Estimation Of The Aging Resistance Of Membrane Structure Materials Under Thermal, Humid And Ultraviolet Conditions

The properties and functions of membrane structure materials are affected by sunlight,temperature,moisture,atmospheric pollutants and so on in the course of using.With the time extended,they will appear aging phenomenon which present as the decay of physical and chemical properties,such as strength decreases,color darkens,thus the functions and properties will lose partially or even completely.Therefore, membrane structure materials require not only certain resistances to light, heat,wind,and humidity,but also some thermal insulation,transmittance, etc.In view of them,several existing materials were evaluated and screened in this aspect,and ePTFE(expanded PTFE)and PVC(polyvinyl chloride)membrane structure materials were selected as the experimental objects.Considering that the thermal,humid and ultraviolet effects are more remarkable,especially when the membrane structure materials are used in the tropical humid windy environment,ePTFE and PVC membrane structure materials were investigated through the accelerated aging tests under 100℃and 125℃thermal conditions,70℃and 100℃hygrothermal conditions,and ultraviolet condition respectively.Their respective aging resistances to heat,humidity and light were evaluated,so as to accumulate data for the correct selection,performance estimation, and aging behavior prediction of membrane structure materials,and to establish reliable evaluation methods.By measuring the coating surface morphology,tensile property,tearing performance,transmittance,thermal insulation and humidity resistance of ePTFE and PVC membrane structure materials,the performance differences of the same materials under different conditions and the different materials under same condition were discussed and analyzed, The results were obtained as follows:(1)Under thermal conditions,ePTFE membrane structure material coating surface morphology almost unchanged;the maximal loss rates of the fracture stress,tear strength and transmission were higher than 19%, 20%and 4.1%respectively;the ratios of thermal conductivities with different time to the initial value were fluctuate from 97.2%to 104.1%; the changes of water vapor transmission were less than 2 times of the initial value.PVC membrane structure material coating appears wrinkling surface or cracks;the maximal loss rates of the fracture stress,tear strength and transmission were higher than 35%,33%and 96.8% respectively;the maximal growth rates of the thermal conductivity and water vapor transmission were higher than 21.2%,and 500%respectively. Therefore,the impairments of PVC membrane structure material were more severe under thermal conditions.(2)Under hygrothermal conditions,ePTFE membrane structure material coating became rough and existed holes;the maximal loss rates of the fracture stress,tear strength and transmission were higher than 17%, 16%and 6.9%respectively;the maximal growth rates of the thermal conductivity and water vapor transmission were higher than 7.4%,and 200%respectively.PVC membrane structure material coating became very rough and had more holes;the maximal loss rates of the fracture stress,tear strength and transmission were higher than 44%,40%and 70.5%respectively;the maximal growth rates of the thermal conductivity and water vapor transmission were higher than 10.7%,and 350% respectively.Therefore,ePTFE was superior to PVC membrane structure material in the hygrothermal aging resistance.(3)Under ultraviolet condition,both ePTFE and PVC membrane structure materials coatings unchanged basically;the fracture stress,tear strength,transmittance and thermal conductivity fluctuated between -2.5%and 2.5%around their respective initial value;water vapor transmission fluctuated within 0.5～1.5 times of the initial value respectively.Therefore,both of the two materials had strong ultraviolet aging durability.(4)The damage extent of all properties of the same materials aggravated with the temperature increase under thermal or hygrothermal conditions.The loss rates of the fracture stress,tear strength of ePTFE membrane structure material were higher than 17%,18%and 15%,16% under 100℃thermal and hygrothermal conditions respectively;The loss rates of the corresponding indexes of PVC membrane structure material were higher than 45%,40%and 25%,30%respectively.This shows that the damage extent of the tensile property of the same materials was more severe when they were aged under hygrothermal condition than that under thermal condition,obviously,humidity intervention accelerated the aging of materials.