The Fabrication And Properties Of Photochromic Wood-Plastic Composites

Wood-platic composites(WPCs)are a group of innovative green building materials consisting of mainly renewable resources.Now WPCs have been mainly used in building industry,such as outdoor architecture,outdoor surface floor,interior or exterior building hanging boards.A few of WPCs have been used in automotive products such as automotive interior decorations.It's always being a topic issue about how to expand the applications of WPCs furthermore.This research has proposed that giving WPCs the function of photolumisence,then the decorations of covering have been modified too.This functional WPCs are respected to used in ultraviolet light sensors,photosensitive indicators indoor or outdoor,decorations,the art design of enviroment,the furniture productions,even as the replacement of some optical components.The main contents and conclusions of this paper are shown as follows.(1)Photochromic wood-plastic composites(P-WPC)were fabricated through hot-pressing method.The functional additives were photochromic powders and the matrix was polyprolene,then the composites of polyprolene and photochromic powders were pepared.This comosites were hot pressed into potochromic surface layers with lmm thickness.Then the surface layers were hot pressed onto the surface of high density polyenthylene wood-plastic composites.The analyzing methods including SEM,X-ray photo-electric spectrometry,FTIR and Vis-UV light spectrum were carried out.The results showed that photochromic powders was sphere with diameter between 1 ?m-6 ?m and it could absorb the UV light with wave length between 350nm-400nm.The main component of the photochromic powders were spirooxazine and the derivative.(2)Dimethyl silicone oil(commonly known as white oil)was added into one group of the composites of polypropylene and photochromic powders while the fabrication process.It was expected as lubricant agent in order to modify the distribution of photochromic powders in the polypropylene matrix.The observations of SEM showed that two groups of samples all had behaved good uniformity of the distribution of photochromic powders.Whether the dimethyl silicone oil was added or not diden't has significant effect on the distribution of photochromic powders in the polypropylene matrix.Because the surface thickness of the P-WPC fabricated as the forward method was only 1mm,so the content of photochromic powders in the surface layers should not lower than 2%.The artificial aging test showed that the addition of photochromic powders had obviously effects on the time of keeping the potochromic function.So more addition of photochromic powders could bring longer fatigue resistance time.(3)Co-extrusion method was used to prepare photochromic wood-plastic composites(CP-WPC)with core-shell structure.The shell layer was the composites of high density polyenthylene(HDPE)and potochromic powders.The core was HDPE WPCs.There were two different methods of preparing the samples to test physical and mechanical properties of CP-WPC.One type of the samples was with the whole co-extrusion structure and the other type was without the whole co-extrusion structure(just remaining the top and bottom surface layers).The indexes of physical and mechanical properties of these two types showed the same changing tendency.The one-way analysis of variance(one-wayANOVA)was carried out.The results showed that the addition of photochromic powders in shell layer only had significant influence with the flexture properties of whole co-extrusion samples and didn't have siginificant influence with ohrt indexes.The SEM showed that there were no cracks or interfaces between the shell layer and the core,so the interface between the shell layer and the core was very well.The artificial aging test and whether aging test showed that the addition of photochromic powders in shell layer would directly influence the fatigue resistance time and the colour saturation would be higher with the increasing of the addition of photochromic powders in shell layer too.(4)The physical and mechanical properties of CP-WPC was not very well enough,the chopped carbon fibers(CCF)was added into the shell layer as a try.In order to identify the effect of the length of CCF,the interfaces between CCF and matrix on the properties of the composites,firstly the CCF was added within the whole compsites.The results showed that the composites with CCF of 4mm length behaved superior than others and the maleic anhydride grafted polyethylene(MAPE)could obviously play good ef-f-ect as the coupling agent between the CCF and HDPE.Then the CCF reinforced co-extruded photochromic wood-plastic composites(CCF-CP-WPC).The CCF was only added into the shell layer.The physical and mechanical properties,the colors before and after the irradiation of UV light,artificial aging test and weather aging test were all carried out.The results showed that flexure strength and tensile strength would increase obviously when the addition of CCF in shell layer was 6%and above.But the reaults of colors test and the aging test all showed that there were seriously negative effects on the potochromic function of the composites.So this reinforcing method was not adaptable to CP-WPC.(5)Through adding wood powders with different weight ratio into the shell layer of co-extruded photochromic wood-plastic composites,the wood powders reinforced co-extruded photochromic wood-plastic composites(W-CP-WPC)were fabricated.It was found that the physical and lmechanical properties of CP-WPC prepared by this method could reach the common HDPE WPCs.And no matter adding wood powders or not into shell layer the effect on the photochromic function of CP-WPC were very little.The optimun addition of wood powders was 2%?6%.The flexure strength of W-CP-WPC could come up to about 58Mpa(without the whole co-extrusion structure).The results of color testing showed that the samples had the capacity of phototropy.Chromatic aberration between irradiation of UV light before and after of the samples behaved a gradual decline tendency following with the increasing of the addition of wood powders in the shell layer,but the decrease was not very big.Artificial aging test and weather aging test both showed that the fatigue resistance time of W-CP-WPC was longer than CP-WPC because there are some UV sensitive component exsisting in the wood powders.These components could absorb some UV light then the fatigue resistance time of W-CP-WPC became longer.Comprehensively considering the propertiesand appearances,the method of adding wood powders into shell layer was the best fabrication method of preparing the CP-WPC.