In recent years, with the import quota of foreign waste, the price of domestic waste has risen all the way, and the structure of raw materials for domestic packaging paper production has changed greatly. As we all know, most American waste (AOCC) is recycled once, and most of its original fiber is coniferous wood fiber, while most national waste (cocc or OCC) is recycled twice or even more than three times, with short fiber and poor strength, In this environment, papermaking enterprises, especially packaging paper enterprises, are faced with the problems of low raw material strength, difficult papermaking and rising demand for dry strength agents, starch and other chemicals. What are the root causes of poor raw material strength and how to effectively correct it? This is what every practitioner is thinking about.

We know that in the production process of paper, the pulp will go through the processes of online dehydration, pressing and drying, and the wet end pressing and drying will cause irreversible changes to the fiber, which will lead to the decline of the water filtration performance of the pulp when reused. In this environment, wet end filter aid chemicals such as water filter came into being. The decrease of swelling capacity leads to the decrease of toughness or plasticity of wet paper, which is characterized by low tensile, folding and breaking resistance when it is applied to the finished paper. It is found that during the drying process of the drying part, due to the thermal shrinkage of the fiber, the fiber structure becomes compact, and the smallest gap on the fiber surface is closed, resulting in a significant reduction in the elasticity and swelling capacity of the fiber. The wet end pressing will also cause fiber keratinization. With the increase of pressure and pressing time, the fiber cell cavity is crushed and the pores are irreversibly closed. With the decrease of paper moisture, the degree of fiber keratinization further increases.

In terms of pulp types, in the process of wet end pressing and drying, the degree of keratinization is followed by fully bleached chemical pulp, natural color chemical pulp, chemical mechanical pulp and mechanically ground wood pulp from large to small, that is, the higher the lignin content, the lower the degree of fiber keratinization in the process of pressing and drying. In this regard, recycled paper can give priority to the paper with high mechanical pulp content such as uncoated paperboard, so as to reduce the impact of poor papermaking filtration and low strength caused by fiber keratinization. In terms of the papermaking process, an appropriate amount of caustic soda is added during beating to prolong the disintegration time, enhance the degree of fiber swelling, and appropriately mitigate the impact of keratinization.

For the fiber raw materials with high degree of diagonal quality, it is appropriate to mix them with the waste paper with high content of recycled mechanical pulp, and add appropriate reinforcement chemicals such as dry strength agent and starch. In terms of wet end dehydration, it is considered to add an appropriate amount of water filtering agent to improve the papermaking performance.

According to the current situation of raw materials, it is suggested that paper enterprises establish a raw material fiber database to monitor the fiber morphology data of different batches of raw materials, so as to optimize the process in real time with the situation of raw materials. They can also strengthen cooperation with corresponding chemical suppliers in on-site service, and try to choose suppliers with perfect after-sales service system to buy products and services.