102 ISSN 1683-0377. Proceedings of BSTU. 2014. No. 4. Chemistry, Organic Substances Technology and Biotechnology УДК 676.16:677.494.745.32 P. A. Chubis, PhD (Engineering), senior lecturer (BSTU); E. P. Shishakov, PhD (Engineering), leading research engineer (BSTU); V. V. Koval, student (BSTU); G. V. Krivov, student (BSTU) SOFTWOOD KRAFT PULPING WITH POLYACRYLONITRILE FIBERS This article presents data on the polyacrylonitrile (PAN) effect upon the elastoplastic and mechanical properties of kraft pulp (unbleached softwood sulphate pulp). In the present research the possibility of ob- taining in vitro sulphate pulp together with reinforcing agent of polyacrylonitrile was studied. PAN con- sumption was varied from 0.05 to 0.20 wt % based on the dry weight of the chips. Micrographs of cellu- lose samples showed that PAN was distributed on the surface of cellulose fibers in the form of fine spheri- cal shape particles and made it possible to increase the strength of kraft pulp by 15−18% (breaking length was increased from 8,480 up to 9,990 m, breaking strength − from 93.8 up to 109.5 N, energy absorption at break − from 76.0 up to 92.6 J/m2 and folding endurance − from 7 up to 13 double folds). Introduction. In accordance with GOST 11208 uor) and pulpchips parameters. As is known, alka- there are four brands of sulfate unbleached pulp line medium (due to the presence of NaOH and produced from softwoods: HC-1 – for making Na2S) and high temperature created in a digester high-strength technical and packaging paper, wet- during kraft process can lead to alkali hydrolysis of strength base paper for making abrasive cloth, tel- polymer materials. Sulphate pulping technique to- ephone-cable paper, cartridge paper and waxed gether with polyacrylonitrile (PAN) fibers (Fig. 1) paper; HC-2 – for making bag paper, opaque pa- and the possibility of getting strengthening agent per, paper for textile spools and tapers, for from PAN in the pulp structure was of scientific gummed tape base paper, for top liner cardboard, interest. Study of the effect of this component on boxboard, water-resistant board, waterproof uphol- the pulp and black liquor properties are also of sci- stery covering board, gasket board, cardboard for entific interest. footwear and other types of paper and cardboard; HC-3 – for making wet-strength paper, base paper for the inner layers of laminated decorative plastic, cardboard end caps of filter elements. It is known that all the above mentioned cellulose brands should have high strength indexes (breaking length should not be less than 7800 m, absolute bursting strength should not be less than 470 kPa and abso- lute tear resistance should not be less than 630 CH2 CH mN) [1]. However, the only production of high nn pulp brand mark HC-1 is difficult to reach. Pulp is CN assigned to a low quality grade if strength charac- Fig. 1. Staple fibers from PAN teristics are lower than standard specifications. Main part. In the process of kraft pulping The purpose of the research was to study the wood chips are treated by cooking liquor, the com- effect of polyacrylonitrile fibers on the yield and ponents of which interact with lignin, extractives, quality of softwood pulp received during kraft hemicelluloses and cellulose itself partially de- pulping process. stroying them. The main part of wood components The objectives of the study were as follows: (45–55 wt %) is transferred to the cooking liquor – to carry out the softwood kraft pulping in and cellulose fibers structure remains intact. Con- vitro with PAN-fibers; sequently the high-strength pulp consisting of cel- – to keep accurate control of pulping profiles lulose, residual amount of lignin and other compo- (T = f(τ) and P = f(τ)); nents of the original wood is produced. – to compare the properties of cellulose received Currently, there are several techniques of kraft in the softwood kraft pulping process with PAN- pulping process and the two main are batch pulp- fibers to the properties of kraft cellulose received ing and continuous pulping. Batch pulping may be also in vitro without PAN-fibers and to the data of prolonged (8 h), accelerated (5 h) and rapid – GOST 11208 “Softwood sulphate unbleached pulp”. “quick cook” process (4 h). The main factors of the Pulpchips and all the necessary reagents were pulping process, which affect the yield and the prepared at the beginning of research in the labora- pulp quality, are temperature and pressure in a di- tory of the Department of chemical processing of gester, cooking time, H-factor, the concentration of wood. Raw material and reagent’s characteristics active reagents in the