Mechanical, thermal and hydrodegradation behavior of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) composites with agricultural fibers as reinforcing fillers

Abstract

Fully biodegradable polymer composites based on the bacterial polyester, poly (3-hydroxybutyrate-co-3-hydroxyvalerate), (PHBV), were produced using injection molding. Agricultural reinforcements in the form of nettle fibers (stalks and leaves), pine cones flour, and walnut shells flour were used in the amount of 15 wt%. The impact of natural additives on mechanical properties (tensile, flexural, and impact) at three different temperatures (−24, 23, and 80 °C) has been studied. For all the tested composites, Young's modulus was improved by ~20% with a slight decrease in the tensile strength. The mechanical properties correspond well with the DSC results. The values of the degree of crystallinity for the composites are higher or equal to those for neat PHBV, only the composites with stalk nettle fibers were characterized by a reduced degree of crystallinity. Research has shown that composites have higher stiffness stability at elevated temperatures.Furthermore, the materials were subjected to hydrolytic degradation at 38 °C to determine the synergistic effect between water uptake and water temperature on tensile and flexural properties. The work reveals that the addition of natural fillers increases the possibility of water absorption and decreases the value of the tested properties by ~40% after two weeks of water incubation.Recent work has shown that it is possible to produce fully biodegradable polymer composites using agricultural wastes. The addition of fibers not only reduces the price of materials but increases the stiffness of the polymer whilst controlling the biodegradation process. Moreover, in this approach, waste materials will be able to act as an efficient filler, what will lead to their effective management.