deionized water in any ratio.
Example manufacturer data, Alberdingk Pur Matt 310: Aliphatic polyurethane dispersion; solids 41–43 percent; pH 7.0–9.0; minimum film formation temperature about 10 °C; density 1.0–1.1 g/cm³; film tensile strength about 16 N/mm², elongation at break about 750 percent; packaging as 120 kg plastic drums and about 1000 kg containers.
Example manufacturer data, Baybond PU 403: Polyester urethane dispersion; about 39 percent solids; viscosity below 250 mPa·s; mean particle size 0.3 µm or smaller; used in glass fiber sizing, and film properties improve with heat treatment at 170 °C for 30 minutes.
Main fields of use:
• Wood, plastic and metal coatings, matt and soft-touch surfaces
• Heat-activated lamination adhesives, packaging and automotive interiors
• PVC foil lamination in furniture and shoe bonding
• Textile coating, synthetic leather, film primer, ink binder and glass fiber sizing
Strengths:
• Low solvent content and low VOC
• Good UV and weather resistance in aliphatic types; in well-prepared formulations, less than 5 percent gloss loss in 2000 hours of accelerated weathering has been reported
• The possibility of increasing resistance by making them two-component with a polyisocyanate crosslinker
Limitations:
• Decrease in the water resistance of the film as ionic content increases
• Sensitivity to freezing and to temperatures above 30 °C
• Risk of microorganism contamination in storage and film formation in an open container
• Higher cost and processing difficulty in shoe bonding compared with solvent-based systems
Storage: Manufacturers generally recommend storage at 5–30 °C in the original sealed container, give a shelf life of 6–12 months, and advise retesting afterwards.
According to a market study, the polyurethane dispersion market was about 2.2 billion dollars in 2023, and water-based types made up more than half of it. The low-VOC trend is cited as the main factor supporting growth in this area.
4. THERMOPLASTIC POLYURETHANES
Thermoplastic polyurethanes are linear block copolymers made up of alternating hard and soft segments. The hard segment consists of an aromatic isocyanate (mostly diphenylmethane diisocyanate, CAS 101-68-8) or aliphatic 4,4′-methylenebis(cyclohexyl isocyanate) with a short-chain diol.
The soft segment comes from a polyether, polyester or polycaprolactone polyol. The microphase separation between the two segments forms a physical network that softens and can be processed when heated but behaves like an elastomer at room temperature.
Hardness is adjusted by the share of the hard segment. 30–60 percent hard segment by weight corresponds to roughly Shore A 60–98 and Shore D 40–75; the commercial range extends from Shore A 60 to Shore D 80.
Positioned between rubber and rigid plastic, this material is sold as granules and processed by injection molding, extrusion, blow molding, calendering and film production. Production scrap can be reground and used without a significant loss of properties.
General ranges: Tensile strength about 25–70 MPa; elongation at break about 300–800 percent; tear strength about 30–150 kN/m; Taber abrasion loss about 20–50 mg per 1,000 cycles; processing temperature 180–230 °C; injection pressure 20–110 MPa; mold temperature 20–50 °C.
In terms of degradation, hard segments begin to decompose at about 280–320 °C and soft segments at 350–420 °C. Before processing, the granules are dried at 80–110 °C for 2–4 hours to bring moisture below 0.02 percent.
Polyester types provide oil, hydrocarbon and abrasion resistance but are open to hydrolysis. Polyether types are more resistant to hydrolysis, microbes and low temperature; polycarbonate types stand out in UV, heat and hydrolysis resistance, and water absorption below 1.5 percent has been reported in one example.
Aliphatic types do not yellow and are suitable for outdoor use. In a comparative study, diphenylmethane diisocyanate-based types gave higher tensile strength, elongation, hardness and chemical resistance, while aliphatic types yellowed much less after UV.
Expanded or microcellular grades are used in shoe midsoles and sports padding, and flame-retardant grades (UL 94 V-0) in cable jackets.
