Synthesis of rice straw biopolymers based hydrogels and their use as media for growth of monocot (wheat) and dicot (moong bean) plants

Burning of rice straw has been causing a number of environmental issues in Northern India which enforces researchers to find out different ways for valorization of this unavoidable biomass. Rice straw biopolymers, i.e. cellulose, hemicellulose and lignin can be used for production of various sustainable organic products. In the present study, microcrystalline cellulose (MCC) and lignin were extracted from rice straw by dilute acid pre-treatment method followed by alkaline hydrolysis. MCC and lignin were used as raw material for synthesis of hydrogels using polyvinyl alcohol as matrix template, glutaraldehyde/epichlorohydrin as cross-linkers. The characterization of synthesized hydrogels with FT-IR and SEM analysis revealed that hydrogels using glutaraldehyde have less porosity and tight bonding network whereas epichlorohydrin caused loose bonding between polymers and resulted in formation of large pores in hydrogels. Swelling ratio and reswelling capacity of hydrogels showed that lignin hydrogels performed best than all other hydrogels. The effects of hydrogels on total fresh and dry biomass, leaf area, seedling length of germinated seedlings of wheat and moong bean were observed under control and water stress conditions. All hydrogels performed well under stress conditions as compared to control. However, both lignin hydrogels performed best and gave significant highest growth under stress conditions. These biopolymer based hydrogels can be recommended for use as growth media ingredient in water deficient soils. Graphical abstract