Study Of Surface Modification Of Coal By Soy Protein And Their Biodegradation

In the biodegradation process of coal-soy protein plastic, not only the biodegradation property of coal but also the interface interaction between coal and soy protein has critical effect on the biodegradation of coal, hence affect the biodegradation of the blends. The surface modification of coal was conducted by adsorption and grafting method using soy protein isolate (the coal modified by adsorptive soy protein isolate limited as adsorbed coal; by grafting modified limited as grafted coal), based on the reactions among the functional groups of -NH2 and -COOH of SPI and –COOH and -OH of coal. The effects of SPI modification and the interface interaction on the biodegradation of coal and coal- soy protein isolate (SPI) plastics were explored. The surface grafting modification of coal was conducted in SPI solution. In order to enhance the surface reaction activity of coal, methylolated coal was prepared by methanol with BPO. The SPI graft ratio, structure, and thermal properties of the modified coals were characterized by Kjeldahl method, FTIR, and thermal analysis. The results showed that, the lower the coal rank, the easier the surface grafting reaction is performed, because low rank coals contain higher activated functional groups content than high rank coals. Thus the SPI graft ratio of low rank coals is higher than that of high rank coals. The adsorptive characteristic of coal was discussed by liquid adsorption method. The effects of temperature, time, monomer concentration, pH value, and degree of coalification on the SPI adsorptive capacity of coal were investigated. The results showed that, the adsorptive effects could be improved by the activated functional group of coal surface. The nitric acid oxidization treatment is able to increase -OH and –COOH on coal surface; it results in SPI adsorptive capacity increased efficiently. The mechanism for coal adsorptive SPI can be explained on the porous structure of coal surface and the hydrogen bond formed between coal macromolecule and SPI macromolecule. The aerobic-biodegradation of coals and SPI modified coals was carried out using compound microorganisms separated from soil. CO₂ yield, weight loss, humic acid (HA) content, elemental analysis and FT-IR of the solid residues and UV-VIS adsorption of liquid products were applied to characterize the biodegradation properties of the samples. The results showed that, although the biodegradation process became easier when using lower rank coals, yet the low rank coals are hard to be biodegraded, even have some inhibited effect on the biodegradation. By means of the coal modified by SPI adsorption and grafting, the nitrogen content and functional groups in coal surface were increased; the biodegradability of coal can be promoted either. The nitric acid oxidization treatment can break weak bands in coal structure to form extra –OH and -COOH, meanwhile, the hydrophilic property of coal was enhanced. At these conditions, the biodegradation of protein modified oxidized coal is better than that of not oxidized coal. The CO₂ yield of grafted coal is lower than that of adsorbed coal, but the weight loss and HA content are higher than that of adsorbed coal. The difference of protein adsorbed coal and grafted coal during interfacial interaction result in different biodegradation mechanism; the biodegradation products of grafted coals are mainly HA in both liquid and solid phase. While the biodegradation products of adsorbed coals are mainly CO₂ because the hydrogen bond controls the interaction between coal and SPI.