Effects of gamma irradiation on properties of PLA/flax composites

Polylactic acid (PLA) is a well-known renewable and biodegradable polymer but is still limited by its low heat distortion temperature and brittleness. In this study, a PLA/flax composite containing flax fiber strands (5 wt%) was prepared through melt-compounding process followed by gamma irradiation at doses ranging from 0 to 20 kGy in the presence of a small amount of triallyl isocyanurate (TAIC) as cross-linking agent. The gel fraction of the composite was tested, and the datum showed that the gel fraction sharply increased first, and then slightly decreased with increasing irradiation dose. Gamma irradiation induced cross-linking of the polymer to form a three-dimensional network in the PLA/flax composite system. Irradiated composite could only swell instead of dissolving completely in chloroform, and the swollen morphology correlated with irradiation dose. The thermal stability of the PLA/flax composite was characterized using thermogravimetric analysis (TGA) temperature, and dimensional stability. Overall, irradiation modification improved the thermal resistance and dimensional stability of PLA composites. The mechanical property tests of the irradiated composites revealed increased tensile and impact strengths, reduced elongation-at-break, and unchanged tensile modulus. The analysis of water absorption of the composite demonstrated that the irradiation cross-linking induced no obvious effect on water absorption. Irradiation cross-linking modification cannot change the hydrophilicity or hydrophobicity of PLA composites. Overall, these findings look promising for future use in reinforcement and improvement of the thermal resistance of PLA/flax composites.