aliphatic thermoplastic polyurethane elastomer (tpu): a comprehensive overview

introduction

aliphatic thermoplastic polyurethane elastomer (aliphatic tpu) represents a specialized class of thermoplastic polyurethanes distinguished by their enhanced resistance to yellowing and degradation upon exposure to ultraviolet (uv) radiation and atmospheric conditions. unlike their aromatic counterparts, aliphatic tpus are synthesized using aliphatic diisocyanates, leading to superior color stability and long-term performance in demanding applications. this article provides a comprehensive overview of aliphatic tpu, encompassing its chemical structure, synthesis, properties, processing techniques, applications, and future trends.

1. chemical structure and composition

tpus are block copolymers consisting of alternating hard and soft segments. the hard segments provide strength and rigidity, while the soft segments impart flexibility and elasticity. the fundamental building blocks of aliphatic tpu are:

• aliphatic diisocyanates: these are the defining components that differentiate aliphatic tpu from aromatic tpus. common examples include:

  • hexamethylene diisocyanate (hdi)
  • isophorone diisocyanate (ipdi)
  • dicyclohexylmethane diisocyanate (hmdi or h12mdi)
  • these diisocyanates lack the aromatic rings present in materials like mdi (methylene diphenyl diisocyanate) or tdi (toluene diisocyanate), hence their excellent uv resistance.

• polyols: these are long-chain diols that form the soft segments. common polyols used in aliphatic tpu synthesis include:

  • polyester polyols: offer good mechanical properties and chemical resistance. examples include polycaprolactone (pcl) polyols and polyadipate polyols.
  • polyether polyols: exhibit excellent hydrolysis resistance and low-temperature flexibility. examples include poly(tetramethylene ether) glycol (ptmeg) and polypropylene glycol (ppg).
  • polycarbonate polyols: provide superior hydrolysis resistance, heat resistance, and mechanical properties compared to polyester and polyether polyols.

• chain extenders: these are short-chain diols or diamines that link the diisocyanate and polyol segments, forming the hard segments and influencing the overall properties of the tpu. common chain extenders include:

  • 1,4-butanediol (bdo)
  • ethylene glycol (eg)
  • 1,6-hexanediol (hdo)
  • ethylenediamine (eda)

the specific selection of diisocyanate, polyol, and chain extender dictates the final properties of the aliphatic tpu.

2. synthesis methods

the synthesis of aliphatic tpu generally follows two primary methods:

• one-shot process: all three components (diisocyanate, polyol, and chain extender) are reacted simultaneously. this method is simpler but may result in less control over the molecular weight distribution and block structure.

• prepolymer process: the diisocyanate is first reacted with the polyol to form a prepolymer with isocyanate end groups (-nco). the prepolymer is then reacted with the chain extender to form the final tpu. this method allows for better control over the reaction and results in a more defined block structure.

the reaction is typically carried out in a reactor under controlled temperature and mixing conditions. catalysts, such as tertiary amines or organometallic compounds, may be used to accelerate the reaction. following the reaction, the tpu is often pelletized for ease of processing.

3. properties of aliphatic tpu

aliphatic tpus exhibit a unique combination of properties that make them suitable for a wide range of applications.

property	description	typical values	test method
hardness	resistance to indentation.	60a – 85d (shore a to shore d)	astm d2240
tensile strength	resistance to breaking under tension.	20 – 60 mpa	astm d412
elongation at break	ability to stretch before breaking.	200 – 700%	astm d412
tear strength	resistance to tearing.	20 – 120 kn/m	astm d624
abrasion resistance	resistance to wear from friction.	excellent	astm d4060 (taber)
low-temperature flexibility	ability to remain flexible at low temperatures.	good to excellent (depending on the polyol type)	astm d746
chemical resistance	resistance to degradation from chemicals such as oils, solvents, and acids.	good to excellent (depending on the polyol type)	astm d543
uv resistance	resistance to yellowing and degradation from ultraviolet radiation.	excellent (superior to aromatic tpus)	astm g154
hydrolysis resistance	resistance to degradation from water and humidity.	good to excellent (especially polycarbonate and polyether-based tpus)	astm d3137
transparency	clarity and ability to transmit light.	excellent (can be formulated for high transparency)	astm d1003
rebound resilience	ability to return to its original shape after deformation.	good to excellent	astm d7121
service temperature	the range of temperatures at which the material can be used without significant degradation.	-40°c to 120°c (depending on formulation)	–

key advantages of aliphatic tpu:

