Study On The Paper Barrier Coating And Its Barirer Properties

Paper and paperboard are widely used in the field of packaging, but gas and water vaporbarrier properities are usually very poor for the porosity of paper and hydrophilic of fiber. Atpresent, the better barrier performance is usually gained by impregnation processing,composite technology and barrier coating. In order to meet the environmental friendlyrequirements, renewable and biodegradable biopolymers become one of the research focusesfor good development prospect. Chitosan as a biodegradable polymer is the second mostabundant natural renewable biopolymer after cellulose. Therefore, the application inenvironmental friendly paper coating areas has attracted many foreign researchers. This paperfocuses on the study of chitosan used in paper barrier coating, and chitosan based on bi-layerand composite coating are discussed. All these works will lay a foundation for the furtherresearch and application of chitosan in paper barrier coating.In the study, the effect of chitosan solution and base papers on paper barrier coating werestudied firstly. Secondly, chitosan used in packaging base paper and white cardboard weredetailedly discussed about the oxygen barrier properties, moisture barrier properties as well asoil resistance. At the same time, coating structure was analysed and characterized by SEM,AFM, FTIR-ATR and CLSM. Then, PVDC was applied in paper barrier coating, andchitosan/PVDC bi-layer coating was studied to improve water vapor and water resistance.Finally, a preliminary research that was about chitosan/montmorillonite(MMT) compositecoating was made, and the mechanism of barrier properties caused by MMT was discussed.The main results obtained from the paper are:1. The concertration of chitosan solution which need to be less than2wt%with massratio between chitosan and acetic acid at1:0.5is suitable for barrier coating. Chitosan solutionhas a very good film formation performance and film uniformity on paper surface with thehigher smoothness and lower air permeability of paper.2. After coating chitosan on the surface of packaging base paper, SEM and AFM showthat the pores among fibers are sealed, paper surface become smooth, and an uniform film is formed while increasing the amount of chitosan. Chitosan coating reduces air permeabilitygreatly, and the oxygen transmission rate (OTR) at coating weight1.87g/m~2decreases by83.4%at least compared with base paer. The OTR is322.7cm~3/m~2·24h·0.1MPa whenincreasing coating weight to3.68g/m~2which reduces98.1%relative to1.87g/m~2coatedpaper. Chitosan coated paper obtains good oxygen barrier property. Meanwhile, chitosancoated papers gain excellent oil resistance and strength performance, but moisture barrierproperties changes little with water resistance declining.3. Chitosan applied in cardboard coating, SEM and AFM characterizations show thatthe film is uniform, continuous and without pores. CLSM analysis shows that chitosan stayswell on the paper surface. OTR of one layer coating with1.96g/m~2chitosan has dropped by99.3%at least compared with base paper, which means oxygen barrier property is greatlyincreased. OTR has fallen to less than200cm~3/m~2·24h·0.1Mpa at3g/m~2chitosan coatingweight. Chitosan coating makes the paper better oil resistance and stiffness, while moisturebarrier performance decreases and the surface is more sensitive to water. Moreover, barrierproperties of chitosan coated on the back side of paper is not as effective as that on the topside for its worse surface performance.4. PVDC coated paper gains oxygen barrier properties, moisture barrier performanceand water resistance. Water vapor transmission rate (WVTR) of PVDC coating weight at7.73g/m~2falls by33.9%compared to base paper, but to obtain the same OTR, PVDC coatingweight is about two times as the chitosan weight, which indicates that moisture barrierperformance of PVDC coated paper is better than chitosan coated paper, while its oxygenbarrier properties is worse than the latter, so chitosan/PVDC bi-layer coating may compensatefor the shortcomings of each other. As for chitosan/PVDC bi-layer coating, the WVTRreaches to223.3g/m~2·24h, which decreases by59.3%compared to base paper and reduces to66.3%compared to chitosan coated paper, at the same time oxygen barrier properties andsurface water resistance have a larger lifting.5. The WVTR of chitosan/MMT composite coated paper is lower than that of chitosancoated paper. According to the dosage of chitosan and MMT, WVTR of composite coated paper decreases by17.8~39.7%relative to chitosan coated paper. Nielsen model andBharatdwaj model combined with XRD analysis show that, chitosan and MMT is mainly inthe phase separate state, with part of intercalation. Meanwhile, the oxygen barrier propertiesand water resistance improve obviously.