Study on Volatile Organic Compounds (VOCs) in Polypropylene Composites and Adsorption of Vocs by Micro-Mesoporous Silicon Materials
Supervisor:sun guang ping
Study on Volatile Organic Compounds（VOCs）in Polypropylene Compositesand Adsorption of VOCs by Micro-Mesoporous Silicon MaterialsIn order to solve the problem of air pollution caused by organic small molecules of volatile organic compounds（VOCs）released by modified polypropylene PP composite materials such as internal instrument panels and decorative materials in automobiles,the formulation design of environmentally friendly interior materials for automobiles was carried out.For the first time,we have studied and analyzed the adsorption behavior and mechanism of volatile organic compounds in automotive PP composites with new,highly functional,highly efficient and porous inorganic materials.Adding this natural inorganic mineral silica material,the opal shale,to the polypropylene PP composite,the opal shale can replace talc as a mechanical enhancer.We first discovered that the most obvious application value of this opal shale is to significantly reduce the VOCs in polypropylene composites,in particular,two molecular methylcyclohexane and 2,4-dimethylheptane with high peak area in PP composites.We first evaluated the effect of the opal shale on volatile organic compounds in PP composites,and discussed the adsorption mechanism of the opal shale on volatile organic compounds released from PP composites from the corresponding relationship between pore structure,pore size distribution and adsorption capacity.The specific surface area and pore capacity of the opal shale were determined by nitrogen adsorption experiments.The selective adsorption of two alkane molecules,methylcyclohexane and 2,4-dimethylheptane,by the microporous and mesoporous synergies of the opal shale was studied.We have found a breakthrough way to effectively reduce methylcyclohexane and 2,4-dimethylheptane emissions.This study has certain guidance for selective adsorption of small molecules of alkanes released from polymers.The main innovation of this thesis is to reduce VOCs emission by using porous lightweight shale opal as filling material with high function and high efficiency and low cost.Through the twin screw extrusion experiment of polypropylene resin monomer alone,we give the main volatile organic compounds that the PP resin monomer will release for the first time and discuss the sources of several organic compounds that volatilize of polypropylene monomer.2-methylpentane and 2,4-dimethylheptane are the transfer of free radicals in polypropylene,which are formed by thermal degradation.The 2,4-dimethylheptane is an organic small molecule with high volatilisation in PP composites.The new inorganic mineral material shale has an excellent adsorption effect on it and effectively controls the emissions of 2,4-dimethylheptane.For the first time,the additives widely used in the domestic PP plastics industry was mixed with PP resin,and the volatile organic compounds in PP composites were studied.This is of significance for reducing VOCs emission in automotive interior PP composites by selecting additives.We first discovered that methylcyclohexane is not the product of the thermal decomposition of the polypropylene resin,but the polyolefin elastomer POE（toughening agent）was introduced methylcyclohexane into the PP composite system.Methylcyclohexane is also a highly volatile organic molecule in the PP composite system.The opal shale can effectively adsorb methylcyclohexane.We have introduced the GC/MS/SNIFF olfactory system to conduct one-to-one odors of volatile organic compounds in PP composites originally.This research method is very advanced in the field of automotive plastics in China.We have found the volatile organic compounds in the PP composite materials that correspond to the unpleasant and smelly odor,which are released under the two formulas TD-5 and TD-10 developed for FAW’s PP materials.The main alkane volatile products are not the source of unpleasant odors under two formulations.Unlike in the past researches,aldehydes and ketones in PP resins were considered to be the main sources of odor.We first discovered that the chemical structure of the odor in the formula is strange,unpleasant,and even the odor material has one thing in common,that is,the long chain end or side base is double bond,and there is only one double bond.In this case,olefins have2-methyl-4-nonene,5-methyl-5-eleven,and 2,4-dimethyl-1-heptene,4-methyl-1-decene,5-methyl-5-decene,1-dodecene,4,6,8-trimethyl-1-nonene.The main content of this paper is divided into the following parts:1、The study on the reduction of VOCs emission from automotive interior trim materials was completed in the selection of resin raw materials and optimization of additives.The effects of volatile organic compounds（VOCs）in polypropylene resin monomers and the additives of PP composites on volatile organic compounds（VOCs）in polypropylene composites were studied.We first discovered that methylcyclohexane is not the product of the thermal decomposition of polypropylene system,but the polyolefin elastomer POE（toughening agent）was introduced into the PP composite system.Using the PV 3341 method（emission test standard for organic compounds from automotive interior non-metallic materials）for the analysis of polypropylene raw materials by means of a combination of headspace-gas chromatography（polar column）-mass spectrometry,for the first time,we have specifically studied that the main volatile organic compounds released by several PP raw materials are are butene,2-methylpentane,methylcyclohexane,2,4-dimethylheptane,4-methyloctane,C10C11 alkanes,C12C13alkanes and the sources of these organics are discussed.At the same time,the effects of different additives on volatile organic compounds in polypropylene composites were studied:the addition of antioxidant 1010 increased the peak area of polypropylene composites under the formula of PP/POE/talc powder.Excluding the