Obtaining micrometric-scale hollow fibers from wastes aged coir by oxidative chloro-sulfonation of lignin: HClO/H2SO4

Abstract

Coconut fiber is a lignocellulosic material extracted from the coconut mesocarp. Due to its mechanical properties, coconut fiber has been used as reinforcement in composite materials, which contrasts with a relatively small number of studies where coconut fiber is evaluated as a functional polymeric material. In this research, the extraction and transformation of aged coconut biofibers are proposed for their use as substrate/support into making of functional polymers, specifically for slow release of fertilizers. An interesting property of this material is its hollow-type morphology at micrometric scale. Thus, coconut biofibers (BFs) were mechanically extracted and delignified using mixed-oxidizing system constituted by NaClO and H2SO4 at different pH values (2.0 ≤ pH ≤ 12.0). BFs were thermal, spectroscopic and functionally characterized by different techniques, including infrared and ultraviolet-visible spectroscopies, thermogravimetric analysis, scanning electron microscopy, among others. The bleaching of the fibers and the removal of lignin were evidenced by microscopy. The best results of this stage were seen at pH 4.0, 7.0 and 8.0, being possible obtain different materials depending on three acidity regimens (2.0 ≤ pH ≤ 4.0, 4.0 < pH ≤ 8.0 and 8.0 < pH ≤ 12.0). In addition, delignification achieved is function on pH with a value close to 80 % according to the change of surface color intensity. It is concluded that coconut biofibers are natural structure which can be used as support for the making of functional materials.