Study On Control Technology Of VOC Emissions From The Strengthened Poplar Wood

Fast growing poplar wood has replaced natural forest wood as the main material to meet the increasing demand.Due to its characteristics such as low density,poor quality,and readily susceptible to biodeterioration,fast growing poplar wood is limited to indoor applications.Therefore,it is important that fast growing wood is modified by chemicals for improving its physical,mechanical,and biological properties.However,low-density wood treated with resin penetration also released VOC and formaldehyde,resulting in poor IAQ.This paper researched on poplar wood treated with UF resin.The influence factors of VOC emissions from treated wood were analyzed and the optimal production process was obtained on the premise of meeting the requirements of mechanical performance,processing costs and environmental performance.Furthermore,it will be discussed whether a sustainable reduction or control of emissions from wood treated with the optimal process parameter can be achieved by modifying UF resin with TiO2,SiO2 and urea under the conditions of ultrasound and ultraviolet.The main conclusions and the mechanism of VOC and formaldehyde control technology are summarized as follows:(1)Aldehydes and alkanes were the predominant compositions indentified in the VOC emissions,although low amounts of ketones,terpenes and alcohols were also found.VOC components were not affected by production parameters and the increase of WPG.(2)VOC emissions are obviously influenced by the process parameter,which is directly related to the degree of impregnation of low molecular weight thermosetting resin into low-density wood.With increasing the WPG,there was a clear increase in the TVOC,aldehydes alkanes and formaldehyde emissions.However,the emissions started to decrease when the WPG continuously was over a certain value(37.64%-44.41%in this work).(3)In accordance with the BBD experimental design,the models between the process parameters and 4 response values(MOE,WPG,formaldehyde emissions and TVOC emissions after 28 days)were established by using the software of design expert.The linear regression equations of MOE and WPG about the process parameters were obtained,while the regression equations of formaldehyde emissions and TVOC emissions were multivariate.The significances and R-squared of the equations were also better and the effect of process parameters on 4 response values,in descending order of magnitude,were the resin concentration,pressing time and pressure.When the mechanical properties,production costs and environmental performance were comprehensively considered,the optimal process parameters of strengthened poplar wood were the resin concentration 32%,pressing time 2.5 h and pressure 0.89 MPa.The feasibility and accuracy of optimal process parameters from the BBD experimental design were proved by the verified experiments.(4)Nano-TiO2,nano-SiO2 and urea were blended with urea-formaldehyde resin under different conditions,respectively.According to the optimal process parameters,poplar woods were impregnated with mixed resins.VOC emissions,formaldehyde emissions and mechanical properties of treated woods were detected.VOC and formaldehyde emissions effectively decreased and mechanical properties obviously improved because of the addition of TiO2 and SiO2,which were significantly impacted by the amount of TiO2 and SiO2.With the increase in the amount of TiO2 and SiO2,VOC and formaldehyde concentrations decreased and mechanical properties increasing first.However,the above performances were reduced when the amount reaches a certain value.When the dosages of TiO2 and SiO2 were also 0.5%,the removal efficiency of TVOC,aldehydes,alkanes and formaldehy was the best and the mechanical strength was the highest.Compared with wood only treated with UF resins,removal rates of VOC and formaldehyde after 28 days from the samples of 0.5%TiO2 were 48.58%and 52.98%and the ones of 0.5%SiO2 were 21.42%and 48.37%,respectively.After urea was added to UF resins,the strength of samples improved.The initial release of formaldehyde emissions significantly decreased while formaldehyde concentrations after 21 days were close to the ones from the impregnated wood with untreated UF resins.The reason was that the unstable reaction of urea and formaldehyde leaded to the release of formaldehyde from the samples.(5)The mechanism that environmental and mechanical performances of samples were influenced by the addition of TiO2 and SiO2 was analyzed by FTIR.The results showed that TiO2 were effectively impregnated into the poplar wood.Because methylolurea(-NH-CH2OH)from UF resins reacted with the free radicals in wood or the condensation reaction of methylolurea formed acylamino in the field of the ultrasonic and high reactive unsaturated bonds on the surface of TiO2,it was helpful to improve the cohesion of resins and bonding strength between UF resin and wood.After adding SiO2,the number of hydroxyl groups on the surface of cellulose was reduced.It was beneficial to improve the dimensional stability of the wood.(6)The mechanism that environmental and mechanical performances of samples were influenced by the addition of TiO2 and SiO2 was analyzed by SEM/EDS.Compared with the natural wood,part of pits of treated wood with UF resins were blocked,and UF resin uniformly dispersed in the inner wall of the vessels.This indicated that it could not only improve the strength of wood,but also production cost could be saved when the vessels were not completely filled at the WPG level in this work.The impregnation of UF resins into the poplar wood was not affected by the addition of TiO2 and SiO2.Low levels of TiO2 and SiO2 could be uniformly mixed with UF resins under the conditions of ultrasonic dispersion and could be impregnated into the wood.With increasing amount of TiO2 and SiO2,Ti and Si percentages which were detected by EDS also increased,but colloid structure which was formed from nanoparticles and resin could clearly observed in the figure of SIM when the addition of TiO2 and SiO2 reached 0.8%and 1.0%,respectively.