The effect of the cyclic hornification on the hygromechanical and surface characteristics of rice stubble agriculture waste

Abstract

An indiscriminate burning of rice stubble waste in the farms poses a major environmental challenge worldwide. The stubble waste can be utilized to fabricate the natural fibre polymer composites for several mild- to low-load-bearing applications in the civil construction. However, the susceptibility to long-term environmental moisture limits the use of stubble waste. In this work, we analyse the effect of water and alkali hornification as a pre-treatment technique on the moisture uptake, surface roughness, wettability and mechanical strength of rice stubble straw, and the results are compared with untreated stubble straw. The water retention value was reduced by ∼49% and ∼60% after four hornification cycles under the water and alkali mediums, respectively. Preliminary visual and microstructural assessments revealed the reduction in hydrophilic cellulose and lignin contents with both types of pre-treatments. It is observed that in comparison to alkali hornification, the water hornification technique leads to a significant improvement in hygromechanical characteristics of stubble straw. When compared to untreated stubble, one cycle of water hornification leads to approximately ∼16% reduction in the moisture uptake, and ∼42% increase in the tensile strength. On the other hand, the alkali hornification resulted in the improvement in tensile strength by ∼36%, but it led to an increased water uptake. The results indicated that the thinning and surface roughening of the fibres is primarily caused by the removal of amorphous contents during the pre-treatment. For an improved environmental durability with better mechanical strength, it is recommended to do the pre-treatment of the stubble waste using one water hornification cycle before it is used further.