Bwire Ndazi | University of Dar es Salaam (original) (raw)
Papers by Bwire Ndazi
Chemical and thermal stability of rice husks against alkali treatment with 2 to 8% w/v NaOH are p... more Chemical and thermal stability of rice husks against alkali treatment with 2 to 8% w/v NaOH are presented and discussed in this paper. The thermal stability of the rice husks was examined by using a thermal gravimetric analysis instrument. Chemical stability was evaluated by examining the organic components of rice husks using proximate analysis. The results indicated that the proportion of lignin and hemicellulose in rice husks treated with NaOH ranging from 4 to 8% decreased significantly by 96% and 74%, respectively. The thermal stability and final degradation temperatures of the alkali-treated rice husks were also lowered by 24-26°C due to degradation of hemicellulose and lignin during alkali treatment. Absence of the onset degradation zones in the alkali-treated rice husks was a further indication that hemicellulose and other volatile substances degraded during alkali treatment. This leads to a conclusion that alkali treatment of rice husks with more than 4% NaOH causes a substantial chemical degradation of rice husks, which subsequently decreases their thermal stability.
Industrial Crops and Products, 2011
Biocomposites derived from polymeric resin and lignocellulosic fibers may be processed at tempera... more 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.▶ Tensile strength and percentage elongation at break decrease as temperature and durations increase. ▶ The effect of the increase of temperature at the same duration of heating is probably the same to the effect of increasing the durations of heating at the same temperature, provided that the temperature is above the critical temperature for the beginning of thermal degradation of lignocellulosic fibers. ▶ Stiffness is less affected by temperature compared to tensile strength and percentage elongation at break. ▶ By exposing lignocellulosic fibers such as coir fibers to temperatures near 150 °C for durations not above 20 min that could probably be less detrimental to the mechanical properties of the fibers.
Journal of Materials Science, 2006
Rice husks are amongst the typical agricultural residues, which are easily available in huge amou... more 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.
Journal of Materials Science, 2006
Plant-based composites (bio-composites) may in the future, become materials to replace polymer ba... more Plant-based composites (bio-composites) may in the future, become materials to replace polymer based composites and wood in terms of their attractive specific properties, lower cost, simple processing technologies, eco-friendliness, and ability to be recycled after use. The quality and performance of plant fibre-based composites can further be improved by adopting appropriate engineering techniques. Although plant-based fibres have these advantages, they also have some limitations. One of the serious problems of plant fibres is their strong polar character, which creates many problems of incompatibility with most thermosetting and thermoplastic matrices. Production of bio-composites with high quality and performance is therefore based on adjusting the properties of the constituents to meet the requirements of the composite material i.e. a product with consistent, uniform, predictable, and reproducible properties. Such adjustments involve creating strong interfacial bonds between the lignocellulosic substrates and the binder. Successful development of bio-composites therefore stem from a careful understanding of the influence of these adjustments on the composite properties. This paper suggests some opportunities available in producing bio-composites from non-wood resources, and the challenges that must be overcome to make this technology commercially viable. Gaps in knowledge and information required before full commercialisation of these materials are identified.
Composites Part A-applied Science and Manufacturing, 2007
Modifications of rice husks surfaces by steam and sodium hydroxide (NaOH) were carried out in ord... more 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.
Chemical and thermal stability of rice husks against alkali treatment with 2 to 8% w/v NaOH are p... more Chemical and thermal stability of rice husks against alkali treatment with 2 to 8% w/v NaOH are presented and discussed in this paper. The thermal stability of the rice husks was examined by using a thermal gravimetric analysis instrument. Chemical stability was evaluated by examining the organic components of rice husks using proximate analysis. The results indicated that the proportion of lignin and hemicellulose in rice husks treated with NaOH ranging from 4 to 8% decreased significantly by 96% and 74%, respectively. The thermal stability and final degradation temperatures of the alkali-treated rice husks were also lowered by 24-26°C due to degradation of hemicellulose and lignin during alkali treatment. Absence of the onset degradation zones in the alkali-treated rice husks was a further indication that hemicellulose and other volatile substances degraded during alkali treatment. This leads to a conclusion that alkali treatment of rice husks with more than 4% NaOH causes a substantial chemical degradation of rice husks, which subsequently decreases their thermal stability.
Industrial Crops and Products, 2011
Biocomposites derived from polymeric resin and lignocellulosic fibers may be processed at tempera... more 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.▶ Tensile strength and percentage elongation at break decrease as temperature and durations increase. ▶ The effect of the increase of temperature at the same duration of heating is probably the same to the effect of increasing the durations of heating at the same temperature, provided that the temperature is above the critical temperature for the beginning of thermal degradation of lignocellulosic fibers. ▶ Stiffness is less affected by temperature compared to tensile strength and percentage elongation at break. ▶ By exposing lignocellulosic fibers such as coir fibers to temperatures near 150 °C for durations not above 20 min that could probably be less detrimental to the mechanical properties of the fibers.
Journal of Materials Science, 2006
Rice husks are amongst the typical agricultural residues, which are easily available in huge amou... more 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.
Journal of Materials Science, 2006
Plant-based composites (bio-composites) may in the future, become materials to replace polymer ba... more Plant-based composites (bio-composites) may in the future, become materials to replace polymer based composites and wood in terms of their attractive specific properties, lower cost, simple processing technologies, eco-friendliness, and ability to be recycled after use. The quality and performance of plant fibre-based composites can further be improved by adopting appropriate engineering techniques. Although plant-based fibres have these advantages, they also have some limitations. One of the serious problems of plant fibres is their strong polar character, which creates many problems of incompatibility with most thermosetting and thermoplastic matrices. Production of bio-composites with high quality and performance is therefore based on adjusting the properties of the constituents to meet the requirements of the composite material i.e. a product with consistent, uniform, predictable, and reproducible properties. Such adjustments involve creating strong interfacial bonds between the lignocellulosic substrates and the binder. Successful development of bio-composites therefore stem from a careful understanding of the influence of these adjustments on the composite properties. This paper suggests some opportunities available in producing bio-composites from non-wood resources, and the challenges that must be overcome to make this technology commercially viable. Gaps in knowledge and information required before full commercialisation of these materials are identified.
Composites Part A-applied Science and Manufacturing, 2007
Modifications of rice husks surfaces by steam and sodium hydroxide (NaOH) were carried out in ord... more 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.