Chemistry, Physics and Technology of Surface

ISSN 2518-1238 (Online), ISSN 2079-1704 (Print)

Polylactic acid is a biodegradable material, for which the optimal condition for biodegradation is decomposition of the material into water and carbon dioxide. Since the initial stage of biodegradation is the saturation of the polymer with water, it is of considerable interest to study the water absorption of PLA and the effect on it of the presence of a limited amount of substances capable of being absorbed by the polymer. The state of water in polylactic acid in the presence of deuterochloroform and of a 6: 1 mixture of CDCl₃ with trifluoroacetic acid was studied by low-temperature ¹H NMR spectroscopy It is shown that the samples of polylactic acid absorb no more than 1 % of water during the first hour and 10 % of the mass for the next seven days of saturation with water. When a sample of polylactic acid is held in an aqueous medium for a week, the shape of the spectra changes, so indicating changes occurring in the polymer matrix. On the basis of changes in the spectra of absorbed water, it can be concluded that initially, water is absorbed in the form of polyassociates, and with time, due to the diffusion process, is localized near the electron-donating centers of the polymer (carbonyl and ether groups) with which it forms hydrogen-bound complexes. These complexes are characterized by lower values of the chemical shift. When a trifluoroacetic acid is introduced into the system, water-acid clusters with a different acid content form in the polymer matrix. This is manifested spectrally in the appearance of several signals in the region d_H = 6–9 ppm, differing in magnitude of the chemical shift. Clusters with a higher concentration of acid correspond to larger values of the chemical shift.

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