Composite sheets based on polylactic acid and sugar beet pulp

Sugar beet residues (SBR) were converted into thermomechanical pulp (sugar beet pulp, SBP) and compounded with either polylactic acid (PLA) or high-density polyethylene (HDPE) as matrix. Pressed, thin sheets made with the compounds were placed on soil for 16 weeks outdoors and changes in material properties, including weight losses, monitored. Chloroform extraction showed that proportionally more SBP than PLA was degraded after biodegradation. A reduction in molecular weight of the PLA in composites during processing was determined, which was attributed to moisture in SBP and led to PLA hydrolysis. No further significant reduction in molecular weight of the PLA in composites occurred during outdoor exposure. In case of the HDPE-SBP composites, results of acid hydrolysis indicated that primarily, the SBP component was degraded. Tensile strength tests, microscopy, FT-IR spectroscopy and thermal analyses were also performed with the composites. Under the conditions of this study, it was shown that PLA composites with 70% (wt.) of SBP were completely disintegrated before completion of 12 weeks exposure. The addition of SBP to PLA accelerates biodegradation significantly which is an asset for agricultural (mulch films), forestry, horticulture and packaging applications.