Poly(3-hydroxybutyrate) (PHB) oligomer as a modifier in PHB/nanocellulose composites

In this work, nanocellulose (NC) obtained from a by-product of the mushrooms industry and a poly(3-hydroxybutyrate) (PHB) oligomer (M) obtained through the controlled degradation of PHB were used as modifiers in a PHB biopolymer to improve its properties and reduce costs. NC showed less than 100 nm in width, an aspect ratio higher than 50, and better thermal stability than the lignocellulosic source. The M modifier showed a number-average molecular weight of 11 kDa, an onset degradation temperature over 50 °C higher than the melt processing temperature of PHB, and higher crystallinity compared to the PHB pellets used as source. The AFM investigation of the PHB/NC and PHB/NC/M nanocomposites showed a certain degree of disorder in the PHB's structure after NC addition, while the SEM analysis of the tensile specimens' cross-section indicated differences in the fracture mechanism of PHB after the addition of NC and M, which correlated with the mechanical properties. The highest tensile strength and modulus were obtained for the PHB/NC/M1 nanocomposite (containing 1 wt% M), while PHB/NC/M3 (3 wt% M) exhibited only a slight increase in the storage modulus when compared to PHB, indicating the different role of M in the nanocomposites, as a compatibilizer or processing agent. All nanocomposite films displayed excellent color stability and uniformity, higher transparency as compared to the PHB film, better processability highlighted by the lower torque values, and good water barrier property, similar to that of PET, which recommend them as a good solution for the packaging industry.