Thermoplastic elastomers recent developments

Recently Developed Thermoplastic Polyurethane and Polyester Elastomers , ERDE TR 136 (1973) 4) RP. Rastogi K. Kishore, Poly-... 

Elastomers are often blended with plastics either to improve the impact resistance or to develop new materials having both plastic and elastic behavior. When the elastomer in the blend is dynamically vulcanized, the product is called a thermoplastics vulcanizate (TPV). Blends with unvulcanized mbber phase are usually known as thermoplastic elastomers. TPVs are discussed in another section of this book. This section will deal with recent developments in rubber-plastic blends. 

There are two approaches to the combining of scrap rubber and plastics. The initial interest was to use the cmmb in minor proportions to toughen the plastics improving impact strength and reduce the overall cost. A more recent interest is to develop a type of thermoplastic elastomer (TPE) wherein the mbber is the major component bonded together by thermoplastics, which can be processed and recovered as thermoplastics. 

Recent Developments on Thermoplastic Elastomers by Dynamic Vulcanization... 

Primary aminoalkylsilanes are important compounds in application fields like adhesion promotion, surface modifying, and crosslinking, but are also used for endcapping of various substrates. Currently in focus is the recently developed endcapper (Fig. 1) which is the key molecule for the preparation of thermoplastic silicone elastomers (TPSE). Modification of silicone resins and fumed silica with 1 leads also to products with interesting economical potential. 

Thermoplastic elastomers are a more recently developed class of polymer in which the neat polymer has inherently elastomeric properties, yet it behaves thermoplastically. With some limitations, these materials can be formed by essentially the same operations as thermoplastics, but the final object has elastomeric behavior. Objects molded with thermoplastic elastomers can be melted and re-shaped. Since these are not crosslinked, their creep resistance and extended high temperature use are limited. 

Recently developed thermoplastic rubbers (e.g., Santoprene developed by Monsanto) are taking over some of the market niches, which were formerly reserved for vulcanized (cross-linked) rubbers [34]. Not only does this material lend itself to convenient processing like a thermoplastic, but once an item made from a thermoplastic rubber has outlived its usefulness it can be much more readily reprocessed. However, thermoplastic elastomers generally have lower strength, less abrasion resistance, and lower tolerance to high temperatures than vulcanized rubber so these materials will only encroach on conventional rubber applications in areas where these properties are less important. 

Polystyrene (S) was grafted on the butyl backbone by converting the ally lie chloride sites to initiating carbonium ions (R AlR Cl ). The product has thermoplastic elastomer properties. Most recently Kennedy and coworkers have developed techniques for grafting... 

The sulfonation of EPDM as shown in Reaction 41b has recently been announced to be under commercial development by Uniroyal (78). Sulfonated EPDM can be classified as an ionic thermoplastic elastomer, whereby ionic interactions between chains act as thermally reversible cross-links. Above certain temperatures these ionic interactions break down, and plastic flow can occur. Upon cooling, these ionic cross-links reform to give the desired property characteristics. To enhance the processability of sulfonated EPDM an ionic plasticizer "ionolyzer" (i.e., zinc stearate) is added to about 20 phr (parts per 100 rubber). Care must be taken to ensure complete neutralization, because it was observed that residual acid can result in covalent cross-linking during fabrication. 

More recently, blends of a partially crosslinked thermoplastic elastomer with 5-40 parts of a PO (viz. LLDPE, PP, EPR, or PB-1) were developed for low density, foamable alloys [Okada et al, 1998a]. The density was reduced at least by a factor of two. In the following patent 1-17 wt% of a long-chain branched PP was also added [Okada et al, 1998b]. The extmded foam was free of surface roughness caused by defoaming, was soft to the touch and showed excellent heat and weathering resistance. 

The appearance of several new types of rubbers called thermoplastic elastomers was apparently a most exciting development in recent years. These materials have properties of conventional rubbers such as high strength, and they are readily fabricated by various melt-processible techniques, which are characteristic of thermoplastic materials because they do not have any chemical cross-links in the... 

Recently, impact modifiers have been developed for plastics other than PVC. Polybutylene and other olefinic thermoplastic elastomers, for example, are being used to enhance the processability, toughness, and heat stability of polypropylene film. Hydroxy-terminated polyethers are being used to increase the impact resistance of polystyrene. Other conunon applications are polycarbonate, polyurethane, thermoplastic polyester, epoxy, and polysulfone. 

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