| In this paper,poly(vinylidene fluoride-chlorotrifluoroethylene)(P(VDF-CTFE),VDF:CTFE=1:4)membrane was prepared by solution casting method.The membrane was radiated with 60Co source by different doses of gamma irradiation at air atmosphere and room temperature.Several methods,such as FTIR,XPS,1HNMR,GPC,XRD,SAXS,SEM,TGA,tensile test and ESR were used to study the change of structure and properties of P(VDF-CTFE)membranes after gamma irradiation.The structural and property changes of P(VDF-CTFE)membrane radiated under high dose(150,300,600,900,1200kGy)and low dose(10.2kGy)gamma irradiation were analyzed,and the reasons for the changes were discussed.The experimental results showed that the residual THF in the P(VDF-CTFE)membrane prepared by solution casting with THF was difficult to be completely removed due to the large thickness(400?600?m).These residual THF will be involved in the gamma irradiation reaction,promote dehydrohalogenation reaction,and lead to introduce of the C=C bonds into polymeric chains of P(VDF-CTFE).These C=C bonds make the color of the membrane from translucent white to black.As a comparison,the color of P(VDF-CTFE)membrane made with ethyl acetate(EtOAc)only turned to yellow under the high dose of gamma radiation,and even no change under low dose of gamma radiation.The reason is that the polarity of THF is stronger than EtOAc,and the oxygen atom in THF can combine with proton,thus can be regarded as a lewis base.Therefore it is beneficial to absorb the halide during gamma radiation,and thus promote the dehydrohalogenation reaction.When P(VDF-CTFE)-THF membrane radiated by high dose of gamma radiation,the color of the membrane directly changed from translucent white into black.FTIR results showed that the new peak in 1631cm-1 was attributed to C=C stretch vibrations.These C=C bonds might result in the change of membrane color.With the increase of radiation dose,the peak intensity of C-H,CF,CF2 and C-Cl gradually weakened,suggesting that the C=C bonds was introduced into polymeric chains by dehydrohalogenation reaction during radiation.SEM photos showed that after 1200kGy radiation,P(VDF-CTFE)-THF membrane obviously experienced irradiation embrittlement.This result was also confirmed by tensile test.The mechanical properties of P(VDF-CTFE)-THF membrane decreased obviously,especially the sample of 1200kGy.XRD results showed that the high dose gamma radiation can directly reduce the degree of crystallinity of P(VDF-CTFE)-THF membrane and affect the ability of recrystallization of P(VDF-CTFE)melt during cooling.SAXS results showed that P(VDF-CTFE)-pTHF film has a laminated structure,whose long period L=31.4nm.After radiation,hole structure may appear in the film and cover up the original scattering signal of long period structure.When P(VDF-CTFE)-THF membrane radiated after low dose of gamma radiation,the color of membrane changed from translucent white to brown,then gradually deepened,and finally become black.FTIR results showed that unsaturated C=C bonds were introduced into P(VDF-CTFE)-THF membrane by gamma radiation,leading to the change of color of membrane.This conclusion was also confirmed by 1H NMR and XPS.GPC and TGA results showed that the properties of P(VDF-CTFE)-THF after low dose radiation changed not obviously.The result of tensile test showed that the tensile strength and yield strength P(VDF-CTFE)-THF film after low dose gamma radiation great increased.In contrast,the structure and properties of P(VDF-CTFE)EtOAc membrane did not change significantly after low dose gamma radiation.Finally,ESR was used to characterize the free radicals generated after irradiation,and the possible mechanism of dehydrohalogenation reaction induced by irradiation was proposed... |
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