NRU :: Browsing by Author "Yiga, Vianney Andrew"

Browsing by Author "Yiga, Vianney Andrew"

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Application of Response Surface Methodology for Optimizing Tensile Strength of Rice Husk Fiber-Reinforced Polylactic Acid Composites
(MDPI, 2021) Yiga, Vianney Andrew; Lubwama, Michael; Olupot, Peter Wilberforce
Filler/fiber loading and surface modification significantly influence tensile properties of natural fiber-reinforced plastic composites. It is therefore pertinent that they are suitably selected in order to yield the optimum tensile properties. Fiber-reinforced PLA composites were prepared us-ing compression molding with Box-Behnken Design experimental design approach. Factors, namely clay filler loading (1−5 wt.%), rice husk fiber loading (10−30 wt.%), alkali concentration (0−4 wt.%), rice husk variety (K85, K98) and alkali type (NaOH, Mg(OH)2) were varied. ANOVA determined significance of the factors affecting composites’ tensile strength. ANOVA results revealed the re-duced cubic model as best fit for tensile strength response. The desirability function revealed that variable values leading to optimum tensile strength (33.67 MPa) were 4.97 wt.%, 11.16 wt.% and 3.99 wt.% for filler loading, fiber loading and alkali concentration, respectively.
Characteristics of briquettes developed from rice and coffee husks for domestic cooking applications in Uganda
(Renewable Energy, 2017) Lubwama, Michael; Yiga, Vianney Andrew
The goal of this study was to develop briquettes from coffee and rice husks agricultural wastes as sustainable fuel sources for domestic cooking applications. Clay and cassava starch were used as binders. Physial properties of the coffee husks and rice husks as well as the developed briquettes were determined using Thermogravimetric analysis. Higher heating value (HHV) results were determined using bomb calorimetry. Drop test method was used to determine the mechanical and storage integrity of the developed briquettes. The results showed that the type of binder used in the development of the briquettes significantly affected both their physical properties and calorific values. Average higher heating values for briquettes developed with cassava starch binder ranged from 21.9-23.0 MJ/kg for coffee husks and 15.9-16.6 MJ/kg for rice husks. For coffee and rice husk briquettes developed with clay binder, average higher heating values ranged from 13.0-19.5 MJ/kg and 9.5-13.8 MJ/kg, respectively. Generally, cassava starch binder imparted higher drop strengths (over 95%) onto the briquettes than clay binder material. The characteristics were influenced by the physical properties of the raw biomass material as well as the high SiO2 ash in the clay binder
Development of groundnut shells and bagasse briquettes as sustainable fuel sources for domestic cooking applications in Uganda
(Renewable Energy, 2017) Lubwama, Michael; Yiga, Vianney Andrew
In this study groundnut shells and bagasse briquettes from agricultural wastes were developed with cassava and wheat starch binders using low pressure and high pressure techniques. In the low pressure technique, briquettes were produced after carbonization of groundnut shells and bagasse. The resulting bio-char was mixed with 30, 50, 70 and 90 grams of cassava and wheat flour starch binder for each 1000g of groundnut shells and bagasse bio-char. Groundnut shell briquettes were also developed under high pressure (230 MPa) using groundnut shells (1000g) without a binder, groundnut shells (1000g) with cassava flour starch binder (250g) and groundnut shells with wheat flour starch binder (250g). Thermo-physical properties of the briquettes were determined using thermo-gravimetric analysis. A Bomb calorimeter was used to determine the higher heating values of the briquettes. Thermal characteristics were determined by observing the flame temperature during combustion. The mechanical integrity of the briquettes was determined using the drop test method. The higher heating values for groundnut shell and bagasse briquettes developed using low pressure techniques were between 21 and 23 MJ/kg for both cassava and wheat starch binders. The results were all above the 16 MJ/kg average recorded for non- carbonized groundnut shell briquettes developed under high pressure.
