Preparation Of Selective Oxidation Chitosaii Derivatives And Applications In Paper Making

In the selective oxidation of chitosan using sodium periodate, chemical bonds betweenC2and C3in the pyranose ring were opened. Meantime, the aldehyde group is introducedinto the oxidation products of chitosan. The oxidation products of chitosan by sodiumperiodate were always called dialdehyde chitosan (D-CTS), which shows broad applicationprospects in the paper industry and biomaterials science. D-CTS has the chelation capacity ofmetal ion. Aldehyde group in D-CTS can be further reduced. Therefore, D-CTS can be usedto stabilize and prepare nanoparticles. Aldehyde group in D-CTS plays a role in improvingcomplex formulation with other additives for papermaking (such as cationic starch andpolyacrylamide), which can lower cost of chitosan. The D-CTS and cationic starch (CS) couldbe mixed to prepare a sizing agent, which can enhance the mechanical properties, water vaporbarrier properties and grease resistance. The coated paper has broad application in thepackaging industry. The aldehyde D-CTS is a new active site, which can be grafted functiongroups to prepare biomaterials with different functions.The molar ratio of IO4/GlcN has an important impact on the oxidation products in theselective oxidation of chitosan using sodium periodate. Sodium periodate is not entirelyconsumed in the ring-opening reaction between C2and C3in the pyranose. It is partiallyconsumed in degradation of backbone of chitosan. When the degree of oxidation (DO) isabove46.3%, DO continues to grow slowly as the content of sodium periodate increases. Thismay be due to more aldehyde generated in the oxidation reaction, which may influence theamino and hydroxyl groups in the sugar ring. The optimal pH value in the oxidation reactionis between3and4. Lower pH value would make amino groups to be protonated, which couldhinder the reaction process. Higher pH value would make chitosan swelling, which couldprevent periodate permeating into the internal of chitosan molecules. Amine groups inchitosan are acetylated, which can reduce degradation of the molecular chain. XRD analysisshows crystal diffraction peak absorption peak (2?=11.2?2?=20.1) disappears with thedegree of oxidation raised. With the improvement of DO, the number of open-loop ofpyranose increases, which would weaken the hydrogen bonding between molecules ofchitosan. Chitosan would be amorphous state after the oxidation. DSC analysis shows thethermal stability of D-CTS is reduced. This is mainly because of the ring-opening of chitosanand corrupted crystalline morphology. TG analysis indicates that the decompositiontemperature of D-CTS decreases as the degree of oxidation raised.A simple, green method was developed for the synthesis of silver nanoparticles (AgNPs)by using dialdehyde Chitosan (D-CTS) as the reducing and stabilizing agents. Amino groupsand aldehyde groups in D-CTS can improve the chelation capacity of metal ion. Themorphology and size distribution of the AgNPs were found to vary with the dialdehydecontent of D-CTS and the pH value of the reaction solution. The synthesized AgNPs werecharacterized by UV-Vis spectroscopy and dynamic light scattering (DLS). When the degreeof oxidization was32.3%and the pH value of the reaction solution was3, AgNPs possessed aminimum size of30-40nm. XRD results indicated the presence of nano-silver had the face-centered cubic structure (111) and (200) corresponding to crystal diffraction peaks(37.45°and44.47°). SEM results showed that nano-silver particles of30to40nm in sizewere homogeneously dispersed in the solution. FT-IR spectra revealed that the aldehydegroups and the amino groups were the major agents that stabilizing the AgNPs. The possiblemechanism of D-CTS on the reduction and stabilization of AgNPs analyzed by Job methodmay be due to the formation of four coordinate complexes. The synthesized AgNPs remainedstable for more than three months.Due to the aldehyde groups generated in the oxidation of chitosan using sodiumperiodate, D-CTS has a better cross-linking properties, which can improve the compatibilitywith other additives for papermaking. The sizing agent of D-CTS/CS was prepared by mixingcationic starch with D-CTS. The package performances of the paper coated by D-CTS/CScould be improved, which can broaden the applications in food packaging. As the DO ofD-CTS increases, the