| Traditional agricultural film cannot be biodegradable,and the plastic residue in the soil can cause soil pollution and hinder the growth and development of crops.Biodegradable agricultural mulch will gradually become a substitute for traditional mulch.Among them,polybutylene adipate terephthalate(PBAT)material with high flexibility can biodegrade into carbon dioxide and water in natural environments,which is environmentally friendly and widely used in biodegradable film products.In addition,adding natural polymer materials through blending is currently a new research topic.The commonly added natural polymer materials include starch,cellulose,lignin,etc.After decomposition,their main components are still carbon dioxide and water.This paper studies the addition of silk degumming waste-sericin protein-to PBAT to form a degradable plastic film while providing nitrogen fertilizer to the soil.Not only does it endow agricultural mulch with new functions,but it can also turn waste into treasure and reduce the difficulty of treating sericin wastewater.This article combines sericin with PBAT to prepare a biodegradable film that can provide nitrogen fertilizer.However,when blending the two,there may be problems such as poor mechanical properties and lack of high-temperature resistance.This is because sericin protein contains hydroxyl,carboxyl,amino and other functional groups,with strong hydrophilicity,while PBAT belongs to aromatic fatty polyester compounds and is a hydrophobic substance.The polarity difference between the two is significant,and the interfacial compatibility is poor,resulting in a significant decrease in the mechanical properties of the material after physical blending.Therefore,it is necessary to improve the hydrophobicity of sericin protein,shorten the polarity gap,and reduce the loss of mechanical properties.In addition,plastic products generally need to be processed and formed at high temperatures,while sericin protein is a natural polymer that can turn yellow or even carbonize at high temperatures.Therefore,improving the heat resistance of sericin protein is also an urgent problem to be solved.Therefore,on the one hand,this article modifies sericin protein through chemical methods to improve its hydrophobicity and heat resistance.On the other hand,adding a certain amount of compatibilizer that can play a bridging role improves the compatibility of the two phase materials.This paper consists of the following three parts.The first part is to study the appropriate high-temperature and high-pressure water degumming process for silk and the modification of sericin protein.A suitable degumming process is beneficial for reducing recycling costs,improving the purity of sericin protein,and reducing the negative impact of alkaline additives on crops.The extracted sericin protein was hydrophobic and thermoplastic modified using monomer glycidyl methacrylate(GMA).Single factor analysis was used to evaluate the grafting rate and efficiency.The optimal grafting conditions were obtained as follows: the amount of GMA accounted for 100% of the mass of sericin protein,the amount of initiator 22.5g/L,and 80 ℃ X 4h.The results of infrared,contact angle,SEM and other tests showed that the modified sericin protein(GMS)was successfully grafted with GMA;The higher the grafting ratio,the higher the hydrophobicity and heat resistance,and the better the hot working performance.The second part is to prepare compatibilizers to improve the compatibility of two-phase materials and investigate the compatibilization effect.Monofunctional compatibilizer MAH-g-PABT(MPB)and bifunctional compatibilizer GMA/MAH-gPBAT(GMPB)were prepared by grafting maleic anhydride(MAH)and glycidyl methacrylate(GMA)with PBAT.Through orthogonal experiments,the effect of reaction conditions on the grafting rate of grafted products was studied.At the same time,compare with the commercially available product ADR-4370 S to investigate the effects of the three on the mechanical properties,thermal stability,processability,and other aspects of Sericin/PBAT composite materials.The test results show that compared to composite materials without compatibilizers(fracture strength 14.8Mpa,fracture elongation 331%),all three can significantly improve their mechanical properties,with MPB having the best compatibilization effect,with a fracture strength increase of 7.2Mpa and a fracture elongation increase of 49.5%;The addition of GMPB and ADR-4370 S can increase the maximum decomposition temperature of the composite material by 2-5 ℃;However,their addition did not significantly improve the rheological properties,and the differences among the three were not significant.The third part is to prepare a Sericin/PBAT composite material into a thin film with an average thickness of 0.05 mm,and to benchmark the relevant indicators in the national standard GBT35795-2017 "Fully Biodegradable Agricultural Ground Cover Film".The mechanical properties of films with different sericin protein content and modified films were studied,as well as related indicators such as moisture retention,insulation,degradability,and nitrogen release.The data shows that when the Sericin content in the Sericin/PBAT composite film reaches as high as 20%,the breaking strength is 7.92 N,and the elongation at break is 517.75%,which meets the mechanical requirements;Compared to pure PBAT film,the insulation performance is almost the same;But the moisture retention will slightly decrease with the increase of Sericin content,with a maximum decrease of 1.5% in moisture content.After 28 days of simulated degradation using alkaline solution and soil burial,the weight loss rate of PBAT membrane was 0.93% and the membrane in soil burial turned yellow;As the sericin content increases,the Sericin/PBAT film loses more weight,reaching a maximum of 11.91%.The nitrogen content in the corresponding solution was approximately 23 mg/L on the 7th day and 32 mg/L on the 28 th day.Soil burial showed mold on the 14 th day and the membrane had become brittle on the 21 st day.The above experiments indicate that the biodegradable composite film developed in this project has degradability and nitrogen supply efficiency. |
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