As an example, Covestro’s Desmopan 5080A is offered as an ester/ether thermoplastic polyurethane with improved hydrolysis and microbial resistance for seal and membrane applications.
Main fields of use:
• Shoe soles, shoe side parts and sports equipment
• Automotive interior surfaces, protective films and seals
• Cable jackets, hoses, pipes, conveyor belts and wheels
• Film, sheet and coated fabrics
• Medical tubing and catheters (the relevant biocompatibility tests are required separately)
• 3D printing filament
Strengths:
• Flexibility without plasticizers and high elastic recovery
• Abrasion, tear and impact resistance
• The ability to reuse production scrap
Limitations:
• Degradation of polyester types under continuous moisture and steam
• Drop in mechanical properties above about 80–100 °C and permanent deformation at high temperature
• Yellowing under UV in aromatic types
• Need for drying
5. ISOCYANATE PREPOLYMERS AND TWO-COMPONENT SYSTEMS
Prepolymers are obtained by reacting excess isocyanate with polyol, generally at 60–90 °C under nitrogen for 2–6 hours, and carry free NCO groups at their ends. Production can be carried out by the one-shot, prepolymer or quasi-prepolymer method.
In commercial prepolymers the NCO content varies between 3 and 46 percent; the reported ranges are generally 10–40 percent in coatings and adhesives, 20–40 percent in moisture-curing foams, 25–35 percent in structural adhesives, and 8–15 percent in diphenylmethane diisocyanate-based sealants.
One-component systems cure with moisture from the air. The NCO group reacts with water, releases carbon dioxide and forms a urea linkage; the suitable humidity range is generally 40–70 percent relative humidity. If the humidity is too high, there is a risk of foaming. Additives such as acidic phosphoric acid esters can extend shelf life from 3–6 months to 12–18 months.
In two-component systems the polyol component and the isocyanate hardener are mixed before use; the NCO/OH equivalent ratio is generally 1.0–1.1. Curing takes place at room temperature, and forced drying up to 80 °C shortens the time.
Blocked isocyanates, on the other hand, are stable at room temperature, react by releasing the blocking group at 120–200 °C, and have no pot life limit.
Example manufacturer data, Desmodur L 75: Aromatic, toluene diisocyanate-based polyisocyanate; NCO content 13.3 ± 0.4 percent; solids 75 percent (solvent ethyl acetate); viscosity about 1,600 mPa·s; equivalent weight about 315; stored at 10–30 °C, with properties reported valid for 6 months. It is used as a two-component hardener in furniture, parquet, metal and plastic paints.
Example manufacturer data, Desmodur ultra E 30600: Aliphatic, hexamethylene diisocyanate-based prepolymer containing ether groups; NCO content 6.0 ± 0.5 percent; viscosity about 2,500 mPa·s; used as a hardener giving flexibility in pipe coating systems; stored at 10–25 °C, protected from moisture, and at high temperature its viscosity increases while its NCO content falls.
Desmodur E 1660, on the other hand, is an aromatic prepolymer based on toluene diisocyanate; it is used in fast-drying one-component moisture-curing coatings and as a hardener in two-component systems.
The difference between aromatic and aliphatic isocyanates is the basis of selection. Fast curing and low cost are the advantages of aromatic types, but they yellow in sunlight. Aliphatic types provide UV durability and weather resistance, cure more slowly and are generally more expensive.
Linear aliphatics (hexamethylene diisocyanate, CAS 822-06-0) give softer and more flexible products, cycloaliphatics (isophorone diisocyanate, CAS 4098-71-9) harder and more durable ones. Because cycloaliphatics react more slowly, a very small amount of tin catalyst may be needed.
