Study On Preparation Of Low Gelatinization Temperature Starch Adhesive And Its Physical And Chemical Properties

As a kind of renewable resources, starch is widely used in many industries, such as adhesive, textile, papermaking industries and so on. Along with the development of the technology and society, more and more high-speed glue coating machine will be used in starch adhesive industry in order to improve work efficiency. In order to make starch adhesive can be applied to high-speed sizing machine, it is required to paste rapidly at high temperature and produce bonding strength and must has good coating uniformity at the same time. So how to reduce the gelatinization temperature of starch has become the key to prepare low-gelatinization temperature starch adhesive.1. The crystal structure and gelatinization properties of cassava starch can be changed when it is processed under high temperature and high pressure. The starch granules still have half-crystal structure after processed in high temperature and high pressure, but its crystallinity has been changed and easy to aggregation. Processing in high temperature and high pressure can reduce the gelatinization enthalpy of starch granules and make it easier to gelatinized, but the stability of starch paste viscosity has been decreased. We have investigated the gelatinization temperature and the surface morphology changes of cassava starches containing different moisture treated in high temperature and high pressure. The granular morphology and crystal structure of it were further characterized using scanning electron microscopy, X-ray diffraction, polarized light microscopy and the gelatinization temperature was characterized using DSC, rheometer and polarized light microscopy. The results indicated that high temperature and pressure treatment of starch could change crystallinity of it, thus affect the gelatinization temperature. After high temperature and high pressure treatment, cassava starch was easier to gelatinize but the viscosity stability of starch paste reduced. The crystallinity of treated starches containing 18% and 31% moisture increased so that the gelatinization temperature increased. However, the crystallinity of treated starches containing 5% moisture decreased which induced the gelatinization temperature decrease.2. The granule structure can be changed when starch is treated by microwave and ultrasonic treatment, thus affect gelatinization temperature and gelatinization enthalpy of starch. Starch granule can absorb energy when processed in microwave so that the crystallinity and gelatinization temperature of starch will be increased. After absorbing energy from microwave, there appear some pits on the umbilical cord of starch granules. Some energy is stored by starch granules; the gelatinization enthalpy is decreased so that it can gelatinize more easily than the native starch. When treated by ultrasonic, starch has degradated under high-speed vibration from different directions and mechanical shearing action generates. The gelatinization temperature, gelatinization enthalpy and pasting viscosity of treated starch are all lower than the native starch because of destroying of the granular structure and crystal structure. So that it is easier to gelatinize than native starch. Due to starch molecules cross-linked each other processed in thermal and mechanical energy, the viscosity of starch paste has becoming more stable.3. The gelatinization temperature and gelatinization time of cassava starch can be reduced effectively when starch is heated in organic solvent. The surface part of the starch has gelatinized because starch granules are heated in the phenomenon with little or no water. Among them 1, 4-Dioxane is the best one. The gelatinization temperature can be dropped to 60.9℃and the gel time can be reduced to 9s when cassava starch is heated in 1,4-Dioxane.4. In order to make starch adhesive apply on high-speed sizing equipment. We have prepared a kind of low-temperature gelatinization starch adhesive which has low viscosity and high solid content. This kind of starch adhesive can be fast gelatinization at high temperature. There are two parts in the formulation of our starch adhesive:the main part and the carrier part. We choose the low-temperature gelatinization cassava starch granules coming from treatment in high temperature and high pressure as the main part of the starch adhesive. There are two parts in the carrier part of our starch adhesive:the dispersed phase and the thickening agent. We choose the 30% concentration of oxidized starch as the dispersed phase and carboxymethyl starch as the thickening agent. We have studied the effect of pH and many kinds of salts on the viscosity of the pasting carboxymethyl starch. We find that 1% CaCl2 solution is very useful to lower its viscosity. In order to improve the storage stability of starch adhesive, we need to add some pasting agent in the main part to make it pre-gelatinized. We have investigated the effect of NaOH, NaHCO3, and urea on gelatinization temperature of cassava starch. And ultimately we have determined to choose 8% urea solution as the pasting agent of the main part. We have got the best formula through the formula optimization, and tested the bonding strength of this kind of starch adhesive. This kind of starch adhesive can be applied on high-speed cigarette machine in cigarette factory of our country. The results of testing show that the high-speed cigarette machine can achieve maximum speed, the bonding strength and the rejection rate can also comply with the standards of cigarette.5. [AMIM]Cl is a kind of ionic liquid. It has a good solubility for starch, and can help to reduce the gelatinization temperature of starch granules. We have synthesized cassava starch-vinyl acetate graft copolymer in [AMIM]C1 using ammonium persulfate as initiator. This graft copolymer maintains the crystal structure. The best reaction condition is:the weight ratio of cassava starch and vinyl acetate is 3.0, the concentration of initiator is 22mmol/L, the reaction time is 1 hour, the reaction temperature is 60℃, the grafting rate can reach 24% and the grafting efficiency can reach 78%. The surface of starch-vinyl acetate grafted copolymer that we synthesized in [AMIM]C1 appeared a layer of "small pieces", that indicated the vinyl acetate grafting on the starch. The gelatinization temperature of the graft copolymer is lower than native starch.