Effect of acid treatment of eucalyptus fibers for improved poly(3-hydroxybutyrate) nanocomposites

Nanocomposites of poly (3-hydroxybutyrate) (PHB) containing fibrillated cellulose extracted from eucalyptus fibers were prepared and characterized. This study focuses initially on the method to follow the acid treatment of eucalyptus cellulose fibers (ECF) through an experimental design, where the studied parameters were the H2SO4 concentration, hydrolysis time, and reaction temperatures as independent variables for statistical analysis. The thermogravimetric analysis (TGA) of the ECF revealed that mild hydrolysis conditions shifted the degradation temperature of the fibers to higher values. The crystallinity index (CI) obtained by the X-ray diffraction was greater when intermediate hydrolysis conditions (30% H2SO4, 60 °C, 150 min) were employed. Afterward, the most promising ECFs hydrolyzed according to the experimental design were used to produce nanocomposites of PHB(ECF/PHB) containing 5 wt% of the fiber reinforcement via twin-screw mini extruder Haake MiniLab II operating at 180 °C, and varying the rotation speeds (60, 120, and 180 rpm). The ECF/PHB nanocomposites were characterized by TGA and dynamic mechanical analysis (DMA), through which the selected composites with higher thermal and mechanical properties were analyzed by differential scanning calorimetry (DSC), tensile test, and scanning electron microscopy (SEM). ECF/PHB nanocomposites processed at 120 rpm resulted in a material with improved properties. The DMA storage and loss moduli as well as the tensile elastic modulus increased 65%, 196% and 15%, respectively, as compared to the neat PHB. The SEM of the composites revealed nanowhiskers, microcrystalline and microfibrillated cellulose incorporated into PHB, which were attributed to improvements in the thermal and mechanical properties of the PHB matrix.