Preparation Of Modified Urea-fromaldehyde To Improve The Water-resistance Of Starch Adhesive

Starch adhesive is now widely used in packaging industry, but the application on it was affected with the poor water resistance,mainly due to its main chain linked with too many hydrophilic groups-OH, and being failed to form an effective network structure. Rencently, in order to improve the water resistance of starch adhesive, compared to synthesize a new type of watertight starch adhesive, the way of adding the waterproofing agent to blend into the starch adhesive is more convenient and fast.Furthermore, using the urea-formaldehyde resin (UF) to compound with starch adhesive to improve the water resistance of starch adhesive properties, is already a very mature technology, so a new type of synthesis technology of modified UF resin to improve the water resistance of starch adhesive was systematically studied in this paper.With the hole of synthesis process of modified UF resin used in starch adhesive, a better synthesis route of modified UF resin was found in order to significantly improve the water resistance of starch adhesive. By mixing epichlorohydrin(ECH), and the synthesis of PPE into the polycondensation of UF resin, to expand the structure of the UF molecular chain, and then by adding into the starch adhesive to increase the amount of crosslinking radical, as to improve the water resistance of starch adhesive.The mole ratio of formaldehyde and urea [namely n(F)/n(U)ratio], the dosage of ECH, the time of graft copolymerization and the polycondensation temperature on the properties of products and the effect on the water resistance improvement of starch adhesive were investigated in the polymerization experiment of modified UF by ECH. On the basis of single factor experiments, the optimum conditions were obtained by the orthogonal experiments,and being showed as follows:the mole ratio of formaldehyde and urea [namely n(F)/n(U)ratio]was2, the dosage of ECH was8g, the polycondensation temperature was90℃and the time of graft copolymerization waslh15min. The structure of product was characterized by IR spectrum. In the polymerization experiment of modified UF by PPE, seven factors such as the dosage of PA, the polycondensation time of PA, the dosage of ECH, the mole ratio of formaldehyde and urea [namely n(F)/n(U)ratio], the earlier polycondensation time of UF, the later graft copolymerization time and temperature of modified UF, have been systematically studied by single factor experiments. And the properties of products and the final effect on the water resistance improvement of starch adhesive were investigated in detail respectively. By the orthogonal experiments again, the optimum process conditions were:the mole ratio of formaldehyde and urea [namely n(F)/n(U)ratio]was2, the dosage of PA was14g, the later graft copolymerization temperature of modified UF was55℃, the polycondensation time of PA was2h, the dosage of ECH was8g, the earlier polycondensation time of UF was70min, and the later graft copolymerization temperature of modified UF was1h20min. The effect of storage time of the compound on water resistance of starch adhesive was also discussed in this study,and the results showed that, the modified UF resin by PPE can be used by compounding into the starch adhesive in the normal temperature, and the effect on improving water resistance was better with the prolonging in the storage time. The structure of modified product was characterized by IR spectrum in the research of its structural feature.