tensile strength and grease-resistance index of coated paper increasedramatically. When the concentration of D-CTS, pH values of the sizing agent, dryingtemperature, ambient temperatures and ambient humidity are0.3wt%,80?,20-30?and50-60%respectively, the coated paper possesses the best grease-resistance index (the greaseresistance index could reach10). As the DO of D-CTS increases, WVP of coated paperdecreases. The increasing coating weight can improve the water vapor barrier propertiesdramatically. ATR-FTIR analysis indicates: the absorption peaks of C-ONR2and C-O-Cgroups increase significantly. It shows that the degree of crosslinking among D-CTS, CS andfibers is raised. TG analysis of D-CTS/CS shows that the beginning temperature of weightloss is230?. DSC analysis shows that the exothermic area (230-365?) first increases andthen decreases, which is in accordance with the changes of mechanical properties of thecoated paper. With the addition of D-CTS, the surface smoothness of coated paper has beensubstantially improved. It shows that the film formation performance of the coated paper hasbeen greatly improved. SEM analyses show that the surface of the paper coated by D-CTS/CSbecomes smoother. The pores among the fibers become smaller. The contact angle of waterreduced after the paper coated by D-CTS/CS. When the contact time is between0.1s and0.5s,the contact angle decline more slowly. It shows that the film is formed on the surface of thepaper. Meantime, the paper surface porosity decreases. The water droplets on the surface ofpaper permeate slowly, which indicates the water resistance of the coated paper increases.Liquid paraffin spreads on the surface of coated paper. When the contact time is between0.1sand0.5s, the contact angle declines very slowly. It indicates that the sizing agent has slighteffect on the surface energy. There is an attraction between oil droplets and the surface of thecoated paper. This attraction may be related to the electrostatic force between oil droplets andthe sizing agent, which can impede the oil droplets penetrating into the inside of paper.D-CTS has difficulty in wet-end as strengthening agents, due to its small molecularweight and poor bridging capabilities. In order to enhance the bridging properties of D-CTS,Girard's Reagents (GT) were used to graft onto the aldehyde groups in D-CTS to synthesis ofcationic dialdehyde chitosan (CDCTS). The tertiary amine groups in GT reagents can improvepositive ion intensity and mechanical properties of the paper. Meantime, the grafted polymerwith better bridging performance can improve retention properties. In addition, the tertiary amine groups in GT reagents can further enhance the antibacterial properties of the paper.When the molar ratio of GT/CHO, the aldehyde content of D-CTS, the reaction temperatureand the reaction time is2,92.6%,60?and30min, the percentage of grafting (PG) can reach52.1%. FTIR and1H-NMR analysis show that GT reagents have been grafted onto the D-CTS.As the PG of CDCTS increases, the number of branched-chain and electrolyte concentrationsis raised. With the bridging performance of CDCTS improved, more physical bridges could beformed between fillers and fibers. The physical bridges can improve the force among finefibers, fibers and fillers. At the same time, the ash content of the paper went up for theimproved retention capacity of CaCO3. Zeta analysis showed that there was more CDCTSadsorbed to the surface of fibers compared with D-CTS. Because the wall surface of the fiberincreases, the mechanical properties of paper were improved. With the PG of CDCTSincreasing from0%to52.1%, the antibacterial index against S. aureus was raised from76.2%to98.3%. At the same time, the antibacterial index against E. Coli increased from67.4%to78.4%. Compared with S. aureus, the PG has less effect on the antibacterial index againstE. Coli. With the concentration of CDCTS increasing, the antibacterial indexs againstS. aureus and E. Coli were improved significantly. CDCTS with more branches is more likelyto form a barrier coating on the surface of S. aureus, which can prevent nutrients and othersubstances passing through the cell wall of S. aureus. It may inhibite the bacterial growing.On contrary, CDCTS with more branches has difficulty in penetrating into the cell wall ofE. Coli, which can slow growth of antibacterial properties against E. Coli.