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 (SnOct2) 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 PLA blend which contains 1 wt% m-PLLAs indicate that m-PLLAs induce the crystallization of PLA as evidenced from the decreases in glass transition temperature (Tg) and crystallization temperature (Tc), and the increase in degree of crystallinity (χc) under the α-form of perfect crystalline in PLA. Isothermal crystallization studies related to Avrami exponent (n), kinetic constant (k) and crystallization half-time (t1/2) 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.