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TPE-V – the best of both thermoplastic elastomers and EPDM rubbers
The most modern materials for producing seals are thermoplastic elastomers (TPE-S) based on SEBS (Fig. 1). SEBS is a rubber that does not require vulcanization, i.e., a chemical reaction that cross-links macromolecules. SEBS is structurally similar to EPDM rubber (Fig. 2); like EPDM, it contains approximately 70–80% ethylene units. In addition to these units, SEBS contains polystyrene monomers, which perform the function of "physical vulcanization." EPDM contains an unsaturated monomer that cross-links (vulcanizes) the EPDM polymer chains.
The TPE-S thermoplastic elastomer is easily processed by extrusion, including recycling. SEBS is a material resistant to the low subzero temperatures of the northern regions of the country and the scorching sun of the southern regions. Moreover, SEBS has an advantage over EPDM rubber in that it requires no chemical additives for vulcanization. Therefore, the material is more environmentally friendly, is approved for contact with food products, and is also used in the manufacture of medical devices.
The following features of SEBS seals are worth highlighting:
- Low cost;
- Good elastic properties;
- High resistance to ozone and UV degradation;
- High deformation and strength properties comparable to rubber;
- Wide range of applications (almost any type of seal, food containers, medical devices, etc.);
- Retain elasticity even at temperatures below -50°C;
- Easy to weld, coextruded seals are possible;
- High manufacturing efficiency, no waste;
The price of colored seals is virtually the same as that of black ones. EPDM (Fig. 2) has long been used to manufacture rubber products exposed to the environment. The material exhibits good weather resistance and good elasticity at low temperatures.
Vulcanized rubbers are traditionally made from EPDM rubber. EPDM rubber can be vulcanized using sulfur or resin vulcanizing compounds. The chemical vulcanization process cross-links the rubber macromolecules, forming a three-dimensional, continuous molecular network. This cross-linking allows rubber to recover from mechanical deformation (impact, stretching). Rubber production is an energy-intensive process that also requires significant capital investment. In addition to producing the profile in a special extruder, continuous vulcanization of the resulting seal is required. All this contributes to the high price of EPDM seals. Cheap EPDM seals contain little rubber, a lot of carbon black, and have low deformation-strength characteristics and durability indicators.
For over 30 years, the most high-tech EPDM-based compound in Western Europe has been dynamically vulcanized thermoplastic elastomers (TPE-V) (Fig. 3). It contains higher amounts of EPDM than conventional rubber. TPE-V is carbon-black-free. Essentially, TPE-V is vulcanized EPDM rubber but possesses thermoplastic properties (flow at processing temperatures) due to its special structure and the presence of a thermoplastic phase. EPDM rubber vulcanization occurs under dynamic conditions when the compound is mixed in a twin-screw extruder. Thus, dynamically vulcanized EPDM-based thermoplastic elastomers possess the same properties as EPDM rubber but are significantly more processable and can be recycled at temperatures above 180°C. TPE-V offers the best of both thermoplastic elastomers and EPDM rubbers.
The following features of EPDM-based thermoplastic elastomers are worth highlighting:
- Average price, lower than EPDM rubber;
- Excellent elastic properties;
- High resistance to ozone and UV degradation;
- High deformation and strength properties comparable to rubber;
- Wide range of applications (almost any type of seal, including food packaging and medical devices);
- Retain elasticity even at temperatures below -60°C;
- Easy to weld, allowing for coextrusion;
- High manufacturing efficiency, eliminating waste;
- The price of colored seals is virtually the same as that of black ones.
So, as you can see, there are various materials available for seal production on the market. All of the materials described above meet the requirements of GOST 30778-2001 “Elastomeric sealing gaskets for window and door units. Specifications.” Each of these materials has its own price range, but SEBS- and EPDM-based TPE seals have recently emerged as the leading choice in this area of technology in terms of combined characteristics and price.
In 2017, the Standard Prof® plant began producing TPV-based seals, unique to the Russian market. TPV-based seals outperform TPE-S-based seals in terms of physical and mechanical properties, weather resistance, and elasticity at subzero temperatures. TPV seals are comparable to traditional rubber seals in terms of EPDM content. They have a pleasant velvety surface, are easy to install, have no unpleasant rubber odor, leave no soot marks on the structure, and are easily and securely installed into the profile. Speaking of profile durability, it is useful to know that all door and window seals on imported premium cars are made of similar EPDM-based TPV. Russia’s polymer industry is developing rapidly. Traditional rubber for seal production, a relic of the Soviet legacy, is becoming a thing of the past, giving way to modern, environmentally friendly, and technologically advanced products. The experience of developed countries is excellent proof of this.
PhD, the CEO of the Standard Prof Factory
Vasilii Novokshonov
