Research On The Improvement Of Strength And Water-Resistance Of Corrugated Paper In High Humidity Environment

In certain parts of Southern China, the strength and water-resistant properties of corrugated paper are often negatively influenced by high temperature and humidity of the environment. During the manufacturing and storing processes of corrugated paper, paper strength can be strikingly reduced. Therefore, the improvement of strength and water-resistant properties of corrugated paper in high humidity environment has been one of the urgent considerations of papermakers.In this work, the preparation of surface sizing agent based on glyoxal and urea was studied, and the parameters including pH, reaction temperature, reaction time, concentration of the reaction medium, and addition of the reactants, was discussed. The relative viscosity was used as an important parameter for the optimization of the copolymerization process. Based on the experimental results, the optimum reaction conditions were as follows:pH of 5.0-6.0, reaction temperature of 80℃, reaction time of 120 min, glyoxal/urea molar ratio of 1.50 to 1, concentration of the reaction medium of 45%, adding speed of glyoxal of 2 to 3 droplets per second. Under the optimum conditions, the polymer viscosity of as high as 5.058×10-3Pa·S was achieved.Glyoxal-urea resin was mixed with oxidized starch for use in surface sizing of the corrugated paper, and the optimum conditions for sizing were as follows:ratio of oxidized starch to glyoxal/urea resin of 90 to 10, solids content of the sizing agent of 6%, dosage of sizing agent of 8g·m-2. It was found that, when surface sizing was applied, the ring crush strength of the paper increased by 215.23%; also, breaking strength, stiffness, and folding strength of the paper increased by 112.15%,175.41%, and 125.00%, respectively. Experimental simulation of Field Production of high temperature and humidity conditions, the water resistance of the sheet was evaluated and paper's retention rate of ring crush strength increased by 65.89%. Taking humidity and polymer penetration into consideration, the influence of surface sizing on paper strength and water-resistance was analyzed, and the relevant mechanisms were also speculated and discussed.The use of glyoxal-urea resin in surface sizing of paper was also compared with styrene-acrylate polymer emulsion. The use of the two agents all strikingly increased the ring crush strength, stiffness, breaking strength, and folding strength of the paper, and the paper properties was approaching or even above the national A grade. Regarding ring crush strength, stiffness, and breaking strength, glyoxal-urea resin was superior to styrene-acrylate polymer emulsion. However, the use of styrene-acrylate polymer emulsion resulted in higher folding strength of the paper in comparison to glyoxal-urea resin, and it could also give better surface film- forming properties, better compatibility with oxidized starch, and higher water-resistance of the surface-sized paper. Nevertheless, the use of glyoxal-urea resin in surface sizing of corrugated paper has potential advantage regarding the product cost.