PROCEDURE FOR MANUFACTURING LIGNOCELLULOSIC MATERIAL PRODUCTS

Abstract: A procedure for manufacturing lignocellulosic material products and for improving their strength and water resistance characteristics, high-molar mass lignin derivatives being added to the lignocellulosic material, of which at least 35 % by weight are over 5000 in molar mass.

Description: PROCEDURE FOR MANUFACTURING LIBNDCELLULOSIC MATERIAL PRODUCTS The present invention concerns a procedure for manufac uring lignocellulosic material products and for improving their strength and water resistance pro¬ perties using high-molar mass lignin derivatives. Such products a.re e.g. those of the paper and cardboard industry and those of the industry manufacturing build- ing materials, such as corrugated board, cardboard, raft-1 iner , paper cores, wood composites, fibreboard and chipboard, and insulation materials. It is possible to improve by the procedure not only the characteristics of products made o f primary fibres but also to enable high-grade products to be made of lower grade raw ma¬ terials such as reclaimed fibres. In cellulose manufacturing processes in which wood chips are heated in a cookng solution under pres¬ sure, about half of the wood is dissolved, forming the so— alled waste liquor. One of the main organic com¬ ponents of waste liquor is lignin. In the sulphite process, in which an acid bisulphite/sulphur dioxide solution serves as digesting liquor, lignin is present in the waste liquor in sulphonated form, as so-called 1 ignosulphonates . In this form, lignin is soluble in water also in acid solutions. On the other hand, in alkaline cellulose manuf c uring processes, such as the soda process (NaOH as digesting solution) , in the kraft process (NaOH, Na s S„ NaHS as digesting solution) or in the oxygen/al ali process (with NaOH in the presence =Θf oxygen), lignin is present in the form of an Na salt in the waste liquor, and it is water-s.o luble in alkaline solutions . It is known in the art that the characteristics of e.g. paper, cardboard and fibre boards can be im¬ proved by adding lignin to the fibres, most often in the form of waste liquor. The problem has, however, been the poor retention of said lignin products, that is, poor adhesion to the fibres. For instance, it has been possible to improve the strength properties of corrugated board by adding to the fibre stock 6'/. by weight, calculated on the dry matter of the stock, thermally processed lignin isolated from sulphite waste liquor (Zellstoff und Papier Ξ£ (1975): 9, Ξ69-70). It is observed, however, in the reference that using lignin cannot be contemplated because the BOD values of the waste liquor become too high owing to its poor reten- tion. In the Canadian Patent CA 789,14-0 lignin is used in the form of sulphite waste liquor or black liquor for improving the strength characteristics of paper. Of the dry matter of the black I iq.uor only Ξ67. by weight could be made to adhere to the fibres. All the same, the procedure was considered to be economi¬ cally advantageous because the concora values of the paper increased from 66.3 points to 87.6 points. A retention of equal degree, about 30'/. by weight, has also been reached in a Russian study (Bumazh Prom. 11 (19S4-): 18—19) , in which kraft lignin was precipitated with alum onto the paper fibres. The lignin quantity used was over 8 * /. by weight of lignin dry matter, calcu- lated on the dry matter of the fibres. In spite of poor retention, the breaking, punching and rigidity charac¬ teristics of the paper could be improved. The effect of kraft lignin on the strength of fibre board made from waste paper has been compared in an American study (Forest Products J. 28. (1978) : 77-8E) with the effect of phenol formaldehyde resin. Of the dry matter of the kraft lignin product used, 5 .8*/. by weight was organic matter and * /. by weight was inor¬ ganic matter. When pH was adjusted with sulphuric acid to- ^.5, only 15 g dry matter out of 100 g were precipi¬ tated. Preci i ation could be somewhat improved by raisin the reci i ation tem erature to 70.C althou h lignin had to be added 11'/. by weight, calculated as dry matter related to the dry matter of the fibres, in order to achieve equally good strength characteristics as with 3'/. by weight phenol formaldehyde addition. Cost calcula- tion analysis revealed that phenolic resin was somewhat more favourable in use than lignin owing to higher lignin addition and oxygen consumption, and to the heating required in precipitating it. Corrugated board manufactured from reclaimed fibre stock has been impregnated, in Italy, in a sizing press with both NSSC waste liquor and black liquor (Eucepa Conference, Florence, October 6 - 10, 1986, Proc. Vol. 11 ,24 ; 1-31) . Subsequent to impregnation, the board was dried at lOO-l^O ^ C. The waste liquors originated from poplar and straw cookings. In most of the experiments, the characteris ics of the board im¬ proved owing to the impregnation. Better results were obtained using the waste liquor at dry matter content 80-30*/. by weight than when it was used in dilute solu- tions, which necessitated performing