Effect of Alkaline Surface Modification and Carbonization on Biochemical Properties of Rice and Coffee Husks for Use in Briquettes and Fiber- Reinforced Plastics
(Journal of Natural Fibers, 2019) Yiga, Vianney Andrew; Lubwama, Michael; Olupot, Peter Wilberforce
Effects of alkaline surface modification and carbonization on biochemical properties of selected rice and coffee husk varieties in Uganda were studied. Alkali pre-treatment was done by washing the husks in NaOH at a 15:1 liquor ratio. Pre-treatment is used in biomass conversion to overcome chemical and structural difficulties. Carbonization resulted in production of bio-char. Results showed increased cellulose contents for both the husks and their bio-chars after pre-treatment with NaOH solution. Lignin and hemi-cellulose compositions were reduced after pre-treatment in NaOH solution. Bio-chars for all rice husk varieties showed an increase in lignin content after carbonization. Lignin contents for Robusta coffee husks also increased after carbonization. Cellulose content in bio-chars of both rice and coffee husks reduced drastically after carbonization. A simple regression model relating bulk density and biochemical composition was developed at an accuracy of 70%. Alkaline surface modification and carbonization effects on biochemical properties are due to their impact on the non-cellulosic material and hydrophobicity, respectively, on the fibers.
Effects and interactions of the agricultural waste residues and binder type on physical properties and calorific values of carbonized briquettes
(Water, 2022) Lubwama, Michael; Yiga, Vianney Andrew; Nalubega Lubwama, Harriet
Multiple factors are responsible for the properties of developed briquettes. The effect of the agricultural residue type in determining resulting properties of developed briquettes is seldom elucidated. Agricultural residue biochars from groundnut shells, sugarcane bagasse, coffee husks, and rice husks were used in developing carbonized briquettes using the low-cost compression method. In this study, a general factorial multi-level categorical experimental design method was used to investigate the effects and interactions of the carbonized agricultural type, binder type, and binder amount on physical properties and calorific values of developed briquettes. Statistically significant models (p < 0.05) were obtained for physical property responses of fixed carbon, ash content, volatile matter, and moisture content as well as calorific values for the developed briquettes. In experiments where only cassava starch binder (30 g and 50 g) was used, carbonized agricultural residues played a significant role in the resulting physical property. Increasing the cassava starch binder from 30 to 50 g had a minimal impact on the resulting briquette physical property. In experiments where cassava starch binder and wheat starch binder were used, it was clear that the physical property of the developed briquette was affected significantly by the carbonized agricultural residue used and binder type. Calorific values of groundnut shell and bagasse briquettes were observed to be significantly affected by the agricultural residue type. The highest calorific values of 23.9 MJ/kg and 23.3 MJ/kg were obtained for groundnut shell and bagasse biochar briquettes, respectively, when only 30 g of cassava starch binder was used. Changes in cassava and wheat starch binder amounts did not significantly affect heating values of developed groundnut shell and bagasse briquettes.
Flame retardancy and thermal stability of agricultural residue fiber-reinforced polylactic acid: A Review
(Polymer Composites, 2021) Yiga, Vianney Andrew; Lubwama, Michael; Pagel, Sinja; Benz, Johannes; Olupot, Peter Wilberforce; Bonten, Christian
Biocomposites containing natural fibers and biopolymers are an ideal choice for developing substantially biodegradable materials for different applications. Polylactic acid is a biopolymer produced from renewable resources and has drawn numerous interest in packaging, electrical, and automotive application in recent years. However, its potential application in both electrical and automotive industries is limited by its flame retardancy and thermal properties. One way to offset this challenge has been to incorporate natural or synthetic flame retardants in polylactic acid (PLA). The aim of this article is to review the trends in research and development of composites based on agricultural fibers and PLA biopolymers over the past decade. This article highlights recent advances in the fields of flame retardancy and thermal stability of agricultural fiber-reinforced PLA. Typical fiber-reinforced PLA processing techniques are mentioned. Over 75% of the studies reported that incorporation of agricultural fibers resulted in enhanced flame retardancy and thermal stability of fiberreinforced PLA. These properties are further enhanced with surface modifications on the agricultural fibers prior to use as reinforcement in fiber-reinforced PLA. From this review it is clear that flame retardancy and thermal stability depends on the type and pretreatment method of the agricultural fibers used in developing fiber-reinforced PLA. Further research and development is encouraged on the enhancement of the flame retardancy properties of agricultural fiber-reinforced PLA, especially using agricultural fibers themselves as flame retardants as opposed to synthetic flame retardants that are typically used.
