Natural dry-strength additives

Cationic starch will adsorb onto the fiber until the fiber surface is fully covered by starch or the fiber surface charge is fully [over] compensated [73,75]. 

Special cationic pol5miers, which react with starch [native or anionic] by fixation and/or precipitation, proved to be even more effective in dry-strength improvement than cationic starch. Pol5nnnylamine was found to be especially useful in such applications. It forms a very stable complex with starch and paper fibers, which results in very good retention [23]. 

The mechanism of dry-strength improvement by wet-end starch is based on interfiber bonding. The free glucose hydroxy groups of starch participate in hydrogen bonding with cellulose molecules on fiber surface. This actually results in a kind of chemical hydration of the fiber network. Additionally, starch improves retention of fines and fillers as well as contributes to more uniform distribution of bonds between fibers. In other words, in addition to strength boost, the wet-end starch improves the sheet formation. 

Packaging paper produced from 100% of recovered fibers [e.g., testliner, corrugating medium] can only obtain the required quality if its manufacture is assisted by the addition of dry-strength agents. The bios5mthetic starch derivatives are a good 

Moreover, starch is sometimes sprayed between the plies of multi-ply board to strengthen inter-ply bonding. 

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Many water soluble, hydrogen bonding polymers will act as dry strength additives. In fact, wood fibers contain their own natural dry strength additive in the form of hemicelluloses. It is well-known that the removal of hemiceUuloses from wood fibers makes it more difficult to develop their bonding characteristics. 

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