| In recent years, synthetic polymer surface sizing agents have developped rapidly, because they can endue papers with superior surface properties, improve the printability of papers, and so on. The purpose of this study was to search out an optimum synthetic process, which can synthesize a new kind of synthetic polymer surface sizing agent. The surface strength, water resistance and bursting index of papers which were sized by this synthetic surface sizing agent can be improved significantly. The innovations of synthesizing the new surface sizing agent in this study mainly reflected in two aspects: One was using amylase to hydrolyze starch into small molecules, which can reduce the viscosity of starch greatly, increase the mobility of starch. Then use the enzyme-converted starch to graft the monomer styrene, acrylic acid and butyl acrylate. The other was that no emulsifiers should be added, enzyme-converted starch not only worked as a reaction raw materials but also replaced the role of emulsifiers.The Design of Experiment method was used in this study, including Plackett-Burman Design and the program of 1/2 part implementation in Full Factorial Design. Regard increasing the surface strength of papers as the main research purpose, considerating the Cobb value and bursting index of papers comprehensively, the study arrived at the final synthetic process: the reaction temperature of amylase is 80℃, the reaction time of amylase is 10min, the mass ratio between starch and monomer is 1﹕1, the mass ratio between monomer St and BA is 6﹕1, dosage of AA is 2.0%(on the proportion of the total mass of starch and monomer), dosage of initiators(H2O2-FeSO4)is 0.8%(on the proportion of the total mass of starch and monomer), the mass ratio between initiator H2O2 and FeSO4 is 1﹕1, reaction temperature is 80℃, the dropping time of monomers is 3h.The appearance of the synthetic surface sizing agent was red-brown liquid. The test results of its properties are as following: solid content is 26.13%, pH value is 2.24, viscosity is 28.3mPa ? s, the total charge amount is 10.81c·g-1, the glass transition temperature is 70.72℃. All of those complied with the operating requirements of surface sizing agents. The FT-IR chart illustrated that all the monomers have been grafted on to the enzyme-converted starch; SEM scanning electron micrographs compared the surface morphology of papers sized by oxidized starch alone and the oxidized starch being added a certain proportion of synthetic surface sizing agent from the microscopic point of view, which explained that the synthetic surface sizing agent can significantly improve the surface strength, water resistance and bursting index of papers; The molecular weight Mηof the synthetic surface sizing agent measured by the viscosity method is 5.59×105. During the application research of the surface sizing agent, the author mainly investigated the effects on paper properties, those papers were sized by different compositions of sizing agent, different sizing amount, different sizing methods, different sizing temperature, different calendering pressure. The results indicated: in the case of ensuring the greatest surface strength of papers, and making the Cobb value of papers as low as possible, the bursting index of papers as high as possible, the amount of surface sizing agent accounting for the proportion of dry oxidation starch should be set as 3%～4%, the sizing amount should be set as 2.0 g·m-2, the sizing method should use the machine sizing way, the sizing temperature should be set as 60℃, and the calendering pressure should be set as 1Mpa. In this phase, the author compared the paper properties of papers sized by the synthetic surface sizing agent and some surface sizing agents used commonly in the market, and the results indicated that the surface strength, water resistance and bursting index of papers which were sized by this synthetic surface sizing agent can be improved significantly. |
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