Reactive hot melt (PUR) adhesives also fall into this group. As an example, Henkel Technomelt PUR 149C is a 100 percent solids, one-component hot melt; a viscosity of 14,000 mPa·s at about 121 °C, an application temperature of 121–135 °C, an open time of 4–5 minutes and a shelf life of 6 months have been reported. It cures with air moisture, and MDI monitoring is recommended in workplace surveillance.
Main fields of use:
• Two-component paints on wood, metal and plastic
• Floor, parquet and pipe coatings
• Moisture-curing one-component coatings and adhesives
• Reactive hot melt adhesives, flat lamination
Strengths:
• Curing speed that can be adjusted to application conditions
• High surface hardness, chemical resistance and adhesion
• Design flexibility through a wide range of NCO and equivalent weights
Limitations:
• Need for strict moisture protection because of reaction with moisture and water
• Risk of respiratory and skin sensitization because of the isocyanate content
• In the European Union, a user training requirement from 24 August 2023 for products containing 0.1 percent or more monomeric diisocyanate by weight
CHEMICAL STRUCTURE AND MOLECULAR PROPERTIES OF POLYURETHANE RESINS
The basic unit of polyurethane is the urethane linkage formed by the reaction of the isocyanate group (–N=C=O) with the hydroxyl group. The N–H group in the linkage is a hydrogen bond donor and the carbonyl oxygen is an acceptor; the bonds formed between chains keep the hard segments bound to one another.
The chain consists of two kinds of segments. The soft segment comes from the polyol and is flexible; the glass transition temperature in dispersion films is reported as about –60 to –20 °C. The hard segment is made up of the isocyanate and a short-chain diol, and its glass transition temperature is about 80–150 °C.
The two segments separate on a micro scale, and the hard segments behave like physical crosslink points. The functionality of the raw materials determines the network structure: difunctional ones give a linear chain, those with three or more functional groups give a permanently crosslinked network.
Aromatic rings provide hardness but cause yellowing under UV; aliphatic and cycloaliphatic structures do not yellow. Ester linkages are prone to hydrolysis and ether linkages to oxidation; carbonate-based structures are more resistant to both. Polyurethanes are not soluble in water, and water-based types remain dispersed thanks to ionic groups.
PHYSICAL AND CHEMICAL PROPERTIES OF POLYURETHANE RESINS
Physical appearance: Solutions are clear, light yellow to amber liquids; dispersions are milky white liquids; thermoplastic types are granules; cured products are films, coatings or elastomers
Chemical character: Polar, neutral polymer; components containing isocyanate are reactive
Molecular formula: There is no fixed formula; it consists of repeating units containing the urethane linkage
Molecular weight: Depends on the product type; low in polyols and prepolymers, high in thermoplastic polyurethane and dispersion polymers
CAS No: There is no single number; 9009-54-5 is frequently used for general polyurethane
EC / EINECS No: There is no single number because it is a polymer
Solids content: About 30–50 percent in dispersions; about 75 percent in hardeners in solution; 100 percent in thermoplastic types and reactive hot melts
Density: In liquid products about 1.0–1.1 g/cm³ as an example; in cured products it depends on the composition
Viscosity: 50–500 mPa·s in dispersions; about 1,600 mPa·s as an example in a polyisocyanate solution; 16,000–31,000 mPa·s in polyester polyols
NCO / OH content: 6.0–13.3 percent NCO in example products of isocyanate components; 3–46 percent in commercial prepolymers; 1.73–5.3 percent OH as an example in polyester polyols
Solubility in water: Insoluble; dispersions can be diluted with water, isocyanate components react with water
pH (aqueous solution): Meaningful only for dispersions; about 6.5–9.0 in example products
Decomposition: Polyester types degrade by hydrolysis, polyether types by oxidation, aromatic types by loss of color under UV; film degradation generally begins at 250–300 °C
Moisture: Critical for isocyanate components; in thermoplastic polyurethane, moisture is brought below 0.02 percent before processing
Reactivity: Isocyanates react with hydroxyl, amine and water; they are kept away from acids, bases and amines; the cured product is largely inert
Short Description of Physical Properties
In technical data sheets, solids content, viscosity, NCO or OH content and, in dispersions, pH are monitored most; since these values vary with the manufacturer and the batch, the document of each product should be consulted.
