Synthesis and properties of molded polyurethane foam from liquefied kenaf for the application of slow-release fertilizer

Abstract

The use of polyol from non-renewable resources in the production of polyurethane foams (PUFs) has given an impact to the environment due to their high toxicity which is hazardous and non-biodegradable. Thus, renewable bio-based polyols can be made by using liquefaction process to convert lignocellulosic biomass into high value-added products. In this research, lignocellulosic biomass like kenaf was used to study the liquefaction process. The liquefying solvent that was the combination of polyethylene glycol/glycerol (PEG/Gly, 4:1) was used to liquefy kenaf at the designated parameters of temperature, time and ratio of catalyst composition. The best kenaf polyol was used to produce rigid PUFs with the modified EFB fiber as reinforcement and further used as the slow-release fertilizer (SRF) medium. The aims in this study were, (i) to evaluate the effects of liquefaction temperature (130, 145 and 160 °C), time (60, 90 and 120 min) and ratio of catalyst composition (sulphuric acid: lactic acid, w/w, 3:0, 3:1, 3:2 and 3:3) on the liquefaction yields and residues of kenaf, (ii) to determine the effects of liquefaction temperature, time and ratio of catalyst composition on the physical and chemical properties of kenaf poyol produced from liquefaction of kenaf, (iii) to determine the physical, chemical, and mechanical properties of rigid polyurethane foams derived from kenaf with (KPFs-EFB) or without the modified filler from EFB fiber (KPFs) at different isocyanate (NCO) indexes and (iv) to evaluate the released of different percentage (10, 20 and 30 wt%) of urea fertilizer incorporated in KPFs-EFB in the water. The percentage of yield product was represented as the percentage of residues (%). Liquefied kenaf at 160 °C for 90 min obtained the lowest amount of residue (10.1%) with hybridized ratio of catalyst composition, 3:1 (sulphuric acid: lactic acid). The hybridization of sulphuric acid and lactic acid greatly reduced the kenaf residue and produce kenaf polyol with the best value of OH number (335.6 mg KOH/g) and acid number (7.1 mg KOH/g). The best kenaf polyol was used to fabricate the rigid PUFs called KPFs and KPFs-EFB in this research with the variation of NCO indexes (100, 110, 120, 130 and 140). The increased of NCO indexes was observed according to their physical, chemical and mechanical properties of KPFs and KPFs-EFB. KPFs-120 with the larger cell diameter gave low apparent density (68.16 kg/m3), good compressive strength (170 kPa) and high water absorption ability. Besides, the apparent density and compressive strength of KPFs-EFB increased as the NCO index increased. The cellular morphology of KPFs-EFB started to decrease at KPFs-EFB-130 which resulted in the cell disruption of KPFs-EFB-140. However, both KPFs and KPFs-EFB shows excellent biodegradation rate and thermal stability properties when increase in NCO index. The incorporation of urea fertilizer during foaming process of KPFs-EFB for SRF application gave a significant effect on the physical and chemical properties. The presence of modified EFB fiber in KPE-EFBs enhance the strength and helped to delay the fertilizer release. KPFs-EFB-120 with the highest urea fertilizer percentage (KPFs-EFB-120/30) have high crosslinking density, low swelling degree, lowest water absorption ability and capable to hold the fertilizer longer compared to the other samples. The EDX mapping of nitrogen confirmed the sample still hold the fertilizer with 14.6% even after 24 h released. The closed cell structure of KPFs-EFB-120/30 minimize the immediate release of fertilizer and avoid the environmental issues to occur.