Investigation On Char Residues And Mean Reactivity Of Compression Molded Rice And Coffee Husks Biochar Reinforced Polypropylene
(In ASTFE Digital Library, 2020) Yiga, Vianney Andrew; Lubwama, Michael; Olupot, Peter Wilberforce
Fiber-reinforced plastics have gained utilization in recent years for many applications because they are a cheaper alternative to the ordinary petroleum-derived materials. On the other hand, considerable amounts of agricultural wastes still lack enough utilization. In this study, bio-chars of husks from two rice and two coffee varieties in Uganda were utilized as fillers to reinforce polypropylene (PP) and thus develop fiber-reinforced plastics. Bio-char filler material was varied between 0 % and 20 %. The plastics were prepared via melt mixing followed by compression molding. Effects of bio-char content on the thermal stability of the developed plastics were studied by use of an Eltra Thermostep Thermogravimetric analyzer. Thermogravimetric analysis (TGA) results showed that inclusion of bio-char improved the thermal stability of the developed fiber-reinforced plastics. Maximum rate of weight loss ranged from -0.0414 %/min (for 15 % unmodified Wita-9 rice bio-char) to 0.0023 %/min (for pure PP), corresponding to respective peak temperatures of 680.8 °C and 604 °C respectively. Peak temperatures generally increased with increase in filler loading. It was found out by this study that incorporation of bio-char fiber material resulted in increased char residues. These residues tended to hinder combustion. The highest char residues (17.4 %) were obtained when PP was loaded with 15 % neutral Wita-9 rice husks bio-char. The highest mean reactivity attained was 6.1×10-5 %/minute/°C obtained when 10 % unmodified Pussa rice husks bio-char was used to reinforce PP.
Optimization of tensile strength of PLA/clay/rice husk composites using Box‑Behnken design
(Biomass Conversion and Biorefinery, 2021) Yiga, Vianney Andrew; Lubwama, Michael; Pagel, Sinja; Olupot, Peter Wilberforce; Benz, Johannes; Bonten, Christian
Abstract It is extremely important to save costs and time while enhancing accuracy in experimentation. However, no study has utilized response surface methodology (RSM) to obtain the effects of independent parameters on properties of PLA/clay/rice husk composites. This study focused on optimization of tensile strength of fiber-reinforced polylactic acid (PLA) composites. RSM using Box-Behnken design (BBD) was used to determine optimum blending parameters of the developed composites. Fiber-reinforced PLA composites were prepared using compression molding. Rice husk fiber and clay filler were used to enhance tensile properties of PLA. Five factors, namely, clay filler loading (1 − 5 wt.%), rice husk fiber loading (10 − 30 wt.%), alkali concentration (0 − 4 wt.%), rice husk variety (K85, K98), and alkali type (NaOH, Mg(OH)2) were varied with 68 individual experiments. Tensile tests were carried out according to ASTM D638 standards. ANOVA results revealed that the quadratic models best fit the tensile strength response, with filler loading and fiber loading factors as the most significant model terms. Interaction effects were more predominant than linear and quadratic effects. The developed models used to determine maximum tensile strengths of PLA/clay/rice husk composites were in close agreement with experimental findings (R2 values of 0.9635, 0.9624, 0.9789, and 0.9731 for NaOH-modified K85 rice husks, Mg(OH)2-modified K85 rice husks, NaOH-modified K98 rice husks, and Mg(OH)2-modified K98 rice husks respectively). Individual optimal conditions were used to predict maximum tensile strengths in each set of developed composites. The predicted tensile strengths were 32.09 MPa, 33.69 MPa, 32.47 MPa, and 32.75 MPa for PLA/clay composites loaded with NaOH-modified K85 rice husks, Mg(OH)2-modified K85 rice husks, NaOH-modified K98 rice husks, and Mg(OH)2-modified K98 rice husks, respectively, which were very close to the obtained experimental values of 31.73 MPa, 33.06 MPa, 32.02 MPa, and 31.86 MPa respectively.
