By Bi Kezhen, Lu Wei, Hangzhou Research Institute of Chemical Industry
Paper chemicals are a collective name of various chemicals and additives used in the making of paper. They have 4 major categories of pulp making chemicals, paper making chemicals, paper processing chemicals and pollution control chemicals. Paper chemicals have extremely extensive applications in the entire process production of pulp and paper. They are included in the “Guidelines for Priority Areas of High-Tech Industrialization in Current Development”.
Present development status of several paper chemicals
1. Pulp-making deinking agents
Pulp-making deinking agents mainly refer to waste paper deinking agents. Waste paper deinking agents used in early days were mostly nonionic and anionic surfactants synthesized through petrochemical routes and their compounded products. With constant advances of biotechnology, bio-enzyme compound preparations have made a rapid development in paper industry today on strength of their sound application performance and low production cost. Nevertheless, the stability and the environment adaptability of bio-enzyme deinking agents are quite poor. In waste paper deinking systems with complicated environment the activity of enzymes is hard to control. In this way the large-scale application promotion of enzymatic deinking technology is restricted. Efforts should therefore be made to develop bio-enzyme deinking agents with wide application scope, high activity and simple process and unfold researches on surfactants with good synergistic effect with enzymes and their compounded products so as to enable bio-enzyme deinking technology to gradually replace traditional chemical deinking technology.
2. Dry strengthening agents
The use of dry strengthening agents is mostly intended to increase the strength of paper. Dry strengthening agents used quite often in paper industry in China today mainly include starch-based substances and polyacryl amines (PAM). Owing to their good acting effect, low application cost and simple operation, starch-based substances are most-welcome dry strengthening agents today. A large number of researches on the use of modified chitose, modified guar gum and modified carboxymethyl cellulose as dry strengthening agents have also been conducted. Researches on dry strengthening agents made both at home and abroad in recent years are mainly concentrated on the application and development of new processes and new products. New processes shift the traditional pulp internal addition of dry strengthening agents into paper external addition through impregnation method. New dry strengthening agents mainly include polyvinyl amines, cationic modified polyvinyl alcohols and hyper-branched polymers.
China has already made rather intensive researches on papermaking dry strengthening agents and also successfully developed quite a few varieties. The application promotion of new products is yet to be further intensified. In view of the feature that fiber raw materials used in the making of paper in China are mainly straw pulp and recycled pulp, the independent development of new technologies and the rational introduction or utilization of foreign advanced technologies should be made in future to develop and produce suitable papermaking dry strengthening agents with high performance and low cost.
3. Sizing agents
The use of sizing agents in paper industry is mainly intended to improve the waterproof property of paper and paperboards. Sizing agents with extensive applications today include natural varieties and synthetic varieties. Natural sizing agents mainly have rosin gum and starch. Major synthetic sizing agents used most often today are alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA). As AKD has defects of sizing lagging and easy hydrolysis, its fast curing technology has achieved an outstanding development. The fast curing of AKD is mainly done from following two aspects. One is that alkali substances that can promote the ring opening of AKD are added in the emulsification of AKD to accelerate the reaction of AKD with fibers. The other is that modification is conducted to AKD molecules themselves to increase their curing speed. ASA is a papermaking sizing agent with medium alkalinity. Its most prominent features include high reactivity, fast sizing curing and no sizing lagging. Its stability in water is however not as good as AKD. How to improve the stability of ASA emulsion has therefore become a hot research spot.
4. Retention/drainage agents
The main role of retention agents used in paper industry is to increase the retention rate of fillers and micro components and the ash content of paper. Drainage agents can improve water drainage property and increase water removing speed. Technologies for papermaking wet-end retention/drainage agents have experienced a development course of one-component retention/drainage systems, two-component retention/drainage systems, micro-particle retention/drainage systems and network retention/drainage systems. Retention/drainage agents used most often today mainly include starch, PAM and micro-particle retention/drainage systems. Micro-particle retention/drainage systems with quite a lot of researches include cationic polyacryl amide (CPAM)/modified bentonite system and cationic starch/colloidal silicon dioxide system. The cost for the use of micro-particle retention/drainage systems is still higher than one-component retention/drainage systems and two-component retention/drainage systems today. It is also a factor that needs to be considered by paper mills when they select the most optimal retention/drainage technology.
Researchers have made intensive researches on flocculation mechanisms of various systems. The development of new systems is therefore boosted. Future retention/drainage technologies will be faced with all kinds of pressures such as greater machine speed, higher untrimmed width, twin-wire forming, dilute water head-box, closed cycle, high ash content, new fillers, low cost and higher paper machine efficiency. Synthesizing new multi-functional highly-branched polymers and developing their applications in paper industry by relying on the rapid development of polymer science will become a hot research spot.
Development prospect of paper chemicals
1. Special chemicals for waste paper reclaimed fibers
The consumption of waste paper pulp in China reached 63.02 million tons in 2017, accounting for 63% of the total pulp consumption. The use of waste paper pulp in great quantities has made the demand of special chemicals for waste paper reclaimed fibers become more urgent. Special deinking agents, strengthening agents, retention/drainage agents and pitch controlling agents will be needed. The research and development of related products and technologies should have greater attention and intensification.
2. Special chemicals for fillers
In papermaking raw materials the consumption of inorganic fillers holds the second place, only next to fibers. Inorganic fillers and fibers however lack affinity with each other. As the consumption proportion of fillers goes up, the bonding force between fibers is coming down. The internal bonding strength and the surface strength of paper are therefore affected. In advanced countries the ash content in cultural paper has already reached 30%. In China however the ash content in similar paper is still very low and it is imperative to add development impetus.
3. Special chemicals for energy conservation and emission reduction
According to data from the National Bureau of Statistics, the emission amount of waste water from papermaking and paper products in China was 2.76 billion tons in 2014, accounting for 14.7% of the total industrial waste water emission amount. The emission amount of COD in waste water was 478 kt, accounting for 17.4% of the total industrial COD emission amount. The emission amount of ammonia nitrogen was 16 kt, accounting for 7.8% of the total industrial ammonia nitrogen emission amount. Remarkable advances in environmental protection have been achieved with strenuous efforts made by paper industry, but pressures are still enormous. The development and application of special chemicals for energy conservation and emission reduction should therefore be accelerated.
4. Functional chemicals for high-grade paper and special chemicals for specialty paper
High-grade paper and specialty paper with heavy dependence on chemicals are high-profit zones in paper industry. Due to needs in the development of new products and new processes in papermaking, special chemicals for high-grade paper and specialty paper have kept emerging. China is still unable to fully satisfy needs in the development of paper industry today and imported products are needed to bridge the gap.
Take coated printing paper in high-grade cultural paper for instance. The output of such paper in China was 7.65 million tons in 2017, accounting for 6.87% of the total paper and paperboard output. In addition to wet-end chemicals such as strengthening agents, retention agents and drainage agents, functional surface chemicals are especially needed in high-grade cultural paper. The research and development of functional surface special chemicals in China is still lagging behind. Indicators such as surface strength, finishing behavior and printability more often than not fail to meet relevant requirements. It is therefore essential to intensify the development of functional surface chemicals.
The output of specialty paper and paperboards in China was 3.05 million tons in 2017, accounting for 2.74% of the total paper and paperboard output, being much lower than the level in advanced countries. Future development potentials are huge. It is imperative to develop special chemicals needed in specialty paper and paperboards such as fruit packaging paper, formaldehyde-free paper, heat-sensitive paper, antistatic paper, electro-conductive paper and anti-falsification paper.
