Conclusions
The preliminary chemical and morphological studies showed that rice straw is an effective alternative cellulosic raw material for pulp and papermaking. Based on the experimental results the optimized conditions for alkaline pre-extraction of rice straw were found to be: maximum temperature 160 °C, time at maximum temperature 60 min and S:L ratio 1:4 (w/w). The optimal alkali charges for un-extracted and extracted samples were found to be 14% and 8%, respectively. It is to be noted that these conditions involve a lower soda, temperature, time and beating than those required to maximize the studied paper properties, they can save chemical reagents and energy for industrial scale. Pulping results showed that the extracted rice straw had different behaviors in terms of physical and mechanical properties in comparison to the un-extracted rice straw. The pre-extraction affected tensile and burst indices of produced pulp because of the removal of considerable amount of hemicelluloses. All physico-mechanical properties improved considerably when the CNFs were added to furnish. However, the effect of CNFs on the properties of sheets under un-extracted condition was a little better than extracted condition. In general, addition of CNFs and pulp beating could significantly improve strength properties in terms of tensile and burst indices. SEM micrographs showed that the network of tiny CNFs is uniformly adhered to the thick rice straw fibers and exhibited relatively smooth and uniform surface.