| Traditional agricultural mulch film is difficult to degrade and recycle in soil,which affects the sustainable development of agriculture.In recent years,the preparation of mulching film using natural polysaccharide polymer as raw material has become a research hotspot.In this paper,cellulose,chitosan and other natural polysaccharides were used as the main film materials,by regulating the concentration of each component of the film to control the structure and performance of the film,the mulching film with high strength,heat preservation and water conservation,good thermal stability,excellent shading performance and stable performance was prepared.The main research contents are as follows:Firstly,Na OH/humic acid/urea（Na OH/HA/urea）system was prepared as the solvent for cellulose（CE）,and the humic acid/cellulose mulching film（HA/CE film）was prepared by phase transformation method using citric acid solution as coagulation bath.The thickness,water content,water solubility and mechanical properties of the HA/CE film,as well as the viscosity and p H of the casting solution were controlled by regulating the concentration of HA and CE.The light transmittance,water vapor permeability,thermal insulation,aging resistance and degradation properties of HA/CE film were studied and adjusted.The HA/CE film was characterized and analyzed by means of POM,DRIFTS,SEM,contact angle,TG and XRD.The results showed that when the concentration of HA and CE in casting solution was 1.5%and 3.5%,the comprehensive performance of mulch film was the best.At the same time,the viscosity of casting solution was 1.27×104m Pa·s,the tensile strength and elongation at break of HA/CE film were 41.81MPa,5.73%（dry state）and 9.43MPa,7.98%（wet state）,the thickness,water content and water solubility were 86μm,1.25%and 4.35%,respectively.The maximum light transmittance was 0.77%,the WVP value was 1.07×10-10g Pa-1s-1m-1,and the film had a good heat preservation effect.The weight loss rate was 39.68%after degradation for 80 days.No natural fiber structure was found from POM,so it was considered that the cellulose was dissolved better in the Na OH/HA/urea system.The good compatibility between humic acid and cellulose was confirmed by characterization.The contact angle of HA/CE film was 73.14°.The HA/CE film showed good thermal stability.The addition of humic acid improved the crystallization ability of film,and the crystal structure was tightly arranged,which was helpful for the application of cellulose and humic acid in mulch film.Secondly,chitosan（CS）and nepheline powder（NE）were mixed with the glycerol as plasticizer,then the blend chitosan coating solution（NCS）was coated on the surface of HA/CE film,and the NCS-HA/CE film with high strength was prepared by control.The regulation of the concentration of each component on the mechanical properties of NCS-HA/CE film was discussed.The light transmittance,water vapor permeability,thermal insulation,aging resistance and degradation performance of NCS-HA/CE film were studied and adjusted.The characterization and analysis of NCS-HA/CE film were carried out by means of DRIFTS,SEM,contact angle and TG.When the casting solution consisted of3.5%cellulose,1.5%humic acid,2%chitosan,0.75%nepheline powder and 6%glycerol,the tensile strength and elongation of NCS-HA/CE film reached the maximum 57.98MPa,15.51%（dry state）and 25.84MPa,25.13%（wet state）,respectively,and the comprehensive performance of the film was the best.At this time,the thickness,water content and water solubility of the mulching film were 90μm,1.47%and 2.94%,respectively.The maximum light transmittance was 0.44%,and the WVP value was 0.87×10-10g Pa-1s-1m-1.The NCS-HA/CE film had good heat preservation,lightproof and aging resistance effect,and the weight loss rate reached 78.21%after 80 days degradation.Compared with HA/CE film,the properties of NCS-HA/CE film were improved to varying degrees.The coating of chitosan solution makes the film structure more compact,and improves the mechanical properties,water resistance and thermal stability.Thirdly,based on humic acid/urea complex as strengthening agent,glycerol as the plasticizer,glutaraldehyde（GL）as crosslinking agent,chitosan（CS）was modified by crosslinking,then glutaraldehyde crosslinking chitosan coating liquid（GCS）was coated on the surface of HA/CE film.The HA/CE film coated with glutaraldehyde crosslinked chitosan（GCS-HA/CE film）with high strength and water resistance was prepared by regulation and control.The optimal crosslinking conditions were determined as follows:40℃,30min.The regulations of HA,urea concentration and dosage of GL on the mechanical properties of GCS-HA/CE film and the effects of dosage of GL on the thickness,moisture content and water solubility of GCS-HA/CE film were regulated.The GCS-HA/CE film was characterized by light transmittance,water vapor permeability,thermal insulation,aging resistance,degradation performance,DRIFTS,SEM,contact angle,TG,and XRD.The consequences showed that when the concentration of CS,HA,urea and glycerol in the coating solution were 1.5%,3%,5%,and 6%,and the concentration and dosage of GL were2%and 2g/100g,the comprehensive performance of the film was the best.At the same time,the tensile strength and elongation at break of GCS-HA/CE film were 53.07MPa,12.59%（dry state）and 29.14MPa,19.57%（wet state）,the thickness,water content and water solubility were 101μm,1.41%and 1.14%,respectively.The maximum light transmittance was 2.9%,WVP value was 0.79×10-10g Pa-1s-1m-1,the heat preservation effect was similar to that of PE film,and the aging resistance was good.After degradation for 80d,the weight loss rate was 33.59%.The contact angle was 94.205°.Compared with HA/CE film,the comprehensive performance of the film after GCS coating was improved,the properties were more stable,the surface morphology was finer,and the hydrophobicity and thermal stability were better.It was more helpful for the application of cellulose and chitosan in agriculture,and it broadened the idea for the research and development of natural polysaccharide polymer base mulch film. |
