Effect of the Chemical Treatment on the Inorganic Content of Kenaf Fibers and on the Performance of Kenaf-Polypropylene Composites
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Composites consisting of natural fibers and a polymer-based matrix have received considerable attention as an alternative to traditional mineral fibers such as glass-fiber. Composites containing natural fibers have the benefit of being light-weight and environmentally friendly but fall short with their mechanical properties, moisture resistance and thermal resistance, limiting their use to non-structural applications and low moisture environments. The objective of this thesis was to evaluate kenaf fibers as an alternative natural fiber in the development of polypropylene composites. The chemical composition and inorganic content of kenaf fibers was quantified. The effect of alkalization of milled kenaf fiber (MKF) with sodium hydroxide on inorganic content was assessed. The effects of MKF alkalization and the addition of the coupling agent maleic anhydride were investigated. MKF was treated for two hours with aqueous sodium hydroxide (NaOH) at different concentrations (0%, 3%, and 6%) and two temperatures (room temperature and 80°C). The treated MKF was analyzed by optical microscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and chemical composition analysis to assess the effect of sodium hydroxide treatment. Optical microscopy showed the presence of thin protrusions with MKF treated with 3% and 6% NaOH at 80°C. SEM images showed a smoother fibrillar surface of MKF when treated with 3% and 6% NaOH at 80°C. TGA analysis indicated that the hemicellulose shoulder between 240°C and 325°C disappeared when treated with 3% and 6% NaOH at room temperature and 80°C indicating removal of hemicellulose. This was confirmed by chemical composition analysis which showed a decrease in hemicellulose mass fraction and an increase in cellulose mass fraction when MKF was treated with NaOH at 3% and 6% at room temperature and 80°C. The inorganic content for alkalized MKF was obtained with inductively coupled plasma optical emission spectroscopy (ICP) for 20 elements. Major elements (greater than 150 µg element/g fiber) were Fe, Ca, Na, Mg, K, Al, and B. Minor elements (less than 150 µg element/g fiber) were Ni, Mn, Ba, Zn, Pb, Sr, Cr, Y, Cu, Co, Cd, Li and V. Calcium had the greatest content (4503- 4982 µg element/g fiber). Analysis of variance (ANOVA) was used to determine the effects of NaOH treatment concentration and temperature on elemental concentration. Of the major elements, NaOH concentration had an effect on Fe, Ca, Na, K, Al and B while treatment temperature had an effect on Na, K and Al. The interaction between NaOH concentration and treatment temperature had an effect on all major elements. The inorganic elements analyzed by ICP accounted for 0.76-0.94 wt.% of kenaf depending on the alkali treatment conditions. Composites were prepared with MKF subjected to alkalization treatments and polypropylene (PP) using twin-screw extrusion and injection molding. Polypropylene grafted maleic anhydride (MAPP) was added to assess its effect on composite performance. MKF-PP composites were tested for tensile strength (28.9-30.3 MPa), elongation at break (5.1-6.0%), and Young’s Modulus (665.5-710.9 MPa). Tensile tests showed 3% and 6% NaOH treatment at room temperature and 80°C of MKF did not affect the mechanical performance (tensile strength, elongation at break, and Young’s modulus) of the composite. Addition of MAPP to composites, with and without NaOH treatment, improved the tensile strength (31.6-35.0 MPa) of the composite. SEM showed that composites without MAPP had poor fiber wetting and showed fiber pull out in the fractured composite cross-sections. SEM of MKF-PP composites with MAPP showed a polymer coating on the surface of MKF. Energy dispersive x-ray spectroscopy (EDX) analysis of composites showed carbon and oxygen on all composites. Room temperature treated MKF composites showed higher oxygen concentrations in samples without MAPP. 80°C treated MKF composites showed lower oxygen concentrations in samples without MAPP. Future work should consider the effects of NaOH treatments at higher concentrations and temperature and their effects on cellulose, hemicellulose, lignin, and inorganic content. It would also be interesting to see if adding inorganic content to kenaf fiber alters its performance in polypropylene based composites.
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Nikole Lyn (2018). Effect of the Chemical Treatment on the Inorganic Content of Kenaf Fibers and on the Performance of Kenaf-Polypropylene Composites. UWSpace. http://hdl.handle.net/10012/13979