Simple preparation of multi-branched poly(L-lactic acid) and its role as nucleating agent for poly(lactic acid)

The present work proposes a simple preparation of multi-branched poly(L-lactic acid)s (m-PLLAs) and their performance as nucleating agents for PLA. By a simple polycondensation of L-lactic acid (L-LA) on the multi-functional core molecules of succinic acid (SA), malic acid (MA) and citric acid (CA) using stannous octanoate (SnOct(2)) as a catalyst, the m-PLLAs as two, three, and four branched PLLA can be obtained easily. Averagely, about 80% of the L-LA feed contents are successfully polymerized on core molecules. Non-isothermal crystallization studies of the PIA blend which contains 1 wt% m-PLLAs indicate that m-PLLAs induce the crystallization of PIA as evidenced from the decreases in glass transition temperature (T-g) and crystallization temperature (T-c), and the increase in degree of crystallinity (chi(c)) under the alpha-form of perfect crystalline in PTA. Isothermal crystallization studies related to Avrami exponent (n), kinetic constant (k) and crystallization half-time (t(1/2)) indicate that the blend maintains its three-dimensional growth for the film thickness 0.05 mm, whereas the crystallization growth rate increases more than 4 times as observed from polarized optical microscope (POM). Among m-PLLA, the highest number of multi-branches with the shortest chain PLLA, i.e. CA-PLLA1, initiates the blends to increase its tensile strength and elongation at break for as high as 1.5 times and 1.2 times, respectively. (C) 2012 Elsevier Ltd. All rights reserved.