The conflict between needs that must be met when designing a hot melt adhesive can lead to a compromise that falls short of meeting any of them comprehensively. For example, styrene-ethylene-butylene-styrene (SEBS), an especially robust block copolymer, often needs to be formulated together with other styrenic block copolymers (SBCs). Yet, formulations using high molecular weight SEBS can overcome tack issues often otherwise seen with this polymer, and stop staining by components that might leach from the adhesive. Moreover, by combining SEBS and VAE, researchers this year claim to have provided levels never seen before in SEBS hot melts. SEBS is produced by hydrogenating SBS with an elevated vinyl content in order to avoid the ethylene-butylene elastomeric mid-block crystallizing. Though SEBS alone often possesses unsatisfactory tack for adhesive use, its low double bond content is desirable. SBCs with unsaturated middle blocks have low stability to ageing, through the influence of ultraviolet radiation, heat and ozonolysis.
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