Effect of coconut fibers chemically modified with alkoxysilanes on the crystallization, thermal, and dynamic mechanical properties of poly(lactic acid) composites

Currently, the use of composites, based on natural fibers and polymeric matrix, in diverse industrial sectors is gaining interest. The interaction between fibers and polymeric matrix is essential to have a composite with the desired thermal and mechanical properties. Nevertheless, most of the natural fibers do not have a good interaction with polymers and they need to be modified to enhance such interaction. Therefore, in this work, the chemical modification of coconut fibers, using different silanes agents like glycydoxipropyl trimetoxi slane (GLYMO), vinyl trimetoxi silane (VTMS), and tetraetoxi silane (TEOS) was carried out to promote the interfacial interaction with the polymeric matrix of poly (lactic acid) (PLA). The FTIR spectra confirmed the silanization of the fibers by detecting the bands related to Si-O-Si, at 1133 y 1106 cm(-1), and Si-O-Cellulose bonds, at 1165 y 955 cm(-1), as the product of the silanols reactions. The thermal stability was determined by thermal thermogravimetric analysis, which shows that the chemical modification of fibers increased their thermal stability regarding the fibers non-modified. On the other hand, the DSC showed that interfacial interactions between the fiber and PLA chains increased when the fiber was previously silanized because the silanes promoted the crystallinity of PLA from 48.95 to 60.08% with GLYMO, to 63.94 with VTMS and to 63.35 with TEOS. Regarding the crystallization study, the composites with VTMS presented higher activation energy at the beginning, but as the relative crystallinity increased, the polymer chains' arrangement was facilitated, considerably increasing the elastic modulus of PLA by 325%. The increase in crystallinity due to the incorporation of the silanized fibers shifted the maximum Tan delta value toward lower temperatures, increasing the application window of the polymer.

Automated summary

Interest in the use of composites based on natural fibers and polymeric matrix is growing in diverse industrial sectors. Chemical modification of coconut fibers using different silanes agents was carried out to enhance the interaction with poly (lactic acid) (PLA). The results showed that silanization of the fibers improved their thermal stability and increased the interfacial interactions with PLA chains, leading to higher crystallinity and elastic modulus of PLA composites. The incorporation of silanized fibers also expanded the application window of the polymer.