In recent years, my country's paper industry has developed rapidly. In 1995, the output of machine-made paper and paperboard in the country was 2400x104t, ranking third in the world (first in the United States and second in Japan), an increase of 3.5 times from 563x104t in 1980, with an average annual increase of 10.5%. In 2018, China has become the first major producer, and its output has increased by hundreds of times.There is a shortage of wood pulp, especially long-fiber wood pulp in my country. Many paper types need to be equipped with short-fiber broad-leaved wood pulp, straw pulp, and recycled pulp. This will inevitably lead to a reduction in paper degree, so it is necessary to take measures to increase paper strength. The strength of the paper is controlled by the bonding strength between the fibers. The bonding strength between fibers is directly related to the number and quality of hydrogen bonds formed by the bonding part. The application of paper reinforcement is a good way to strengthen the bonding between fibers, which can avoid the increase in the tightness of the paper and the increase in temperature deformation caused by the increase in beating. The opacity, absorbency, air permeability and even tearing degree are reduced.
At present, the main paper enhancers can be divided into dry enhancers and wet enhancers according to their functions. Dry strengthening agents (hereinafter referred to as dry strength agents) mainly include starch, modified starch, vegetable gum, polyvinyl alcohol, and polyacrylamide (PAM), among which the most commonly used are PAM and cationic starch. PAM can be divided into non-ionic (NPAM), cationic (CPAM), anionic (APAM) and amphoteric (EPAM) according to its basic structural characteristics. The retention rate of paper enhancer decreases, and the enhancement effect of paper decreases. In the past two to thirty years, the research and development of enhancers can be said to be a method of assisting retention. Because there are anionic impurities in the wet end of the paper machine, the retention performance of the cationic reinforcement is relatively good. NPAM is not easy to be absorbed by the fiber, so the reinforcement effect is not good.Polyacrylamide for paper industry APAM has the same negative charge as fibers and fillers, and aluminum sulfate is needed to increase the adsorption of APAM to fibers and fillers. However, since acid sizing usually uses aluminum sulfate as a precipitating agent, APAM is generally used in papermaking systems for acid sizing. CPAM is suitable for a wide range of pH and can be used in papermaking systems for acid sizing and neutral sizing. Relatively speaking, the stability of CPAM is worse than that of APAM, and the price is also higher. To solve these problems, many methods have been proposed.
PAM paper enhancers have been in practical use for more than 40 years. During this period, the raw materials and papermaking environment have undergone significant changes, and the additives have also been improved in various ways. It is difficult to obtain satisfactory results by using a certain additive alone. It is developing in the direction of mixing APAM and CPAM, cross-linking high-density PAM, PAM-starch, and then developing a formula that can be applied under complex papermaking conditions.
Because the hydrogen of the Polyacrylamide for paper industry amide group is easily combined with the hydroxyl group in the fiber, the bonding effect of the oxygen bond is strengthened, and the strength of the paper is increased. Polyacrylamide is a very effective reinforcing agent for papermaking. It has the advantages of low dosage, convenient operation and obvious effect. Not only can it improve the strength of the paper, but also has a good retention and filtering effect, which can reduce the consumption and cost of paper pulp. Due to the large proportion of grass in my country's papermaking raw materials, there is an urgent need to develop better pulp enhancers. Therefore, it is necessary to make full use of the advantages of various types of enhancers, and to develop a cheap and stable performance enhancer suitable for my country's paper production, especially grass and waste paper raw materials.