Preparation Of A Flexible PLA Melt-blown Nonwovens Humidity Sensor Based On Polyelectrolyte And The Sensitive Performance

With the rapid development of society,the portable flexible humidity sensors with the high performance and low cost have been widely used in healthcare,food storage and other industries.At present,the substrates of the flexible humidity sensor mainly include fabric,polymer film,paper materials,etc.Compared with the traditional flexible substrate,the melt-blown nonwoven materials have the advantages of simple preparation process,flexibility,good air permeability and low cost.Thus,the melt-blown nonwoven materials are suitable for being used as he substrates of the flexible humidity sensor.Polyelectrolyte has the advantages of Polyelectrolyte has the advantages of good humidity sensitivity,low cost,easy processing and strong compatibility,so it can be used as a humidity sensing material for flexible humidity sensors.However,polyelectrolyte is easy to be deliquescent under high humidity.Therefore,in this paper,biodegradable polylactic acid melt-blown nonwoven material(PLA MB)is selected as the substrate of the flexible humidity sensor,and 2-(dimethylamino(ethyl methacrylate quaternary ammonium salt)(DEB),a kind of polyelectrolyte,was used as the humidity sensing material.Furthermore,methyl methacrylate(MMA)and polyaniline(PANI)were doped with DEB to improve its humidity sensing performance.Then these humidity sensing materials are loaded on the surface of PLA MB,respectively,to prepare the PLA MB based flexible humidity sensors.The research in this paper can provide a new idea for the preparation of flexible humidity sensors for nonwoven material substrates used for monitoring humidity in various environments.DEB/MMA with different mass ratios was first synthesized by use of a crosslinking agent of 1,6-hexadiol diacrylate(HDDA).Then,DEB/MMA@PLA MB flexible humidity sensor was fabricated by loading DEB/MMA with different mass ratios on PLA MB surface vis UV curable crosslinking reaction.It was found that DEB/MMA could formed uniformfilm on the surface of PLA MB.Compared with the original PLA MB,the terminate thermal decomposition temperature of DEB/MMA@PLA increased.When the mass ratio of DEB/MMA was 1:2,DEB/MMA@PLA MB sensor had good sensing performance in the range of relative humidity ranging from 10%to 90%,high linearity(R~2=0.970),fast response time(10-80 s),long-term stability and good cyclic stability.Compared with the original PLA MB,the tensile strength of the DEB/MMA@PLA MB flexible humidity sensor decreased,but the elongation at break significantly increased.Next,PANI was synthesized by chemical oxidation method.Aniline was monomer,ammonium persulfate(SSA)was selected as oxidant and sulfosalicylic acid(APS)were the doped acid.Then PANI was doped with DEB/MMA with the mass ratio of 1:2.PANI/DEB/MMA@PLA MB flexible humidity sensor was prepared by loading PANI/DEB/MMA onto the surface of PLA MB vis UV curing reaction.The results showed that PANI/DEB/MMA may formed uniform film on the surface of PLA MB.Compared with DEB/MMA@PLA MB flexibly humidity sensor,the terminate thermal decomposition temperature of PANI/DEB/MMA@PLA MB was further.enhanced.When the doping concentration of PANI was 3%,PANI/DEB/MMA@PLA MB sensor had better sensing performance in the range of relative humidity from 10%to 90%,higher linearity(R~2=0.997),faster response time(10-30 s),good long-term stability and cyclic stability.Compared with the DEB/MMA@PLA MB flexible humidity sensor,the tensile strength and elongation at break of PANI/DEB/MMA@PLA MB sensor significantly enhanced its.Finally,the graphene(GPE)was printed on the surface of PLA MB by screen printing method to prepare PLA MB with GPE conductive coating(G-PLA MB).Then PANI/DEB/MMA with the optimal ratio was loaded on the surface of G-PLA MB by UV curable crosslinking reaction to obtain PANI/DEB/MMA@G-PLA MB flexible humidity sensor.Through characterization and testing,it was found that PANI/DEB/MMA formed a layer uniform film with larger specific surface area on the surface of G-PLA MB.The introduction of GPE further improved the thermal stability of PANI/DEB/MMA@G-PLA MB flexible humidity sensor.Compared with PANI/DEB/MMA@PLA MB flexible humidity sensor,PANI/DEB/MMA@G-PLA MB flexible humidity sensor had the best sensing performance in the range of relative humidity from 10%to 90%,the highest linearity(R~2=0.992),the fastest response time(5～15 s),and the best long-term stability and good cyclic stability.