the impregnation in a plurality of steps. On the other hand, lowering the pH of the waste liquors reduced the strength proper¬ ties of the board. The board impregnated with waste liquor obtained from straw cooking absorbed more ois- ture than untreated corrugated board. Lignin has been chemically modified, parti¬ cularly for improving its water resistance properties. It has for instance been reacted with amines (wochenblat fur Papierfabrikation ___ (1966) : 4, 107 - 110) , where- after it has been reacted with formaldehyde' -J, (US 3,079,353) or peroxide ( SU 520, Ξ60) . Alkali lignin has, for instance, been sulphonated and used together with starch in order to increase the rigidity of a liner manufactured from waste paper (US 3,644,167) . From rice soda black liquor, cyanoethy11 ignin and aminolignin have been manufa tured, and they have been used e.g. in paper sizing (Paperi ja Puu 62 (1980) : 10, 589 - 59Ξ, 614-). Lignin has also been heat-treated: e.g. Iignσsul- phonates at about 250 to 300^0^0, with the purpose of con— verting them into a form insoluble in water (US 2,934-,531 and Zellstoff und Papier 1J3 (1969): 11, 328—332). Using this kind of products it has been possi¬ ble to improve the characteris ics of corrugated board and kraft. Kraft lignin, having average molar mass 25,000-30,000, has been used in manufacturing cardboard, corrugated board and wrapping paper (SU 681,14-0) . As disclosed in said reference, the lignin is added to an aqueous solution containing 2-407. by weight fatty acids and resin acids, and the mixture is heated in an alkali at 80 to 85 0 C before use. The dry matter content of the mixture is about 14-—187 by weight and the pH is 8-9. The fatty acids and resin acids have probably been added in order to improve the hydrophobic properties. When this mixture was added to a cardboard fibre stock in amount 37. by weight, calculated as dry matter related to the dry matter of the stock, the bursting strength of the cardboard was improved 57. and the tensile strength, 187.. High—molar mass alkaline kraft lignin has been added 1 to 77. by weight, calculated as dry matter re- lated to the stock dry matter, to a fibre stock used in manufacturing paper and cardboard (SU 374-,4-07). The lignin is added as an alkaline aqueous solution to the stock, and thereafter, 37. by weight of divinylstyrene/— rubber latex in emulsion form, containing 757. by weight styrene related to the latex dry matter, is added* there¬ to. Thereafter, the components are precipitated with aluminium sulphate. The rigidity of paper and cardboard could hereby be improved, in comparison with products reinforced with latex alone. The additions a.re compara- tively low, only about 1—77. by weight lignin. Improved absorptive paper suitable for lamina¬ tion can be manufactured by adding to the aper in the sizing press, after web formation, high-molar mass lignin, of which at least 507, by weight is over 5000 in molar mass (FI 58,961). The lignin product may consist of 1 ignσsulphαnates or kraft lignin, and the additions are 0.1 to 107. by weight of the dry paper weight. Ac¬ cording to the reference, lignin accelerates the absorp¬ tion of phenolic resin in the paper but does not affect the tensile strength of the paper. In the Finnish Patent FI 58788, lignin deriva- tives are used, of which at least 357. by weight, ad¬ vantageously 407. by weight, are over 5000 in molar mass. By mixing them with phenol formaldehyde resin and ad¬ justing pH of the bonding agent to be in the range 8-14, preferably 9-13, a waterresistant bonding agent can be manufactured for hipbαard ,p 1ywαod and fibre boards. As will be evident from the foregoing, the greatest problems in using lignin as a reinforcing agent for various materials has been caused by the poor reten¬ tion of lignin products, that is, their poor adhesion to fibres. In the Patent SU 681,140, a lignin product having a given average molar mass (25,000-30,000) has been used. Since lignin is not homogeneous in structure but consists of lignin derivatives differing greatly in molar mass, the value stated for the average molar mass in fact fails to specify the kind of the lignin product used. It may consist of very high-molar mass and very low-molar mass lignin derivatives in varying propor¬ tions so that the mean of their molar masses will be 25,000-30,000. It is probably Because of the poor ad¬ hesion to fibres of low-molar mass lignin derivatives that fatty and resin acids had to be used in addition in this instance in order to improve the hydrophobic propert ies. Endeavours have also been made to improve the retention of lignin and the strength and water resis¬ tance properties of fibre material chemically by modify- ing lignin, but the economy of the procedure has suf¬ fered in that case. With the aid of the procedure of the invention, a decisive improvement is achieved regarding the draw- backs mentioned in the foregoing. The procedure of the invention is characterized by that which is stated in the characteris ic features part of claim 1. The most significant advantage of the invention is that by applying it, products can be manufactured of various