Biocomposites based on the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) matrix with the hemp fibers: thermal and mechanical properties

The poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was used to prepare biocompatible composites modified by the hemp fibers. The aim of the study was to assess the structure and selected thermal and mechanical properties of the obtained biocomposites. The morphology of samples was analyzed using a scanning electron microscope and a computed tomography analysis. The phase transitions of composites and polymer matrix were investigated using differential scanning calorimetry. Moreover, the non-equilibrium and equilibrium thermal parameters of composites and the unfilled PHBV were established based on the thermal history. Knowing equilibrium parameters, i.e., the heat of fusion for the fully crystalline materials, ΔHf (100%), and the change of heat capacity at glass transition temperature (Tg) for the fully amorphous, ΔCp (100%), composites, the degree of crystallinity, mobile, and rigid amorphous fractions were estimated. The addition of hemp fibers to the PHBV matrix caused around a two-time increase in the degree of crystallinity in reference to the unfilled PHBV. It was also observed that the addition of hemp fibers caused a decrease in heat capacity for fully amorphous material for all the biocomposites obtained. A similar relationship was observed in case of values of the heat of fusion for fully crystalline material. Simultaneously, the decrease in amorphous phase contents was noted. It was also noted that the rigid amorphous fraction exists only for the unfilled polymer matrix. Some mechanical properties of investigated materials were also measured and presented.