Application of the talc-starch composite system in surface sizing of corrugated base paper.

Abstract: This study mainly investigates the application of the talc-starch composite system in surface sizing of corrugated base paper. Talc is used to replace a certain proportion of surface sizing starch for surface sizing of corrugated base paper. The results show that under the conditions of 10% talc, 75% surface sizing starch, and 15% fixed starch substitute (all based on total surface sizing agent), after sizing (sizing amount 6g/n12), the transverse ring crush index of the corrugated base paper reaches 5.30 N-m/g, and the longitudinal ring crush index reaches 7.55 N-m/g; the transverse tensile index reaches 46.2 N-m/g, and the longitudinal tensile index reaches 95.9 N-m/g; the transverse folding endurance reaches 11 times, and the longitudinal folding endurance reaches 35 times.

    The morphology of talc mineral fiber is between that of plant fibers and traditional filler calcium carbonate, with properties comparable to fine plant fibers, having a high length-to-diameter ratio, good thermal stability, and chemical stability; it has high whiteness, which not only serves as a traditional paper filler but can also partially replace plant fibers and interweave with plant fibers to form a new type of 'plant fiber-mineral fiber' network structure.

    Currently, the common method used in the paper industry to increase the ring crush strength of paper is to use degradable starch during the surface sizing process. However, this method has the following issues: 1) Starch, as a major component of food, is expensive; 2) The load of wastewater increases when recycled paper is used (too much anionic waste), requiring the addition of expensive anionic waste capture agents. Therefore, developing new types of paper surface sizing agents is imperative. This experiment uses talc for surface sizing of corrugated base paper and analyzes its impact on the ring crush strength, tensile strength, and other indicators of the corrugated base paper.

Experiment

1.1 Experimental Materials

    Talc: Structural formula is Ca3Si309, chemical composition is SiO2 content 40%-50%, CaO content 45%-50%, provided by Daye Jinpeng Friction Material Co., Ltd.

    Starch substitute: Provided by a certain additive factory in Shandong.

    Surface sizing starch: Provided by Qingzhou Chenming Modified Starch Factory.

1.2 Experimental Instruments

JJ-1 precision electric stirrer, Changzhou Rongguan Experimental Analysis Instrument Factory; HHS type constant temperature water bath, Tianjin North China Experimental Instrument Co., Ltd.; 202-1 type electric drying oven, Huanghua Aerospace Instrument Factory; ZBK-100 paper surface absorption weight measuring instrument, Changchun Yongxing Instrument Co., Ltd.; TTM-500A ring crush strength compression instrument, Changchun Yongxing Research Paper Instrument Co., Ltd.; ZYD-3 computer tensile testing machine, Changchun Yongxing Instrument Co., Ltd.; KCC101 paper folding endurance measuring instrument, Changchun Small Testing Machine Factory; ST-1-260 type automatic coater, Shaanxi University of Science and Technology Mechanical and Electrical College Training Center.

2 Experimental Methods

2.1 Preparation of Talc-Starch Composite Sizing Solution

    Accurately weigh the surface sizing starch, talc, and starch substitute in proportion, mix the three evenly, then add an appropriate amount of deionized water to prepare a uniform gel with a mass fraction of 5%. Start the stirring water bath for heating, maintain the stirring speed at 100 r/min, keep at 90°C for 30 minutes, and after gelatinization is complete, discharge for later use.

2.2 Surface Sizing

    Using an automatic coater, evenly apply the self-made talc-starch sizing solution on the corrugated base paper, with a sizing amount of 6g/m2, and then dry and treat at constant temperature and humidity for 24 hours to balance moisture.

2.3 Performance Measurement

    According to GB/T 2679.8-1995, use a ring crush strength compression instrument to measure the ring crush strength of the corrugated base paper; according to GB/T 453-1989, use a horizontal tensile strength testing machine to measure the tensile strength of the corrugated base paper; according to GB/T 457-1979, use a paper folding endurance measuring instrument to measure the folding endurance of the corrugated base paper; according to GB/T 1540-2002, use a surface absorption weight measuring instrument to measure the water resistance of the corrugated base paper.

3 Results and Discussion

3.1 Scanning Electron Microscopy and Infrared Spectral Analysis

    It can be seen that talc appears needle-like and fibrous, with a length of 100-300 μm and a length-to-diameter ratio of about 30, comparable to fine plant fibers. With its high length-to-diameter ratio, talc can effectively combine with fibers, thus remaining on the surface of the paper.

At 3462 cm-1, there is a broad strong absorption peak, which corresponds to the symmetric and asymmetric stretching of crystal water. At 2409 cm-1 and 1622 cm-1, there are absorption peaks corresponding to the bending vibration of crystal water, indicating that this product contains a large amount of crystal water. The absorption peaks at 1104 cm-1 and 988 cm-1 correspond to the vibrations and rotations of SO2-, and the absorption peak at 613 cm-1 corresponds to the Fe-O bond, thus preliminarily identifying the starch substitute component as ferrous sulfate. The standard infrared absorption spectrum of ferrous sulfate is shown in Figure 3, and the absorption peaks of the starch substitute correspond to it, concluding that the starch substitute component is ferrous sulfate, which can be used as a sizing agent in the paper industry to improve the water resistance and impermeability of paper, effectively avoiding the problem of reduced water resistance caused by not adding AKD, while also reducing sizing costs.

