| In recent years, with the vigorous development of Chinese papermaking industry, the demand and consumption of modified starch becomes more and more big.The advantages of starch are nontoxic, biodegradable, wildly, inexpensive and renewable. But natural starch is expansion and gelatinized. Its mechanical performance, water-resistant and emulsifying ability are poor, so application of natural starch is very limited. In order to expand the application of starch, it is necessary to modify the structure of starch. Grafting polymerization is one of the main methods of starch modification. Grafted starch copolymer consists of two parts; one is the hydrophilic of semi-rigid chain starch macromolecular as the skeletons, the other is unsaturated monomer with polar groups. The copolymer includes both properties of natural polymer and synthetic polymer, so it expands the application of starch. The modification of grafted copolymer of starch becomes one of attractive field for the scientific workers.In this paper, functional monomers and modified starch were used as materials. Cationic grafted starch copolymer was successfully synthesized, which had superior performance .The grafted starch was discussed as the surface sizing agent.Firstly, different influencing factors of graft copolymerization were studied. Such as pretreatment methods of starch, species and wight ratio of monomers, types and additive dosage of initiator, temperature and reaction time, and so on.Secondly, different starch grafted copolymers were studied as surface sizing agent of corrugated paper and APMP. Thirdly, grafted starch copolymer was modified and blended with other hydrophobic polymers, the sizing performances of grafted starch copolymer were further improved in this way. Finally, grafted starch copolymer was characterized by the instrument analysis, such as IR, DSC, and SEM, particle size, stability and viscosity.The results showed that better grafted starch copolymers starch synthesis conditions were:as follows: pretreatment of starch was cationic reaction before oxidation, dosage of antioxidant hydrogen peroxide (wight fraction is 30.0%) was 18.0% of dry starch, initiator was H2O2-FeSO4, dosage of hydrogen peroxide(wight fraction is 30.0%) was 2.0% of the monomer, weight ratio of monomer to starch was 2:1, weight ratio of styrene to butyl acryl ate was 1.5:1, polymerization temperature was 85.0℃, reaction time was 3.0h.Compared with blank corrugated paper, Cobb of sized paper reduced from 59.7g/m2 to 22.3g/m2, ring crush index increased from 4.5N·m/g to 6.6N·m/g. Compared with the blank hand sheet of APMP, Cobb of sized paper reduced from 62.3g/m2 to 27.1g/m2, tensile index increased from 12.4N·m/g to 42.2N·m/g, burst index increased from 0.6kPa·m2/g to 1.9kPa·m2/g,and tear index increased from 6.1mN·m2/g to 6.5mN·m2/g。Polyurethane prepolymer was used as a special water-resistant monomer; polyurethane-based cationic grafted starch agent with good performance was synthesized. The better synthesis conditions of prepolymer were as follows: amount of toluene di-isocyanate is 15.0% of 1, 4-butanediol, temperature is 80.0℃. The optimization synthesis conditions of sizing agent were as follows: amount of prepolymer was 10.0% of starch, weight ratio of monomer to starch was 2:1, weight ratio of styrene to butyl acryl ate was 1.5:1. Compared with blank corrugated paper, Cobb of sized paper reduced from 59.7g/m2 to 21.2g/m2, ring crush index increased from 4.5N·m/g to 6.8N·m/g.It was showed by IR and SEM that the monomer successfully grafted on the starch, cationic starch grafted copolymer formed reticulation tough film, and its sizing performance was good. |
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