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

Abstract

The macromolecular structure of untreated and cold plasma-treated cellulosic kapok fiber was investigated by means of small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). Subsequently, the macromolecular structural transition of the fiber was correlated with the dielectric properties of their reinforced epoxy polymer composites. WAXD patterns of the fibers resemble the cellulose I𝛽 structure of the cellulose. The X-ray diffractogram of untreated and treated fiber samples shows typical cellulose I𝛽 peaks within the Bragg Diffraction angle 10° to 50° (2𝜃 16.68° (1-10/110), 22.42° (200) and 34.82° (004)). The crystallinity index (CI) and crystallite size (CS) are calculated using Segals and Scherrer’s formula respectively. The one-dimensional and three-dimensional correlation functions are calculated from background-corrected smeared-out SAXS intensities [1]. The SAXS profile of the fiber showed drastic change, with cold plasma treatment and the intensities at the tail region deviate from the porod’s law which conforms the non-ideal nature of the fiber, signifying the continuous variation of electron density at the phase boundary [2,3]. Further, the theories developed by Vonk and Ruland were used to estimate different macromolecular parameters such as transversal length in the matter region (𝑙1̅), transversal length in the void region (𝑙2̅), periodicity transverse to the layers (𝐷), the width of the transition layer (𝐸) by Ruland and Vonk method, specific inner surface area (𝑠/𝑣), matter phase volume fraction (ϕ1), void phase volume fraction (ϕ2), the volume fraction of transition layer (2𝐸𝑉𝐷) coherence length (𝑙𝐶), range of inhomogeneity (𝑙𝑟̅) and characteristic number (𝑙𝐶) from correlation functions, considering the fiber has a non-ideal two-phase structure [1-3]. A Fortran program developed by our research group is used to investigate the SAXS data and calculate different macromolecular parameters.