SYNTHESIS OF NATURAL RUBBER-BASED TOUGHENING AGENTS FOR POLY(LACTIC ACID)
Keywords:
Poly(lactic acid), hydroxyl terminated natural rubber, block copolymer, toughening agentAbstract
Two types of modified natural rubber (NR) which are a low molecular weight hydroxyl terminated NR (HTNR) and its triblock copolymer with poly(lactic acid) (PLA), were synthesized and applied as toughening agents for PLA. The HTNR was achieved by depolymerization and hydroxylation using an ultraviolet radiation reaction. The HTNR with a hydroxyl functionality of 1.77±0.21 had a number-average molecular weight (𝐌̅n) of 28000 g/mol. Triblock copolymers of HTNR with 2 different low molecular weight PLA, PLA1 (𝐌̅n ≈ 3000) and PLA2 (𝐌̅n ≈ 9700 g/mol), were prepared by direct condensation polymerization. The formation of triblock copolymers was confirmed by nuclear magnetic resonance spectroscopy, 1H-NMR and 13C-NMR. The toughening efficiency of the HTNR and its triblock copolymer on the mechanical and morphological properties for PLA was evaluated. The amount of NR, HTNR, and block copolymer in the blend was 10 percent by weight (%wt). The PLA/HTNR blend showed the highest impact strength and elongation at break. Compared to other blends, the PLA/PLA2-NR-PLA2 triblock copolymer blend showed the highest tensile strength. However, the value was still lower than that of neat PLA.
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