The Macromolecular Transition of Kapok Fiber by RF Plasma Treatment Investigated by SAXS/WAXD Studies and Their Correlation With Electrical Properties of the Fiber-Reinforced Composites

Abstract

The macromolecular structure of untreated and RF plasma-treated kapok fiber (KF) was investigated employing small-angle x-ray scattering (SAXS) and wide-angle x-ray diffraction (WAXD). Subsequently, the macromolecular structural transition of the KF was correlated with the dielectric properties of their reinforced epoxy polymer composites. WAXD patterns of the KF resemble the Iβ structure of the cellulose. The crystallinity index (CI) and crystallite size (CS) values of KF are found to increase from 48.8% and 3.0 nm to 55.6% and 3.6 nm, respectively, after plasma treatment on KF at a power of 30 W for 30 min. The one-dimensional and three-dimensional correlation functions are calculated from background-corrected smeared-out SAXS intensity data. The theories developed by Vonk and Ruland were used to estimate different macromolecular parameters from correlation functions, considering the KF has a non-ideal two-phase structure. The maximum value of CI, CS and the minimum value of transversal length in the void phase ($\overline{l_2}$) and volume fraction of void phase (${\varphi }_2$) are obtained for KF treated with RF plasma at a power of 30 W for 30 min. Consequently, reinforced composites exhibit low dielectric constant (12) and low dielectric loss (0.5), enhancing their suitability for use in printed circuit boards.