HOW DO POLYURETHANE RESINS WORK AT THE MOLECULAR LEVEL?
In the basic reaction, the oxygen of the hydroxyl group attacks the isocyanate carbon and the urethane linkage forms. The reaction is exothermic; tertiary amines and organotin compounds accelerate it.
When the isocyanate meets water, unstable carbamic acid forms, and this acid breaks down into an amine and carbon dioxide. The amine gives a urea linkage with another isocyanate. One-component moisture-curing systems are crosslinked in this way, and the same route is the gas source in foam production.
In two-component coatings, the polyol and the polyisocyanate are mixed at an NCO/OH ratio of about 1.0–1.1; the viscosity increases and the film turns into a network structure. In thermoplastic types, instead of crosslinks, hard segments held together by hydrogen bonds do the work.
In water-based dispersions, the carboxylate groups bound to the chain make the particles repel one another. As the water evaporates the particles coalesce and the film forms.
IN WHICH SECTORS ARE POLYURETHANE RESINS USED?
Paint and coating: Wood, metal, plastic and floor paints, pipe protection coatings
Adhesives and sealants: Lamination, furniture, automotive interior, footwear and reactive hot melt adhesives
Textile and leather: Synthetic and natural leather coating, fabric coating
Footwear, furniture and automotive: Soles, foam, seats, interior surfaces and gaskets
Electrical and packaging: Cable jackets, encapsulation, lamination and ink binders
Glass fiber and medical devices: Fiber sizing, tubing and catheter parts
ARE POLYURETHANE RESINS USED IN COSMETIC, FOOD AND PHARMACEUTICAL APPLICATIONS?
Cosmetics: Yes, but only specially developed grades are used. Polymers registered under INCI names such as Polyurethane-34, Polyurethane-35 and similar are included as film formers in hair styling products, sun and skin care, and makeup. Industrial paint or adhesive resins cannot be used for this purpose.
Food: It is not used as a direct food additive. On food-contact surfaces, certain polyurethane resins are evaluated in the United States under 21 CFR 177.1680 with the raw materials listed for surfaces in contact with dry food. Compliance with Turkish and EU legislation must be verified product by product.
Pharmaceuticals: It is not used as an active substance or excipient. Thermoplastic polyurethanes are found in medical device parts such as tubing and catheters, and biocompatibility tests such as ISO 10993 are required for these uses. Some manufacturers state explicitly that their dispersions cannot be used in food, cosmetic and medical products.
INDUSTRIAL APPLICATIONS OF POLYURETHANE RESINS
In paint and coating, a polyol resin and an isocyanate hardener are used together to obtain a hard film resistant to chemicals and abrasion. Aliphatic types keep color and gloss outdoors, while aromatic types are preferred indoors and in primers.
In adhesives and lamination, the resin forms a flexible and strong bond between different surfaces. Water-based dispersions are chosen for their low solvent content, and reactive hot melts for their fast bond formation.
In synthetic leather and textiles, dispersions provide a soft touch and abrasion resistance. In pipe and floor coatings, flexible prepolymer hardeners provide impact resistance; they are more flexible than epoxy.
POINTS TO CONSIDER WHEN USING POLYURETHANE RESINS
• The manufacturer’s technical data sheet and safety data sheet should be read before use
• Since isocyanate components react with moisture, containers should be closed tightly immediately after use
• In two-component systems, the mixing ratio should be calculated from the NCO and OH values, and the mixture should be used within the pot life
• Loss of adhesion and gas bubbles may form on a damp or oily substrate
• For outdoor use, aliphatic isocyanate-based systems should be preferred
• Water-based dispersions should be protected from freezing, high temperature and microbial contamination
• Respiratory and skin contact with uncured product should be avoided, and ventilation should be provided for solvent-based products
STARTING FORMULATION APPROACHES FOR POLYURETHANE RESINS
The approaches in this section are short starting examples showing how the product family can be evaluated in paint, water-based coating and adhesive applications. The examples are not verified commercial recipes or final formulas; the proportions are for preliminary laboratory trials, and the total of each formula is 100%.
