Explorations For Processing And Properties Of Lignin/Poly(L-Lactic)ACID Composites

Nowadays, with the quick decrease of the petroleum energy resource and environmental pollution coming from the petroleum-derived plastics, developing and utilizing biomass resources have become the future direction. Lignin, the most abundant biopolymer, second only to cellulose, serves as a continuous matrix component in plant cell walls, providing mechanical strength and structural support. However, almost99%of all lignin was universally burned in an energy recovery step for the pulping process or disposed in waste streams. This not only produced large amounts of carbon dioxide polluting the environment but also wasted the resources. Extrapolating just1%of these available renewable raw materials would cause a revolution of environment and energy. In this graduation thesis, lignin was introduced into Poly(L-lactic) acid (PLLA), which is currently the only commercially available bio-polymer around the world, to produce Lignin/PLLA composites and investigated their properties.When adding lignin into PLLA, the tensile strength of the composites decreased sharply because of the poor interfacial properties between PLLA and lignin. But at the same time, adding a small amount of lignin (such as less than10wt%) could greatly improve the toughness of Lignin/PLLA composites ascribed to lignin having a heterogeneous nucleation effect on PLLA. When lignin dosage was5wt%, impact strength of the composites increased by52.4%.In order to improve the interfacial properties between PLLA and lignin, PLLA grafting maleic anhydride (MPLLA) and silane coupling agent were put into detailed investigation.MPLLA could improve the compatibility of Lignin/PLLA composites and then improve the tensile strength of the composites. However, since PLLA had yielded an oxidative degradation during the reactive extrusion process of grafting maleic anhydride, there had not much increase on tensile strength of Lignin/PLLA composites after MPLLA modification. The elongation at break of Lignin/PLLA composites decreased slightly after MPLLA modification. Silane coupling agents KH550, KH560and KH570were adopted to improve the interfacial properties of Lignin/PLLA composites. KH550or KH560could enhance the interfacial adhesion of Lignin/PLLA composites significantly. The composites of PLLA and lignin surface treated by KH550were strong and tough. The composites of PLLA and lignin surface treated by KH560were strong and brittle. KH570had no obvious effects on the tensile properties of PLLA and lignin composites because KH570could only improve the dispersion of lignin in PLLA. We found that whether to use only water, only ethanol or water-ethanol as a solvent for KH550, the modification results were almost similar. When only water was used as the solvent of2wt%silane coupling agent KH550and lignin addition was5wt%of the composites, both tensile strength and the elongation at break were higher than pure PLLA. When lignin content reached10wt%, the tensile toughness of the composite was not lower than pure PLLA and the tensile strength of it was slightly lower than thatFor PLLA and lignin composites, whether they were modified or not, lignin can improve the hydrolytic biodegradable properties of Lignin/PLLA composites in a sodium hydroxide solution with the pH value of13.