TPE - Thermoplastic polymers, elastomers and additives

TPE is the general name for Thermoplastic Elastomer, also called thermoplastic rubber.

Thermoplastic elastomers (TPE) are a class of polymeric materials that have the elastic behavior of rubber and the processability of thermoplastics. The rubbers have been of strategic importance since the beginning of the automotive industry. Thermoplastic elastomers can function like a rubber. TPEs are generally low modulus flexible materials that can be repeatedly stretched to at least twice their original length at room temperature, with the ability to return to their approximate original length when stress is released. They also have the ability to be reprocessed when heated above the melting transition temperature. The TPE has the behavior below the melting temperature of being elastic as a thermoset rubber.

Thermoplastic elastomers (TPE) have two major advantages over thermosetting (vulcanized) elastomers, namely, ease and speed of processing. Other advantages of the TPE are the scrap recycling capacity, the lower energy costs for processing and the availability of uniform grades (not generally available in thermosetting). TPEs are molded or extruded into standard plastics processing equipment at significantly shorter cycle times than those required for compression or transfer molding of conventional rubbers.

The double capacity of the elastomeric properties and recyclability are achieved using one of several 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 more elastic chains. These are held together by the crystalline domains which have 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.

The thermoplastic elastomers are classified, according to ISO 1043, with the abbreviation TPE (thermoplastic elastomers), at the end of the acronym TPE, it is added to a letter that determines the chemical nature:

TPE-A (Co-polyamides) often abbreviated as TPA or COPA or PEBA's

TPE-E TPEE (Copolyesters) often abbreviated or TPC-ET, COPE's, TEEE, TPEE

TPE-S often abbreviated as TPE's, TPS or SBS, SEBS, Styrenics (S-TPE)

TPE-U often abbreviated as TPU or TPU's or Polyurethanes

New participants in TPE

TPO reactor (R-TPO)

Polyolefin plastomers (POP)

Polyolefin elastomers (POE)

Silicone elastomers TPSiV

TPE-V (Polyolefin alloys often abbreviated to TPV or TPV's

TP-O (Polyolefin blends) often abbreviated as TPO

New TPE

TPO reactor (R-TPO)

Polyolefin plastomers (POP)

Polyolefin elastomers (POE)

Styrenic block copolymers, SBS is based on two-phase block copolymers with hard and soft segments. The styrene end blocks provide the thermoplastic properties and the intermediate blocks of butadiene provide the elastomeric properties. SBS is probably the highest volume material produced by TPE-S and is commonly used in footwear, adhesives, modification of bitumen and seals and seals at lower specifications, where resistance to chemicals and aging have a lower priority. The SBS when hydrogenated becomes SEBS, since the elimination of the C = C bonds in the butadiene component generates ethylene and butylenes in the middle of the block, hence the acronym SEBS. SEBS is characterized by a much improved heat resistance, mechanical properties and chemical resistance. They are generally compound made of polypropylene PP, PE PE, PS polystyrene and styrene elastomers (eg, SBS, SEBS, SEEPS, SIS, etc.) and plasticizer (mineral oil, naphthenic oil) and filler (calcium carbonate, talc, etc.).

Styrenic block copolymers, the base polymers in TPE-S, are exceptionally versatile polymers and are in themselves a thermoplastic elastomer material but are not considered final products. The styrene block copolymers are based on simple molecular structures, such as an SES block copolymer, where S is a polystyrene segment and E is an elastomer segment and are differentiated by molecular weight, styrene content percentage (PSC) ) and the type and length of the elastomeric intermediate block. The most common styrenic block copolymers are those for which the elastomeric segment is olefinic. The morphology of styrenic block copolymers can best be described by domain theory. If the elastomer is the main constituent, the block copolymers will have a similar morphology, where the polystyrene end segments form separate spheroidal regions, i.e., domains dispersed in a continuous phase. At room temperature, these polystyrene domains are hard and act as physical crosslinks, joining the elastomeric middle segments in a 3D network. In a way, this is similar to the network domains formed during the vulcanization of conventional rubbers using sulfur crosslinks. The difference is that these domains lose their strength when the material is heated. This allows the polymer to flow. When the material cools, the domains harden and the networks recover their original integrity. The functional compounds of TPE-S are created by combining styrenic block copolymers with a series of selected additives (such as PP, PE, mineral oil, lubricants or antioxidants) during the mixture of compounds. This is generally known as a TPE-S compound. The specific formulations combined with the additives of choice can offer a wide range of properties and it is this versatility that allows the TPE-S compounds to be used in numerous components of extruded and injection molded medical devices. Originally marketed as a cost-effective alternative to rubber in many applications, in more recent years, the development of styrene block copolymer chemistry has led to improvements in compatibility and clarity with polypropylene, and the ability to formulate soft compounds without the use of mineral oils or plasticizing agents. This has allowed TPE-S compounds to target medical device applications where PVC compounds have traditionally been the material of choice.

These materials are mixtures of polypropylene (PP) and non-crosslinked EPDM rubber; in some cases, there is a low degree of crosslinking to increase the heat resistance and properties of the compression assembly. They are used in applications where greater strength is required over conventional PP copolymers, such as in bumpers and automotive panels. The properties are restricted to the upper end of the hardness scale, typically> 80 Shore A and with limited elastomeric properties. Historically, these products were mechanical mixtures of the 2 polymers. However, with the new catalyst technology it is now possible to combine the EPDM and the PP in the reactor, therefore, these types of TPE are now available in the main polymer manufacturers. These products are suitable for high volume and low cost applications, however, there is still a market for the customized mix of TPE-O.

