Chemical control of contaminants in the pulp and paper manufacturing process

Nell’industria della pasta e della carta, la presenza di contaminanti nel processo di fabbricazione è associata ai depositi sui macchinari di lavorazione. Tali depositi causano una riduzione di qualità del prodotto finale, che a sua volta genera un aumento del costo della carta a seguito di perdite di produzione.

Carla Veríssimo - R&D Manager - Contech

Different sources of contamination can be described, yielding an impressive number of contaminants. Based on the raw material used for paper manufacturing, different contaminants can be present in pulping and papermaking processes, which makes highly efficient cleaning programs crucial.
Contamination can be classified as organic, inorganic, or microbiological. Organic contaminants are called pitch or stickies based on their origin - whether natural or synthetic, respectively (Fig. 1). The incidence of organic deposits on the wet end of machinery causes a serious industrial problem. The origin of pitch particles are the lipophilic extractives of wood and comprise a variety of compounds such as fatty acids, fatty alcohols, resin acids, sterols, waxes, etc. Stikies are particles presenting, as the name says, sticky features and other impurities that arise from recycled fiber, usually coming from adhesive labels, ribbons, envelopes, and stamps. Pressure sensitive adhesives, hotmelts, latex, and inks are cited as the main components of this contamination. Stickies particles are also classified according to their size in macro-, micro-, and colloidal stickies (Fig. 2). Macrostickies are particles presenting tacky features, rejected by a 100-µm laboratory screen, whereas microstickies have a diameter smaller than 100 µm down to 1-5 µm in size. Stickies in the colloidal state, with diameters of around 1µm, are considered not harmful to the process, as long as they remain in the colloidal phase. Destabilization of the process - caused by changes in the system’s ionic demand, in temperature, pH, etc. - can lead to the agglomeration of the colloidal particles, making them bigger and able to precipitate, forming damaging deposits on machinery.


ORGANIC DEPOSITS CAN OCCUR ALONG WITH INORGANIC SCALE, also responsible for damages to the papermaking process. Ca2+ and Mg2+ cations are able to interact with anions such as carbonate, sulfate, and oxalates, leading to the precipitation of insoluble deposits. Silicates, barium sulfate, and aluminum hydroxide are also common compounds in scales.


DUE TO AN INCREASING USE OF RECYCLED FIBER, as well as the manufacturers switching to closed-loop water systems, the tendency is the occurrence of higher levels of contaminants enhancing the formation of deposits and increasing the number of defects on the final paper, machinery, and production, causing losses.
Since the occurrence of deposits is proportional to the amount of contaminants, the removal of these contaminants is crucial, otherwise these interfering substances will accumulate and lead to deposits and processing problems.
This scenario shows the essential role of suitable and highly efficient contaminant control programs in pulp and paper processes. At this point, defining accurate strategies to avoid the formation of deposits is very important for the proper operation of the papermaking system. Treatments based on the application of a dual system of products is a very effective approach: product one, with a high-power dispersive action, reduces the size of the contaminant particles so that they remain stabilized in colloidal form; product two acts by an encapsulation mechanism of pitch and stickies particles, with rear fixing of the particle on the paper fiber, inhibiting the damaging agglomeration, and eliminating the tacky feature of the particles both in the papermaking and in the converting process.


CONTECH, A CHEMICAL COMPANY FOCUSED ON THE DEVELOPMENT OF SOLUTIONS FOR THE PULP AND PAPER SEGMENT, has been continuously making efforts in R&D seeking the best answers for a cleaner papermaking process and, thus, more efficient results. The contaminant control developed by the company consists of pulp treatment with Contech’s dual system.
In the case of dispersion, Fig. 3A shows the size of pitch particles for a pulp sample and Fig. 3B presents the efficiency of the dispersion with the reduction of their size from 1 to 0.75µm. Figure 3C shows a graph for a raw sample containing stickies particles and, after the application of product one, the size of the particles decreased from 1.8 to 0.45 µm (Fig. 3D). For detackification and fixing (product two), Fig. 4A shows the variation in the amount of contaminant particles based on different treatment strategies for the same cellulosic mass, whereas the optical micrographs in Figs. 4B, C, and D exemplify the removal of contaminant particles after the treatments.


CONTECH ESTABLISHED ITS POSITION ON THE MARKET WITH TECHNOLOGIES AND PRODUCTS developed by experts and researchers from different specialties and engineering. The company patented innovative solutions, developed systems adaptable to several customers’ needs, and solidified its brand by providing excellence in products and services. The patented mechanical system for the application of chemicals for the conditioning of pulp and paper machinery presents the advantage of being able to perform cleaning operations with the paper machine running. Chemical agents responsible for felts and wire treatment are applied without stopping the machine, allowing production savings in time. Effective in batch or continuous cleaning for the removal of contaminants found on wires and wet felts, clothing treatment promotes a reduction in shutdown time, and increase in the service life of clothing, and improved machine productivity and paper quality. Figures 5A and 6A show pictures of used clothing collected from different machines presenting incrustations. After clothing treatment with appropriated products, the effectiveness of the cleaning process can be seen in Figs. 5B and 6B.


CONTECH IS CONTINUOUSLY PUTTING EFFORTS IN PREVENTIVE TREATMENTS FOR CLOTHING MAINTENANCE. The preventive treatment for felts and forming wires aims to inhibit the adhesion of insoluble materials, forming a protective layer on the surface of the felt and increasing resilience. This treatment is based on the passivation of the cloth with appropriate chemicals and minimizes the incidence of holes and defects on the paper sheet. Any residual product goes into the white water system and acts on the reduction of adherence in blades, rolls and in the suction box, preventing substances from depositing. In general, improved productivity and final paper quality can be observed as results of the treatment.

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