Rheological and thermal behavior of PHB/piassava fiber residue-based green composites modified with warm water

The search for increasingly biodegradable materials motivated us to investigate composites of poly(3-hydroxybutyrate) (PHB) and piassava fiber residue. The composite mixing process for 10 and 30% (w/w) mixtures was conducted in an internal mixer at 180 °C and 60 rpm for 10 min. The fiber residue was washed with a detergent solution, treated in warm water at 50 °C, and then ground to a particle size of smaller than the 270 mesh. The fiber residue had a higher surface area, higher crystallinity index, and smaller particle size than the residue that was only washed. The fiber had thermal stability up to 224 °C. The thermal treatment neither altered the constitution nor crystalline structure of the fiber, which suggested that a major concentration of the thermal fiber led to more effective defibrillation of the fiber residue, which facilitated the mixing process of the 30% (w/w) composite and increased its degree of crystallinity by 8.8%. However, the maximum degradation temperature of the fiber was significantly reduced (by 58 °C) for this composite with respect to PHB. For the other composites, the presence of the residue caused a smaller decrease in the thermal stability of the polymer.