Paper packaging improvement using corona discharge and spray coating of cellulose nanofibrils and nanoclay

Abstract

The cellulose nanofibrils (CNF) from wood, non-woody plants and agricultural residues as one of the most abundant natural biopolymer on earth is an interesting new material that has attracted increasing interest due to its renewability, nontoxicity, biodegradability and low cost, which has been used as an important and fundamental materials in various fields such as paper, paper coating, medicines, plastics, cosmetics and etc. A natural use for these nanofibrils can be in the production of paper and paper packaging materials. Actually, the packaging industry has always been using cellulose-based materials, and nowadays, cellulosic packaging is an assorted category, which includes both wrapping materials and containers. In the first phase of this study, CNF water base suspension were coated on kraft writing and printing papers to investigation on the enhancement of the tensile and barrier properties of paper to use in paper packaging. An experimental assembled spray coater was used to coating paper substrate with CNF suspension. The spray variables i.e. concentration of suspension, time, distance and pressure of spray were studied. The coated papers were analyzed in terms of the oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) in order to quantify the barrier effect of the applied coatings. In addition, the tensile strength was determined and image analysis of the structure was performed to examine the coating adhesion. The WVTR and the oxygen permeability of the papers decreased while tensile strength increased with a one-layer coating of CNF. The tensile and morphological properties of the coated papers indicate good adhesion between the coating and the base substrate using spray coater. The properties improved with increasing spray time and pressure and decreasing with concentration and distance. In the second phase, CNF and nanoclay as an aqueous slurry suspension was sprayed on the kraft writing and printing paper surface to achieve a coated sheet. Upon drying, the suspension on the paper surface formed a hybrid nanocomposite layer with CNF (matrix) and nanoclay (mineral filler). The corona discharge was used in order to enhance the wetting of paper surfaces and the resulting in improvement of adherence between paper and hybrid composite. It was observed that by increasing the spray time, all of the properties were improved, while by increasing the nanoclay content, the barrier properties were improved and the tensile strength was decreased. The properties of coated sheets improved with corona discharge. The analysis of tensile strength and morphological properties of the coated sheets indicated good adhesion between the base substrate and the hybrid composite.