Degradation phenomenon of compostable poly(lactic acid) films induced by pure halogenated liquid chemicals and mixtures with water

A circular economy requires that plastic packaging should be recyclable or compostable as well as reusable. Compostable/biodegradable poly(lactic acid) (PLA) is an alternative to conventional packaging materials for films, bags, and containers. Packaging is not only for food and beverages but also for medicine, agricultural chemicals, industrial chemicals, and waste solvents such as chlorinated solvents, which sometimes contain water. This study determined that PLA films were completely soluble in dichloromethane and chloroform, insoluble but strongly swollen in trans-1,2-dichlorocycrohexane, o-dichlorobenzene, and carbon tetrachloride, and insoluble with retained film shape in tetrachloroethylene (TCE), 1,2,4-trichlorobenzene (1,2,4-TCB), and 1-bromonaphthalene (1-BN). The equilibrium mass uptake values of pure insoluble solvents in PLA films were 0.977 ± 0.219 wt% for TCE, 1.716 ± 0.631 wt% for 1,2,4-TCB, and 3.351 ± 1.936 wt% for 1-BN. After sorption of the three insoluble pure solvents, the α’-type crystals of PLA films changed to α-type crystals. This phenomenon was based on the molecular size and electrostatic potential value of the solvents. When insoluble solvents were mixed with water, the water-in-oil mixture enhanced the mass uptake for TCE and 1,2,4-TCB but reduced it for 1-BN. The oil-in-water mixture distinctly reduced the solubility for all solvents. The α-type crystal structure was stable in TCE and 1-BN. If an industrially appropriate method of α-type crystal structure formation could be realized selectively, then PLA could be used as packaging materials for films, bags, and containers for these solvents without any further modification.