SBS and Thermoplastic Rubbers
As we have discussed previously in the post called Thermoplastic Rubber, TPE is the abbreviation of the name Thermoplastic Elastomer and TPR is the abbreviation of Thermoplastic Rubber. They both have the plasticity of plastic and the elasticity of rubber and they are both thermoplastics. SBS and SEBS are used as modifiers to give TPE’s/TPR’s these properties.
“The formal definition of a thermoplastic rubber or elastomer (TPE) is “a polymer blend or compound which, above its melt temperature, exhibits a thermoplastic character that enables it to be shaped into a fabricated article and which, within it’s design temperature range, possesses elastomeric behaviour without cross-linking during fabrication. This process is reversible and the products can be reprocessed and remoulded.” 1
However today we will go into further detail about SBS and touch on SEBS.
SBC’s, SBS and SEBS
“Styrenic block copolymers (SBCs) are the largest volume and lowest priced category of thermoplastic elastomers. SBCs are based on simple molecules (A-B-A type) that consist of at least three blocks, namely two hard polystyrene end blocks and one soft, elastomeric midblock. The midblock is typically a polydiene, either polybutadiene or polyisoprene, resulting in the well-known family of styrene– butadiene–styrene (SBS) and styrene–isoprene-styrene (SIS). The major applications for SBCs are footwear and adhesives and sealants. They are also used in modifying the performance of asphalt for roofing and roads, particularly under extreme weather conditions. SBS block copolymers are among the most commonly modifiers for this application.” 2
Styrene-butadiene Styrene is a synthetic rubber. It is made with two monomers- styrene and butadiene using living anionic polymerization. The rubber is classified as a block co-polymer. The structure of SBS allows for a blend of hard plastic and elastic properties. Due to these properties, it is widely used as a modifying agent especially in plastics. Being a hard rubber with elastic properties it is used commonly for shoe soles, tire treads, asphalt, adhesives and other places where durability is important. SEBS is a product of the SBS hydrogenation, it has a saturated molecular structure, which is resistant to aging, yellowing, heat and corrosion. It is proven that SEBS acts as a better modifier than SBS in improving asphalts rutting resistance due to its double bond saturation, which makes SEBS more rigid than SBS..2 SBCs can also be compounded to produce materials that enhance grip, feel, and appearance in applications such as toys, automotive, personal hygiene and packaging.2 Green Peace lists SEBS as an acceptable alternative to PVC in toys.
2General Purpose Elastomers: Structure, Chemistry, Physics and Performance Robert A. Shanks and Ing Kong Springer-Verlag Berlin Heidelberg 2013