In this work, we describe the role of coupling efficiency and styrene content in styrene-isoprene block copolymer based adhesive formulation. The polymers are blends of linear styrene-isoprene-styrene triblock copolymer and styrene-isoprene diblock copolymer.
A series of model structures has been synthesized by batch anionic polymerization at micro-pilot scale and fully characterized. Furthermore, the dynamic-mechanical behaviour of raw polymers as a function of temperature has been tested and correlated with polymer structure.
An extensive technological and dynamic-mechanical characterization has been performed on the prepared hot-melt adhesives. A typical formulation for label application has been chosen to evaluate the effects of the polymer structure. In particular, results of advanced DMA and creep testing, performed with a rotational stress controlled rheometer (MCR 301, Anton Paar-Physica) equipped with 25 mm parallel plates geometry, are presented and correlated with the most relevant properties of the hot-melt adhesive (e.g. Brookfield viscosity, SAFT and HP). The coupling efficiency has a significant effect on both the rubbery plateau modulus and cohesive properties. The styrene content was found to have an effect mainly on cohesive properties. The observed results are discussed on the base of existing knowledge on polymer physics.
Ing. Salvatore Coppola, Dr Alessandro Balducci