Equilibrium moisture content in wet pressing of paper

Equilibrium moisture is a limiting factor in achieving high solids in the later stages of pressing or pressing low basis weight grades. We have developed a model that relates equilibrium moisture directly to the pore size distribution of fibers as measured by the solute exclusion technique. The model shows that chemical pulping and refining increase equilibrium moisture by increasing pore volume at given pore sizes in fibers, which leads to lower pressed solids and greater energy expenditure in the dryer section. Means to increase equilibrium moisture without compromising pulp strength are briefly discussed.

Maximizing pulp output and quality through measurement of plate gap temperature in high-consistency refining

The largest mechanical pulp production units are high-consistency refiners. In the high-consistency refiners, in-situ measurements of pulp quality are rare. Temperature profile is one of the measurements that is industrially applicable to estimate pulp quality. It measures the steam temperature in the refining area – but how it can detect deteriorated pulp quality will be shown. This paper analyzed the high-consistency refiner plate temperature and its correlation to pulp quality in a 1.34 MW pilot-scale Sunds RGP-44 variable speed refiner in a variety of operating conditions and particularly at production rates close to maximum refiner capacity. The study showed that there was a narrow band of optimal refining conditions at the maximum refiner production level just before pulp quality drastically decreased. When the refiner was pushed above this optimal point of operation, the plate temperature rapidly increased above normal refining temperature, causing reduction of fiber length and consequently lower pulp strength and quality. Thus, refiner plate temperature measurement was found to be a quick way and an effective tool for preventing low-quality pulp production through overloading the refiner.

Properties of bleached pulp sheets of avocado wood (Persea americana Mill.) pulped by Kraft and Soda processes

Chips of avocado wood (Persea americana Mill.) were pulped by means of conventional Soda and Kraft pulping processes. The pulps were bleached with an elemental-chlorine-free sequence OD1-Eop-D2, pre-setting reaction conditions for the first chlorine dioxide stage (D1) . The results show that during the chemical pulping process, avocado wood is easier to cook than other hardwoods such as eucalyptus. The avocado pulp also showed a very good bleachability, reaching brightness levels of up to 92% ISO compared to 84% for eucalyptus after the ECF bleaching sequence. The avocado Kraft pulps required more chemical input in the bleaching sequence than the Soda pulps. On the other hand, the physico-mechanical properties of the pulp were not notably reduced by the bleaching process, the Kraft pulp being stronger than the soda pulp. Strength properties of avocado are similar to those of eucalyptus; therefore this raw material constitutes a worthwhile choice for cellulosic fiber supply.

Modification in the properties of paper by using cellulase-free xylanase produced from alkalophilic Cellulosimicrobium cellulans CKMX1 in biobleaching of wheat straw pulp

Alkalophilic Cellulosimicrobium cellulans CKMX1 isolated from mushroom compost is an actinomycete that produces industrially important and environmentally safer thermostable cellulase-free xylanase, which is used in the pulp and paper industry as an alternative to the use of toxic chlorinated compounds. Strain CKMX1 was previously characterized by metabolic fingerprinting, whole-cell fatty acids methyl ester analysis, and 16S rDNA and was found to be C. cellulans CKMX1. Crude enzyme (1027.65 U/g DBP) produced by C. cellulans CKMX1, having pH and temperature optima of 8.0 and 60 °C, respectively, in solid state fermentation of apple pomace, was used in the production of bleached wheat straw pulp. Pretreatment with xylanase at a dose of 5 U/g after pulping decreased pulp kappa points by 1.4 as compared with the control. Prebleaching with a xylanase dose of 5 U/g pulp reduced the chlorine charge by 12.5%, increased the final brightness points by approximately 1.42% ISO, and improved the pulp strength properties. Xylanase could be substituted for alkali extraction in C–Ep–D sequence and used for treating chemically bleached pulp, resulting in bleached pulp with higher strength properties. Modification of bleached pulp with 5 U of enzyme/g increased pulp whiteness and breaking length by 1.03% and 60 m, respectively; decreased tear factor of pulp by 7.29%; increased bulk weight by 3.99%, as compared with the original pulp. Reducing sugars and UV-absorbing lignin-derived compound values were considerably higher in xylanase-treated samples. Cellulosimicrobium cellulans CKMX1 has a potential application in the pulp and paper industries.

