Cross-linking refers to a chemical process where covalent bonds are formed between different polymer chains. This results in the formation of a three-dimensional network of interconnected polymer chains, which imparts the material with improved mechanical and thermal stability. Cross-linking is commonly used in the production of synthetic rubber, plastics, and adhesives, among other materials.
Cross-linking in modified starch refers to the process of chemically bonding the starch molecules together to form a three-dimensional network, which imparts improved stability, strength, and improved resistance to heat and shear. This process can be achieved through a variety of methods including treatment with chemicals such as cross-linking agents like epichlorohydrin, or using high temperature and pressure in the presence of organic compounds like di- or polyfunctional alcohols. The result is a modified starch with increased functionality, which can be used in various industrial applications, such as in the production of paper, adhesives, textiles, and more.
Purpose
Cross-linking is done to enhance the strength and stability of the swollen granules of starch. This helps to resist the breakdown of viscosity caused by mechanical shear, high temperature, or acid conditions.
Process
Cross-linking in modified starch is the process of chemically bonding the starch molecules together to form a three-dimensional network. This process is usually performed using chemical agents such as cross-linking agents. The aim of cross-linking is to modify the physical and functional properties of starch, such as increasing its resistance to viscosity breakdown, improving its stability and heat resistance, and enhancing its functionality in various applications. The extent of cross-linking and the type of cross-linking agents used will affect the properties of the modified starch. In general, cross-linked starches have improved thermal stability, higher paste viscosity, and improved ability to retain their shape after processing.
Effects
Cross-linking in modified starch can have various effects on its properties and characteristics, depending on the extent of the reaction and the source of the starch. Some effects of cross-linking include:
- Improved stability: Cross-linking enhances the stability of the swollen granules of starch, making it resistant to viscosity breakdown under conditions of mechanical shear, high temperature, or acid.
- Increased swelling power: In some cases, cross-linking can increase the swelling power of the modified starch, allowing it to attain a higher degree of granule swelling during heating compared to unmodified native starch.
- Higher paste viscosity: Cross-linked modified starch can exhibit higher paste viscosity, providing better thickening and gelling properties.
- Altered texture: Cross-linking can also affect the texture of modified starch, leading to a change in its consistency and mouthfeel.
- Reduced solubility: Cross-linking can also result in decreased solubility of the modified starch, which can affect its usability in certain applications.
Applications
Cross-linking of modified starch is used in several applications to improve the properties of starch. Some of the common applications of cross-linked modified starch include:
- Food industry: Cross-linked modified starches are used as thickeners and stabilizers in processed food products such as sauces, soups, and custards.
- Papermaking: Cross-linked modified starches are used as sizing agents in the production of paper and paperboard, to improve the strength and size stability of the final product.
- Textile industry: Cross-linked modified starches are used as binders in the production of textiles, to improve the bonding strength and durability of the final product.
- Pharmaceutical industry: Cross-linked modified starches are used as controlled-release carriers in the formulation of drugs, to improve the release rate and bioavailability of the active ingredient.
- Construction industry: Cross-linked modified starches are used as binders in the production of building materials such as cement and gypsum, to improve the strength and durability of the final product.
These are some of the main applications of cross-linked modified starch, but there are many others as well.
Importance
Cross-linking modified starch is important as it improves the stability, viscosity, and texture of the starch-based products, making them suitable for various industrial applications.