Study on New Nano Sun Shading Films

Jia WANG,Ninglin ZHOU, ,Xiaoling ZHU,Yutian SU,Maoni SHAO,Lu TIAN,Ming ZHANG,Wenxiu LI,Yuanyuan CHEN

1.Jiangsu Key Laboratory of Biomedical Materials,College of Chemistry and Materials Science,Nanjing Normal University,Nanjing 210023,China;

2.Nanjing Zhou Ninglin Advanced Materials Technology Co.,Ltd.,Nanjing 211505,China

Responsible editor:Xiaoxue WANG Responsible proofreader:Xiaoyan WU

The material on basis of crop growth is the organic compounds from production and accumulation of photosynthesis.To a certain degree,light intensity directly affects photosynthesis.When the light intensity exceeds a certain limit,for example,efficiency of photosynthesis be come saturated[1].Since the light intensity may lead to changes in the microclimate of the system including temperature and humidity and cause adverse effects on crops,how to obtain appropriate light intensity must be taken into consideration.With the rapid development of protected cultivation,uncontrolled high indoor temperature during summer and autumn has become an urgent problem for greenhouse growers.External strong light and over high temperature in greenhouse make it difficult to improve yield and quality of crops and even increase the risk of crop failure.Too much light radiation can interfere with plant growth and even burns the plants.If the temperature exceeds 35 ℃,photosynthesis and nutrient translocation will be blocked,resulting in slow growing speed,poor resistance to disease and physiological pest damage.When temperature is higher than the desired temperature,crops would tend to die and regular growth is quite difficult to achieve.

The design and preparation of nano sun shading material was based on diffuse scattering and reflection of nano sun shading master batch by nano light conversion technology.The structure and properties of nano sun shading films were characterized by XRD,TG,UV-Vis-NIR and FA.Then the cooling effect of different types of nano sun shading films was preliminary tracked by measuring indoor and outdoor temperature.

Experiment

Materials and preparation

Nano sun shading agent (made by Nanjing Zhou Ninglin Advanced Materials Technology CO.,Ltd.,),cooling synergistic agent (made by Nanjing Zhou Ninglin Advanced Materials Technology CO.,Ltd.,) and PE based carrier are mixed in a high -speed mixer.Nano sun shading master batch (marked as NANO-JW-M)are made through the double screw extruder.And then different shading rate of nano sun shading films were prepared by polyethylene material,nano sun shading master batch and longevity anti-aging master batch through blow molding,denoted as PE/NANO-JW-1,2,3.

The control films,marked as PE/DZ,are polyethylene films without nano sun shading master batch.The rest is the same with PE/NANO-JW-1,2,3.

Characterization

The XRD patterns of the dried samples were obtained by using X-ray diffraction (Rigaku D/max,Tokyo,Japan) equipped with a vertically mounted goniometer and a Cu Kα Xray source.The diffract meter was operated at 45 kV and 40 mA at a scanning speed of 2 ° /min.UV-Vis-NIR spectra were measured at room temperature on VARIAN Cary-5000 from 200 nm to 800 nm,using BaSO4as reflectance standard.Thermo gravimetric measurements were performed on a Perkin-Elmer TG7 instrument using a heating rate of 20 ℃/min up to 800℃in nitrogen atmosphere.The fluorescence emission spectra were recorded on a Perkin-Elmer LS-50B luminescence spectrometer.

Results and Discussion

X-ray diffraction analysis(XRD)

The XRD patterns of NANO-JWMand PE/NANO-JW-1,2,3 are shown in Fig.1.NANO-JW-M presents a main crystalline peak around 5.52°,which corresponds to the basal interlayer spacing (d001)of 1.63 nm.With intercalation with NANO-JW-Mat different ratios,the crystalline peak disappears.This is due to the presence of nano layer structure in NANO-JW-M displays diffraction peaks in XRD.After full melting intercalation,no obvious peak can be observed,for lamellar structure is destroyed and NANO-JWM is uniformly dispersed on PE matrix.

Ultraviolet visible near infrared analysis(UV-Vis-NIR)

The photosynthesis of plants mainly absorb visible light (400-700 nm),of which the largest absorption part is red orange light and blue violet light.Regular growth of corps can not be maintained in near ultraviolet light(below 290 nm).The aging of greenhouse film is also quite serious around this range of light.Nevertheless,a modest amount of ultraviolet light is still necessary for crop growth.Similarly,ultraviolet light in the region of 260-360 nm can inhibit the growth of crops,but in turn can prevent high growth of crops in order to make the seedling and adult plant thrive,enhance the resistance,increase the vitamin content and improve brightness of the product(Table1).

UV transmission (300-400 nm)will affect the crop morphology,color,texture and resistance.Photo synthetically active radiation transmittance(400-700 nm) would affect the growth of crops.Transmittance between 400-700 nm bands has a promoting effect on the growth of crops,so need of transmittance in this band of the cooling films is relatively high,whereas high transmittance will cause heat increasing.Near infrared (700-2 500 nm)transmittance is the main factor of temperature increasing in greenhouse,and affects heat insulation and cooling effect,so the transmittance in near infrared band of the cooling films should be kept at a low degree.Meanwhile,near infrared light also affect the micro climate and energy balance of soil temperature and crops.Taken all three points into account,PE/NANO-JW-2 is most appropriate.UV transmission,photo synthetically active transmission and near infrared transmission would be balanced,which not only has a good cooling effect,but also not affect the normal growth of crops.

