| Starch and modified starch have been widely used in paper production for their low price,biodegradability and less harm to the environment. Therefore it meets the demands ofenvironmental protection to develop starch based adhesive as alternatives for petroleum-basedlatex. But most modification methods used now are chemical methods which can cause pollution.In this paper screw extrusion is used as the basic modification method with which high qualitystarch based adhesive may be prepared with less pollution.In this paper, cassava starch was used as a raw material and plasticized starch was preparedby using glycerol as plasticizer and extrusion as treatment. Effects of glycerol dosage,temperature, extrusion time, and rotation speed on properties of plasticized starch were studied;the optimal preparation process parameters were determined as: plasticizer dosage33%,temperature120℃, extrusion time120s, and rotation speed110r/min.On the basis of experimentabove NaH2PO4was used as esterifying agent and plasticized phosphorylated starch wasprepared. Effect of esterifying agent dosage on starch viscosity and coated paper properties werestudied; the optimal dosage of NaH2PO4is2%. Plasticized starch was used as raw material andplasticized grafted starch was prepared by using potassium persulfate as initiating agent andstyrene as monomer. Effects of initiating agent dosage, value of St: styrene, oxygenant dosage,emulsifier dosage were studied; the optimal preparation process parameters were determined as:initiating agent dosage4.5%, value of St: styrene4:1, oxygenant dosage5%, emulsifierdosage1.5%.The molecular structure, crystal structure and particle morphology, paste nature of cassavastarch and modified starch were analyzed by fourier transform infrared spectroscopy (FTIR),X-ray diffraction (XRD), scanning electron microscopy(SEM), differential scanningcalorimetry(DSC) respectively. The main results obtained from the analysis are：1. the final product that the plasticizing process didn’t produce new group on starch;NaH2PO4reacted with starch and produced P-O-C and P=O link among starch; the graftpolymerization planed styrene monomer on starch molecular chain.2. Modification process caused damage to the original crystalline structure of starchgranules; esterifying and graft polymerization produced new crystalline structure on starch;3. the granules surface of modified starch showed that starch are no more dispersed granulestructure, the dividing line among granules disappeared and show out successive block structure. 4. The analysis on paste properties of modified starch showed that gelatinization temperatureof plasticized starch and plasticized grafted starch had been lower, however,it gets higher forthe plasticized phosphorylated starch.By substituting modified starch for latex partly in coating color, effect of them on coatingcolor and coated paper are studied. The result showed that the plasticized phosphorylated starch isbetter than the other two modified starch on using properties, the optimal value of plasticizedphosphorylated starch: latex is5:7and the coating color showed stability on viscosity. |
