Soft Thermoplastic Polyurethane Research Articles

Engineered nanofillers: impact on the morphology and properties of biomedical thermoplastic polyurethane nanocomposites

The viability of siloxane-based thermoplastic polyurethane (TPU) nanocomposites as a new insulation material for implantable and electrically active medical devices is investigated. We show that manipulating and controlling the specific interactions between the TPU segments and the engineered nanofiller greatly varies the TPU properties. The incorporation of dual modified organofluoromica as the nanofiller successfully enhanced the tensile strength, toughness and tear strength of the TPU. This is due to the presence of dual surfactants, which form regions of higher and lower surface energy on the layered silicate surface, thus enabling molecular interactions between the organofluoromica and both the hard and the soft TPU segment populations. We show that the addition of a second choline-based modifier with reactive –OH functionality may lead to the formation of positively charged TPU chain end groups as a result of trans-urethanization reactions during high temperature compounding, thus introducing labile “grip-slip-grip-slip” interactions between the TPU and the nanofiller. These molecular interactions assist in achieving a reduced level of stiffening, while at the same time enhance the toughening mechanism. The increase in the creep resistance and retardation in the stress relaxation of the TPU provides evidence that the dual modified organofluoromica also serves to enhance the dimensional stability of the TPU.

Interfacial Shear Strength in a Metal-Thermoplastic Composite

Hybrid materials featuring thermoplastic polymer composites in conjunction with steel cords are being considered as structural materials in infrastructure, transportation and military applications. The present study focuses on understanding the mechanical performance of metal cord-thermoplastic composites. Since the optimal performance of a composite strongly depends on the behavior of the interface, finite element modeling has been adopted to characterize the interface between steel fibers and thermoplastic composite material. The mechanical interactions between thermoplastics and steel have been studied with a goal to improve interfacial shear strength and cohesive strength. Steel cord was combined with nylon, polypropylene, soft thermoplastic polyurethane and hard thermoplastic polyurethane to find the parameters that affect mechanical bonding via pull out tests and friction coefficient tests. The test parameters have been correlated to interfacial shear strength using both experimental and modeling approach.

Thermoplastic Polyurethane Elastomers Made from High Molecular Weight POLY-L® Polyols

High molecular weight polyether polyols formed by the poly merization of epoxides, especially propylene oxide, using conventional KOH catalysis contain high levels of unsaturation. This unsaturation is in the form of allyl and isopropenyl end groups and results in a loss of functionality. A diol that ideally has a functionality of 2.0 can be as low as 1.70 for a conventional 4000 molecular weight polyol. As the molecular weight increases the func tionality decreases. Since the unsaturation is a function of molecular weight, a limiting molecular weight will be reached where further propylene oxide fails to add to the chain and to increase molecular weight. High molecular weight polyether diols containing low unsaturation were pre pared using double metal cyanide catalysts. With these catalysts ultra high molecular weight polyols can be made without a concomitant increase in the rate of formation of unsaturated end groups. A 4000 molecular weight diol was made that had unsaturation levels five times lower than a comparable polyol prepared by conventional KOH catalysis. Additionally, 5500 and 6600 molec ular weight diols containing very low unsaturation levels were also made. All of the polyols were capped with ethylene oxide to give high levels of primary hydroxyl groups. These polyols were evaluated in thermoplastic polyurethane elastomer formulations. The thermoplastic polyurethane elastomers were based on MDI and chain ex tended with butanediol. Those prepared from polyols with low unsaturation levels had significantly higher physical properties than thermoplastic polyurethane elastomers prepared with conventionally made polyols. Soft ther moplastic polyurethane elastomers were made from high molecular weight polyols containing low unsaturation levels. These soft thermoplastic polyure thane elastomers are softer than any currently commercially available. They exhibited good tensile strength, excellent elongation and high resilience prop erties.