Preparation Of Alkali Catalyzed Polyvinyl Alcohol Carbonate Sponge Materials And Research Of Electrical Performance

The preparation of the conventional polyvinyl acetal sponge generally needs to undergo two processes of condensation reaction and foaming. The condensation reaction process means that polyvinyl alcohol and aldehydes are condensed to polyvinyl acetal compounds under acid catalysis. The foaming process means that polyvinyl acetal compounds are foamed to polyvinyl acetal sponge through the action of aerating powder. Aldehydes are a class of high toxic organic compound, the polyvinyl acetal sponge prepared by aldehydes often contains free aldehydes which can cause some damage to human health. In order to reduce the influence of free aldehydes inside polyvinyl acetal sponge on human health, the purpose of this dissertation is to prepare a sponge without free aldehydes. Therefore, aldehydes are replaced by dimethyl carbonate, and the condensation reaction is replaced by transesterification, and then polyvinyl alcohol carbonate sponge and expanded graphite /polyvinyl alcohol carbonate composite sponge are prepared without free aldehydes in the dissertation. The research of entire dissertation consists of the following four aspects.1. Preparation and characterization of polyvinyl alcohol carbonate spongeUnder the alkaline catalysis of K2CO3, polyvinyl alcohol carbonate was synthesized via a transesterification of polyvinyl alcohol(PVA) and dimethyl carbonate(DMC); and then, the polyvinyl alcohol carbonate was foamed to polyvinyl alcohol carbonate sponge under the action of n-pentane used as the aerating powder; at last, the structure of polyvinyl alcohol carbonate was confirmed by IR, and the polyporous morphology of polyvinyl alcohol carbonate sponge was also confirmed by SEM. In order to screen the optimum condition which prepared polyvinyl alcohol carbonate sponge, the effects of H2 O, K2CO3, PVA,polyoxyethyleneoctylphenyl-10(OP-10) and n-pentane of dosage on the water retention capacity of polyvinyl alcohol carbonate sponge were investigated, and the effects of the reaction temperature and reaction time were also investigated. On the basis of the investigations, the optimum condition which used transesterification-foaming technology to prepare polyvinyl alcohol carbonate sponge was screened in accordance with the maximum water absorption. The optimum condition was obtained as follows: H2 O dosage was 50.00mL;K2CO3 dosage was 2.00 g; PVA dosage was 9.00 g; OP-10 dosage was 4.50 m L; the dosage ofn-pentane was 5.00mL; reaction temperature was 75℃; reaction time was 2.5 h.2. Preparation of alkaline expanded graphiteUsing the method of ultrasonic radiation,-100 mesh of flake graphite and three doses of Na2CO3 as raw materials, three kinds of alkaline expanded graphite were prepared; then, the their pH values were measured respectively, which were pH(Na2CO3,3.00g) = 10.49,pH(Na2CO3,4.00g) = 10.61 and pH(Na2CO3,5.00g) = 10.73; lastly, the alkaline expanded graphite prepared by 4.00 g Na2CO3 was selected as the alkaline catalyst in the preparation of expanded graphite/polyvinyl alcohol carbonate composite sponge through the comparison with K2CO3 alkalinity.3. Preparation and characterization of expanded graphite/polyvinyl alcohol carbonate composite spongeUnder the catalysis of alkaline expanded graphite, polyvinyl alcohol carbonate was synthesized via a transesterification of PVA with DMC, and expanded graphite and polyvinyl alcohol carbonate were mixed together to form expanded graphite/polyvinyl alcohol carbonate composite; then, the expanded graphite/polyvinyl alcohol carbonate composite was foamed to expanded graphite/polyvinyl alcohol carbonate composite sponge under the action of n-pentane used as the aerating powder; lastly, the cross-linked structure of expanded graphite and polyvinyl alcohol carbonate was confirmed by IR, and the polyporous morphology of expanded graphite/polyvinyl alcohol carbonate composite sponge was characterized by SEM. In order to screen the optimum dosage of alkaline expanded graphite which prepared expanded graphite/polyvinyl alcohol carbonate composite sponge, the effect of the dosage of alkaline expanded graphite on the water retention capacity of expanded graphite/polyvinyl alcohol carbonate composite sponge was also investigated. The reaction condition was as follows: H2 O dosage was 50.00mL; K2CO3 dosage was 2.00 g; PVA dosage was 9.00 g; OP-10 dosage was 4.50mL; the dosage of n-pentane was 5.00mL; reaction temperature was 75℃; reaction time was 2.5 h, on the basis of the investigation, the optimum dosage of alkaline expanded graphite which used transesterification-foaming technology to prepare expanded graphite/polyvinyl alcohol carbonate composite sponge was screened in accordance with the maximum water absorption. The optimum condition of alkaline expanded graphite was obtained as follows: the dosage of alkaline expanded graphite was 1.60 g.4. Electrical performance investigation of expanded graphite/polyvinyl alcohol carbonate composite spongeThe surface resistance of the expanded graphite/polyvinyl alcohol carbonate composite sponge was measured using the environmental megohmmeter(ACL800), and the influence of alkaline expanded graphite dosage on the surface resistance of expanded graphite/polyvinyl alcohol carbonate composite sponge was studied. On the basis of those, it was found that the surface resistance of expanded graphite/polyvinyl alcohol carbonate composite sponge was4.36×107ohms /sq when the dosage of alkaline expanded graphite was 1.60 g. In accordance with the relationship of surface resistance and antistatic properties, it was confirmed that expanded graphite/polyvinyl alcohol carbonate composite sponge was a sponge with antistatic performance. In addition, the effect of the relative humidity on the surface resistance was also studied, and it was found that the surface resistance of expanded graphite/polyvinyl alcohol carbonate composite sponge would reduce with the increase of relative humidity.