Starch is a natural polymer material that is rich in hydroxyl groups and has no thermoplasticity.When it is blended with a polymer,its polarity is not similar to that of the matrix material,and the two phase is immiscible.Chemical modification can give starch thermoplasticity,at the same time,change its polarity.The modified starch can be blended with polymer by hot-melt process to obtain polymer/starch composite with good compatibility.The methods and mechanism of starch modification are as follows.The modifier reacts with the hydroxyl groups on the starch macromolecular chain,and starch is modified by grafting,esterification,cross-linking,oxidation,etc.These chemical modifications can change starch from hydrophilic to hydrophobic.The polarity of starch is closer to that of polymer,and even starch and polymer can be linked by covalent bond through chemical reaction.The addition of modified starch to the polymer matrix can improve compatibility between blend system,and obtain a polymer/starch composite material with excellent comprehensive properties and low cost.In addition,the researches of low-cost,high-activity,functional modifier,controllable starch polarity,and the optimization of modification process will become research focus in the future.
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