Study On The Preparation And Performance Of Sodium Alginate Based Degradable Mulch

Mulch plays a key role in agricultural production on reducing the threat of weeds,preventing soil erosion,keeping soil temperature,protecting against pests and diseases,promoting crop growth and retaining soil moisture.However,the“white pollution”caused by the widely used plastic mulch,which is difficult to be naturally degraded,has brought great harm to the ecological environment and crop growth.The development of degradable natural occurring sodium alginate based mulch film would provide a workable idea and solution to solve the environmental and ecological problems and the adverse effects on crop production caused by plastic mulch film.In this paper,the effect of polyvinyl alcohol content on the structure and properties of sodium alginate based mulch film was studied,in order to find the appropriate additive amount of polyvinyl alcohol in the prepared biodegradable sodium alginate based mulch film.Fourier transform infrared spectroscopy（FT-IR）,scanning electron microscopy（SEM）and light transmittance analysis showed that hydrogen bonds were found among the molecules of sodium alginate and polyvinyl alcohol,which indicating the good compatibility between each other.When the mass ratio of 2.0 wt.%sodium alginate solution to 2.0 wt.%polyvinyl alcohol solution was 4:6,the degradable sodium alginate based mulch film gave the optimum comprehensive performance.In order to improve the flexibility and mechanical property of degradable sodium alginate based mulch film,the influence of plasticizer on degradable sodium alginate based mulch film was studied.The test results of water vapor transmittance,mechanical property,water solubility,light transmittance,contact angle showed that the flexibility of degradable sodium alginate based mulch film significantly improved and possessed the best comprehensive performance when the additive amount of glycerin was 0.3wt.%.In order to regulate the water solubility of degradable sodium alginate mulch film,Ca Cl₂ was selected to spray on the surface of degradable sodium alginate mulch film.The test results of water vapor permeability,mechanical property,water solubility,light permeability and contact angle showed that when 2.0 wt.%Ca Cl₂ solution was used at ratio of 3:10（weight of Ca Cl₂ solution:mulch film surface area,kg:m²）,the water solubility of degradable sodium alginate mulch film was significantly reduced,meanwhile the comprehensive performance of the prepared mulch film was optimal.In order to regulate the light transmittance of sodium alginate based degradable mulch film,carbon black was selected as colorant to prepare black sodium alginate based degradable mulch film.Water vapor transmittance,mechanical properties,water solubility,light transmittance and other performance tests,the results show that:When the amount of carbon black was 0.7%,the light transmittance of black alginate based degradable mulching film was 9.4%at 400 nm,10.6%at 500 nm and 12.6%at 600 nm.It is similar to the light transmittance of commercially available polyethylene black mulch film（8.7%at 400 nm,12.5%at 500 nm and 14.3%at 600 nm）.The field experiment showed that the degradable sodium alginate based mulch film had good water retention capacity,as the accumulated water loss rate was 28.52%in 8d,52.24%lower than that of blank control group.The prepared mulch film could shorten the germination time of seeds and increase the germination percentage of seeds,as the germination percentages of Xia Yang cabbage,Shanghai rape seed and coriander increased by 7.14%,6.41%and 3.65%in the experiment.he prepared mulch film also could effectively promote the growth of crops,as the average plant height of cucumber seedlings in the degradable sodium alginate based mulch film group was 180.11 cm,4.74cm higher than that in the commercially available polyethylene mulching film group,and 6.48cm higher than that in blank group.In addition,the degradation rate of the prepared sodium alginate based mulch was only up to 13.30%after 240 days of air exposure（the common growth cycle of crops）,while the degradation rate of the prepared sodium alginate based mulch was as high as 80.81% after 28 days buried in soil.