POP and POE have olefin-like performance in the TPO range. The principal examples are the α-olefin / ethylene copolymers, called polyolefin plastomers (POP) when they have high ethylene content. The low ethylene content plastomers are termed polyolefin elastomers (POE). Both can be considered generically compatible with many other non-polar polymer systems and will provide toughness, strength, elasticity, processability, etc. At this early stage of POP and POE, the costs are significantly higher than those of olefin materials of conventional technology, for example, PP copolymers, rTPOs and PEs. The new POE and POP (Olefinic thermoplastic elastomers) are essentially linear polyethylenes of low density and very low molecular weight (VLMW-LLDPE). The results of advances in polymerization catalyst technology, these materials were originally developed to improve the characteristics of flexible packaging film. Recently, these more flexible polyethylenes have been seen as low-cost rubber substitutes for some non-demanding molded product applications. These mainly include products that will not be exposed to extreme temperatures, pressures, burdens or stress environments. The copolymers of low ethylene content with α-olefins, called polyolefin elastomers (POE), are much softer and highly elastic but thermoplastic. These new olefins have some similarity to olefin mixtures, but have distinct advantages in having a crystalline section and a rubber section in a single copolymer. In molded products, these new materials are being used where a more or less limited degree of flexibility or tactile sensation is desired, but they are not true elastomers.

These materials are the next step in the performance of TPE-O. These are also rubber compounds of PP and EPDM, however, they have been vulcanized dynamically during the composition stage. They have seen strong growth in the replacement of EPDM for automotive seals, pipe seals and other applications where a heat resistance of up to 120 ° C is required. The hardness values ​​of the shore typically vary between 45A and 50D. The TPV HT increases the temperature limit above 140 ° C with large improvements in long-term compressive strength compared to the standard TPE-V materials. PP / EPDM thermoplastic vulcanizates (TPV) are gradually replacing traditional vulcanized rubber, especially in the need of timely delivery and high volume production requirements, the POS terminal better reflects the ease of rapid processing, with POS in this area so so much more competitive. With the increase in environmental protection has become increasingly, elastomeric products, will also be biased in favor of POS. In general, for 65 Shore A, for example, the temperature does not exceed 130 ° C, the deformation requires not less than 35%, the tensile strength is not higher than 7MPa, the oil requirements and the vulcanized EPDM, for what can be sure that the choice of TPV.

A series of new TPE-Vs, called "3rd generation TPVs" are being introduced, which are based on engineering plastics mixed with high performance elastomers, which can offer a much higher chemical and heat resistance.

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 silicone rubber called 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 qualities that have improved features.Top 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 coloring 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.

These materials can be based on polyester or polyether urethane types and are used in applications where a product requires excellent tear strength, abrasion resistance and flexural fatigue resistance. They are a product of the reaction of a diisocyanate and polyether, polyester or caprolactone glycols of long and short chain. The polyols and the short chain diols react with the diisocyanates to form linear polyurethane molecules. This combination of diisocyanate and short chain diol produces the rigid or hard segment. The polyols form the flexible or soft segment of the final molecule. The properties of the resin depend on the nature of the raw materials, the reaction conditions and the proportion of the starting raw materials. The polyols used have a significant influence on certain properties of the thermoplastic polyurethane. Polyether and polyester polyols are used to produce many products.

Good resistance to oil / solvent

Good resistance to UV rays

Abrasion resistance

Good heat resistance

Mechanical properties

TPUs based on polyether have the following characteristics:

Resistance to bacterias

Low temperature flexibility

Excellent hydrolytic stability

Acid / base resistance

Thermoplastic copolyesters (TPE-E or COPE or TEEE or TPEE or TPC-ET)

Thermoplastic copolyesters (TPE-E or COPE or TEEE) are used where greater chemical resistance and heat resistance up to 140 ° C are required. They also exhibit good fatigue resistance and tear resistance and, therefore, are used in automotive applications such as blow molded boots and bellows, cables and wires, and industrial hose applications. Again, the hardness is restricted to the high end and is typically between 85A to 75D.

Melt processable rubber (MPR) is designed for more demanding applications that require chemical resistance, especially resistance to oil and grease, where the MPR replaces the crosslinked nitrile rubber. It also possesses properties similar to those of vulcanized rubber in noise dampening applications and has similar properties of stress relaxation. MPR applications include automotive components, such as weather strips and handles, where a good bond to PVC, polycarbonate or ABS is required. Compression fit values ​​are still much higher than for thermoset elastomers, so penetration into the higher performance seal market has been limited.

These products offer good resistance to heat, have good chemical resistance and are bonded to polyamide engineering plastics. Its applications include cable coatings and aerospace components.

In summary, it must be concluded that there is a lot of new developments in the TPE industry. There are new types of TPE with the entry of POPs and metallocene SOPs, high temperature TPSiV, high temperature AEM TPV, a new SBC series with improved moldability, low hygroscopicity TPV, TPV bonding grades, new grades of TPU of molding and extrusion and a soft grade of COPE TPV to cite some. The number of suppliers in the industry continues to grow and some are consolidating efforts. New applications have been developed, for example TPV weather seals. The new process developments for TPE are part of the industry's growth as well. Two-shot molding has become a standard for many grips, appliances, automotive components and more. TPUs foamed by water foam and similar approaches are offering new climate sealing technology options based on TPE. The robotic extrusion of TPE on substrates has been developed for edge seals. There is a series of directional tendencies in progress in the TPE. New TPE alloy products are being developed and the pace of new product introduction is accelerating. The tendency is to make the TPE increasingly smooth.