Thermoplastic Elastomer - Thermoplastic polymers, elastomers and additives

approaches to prepare the TPE. The three main types of TPE are:

• block copolymers,

• rubber / plastic mixtures

• dynamically vulcanized rubber / plastic alloys called thermoplastic vulcanizates

Each of these achieves the characteristic elastic performance of a rubber in different fashions. The double-phase nature combined with the polymer chemistry dictates the performance capabilities of the TPE. The TPEs form a continuous domain of softer and elastic chains. These are held together by the crystalline domains having the copolymer chains blocked together in a crystalline structure. When these copolymers are deformed the hard blocks remain crystalline and do not deform The soft rubber domain easily deforms and provides a gummy behavior. The recovery of these materials is good as long as the domains are not too tight and the temperatures are well below the crystallization temperature. On the crystalline melting temperature the chain block copolymer are no longer blocked in their position and all the chains are free to flow. In the melting temperature range a block copolymer will be easily processed in typical thermoplastic processing equipment this behavior is exhibited by all the block copolymer TPE.

Thermoplastic elastomers

A new development, based on the new metallocene catalyst, to polymerize olefins has led to a different class of block copolymers. Controlling the monomer sequences and molecular structure allowed the development of a technology to make copolymers of ethylene content with alpha-olefins. These block copolymers are called polyolefin (COP) plastomers and have higher elasticity, strength and improved processing. Similarly, copolymers of low ethylene content with α-olefins, called polyolefin elastomers (POE), have been developed and are softer and highly elastic being a thermoplastic. These new olefins have some similarity to olefin mixtures, but have distinct advantages by having a crystalline section and a gummy section in a single copolymer.

The first TPEs were made by customizing molecules of copolymers consisting of a multiple block or three block copolymer structure. The final block of the copolymer molecules will crystallize. These copolymer molecules are bonded when they are below the melting temperature, thus virtually forming a crosslinked network. Between these crystallized ends is the central block which is amorphous and has rubber-like properties in the range of ambient temperature. These block copolymers can be divided into classes based on their chemistry. They include:

One of the first thermoplastic elastomers was prepared by mixing a rubber and a thermoplastic polymer. Rubber and plastic polymers should be somewhat incompatible with each other. The most popular rubber / plastic blend is polypropylene with EPDM or ethylenepropylene copolymer rubber (EP) and is called thermoplastic olefin (TPO). These polymers form separate phases. In some TPOs, the EPDM rubber is partially or slightly cross-linked TPV. In some situations the rubber phase can be a continuous phase. The rubber particles also change shape freely. This allows TPO to flow freely and results in good injection processing characteristics. The rubber / plastic mixtures and especially the TPO are made of low cost materials. They enjoy a wide use where the temperature or fluid performance requirements are not excessively high. New developments in rubber / plastic blends are directly related to the development of new rubber or plastic polymers. Recent advances based on technology with metallocene catalyst have been developed new ethylene / α-olefin copolymers and have already begun to have an impact on the technology (TPE 4th Generation) of commercially available TPOs. TPOs can now be made in the reactor as reactors rTPOs reducing manufacturing costs.

A third class of TPE is thermoplastic vulcanizate (TPVs). The designation used in TPV generally refers to the EPDM / PP compound. TPVs are usually prepared by dynamic vulcanization first performed by Fisher, but not applied to the development of a complete cure. The first fully cured EPDM / PP TPV was developed by Coran and Patel. TPVs have grown in commercial use becoming one of the main classes of TPE. A TPV is a mixture of thermoplastic with completely crosslinked, ie vulcanized, rubber. The thermoplastic is the continuous phase and the rubber is crosslinked. TPVs are prepared by dynamic vulcanization where the rubber phase is crosslinked during the mixing process when the polymers are mixed together. The crosslinking of the rubber phase is almost 95% and must exceed 97% to have a good resistance to fluids, recovery and retention of seal stress. The properties of TPVs are close to those of a thermosetting rubber due to the complete vulcanization of the rubber phase. The best physical properties are achieved when the particles are approximately 1 μm in diameter. The TPVs are made with a variety of rubber and plastic pairs. The most common are the EPDM / PP TPV. The POS provides a great advantage by eliminating the need for drying before processing.

There are new developments in TPV based on dynamic vulcanization of the highest temperature rubber and plastic combination of ethylene-acrylate rubber and polyester (polyethylene terephthalate (PET) or polybutylene terephthalate (PBT)), called TPE 3rd generation. new TPV based on silicon-labeled rubber TPSiV has been developed and marketed These TPVs provide higher temperatures and / or higher resistance to fluids than PP-based TPs The available TPV products have also been expanded to develop new grades that have Enhanced features.PVT next-generation products that have been developed that have very low hygroscopicity and can be processed without drying.These next-generation TPVs also have very high colorability.Require less colorant and lighter, brighter colors can be achieved. These POS are marketed with specific grades optimized for extrusion processing or by injection molding TPV products that have a link to a variety of substrates have been introduced.