• superior uv resistance: this is the most significant advantage, preventing yellowing and maintaining aesthetic appearance over time.
• excellent abrasion resistance: aliphatic tpus are highly resistant to wear and tear, making them suitable for demanding applications.
• good chemical resistance: they exhibit resistance to a wide range of chemicals, including oils, solvents, and acids.
• high flexibility and elasticity: the soft segment composition allows for a wide range of flexibility and elasticity.
• good mechanical properties: aliphatic tpus possess good tensile strength, tear strength, and elongation at break.
• hydrolysis resistance (depending on polyol): polyether and polycarbonate-based aliphatic tpus offer excellent resistance to hydrolysis.

4. processing techniques

aliphatic tpus can be processed using various techniques, including:

• injection molding: this is a common method for producing complex shapes with high precision. the tpu pellets are melted and injected into a mold cavity.
• extrusion: this method is used to produce continuous profiles, such as sheets, films, tubes, and profiles. the tpu pellets are melted and forced through a die.
• blow molding: this method is used to produce hollow articles, such as bottles and containers. a parison (a hollow tube of molten tpu) is inflated inside a mold cavity.
• thermoforming: this method is used to shape sheets of tpu into desired forms by heating and stretching them over a mold.
• solution casting: the tpu is dissolved in a solvent, and the solution is cast onto a substrate. the solvent is then evaporated, leaving a film of tpu.

processing considerations:

• drying: tpu pellets are hygroscopic (absorb moisture) and must be dried before processing to prevent bubbles and surface defects.
• temperature control: precise temperature control is crucial to ensure proper melting and flow of the tpu.
• mold design: proper mold design is essential to ensure uniform filling and prevent warping or shrinkage.
• screw design: the screw design in injection molding and extrusion equipment should be optimized for tpu processing.

5. applications of aliphatic tpu

the unique properties of aliphatic tpu make it suitable for a wide range of applications where uv resistance, durability, and aesthetics are critical.

application	description	advantages
automotive exterior parts	bumper covers, spoilers, rocker panels, seals, and protective films.	excellent uv resistance, impact resistance, and abrasion resistance. maintains aesthetic appearance over time.
outdoor sporting goods	ski boots, inline skate wheels, golf balls, and protective gear.	high abrasion resistance, flexibility, and impact resistance. provides comfort and protection.
medical devices	catheters, tubing, and surgical films.	biocompatibility, flexibility, and sterilization resistance.
consumer electronics	phone cases, watch bands, and keyboard covers.	excellent abrasion resistance, flexibility, and aesthetic appearance. provides protection and enhances the look and feel of the device.
industrial applications	hoses, seals, gaskets, and conveyor belts.	high abrasion resistance, chemical resistance, and flexibility. withstands harsh environments and provides long-lasting performance.
films and coatings	protective films for automotive paint, architectural films, and textile coatings.	excellent uv resistance, abrasion resistance, and flexibility. provides a protective barrier and enhances the durability of the substrate.
adhesives	bonding of various materials, including plastics, metals, and textiles.	strong adhesion, flexibility, and durability.
wire and cable jacketing	protection of electrical wires and cables from abrasion, chemicals, and uv radiation.	excellent abrasion resistance, chemical resistance, uv resistance, and electrical insulation properties.
roofing membranes	single-ply roofing systems for commercial and residential buildings.	excellent uv resistance, weatherability, and flexibility. provides a durable and long-lasting roofing solution.
textile coatings and laminates	waterproof and breathable fabrics for outdoor apparel and footwear.	excellent waterproofness, breathability, and flexibility. enhances the comfort and performance of textiles.
win glazing	flexible edge seals in insulated glass units.	excellent uv resistance, weatherability, and flexibility. maintains seal integrity over time.
3d printing (additive manufacturing)	production of prototypes and functional parts with complex geometries.	excellent flexibility, impact resistance, and uv resistance. opens up new possibilities for design and manufacturing.

6. market trends and future outlook

the global market for aliphatic tpu is experiencing steady growth, driven by the increasing demand for durable, uv-resistant, and aesthetically pleasing materials across various industries. key trends shaping the market include:

• growing demand for automotive applications: the automotive industry is a major consumer of aliphatic tpu, particularly for exterior parts where uv resistance is crucial. the increasing adoption of electric vehicles (evs) is further driving demand, as aliphatic tpu is used in battery housings and other components.

