Browsing by Author "Kamweru, P.K."

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Effects of UV Light on Mechanical Properties and Production of Vitamin D2 in Mushrooms
(Chuka University, 2016) Tindibale, E.L.; Kamweru, P.K.
The sun emits ultraviolet radiation in form of ultraviolet-A (UV-A), ultraviolet-B (UV-B), and ultraviolet-C (UV-C) bands. Ultraviolet light may boost vitamin D2 production in mushrooms which human bodies cannot synthesize. The ergosterol in mushrooms, a component of fungal cell membranes which serves the same function as cholesterol in animal cells, can be converted into vitamin D2 by ultraviolet light. However, mushrooms are conventionally grown in the dark, necessitating artificial ultraviolet irradiation. This study investigated the effects of UV-A and UV-C light on concentration of vitamin D2 in oyster mushrooms during growth and mechanical properties post-harvest. UV exposure times were varied from 10 to 60 minutes per day at intervals of 10 minutes, and irradiation done for three days. UV spectroscopy was used to determine the amounts of Vitamin D2 and the mechanical properties were investigated using dynamic mechanical analysis (DMA 2980). Absorbance of vitamin D2 for UV-A light ranged from 0.18 to 0.49 for 10 to 60 minutes of irradiation, respectively, while for UV-C light the vitamin D2 content absorbance was 0.38 to 0.81 for 10 to 60 minutes of irradiation, respectively. The storage modulus, loss modulus, and loss factor of the irradiated samples and control samples were determined for both UV bands. UV-C light irradiated samples had higher loss modulus and loss factor, but low storage modulus as temperature increased from 35-100oC with respect to the control sample, while UV-A light irradiated samples had lower loss modulus, low loss factor, and higher storage modulus than UV-C irradiated samples. Thus, oyster mushrooms with a well-defined content of vitamin D2 can be obtained without largely affecting the mechanical properties and the quality of the mushrooms.
Structural properties of high density polyethylene matrix composites reinforced with open air and furnace rice husks ash
(Journal of Chemical Engineering and Materials Science, 2021-12) Jonathan, M.K.; Osamong, G.A.; Butembu, S.; Kamweru, P.K.; Gichumbi, J.M.; Ndiritu, F.G.
In this work, rice husks ash (RHA) was introduced to pure and recycled high density polyethylene (HDPE) matrix, at varying ration (0-50%) to formulate rice husks ash High density polyethylene (RHAHDPE) composite. RHA was obtained by burning fresh rice husks either by open-air burning (oRHA) or furnace calcination at 700°C (fRHA). The composite samples were made by melt-mixing the HDPE in an oven at a temperature of 150°C and adding different percentages of RHA in presence of maleic anhydride compatibilizer. Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) were carried out to determine the structural properties of the samples, and both suggest occurrence of composting chemical changes. For all RHA-HDPE samples, a broad band was noted between 970-070cm-1 . This was highly contributed by the RHA and associated to Si-O-Si stretching modes. Other peaks are associated with Si-O-C interaction and O-Si-O bending vibrations in the samples. Scanning electron Microscopy (SEM) micrographs for HDPE indicated a smooth and uniform surface with a number of voids. On addition of RHA, the particles filled these voids making the sample surface rough. This roughness is seen to increase with increased percentage of RHA. The studies conclude that the cheaply obtained oRHA is as good as the fRHA in making RHA-HDPE composite.