cooking liquor (pulping liq- are shown in Table 1. Chemistry and Technology of Wood Processing 103 Table 1 To compare the PAN-fibers influence on the Pulp-making materials and pulping reagents charge kraft pulp properties the check softwood kraft pulping without PAN-fibers was performed. Thus, Parameter Value the total number of kraft cooks was five. Wood species Pine Reliefs out of the autoclave were performed Felling period 09.2012 during the pulping process using blow vent 6 in the Wet chips charge, g 300.0 time interval 60–120 min, in this case pressure rise Chip moisture, wt % 31.2 inside the laboratory digester slowed down as is Oven-dry chips charge, g 206.0 seen from the pulping profile (Fig. 3). Manometer Chips dryness coefficient 0.687 5 was used for pressure control. The temperature in Chips moisture content, g 94.0 the digester was regulated using a voltage regulator Pulping liquor charge at a given liquor-to- 11 and controlled by a mercury thermometer. 3 wood ratio, cm : – white 1000 200 1.01,0 – black 0 180 0.90,9 3 Liquor-to-wood ratio, cm /g 5.3 160 0.80,8 Total active alkali charge for pulping, wt % 50.4 0.8 °C 140 0,7 , Degree of liquor sulfidity, wt % 19.0 120 0.70,6 MPa 0.6 , Active alkali (AA), g Na2O/l 145.7 ature 100 0,5 r 0.5 Effective alkali (EA), g Na O/l e 80 0,4 2 103.8 p 0.4 Sulfidity, g Na2O/l 19.8 60 0,3 0.3 Pressure H-factor in cooking stage 3250 Tem 40 0.20,2 temperatureтемпература pдавлениеressure Time of start cooking, h 800 20 0.10,1 Time of end cooking, h 1200 0 0.00,0 Cooking period at 175°C, h 210 0 30 60 90 120 150 180 210 240 Total cooking time, h 400 Cooking time, min а Chips’ processing by white pulping liquor was 200 1.01,0 performed in a laboratory autoclave (Fig. 2) in ac- 180 0.90,9 cordance with temperature profile of a quick kraft 160 0.80,8 pulping. The amount of the polyacrylonitrile fibers 140 0.80,7 input was changed from 0.05 to 0.2 wt % of oven- 120 0.70,6 0.6 dry wood in increments of 0.05 wt %. 100 0,5 0.5 80 0.40,4 60 0.30,3 Pressure, MPa Temperature, °C 40 0.20,2 температураtemperature pдавлениеressure 0.1 5 6 12 13 20 0,1 0 0.00,0 0 30 60 90 120 150 180 210 240 4 Cooking time, min b Fig. 3. Temperature profiles of quick kraft pulping: a – practical; b – theoretical 3 For ensuring the equal pulping conditions in 2 7 8 9 10 11 the autoclave temperature and pressure were regu- lated in accordance with the pulping profile (Fig. 1 3, a). Naturally, it's impossible to attain an exact compliance of temperature and pressure of five kraft pulping processes with theoretical pulping temperature and pressure profile (Fig. 3, b). There- Fig. 2. Laboratory autoclave (digester) fore, it is necessary to adjust the H-factor, which for chips cooking: equals to the surface area under the pulping tem- 1 – cylindrical unit case; 2 – cover device; perature curve and is characterized by the chemical 3 – locking clamp; 4 – hopper; 5 – manometer; reaction constant (eq. 1). 6 – blow vent; 7 – liquor sampling valve; τ 8 – mesh sleeve; 9 – transformer; 10 – voltmeter; HKd=⋅τ , (1) 11 – voltage regulator; 12 – wash tank; 13 – absorber 0 104 ISSN 1683-0377. Proceedings of BSTU. 2014. No. 4. Chemistry, Organic Substances Technology and Biotechnology where K – reaction constant; τ – time of kraft pulp beater tank (Valley beater). Slurry density during cooking, h [2, 3]. pulp beating was 0.75 wt %. To achieve pulp After cooling the contents of the digester the slurry freeness equal to 60oShR it was necessary to remainder was separated into kraft pulp, concen- regulate the time of refining (23 min) as well as trated kraft liquor (black liquor) and undercooked pressing of beating roll with a matching grooved pulp (solid bits of wood chips that didn’t separate stainless steel bedplate. Freeness was controlled by into fibers during the washing process). Conse- using Schopper-Reigler unit – SR-2 (ISO 5267-1, quently it was obtained weak kraft liquor while GOST 14363.4). pulp washing with water. Pulp handsheets samples were manufactured Thereupon in accordance with conventional from the refined pulp slurry, the samples being methods the kraft pulp was tested for the degree of 75 ± 2 g/m2 and 0.2 m in diameter. Pulp hand- delignification (Kappa or permanganate number), sheets making was performed on a Rapid-Ketten the pulp yield and amount of the undercooked pulp sheet former (Ernst Haage Company, Germany) in depending on the polyacrylonitrile charges [4]. accordance with the requirements of ISO 5269-2. Also density and residual content of active compo- For reproducibility of results the pulp handsheets nents were determined in black liquor (Table 2).