Premium
Poly( L ‐lactide). X. Enhanced surface hydrophilicity and chain‐scission mechanisms of poly( L ‐lactide) film in enzymatic, alkaline, and phosphate‐buffered solutions
Author(s) -
Tsuji Hideto,
Ishida Takuya
Publication year - 2002
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.11605
Subject(s) - autocatalysis , hydrolysis , chemistry , enzymatic hydrolysis , contact angle , alkaline hydrolysis , polymer chemistry , chemical engineering , organic chemistry , catalysis , engineering
Attempts were carried out to enhance the surface hydrophilicity of poly( L ‐lactide), that is, poly( L ‐lactic acid) (PLLA) film, utilizing enzymatic, alkaline, and autocatalytic hydrolyses in a proteinase K/Tris–HCL buffered solution system (37°C), in a 0.01 N NaOH solution (37°C), and in a phosphate‐buffered solution (100°C), respectively. Moreover, its chain‐scission mechanisms in these different media were studied. The advancing contact‐angle (θ a ) value of the amorphous‐made PLLA film decreased monotonically with the hydrolysis time from 100° to 75° and 80° without a significant molecular weight decrease, when enzymatic and alkaline hydrolyses were continued for 60 min and 8 h, respectively. In contrast, a negligible change in the θ a value was observed for the PLLA films even after the autocatalytic hydrolysis was continured for 16 h, when their bulk M n decreased from 1.2 × 10 5 to 2.2 × 10 4 g mol −1 or the number of hydrophilic terminal groups per unit weight increased from 1.7 × 10 −5 to 9.1 × 10 −5 mol g −1 . These findings, together with the result of gravimetry, revealed that the enzymatic and alkaline hydrolyses are powerful enough to enhance the practical surface hydrophilicity of the PLLA films because of their surface‐erosion mechanisms and that its practical surface hydrophilicity is controllable by varying the hydrolysis time. Moreover, autocatalytic hydrolysis is inappropriate to enhance the surface hydrophilicity, because of its bulk‐erosion mechanism. Alkaline hydrolysis is the best to enhance the hydrophilicity of the PLLA films without hydrolysis of the film cores, while the enzymatic hydrolysis is appropriate and inappropriate to enhance the surface hydrophilicity of bulky and thin PLLA materials, respectively, because a significant weight loss occurs before saturation of θ a value. The changes in the weight loss and θ a values during hydrolysis showed that exo chain scission as well as endo chain scission occurs in the presence of proteinase K, while in the alkaline and phosphate‐buffered solutions, hydrolysis proceeds via endo chain scission. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1628–1633, 2003