Lactic acid based polymers as hot melt adhesives for packaging applications

The suitability of biodegradable copolymers based on poly(l-lactide) (PLLA) and poly(ε-caprolactone) (PCL) with molar ratio of 81:19 for a packaging hot melt adhesive was evaluated. Typical hot melt adhesive properties such as open time, setting time, hot tack development, viscosity and weight loss were measured for an unstabilized and for two chemically stabilized samples. Mechanical testing included tensile strength, lap shear strength and elongation measurements. The results show that PLLA/PCL copolymer is a potential candidate for a biodegradable hot melt adhesive for a packaging application. Most of the measured properties were comparable to a conventional, non-biodegradable poly(ethylenevinylacetate) (EVA) based hot melt adhesive, which was used as a typical commercial reference. The stability of the PLLA/PCL copolymer is, however, a limiting factor: mechanical properties change within few days depending on the geometry of the samples. Also the degradation during processing of the PLLA/PCL copolymers was severe. The drying of the samples before processing or the use of nitrogen as a protective gas during processing seemed to have no observable effect on the stability. However, chemically stabilized polymers performed better during processing and also retained their mechanical properties better than the unstabilized copolymer.