lignocellulosic materials in a sensible way, more advantageously in technical and economical respect than by any other method. Using the procedure now in¬ vented, strong bonds, probably hydrogen bonds, are obtained between the lignin derivatives and the lig- nocellulosic material, owing to which the products possess excellent strength and water resistance proper¬ ties. Since the retention of lignin in lignocellulosic material is nearly complete applying the method now invented, lignin can be made adherent to the lignocel— lulosic material up to 10 7, by weight, calculated as dry matter related to the dry matter of the lignocel¬ lulosic material, at the same time improving the propei— ties of the products. Owing to lignin addition, the production of some products can be increased up to 507.. The procedure enables recycled raw materials advanta¬ geous in price to be used e.g. instead of virgin fibres. Applying the procedure of the invention, the strength and water resistance properties of products produced from second grade fibres can be improved to be on a level with products based on virgin fibres. The procedure is also advantageous from the viewpoint of the cellulose mill because the lignin going to fuel can now be utilize. There will be free recovery boiler capacity, and the production of cellulose may there- fore be increased without having to invest in a new recovery boiler. The removal from the waste liquor — to be evaporated to higher dry matter content prior to the recovery boiler, without any difficulties with viscosity. Hereby the energy required in the soda boiler for evaporating water will be less because the quantity of feed water is significantly less. The procedure is furthermore economically advantageous e.g. from the viewpoint of the plant manu¬ facturing lignocellulosic products because to the lig- nocellulose suspension, mostly used at high dilution, lignin solution, lignin suspension or lignin powder with partly considerably higher dry matter content is added. Hereby, the amount of water to be evaporated per ton of product will be less. In addition, lignin is advantageous in price, e.g. compared with many wet— strengths resins, such as urea-formaldehyde resin o r po lyethylene-imine . - To the 1 ignosel lulosic material products manu¬ factured with the procedure of the invention any addi¬ tives and components, known per se e.g. plastic raw materials may be added for instance for improving the strength and water resistance or other properties of the products. Thus e.g. r.esin or resin raw materials, such as phenol formaldehyde resin may be added to the lig¬ nocellulosic material in any concentra ion, for instance less than 10 7. by weight or less than 5 7. by weight calculated as dry matter on the mixture of the lignin derivatives and resin, e.g. before or after the addition of the lignin derivatives to the lignocellulosi mate¬ rial. It is to be nrjted that it is not mandatory in the procedure of the invention to co-polymerize the lignin derivatives in question with resins. So the lignocellulosic material products may be free of resin. « As regards environmental protection, it is a remarkable advantage ofthe present invention that when it is applied the lignin is mearly 1007. attached to the fibres. Furthermore, the BOD values of the plant's effluents will not increase, as is the case when impure lignin products containing organic acids and other low-molar mass compounds in abundance are used. When using lignin derivatives according to the invention, no toxic low— olar mass sulphur compounds, such as hydrogen sulphide for instance, are released during the manufac¬ turing process, as are for instance set free from sul¬ phate waste liquor in acid conditions. The invention is described In the following in detail. The high-molar mass lignin derivatives used in the procedure of the invention are isolated e.g. from waste liquor of an alkaline cellulose process or from waste liquor after bleaching by a lignin frac ionating method known in itself in the art, such as precipi ation with acid, or by an ultra i 1 ration process. At least 357. by weight of the high—molar mass lignin derivatives should have molar mass higher than 5000. The molar mass distributions of lignin derivatives can be determined using gel chromatograph , as Is disclosed In detail in the Finnish Patent No. 58788. The so-called degree of purity of the lignin has a great significance because when impure lignin products are precipitated onto lignocellulosic mate¬ rials, the impurities will not adhere to fibres and are discharged into the plant's effluent circulation. Of the lignin derivatives used in the procedure of the invention, over 707. by weight of the total dry matter of the lignin fraction should precipitate from a -1-57. by weight solution with 1 M hydrochloric acid at pH 3. The degree of purity of the "iignin fraction can be found out with the aid of hydrochloric acid pre i i ation, since low-molar mass phenolic compounds, and other inor¬ ganic and organic impurities, will no be precipitated in such a determina ion. The lignin derivatives of the invention may be used in the form of a dilute