Study On Irradiation Effect And Irradiation Grafting Modification Of ETFE

Fluorinated polymers are used in many industrial equipment because of their high stability to temperature,chemicals,radiation and their unique high stability.Among them,some fluorinated polymers,such as ethylene-tetrafluoroethylene copolymer（ETFE）,are widely used in pipelines,insulated wires and battery separators under harsh conditions due to the high stability of fluorine chemicals and the melting processability of thermoplastic polyolefins.When ETFE is used in strong radiation environment or in the process of ETFE functionalization irradiation modification,ETFE will inevitably be radiated by various high-energy charged particles.Under the action of high energy,the bonding electron cloud can quickly change into the breaking bond energy,resulting in a series of physical and chemical changes in the internal molecules of ETFE,such as bond breaking,free radical formation,carbonization,surface molecular desorption and dehydrogenation,amorphization,and cross-linking between small molecular monomers.Its inherent physical,chemical,mechanical and thermal properties are changed,which affect its life and stability during using.In order to clarify the change mechanism between structure and properties of ETFE film during irradiation,ETFE films were irradiated by electron beam in the absorbed dose range of 0～300 k Gy,and the stretching deformation behavior of ETFE films irradiated with different absorbed doses was studied by small angle X-ray scattering（SAXS）combined with in-situ uniaxial stretching.The effects of different absorbed doses on the structure and properties of ETFE films and the microstructure evolution during uniaxial stretching were studied.Subsequently,polyacrylic acid（PAA）was grafted on the surface of ETFE film by electron beam co-irradiation grafting method.The effect of irradiation with different absorbed dose on grafting was studied.The structural properties and microstructure evolution of ETFE film grafted with PAA（ETFE-PAA）during uniaxial stretching were analyzed by SAXS technology combined with in-situ uniaxial stretching.The main conclusions are as follows:（1）The surface of ETFE film is oxidized after irradiation.New infrared characteristic peaks appear at 1758 cm^-1and 1850 cm^-1,and the internal molecular chain is broken to produce alkane free radicals.When ETFE is irradiated at low doses,the proportion of small molecular chains is increases continuously.With the increase of absorbed dose,the molecular main chain rupture continues to increase,the oxidation of the membrane surface gradually increases,the long period of ETFE becomes shorten,and the radius of gyration becomes smaller.When the absorbed dose is 300 k Gy,the long period of ETFE and radius of gyration are the smallest,which are respectively 41.89 nm and 7.55 nm.However,the crystal structure of ETFE film remains unchanged after irradiation,and X-ray diffraction peaks appeare at 2θ=19°.（2）In the range of 0～300 k Gy absorbed dose,with the increase of absorbed dose,the breaking strength and elongation of ETFE increase first and then decrease.When the absorbed dose is 120 k Gy,the breaking strength and elongation of ETFE reach the maximum,which are 136.8 MPa and 135.8%,respectively.In addition,stretching has a certain effect on the thermal properties and lamellar crystal of ETFE.Compared with the properties of unstretched ETFE film,the melting point and crystallinity of ETFE after stretching show a certain increase,and the crystallization temperature shows a significant downward trend when the range of absorbed dose is 0～300 k Gy.At the same time,stretching also destroys the lamellar structure of ETFE.As the stress increases,the scattering ring image gradually changes from a circular shape to a semi circular shape and eventually to an elliptical shape,and an obvious orientation structure appears in the meridian direction.The size and spacing of the crystal region tend to be uniform,resulting in the continuous enhancement of the scattering peak signal and the continuous decrease of the long period.（3）After ETFE irradiation grafting of PAA,compared with the unmodified ETFE film,ETFE-PAA shows new C=O infrared characteristic peaks at 1725 cm^-1,and new XPS characteristic peaks of C=O and C-O at 288.2 e V and 286.3 e V,respectively.The contact angle decreases from 102°to 44°,and the thermal decomposition process changes from one decomposition stage of ETFE to four decomposition stages of ETFE-PAA,which indicates the successful grafting of PAA onto the surface of ETFE film.In addition,with the increase of absorbed dose,the grafting rate increases,and the radius of gyration and crystallinity decrease.（4）In the range of 0～120 k Gy absorbed dose,with the increase of absorbed dose,the breaking strength and elongation of ETFE-PAA show a gradually decreasing trend.When the absorbed dose is 120 k Gy,the breaking strength and elongation of ETFE-PAA reach the minimum,which are respectively 7.7 MPa and 14.5%,and the mechanical properties are completely lost.Under the condition of meeting the mechanical properties requirements of the battery separator for ETFE,the optimal absorbed dose is 60 k Gy.The prepared ETFE-PAA-60 has good hydrophilicity and mechanical properties.The contact angle,breaking strength and elongation of ETFE-PAA-60 are 68°,13.0 MPa and 72.6%,respectively.（5）Stretching can change the thermal properties of ETFE-PAA and destroy the lamellar structure of ETFE-PAA.In the range of 0～120 k Gy absorbed dose,the melting point and crystallinity of ETFE increase with the increase of absorbed dose,and the crystallization temperature shows a significant downward trend.There is not obvious scattering peak signal in the microstructure,and there is no long period structure.However,the scattering ring image gradually changes from a circular shape to an elliptical shape,and there is obvious orientation structure in the meridian direction.The scattering intensity of ETFE-PAA decreases continuously.