Study On Enzymatic Deinking Of Laser Printed Waste Paper

With the rapid development of office automation and information, the proportion of laser printed paper in the consumption of office paper has been increasing day after day. People pay more attention to recycle of waste paper for the protection of forest resources and environment. Paper mill will gain profit from the utilization of recycled fiber, it is profitable to decrease pollution, cost, and investment. Therefore, waste paper recycling is becoming one of the top topics all over the world.Laser printed toner is made of carbon black, thermoplastic resins and electric-magnetic iron oxide. The thermoplastic resin that we commonly use are polystyrene, the copolymerization of ethylene and vinyl acetate, nitro cellulose , polyvinyl chloride(PVC), polyamide(PA) and polyester, etc.Conventional de-inking technology with alkali can not get great efficiency to laser printed paper and has threatened environment badly. Consequently, experts paid more and more attention to new de-inking technologies and. The research of bio-de-inking technology has opened up a new way for paper de-inking. Besides, ultrasonic and other technology has begun to be investigated by some researchers, which is still in its starting stage.In this paper, laser printer paper as the research object,through research of situation analysis and enzyme deinking method. All kinds of enzymes deinking were examined, in order to identify the best soluble enzyme for laser printing paper deinking. The results showed that the mixture deinking of cellulase and amylase was best, the brightness of paper pulp coudle be increased by 12%. Various processing conditions of cellulase and cellulase and amylase were study on the laser-printed waste paper deinking, cellulase and amylase of different dosage, reaction time, reaction temperature, pH and processing conditions were studied on deinking of laser printed waste paper, in order to determine the optimal process conditions. Effect of Cellulase and amylase was studied on the strength properties of fiber. The deinking mechanism of cellulase and amylase was study.In this paper, several process routes were used for experiment research of deinking, the experiment characterization was used by brightness and dirt area, in order to study the optimal design of enzyme deinking line, the best process route is low environmental pollution, low energy consumption. The deinking of ultrasound and enzymatic, and the deinking of UV and enzymatic were studied. By comparing the various technology of deinking, the best de-inking technology of enzymes was high efficiency, energy saving, environmental protection, and its deinking mechanism was studied. The proper de-inking technology is alkali (pH9-10) pre-treating→pulping→enzymatic process→ultrasonic process→flotation→filtration→drying, or UV irradiation→pulping→enzymatic process→flotation→filtration→drying. To be brief, these two combined technologies are simple, economical and environment-friendly. Combined de-inking technology with ultrasonic and enzymes can improve the brightness and dirt area ratio of pulp in some degree. Influence of UV irradiation time and ultrasonic processing time on brightness and dirt area were studied.Enzyme is high efficiency biocatalyst. It has been successfully employed in chemistry, biological engineering, medicine, life sciences and other fields. In recent years,It has also applied on waste paper de-inking. However, its application is restricted because of the following shortcomings. (1) Enzyme can affect the quality of product because the separation of enzyme solution and product is difficult . (2) Enzyme solution has poor stability. In order to solve these problems, immobilized enzyme technology is used. Enzyme is immobilized onto certain carrier by physical or chemical method. Immobilized enzyme has good stability and re-using advantages. It is easy separation from product and the catalytic activity of enzyme is still retained.There are many types of immobilized enzyme technologies, e.g., adsorption method, embedding method, covalent binding method, and cross-linking method. In adsorption method,enzyme is fixed to the carrier surface by physical action. This method is relatively simple, less loss of enzyme activity, but the force of enzyme with the carrier is weak. In embedding method, enzyme is enwrapped by carrier (chitosan, gelatin, sodium alginate, etc.) as aggregation, precipitation or gelation, which has less strength. In cross-linking method, enzyme is linked to the surface of carrier by dual- reagents, so the combination of enzyme and carrier is stronger.In order to choose a good carrier, the intensity of spherical silica gel, PVA membrane, and chitosan ball were measured according to waste paper deinking process condition, the most suitable carrier was spherical silica gel carrier. In this paper, a covalent cross-linking process using glutaraldehyde was used to immobilize cellulase and amylase onto silica gel carrier(support) . The immobilized enzyme was introduced into the de-inking process of HP laser printed paper.Immobilization time of cellulase and amylase will impact activity of enzymes, so different immobilization times were assessed. The de-inking efficacy of the soluble and immobilized cellulase and amylase were evaluated. The results show that the brightness of immobilized enzymes which was equivalent to 5mg soluble enzymes was higher 1.88% (%ISO) than that of 40mg soluble enzymes. Therefore, the de-inking efficiency of immobilized enzymes excelled obviously soluble enzymes. Enzymes usage could be further reduced. Immobilized cellulase and amylase was applied on laser printing waste paper de-inking. It could be reused repeatedly for 4 times in the de-inking process. Cellulase activity of immobilized enzymes retained over 50% for 4 times de-inking. The activity of immobilized enzymes for storage 14 days retained 81%, which illustrates immobilized enzymes have storage stability. The deinking mechanism of immobilized cellulase and amylase was study. The reason which immobilized cellulase and amylase had better de-inking efficacy than soluble cellulase and amylase was studied.The deinking comparison of soluble cellulase with alkali, the deinking comparison of soluble cellulase and amylase with alkali, and the deinking comparison of immobilized cellulase and amylase with alkali were carried out. The results showed that the deinking of immobilized cellulase and amylase was superior to alkaline de-inking. This reduced use of a large number of chemicals, reduced the pollution of the environment. The conomic balance of the soluble and immobilized cellulase and amylase were evaluated. The results showed that immobilized cellulase and amylase was effective, and they can be recycled. This greatly reduced the cost of de-inking.Through the industrialization analysis of immobilized cellulase and amylase, if there is no alkali, immobilized cellulase and amylase achieve the deinking of laser printed waste paper. It showed immobilized enzymes deinking is low environmental pollution, low energy consumption and provides the conditions for industrial production.