Pineapple leaf fiber extraction and its application as kraft paper

Abstract

Cultivation of pineapple in Malaysia produces wastes such as leaf and crown where these wastes are discarded or left in the field. A systematic pineapple leaf fiber (PALF) extraction method was designed to maximally utilized this waste and make pineapple plantation more sustainable. Therefore, these four-parts of studies were conducted in order to develop an effective fiber extraction method. In Part 1 (method selection), PALF from Josapine cultivar was successfully extracted via manual retting (combing), water retting, chemical extraction or mechanical-chemical extraction methods. The mechanical-chemical method was found to be the best method to produce the whitish pulp while larger yield (4.0 wt%) of fine and clean fibrils of PALF was obtained using 3 wt% of sodium hydroxide (NaOH). In Part 2, (extraction parameter), the PALF extraction was done by cooking the PALF in NaOH at 1 wt% to 11 wt% NaOH concentrations for 30 to 180 minutes. Scanning electron microscopy images showed that the structure of fibre was starting to deteriorate when the concentration of NaOH was more than 10 wt%. Thermogravimetric analysis revealed that at the concentration of less than 3 wt% NaOH was insufficient to remove the hemicellulose layer from the fiber. It was also found that the amount of lignin removal was constant at 7 wt% NaOH onwards, as revealed by the value of Kappa number. Fourier transform infrared spectroscopy shows that at 3 wt% NaOH was sufficient to remove the hemicellulose and lignin from the PALF. In conclusion, 3 wt% NaOH concentration, 90 minutes of cooking time at 90 °C were identified as the optimum parameter to be used in the delignification process. Further discovery revealed that the NaOH solution can be reused one time only for the extraction process without significantly affected the extracted PALF’s properties. In Part 3 (kraft paper production), kraft papers produced using the PALF extracted at different NaOH concentrations (1, 3, 5, 7, 9, and 11 wt%) and NaOH solution recycle were characterized in terms of tensile strength, tear strength and water absorption properties. It was found that the average tearing force of the kraft paper reached its maximum (216604.8 mN) at the NaOH concentration of 9 wt% while the tensile strength was at its maximum (13 MPa) at 3 wt% NaOH. It was also observed that by recycling 3 wt% NaOH solution led to the reduction of PALF paper tensile strength from 12.6 MPa (fresh NaOH) to 11 MPa (1st recycle) and 6.5 MPa (2nd recycle). At 3 wt% NaOH concentration and only one time of NaOH recycling were good processing parameters for obtaining PALF kraft papers with balance properties. In Part 4, the kraft paper prepared at the selective parameter (3 wt% NaOH, 90 minutes cooking time at 90 °C) was used as a reinforcing layer in the epoxy resin. The kraft paper/epoxy composites were prepared at different number of layers i.e. 1, 2 and 3 layers. The properties of the composites were measured via tensile test and Izod impact test. Results showed that the insertion of the papers' layers made of NaOH extraction into the epoxy resin had reduced the density and the tensile properties of the composites. However, the impact properties of the composites improved corresponding to the fiber pull out as a result of weak fiber-matrix bonding. In contrast, the composite that used the papers made of manual retted PALF have weak impact strength due to the stronger fiber-matrix adhesion.