solution, of an evaporated concentrated solution, of a suspension, or of a pow- der, e.g. spray-dried. Their dry matter content at the moment of use may therefore vary, depending on the manufacturingprocess of the product, in the range 0.1 to 1007. by weight. The acid quantity required to lower pH below 7 may be added to the lignin, to the lignocellulosic material or to the 1 ignocel lulose/1 ignin mixture, de¬ pending on which is most advantageous in view of the manufacturing process. It is possible to add to the lignocellulosic material, in addition to lignin, bivalent o r trivalent metal salts, such alum, ferric o r ferrous sulphate, or ferric chloride. Also organic, commonly known cationic precipita ion chemicals, such as polyethylene imine, may be used. The amount of precipitation chemical added depends on the pH of the lignin derivatives and of the lignocellulosic material, and it is usually 0.5-207. by weight, calculated as dry matter related to the dry matter of the 1 ignin/ 1 ignocel lulose mixture, advan- tageously about 1-37. by weight. The amount of high-molar mass lignin deriva¬ tives added to the lignocellulosic material varies in general in the range between 1 to 1007. by weight, calcu¬ lated as dry matter related to the lignocellulosic material dry matter, depending on the requirements set for the product. The lignin derivatives may, as taught by the " invention, be added e.g. to finely divided lignocel¬ lulosic material, such as to fibres, to chips or to an aqueous suspension made thereof, before the manufactur¬ ing process of the product or in conjunction therewith, e.g. on the paper machine or in the sizing press. As taught by the invention, the lignin may also^be added to the lignocellulosic material, or on the surface of the product produced, or to be produced, thereof., as a coating or sizing, or it may be added as a bonding agent to the li nocellulosic material between different la - ers. The lignocellulosic material, or the product manu¬ factured thereof, may also be Impregnated with a lignin solution or suspension e.g. when manuf cturing insulat¬ ing materials. If desired, the lignin derivatives of the invention may also be chemically modified, e.g. by condensation with formaldehyde, by oxidation with air, or by binding amine groups thereto; in most cases, however, fully satisfactory properties are achieved by using the above-mentioned lignin derivatives as such. The following examples describe the present invention, however without confining it. Example 1. The effect of the properties of lignin on its retention and on the character1stices of liner.made from reclaimed fibres From a kraft process, black liquor was isolated by ultrafiltration, on the basis of molar mass, lignin derivatives of different molar mass distribution and purity level. In Table 1 ar e stated the characteristics determined for said lignin fractions (R_τ, R- + , R;?.-, R< ? , Ri3, R 8* and R 3 ε> and for the kraft black liquor after uitrafi 1 ration. In Table 1, the molar mass distribu ions (MWD) of the lignin derivatives have been determined accord¬ ing to the method given in the Finnish patent applica¬ tion No. 58788, and they are stated as proportion αf lignin derivatives exceeding molar mass 5000, in per cent by weight of 'all lignin derivatives. The proportion of precipitating stated In per cent by weight of the total dry matter of the lignin fraction when precipitat¬ ing lignin from a solution with dry matter content l-?57. by weight with 1 M hydrochloric acid at pH 3. Sodium sulphide, sodium and ash content are stated In per cent, by weight calculated on the dry matter of the lignin fraction. Table 1. Characteristics of the examined sul¬ phate lignin fractions and sulphate waste liquor subse¬ quent to ul trafi 1 tration (7. b.w. ) Lign. MWD Prec . Mean Dens . Na_.S N a i sh Visc . fract . , M>5000 1 ign. cont . (S3 β C> (23°C) 7. 7. 7. g/cm 7. 7. 7. m Pa-s Waste 1 iquor 21 31 27,0 1 , 1607 5,3 20,4 4-9,9 2 R 3 30 57 23,0 1 , 1248 2,4 15,7 36,7 3 R- * 32 65 25,5 1 , 1346 2,0 14,5 33,3 3 RB. 35 70 27,8 1 , 1435 1,6 13,2 31,4 3 R* 40 78 22, 1 1 , 1028 0,6 10,9 25,2 5 R13 46 82 19,7 1 ,0872 ' 0,2 9,3 20,6. 7 Re-i- 49. 87 17,0 1 ,0709 0,02 7,2 13, 1 9 °as 54 89 21 , 1 1 ,0878 <0,01 7,3 15,9 10 As a measure measure of the degree of purity of lignin one may take the proportion of precipitable lignin, which varied, as can be seen in Table 1, between 31 and 897. by weight. The impure fractions contained large quantities of sodium sulphide, which is converted into toxic hydrogen sulphide gas when pH is lowered ■ into the alkaline range. This phenomenon is already in itself a bar to using impure, lignin derivatives with high content of low-molar mass compounds in the range below pH 7. By using high-molar mass, pure lignin deri¬ vatives this drawback was eliminated. The high-molar mass fractions -with higher purity also contained less sodium than the low-molar mass fractions, and this is advantageous in view of the acid and/or alum quantity used in precipitation. The pH values of the lignin fractions entered in Table 1 were adjusted with sulphuric acid to pH 6.6 and they were added to