Degradation of poly(lactic acid) powder and microparticles.

Two samples of poly(lactic acid) (PLA) with distinct molar masses were evaluated regarding thermal stability, glass transition temperature, morphology and mass loss, due to exposure to three media normally found in the petroleum industry: neutral (distilled water), saline (brine) and organic (toluene). PLA microparticles were produced using the emulsion/solvent evaporation technique. The system had an organic phase (based on PLA) and an aqueous phase (based on polyvinyl alcohol), with variation not only of the polymer's molar mass, but also the emulsifier's concentration. The greatest mass loss percentage in function of time was observed in the organic medium (65 %), followed by the neutral (35 %) and saline medium (20 %). The morphological analysis revealed that only the samples exposed to the neutral and saline media showed signs of erosion, while the sample exposed to the organic medium swelled. This was related to the fact that organic media act only to dissolve the material, while aqueous media degrade the chains, reducing the molar mass by up to 50 %. The morphology, size and size distribution of the microparticles with low molar mass were found to be more susceptible to the preparation method than those with high molar mass. Therefore, these microparticles have potential for use in controlled release of chemical additives in the oil industry, and the timing of this release can be controlled by varying the molar mass of the polymer and/or the conditions for preparing the microparticles. [ABSTRACT FROM AUTHOR]