Preparation Of Dialdehyde Carboxymethyl Chitosan And Study Of The Composites Of Dialdehyde Carboxymethyl Chitosan/Cationic Starch On Paper Strength

Carboxymethyl chitosan (CMCS) is a water-soluble chitosan derivative by carboxy-methylation of chitosan. CMCS can be widely employed in the field of papermakingadditives， due to its linear and similar chemical structure with cellulose. However, CMCShas disadvantages of large consumption and high cost as a papermaking additive.Therefore， CMCS is often composites starch derivatives to prepare the composite,improving the quality of paper. To achieve a high degree of composite reaction ratio, sometoxic crosslinking agents such as formaldehyde and glutaraldehyde are added， and thusincreasing the cost and making our environment polluted. Therefore， the aim of this thesisis to replace these traditional and toxic crosslinker by eco-friendly dialdehyde carboxymethylchitosan (DCMCS)， and achieve higher composite degree and lower cost， making DCMCSmore valuable in paper-making industry.In this paper, a new type of crosslinking agent DCMCS was prepared with sodiumperiodate (NaIO4) by the selective oxidation of CMCS. Moreover, a new paper additive，dialdehyde carboxymethyl chitosan-cationic starch (DCMCS-CS)，was also prepared bycomposite cationic starch (CS). Various modern testing instrument and analysis methods wereapplied to characterize the performance and structure of DCMCS and DCMCS-CS，and theoxidation mechanism and the enhancement mechanism of paper were also studied.The experiment results revealed that DCMCS exhibited relatively high oxidation degree(44.83%)， high molecular weight (Mη=63.1k Da) and lighter color when the mass ratio ofNaIO4to CMCS was1.0:1.0under constant stirring at40℃and pH8.0in dark for20h.FTIR， XRD and1H NMR analyses showed that the aldehyde groups were formed at C2and C3positions of CMCS and increased in a certain range and the crystallinity of DCMCSwas accordingly decreased. DSC and SEM measurements suggested that the main chain ofDCMCS get shortened. What is more, the particle size of DCMCS with state aggregationdecreased and the shape turned to be sphere like with increasing oxidation degree.The single factor experiment results revealed that DCMCS-CS achieving the maximumstrength-improving effects when the mass ratio of CS to DCMCS was5:1under constantstirring at the DCMCS (the xidation degree was26.21%) and80℃for2h.Research showed that it could obtain a good effect at charge of DCMCS-CS0.6%， thepaper tensile index57.6%higher than that of blank sheet, tear index increase43.5%andsuitable for manufacture paper with pulp of the partial neutral or weak alkaline environment.Under the condition of the same dosage, the strength of pulp were best when added theDCMCS-CS by comparative analysis which showed DCMS can be as a grafting wirhcomposite reaction of CS. Besides， SEM showed that DCMS-CS could efficiently improvefiber bonding strength and the area of component fiber, and sequentially increase the strengthof paper sheets.