Biocomposites from polyhydroxybutyrate and bio-fillers by solvent casting method

Biocomposites from polyhydroxybutyrate (PHB) and some bio-fillers such as lignin (L), alpha cellulose (AC) and cellulose nanofibrils (CNFs) were prepared to investigate the effect of the bio-fillers on the properties of PHB by a solvent casting method. The thermal properties by thermogravimetry analysis (TGA–DTG and DTA) and differential scanning calorimetry (DSC) were determined; morphological characterization by scanning electron microscopy (SEM) and structural analysis by X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) of the biocomposites were performed. TGA curves showed that the highest values for T 10%, T 50% of the biocomposites were 278.2∘C for PHB+2%AC and 291.7∘C for PHB+2%CNFs; however, the best value for T 75% was obtained as 381.5∘C for PHB+2%L. According to DTG curves, the best results were found for PHB+0.5%L and PHB+0.5%CNFs. DTA showed an increase in temperature of maximum degradation with loading of lignin and CNFs. The addition of bio-fillers increases T c and T m for both first cooling/heating and second cooling/heating. T c and T m values for first cooling/healing were found to be lower as compared with second cooling/healing. Furthermore, the addition of bio-fillers acts as a nucleating agent in PHB and SEM pictures showed the porous structure in all biocomposites. SEM images revealed uniform distribution of the reinforcing particles in the polymer at low loadings (0.5 wt%), while higher loadings (2 wt%) of L and CNFs contributed to easy aggregation within the PHB matrix. In XRD studies, PHB in the range 5–55∘ shows 6 main peaks. XRD patterns of the PHB biocomposites revealed 3 main peaks at 13.57∘, 16.87∘ and 22.1∘, and the other peaks disappeared in the patterns. The largest and lowest values of X c were found for PHB+2%AC and PHB+2%CNFs, respectively.