The amount of hardener is calculated from the OH value of the resin and the NCO value of the hardener. In every application, occupational safety and regulatory checks must be carried out.
EXAMPLE 1: EFFECT OF THE NCO/OH RATIO ON HARDNESS AND SOLVENT RESISTANCE IN A TWO-COMPONENT SOLVENT-BASED POLYURETHANE TOPCOAT
Purpose: To monitor the effect of the NCO/OH ratio on film hardness, adhesion and solvent resistance in a coating consisting of a polyol resin and an aliphatic polyisocyanate hardener.
Starting approach (ready-to-use paint):
Polyol resin (in solution): about 45.0%
Aliphatic polyisocyanate hardener: about 20.0%
Solvent mixture (ester solvents): about 26.0%
Pigment and filler: about 8.0%
Additive package (flow, defoamer, UV absorber): about 1.0%
Application approach:
• The NCO/OH ratio is screened at 1.0, 1.05 and 1.1; the hardener is added immediately before use and applied within the pot life.
• The film cures at room temperature at constant temperature and humidity; hardness, adhesion and solvent rub resistance are monitored over time.
• Eye, hand and respiratory protection is used in a ventilated environment.
EXAMPLE 2: EFFECT OF THE COALESCING SOLVENT LEVEL ON FILM FORMATION IN A WATER-BASED POLYURETHANE DISPERSION WOOD COATING
Purpose: To monitor the effect of the coalescing solvent level in a water-based polyurethane dispersion on film formation, gloss and surface appearance.
Starting approach:
Polyurethane dispersion (about 40% solids): about 65.0%
Deionized water: about 25.0%
Coalescing solvent: about 5.0%
Wetting agent and defoamer: about 1.5%
Thickener: about 1.0%
Matting agent and filler: about 2.5%
Application approach:
• The coalescing solvent is tested at about 3%, 5% and 7%; the minimum film formation temperature of the dispersion is evaluated according to the manufacturer’s data.
• The film is applied to wood at constant thickness and dried at room temperature; gloss, crack formation and blocking are monitored.
EXAMPLE 3: EFFECT OF THE CROSSLINKER AMOUNT ON BOND STRENGTH IN A WATER-BASED POLYURETHANE LAMINATING ADHESIVE
Purpose: To monitor the effect of the amount of polyisocyanate crosslinker in a water-based polyurethane dispersion adhesive on bond strength and heat resistance.
Starting approach:
Polyurethane dispersion: about 94.5%
Polyisocyanate crosslinker (suitable for aqueous systems): about 2.0%
Deionized water (viscosity adjustment): about 2.0%
Wetting agent: about 0.5%
Defoamer: about 0.3%
Thickener: about 0.7%
Application approach:
• The crosslinker is tested at about 0%, 2% and 4%; in the literature, a heat-curing structure with a crosslinker at about 2% has been reported.
• The adhesive is applied, the water is evaporated, and lamination is carried out by heat activation; peel strength is measured after 24 hours and 7 days.
• Since the crosslinker contains isocyanate, respiratory and skin contact is avoided.
SIMILAR PRODUCTS AND ALTERNATIVES TO POLYURETHANE RESINS
Epoxy resins serve the same function as polyurethane in two-component coatings and adhesives. They are more rigid and highly resistant to chemicals; they reach their full properties within days and are not flexible. They stand out in floor and tank coating, while polyurethane is advantageous on moving surfaces.
