1.4.2 RESULTS The fermentation broth containing lactic acid has been purified through a series of steps to yield a pure form of lactic acid. The lactic acid has thereafter been used in trials of ring-opening polymerization (ROP) to attempt to produce high-density PLA (HDLPLA). However, since the attempts to produce HDLPLA were unfruitful, and trials using various catalysts were unsuccessful, we opted to produce PLA of lower density (LDLPLA) through direct polycondensation of the produced lactic acid (figure 14-15) to gain PLA that could be used in application testing.
Figure 14. Water removal (left) and distillation of lactate ester (right) from fermentation broth (saw dust) containing lactic acid
The polymerization process has involved several reaction steps including removal of water and undesired salts, esterification of the crude lactic acid and direct polycondensation of purified lactic acid (figure 14). Reactions have been optimized regarding reaction times and temperature and attempts have been made to recycle reaction chemicals. For instance, ethanol that has been used during the process can be re-used after distillation and ammonium sulphate produced during neutralization can be filtered and re-used. We have been able to produce LDPLA using both fibre sludge and saw dust as raw materials and by polycondensation we have produced roughly 1 kg of L-LDPLA from lactic acid produced in fibre sludge hydrolysate (figure 15).
Figure 15. Roughly 50% pure lactic acid (left) produced from fermentation broth (fibre sludge). PLA (middle & right) produced from the pure lactic acid
GREEN BIORAFF SOLUTIONS
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