Two-Step Process for Continuous Polymerization of Polylactic Acid
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We examined a two-step process concept for PLA polymerization with a small amount of catalyst addition to achieve both a high conversion ratio and a small degree of yellowing. First, we developed a calculation program for the chemical reactions. Next, we carried out beaker-scale PLA polymerization experiments to measure the degrees of yellowing. The measured values were compared to amounts of thermal degradation estimated from the calculations simulating the experiments. Then, bench-scale equipment experiments were carried out on the basis of the obtained conditions. The conversion ratios and the degrees of yellowing of the PLA samples obtained from the bench-scale equipment were compared to the numerical simulation results to verify the process concept and conditions. 170°C was good for a first polymerization temperature to avoid a runaway reaction due to heat generation in the ring-opening polymerization. To minimize the degree of yellowing at conversion ratio of 0.9, we chose 5 h as both the first polymerization time at 170°C and the second polymerization time at 190°C. From bench-scale continuous polymerization experiments, we got PLA that had a conversion ratio of 0.92, a weight average molecular weight of 1.96 × 10<SUP>5</SUP>, and a <I>b</I>-value of 2.42 to verify the concept of the two-step process.
- JOURNAL OF CHEMICAL ENGINEERING OF JAPAN
JOURNAL OF CHEMICAL ENGINEERING OF JAPAN 41(6), 474-484, 2008-06-01
The Society of Chemical Engineers, Japan