Browsing by Author "Karlssion, 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 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 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 Mechanical Properties of Thermally Exposed Coir Fibres(2009-12-18) Ndazi, Bwire S.; Ezekiel, N.; Nyahumwa, C.; Karlssion, S.Item 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.Item Properties of Rice Husk Particleboards Bonded by Tannin Based Resin(Uhandisi Journal, 2002) Ndazi, Bwire S.; Tesha, J. V.; Bisanda, Elias T. N.; Karlssion, S.