Poly(L‐lactide). IX. Hydrolysis in acid media

Abstract

Amorphous and crystallized poly(l-lactide) (PLLA) films are prepared by quenching and annealing at 140°C for 600 min, respectively, from the melt. Their hydrolysis is investigated at pH 2.0 in HCl and dl-lactic acid (DLLA) solutions (37°C) for up to 300 days, and the results are compared with those obtained for PLLA films hydrolyzed at pH 7.4 (phosphate-buffered solution) and pH 12 (NaOH solution). The changes in the weight loss and molecular weight distribution of the PLLA films during hydrolysis in the acid media reveals that their hydrolysis proceeds homogeneously along the film cross section by mainly a bulk erosion mechanism. Moreover, the durability of PLLA films in the acid media is very similar to that in the neutral medium but higher than that in the alkaline medium. The hydrolysis rate constant values (k) of the initially amorphous PLLA0 film evaluated from the changes in the numberaverage molecular weight were 3.0 and 2.4 ϫ 10 Ϫ3 day Ϫ1 at pH 2.0 in the HCl and DLLA solutions, respectively. These k values are very similar to 2.6 ϫ 10 Ϫ3 day Ϫ1 at pH 7.4 in the phosphate-buffered solution. The similar k values and the negligible weight loss after the hydrolysis for 300 days reflect that the hydronium ions and the lactic acid oligomers and monomers have insignificant catalytic effects on the hydrolysis of the PLLA films. Increasing the initial crystallinity of the PLLA film increases the hydrolysis rate in the HCl solution, whereas increasing the initial crystallinity of the PLLA film does not alter the hydrolysis rate in the DLLA solution. The differential scanning calorimetry results show that the crystallization of PLLA chains occurs during the hydrolysis, irrespective of the hydrolysis acid media and the initial crystallinity.

Comparison of the degradability of poly(lactide) packages in composting and ambient exposure conditions

“…The temperature, relative humidity and pH to which the three packages were exposed during the composting conditions are shown in Figure 5a, b. pH is one of the most important factors of hydrolytic polymer degradation, since pH variations can change hydrolysis rates by a few orders of magnitude. [32][33][34][35] In this study, there was a slight alkalization of the pile after the second day of testing, although this difference was not statistically significant at the a = 0.05 level (p = 0.91) during the 30 days of composting.…”

Study of the degradation of a new PLA braided biomaterial in buffer phosphate saline, basic and acid media, intended for the regeneration of tendons and ligaments

“…As there were no changes in the sample weights, this suggests that the low molecular weight chains caused by the chain scission are either not water soluble or remain trapped inside the sample. Tsuji concluded that PLA degradation in basic medium is produced by superficial erosion accompanied by a considerable weight loss, while acid or PBS degradation are produced in bulk with very little weight loss [14,16,27].…”

“…[7]. Many studies have been carried out on its hydrolytic degradation in different media, including: a neutral solution of buffer phosphate (PBS) at 37 ºC or higher to accelerate degradation [8][9][10][11], an alkaline solution at different temperatures [11][12][13][14][15], an acid solution [16,17] and even studies on enzymatic degradation using enzymes as proteinase K [18,19].…”

Mechanical study of PLA–PCL fibers during in vitro degradation

“…The pH of the aqueous medium also affects the degradation reaction rates (Kirby, 1972). Tsuji et al studied the hydrolysis of PLLA films at 37 ºC in alkaline solution (pH 12) acid solution (pH 2.0) (Tsuji and Nakahara, 2001) and phosphate-buffered solutions (pH 7.4) (Tsuji and Ikada, 2000). In the present case, pH can be considered constant.…”