Abstract:
Rice is the main food crop plant in agricultural economy based country like Sri Lanka, which
cultivates in two main seasons annually known as “Yala” and “Maha”. Thus rice husk is one of
the most frequently abundant agro-waste yielded over 20% of the paddy harvest. According to
the statistics it revealed that on average, about 200 kg of rice husks (RHs) were produced from
one ton of paddy harvest. Nevertheless, this crop residue is considered as an agro-waste which
burns in open fields. Thus for the reduction of recent environmental issues such as disposal,
respiratory problems and global warming, utilization of RHs leading to a value added product is
an alternative solution. RH is a frequently available agricultural waste containing cellulose as the
major which has been identified as a frequently available renewable energy source of naturally
occurring biodegradable polysaccharide. Thus isolation of cellulose from RHs and use in
industrial applications would be a convenient solution for the value addition of agro-waste.
Traditional varieties of RHs in Sri Lanka, Pachchaperumal, Kahawanu and Heenati and one of
the frequently consuming genetically improved variety, BG-300 were the RHs mainly focused in
this study. Highly purified cellulose was successfully isolated from RHs of various types
including a series of steps as de-waxing, alkali pretreatment followed by bleaching process. Dewaxing
through soxhelet extraction and alkali pretreatment by sodium hydroxide was conducted
to remove non cellulose constituents in the RHs. Chlorine free environmentally friendly
bleaching process using hydrogen peroxide (H2O2) was continued for further removal of non
cellulose materials, hemicellulose and lignin. FTIR spectroscopy and TG analysis were used to
analyze the isolated cellulose. A range of 37-38 wt% and 35 wt% of cellulose was successfully
extracted from RHs of traditional varieties and genetically improved variety, BG-300
respectively. The substitution of an eco-friendly bleaching agent, H2O2 instead of chemicals
containing chlorine compounds was a significant step which resulted the ability of extracting
white-pale yellowish cellulose powder with higher efficiency rate via only over two times of
bleaching cycles. This procedure confirmed the ability of extraction of cellulose with high purity
from biodegradable wastes; RHs can be used for many industrial applications as a value added
product.
