Hydrolytic and environmental degradation of lactic acid based hot melt adhesives

Abstract

Hydrolytic and environmental degradation of packaging hot melt adhesives based on poly(l-lactide) (PLLA) and poly(ε-caprolactone) (PCL) with molar ratio 81:19 were evaluated. The studied samples were an unmodified copolymer, one end-capped with acetic anhydride and one copolymer modified with t-butylperoxy benzoate. Thin films formed from the samples were immersed in phosphate buffer solution (pH 7.4) at 43 °C and the unstabilized sample also at 25 °C. The degradation behavior was studied by monitoring changes in weight, molecular weight, mechanical properties, morphology and structure during the controlled hydrolytic degradation. The compostability of the copolyesters was studied by placing rod shaped specimens and adhesively bonded boards in municipal compost environment. Rod shaped samples were analyzed visually, with gel permeation chromatography (GPC), with scanning electron microscopy (SEM) and the adhesive bonds visually. It can be concluded that all types of copolyester samples degraded rapidly in the buffer solution and compost environment. Stabilization, which prevents the degradation of the adhesive during processing and during the use of the packaging material, does not limit the degradation in hydrolytic or compost environment. Conventional hot melt adhesive based on non-biodegradable poly(ethylenevinyl-acetate) (EVA), which was used as a typical commercial reference in the studies, remained unchanged when inspected visually and with SEM.