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Changes in mechanical and thermal properties of biodegradable mulches based on plasticized PLA/PHB filled with 3 wt% of carbon black were investigated during natural ageing in real soil environments after application for one season. The natural ageing process changes were evaluated under three different conditions of the mulching films: (a) buried in the soil, (b) exposed to sunlight, and (c) shadowed by plants. In a parallel study, the film was irradiated by a UV–Vis lamp under laboratory controlled test conditions at constant temperature and humidity. All samples were analyzed using GPC, DSC, DMTA and tensile tests. The plasticized PLA/PHB/CB film buried in soil lost its tensile properties faster than when shadowed by plants or exposed to sunlight. The deterioration of mechanical properties during degradation resulted in significant decreases elongation at break, while Young’s modulus values and tensile stress increased. Assessment of the mulching effect on the harvest of sweet pepper fruits, as well as carotenoids and vitamin C contents, was also performed. The obtained results showed that plasticized PLA/PHB/CB film has the potential for application for one season mulches.

The study is focused on modelling the evaluation of recyclability of the biodegradable blend using multiple extrusion of selected composition of PLA/PHB blend which had been more deeply studied before. It was shown that the multiple extrusion reduces viscosity of the tested blend due to multiple thermomechanical stresses and the material was partially degraded. Partial degradation was demonstrated by measuring of molecular characteristics. The degree of degradation of the tested material was determined with relatively high accuracy after creating a colour space/viscosity. Multiple processing and subsequent degradation of the tested material did not negatively affect thermal properties, as well as strength characteristics of the blend. It was concluded that the biodegradable polymer blend of the PLA/PHB type is suitable for multiple processing and material recycling can be applied for this type of bioplastics.

Blends of biodegradable polymers polylactic acid/thermoplastic starch/polyhydroxybutyrate (PLA/TPS/PHB) were prepared using a twin-screw extruder. The TPS content was constant (50 %) and the PHB content in the blends was gradually changed from 0 mass % to 20 mass %. TPS was prepared by melting, where a mixture of native starch, water and glycerol was fed into the twin-screw extruder. Average temperature of extrusion was 180 °C and the concentration of glycerol was 40 mass %. Influence of the PHB concentration in the blend and that of the processing technology on the mechanical and rheological properties of the PLA/PHB composition containing TPS were studied. Mechanical properties were measured 24 h after the film and monofilament preparation and also after the specific storage time to study the effect of storage on the properties. The results indicate that differences in morphology strongly influence the mechanical properties of the studied materials with identical material composition.