stock made froπfreclai ed fibres having consistency 12.2 g/1 and pH 6.9. The composition of the stock was: 557. by weight magazines, 307. by weight newsprint and 157. by weight corrugated board. Lignin was added 57. by weight, calculated as dry matter related to the stock dry matter. Subsequent to the lignin addition, 1.57. by weight of alum was added as a 37. solution, calculated as dry matter related to the stock dry matter. In this example, and in those follow¬ ing therafter, "alum" is understood to meanaluminium sulphate containing crystal water: Al-~2" * CS0~4-~ )~3 .16H~2~0. The retention, or the prαpoi— tion of lignin that has become adherent to fibres of the original lignin quantity, was determined on the basis of ultraviolet absorption measurements (A 280 nm) of the slurry water and the original lignin solution. Of the stock, sheets were madeets in the labo— ratory, having grammages about 150 g/m s and thickness about 0.29 mm. From the sheets thus produced, the fol¬ lowing characteristics were determined: thickness, density, air permeability (SCAN-P 19:78) , compression strength, the so-called SCT (SCAN-P 46-83) and CCT (Corrugated Crush Test, SCAN-P 42:81), tensile strength and tensile index (SCAN—P 16:76, tensile index = tensile strength divided by base weight) , and water uptake of • the sheets by the so-called drop of water method (Drop of Water, TAPPI RC-70). The characteristics and reten- tions are stated in Table 2. Table 2. The characteristics of the sheets achieved using kraft black liquor and various kraft lignin frac¬ ions. MWD Prec . Ret. Dens. Air Cαmp.str. Tens. Tens. Wate >5000 lign. perm. CCT SCT str . index Drop 7. 7. 7. kg/m 3 s/100 kN/m kN/m kN/m Nm/g s ml Without lignin 507 78 1,54 2,19 4- , 8 35,8 13 Waste liquor 21 31 42 505 110 1 ,91 2,85 5,4 36,5 >300 Ra 30 57 77 510 131 1 ,95 2,85 5,8 38,2 R^ 32 65 81 522 140 2,01 2,86 6,0 39,0 Ra 35 70 94 539 158 2.01 3,07 6, 1 39,9 RR<„v 4400 7788 . 9955 551166 114477 1,88 2,90 5,8 40,0 R-3 -46 82 97 525 165 2.02 3,14 5,9 39,9 εa ** 49 87 99 534 181 2,04 3,22 6,0 40,0 R 3 _ 54 89 98 563 216 2,38 3,66 7,0 42,2 As can be seen from the retention values pre¬ sented in Table 2, low-molar mass lignin derivatives' adhered poorly to the fibres. Retentions over 907. were achieved with fractions of which more than 357. by weight had molar mass higher than 5000 and which had degree of purity (proportion of preci tp i table lignin, over 707. by weight of the total lignin. The water resistance properties of the sheets improved in all lignin fractions in comparison with sheets produced from reclaimed fibres alone, the water drop penetrating into the latter in about 10 to 20 seconds. In the case of the sheets containing lignin the measurements were discontinued when 300 seconds had passed . The properties of the sheets all improved with increasing molar mass and-, degree of purity of the lig¬ nin. Improvement of properties could even be achieved with black liquor alone, but its use, like the use of other impure fractions, is rendered doubtful by poor retention, which would create environmental problems for the mill. A very important characteristic, namely the compression strength (SCT) , improved significantly when the molar masses of the lignin derivatives In¬ creased 357. by weight M > 5000 and the degree of purity rose over 707. by weight (Fig. 1) . Example 2. The effect of pH adjustment on the charac— teristics of liner produced from reclaimed fibres The high—molar mass kraft lignin fraction with 74-7. by weight having molar mass higher than 5000 and having degree of purity 897. by weight was isolated from- kraft black 1 i-quor by ul rafiltration. The pH of the fraction as such was 12.6. The fraction was divided Into 8 parts, their pH values being lowered with sulphuric acid to be in the range pH 3 to 10. In the solutions having pH below 6.5, part of the lignin was present In precipitated form as a suspension. The dry matter ocntent of all solu ions/suspensions was 3.07. by weight. From waste paper a stock was produced which had a consistency of 4- g/1. The stock was divided into batches and their pH was adjusted to 7, 5 and 3, respec¬ tively. The above-mentioned lignin-water suspensions were added to the stock batches so that the lignin addition was 307. by weight, calculated as dry matter related to the stock dry matter. Thereafter, 37. alum was added as a BY. by weight aqueous solution, calculated as dry matter related to the stock dry matter. From the 1 ignin/stock;" mixture liner sheets were produced which had base weight were 1 0—150 g/m^ and thickness about 0.25 mm. The characteristics of the sheets are stated in Table 3. Table 3. The effect of the pH values of reclaimed fibre stock, kraft lignin and lignin/fibre mixture on the characteris ics of liner sheets. Stock Lign. Fibre/ Den Air Comp.str. Tens. Cobb_o pH pH 1 ign. /al perm. SCT CCT str . value mi t . index pH kg/m 3 s/100 kN/m kN/m Nm/g g/u 2 ml Without 1 ignin 505 126 2,81 1,77 36,2 151 7 12 , 6 12 546 304 2.74 1,85 38,5 102 9 7 536 208 3,03 1,95 41,7 56 8 7 480 208 2.94 1,70 41,0 54 6 , 5 6 566 320 3,02 2,02 41.,7 21 5 5 682 382 3,58 2,11 40,3 22 4 5 615 487 3,79 2,14 42,2 21 3 4 579 525 3.75 2,19 ' 41,8 25 12 , 6 10 526 193 2.92 1,72 40,0 197 1 100 7 7 520 188 2.95 1 ,77 39,3 94 8 6 532 213 3,07 1 ,96 39,7 25 6 , 6 6 540 233 3,31 2,02 42,6 22 5 5 733 302 3,4 " 8 2,97 37,4 17 4 4 549 314 3,69 2,08 42,6 17 12 , 6 9 596 182 2.93 2,12 38,7 182 10 6 541 217 3,14 1,96 39,1 30 8 5 566 254 3,52 2,03 41,7 18 6 , 6 4 602 332 3,69 2,09 39,9 19 5 4 581 308 3,50 2,06 37,4 28 4 4 634 279 3,68 2,11 37,9 19 As can be seen in Table 3, the charac eristics of the sheets, in particular the SCT, CCT and Cobb values, improved " considerably when the pH of the slur¬ ry/ 1 ignin/alum mixture fell below 7. Example 3. The ef ~ - ~ acid and precipi a _!