The Preparation Of Hydroxypropyl Chitosan And Its Use As A Paper Additive In Neutral Papermaking Systems

Chitosan, a biodegradable, nontoxic, antibacterial, as well as renewable resource commodity, is the second most widespread natural polysaccharide, and has exhibited basic rather than acidic characteristics. This basicity gives chitosan its unique properties. Furthermore, chitosan is easy to be modified to become the dissolved polyelectrolyte, which tends to strongly interact with cellulosic substrates or mineral fillers presenting in wet-end of papermaking systems, and is expected to enhance the physicomechanical characteristics of paper and improve the papermaking process. Therefore, chitosan and its derivatives are used as wet-end potential functional additives in papermaking. The recent advances in the application of chitosan as a wet-end additive in papermaking were reviewed in this paper. Different degrees of substitution of hydroxypropyl chitosan was made and then the paper studied its use as a wet-end additive in neutral papermaking. The results were shown as follows:(1) The preparation and characteration of hydroxypropyl chitosan: it discussed how the temperature, time, solvent influenced the characteration of hydroxypropyl chitosan. The result showed that the best preparation condition lied in the proper weignt ratio of chitosan to NaOH to propylene oxide should be 1:1 :15 and the time of reaction should be 7-9 hours at 45℃.Based on this, we got the proper products having suitable degrees of deacetylation. By the means of IR, the products were analysed. Hydroxypropyl chitosan has definite moisture absorption and moisture retention. Because the structure of chitosan were destroyed by new group importing and it helped to form more hydrogen bonds.(2) Strengthening and dewatering by hydroxypropyl chitosan as a wet-end additive in neutral papermaking: Neutral papermaking has been the trend by use of calcium carbonate . it studied how the different amount of Hydroxypropyl chitosan's addition and the vibration of pH affected the paper's dry strength. And it showed that the optimum addition of this agent was 0.8% and the paper could get better physical properties at pH=7.0. The tensile index enhanced about 24.5% and 12.7% by hydroxypropyl chitosan and hydroxypropyl starch respectively. SEM and IR were used to analysis the strengthening of this additive and it made a conclusion that Hydroxypropyl chitosanhelped to strengthen the effect of the fibers and to form more hydrogen bonds. When the quantity of this additive was 7mg/g, dewatering properties were improved about 19.7% .(3) The study on hydroxypropyl chitosan as surface sizing properties and wet-end sizing additive: Hydroxypropyl chitosan can form good films and be provided with the properties of moisture absorption and moisture retention, so it can be used as surface sizing agent. Through experiment, the IGT enhanced about 54.8% and 103.6% by hydroxypropyl starch and hydroxypropyl chitosan respectively. At the same time , results showed that hydroxypropyl chitosan had better properties in other aspects and higher DS hydroxypropyl chitosan could contact with the fibers completely and get better effect. On the other hand, hydroxypropyl chitosan can strengthen retention. And when it came to sizing in neutral papermaking, it helped to keep more calcium carbonate and form more stable floccule. And it was supposed to be suitable for practical production process.