JAPAN TAPPI JOURNAL

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The graft copolymerization of vinyl acetate onto pulp and the hydrolysis of the grafted pulp were investigated in order to obtain the better understanding of the grafting pulp for the papermaking material.
Copolymerization was carried out at 50°C under nitrogen by using ceric salt as initiator and sodium hydroxide was used as hydrolysis catalyst.
Dependence of ceric salt concentration, monomer concentration and reaction time on per cent grafting or grafting efficiency were confirmed. Relationship between degree of hydrolysis and hydrolysis liquor, reaction temperature and catalyst concentration were studied.
From the result, it was found that the optimum ceric salt concentration to obtain a high per cent grafting was 1.54.5×10^-3 mol/l and it was also found that 13 mol/l of monomer concentration was most effective for grafting efficiency.
In the case of mixture of water and methanol was used as hydrolysis liquor, more catalyst was necessary to obtain the same value of degree of hydrolysi compare to the case where only methanol as the liquor.
High concentration of catalyst dissolve the pulp content (hemi-cellulose etc.) and might cause the weakning of the physical properties of the paper prepared by the grafted pulp. In such ways therefore, the optimum hydrolysis condition for the grafted pulp were to use 100% methanol as liquor and catalyst as little as possible to obtain the given value of the degree of hydrolysis.

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Thermal aging characteristics of polyacrylonitrile fiber in transformer oil with insulating paper and air, compatibility of these components were investigated. The results obtained from the experiment can be summarized as follows :
(1) Polyacrylonitrile fiber has excellent resistance for transformer oil.
(2) Thermal life of oil immersed polyacrylonitrile fiber is extended about 14.7 times compared that of oil immersed cotton fiber.
(3) Oil immersed polyacrylonitrile fiber can be used somewhat 95°C higher than oil immersed cotton fiber.
(4) As the result of thermodynamic discussion for degradation of tensile strength of polyacrylonitrile fiber and cotton fiber, the following equation is obtained t=2, 303/klog100/100-x where t is thermal aging time, k is degradation speed constant, and x is reduction of the tensile strength for its initial value 100.
(5) Thermal decomposition products of polyacrylonitrile fiber is influenced for thermal aging characteristics of insulating paper and oil same as that of cotton fiber.
(6) Thermal decomposition gas of polyacrylonitrile fiber in transformer oil with air is found to be mostly CO, CO₂ and CH₄.

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