•. * - The pH of c_ .' tion as in Example . ' to be pH 5. The dry -- tion was 37. by >. .. required for said p- experiment, directl res, having a consi ;- case, lignin was a * " solu- tion having pr- 307. by weight, cal_ . stock dry matter. Fc ~ used In the experlms- of a 37 by weight se as dry matter relat-.. In the eχ-.-=' lignin, sulphuric a;-: varied. From the produced which had r-- ness 0.25 mm. The 1. tics of the sheets =. - . Table 4. The effect of order of adding lignin ( SA) , acid (H s SO- f ) and precipitation chemical (alum) on the characteristics of sheets. Cases in which sulphuric acid was added to the lignin in advance are marked (SA + H s SO_. ) . Order of Mixt. Ret. Dens. Air Comp.str. Tens. Cobb ώ0 addition pH perm. SCT CCT str . ind . alue 1 to stock 7. kg/m- 'J s/100 kN/m kN/m Nm/g g/m'" ml Stock 6,8 - 505 126 2,81 1,77 36,2 151 ' without 1 ignin 1) (SA+ H β SC > 6,3- 99 585 539 3,77 2,18 40,2 18 2) Alum 1) Alum 6,1 99 601 594 3,88 2,24 39,9 19 2) (SA+H a S0_-) 1) H S SD_. 5,7 99 584 496 3,97 2,18 43,9 17 2) SA 3) Alum 1) Alum 5,7 99 571 544 3,92 2,39 44.0 17 2) SA 3 ) HsSO-,. 1) HeSD_, 5,6 99 588 584 3,97' 2,22 43,6 18 2) Alum 3) SA ' 1 ) SA _ 5,7 97 599 531 3,97 2,36 45,2 11 2) H £ =.S0_ > 3) Alum 1) SCAN-P 12:64, states the water quantity (in g/m 3 ) meter, which the paper or cardboard surface ab¬ sorbs in 60 seconds from a water column 1 cm in height covering it. As can be seen in Table 4, good retentions were achieved Independent of the order in which lignin, acid and alum were added, and the character— istics of the sheets improved in all instances in comparison with reclaimed fibre alone. Example 4. The effect of lignin quantity added on the cqaracteristics of reclaimed fibre liner To stock produced from reclaimed fibres, having pH about 7 and consistency about 10 g/1, was added high—molar mass lignin of which 547. had molar mass higher than 5000, at 0, 0,5, 2.5, 5, 7, 10, 15, 20, 30, 40, 50 and 607. by weight as dry matter, calculated on the stock dry matter. The dry matter content of the lignin solu¬ tion was 37. and Its pH had been adjusted to be below 7 before addition to the fibre stock. After the lignin addition, alum as 37. solution was added 1.5-27. by weight, calculated as dry matter related to the stocky dry matter. The stock/1ignin/ alum mixtures had pH values varying between 5 and 6. The retention was bet¬ ween 94 and 1007. in all cases. The grammages of the sheets were about 150 g/m s and the thicknesses about 0.25 mm; the other characteristics are seen In Table 5. Table 5. The effect of high-molar mass lignin addition quantity on the char cteristics of liner sheets produced from reclaimed fibres. SA Dens . Ai Comp.str. Tens. Tens . Cαbb_,o Water added pe . SCT CCT str. index Drop 7. kg/m 0 kN/m kN/m kN/m Nm/g g/m e ml 07. 5 50000 9 944 2,47 1 ,58 5,01 34,8 159 95 0,5 4 49988 8 866 2,69 1 ,84 5, 10 35,2 23 2 2,,55 5 52211 9 966 2,76 1 ,86 5,33 36,2 77 5 5 5ΞΞ77 1 14466 2,92 1 ,92 5,72 38,6 27 >300 7 5 52200 9 955 2,82 1 ,88 5,74 37,5 >300 10 5 54433 1 16644 3,00 1 ,93 5,30 36, 1 25 15 5 54488 2 20077 3,23 2,03 5,76 39,2 24 2 200 5 57744 2 24444 3,49 2, 16 5,80 39,5 24 25 5 59933 2 27744 3,73 2,37 6,30 41 ,2 30 5 59922 5 53377 3,73 2,20 6,01 40,9 20 40 5 59955 3 37733 3,98 2,43 5,91 39,4 22 50 6 60022 3 39966 3,96 2,36 5,92 40,8 32 6 600 6 61144 4 47777 3,97 2,26 5.72 40.9 19 The results are also shown in Fig. 2, in which the SCT compression strength, CCT compression strength and tensile strength values are calculated as per cent improvement over the with sheets without lignin. As is seen in Fig. 2, the SCT values are bettered up to 607.. The Cobb_o values, i.e., the amount of water absorbed by the cardboard in 60 seconds, were reduced from 159 to about 22 g/m' 2 ' , or by 867. when the lignin add i trions were over 207,. When comparing the results with the charac¬ teristics of sheets made from virgin fibres, e.g. from a kraft stock, one may note that by adding high-molar mass lignin to reclaimed fibres more than 207. by weight, sheets can be produced of which the SCT values are equal to or better than the values of sheets manufactured from a kraft stock (Fig. 3) . Example 5. The effect of the dry matter content of lignin on its adhesion to fibres As Is seen in Table 6, eleven kraft lignin solutions in the dry matter range 0.1 to 207 by weight were prepared. All -solutions had pH 5, and the high- molar mass kraft lignin fraction was the same as in Example 2. Part