The most common thermoplastic elastomers include polystyrene, polyolefin, polyester, polyamide and polyurethane elastomers. We offer a wide range of tubing solutions based on these unique materials. We also offer a unique styrenic-based TPE designed specifically for the medical device industry (Cellene® TPE).
Styrenic thermoplastic elastomers represent a class of elastomers. These materials contain a styrenic polymer and an elastomer in a block copolymer. The styrenic portion controls the hardness and stiffness properties of this family. The choice of soft segment controls the chemical resistance and thermal properties. Cellene® compounds are styrenic-based formulations specifically designed for the medical device industry, offering economical and performance advantages over thermoplastic polyurethanes (TPUs) and silicones.
Thermoplastic polyolefin elastomers are comprised of various mechanical blends of polyolefin resins. The components for these blends are readily available and are relatively inexpensive. These mechanical blends are commonly used in high-volume, non-medical applications. Newer polyolefin elastomers, based on metallocene catalyst technology, are produced in reactors and are more often used in medical tubing, bags and packaging applications.
Thermoplastic polyester elastomers are considered engineering thermoplastic elastomers because of their unusual combination of strength, elasticity and dynamic properties. These copolymers exhibit excellent resistance to heat and chemicals. As such, they are commonly used in flexible tubing components used in medical diagnostic equipment.
Polyamide elastomers are copolymers based on polyamide (nylon) 12 and polyether. These are often referred to as polyether block amide elastomers (PEBA). Through the proper combination of polyamide and polyether blocks, a wide range of grades that offer a variety of performance characteristics is possible. The family is characterized by durometer and flexibility. The higher the durometer and stiffness, the higher the level of nylon 12 in the block co-polymer. These materials offer high resilience and low hysteresis (e.g., the difference between the amount of energy absorbed when stretched and the amount of energy released when relaxed). Because of these unique properties, these thermoplastic elastomers are also used in the medical market for various types of catheters.
Thermoplastic Polyurethane Elastomers
Thermoplastic polyurethanes (TPUs) are produced from a reaction product of a di-isocyanate and long and short chain polyether, polyester, or caprolactone glycols. These form the three main chemical classes of TPUs: polyester, polyether and a smaller class known as polycaprolactone.
- Polyester TPUs are compatible with PVC and other polar plastics. They are unaffected by oils and chemicals, provide excellent abrasion resistance, and offer a good balance of physical properties.
- Polyether TPUs are slightly lower in specific gravity (the ratio of the density of material to the density of water) than polyester and polycaprolactone grades. They offer low temperature flexibility and good abrasion and tear resilience. They are also durable against microbial attack and provide excellent hydrolysis resistance.
- Polycaprolactone TPUs have the inherent toughness and resistance of polyester-based TPUs combined with low-temperature performance and a relatively high resistance to hydrolysis. They are an ideal raw material for hydraulic and pneumatic seals.
In general, polyether types are slightly more expensive and have better hydrolytic stability and low-temperature flexibility than the polyester types. However, mechanical properties of the polyester type are generally higher. The caprolactones offer a good compromise between the ether and ester types.
TPUs can also be subdivided into aromatic and aliphatic varieties:
- Aromatic TPUs are often used for applications that require flexibility, strength and toughness.
- Aliphatic TPUs are often used for applications that require light stability, excellent optical clarity, adhesion and surface protection.