Elastómero estirenico Termoplastico
Thermoplastics > Styrenics
Understand the difference between SBS and SEBS thermoplastic elastomers?
TPE has a two-phase structure. One is a solid dispersed phase with the glass transition temperature (Tg) above room temperature, and the other is a continuous phase of rubber with Tg below room temperature. TPE is in a state of high elasticity at room temperature due to the rubbery phase between Tg and melting temperature (Tf), while its dispersed solid phase is in a rigid and vitreous state with the ability to avoid the phase flow of high elasticity, which guarantees the usability of TPE at room temperature. The solid phase softens when heated to the temperature above its Tg. TPE will be completely in the flow state when its Tf is reached. The Tf of the solid phase is also the lowest temperature of TPE for injection molding. The SBS are block copolymers, thanks to the anionic polymerization, it was possible to build precise polymer chains, with a sequence of styrene repeat units, marked in a sequence of butadiene repeating units and topped with another block of styrene units. This gave a styrene-butadiene-styrene (SBS) block copolymer. It was soon discovered that, at ambient temperatures (below the glass transition temperature of polystyrene), the tails of styrene blocks are aggregated into groups (domains) to act as rigid physical cross-links. This maximizes the high elastic properties of the butadiene block. At elevated temperatures, the styrene domains unravel and the polymer becomes a thermoplastic melt suitable for extrusion and injection molding. The elastic extension and recovery properties of SBS coincide with those of conventional vulcanized elastomers. However, the advantage is that there is no "vulcanization" stage and the process time and energy consumption are considerably reduced. The soft touch features of SBS were soon exploited by designers, particularly in hand tools. The applications now extend to toys, automotive moldings, tubes, wires and cables, footwear and adhesives, sealants and even bituminous additives. However, SBS has degradation problems at high temperatures and the butadiene content makes it prone to oxidation and weathering, without the proper antioxidants. By converting the butadiene block into repeating ethylene-butylene (hydrogenation) units, the thermoplastic elastomers of SEBS have better thermal stability and better weather resistance, without sacrificing too much mechanical performance. The partial hydrogenation of polymers produces important modifications both in the architecture and in the chemical stability of the polymers, since they have various applications because the remaining double bonds are available sites for subsequent modifications. As the degree of hydrogenation increases, the rigidity of the elastomeric part is greater, since the chain acquires a more regular arrangement and with it its glass transition temperature and degree of crystallinity increase. SEBS is also sterilizable by steam. The unsaturated styrene butadiene copolymers (SBS) are the lowest cost and performance of this group, while the styrene-ethyl-butyl-styrene (SEBS) and styrene-ethyl-ethyl-propyl-styrene (SEEPS) hydrogenated / saturated have a higher cost and performance. The compounds of these polymers incorporate suitable thermoplastics (such as PP, PE, PS), oil and reinforcements of a continuous phase morphology.
Both the block copolymers are prepared using the anionic polymerization, he realized that he was witnessing the birth of a new class of materials, thermoplastic elastomers (TPE).
Thanks to the anionic polymerization, it was possible to build precise polymer chains, with
It was soon discovered that, at room temperature (below the glass transition temperature of polystyrene) the addition of styrene blocks in clusters (domains) to act as physical crosslinks as rigid, which maximize the high elastic properties of the butadiene block. At elevated temperatures the styrene domains unravel and the polymer becomes a thermoplastic melt, suitable for extrusion and injection molding. The elastic extension and recovery properties of SBS coincide with those of conventional vulcanized elastomers, but the advantage is that there is no "cure" stage, and the process time and energy consumption are considerably reduced. Also the SBS can be processed from the solution.
The soft touch features of SBS were soon exploited by designers, especially in hand tools. The applications now extend to toys, automotive trims, tubes, wires and cables, footwear and adhesives, sealants and even asphalt additives.
However, the SBS has degradation problems at high temperatures and the butadiene content makes it prone to oxidation and wear, without proper antioxidants. By converting the butadiene block to ethylene-butylene repeating units, SEBS thermoplastic elastomers have better thermal stability and better weather resistance, without sacrificing too much mechanical performance. SEBS is also sterilizable by steam.
Keywords: SBS elastomer, SEBS elastomer, SBS thermoplastic, SEBS thermoplastic, SBS VS SEBS