Chlorination Modification Of Polyvinylidene Fluoride (pvdf) And Its Performance

High molecular weight poly (vinylidene fluoride)(PVDF) has exceptionally good thermal stability,ultraviolet radiation resistance,chemical inertness,and flexibility. These properties make the polymer an ideal candidate for many coating applications where extreme durability and high performance are required. But the polymer is high melting and insoluble in common organic solvents and its adhesion with substrates is poor. These drawbacks limit the application of PVDF.Chlorination can greatly decrease the melting point and increase the solubility of the polymers,and the chlorination process is rather simple,so we investigated the effect of chlorine substitution on the properties of PVDF.Firstly,we studied the effects of reaction conditions such as chloridizing agent,initiators and initiator concentrations,dispersing media,reaction temperature and reaction time on chlorination degree in order to find the best reaction conditions. The results showed that chlorine at a rate of 170ml/min as chloridizing agent,BPO at mass contration of 0.5% as initiator,CCU as dispersing medium and reaction temperature at 76C are the optimum conditions.Secondly,the reaction kinetics in the best reaction conditions is discussed,we find that:The factors effecting on the chlorination are so mnay,the stucture of PVDF crystal is complicated and the strongly electron-withdrawing CF2 groups deactivate the methylene carbons toward electrophilic attack by the chlorine radical,so the micro kinetics of chlorination is complex. It is difficult to analyze in math method. We discussed the macro kinetics of chlorination. The relationship between reaction time and chlorination degree of PVDF,under optimum conditions,is established,and from which,the rate equation is obtained,which reflects the change of chlorination degreewith time,that is,(a=8.9937,b=-1.1070). The results indicate that the relationship between the calculated value(Lc) and the experimental valuers) of this reaction is linear.Finally,under the optimum conditions,we synthesed the chlorinated PVDF with 1.0%-16.3% chlorine and studied the properties of the chlorinated PVDF. As a result,we find that:As the degree of chlorination increases,the crystallinity of the polymers decreases,polymer containing more than 8% chlorine appear to be amorphous;theviscosity data decreases from 57mpa .s to 40mpa . s;the softening point decreases from 163 to 130C;the solubility increases and polymers containing more than 6wt% chlorine are soluble in acetone;adherence is obviously improved;the contact angle with H2O decreases from 90 to 54;the exceptional thermal stability of chlorinated PVDF was demonstrated by thermogravimetric analysis,and in these experiments,we found chlorinated PVDF appears to be only slightly less stable than PVDF.