Properties enhancement of poly(β-hydroxybutyrate) biocomposites by incorporating surface-modified wheat straw flour: Effect of pretreatment methods

Abstract

Poly(3-hydroxybutyrate) (PHB) biocomposites filled with wheat straw flour (WSF) were enhanced through modifying WSF surface by pretreatments, i.e., alkali solution (NaOH 1–7 wt%) dipping, (3-aminopropyl)triethoxysilane solution (APTES 0.5–2 wt%) soaking, or NaOH+APTES synergistic impregnation. The WSF was characterized by microscopy, spectroscopy, diffractometry, thermogravimetry, and wetting. Through different levels of surface etching effect or grafting functional groups, all the pretreatments removed unstable, amorphous substances on WSF, obtaining higher crystallinity by 2–12 %, degradation temperature by 57–83 °C, and lower water contact angle by 7–24°. Compression-molded WSF/PHB biocomposites were examined by mechanical tests, microscopy (fracture morphology), water absorption, calorimetry, and thermogravimetry. Above pretreatments boosted mechanical-, moisture-, and heat-resistances of composites, owing to stronger interfacial interaction of PHB with surface-modified WSF, and the improved physicochemical properties of WSF itself. Alkali treatment worked better in raising mechanical, waterproof behaviors, while silane induced higher temperature for phase transition, decomposition. Enhancement achieved by alkali+silane could surpassed both single treatments. The best outcome occurred in 3 wt% NaOH + 0.5 wt% APTES, which increased strength (flexural, tensile, and impact), modulus (flexural, tensile) by 22–40 % and 14–23 %, respectively, decreased 300 h-water absorption by 18 %, and rose melting, degradation temperatures by 2 and 23 °C, respectively, showing new potential for construction-related application.