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Expert Opinion on Current Trends in the Window and Door Seal Market
In recent years, there has been a clear trend toward using two groups of materials to produce seals for window and door systems. According to the GOST 30778 (2001) classification, these are traditional EPDM rubbers (Group I) and SEBS-based thermoplastic elastomers (Group IV). Compliance of material properties with the technical requirements of GOST 30778 (2001) allows these materials to be used for the production of seals.
GOST 30778 was introduced in 2001, when thermoplastic elastomers in Russia were primarily PVC-plasticized compounds, essentially plastic softened with a plasticizer. The authors of the GOST did not divide thermoplastic elastomers into types and property levels but instead categorized rubbers into Groups I, II, and III, based on EPDM, silicone, and chloroprene rubber, respectively. According to GOST specifications, the properties of rubbers for seals vary significantly. Similarly, thermoplastic elastomers require categorization into groups, as they currently include more than 20 types in industrial use. The authors of the GOST, based on the properties of PVC plastics commonly used in the 2000s, set the performance level of all Group IV thermoplastic elastomers below that of Group I EPDM rubbers. For example, the GOST operating conditions for thermoplastic elastomer seals range from -45°C to +70°C, while for EPDM rubbers, they range from -50°C to +80°C.
More than 20 years have passed, and thanks to the development of new polymers on an industrial scale, a new class of thermoplastic elastomers for the production of seals has emerged – TPE-S, the main component of which is SEBS. Many consumers already know that SEBS rubber in modern TPE-S thermoplastic elastomers is analogous to EPDM rubber. The elasticity of the seals is due to the similar polymer chain links in both rubbers. SEBS is a thermoplastic elastomer, meaning it can melt and be processed above 150°C, and upon cooling, physical bonds are formed in the polystyrene domains, turning SEBS rubber into an elastic material. The production of TPE-S sealants does not require the addition of vulcanizing agents.
Figure 1. Comparison of EPDM and SEBS macromolecular compositions
Elastomer blocks in rubbers with the same composition should produce the same properties as EPDM rubbers and TPE-S thermoplastic elastomers, but experience shows that the rubbers themselves are not the only factor. The properties of the final seals are also influenced by the cross-sectional geometry of the seal and the composition of the polymer compound used to produce the seal. These rules apply to both EPDM rubbers and SEBS thermoplastic elastomers.
Cheap EPDM seal compounds with low rubber content, high carbon black content, and inexpensive vulcanizing agents lead to incomplete vulcanization of the seal during production, seal hardening at low temperatures, soot marks on the profile, and a strong rubber odor.
Cheap thermoplastic elastomer compounds also lead to insufficient elastic properties of the seal at low temperatures, cracking of the seal during use in the profile, and deterioration of the seal under the influence of sunlight. In today's polymer industry, the quality of a seal, in terms of its high level of performance properties, is determined largely not by the grade of the sealing material but by the correct composition of the polymer compound and the proper geometry of the seal's cross-section.
The suitability of a particular material for seal production is determined by the economic effect, that is, the ratio of the seal's price to the level of properties it provides in a window or door structure. GOST states that silicone rubber seals are the best in terms of heat and frost resistance. Because silicone seals are expensive and their performance is often excessive for window and door structures, they have not found widespread use in construction. The performance of high-quality EPDM and TPE-S seals is sufficient to ensure Class A air and water tightness in both summer and winter temperatures.
The tightness of a window structure depends on the profile, reinforcement, hardware, and seal. Since the seal is the most easily replaceable part of the structure, installers try to solve blow-through problems by replacing it. In most cases, replacing the seal with a larger one from a different series solves blow-through problems. A high-quality seal can solve some structural issues, but unfortunately, not all. The higher the elasticity and the ability to recover from compression, the more versatile the seal and the more structural problems it can solve.
Based on partner feedback and taking into account the more stringent requirements for seals from some Russian profile manufacturers than those specified in GOST, in 2019 we began developing a new TPE-S class with properties superior to EPDM. We developed LCS thermoplastic elastomers and seals. LCS (low compression set) seals have reduced residual compression at low negative and high positive temperatures and are more elastic and softer than mass-produced TPE-S seals. During development, the limitation for increasing the performance level of LCS seals was price. The price of LCS seals remains lower than that of EPDM seals.
Figure 2. Photo of LCS seals
The table below compares the characteristics of TPE-S LCS with the requirements of GOST 30778-2001 for thermoplastic elastomers and EPDM rubbers of subgroup "b" with a hardness of 56–75 Shore A.
| Name of Indicator | GOST Group I, EPDM rubber |
GOST Group IV, thermoplastic elastomers |
TPE&S LCS «Standard Prof» |
| Tensile strength, MPa, not less than | 7,5 | 5,0 | 8,5 |
| Relative elongation at break, %, not less than | 200 | 200 | 550 |
| Temperature limit of brittleness, °C, not higher | Minus 50 | Minus 45 | Minus 65 |
| Frost resistance coefficient for elastic recovery after compression, not less than at a temperature of, °C -50 | 0,2 | not standardized | 0,23 |
| Relative residual deformation under static compressive deformation of 25% for 24 hours, %, no more than | 100°С 24 h – 50%1 | 70°С 24 h – 50% | 23°С 72 h – 11% 70°С 24 h – 23% 100°С 24 h – 44% |
| Change in performance after aging in air for 24 hours at 125°C Tensile strength, %, not less than Elongation at break, %, not less than Shore A hardness, Shore A units |
-25 -60 +15 – -15 |
-252 -302 +5 – -52 |
-93 -113 +33 |
| Resistance to thermal and light-ozone aging at 40°C for 96 hours with an ozone volume fraction of (5,0 ±0,5)*10-5% at a static tensile strain of 20%. | no cracks | no cracks | no cracks4 |
1 – tests are carried out at a deformation of 20%;
2 – test conditions: aging for 24 hours at a temperature of 100°C;
3 – test conditions: aging for 1 year at a temperature of 100°C;
4 – the test conditions differ in ozone concentration – 400 pphm, which is 8 times higher than (5,0 ±0,5)*10-5%.
Since 2021, LCS Standard Prof® series seals have been successfully used in PVC windows. It is worth noting that LCS materials have been used in Scandinavian and Mediterranean European countries, as well as in the USA and Canada, since the early 2000s. LCS seals meet the performance standards of DIN 7863-1-2019 Elastomer glazing and panel gaskets for windows and claddings. Further details on the properties of LCS seals will be covered in future information articles.
PhD, the CEO of the Standart Prof Factory
Vasilii Novokshonov
