Treating bast fibres with pectinase improves mechanical characteristics of reinforced thermoplastic composites

The effect of pectinase treatment of hemp (Cannabis sativa L.) fibres on mechanical properties of fibre reinforced polypropylene was investigated. Incubating technical fibres with pectinase (SIHA-Panzym® DF) reduced their cross-sectional area (8.72 × 10−3 vs. 3.67 × 10−3 mm2, control vs. pectinase incubation) and decreased tensile strength (455.4 vs. 171.2 MPa). Polypropylene (PP) was reinforced with these fibres using conventional extrusion and injection moulding techniques. Maleic anhydride grafted PP was applied as compatibilizer. The cross-sectional area of fibres in the composite decreased from 2.58 × 10−4 to 1.21 × 10−4 mm2 for control vs. pectinase. Tensile strength (43.7 vs. 47.6 MPa for control vs. pectinase incubation), flexural strength (49.9 vs. 56.6 MPa) and moduli of elasticity (tensile, 2.62 vs. 3.25 GPa and flexural, 2.28 vs. 2.87 GPa, respectively) all increased when using fibres incubated in pectinase. Qualitatively and quantitatively similar effects, albeit on a decreased level, were obtained when reinforcing PP in absence of the compatibilizer. The data indicate the refining of technical fibres in response to pectinase treatment. This effect was accomplished by (1) enzymatic decomposition of the middle lamellae, (2) mechanical stress exerted by compounding and (3) compression of cell lumina. The separation of technical fibres into smaller bundles and single fibre cells, in turn, resulted in improved tensile and flexural characteristics of thermoplastic composites.