Study of Water Absorption by Polyamide Composites Filled with Lignin-Derived Graphite Materials.

Polyamides are widely used as matrix polymers of composite and structural materials in many industrial technologies. One of the features of polyamide polymers is their noticeable ability to absorb water from the environment in a liquid or gaseous state. The results of the study of the kinetics of water absorption of composites with a polyamide matrix filled with products of thermal modification of hydrolytic lignin in the temperature range of 273–313 K are reported. Graphite from hydrolytic lignin, graphite bisulfate, and thermally expanded graphite, were examined as composite fillers. The plasticizer was vaseline oil. The maximum water absorption after 650 h exposure was 1.1 and 2.2 wt % of water at temperatures of 293 and 313 K, respectively, for the composite filled with lignin-derived graphite with 9% oil. The minimum values ​?of water absorption constants were determined for a composite filled with thermally expanded graphite from lignin with 20% oil. The use of thermally expanded graphite as a filler makes it possible to significantly increase the oil content in the blend, since its oil absorption is significantly higher compared to that of other graphite materials. The rate constants of water absorption were calculated and equations that describe this process for the studied composites were derived. It has been proven that the ability of polyamides to absorb water significantly decreases with an increase in the oil plasticizer content therein, i.e., oil blocks the polar CONH groups of polyamide macromolecules, which reduces the probability ​of water absorption constants were determined for a composite filled with thermally expanded graphite from lignin with 20% oil. The use of thermally expanded graphite as a filler makes it possible to significantly increase the oil content in the blend, since its oil absorption is significantly higher compared to that of other graphite materials. The rate constants of water absorption were calculated and equations that describe this process for the studied composites were derived. It has been proven that the ability of polyamides to absorb water significantly decreases with an increase in the oil plasticizer content therein, i.e., oil blocks the polar CONH groups of polyamide macromolecules, which reduces the probability of hydrogen bond formation in the structure of polyamide composites. [ABSTRACT FROM AUTHOR]