Study On Application Of Natural Polysaccharides And Its Derivertives In The Preparation Of Polyvinyl Acetate Emulsion

Natural polysaccharides ( starch, cellulose, vegetable gums, microbial glues etc. ) and its derivertives substituded (totally or partly) for polyvinyl alcohol (PVA) as the protective colloid in vinyl acetate (VAc) emulsion polymerization were studied in this paper. It has also studied that the modification of polyvinyl acetate emulsion (white glue) by blending it with the oxidized starch solution. And a primary acetalization modification test has been done for the white glue made with the low degree of substitution (DS) starch acetate.The starch acetate is prepared by direct acetylation of corn starch. The starch acetate (St-OAc) prepared can be used to partly substitute for PVA (The mass ration of St-OAc/PVA is equal to or less than 1:1) as the protective colloid in the emulsion polymerization. Compared with the white glue using PVA alone as protective colloid, the above-mentioned white glue has higher viscosity and water resistance. And its cohesive strength can also reach or even be higher than the standard for use. The experiment results show that the properties of white glue will be outstanding when DS of the starch acetate is between 0.81 and 1.16 or so. The cohesive strength of the white glue will be the best when DS of the starch acetate is 0.81. While the water resistance will be better when the starch acetate with low (0.15~0.22) and high (2.52~2.84) degree of substitution is used.The oxidized starch is prepared by oxidizing the corn starch. The results of modifying the polyvinyl acetate (PVAc) emulsion by blending with oxidized starch show that the modified PVAc emulsion has higher solid content and viscocity. At the same time, the raw material cost of the PVAc emulsion can be reduced remarkably by this methed.Nevertheless, the water resistance of this white glue ought to be improved.The emulsion is stable and its particle size is even and fine when using carboxymethyl cellulose (CMC) alone as the protective colloid in the VAc emulsion polymerization. But the viscosity of the emulsion is very low(only from 15 to 660 mPa.S). The emulsion viscosity and cohesive strength can be effectively improved when the emulsion is compounded with hydroxyethyl cellulose (HEC).Using HEC alone as the protective colloid in VAc emulsion polymerization is not very desired. The particle size of the product is too large and will be caking. The stability of the emulsion is not very good. HEC and PVA can produce cooperative effect when they are blended together. The emulsion is homogeneous and has good stability.The result is satisfactory when using gum arabic (GA), guar gum (GG) alone as the protective colloid in VAc emulsion polymerization. But: the viscosity of the emulsion (using GA) is very low (only from 60 to 300 mPa.S) . Properties of the emulsion can reach a desired level when the percent of GG in the emulsion is 10%. Using Xanthan gum (XG) alone as the protective colloid in VAc emulsion polymerization is not very good. The particle of the product is caking. The stability of the emulsion is bad. GG and PVA can produce a cooperative effect when they are blended together. The results is very desired.Gum arabic, guar gum and Xanthan gum have good compatibility. GA and GG can produce a thickening cooperative effect when compounded with XG Then the emulsion viscosity and cohesive strength can be effectively increased.P-cyclodextyin(P-CD) has good emulsifying capability. As far as the product is concerned, the emulsion is homogeneous and has a good stable property. The cavity ofp-CD can absorb hydrophobic small molecule or groups to form clathrate compounds (or inclusion compounds) and such can improve the water resistance of white glue obviously.