Study On The Preparation And Performance Of Polyethylene-based Nano Sun-shading And Cooling Materials

Agriculture is one of the largest industries affected by climate.especially temperature.The facility cultivation need cultivation environment.high temperature is an important influence factor affecting crop distribution,growth and qualities of fruits and vegetables in the spring and summer.Irremediable loss will be caused on crops if the temperature in greenhouse cannot be controlled well.Generally when the temperature reaches 35 ℃,many crops will reduce photosynthesis and nutrient movement is blocked,resulting in slow growth and poor resistance to diseases and pests.If the temperature is higher than the heat level of crops,the crops would tend to die and normal growth is nearly impossible,even for crops used to grow in the tropical area.These risks will directly affect the quality and yield of crops.Therefore,the research of film with sun shading and cooling function is urgent and its prospects will be very broad.Under the background of the national energy-saving emission reduction,the existing cooling measures are reasonably optimized renovation and actively explore new cooling mode.It has great economic benefits and also has significant social benefits.PE films are widely used in agriculture because of its excellent performance and affordable price.The advantages of polyethylene films are good light transmittance,low price and resistance ability,but it has no cooling function.Therefore,this thesis selected polyethylene as the substrate material.Light refraction,reflection,scattering,and optical conversion technology of nano cooling materials was adopted to regulate spectrum.Nano cooling agents can reduce radiation(mainly near infrared and visible light)into the greenhouse.Then nano cooling agents using light conversion function can convert ultraviolet light into visible light.It not only fulfills visible light which the crop needs,eliminating the effect of lacking of light intensity,but also achieves cooling effect.(1)Preparation and characterization of single-layer nano cooling film.Nanocooling agent(NANO-JW),cooling synergistic agent(JW-X)and polyethylene matrix prepare nano cooling master batch(NANO-JW-M)were mixed by direct melt intercalation.then single layer nano cooling film was prepared through the melt intercalation method again.According to add different amount of nano cooling agent study the effects of transmittance,light conversion band,diffuse scattering rate,shading rate of PE film,and XRD,FTIR,TG,FA,UV-Vis-NIR were used to characterize the structure and properties.Also preliminarily tests the cooling experiment in outdoor.The results show that the single layer nano cooling film has cooling function.(2)Preparation and characterization of three layer nano cooling film.Compared with monolayer film production equipment,the three layer coextrusion production equipment has the characteristics of higher yield,low energy consumption,good product plasticizing,simple operation.It can make the quality of PE films better.In order to further improve the cooling effect,five different kinds of nano cooling master batch(NANO-JW-0.2%,0.4%,0.5%,0.8%and 1.2%)are prepared.then by use of three layer coextrusion film blowing unit prepared different shading rate of three layer coextrusion nano cooling films(PE/NANO-JW-0.2%,0.4%,0.5%,0.8%and 1.2%)through two times of melt intercalation method.Through the physical,chemical properties and the influence.on the different bands of light study the reaction conditions of nano cooling agent in different layers,the adding amount,adding mode and other additive synergistic effect.Using XRD.FTIR,TG,FA,UV-Vis-NIR and mechanical properties characterize the structure and properties.The results show that the new cooling films have good cooling effect(The tensile strength increased to 35 Mpa),good thermal stability and good processing performance.The transmittance is relative balance.It also has good heat stability(initial decomposition temperature maximum up to 40 degrees)and excellent processing properties.UV-Vis-NIR spectral transmittance curve shows that this novel nano cooling film can reduce the near infrared transmittance and the temperature in greenhouse.(3)Application test of nano cooling film.Through the combination of laboratory and field experiments,cooling effect of nano cooling film(PE/NANO-JW-0.8%)in different time segments and factors related to the environment(temperature,humidity,and light intensity)were investigated.So this can assess whether the greenhouse environment suits the planting of economic crops(muskmelon).The results show that the average temperature reduced 4 degree during the day.The average relative humidity increased by 4%.Light intensity increased 28.7 Klux.The environment of greenhouse(temperature,humidity,light intensity)reaches the muskmelon planting requirements.New nano cooling film has advantages including low cost,simple operation,automatic adjustment of light and temperature effect,greatly reducing labor costs,no special reaction conditions and high feasibility of the industrial production.New nano cooling films not only have the mechanical strength and good thermal stability,but also have the function of diffuse scattering.Diffuse scattering function can transform direct light into scattering light,which can further reach cooling function,and meet growing requirements of the crops in the summer,like suitable temperature and humidity conditions.The greenhouse can ensure the normal growth of crops with new nano cooling film.This new cooling method simplifies the traditional greenhouse and will open up a new agricultural cooling approach.