Physical and combustion properties of agricultural residue bio-char bio-composite briquettes as sustainable domestic energy sources
(Renewable energy, 2020) Lubwama, Michael; Yiga, Vianney Andrew; Muhairwe, Frank; Kihedu, Joseph
Domestic energy sources in sub-Saharan Africa are still mainly comprised of firewood and charcoal. One of the main challenges affecting the uptake of carbonized briquettes is their inefficiency in transferring heat. In this study bio-composite briquettes were developed from rice husks, coffee husks and groundnut shells, in varying proportions. The briquettes were developed under low pressure (≤ 7 MPa) after carbonization and application of starch binder. Thermal properties of the developed bio-composite briquettes were determined by using a bomb calorimeter and thermogravimetric analysis to determine calorific values and physical properties, respectively. Drop strength tests and particle density determinations were performed to study the mechanical strength and integrity of the developed briquettes. The water-boiling test was used to determine time taken to boil 1 liter of water. Fourier’s Law of heat conduction was used to investigate heat transfer rates across the briquettes for conditions of binder/binder-less bonding conditions. Calorific values for the developed briquettes ranged between 16.6 MJ/kg and 22 MJ/kg. Results for drop strength for the developed composite briquettes were all above 86 %, indicating satisfactory characteristics. Bio-composite briquettes developed using coffee and rice husks bio-chars took less time to boil water compared to all the other bio-composite briquette combinations. Particle densities ranged between 430 kg/m3 and 580 kg/m3. Heat transfer was enhanced when no binder was present and coffee and rice husks were sequentially placed in the briquette composition. This study showed the advantages of producing bio-char bio-composite briquettes over single constituent briquettes. Bio-composite carbonized briquettes produced from rice husks, coffee husks and groundnut shells are a suitable and sustainable alternative to firewood and charcoal use in sub-Saharan Africa.
Thermal and mechanical characteristics of local firewood species and resulting charcoal produced by slow pyrolysis
(Biomass Conversion and Biorefinery, 2021) Lubwama, Michael; Yiga, Vianney Andrew; Ssempijja, Ivan; Nalubega Lubwama, Harriet
The main source of fuel for domestic cooking applications in Sub-Saharan Africa is either locally available firewood species or charcoal produced by slow pyrolysis of these species. However, very few studies exist that characterize and quantify physical properties, burning rates, peak temperatures, and calorific values of typical firewood species and resulting charcoal fuels produced by slow pyrolysis. This study evaluated the mechanical and thermal properties of firewood and charcoal from five tree species namely: Dichrostachys cinerea, Morus Lactea, Piliostigma thonningii, Combretum molle, and Albizia grandibracteata. Characterization was done by scanning electron microscopy, thermogravimetric analysis, bomb calorimetry, Fourier transform infrared spectroscopy, bulk density measurements, and durability, water boiling and absorption tests. SEM images showed the development of macropores on charcoal after slow pyrolysis. Peak temperatures during firewood and charcoal combustion ranged between 515.5–621.8 °C and 741.6–785.9 °C, respectively. Maximum flame temperatures ranged between 786.9–870.8 °C for firewood and 634.4–737.3 °C for charcoal. Bulk densities and calorific values of charcoal species were higher than those for firewood species. Drop strengths for firewood were all 100% while for charcoal were between 93.7 and 100%. Water boiling tests indicated that firewood fuel performed better that charcoal fuel for low amounts of water due to higher maximum flame temperatures obtained during combustion of firewood.
Thermogravimetric analysis of agricultural residue carbonized briquettes for domestic and industrial applications
(MRS Advances, 2020) Yiga, Vianney Andrew; Lubwama, Michael
For a material to be used as energy, understanding its combustion behavior is crucial. Biomass is one such material that is increasingly gaining traction. Biomass may be utilized by direct combustion or transformation into fluid or solid biomass-based fuels. In this work, slow pyrolysis of groundnut shells, bagasse, rice husks and coffee husks was done to produce briquettes with cassava starch binder. Thermogravimetric analysis (TGA) was carried out using an Eltra Thermostep thermogravimetric analyzer. The samples were heated from ambient to 920 deg. Celsius. This analysis provided combustion explanations in terms of the weight loss, burning rates, peak temperatures, char residues and mean reactivity. TGA results showed that binder inclusion reduced the amount of fixed carbon present in the developed briquettes, thus slightly reducing their calorific values. Rice husks briquettes yielded the least weight loss (20.9% and 24.7% for 30g and 50g binder incorporations respectively) compared to others, owing to former’s higher ash contents. Increase in binder contents reduced the amount of char residues, caused by reducing ash contents in the developed briquettes. Peak temperatures and char residues generally increased with increasing binder content. This signifies increasing thermal stabilities of the developed briquettes. Highest char residues were obtained by briquettes developed with rice husks at 30g binder while briquettes developed with bagasse briquettes developed at 50g binder had the least char residues. The highest mean reactivities were obtained in briquettes developed from bagasse and coffee husks while briquettes developed from rice husks had lowest mean reactivities. Briquettes developed in this study showed sufficient combustion properties suitable to provide energy for domestic and industrial applications.

Browsing by Author "Yiga, Vianney Andrew"

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