of the kraft lignin was freeze-dried into a finely divided powder. Prior to drying, the pH of the lignin was adjusted to be 5. The lignin quantity added was 307. by weight as dry matter calculated on the dry matter of stock pro¬ duced from waste paper. The stock had consistency 8.5 g/1 and pH about 7. The alum quantity added after the lignin addition was 2.07 by weight calculated as dry matter related to . the stock dry matter, and it was added in the form of a 37. by weight aqueous solution. The retentions that were determined are stated in Table 6. Table 6. The effect of the dry matter content of high- mαlar mass kraft lignin on its retention. Dry maitter Reten Ion Consistency of slurry/ con . of 1ignin lignin/alum mixture, 7, 7. g/1 0,10 98,4 3,1 0,15 97,1 4,1 0,20 96,0 4,9 0,40 97,8 6,8 0,60 98,5 7,7 0,80 98,5 8,4 1-0 98,8 8,8 3,0 98,8 10,2 5,0 98,9 10,5 10,0 99,0 10,7 20,0 99,9 10,9 Powder (about 1007.) 93,7 11,0 As can be seen in the table, good retentions were achieved within the entire dry matter range 0.1 to 1007.. Selection of appropriate dry matter content is therefore in the first place dependent on the produc¬ tion process used and on whether it is desired to reduce the consumption of water per ton of product, whereby for instance the drying costs will be lower. Example 6. The effect of the alum quantity on retention and on the chara ter istics of liner High-molae mass kraft lignin as in Example 2 was added as a 37. aqueous solution to stock produced from waste paper, at 30 7. by weight, calculated calcu- lated as dry matter related to the stock dry matter. The pH of the lignin solution had been adjusted to about pH 5 with sulphuric acid before addition. The pH of the stock was adjusted to pH 5.3 prior to lignin addition. The alum addition varied in the range 0 to 107, by weight (on the stock dry matter) . Liner sheets were produced in the laboratory, with base weight about 150 g/m Ξ and thickness about 0.25 mm. The retentions and the charac¬ teristics of the liner are stated in Table 7. Table 7. The effect of alum quantity added on retention and on the characteristics of liner sheet. Alum Ret. Dens. Air Comp.str. Tens. Tens. Cobb_,. : added peri SCT CCT str . index value 7. Y. kkgg//mm 5533 ssllOOiO kN/m kN/m kN/m Nm/g g/m s ml Without 1 ignin 500 94 2,47 1,58 5,01 34,8 159 0 97,9 621 226 3,08 1,78 4,76 33,B 60 0,5 98,2 560 283 3.08 1,80 4,88 38,7 £6 11 9999,,00 558833 22BB11 4,06 1,93 5,00 37,6 19 1,5 99,0 587 286 3.09 1 ,92 4,81 37,6 18 2 99,4 563 286 3.14 1,77 4,77 37,0 22 2,5 99,3 601 279 3.15 1 ,74 4,28 34,0 47 3 99,3 597 313 3,40 2,11 5,08 36,9 24 55 9988,,00 559977 332288 3,49 1,89 5,15 36,3 22 7 98,2 619 286 3,52 1,87 5,48 38,3 21 10 98,8 605 300 3,51 2,02 5,10 36,2 24 As can be seen in Table 7, alum addition Is not indispensable, but even with a small alum addition both the retentions and the characteristics of the sheets alrady improve. Example 7. The effect of precipitation chemicals on lignin retention Salts of bivalent and trivalent metals, alum, FeCl 3 , Fe s (Ξ0_ > ) 3 , FeS0_ * , po lyaluminiumchloride (PAC), and cationic precipi ation chemical, polyethylene Imine (Polymin SK, BASF) were used for precipitation chemical for precipitating the high-molar mass 1ignin " -fraction onto reclaimed fibres. The quantity of lignin added was 307. by weight as dry matter, calculated on the slurry dry matter. The degree of purity of the lignin fraction was 897 by weight, and 797, by weight thereof has molar mass higher than 5000. pH of the ' lignin solution had been adjusted to pH 5 with sulphuric acid prior to reci itation and Its dr matter content was 3.07.. The precipita ion chemicals were added as a 37. solution at 27. by weight of the stock dry matter, taking into ac¬ count the crystal water in the chemical, if any. The effect of the chemicals on adhesion of the lignin to ' the fibres is indicated by the retention values, Table 8. Table 8. The effect of precipitation chemicals on lignin retention Precipi tat ion Lignin P H O'f stock/ 1 ignin/ chemical retention, 7. P r ec .chem. mixture - 92,3 6,7 H»S0_. 99,5 3,5 Al e ( SC ) a "« 16H ε .0 99,9 4,8 FeCl a -6H e 0 98, 1 4,6 FeSC -7H_.0 99,7 5,8 PAC 99,7 5,5 Polymin SK 99,7 6,3 As can be seen in Table 8, it is possible, using various pre ipitation chemicals, to increase the retention close to 1007. without substantially increas- ing the acidicity; this is often desirable considering the characteristics of the product, e.g. its sizability and pr intabi 1 i ty . Achieving high retention is also important in view of the plant effluents. Example 8. Use of hoqh- olar mass bleaching lignin in reinforcement of liner ' " From waste liquor from the alkali extraction step following after h1orination, originating from bleaching alkali-digested cellulose, a high- molar mass lignin fraction was isolated which had a molar mass of 377. by weight of M > 5000, pH about 8 and dry matter content 177. by weight. Before pre i itation, the lignin fraction was diluted to37. by weight and its pH was adjusted to be below 3. To a stock produced from reclaimed fibres, having pH 7, 307, by weight lignin fraction and 57. by weight polyimine