Properties and morphology of poly(L-lactide). II. hydrolysis in alkaline solution

Abstract

Hydrolysis of poly(L‐lactide) (PLLA) films in 0.01N NaOH at 37°C was investigated by gel permeation chromatography, differential scanning calorimetry, scanning electron microscopy, and polarizing optical microscopy. The change in molecular weight distribution and surface morphology of PLLA films during hydrolysis revealed that PLLA film hydrolysis in dilute alkaline solution proceeded mainly via the surface erosion mechanism. An insignificant dependence of the rate of weight loss per unit surface area on the PLLA film thickness also supported this conclusion. Etching of the outside of PLLA spherulites resulted in preferred hydrolysis of PLLA chains in the amorphous region. The disorientation of lamella and inhomogeneous erosion in the spherulites implied that hydrolysis of PLLA chains occurred predominantly in the amorphous region between the crystalline regions in the spherulites. The rate of weight loss per unit surface area decreased linearly with the increase in the initial crystallinity of PLLA film, while the radius of spherulites had practically no significant effect on the hydrolysis of PLLA film. The specific low molecular weight of PLLA chains produced by hydrolysis increased with the rise in annealing temperature of the PLLA film, suggesting that the PLLA chains released were the component of one fold in the crystalline region. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 59–66, 1998

Alkali Etching of a Poly(lactide) Fiber

“…It is seen that the observed radii follow eq closely, which is consistent with the premise that the hydrolysis reaction occurs on the fiber surface, even when the weight loss is high (∼80%). This agrees with findings for the alkaline hydrolysis of PLLA films, which also follows a surface erosion mechanism .…”

Physical properties and enzymatic hydrolysis of poly(L‐lactide)–TiO2 composites

“…On the other hand, almost the same weight losses were observed for the films of both thicknesses when assessed based on the unit surface area. These results reveal that these films have been enzymatically hydrolyzed via a surface erosion mechanism in agreement with reported results,16 although two modes of bulk erosion and surface erosion have been proposed as a general hydrolysis mechanism of PLLA 27–31…”

Improving the Hydrolysis Resistance of Poly(lactic acid) Fiber by Hydrophobic Finishing

“…This occurs because hydrolysis of the PLA proceeds much more easily from the structurally loose regions than from the ordered crystalline domains. The degradation of the former part of the polymer results in a larger percentage of the crystalline phase which would be verified by the increase in crystallinity frequently observed. ,,− In our case, this phenomenon was also observed although degradation of the imperfect crystals occurs. The crystallinity of nonfinished sample had increased significantly from 15.8% to 12.8% over the hydrolysis period, while that of the finished samples had remained almost unchanged.…”