Development of high biomass content hot-melt pressure-sensitive adhesives

Abstract

A new approach was introduced for incorporating renewable biomass into existing commercial pressure-sensitive adhesive (PSA) polymers in the form of acrylated macromonomers (MM). MM were prepared with L-lactide and caprolactone via a bulk ring-opening polymerization initiated by N-hydroxyethyl acrylamide (HEAA). Acrylic adhesive copolymers were synthesized by free-radical solution polymerization in presence of 2-ethylhexyl acrylate (EHA), acrylamide and macromonomers. This approach was achieved without sacrificing adhesive performance. Incorporation of the MM into the polymers was confirmed via proton NMR. Properties and adhesive performance of the new polymer were compared with its 100% acrylic commercial version. When synthesized using the same approach, the biomass-containing PSA had a lower molecular weight, higher glass transition temperature (Tg) and lower melt viscosity. Introduction of MM had little impact of tack force, shear time and shear adhesion failure temperature and peel strength increased substantially. Influence of HEAA capped L-lactide/caprolactone MM composition on acrylic hot-melts was also reviewed. A series of MMs, synthesized using catalyzed ring-opening polymerizations, were produced containing a broad range of lactic acid and caprolactone repeat units. Results indicate that the properties and performance of adhesive polymers are strongly dependent on lactide composition. In general, increasing lactide content increases polymer hardness enhancing cohesive strength, while reducing it (i.e., increasing caprolactone content) softens the polymer. Optimal adhesion is found to require a balance between these tendencies as indicated by the existence of a clear maximum in both tack and peel data. The results demonstrate that a broad range of properties is achievable through relatively minor modifications to MM composition. It is expected that these hybrid materials can be optimized for a variety of self-adhesive applications.