Browsing by Author "Ndazi, Bwire S."
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Item Characterization of Hydrolytic Degradation of Polylactic acid/Rice Hulls Composites in Water at Different Temperatures(Express Polym Lett, 2011) Ndazi, Bwire S.; Karlssion, S.. Hydrolytic degradations of polylactic acid/rice hulls (PLA/RH) composites with various rice hulls contents due to water absorptions at 23, 51 and 69°C were investigated by studying the thermal properties, chemical composition, molecular weight, and morphology of the degraded products. The results have attested that the stability of PLA/RH composites in water depends slightly on rice hulls contents but it is significantly influenced by water temperature. Water absorption in 30 days at 23°C was between 0.87 and 9.25% depending on rice hull contents. However, at thermophilic temperatures, the water absorption and degradation of these products were increased significantly. Saturations were achieved in less than 25 and 9 days at 51°C and 69°C, respectively, while hydrolytic degradation was demonstrated by an increase in fragility and development of crystallinity. At 69°C, there were significant reductions of the decomposition and glass transition temperatures of the polymer by 13°C. These changes were associated with the reduction of the molecular weight of PLA from 153.1 kDa to !10.7 kDa due to hydrolysis of its ester group.Item Characterization of the Potential of Soda Cooking to Extract Fibrous Residues from Rice Hulls(. Polymers from Renewable Resources, 2010) Ndazi, Bwire S.; Karlssion, S.In this paper, the potential of soda cooking to extract fibrous residues from rice hulls was investigated. Soda cooking was carried out at 170°C for 60 minutes using 5 to 13% NaOH. The goal was to selectively degrade silica and lignin from the structure of the rice hulls and produce fibrous carbohydrates that could be used as fillers in polymer biocomposites. This was studied by characterizing the physical and chemical properties of the fibrous residues and the spent liquor products. Results of scanning electron microscopy have revealed a substantial fragmentation of rice hulls above 7.5% NaOH charge. The fragmentation was accompanied with a significant removal of silica and lignin and the reduction of fibrous residues yield to 57% at 13%NaOH. Wet chemical composition analyses, infrared spectroscopy and x-ray spectroscopy have also revealed that lignin and silica were partly retained in the fibrous residue while the carbohydrates content were not affected. It is therefore concluded that soda cooking could be among the best processes for dissolving lignin and silica from rice hulls if the cooking conditions are optimized.Item Chemical and Physical Modifications of Rice Husks for Use as Composite Panels(Composite, 2007) Ndazi, Bwire S.; Karlssion, S.; Tesha, J. V.; Nyahumwa, C. W.Modifications of rice husks surfaces by steam and sodium hydroxide (NaOH) were carried out in order to study the effects of these on the surface functional groups properties and performances of the composite panels bonded with phenol formaldehyde (PF) resin. Comparison was made between untreated and ground rice husks. The removal of carbonyl and silica groups as observed by ATR-FTIR improved the rice husk-resin interfacial bonding as revealed by an increase in the modulus of elasticity to 2.76 ± 0.28 GPa, which is above the minimum value of 2.1 GPa recommended in EN 312-3 standard. On the other hand, steam treatment did not lead to any change in the outer surface chemical functional groups. Still, an increase in the mechanical properties of the composite with increase in steam temperature was observed. This showed that other mechanisms than changes in the surface chemical groups led to improved mechanical properties. TGA thermographs of unmodified and NaOH treated rice husks indicated that untreated rice husks exhibited higher thermal stability compared to rice husks treated with NaOH. The decrease in thermal stability of NaOH treated rice husks is an indication of possible degradation of rice husks by the concentrated NaOH used. This study has shown that the use of complementary testing techniques provides useful structure–property relationship in the understanding of the performance of materials.Item . Chemical and Thermal Stability of Rice Husks against Alkali Treatment(Bioresources, 2008) Ndazi, Bwire S.; Tesha, J. V.; Nyahumwa, C. W.Item Compressibility and Stress Relaxation Characteristics of Rice Husks(University of Witwatersrand, 2003-12) Ndazi, Bwire S.; Nyahumwa, C.; Tesha, J. VItem Effect of Rice Husks Modifications on Water Absorption Resistance of Rice Husk Based Panels(2006-10) Ndazi, Bwire S.; Tesha, J. V; Nyahumwa, C.; Karlssion, SItem Effect of Temperature and Durations of Heating on Coir Fibers(Industrial Crops and Products, 2011) Ezekiel, N.; Ndazi, Bwire S.; Nyahumwa, C.; Karlsson, S.Biocomposites derived from polymeric resin and lignocellulosic fibers may be processed at temperatures ranging from 100 ◦C to 230 ◦C for durations of up to 30 min. These processing parameters normally lead to the degradation of the fiber’s mechanical properties such as Young’s modulus (E), ultimate tensile strength (UTS) and percentage elongation at break (%EB). In this study, the effect of processing temperature and duration of heating on the mechanical properties of coir fibers were examined by heating the fibers in an oven at 150 ◦C and 200 ◦C for 10, 20 and 30 min to simulate processing conditions. Degradation of mechanical properties was evaluated based on the tensile properties. It was observed that the UTS and %EB of heat treated fibers decreased by 1.17–44.00% and 15.28–81.93%, respectively, compared to untreated fibers. However, the stiffness or E of the fibers increased by 6.3–25.0%. Infra red spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were used to elucidate further the influence of chemical, thermal and microstructural