• rising adoption in consumer electronics: the demand for aliphatic tpu in consumer electronics is growing due to its excellent abrasion resistance, flexibility, and aesthetic appeal.

• increasing focus on sustainability: there is a growing focus on sustainable materials, and manufacturers are exploring bio-based and recycled aliphatic tpu options.

• development of new formulations: research and development efforts are focused on developing new aliphatic tpu formulations with enhanced properties, such as improved heat resistance, hydrolysis resistance, and flame retardancy.

• expansion of 3d printing applications: the use of aliphatic tpu in 3d printing is expanding, enabling the production of customized parts with complex geometries.

future outlook:

the future of aliphatic tpu looks promising. with ongoing innovations and a growing demand for high-performance materials, aliphatic tpu is expected to continue to gain market share across various industries. the development of sustainable aliphatic tpu options and the expansion of 3d printing applications will further drive the growth of the market.

7. environmental considerations

while aliphatic tpus offer superior performance, environmental considerations are increasingly important.

• recyclability: while tpu is technically recyclable, the infrastructure for recycling tpus is not as well-established as for other thermoplastics like polyethylene or polypropylene. chemical recycling (depolymerization) is being explored as a viable option.

• bio-based tpus: the development of tpus derived from bio-based sources, such as vegetable oils or sugars, is gaining traction. these bio-based tpus offer a more sustainable alternative to traditional petroleum-based tpus.

• life cycle assessment: conducting a life cycle assessment (lca) can help to evaluate the environmental impact of aliphatic tpu from raw material extraction to end-of-life disposal.

8. health and safety considerations

when handling aliphatic tpu, it’s important to follow proper safety procedures.

• dust inhalation: avoid inhaling dust generated during processing. use appropriate respiratory protection if necessary.
• skin contact: avoid prolonged skin contact. wear gloves to prevent irritation.
• eye contact: wear safety glasses or goggles to protect your eyes from dust or molten material.
• thermal burns: molten tpu can cause severe burns. use caution when handling hot materials.
• ventilation: ensure adequate ventilation during processing to remove fumes and vapors.

9. quality control and testing

quality control and testing are essential to ensure that aliphatic tpu meets the required specifications. common tests include:

• hardness testing (shore a or shore d): measures the resistance to indentation.
• tensile testing: measures the tensile strength, elongation at break, and modulus of elasticity.
• tear testing: measures the resistance to tearing.
• abrasion testing: measures the resistance to wear.
• uv resistance testing (astm g154): measures the color change and degradation upon exposure to uv radiation.
• hydrolysis resistance testing (astm d3137): measures the change in properties after exposure to water or humidity.
• chemical resistance testing (astm d543): measures the change in properties after exposure to various chemicals.
• differential scanning calorimetry (dsc): determines the glass transition temperature (tg) and melting temperature ™.
• gel permeation chromatography (gpc): determines the molecular weight and molecular weight distribution.

10. conclusion

aliphatic thermoplastic polyurethane elastomer offers a compelling combination of properties, including superior uv resistance, excellent abrasion resistance, and good chemical resistance. its versatility makes it suitable for a wide range of applications in automotive, sporting goods, medical, consumer electronics, and industrial sectors. with ongoing innovations and a growing focus on sustainability, aliphatic tpu is poised for continued growth and will play an increasingly important role in various industries. however, proper handling and environmental considerations must be addressed to ensure its safe and responsible use.

literature references:

1. oertel, g. (ed.). (1994). polyurethane handbook: chemistry-raw materials-processing-application-properties. hanser gardner publications.
2. hepburn, c. (1992). polyurethane elastomers. springer science & business media.
3. saunders, j. h., & frisch, k. c. (1962). polyurethanes: chemistry and technology. interscience publishers.
4. woods, g. (1990). the ici polyurethanes book. john wiley & sons.
5. ashworth, v., eling, b., & oosterwijk, r. (2006). thermoplastic polyurethanes. applied plastics engineering handbook, 183-206.
6. rosthauser, j. w., & nachtkamp, k. (1987). water-dispersible polyurethanes. advances in urethane science and technology, 10, 121-162.
7. mark, j. e. (ed.). (1996). physical properties of polymers handbook. aip press.
8. randall, d., & lee, s. (2003). the polyurethanes book. john wiley & sons.
9. szycher, m. (1999). szycher’s handbook of polyurethanes. crc press.
10. prociak, a., ryszkowska, j., & uram, k. (2017). polyurethanes: synthesis, modification and applications. william andrew publishing.

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