Total Chlorine-Free Bleaching of Populus deltoides Kraft Pulp by Oxone

Since the bleaching process is one of the most important environmental pollutant stages in the pulp and paper industry, here, the total chlorine-free (TCF) bleaching of poplar kraft pulp by applying Oxone and peroxide under alkaline conditions has been investigated. The pulp samples were bleached in two stages of Oxone (OX) treatment using an AOX1OX2 sequence (A: acid pretreatment), and then the treated pulps were bleached by peroxide (P) to achieve target brightness (about 80%). The influence of various reaction parameters such as alkali charge, temperature, reaction time, and bleaching agent dosage was optimized. The final achieved brightness was more than 78%. Accelerated aging experiments showed more stability in brightness for the Oxone treated pulp, because alkali Oxone bleaching stops thermal degradation. Similarly, the AOX1OX2P bleaching sequence was found to be effective in regaining some strength that had been lost during acidification of the pulp. Improvement in pulp strength made with acid treatment was achieved along with significant amount of lignin removal and it demonstrates the feasibility of Oxone in TCF bleaching. Furthermore, other results indicated the feasibility of Oxone bleaching as an environmentally favorable alternative TCF bleaching sequence, compared with elemental chlorine-free bleaching approaches and also other TCF bleaching sequences.

Influence of cellulose supramolecular structure on strength properties of chemical pulp

The industrially produced chemical pulps have lower strength properties than those obtained under laboratory conditions, and this difference is referred to as the strength delivery (SD) problem. In this study, the hypothesis was put forward that the SD could, at least in part, be accounted for by the supramolecular structure of the cellulose microfibrils of the fiber wall. To test the hypothesis, two bleached softwood kraft pulps (BSKP) were manufactured from the same starting material with different degrees of cellulose aggregation, but the pulps were otherwise as similar as possible in other controllable respects. The chemical and physical properties, including the pulp strength, were tested. A selective increase of the degree of cellulose microfibril aggregation resulted in a pulp with a decreased tear index (TI) at a specified tensile index, and this decrease was similar in magnitude to what is typically encountered in SD. Accordingly, the current experimental study succeeded in mimicking the SD problem. The lateral fibril aggregate dimensions (LFAD) seem to play a pivotal role and it can be safely concluded in general that the supramolecular structure of cellulose in the fibers may be an important factor contributing to the SD problem.

Strengthening Effects of Cleaner Papermaking Additives WEC on Papermaking with Second Fiber

Effects of additives WEC on strength properties of second fiber were investigated in this study. For single use of WEC02A, the improvement of ring crush index was most remarkable, which increased by 21% for bottom pulp and 31% for surface pulp. Significant increase was also achieved in burst index while the improvement of tightness and folding endurance was not obvious. Besides, combined use of 0.2% WEC02 and 0.3% WEC03S improved folding endurance, burst index and ring crush index of pulp by remarkable 105%, 23% and 52%, respectively, showing a great performance for pulp strength enhancement, being beneficial to broadening the utilization of second fiber.

A comparison of fibre deformations from mill like and laboratory kraft cooking of softwood

The fact that industrial pulps have a lower strength than their corresponding laboratory pulps is an unsolved problem affecting in various ways the potential fibre utilisation in different mills. The loss of pulp strength has to a great extent been attributed to changes at the fibre level. In order to clarify in what way changes in fibre properties contribute to the strength losses, cooking experiments were conducted using a laboratory batch digester in which mechanical forces may be introduced. Fibre properties, i.e. fibre structure and fibre strength, of laboratory-made pulps were compared with those of an industrial pulp. It was concluded that two essentially different mechanisms may be identified; one related to the transverse fibre shape, the other to fibre damage. The latter is manifested as lower rewetted zero-span strength which reduces tear resistance and tensile strength of the pulp. The former is a collapse of the fibre, reducing the lumen area and resulting in a pulp with lower water-retaining capacity, given sheets of lower density and a pulp that has to be beaten to a higher degree to reach the desired bonding and the desired tensile strength.

Enhancement of Pulp Strength by Forming Polyelectrolyte Multilayers on APMP Fibers

The layer-by-layer deposition technique was adopted in this paper to improve the physical strength properties of alkaline peroxide mechanical pulp (APMP). The cationic starch (CS), anionic polyacryamide (APAM) and cationic polyacryamide (CPAM) were chosen and used to build-up polyelectrolyte multilayers on surface of APMP fibers. The improvements of physical strength of pulp through adsorption of different polyelectrolyte onto fibers were discussed and compared. The results showed that when the APMP fibers were treated with CPAM, the breaking length and burst index were 53% and 83% respectively, higher than that of untreated pulp. The optimal treatment conditions are 60 mgCPAM/g pulp, 1.5% pulp concentration and 9min treatment time. The pulp deposited by CPAM-APAM polyelectrolyte multilayer gave a highest physical strength compared with pulp with other multilayer deposition such as CS-APAM. At the whole beating degree range investigated in this paper, the CPAM-APAM deposition on fiber surface can improve the physical strength properties significantly, especially when the beating degree is at 40oSR. In addition, the improvement of physical strength can be remained even after pulp refining.