Regenerated amorphous cellulose from pineapple leaf fibers via sulfuric acid treatment

Abstract

Pineapple leaf fiber (PALF) is an agricultural residue available abundantly in Thailand as a renewable resource with high cellulose content. In this research, a simple process using sulfuric acid (H2SO4) treatment has been developed to produce three types of cellulosic products from PALF, which are regenerated amorphous (RAC), microcrystalline (MCC), and nanocrystalline (NCC) cellulose. H2SO4 acid treatment has been done in 25% and 50% (v/v) H2SO4 under three different temperatures (-20, 30, and 50 ºC). In 25% (v/v) H2SO4, various MCC lengths (about 29.57 ± 9.99 to 106.40 ± 61.10 μm) were produced from different temperatures. Different temperatures in this condition gave the ability to control the MCC size without changing the chemical structure, confirmed by OM images and FT-IR spectra. Compared to the commercial MCC, Avicel PH101, MCC PALF obtained in this work offers definite advantages over Avicel PH101 regarding aspect ratio and uniformity. MCC PALF can be a potential alternative to produce a commercial MCC. In 50% (v/v) H2SO4, three kinds of cellulosic products were obtained and could be differentiated using OM, cross-polarizer, FT-IR, and XRD characterizations. RAC was obtained at -20 ºC, confirmed from the gel-like shape morphology, no birefringence shown, the crystalline band's disappearance at 1425 cm-1 and increment of the amorphous band at 897 cm-1 on FT-IR spectrum, and XRD patterns of amorphous cellulose with small peaks corresponding to cellulose II. MCC was obtained at 30 ºC, showing a short fiber morphology in OM image with length and width at 37.63 ± 14.19 and 3.85 ± 0.66 μm, respectively. NCC was obtained at 50 ºC, showing flow birefringence phenomena, confirmed by cross-polarizer. Producing RAC and NCC required adequate acid concentration and temperature treatment. By adjusting the temperature in an appropriate concentration, different products could be obtained.