Short wavelength ultraviolet radiation causes a strong damage to the crop while the long wavelength ultravi-olet radiation is favorable for most crops.As shown in Table2,PE/NANO-JW-2 is the best choice due to low UV-C transmittance and high UVA transmittance.

Table2 Average transmittance of ultraviolet A,B and C

Table3 TG analysis results of PE/DZ and PE/NANO-JW-1,2,3

Fluorescence analysis(FA)

Results show that excess ultraviolet radiation dwarf crop,mainly restrain elongation of internodes[5].The dwarf degree differs from crop species,cultivars and growth stages.The stronger ultraviolet radiation is,the greater influence on plant is found.The solar ultraviolet radiation entering the atmosphere can be divided into three parts:short wave ultraviolet radiation (UV-C,200-280 nm)is lethal radiation;middle wave ultraviolet radiation (UV-B,280-320 nm) is biological effective radiation; long ultraviolet radiation (UV-A,320-400 nm) has no biological effect.O3 in the stratosphere can absorb all the UV-C and 90% UV-B[6].UV-B makes most plants show dwarfing,short internodes[7],minify leaf area,and thicken leaf[8].

The chloroplast is the place for photosynthesis.Absorption of light energy,fixation and reduction of carbon dioxide,amylase synthesis,oxygen release and so on occur in the chloroplasts.Higher plants contain two kinds of pigments:chlorophyll and carotenoid.Most chlorophyll a molecules and all chlorophyll b molecules have a collect function to light.Few chlorophyll a molecules under special condition can also convert solar energy to electricity.Carotenoids also collect light effect,and transfer light energy to chlorophyll a molecules.In addition,carotenoid can prevent photo oxidation of chlorophyll[9].The effective light wavelength of photosynthesis is 380-720 nm.The strongest absorption of chlorophyll consists of two regions:one is the red part between 640-660 nm,and the other is blue violet part light between 430-450 nm.The maximum absorption of carotenoids is proven to be in blue violet part between 400-500 nm,and the absorption strength is much stronger than blue violet absorption of chlorophyll.This is also one reason why carotenoids can protect chlorophyll from photo oxidation[10].

From the fluorescence spectra,PE/NANO-JW-1,2,3 can effectively absorb UV which harm to crop and damage to the film for greenhouse.Fig.2 to Fig.4 demonstrate that this designed films can absorb UV between 260-340 nm and launch blue violet light between 360-480 nm.These results are in agreement with absorption spectra of chlorophyll and carotenoid.Light conversion ratio improved and blue light which photosynthesis needs can also get compensation,so that the photosynthesis be promoted and production is increased.

Thermo gravimetric analysis(TG)

As TG analysis results show,temperature of initial decomposition,maximum decomposition and final decomposition are all higher than those films due to the addition of NANO-JWM.Initial decomposition temperature of PE/DZ is 345 ℃.Initial decomposition temperature of PE/NANO-JW-1,2,3 increased 18,8 and 6 ℃than PE/DZ.The maximum decomposition temperature of PE/DZ is 466 ℃,while the maximum decomposition temperature of PE/NANO-JW-1,2,3 respectively increased by 7,6 and 3 ℃.This is due to the blocking effect of NANOJW-M which slows down the heat decomposition speed,and the heat resistance was improved significantly(Table3).

Temperature curve analysis

Fig.5 indicated that PE/NANOJW-1,2,3 have an obvious cooling effect under high temperature.This is due to the NANO-JW-M which can reflect off a part of infrared light and visible light on the surface of greenhouse.Furthermore,PE/NANO-JW-1,2,3 also has a diffuse scattering function.As the sun incidences,transmittance decreases and diffuses scattering rate increases accordingly.Thus the films have a certain cooling effect[11-13].It is further confirmed that PE/NANO-JW-2 is the most appropriate film for plant growth.

Conclusions

Different proportions PE based nano sun shading films (PE/NANOJW-1,2,3)are prepared by direct melt intercalation.According to XRD test,nano sun shading master batch(NANO-JW-M) is completely stripped in PE film.

Through TG analysis,the initial thermal decomposition temperature of nano sun shading films (PE/NANOJW-1,2,3)was higher than that of the control film(PE/DZ)is raised to 18,8,6℃,which shows the thermal stability of PE based nano sun shading films is effectively improved.

According to the UV-Vis-NIR transmittance spectroscopy of the cooling films,the results show that PE/NANO-JW-2 can provide a balanced distribution of the ultraviolet transmission,photo synthetically active transmission and near infrared effective transmission to ensure the most suitable light intensity for growth of crops.

Light-conversion function of the sun shading films are evaluated by FA.All prepared cooling films can absorb ultraviolet light (about 260-340 nm)and launch Blue light (420-430 nm)which makes blue light photosynthesis needs get compensation.The effectiveness of photosynthesis can be promoted.

Through the temperature test under the control film and nano sun shading film.The results shows that PE/NANO-JW-1,2,3 all have a cooling effect.PE/NANO-JW-1,2,3 can decrease 3.4,4.4,4 ℃relative to the control film (PE/DZ),especially the cooling effect of PE/NANO-JW-2 are the best choice.

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