Selective Depolymerization of PLA in Blends

Formation of a polymer alloy is a common way to improve the property of PLLA. Many kinds of polymers such as polyethylene [70], polypropylene (PP), polystyrene (PS) [71], poly (methyl methacrylate) [72], bisphnol-A type polycarbonate, poly(E-caprolactone), poly(3-hydroxybuty-rate), poly (butylene succinate) (PBS) [73], poly(butylene succinate/adipate) (PBSA), acrylonitrile-butadiene-styrene have been used for preparing PLLA alloys, and some of which have been commercialized. However, there has been no discussion of the thermal degradation behavior of the PLLA component. 

To achieve selective depolymerization of the PLLA component, some polymer blends of PLLA with linear low-density polyethylene (LLDPE) [74, 75], PS [76], PBS [77], and PBSA [77] were prepared and thermally degraded with 

FIGURE 23.7 Possible racemization reactions among lactides and oligomers. 

PLA is well known as a degradable material at higher temperatures. However, the mechanisms of the thermal degradation are complex. To clarify and control the thermal degradation of PLA, many efforts have been made. As a result, the effects of some important factors, such as polymerization catalyst residues, chain-end structures, depolymerization catalysts, stereocomplex structure, racemization, blends with other polymers, and so on, have been clarified. Highly active and selective depolymerization cat- 

Although PLA is synthesized from renewable resources, the production of the polymeric form requires much processing, energy, and fuel. If a highly selective depolymerization of PLA to the cyclic monomer, lactide, can be achieved effectively, it will then become possible to renew PLA by the shortest, most energy-efficient route. 

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