Polyurea coatings cure within seconds and give high flexibility; they require special spray equipment and a higher cost. Acrylic resins and dispersions are more economical and generally UV resistant, but may lag behind polyurethane in abrasion and chemical resistance.
Silicone resins provide high temperature and UV resistance, but their mechanical strength is low. Plasticized PVC and thermoplastic elastomers are cheaper alternatives to thermoplastic polyurethane, but they fall behind in abrasion and tear resistance.
No alternative replaces polyurethane in every application. Performance, cost, compatibility and regulation should be evaluated together.
QUALITY CONTROL AND PURCHASING CRITERIA FOR POLYURETHANE RESINS
• Solids content and viscosity
• NCO content (in isocyanate components) and hydroxyl number (in polyols, ASTM D4274)
• Acid number, water content and free monomeric diisocyanate content
• In dispersions, pH, particle size and minimum film formation temperature
• Color, appearance, batch and expiry date
Manufacturers’ typical values are not considered binding specifications unless confirmed in a written contract. A certificate of analysis, a safety data sheet and a technical data sheet should be requested with every batch.
STORAGE AND TRANSPORT OF POLYURETHANE RESINS
Dispersions are generally stored at 5–30 °C protected from freezing, isocyanate components at 10–30 °C or 10–25 °C, and polyols at 0–30 °C. At low temperature some solutions may solidify and return after brief heating; high temperature increases viscosity and lowers the NCO content.
Containers holding isocyanate should be protected from moisture and kept closed in their original packaging. Shelf life is generally given as 6 to 12 months, and retesting is recommended afterwards.
Transport classification depends on the product. Solvent-containing products are transported as flammable liquids; an example hardener has been reported as UN 1993, class 3, packing group III. Section 14 of the safety data sheet of each product should be checked.
SAFETY INFORMATION ON POLYURETHANE RESINS
Safety should be separated between cured and uncured product. Cured polyurethane does not contain free isocyanate. Uncured resin, prepolymer and hardener, on the other hand, may contain solvent and isocyanate.
In the safety data sheet of an example hardener, the statements flammable liquid (H226), harmful if inhaled (H332), may cause an allergic skin reaction (H317) and may cause respiratory irritation (H335) appear; the flash point is 27 °C.
Isocyanates are counted among the main causes of occupational asthma, and the effects may be permanent. For hexamethylene diisocyanate monomer, the ACGIH threshold limit value is 0.005 ppm as an 8-hour average.
As gloves, butyl rubber (0.5 mm), fluorinated rubber (0.4 mm) or multilayer PE/EVAL/PE are preferred; thin nitrile is only for splashes. In spraying, air-supplied respiratory protection is required.
In a fire, carbon monoxide, nitrogen oxides and possibly hydrogen cyanide may form. In a spill, absorbent material is used and the product is not released into the drain. In case of eye contact, rinse with water for at least 10 minutes, and a doctor should be consulted in every case.
In the EU, industrial or professional users of products containing 0.1 percent or more monomeric diisocyanate by weight must have received training from 24 August 2023. This section is for general information; it does not replace the safety data sheet.
WHAT SHOULD BE CONSIDERED WHEN BUYING POLYURETHANE RESINS?
• Correct product identity: polyester or polyether, aliphatic or aromatic, one- or two-component, solvent-based or water-based
• Technical specifications: solids content, viscosity, NCO or OH value, pH
• Suitability for the intended use: indoor or outdoor, humidity, temperature and chemical exposure
• Packaging, shelf life, batch consistency and certificate of analysis
• The supplier’s technical support, regulatory requirements and user training requirement
• Total cost of supply: cost per unit of solids, waste and processing cost should be evaluated together
SUPPLY OF POLYURETHANE RESINS FROM ATAMAN KİMYA
There are product pages on polyurethane resin on the Ataman Kimya website. Which type, grade and packaging can be supplied varies by product.
