Starch-based plastics
Starch-based plastics use chemical reactions to chemically modify starch to reduce the hydroxyl groups of starch and change its original structure, thereby changing the corresponding properties of starch and turning native starch into thermoplastic starch.
Chinese name
Starch-based plastics
Exterior
Milky white
English name
plastarch
table of Contents
1 basic content
Starch is a kind of natural high molecular polymer. Its molecule contains a large number of hydroxyl groups (molecular structure is II and III). Therefore, the interaction force between starch macromolecules is very strong, which makes it difficult for the original starch to melt processing, and it is in co-polymerization with other polymers. The compatibility with other polymers during mixing is also poor. However, these hydroxyl groups can undergo chemical reactions such as esterification, etherification, grafting, and crosslinking. These chemical reactions are used to chemically modify starch, reduce the hydroxyl groups of the starch, change its original structure, thereby changing the corresponding properties of the starch, and turning the original starch into a thermoplastic starch.
1. Esterification, transesterification or etherification reaction In order to change the hydrophilicity of starch to hydrophobicity, the hydroxyl groups on the starch molecule will undergo esterification and transesterification reactions with fatty acids and fatty acid esters to form starch esters.
2. Crosslinking reaction
In order to improve the strength and heat resistance of starch materials, the starch is cross-linked with compounds with two or more functional groups (such as polybasic acids, etc.), so that the starch is appropriately cross-linked.
3. Independent innovation of blending to copolymerization. Most starch plastics are prepared by filling and blending starch with other polymer materials. The products obtained in this way have poor compatibility and low strength, and their application range is limited. In the starch-based plastic, the starch is copolymerized in the starch modification process to obtain graft copolymers of starch and other polymers, thereby improving the compatibility of starch with other polymer materials. Through chemical modification, three modifications of starch have been realized: hydrophilicity changed to hydrophobicity; heat sensitivity changed to temperature resistance; hard and brittleness changed to plasticity. This modification solves the worldwide problem of starch modification and lays a good foundation for subsequent processing.
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