antioxidant 1010 will cause the system to produce 2,4-tert-butylphenol with a retention time of 17.8 min,however,2,4-di-tert-butylphenol is produced by the decomposition of antioxidant 168;Decamethycyclopentasiloxane emitted by the polypropylene composite formula is a by-product brought in by the scrap-resistant HG600R;The optical stabilizer V9900 reduced the peak area of butene and 4-methyloctane.When the V9900was added 3%,the butene decreased by 30%,and the 4-methyloctane decreased by 17%.2、The odor traceability study was conducted for two odor prominent formulas in PP composite materials developed for FAW’s interior parts.GC/MS/Sniff is currently a mature and feasible method for tracing unknown sources.In this paper,the method has been applied to smell volatile organic compounds in TD-5 and TD-10 composite formulas.The content of different odor compounds and the composition of volatile organic compounds were determined.It is worth mentioning that the volatile organic compounds of olefins are the main sources of unpleasant odors in PP composites,which is different from the viewpoint that the volatiles in the PP resin are mainly aldehydes and ketones.Olefins having a double bond at one end or in the middle of the long chain have an odor and a strange smell,and are a major contribution to the unpleasant odor under the TD-5 and TD-10 formulations.4,6,8-trimethyl-1-decene,1-dodecene,methylcyclohexyldimethoxysilane are common VOCs in TD-5 and TD-10 formulations.Volatile organic compounds with strong odor irritation in PP composites under the two formulations,their one-to-one sniffing odor descriptions are unpleasant,with a rating of 1.5-2.In addition,2-methyl-4-decene,5-methyl-5-undecene is also a major source of unpleasant odor in TD-10formulations,especially the 5-methyl-5-undecene odor is described as stinky and more unpleasant.3、For the first time,we have studied the adsorption of two alkane molecules,that is,methylcyclohexane and 2,4-dimethylheptane,by microporous-mesopores of opal shale.The directed adsorption experiment of small molecules of alkane emitted in the polymer is the innovation of this paper.Methylcyclohexane and 2,4-dimethylheptane are two small molecular substances in the VOCs emission from polypropylene composites,and their peak area is very high.However,when the amount of opal shale in PP composite system increased from 2%,4%,8%,12%to 16%,the emission of methylcyclohexane and 2,4-dimethyl-heptane was greatly reduced compared with the unadded shale.When the amount of shale added was 16%,the peak areas of methylcyclohexane and 2,4-dimethylheptane were reduced by 54%and 38.9%,respectively.By increasing the amount of shale added,it was confirmed that the opal shale did have an effective reduction effect on the emission of methylcyclohexane and2,4-dimethylheptane.The specific surface area,adsorption curve,pore size and pore size distribution of light opal shale were determined by N2 adsorption method.The chemical composition of the shale was analyzed by X-ray fluorescence spectrometry（XRF）and Fourier transform infrared spectroscopy（FTIR）.The pore structure of the shale was obtained by scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.The multi-point BET measured the light weight shale LWS with a specific surface area of 94.2 m 2/g and a total pore volume of 0.317 ml/g.Through a series of studies on shale powder,we found that the strong adsorption performance of the shale is attributed to its high surface area and total pore volume.Micropores are an effective way to reduce the emissions of methylcyclohexane and2,4-dimethylheptane.The shale makes the tensile strength of the PP composite almost unchanged,the bending modulus decreases slightly,and the impact strength decreases.In summary,the micropores contained in the pores of the light weight shale（LWS）can effectively reduce the emissions of methylcyclohexane and 2,4-dimethylheptane.4、We studied the adsorption effect of shale on VOCs in polypropylene composites after heat treatment.It was found that the specific surface area of??shale was the largest、capacity of shale was the highest、pore volume of shale was the largest when the calcination temperature was 700°C compared with the heat treatment temperature of 600℃,800℃and 900℃.Therefore,in the range of 600℃to 900℃,the trend is not that the higher the calcination temperature,the larger the specific surface area of??the shale and the stronger the adsorption capacity.The effect of heat treatment on the specific surface area,total pore volume and micropores of shale in the range of 600℃to 900℃is firstly increased and then decreased.However,the amount of adsorption of 2-octene in the PP composite decreased after the heat treatment of the shale.The shale without heat treatment has a significant effect on the reduction of small molecular alkanes such as methylcyclohexane and 2,4-dimethyl heptane in the PP composite.Therefore,the reduction of crystallization water after shale calcination has a significant effect on the emission of isobutylene and 2,4-di-tert-butylphenol in the PP composite.5、Silane coupling agent is the most representative coupling agent.We use phenyltrimethoxysilane to graft the surface of shale and use phenyl functional silane coupling agent.The main design idea is that the VOCs emission from PP composite contains aromatic hydrocarbons and olefins.We expect that the phenyl functional group on the coupling agent can chemically interact with aromatic and olefinic substances after the phenyl functionalized modified opal shale tunnel.Therefore,chemical adsorption is generated to compensate for the disadvantage of desorption on the physical adsorption of shale.We modified the shale surface by acid-dissolving and chemical modification in the shale,and studied the effect of pore structure and surface properties on the adsorption performance inside the shale.The results show that the adsorption capacity of shale modified by surface silane to toluene is obviously improved,and it is not easy to desorb.