For up-to-date information on stock, origin, documents, delivery time and technical support, contacting ATAMAN KİMYA is recommended.
FREQUENTLY ASKED QUESTIONS ABOUT POLYURETHANE RESINS
What are polyurethane resins?
They are a family of polymers carrying the urethane linkage, formed by the reaction of polyols with isocyanates.
What does polyurethane resin mean?
The name comes from the urethane linkage in the polymer.
What is the CAS number of polyurethane resins?
There is no single number; 9009-54-5 is often used for general polyurethane.
What is the EC / EINECS number of polyurethane resins?
Because it is a polymer, there is no single number; the raw materials have separate numbers.
What is the chemical formula of polyurethane resins?
There is no fixed formula; it consists of repeating units containing the urethane linkage.
What is the INCI name of polyurethane resins?
There is no single INCI name; cosmetic grades are known by names such as Polyurethane-34 and Polyurethane-35.
Are polyurethane resins used in cosmetics?
Only grades developed for cosmetic purposes are used, as film formers.
What is the difference between polyurethane resins and epoxy resins?
Epoxy is more rigid and resistant to chemicals; polyurethane is more flexible.
What are polyurethane resins used for?
They are used for coating, bonding, production of flexible parts and surface protection.
In which sectors are polyurethane resins used?
They are used in paint, adhesives, textile, leather, footwear, automotive, furniture and packaging.
How do polyurethane resins cure?
They cure with moisture, by mixing of polyol and isocyanate, or, in dispersions, by evaporation of water.
What are polyurethane resins good for?
They give hardness, flexibility and abrasion resistance to the surface, and they bond materials.
How do polyurethane resins work in paint and coating?
Polyol and isocyanate crosslink on the surface and form a hard film.
Are polyurethane resins soluble in water?
No; water-based types are present dispersed in water.
How much hardener is used in a coating?
The amount is calculated from the NCO and OH values; the NCO/OH ratio is generally 1.0–1.1.
Are polyurethane resins hazardous substances?
The cured product is generally low risk; uncured products may be flammable and sensitizing.
Why can polyurethane resins cause allergy?
Isocyanates can cause sensitization in the skin and respiratory tract.
Are polyurethane resins registered under REACH?
Polymers are generally exempt from registration; the raw materials are assessed separately.
What is the physical appearance of polyurethane resins?
Solutions are yellowish liquids, dispersions are milky white liquids, and thermoplastic types are granules.
What is the UN number of polyurethane resins?
There is no single number; solvent-based products are flammable liquids, and the safety data sheet should be checked.
Why are moisture and free isocyanate important in polyurethane resins?
Moisture lowers the NCO value and causes bubbles; the free monomer determines the safety obligations.
What does the price of polyurethane resin depend on?
It depends on the type of polyol and isocyanate, the solids content, the packaging and raw material prices.
Is there an alternative to polyurethane resins?
Yes; epoxy, acrylic, polyurea and silicone resins can be alternatives in some applications.
How should polyurethane resins be stored?
In the original closed container, generally at 5–30 °C, protected from moisture and freezing.
Which documents should be requested when buying polyurethane resins?
Safety data sheet, technical data sheet and certificate of analysis.
Which technical properties are important when buying polyurethane resins?
Chemical type, solids content, viscosity, NCO or OH content and shelf life.
POLYURETHANE RESINS – TECHNICAL SUMMARY
Chemical name: Polyurethane (polyaddition polymer of polyols and isocyanates)
CAS number: No single number; often 9009-54-5 for general polyurethane
Chemical class: Polymer, polyaddition polymer containing the urethane linkage
Main functions: Film former, binder, adhesive, elastomer matrix
Important fields of application: Paint and coating, adhesives, textile and leather, footwear, automotive
Parameters critical for quality control: Solids content, viscosity, NCO or OH content, pH
Storage: In the original closed container, generally at 5–30 °C, protected from moisture and freezing.
