Preparation Of Novel Nanocomposite Surface Sizing Agent And Its Application In Cellulosic Paper

Nanocrystalline cellulose(NCC), derived from naturally occurring cellulose, is an emerging renewable nanomaterial that holds great promise in various different application areas. NCC could be used as a reinforcing phase in composite structure because of its unique structure and inherent mechanical properties, which may facilitate the formation of powerful composite network structure, thus improving its mechanical and barrier properties. In this sense, NCC may also be used in surface treatment of cellulosic paper for imparting desired mechanical properties and barrier properties to the end-use products. Nevertheless, due to the negatively charged characteristics of NCC, serious adsorption and aggregation will inevitably occur when NCC encounters cationic surface sizing agent, such as cationic styrene atyrene acrylic emulsion, which will affect the rheological properties of composite emulsion and its application in cellulosic paper. More importantly, the surface of NCC contains large amounts of hydrophilic groups, which is not conducive to the improvement of water resistance of paper. Therefore, in order to improve the compatibility between NCC and emulsion system as well as the application efficiency of surface sizing process on sizing paper, surface modification of NCC is essential prior to targeted application.In the present work, nanocrystalline cellulose was initially prepared from microcrystalline cellulose by sulfuric acid hydrolysis, and subsequently cationically modified with glycidyltrimethylammonium chloride(GTMAC). The obtained product here was named as CNCC. It was found that CNCC exhibited a rod-like structure with a diameter between 10 and 80 nm and a length less than 400 nm, and displayed desired dispersion in liquid suspensions. Moreover, CNCC was found to possess a degree of substitution of 4.1% by nitrogen content determination. Successful modification of NCC was identified by FT-IR and XRD result. In addition, TEM and TG results further confirmed that CNCC had remarkable advantage in dispersibility and thermal stability as compared to NCC.Subsequently, starch/CSA/NCC(CNCC)nanocomposite suspensions were prepared by a physical blending process. The dispersion behavior, particle size distribution level and thermal stability of the resulted suspensions were evaluated, respectiviely. It can be seen that starch/CSA composite suspensions in presence of NCC exhibited a serious aggregation, which lead to the increased average particle size. The dispersion stability of starch/CSA composite suspensions was obviously improved as a function of the added CNCC. TG and DTG results demonstrated that the addition of NCC was not able to improve the thermal decomposition behavior of starch/CSA, but CNCC addition played a positive role in the improvement of thermal stability.Eventually, the possibility and feasiblity of the application of NCC or CNCC in surface sizing of cellulosic paper were investigated. The tensile index, tear index and folding endurance were introduced to evaluate the mechanical properties of the sized paper, and the air permeability and water absoption were determined to evaluate the barrier performances of the resulted paper. The preliminary application experiment showed that, NCC had opportunity in improving the mechanical properties of sized paper, while CNCC was effective in improving the barrier properties of sized paper. Overall, the surface sized paper showed a variation trend of rise first then fall with the increased addition of NCC/CNCC. Specifically, at an addition of 0.2%, the sized paper showed a desired application efficiency of NCC and CNCC. As compared to the controlled paper, NCC reinforced cellulosic paper showed more than 10% improvement in mechanical properties, and the barrier properties of cellulosic paper reinforced with CNCC were enhanced by 20%.