3.2 The Effect of Talc Amount on the Ring Crush Strength of Corrugated Base Paper.

     The effect of talc dosage on the ring crush strength of corrugated base paper. As the amount of talc increases, the transverse ring crush strength of the corrugated base paper shows a slow upward trend. When the talc dosage is less than 15%, the transverse ring crush strength is proportional to the talc dosage; when the talc dosage exceeds 15%, the transverse ring crush strength begins to decrease. When the talc dosage is 15%, the transverse ring crush index of the corrugated base paper increases from 3.75 N-m/g to 5.96 N-m/g, an increase of 58.7%; the longitudinal ring crush strength also shows a rapid upward trend with increasing talc dosage, and when the talc dosage reaches 10%, the longitudinal ring crush strength begins to decrease slowly. When the talc dosage is 10%, the longitudinal ring crush index increases from 4.85 N-m/g to 7.55 N-m/g, an increase of 55.7%.

    The effect of talc dosage on the ring crush strength of corrugated base paper. A comprehensive analysis of the longitudinal and transverse ring crush strength curves shows that after adding talc, the ring crush strength of the paper increases significantly. After talc is gelatinized with starch and starch substitutes, part of it penetrates into the paper with the sizing solution, while part remains on the surface of the corrugated base paper. After drying, it forms a supporting layer with starch on the paper surface. Since mineral fibers are rigid and have relatively high strength, they overall enhance the ring crush strength of the paper. However, when the talc dosage reaches over 10%, the improvement in the ring crush strength of the paper is not as significant, because some fine mineral fiber components in the talc affect the physical interweaving between the paper fibers, partially destroying the hydrogen bonds between the fibers, which is detrimental to the enhancement of the ring crush strength of the corrugated base paper.

3.3 The effect of talc dosage on the tensile strength of corrugated base paper.

    The effect of talc dosage on the tensile strength of corrugated base paper. As the talc dosage continues to increase, both the longitudinal and transverse tensile indices of the corrugated base paper show a slow upward trend, reaching a maximum value when the talc dosage is 10%. Continuing to increase the talc dosage results in a decrease in the tensile index. When the talc dosage is 10%, the longitudinal tensile index increases from 75.4 N-m/g to 95.9 N-m/g, and the transverse tensile index increases from 32.4 N-m/g to 46.2 N-m/g, representing increases of 27.1% and 42.5%, respectively.

    The effect of talc dosage on the tensile strength of corrugated base paper. The most important factors affecting the tensile strength of the paper are the bonding strength between fibers and the strength of the fibers themselves. The main reason for the increase in tensile strength of the corrugated base paper shown in Figure 5 is that starch forms a dense starch film on the surface of the paper, and talc, being rigid, also contributes to the increase in tensile strength. When the talc dosage exceeds 10%, the improvement in tensile strength of the paper is no longer significant, as some fine components in the talc disrupt the starch film, affecting the hydrogen bonds and physical interweaving between the starch and fibers, partially offsetting the previous increase in tensile strength.

3.4 The effect of talc dosage on the folding endurance of corrugated base paper.

    The effect of talc dosage on the folding endurance of corrugated base paper. As the talc dosage increases, the longitudinal folding endurance of the corrugated base paper shows a rapid upward trend, reaching a maximum value when the talc dosage is 10%, increasing from 10 times to 35 times, an increase of 250%. After that, as the talc dosage continues to increase, it rapidly decreases, but remains higher than the longitudinal folding endurance of the corrugated base paper without talc. With the increase in talc dosage, the transverse folding endurance slowly increases, reaching a maximum value when the talc dosage is 10%, increasing from 4 times to 11 times, an increase of 175%. After that, as the talc dosage increases, it also shows a downward trend.

    Compared to tensile strength, the folding endurance of the paper is more dependent on the length of the fibers themselves. After adding talc, the folding endurance of the paper increases significantly. This is because talc mixed within the starch film forms a supporting layer on the surface of the paper, which is the main reason for the increase in folding endurance of the corrugated base paper. However, when the talc dosage exceeds 10%, some fine components in the talc affect the physical interweaving between the starch film and fibers, while also disrupting the hydrogen bonds between the fibers, leading to a certain degree of reduction in the folding endurance of the corrugated base paper.

3.5 The effect of talc dosage on the water resistance of corrugated base paper.

    The effect of talc dosage on the water resistance of corrugated base paper. A smaller Cobb value indicates better water resistance. As shown in Figure 7, with the increase in talc dosage, the water resistance of the corrugated base paper continuously decreases, as talc partially disrupts the sizing film formed by starch and starch substitutes on the surface of the paper, and the more talc is added, the worse the water resistance of the paper becomes.

4 Conclusion

    Using talc to partially replace surface sizing starch and compounding it with some starch substitutes to prepare a sizing solution, the effect of talc on the performance of corrugated base paper is analyzed.

4.1 When the talc dosage is 10%, surface sizing starch is 75%, and fixed starch substitutes are 15% (all relative to the surface sizing agent), under a sizing amount of 6g/m2, compared to the paper sample without added talc, the longitudinal ring crush strength of the corrugated base paper increases by 55.7%, the transverse ring crush strength increases by 41.2%; the longitudinal tensile strength increases by 27.1%, the transverse tensile strength increases by 42.5%; the longitudinal folding endurance increases by 250%, and the transverse folding endurance increases by 175%.

4.2 The addition of starch and starch substitutes gives the corrugated base paper a certain degree of water resistance, but its water resistance decreases with the increase in talc dosage.