Bio-Based Poly(3-hydroxybutyrate) and Polyurethane Blends: Preparation, Properties Evaluation and Structure Analysis

The present work deals with polymer blends produced from poly(3-hydroxybutyrate), P3HB and polyurethane. Linear polyurethane (PU) was here synthesized by reacting polypropylene glycol with 4,4'-diphenylmethane diisocyanate, and was used in amounts of 5, 10 and 15 wt. %. The polymers were melt-mixed using a twin-screw extruder after prior premixing. The obtained blends were tested by differential scanning calorimetry analysis (DSC), Fourier transformation infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX). Their thermal and mechanical properties, including impact resistance, hardness, tensile and flexural properties, were also determined, and the surface topography and roughness were analyzed. FTIR analysis of the prepared blends confirmed the interactions of PU with the P3HB matrix via hydrogen bonding. Analysis of the surface topography of the samples showed that the higher the PU content, the greater the regularity and homogeneity of the surface structure. The roughness of the P3HB blend containing 5 wt. % PU was the greatest. SEM images of the fracture surfaces of the blend samples explain the mechanism of the improvement of their mechanical properties. The obtained polymer blends were characterized by significantly lower hardness, and better impact strength and relative elongation at break compared to native P3HB. The DSC results confirm a decrease in the glass transition, melting and crystallization temperatures with increasing amounts of PU in the blends. The lower melting temperature and the higher degradation temperature of the resulted blends than native P3HB make the processing conditions easier, and prevent the degradation of the material. The best mechanical and thermal properties were shown by blends containing 10 wt. % of PU.