The Soil Biodegradability of Structured Composites Based on Cellulose Cardboard and Blends of Polylactic Acid and Polyhydroxybutyrate

The excessive use of plastics, in addition to the limitative capacities available for plastic waste disposal or recycle increased the interest in degradable polymers. Polylactic acid (PLA) and polyhydroxybutyrate (PHB) are among the most studied biobased polymers for packaging applications. However, their biodegradability in real environment is questionable. Therefore, the purpose of this study was to investigate the biodegradation behavior of PLA/PHB blend films and their sandwich-structured composites containing a cellulose paper interlayer, in natural soil environment, exposed to humidity and temperature conditions specific to different seasons. The study was conducted for 8 months and the biodegradation process was evaluated by measuring the morphological changes, weight loss and tensile properties of the samples. The weight loss data showed that materials were able to degrade under the action of soil microorganisms, water and heat. Moreover, the cellulose layer favored the water retention and enhanced the degradation. SEM images highlighted traces of erosion and biodegradation in the case of the buried samples and FTIR spectra revealed the scission of the ester bonds, which proved the degradation of the aliphatic polyesters. The XRD studies showed that the samples recovered from compost soil were more crystalline than those stored at room temperature, which indicates the degradation of the amorphous phase in the samples. In addition, DMA measurements showed a strong reinforcing effect of the cellulose interlayer on the PLA/PHB matrix. In conclusion, PLA/PHB blend is suitable for long packaging application, but the addition of a cellulose paper interlayer is beneficial to accelerate the decomposition rate.