| Mulching film can play a role in heat preservation,moisture retention,grass suppression and soil fertility increase when used as farmland coverage.Plant fiber mulch has higher permeability and biodegradation potential compared with traditional plastic mulch.However,the low toughness of plant fiber mulch limited its application and development.The purpose of this paper is to improve the toughness of rice straw fiber mulch.Deep eutectic solvents（DES）and streptomyces rochei ZY-2 were used to pretreat rice straw.The effect of pretreatment on rice straw fiber was determined by analyzing the microstructure and physicochemical indexes of straw.Three toughening modification methods were used to modify rice straw pulp in turn,including compounding wood fiber,adding reinforcing agent and surface coating.In this study,the application tests of degradation,grass inhibition and heat preservation were also carried out to ensure that the toughened and modified mulch met the field application standards.The main conclusions are as follows:（1）Rice straw was pretreated by choline chloride/urea DES system,and then homogenized by disc mill.The amount of DES added was 1.5%,2.5%,3.5%,4.5% of the straw mass,and the prepared fiber slurry was labeled as DES1.5%,DES2.5%,DES3.5% and DES4.5%,respectively.The fiber slurry was characterized by X-ray diffraction（XRD）,fluorescence microscopy,scanning electron microscopy（SEM）,and Fourier transform infrared spectroscopy（FTIR）.The chemical composition of the fiber slurry was analyzed by the National Renewable Energy Laboratory（NREL）method.Meanwhile,the mechanical energy consumption of the disc mill and the tensile,burst,and tear properties of the fiber slurry film were calculated.The results showed that the peak intensity of the aromatic ring absorption peak at 1504 cm-1 was significantly weakened after DES treatment,and two splitting peaks were formed at 1654 cm-1,indicating that some lignin was dissolved in the straw because of the formation of H-O · H hydrogen bonds from choline chloride and urea.The fiber has different degrees of damage,the surface roughness and fiber visibility increases.With the increase of DES addition,the autofluorescence effect of cell wall gradually weakened,lignin content decreased by 2.7%,3.7%,5.3% and 6.2%,respectively,and cellulose crystallinity increased by 5.0%,3.3%,8.8% and 12.8%,respectively.In the mechanical properties test of the film,when the amount of DES added was 3.5%,the tensile index reached a maximum of 11.9 N·m/g,and then began to decline.The tear and burst index were 2.4 m N·m2/g and 0.6 k Pa·m2/g,respectively,and then the increasing trend weakened.According to the weighted average calculation formula,DES3.5% straw fiber mulch has the best comprehensive mechanical properties.（2）1%,3% and 5% of streptomyces rochei ZY-2 were added into the DES3.5% pretreated rice straw,respectively,and the inoculation experiment lasted 15 days under 65 ℃.Samples were taken on days 0,3,5,7,10 and 15,and the microbial enzyme activity,mass loss,tensile properties,SEM and chemical composition of treated rice straw were characterized.The pretreated rice straw was ground to form a film,and its tensile,tear and burst properties were analyzed.The results showed that DES combined with biological pretreatment could improve the toughness of rice straw fiber mulch,and the effect was the best when the proportion of DES was 3.5%,streptomyces rochei ZY-2 was 3% and inoculation time was day 7.With the increase of fermentation time,large voids and many pores of different sizes appeared on the surface of straw,straw showed fracture and uneven faults.The epidermal tissue under the waxy silicified layer has gradually emerged,the cell wall and fiber structure have been significantly destroyed,and the overall structure has been seriously damaged.The mass loss rate of rice straw added with 3%streptomyces rochei ZY-2 on the 7th day reached 17% and the enzyme activity was the highest.The tensile properties of the straw section showed an overall upward trend,and the ratio of cellulose to hemicellulose content was negatively correlated with the mechanical strength of the straw section.The maximum tensile properties of rice straw added with 3% streptomyces rochei ZY-2 on the 7th day reached 46.2 MPa.The tensile strength of single fiber decreased continuously during fermentation,and the trend was negatively correlated with the tensile properties of straw section and the microfibril angle of straw section.The mechanical properties of the mulch film after DES combined with biological pretreatment were significantly higher than those after DES pretreatment alone.The tensile,burst and tear indexes increased by 14.1%,5%,and 21%,respectively.（3）The rice straw treated with 3.5% DES and 3% streptomyces rochei ZY-2 on the 7th day was used as raw material,and the rice straw pulp was obtained by disc milling.Toughening modification of rice straw pulp:（1）Compound poplar/Chinese fir pulp,the addition amount was10%,20%,30%,40% and 50% of the total pulp,respectively;（2）Additives were added on the basis of adding 40% poplar pulp: polyamide epichlorohydrin resin（PAE）,aluminum sulfate,cationic dispersed rosin gum,and 7 formulations were formed through the compound of these additives;（3）The mold was coated with B-soybean protein gum/G-soybean protein gum on the basis of adding 40% poplar pulp,aluminum sulfate and cationic dispersed rosin gum,The three times toughening modified slurry film was formed,and its tensile,tearing and bursting properties were analyzed.The results showed that the mechanical properties of the film were significantly improved by adding 40% poplar pulp,aluminum sulfate and cationic dispersed rosin gum to form a film and coating G-soybean protein gum.The dry tensile,wet tensile,burst,tear indexes increased by 117.4%,354.5%,235.7%,66.7%,respectively,and the toughness of the film increased.（4）Rice straw fiber film and commercial film were immersed in paddy soil diluent for 63 days,and the degradation rate of film was recorded.The dynamic contact angle of the film was measured by water contact angle meter,and the change of hydrophobicity of the film surface was analyzed.A pot experiment was conducted to study the dynamic changes of plant height,stem diameter,tiller number and weed growth of rice seedlings under plastic film mulching,straw mulching and no mulching.The temperature at 5 cm below soil was measured every 10 days.The results showed that the rice straw mulching film prolonged the degradation time of the film compared with the commercially available film,and could better protect plants and increase production in practical applications.Mulching rice straw fiber mulch can increase the proportion of rice tillers.The number of rice straw tillers covered with mulch is 10.15,which is 1.52 higher than that of bare land and 1.68 higher than that of commercial mulch.The mulch prepared by rice fiber can significantly inhibit the growth of weeds,the inhibition rate reached 80% compared with no film mulching and increased by 26.92% compared with the commercial film.The highest temperature at 5cm below soil were 14.2°C,14.4°C and 14.5°C,respectively,under no mulching,plastic film mulching and rice straw fiber film mulching.The soil temperature of rice straw fiber film mulching was the highest compared with other mulching. |
PDF Full Text Request