Synthesis of a keratin-starch bio-composite hydrogel for soil health improvement

Abstract

Excessive fertilizer use poses significant problems like increased soil salinity, bio-magnification and excessive nutrient leaching. The latter has detrimental effects on water bodies, the environment and the yield of farmers. With rising concerns on sustainable agriculture peaking due to climate change which has devasted the agricultural landscapes coupled with under-utilized waste, this study used the abundant waste chicken feathers to extract keratin which was used to make a keratin-starch bio-composite hydrogel for effective nutrient management and moisture retention. The extraction process was done through alkaline hydrolysis using sodium hydroxide and several extraction parameters were optimized which showed that the process has high yields of 69 % at a high pH of 13, a concentration of 2 M, a temperature range of 80 - 95 oC and for two hours, of which exceeding the latter three results in low yields due to protein chain degradation. The keratin and bio-composite were characterized by UV-Visible spectroscopy plus biuret test which confirmed the presence of the protein. FTIR spectroscopy showed functional groups and peaks at 1650 cm -1(Amide I), 1540 cm-1 (Amide II), 1230 – 1300 cm-1 (Amide III) and N-H/O-H and C-H stretch vibrations, which show successful keratin extraction Analysis of the bio-composite showed that a new material had been formed through new shifts in peaks for the bio-composite and it still had active functional groups for nutrient capture. XRD spectroscopy confirmed that a hydrogel matrix had been formed since the bio-composite had a broad amorphous halo indicating flexible arrangement of polymer chains which are important for water retention and a sharp crystalline peak due to ordered cross-linked regions for mechanical strength of the bio-composite. The synthesized bio-composite showed good nutrient retention capacities recording 78 % for Nitrate (NO3-) capture, 77.6 % Phosphate (PO4-3) and 92.5 % Potassium (K+) capture, these tests were done using UV-Visible Spectroscopy and Atomic Emission Spectroscopy. It also recorded an 80 % water retention capacity. Chicken feathers proved to be a sustainable source of keratin and the bio-composite synthesized can serve as an effective moisture retaining and nutrient capture agent. This study recommends further field tests to evaluate agricultural applicability.