degradation on the resulting tensile properties of the fibers. The main chemical changes observed at 2922, 2851, 1733, 1651, 1460, 1421 and1370 cm−1 absorption bands were attributed to oxidation, dehydration and depolymerization as well as volatization of the fiber components. These phenomena were also attributed to in the TGA, and in addition the TGA showed increased thermal stability of the heat treated coir fibers with reference to the untreated counterparts which was most probably due to increased recrystallization and cross linking. The microstructural features including microcracks, micropores, collapsed microfibrils and sort of cooled molten liquid observed on the surface of heat treated coir fibers from the scanning electron microscope (SEM) could not directly be linked to the effect of temperature and durations of heating although such features may have largely account for the lower tensile properties of heat treated coir fibers with reference to untreated ones.Item Effectiveness of Steam and Alkali Treatments of Rice Husks on the Mechanical Properties of Particleboards(2005-10) Ndazi, Bwire S.; Nyahumwa, C.; Tesha, J. V; Karlssion, S.Item Effects of Pressing Parameters on the Flexural Properties of Tannin-Formaldehyde Bonded Rice Husks Particleboards(ECOWOOD, 2008) Ndazi, Bwire S.Item Effects of Sawdust Additives on the Properties of Natural Adhesive Bonded Rice Husk Boards(2000-09) Ndazi, Bwire S.; Tesha, J. V; Bisanda, Elias T. N.Item Effects of steam curing and alkali treatment on properties on properties of rice husks(Pontifical University of Catholic, 2005) Ndazi, Bwire S.; Nyahumwa, C.; Tesha, J.; Karlssion, S.Item Evaluation of Physical and Mechanical Properties of Polylactide/Rice Hull Filled Composite Plates(RAPRA JOURNALS, 2012) Ndazi, Bwire S.The influences of rice hull modification and content on the physical and mechanical properties of the polylactide (PLA) composite plates have been investigated in this paper. The rice hull was prepared by soda cooking at 170°C for 60 min and by crushing with a hammer miller. The mixture of the PLA and the rice hull was compounded in the extruder in the presence of fixed amounts of maleic anhydride and dicumyl peroxide. This was followed by compression moulding of the mixture under vacuum for 5 minutes in the Fortune Press to produce approximately 2 mm thick composite plates. The composite plates produced were subjected to flexural and tensile tests using the Instron while the morphology of the fractured surfaces was investigated by scanning electron microscopy. The results revealed that crushed and soda cooked rice hulls both acted predominantly as rigid fillers in the PLA matrix. Their presence did not impart any improvement of the strength of the composite plates. However, the tensile and flexural moduli of the composite plates were found to improve up to 0.46 and 1.1 GPa, respectively, due to addition of the rice hull fillers. The composite plates made of the rice hull pulps generally exhibited higher flexural properties than those produced from ground rice hulls as demonstrated by statistical analysis. This was due to enhancement of chemical interaction between the chemically modified rice hulls and the PLA matrix as also revealed on the nature of the fractured surfaces by SEM. The tendency of the composite plates to exhibit brittle failures was demonstrated by abrupt tensile fractures at lower strainsItem Evaluation of the Performance of Rice Husk Panel boards Bonded with a Tannin- Cashew Nut Shell Liquid Resin(2001-10) Ndazi, Bwire S.; Bisanda, Elias T. N.; Tesha, J. VItem Hydrolytic and Soil Degradability of Green Composites Derived from Polylactide and Rice Hull Fillers(Eldoret Polytechnic, 2012-05-18) Ndazi, Bwire S.Item Mechanical Properties of Thermally Exposed Coir Fibres(2009-12-18) Ndazi, Bwire S.; Ezekiel, N.; Nyahumwa, C.; Karlssion, S.Item Optimization of the Pressing Conditions for Manufacture of Rice Husks-TF and PF-Bonded Particleboards(2007) Ndazi, Bwire S.; Tesha, J.; Nyahumwa, C.Item Oxidative Polymerization of Cashew nut Shell Liquid by Side Chain Cleavage(University of Witwatersrand, 2003-12) Tesha, J. V; Machibya, S.; Ndazi, Bwire S.; Lugoye, M. N.; Nyahumwa, C. WItem Production of rice husk composites from tannin based resin(2002) Ndazi, Bwire S.; Tesha, J. V; Bisanda, Elias T. N.; Karlssion, S.Item Production of Rice Husks Composites with Acacia Mimosa Based Tannin Resin(Journal of Materials Science, 2006) Ndazi, Bwire S.; Tesha, J. V.; Karlssion, S.; Bisanda, Elias T. N.Rice husks are amongst the typical agricultural residues, which are easily available in huge amounts. They have been considered as raw material for composites panels’ production. However, the major hindrance in rice husks utilization for composite manufacture lies in the lack of direct interaction with most adhesive binders to form the anticipated interfacial bonds. Rice husks are highly siliceous and have poor resistance to alkaline and acidic conditions. Manufacture of rice husks composites panels having good interface bond is difficult and largely dependent on a proper understanding of the interaction between the husks and the binder. This paper presents and discusses results on the production of composites boards from a mixture of rice husks and wattle (Acacia mimosa) tannin based resin. The experimental results have shown that the ‘as received rice husks’ when blended with alkali-catalyzed tannin resin do not result in optimum composite panel properties. However, it was found that a slight physical modification of the rice husk particles by hammer-milling resulted in drastic improvements in the interfacial bond strength and stiffness of the composites panels from 0.041 MPa to 0.200 MPa and 1039 MPa to 1527 MPa, respectively.Item Properties and Performance of Treated Rice Husks in the Composite Panel(University of Dar es Salaam, 2014-07) Ndazi, Bwire S.; Nyahumwa, C.; Tesha, J. V; Karlssion, S.