| With the development of military technology and contemporary chemical industry,the threat of new chemical agents on the battlefield and the frequent occurrence of hazardous chemical accidents in social production activities have put forward high protective requirements for chemical protective clothing.The traditional military chemical protective clothing prepared by butyl rubber tape can hardly meet the protection needs in complex contaminated environments.For this reason,protective clothing fabrics have been prepared using fluorine resin film laminated with rubber tape.Fluorine resin membrane is an ideal chemical protection material because of its stable structure,excellent resistance to acid and alkali corrosion and chemical permeability,which can improve the protective performance of protective clothing and retaining the good flexibility of rubber protective clothing simultaneously.However,the non-polar surface and low surface energy of fluorine resin membrane make it difficult for fluorine resin to be bound and integrated to other materials.Currently,it remains a great challenge to improve the surface polarity of fluorine resin membranes without destroying their main structures in attempt to achieve multilayered fluorine resinrubber composites for the application of high-grade chemical protective clothing.In this research,we designed and built an experimental platform to modify three typical fluorine resin membranes,namely,non-perfluorinated ethylene tetrafluoroethylene(ETFE),perfluorinated polytetrafluoroethylene(PTFE)and XXX(FEP),using atmospheric pressure DBD plasma under five atmosphere conditions,i.e.,helium(He),helium/acrylic acid(He/AA),helium/ammonia(He/NH3),helium/divinylbenzene(He/DVB)and helium/methacrylic acid(He/MAA).The effects of treatment atmospheres,working voltages,treatment times and gas flow rates on the modification effect of the fluorine resin film were investigated.ATR-FTIR,IR Pi FM,XPS,SEM,AFM,water contact angle test,T-peel strength test and thermal aging test were used to characterize the functional groups,elemental concentration,morphology and roughness,hydrophilicity and bondability of the membrane surface.The prime focus of this work is to evaluate the changes of surface hydrophilicity and adhesive strength of the membranes before and after plasma treatments,and investigate of the related mechanism of surface modification.The details are as follows:(1)The modification effects of He plasma and He/AA plasma on fluorine resin membranes were analyzed and compared.The changes of the surface chemical properties of the fluorine resin membranes were analyzed using ATR-FTIR,IR Pi FM and XPS,which demonstrated that the helium plasma treatment can generate active sites on the membrane surface and introduce oxygen-containing groups to the surface by adsorbing H2 O,O2 and CO2 from the air.In the other case,the He/AA plasma modification could produce polyacrylic acid(PAA)on the surface of the fluorine resin membranes,which can be further divided into deposited polyacrylic acid(d-PAA)and grafted polyacrylic acid(g-PAA).Although g-PAA occurred only at the nano-level of the membrane surface,it has good stability because most of the g-PAA was retained on the membrane surface even after ultrasonic washing.(2)SEM and AFM morphological analysis showed that He plasma treatment could produce nano-level etching effect on the surface of fluorine resin membrane and increase the surface roughness of fluorine resin membrane;He/AA plasma treatment could produce PAA on the surface of fluorine resin membrane,and a small amount of PAA was randomly distributed at the beginning to increase the roughness Ra value of ETFE membrane surface,and PAA became uniformly distributed on the membrane surface after a large amount of PAA was produced.Instead,the Ra value was reduced to 4.01 nm,which was comparable to the roughness of the original membrane.After the removal of d-PAA by ultrasonic washing with acetone,the exposed g-PAA again led to an increase in the roughness of the membrane surface with Ra = 5.59 nm.AFM studies on the modified PTFE membrane and modified FEP membrane showed that the residual g-PAA had a certain filling effect on the stress fine lines on the original membrane surface,and the size of g-PAA molecular chains should be on the nanometer scale.(3)He plasma treatment generates active sites on the membrane surface,thus reducing the water contact angle and improving the hydrophilicity of the membrane.Compared with FEP and PTFE,ETFE membrane treated with He plasma showed a more significant decrease in water contact angle,and the effect of active site generation is more essential than the effect of micro-nano morphological differences on hydrophilicity of fluorine resin membrane surface.The He/AA plasma treatment introduced PAA on the surface of the fluorine resin membrane,which increased the polarity and surface energy of the membrane surface,and the water contact angle of the modified ETFE membrane could be reduced from 95.8° to 49.95° in the original membrane.The d-PAA removal by washing resulted in a rebound of the water contact angle due to the presence of surface g-PAA,but it was still smaller than that of the unmodified fluorine resin membrane.The stress fine lines on the surface of FEP and PTFE membranes had an effect on the removal of d-PAA,and the change in surface water contact angle was the result of the combined effect of the surface chemistry and surface morphology of the membranes.The He plasma treatment can improve the peel strength of ETFE membrane up to 9.72 N/cm,which is much higher than 0.53 N/cm of the original membrane.The weak boundary layer existing on the surface of the modified membrane has a greater influence on the bonding effect.The peel strength of the ETFE membrane after He/AA plasma treatment increased gradually with the increase of acrylic acid concentration,and the peel strength reached a maximum value of 13.64 N/cm,which was 25.74 times higher than that of the original membrane.After ultrasonic washing with acetone solvent to remove the surface d-PAA,the peel strength value was still up to 11.75 N/cm,which was also higher than the maximum bond strength after He plasma treatment.These results indicate that the residual g-PAA on the membrane surface plays an important role in the bondability of the membranes.(4)The modified specimens were aged at 100°C for 96 h.The water contact angle on the surface of the He plasma-modified membrane became larger,the hydrophilic effect was reduced,and the peel strength of the bonded specimens decreased from 9.72 N/cm to 8.73 N/cm,which was still much higher than that of the unmodified original membrane.The He/AA plasma treated ETFE membrane was treated with hot air for a long time,which led to the aging of PAA on the surface,and the surface hydrophilicity and bondability also decreased.The bonding strength of the modified ETFE membrane before and after washing decreased from 13.63 N/cm and 11.74 N/cm to 12.29 N/cm and 9.70N/cm after aging,respectively,indicating that the fluorine resin membrane surface of the plasma modification effect has good thermal stability.(5)The effect of He/NH3 plasma treatment of fluorine resin membrane was similar to the result of He plasma treatment.The He/DVB plasma and He/MAA plasma treatments were weaker than the He/AA plasma treatment.This research adopts atmospheric pressure DBD plasma to modify the surface of chemically inert fluorine resin membrane,which effectively improves the hydrophilicity of the surface of fluorine resin membrane and the bondable performance of fluorine resin membrane.Besides,this work reveals the mechanism of plasma modification on the surface of fluorine resin membrane through analyzing the effect of treatment conditions and membrane types on the surface properties and bondability of membranes.This work provides new insights into solving the technical problems that have long plagued the surface bonding of fluorine resin membrane,and overcomes the key technical link in the development of protective fabrics for high-grade chemical protective clothing. |
PDF Full Text Request