Adhesion properties of lactic acid based hot melt adhesives and their storage stability in different packaging applications

Adhesion properties and the stability during the use life of the package for two biodegradable hot melt adhesives were evaluated. Adhesives were based on poly (L-lactide) (PLLA) and poly(ε-caprolactone) (PCL) with molar ratio 81:19. One sample was stabilized by end-capping the terminal hydroxyl groups with acetic anhydride. The other sample was unmodified. Reference adhesive that was used in the studies, was a conventional non-biodegradable hot melt adhesive based on poly(ethylene-co-vinylacetate) (EVA). als, which were bonded with these hot melt adhesives, were typical biodegradable packaging materials: a pigment-coated cardboard, a similar cardboard extrusion laminated with film type PLLA and an uncoated cardboard. The storage stabilities of the copolyester films and bonded structures were monitored during an eight week period at room (23°C) and at low (−18°C) temperatures. s in molecular weight and crystallinity of the copolyesters were measured with gel permeation chromatography (GPC) and differential scanning calorimetry (DSC), respectively. Mechanical strength of the adhesive bonds was measured by a tensile testing instrument. Fracture surfaces of the adhesive bonds were subjected to microscopic studies. l adhesion properties of the copolyesters were similar to those of EVA and better in case of PLLA-laminated cardboard. Both biodegradable copolyester samples degraded during the studied period; however, end-capping of the copolymer retarded this degradation rate.