Study On The Application Of Carboxymethyl Chitosan In Paper Barrier Coating

Paper and paperboard are versatile materials produced from renewable cellulose fibersresource. However, due to its porous structure and poor barrier properties to gas, water, oiland other items, limiting its application in the field of packaging and printing electronics, etc.Carboxymethyl chitosan(CMC)，typical chitin derivatives of carboxy methylation, showsgood water solubility, low solution viscosity, and weak alkaline of solution. In this paper,carboxymethyl chitosan was used to process a film from two different base paper that wouldexhibit interesting barrier properties. Moreover, the absorption kinetics of oil on coated papershas been studied to provide further research reference of carboxymethyl chitosan in paperbarrier coating.In this study, the application of carboxymethyl chitosan on paper barrier coating wasstudied systematically. Firstly, the rheological properties of carboxymethyl chitosan solutionwere analyzed. Then, the barrier properties of paper coated with carboxymethyl chitosan fromtwo different base paper, transparent paper and kraft paper, have been studied. The mainconclusions obtained are as below,1. The static viscosity and dynamic rheological properties of CMC solution wereanalyzed. The viscosity of carboxymethyl chitosan solution reach529.9mPa s whenconcentration was8%. pH of CMC solution stay around9.61when concentration from0.5%to8%. Viscosity of CMC solution does not show any change when adjusting pH to13,however, viscosity decreased gradually to23when adjusting pH to5. Solution viscosityvaries with temperature, shear rate increased linearly regularity, and the greater the degree ofconcentration, the greater the effect. Solution shows pseudoplastic fluid characteristic andshear thinning nature, the dynamic rheological properties conform to the description of theOstwald-de Waele power law model.2. Mechanical, optical and absorbing properties of transparent and kraft paperafter coatedwith CMC were studied. SEM figures show that coated paper is covered with carboxymethylchitosan, a film is formed on transparent paper while increasing coating weight, but fibercontour still can be seen on surface of kraft paper. Air permeability of transparent paper and kraft paper can reach instrument measuring lower limitation0.0030μm/(Pa·s) when coatedwith3.6and5.2g/m2, respectively. Mechanical and optical properties of transparent paperunder different coating weights were not significantly different from base paper. When coatedwith5.2g/m2, tensile strength in MD and CD of kraft paper increased to4.81kN/m and2.69kN/m, increased by25.9%and25.9%respectively, tear strength increased to571mN and608mN, increased by13.5%and13.5%respectively. However, brightness dropped to14.92%,gloss increases to16.3%. After coated, cobb of transparent paper increase slowly with theincrease of coating weight and water absorption is mainly decided by the hydrophilic coatinglayer. Cobb value of kraft paper increases after goes down firstly with the increase of coatingweight, water absorption is mainly decided by capillary action.3. Different test methods were used to evaluate the grease-resistance property of coatedpaper. Neither transparent paper or kraft paper have grease-resistance performance, the greasebarrier property of coated papers were significantly improved compared with base paperaccording to Tappi-559kit test. A highest grease rating number of12was obtained and passhot oil test when transparent paper coated with3.3g/m2. However, even coated with6.7g/m2，kraft paper can’t pass the hot oil test. Contact angle of soybean oil on paper increases aftercoated, and it significantly increases when oil proof agent added. Contact angle reaching asteady state with the maximum rate of contact angle change was of merely0.06°/min withinthe first2minutes.4. WVTR and OTR of transparent and kraft paper after coated with CMC were studied.WVTR of transparent paper was meet the minimum of1727.58g/m224h when coated1.7g/m2and reach a stable value of1570g/m224h after a slight increase with coating weightincreasing. WVTR of kraft paper keeping around1625g/m224h when coating weight over3.5g/m2. OTR results of transparent paper and kraft paper can only be gained when coatingweight over1.7g/m2and5.2g/m2, respectively. OTR of transparent paper with coatingweight4.8g/m2drops one order of magnitude to1006.4cm3/m224h0.1MPa, compared to13258.7cm3/m224h0.1MPa when coating weight is1.7g/m2. However, OTR of kraft paperis still as high as12034.7cm3/m224h0.1MPa when coating weight is6.7g/m2.