were added, both calculated as dry matter related to the stock dry matter. Sheets with a grammage of 130 g/m Ξ and thickness about 0.22 mm were produced in the laboratory. The characteristics deter- mined from the sheets are stated in Table 9. Table 9. The effect of high—molar mass lignin fraction isolated from bleaching waste liquor on the characteris¬ tics of sheets produced from reclaimed fibres. Density Porosity Co pr.str. Cobb,_ Water SCT CCT value Drop kg/m 3 s/100 ml kN/m kN/m g/m R s Without lignin 531 184 2,35 1,34 215 13 Bleaching lign. 605 480 3,04 1,66 146 >300 As can be seen In Table 9, good characteris ics were also achieved by using high— olecular lignin iso¬ lated from bleaching waste liquor. Example 9. Addition of lignin to a fibre web (Coating) Using high-molar mass kraft lignin w * ϊth 797. by weight of it exceeding M 5000, six aqueous solutions were prepared having 37. by weight dry matter content, and pH 3. The pH of five solutions was adjusted with sulphuric acid to, respec ively, pH 3, 4, 5, 7 and 9. The first three were partly In suspension form. The lignin—water solutions/suspensions were added as a kind of coating to reclaimed fibre sheets, from which mo=;t of the water had been drained through the wire. The addition was 307, by weight, calculated as dry matter related to the dry matter of the fibres. For precipi¬ tation chemical, alum was used as a 37. solution, the addition being 27. by weight calculated as dry matter related to the dry matter of the fibres. The results are given in Table 10. Table 10. Addition of lignin as a coating and its effect on the characteristics of reclaimed fibre liner. Lign. Dens. Air Compr . str . Tens . Tens . Cobb_. pH perm . SCT CCT str . i nd . value kg/m 3 s/100 kN/m kN/m kN/m kN/m g/m s ml 3 458 321 3,92 2,35 5,6 35,9 58 4 653 448 3,71 2,37 - 5,7 37,3 58 5 641 485 3,98 2,58 6,3 44,6 31 7 473 131 2,24 1 ,25 4,5 39,2 163 9 479 150 2, 12 1 ,27 4,4 38,4 161 13 531 184 2,35 1 ,34 4, 35,7 215 Wi thout 1 ignin 507 174 2,69 1 ,70 5,1 " 35,2 199 As can be seen in Table 10, by adding on the surface of sheets a lignin solution with pH adjusted to be below 7, the characteristics of liner produced from reclaimed fibres could be significantly improve in comparison with liner to which no lignin had been added. Example 10. The effect of lignin addition quantity on the characteristics of liber produced from kraft stock To a kraft stock with a pH of.8.55 and a con¬ sistency of 18 g/1 before precipitation, 0 to 507. by weight of high-molar mass kraft lignin as in Example 2 was added at 0 to 507. by weight dry matter, calculated on the stock dry matter, its pH being adjusted to pH 5 ;rε precipitation. For precipi a ion chemical, alum : 37. by weight solution was used, added to the fibres _7. by weight, calculated as dry matter related to stock dry matter. The grammage of the liner sheets were produced was about 150 g/m Ξ and thickness :t 0.26 mm. The other characteris ics, determined at relative humidity, unless otherwise stated, were as 3ws: .a 11. The effect of high-molar mass kraft lignin on characteristics of liner produced from kraft stock. ■ ;. Dens. Air Comp.str. Tens. Tens. Cobb ώ0 857- perm. SCT CCT str. Ind. value humid. SCT kg/m 3 s/100 kN/m kN/m kN/m Nm/g g/m a kN/m ml 550 5,4 3,10 1,83 6,93 48,5 34 1,64 579 6,5 3.44 1,95 7,54 51,6 32 1,86 574 6,0 3,52 1,99 7,91 53,4 27 1,90 565 5,3 3.45 1,90 7,74 52,7 25 1,90 578 6,2 3,47 2,00 7,79 52,6 27 1,89 596 7,8 3,51 2,11 8,08 54,2 26 1,94 593 9,7 3,65 2,19 8,19 54,6 26 1,96 As can be seen in Table 11, also virgin fibres - oe reinforced with high-molar mass lignin. The SCT ' .'_9S have here Increased by 207, both at 507. and 857. -tive humidity of air. The quantity of lignin added, "ulated < > as '/. by weight dry matter related to the -ck dry matter, implies that when for instance the : ~d quantity is 507 by weight, the composition of the crk/lignin mixture Is 337. by weight lignin ctry matter z 677. by weight stock dry matter. -"Die 11. Production of fibreboards To a fibre suspension which had consistency 10 g/1, high-molar mass kraft lignin was added, as a 57. solution, at 1 and 2.57. by weight. The lignin was pre¬ cipitated onto the fibres with alum, added as a 37. solution at 17. by weight, calculated as dry matter related to the dry matter of the fibres. The production conditions of fibre boards were as follows: hot pressing temperature 205°C, pressure 0.5 Nm/mm ε , and pressing time 6 to 7 minutes. The sheets were post-hardened at 160 ,::, C for 4 hrs. The characteristics of the boards ar e given in Table 12, where also the characteristics of fibre boards made wi th ' pheno 1 ic resin are stated. Table 12. The characteristics of fibre boards Bonding agent Quant. Flexur. Tens. Water Swelling added str. str. uptake 7. N/mm s N/mm s 24 h , 7. 24h , 7. Phenolic resin 1 501 2,22 27,2 16,8 High-molar mass kraft lignin 1 612 2 , 56 23 , 6 15 , 3 D:o 2,5 546 2 , 65 26 , 6 16 , 7 As can be seen in Table 12, the results achie¬ ved with high-molar mass kraft lignin are better than those with phenolic resin. Thus, the strength charac¬ teristics of fibrebαards could be improved in an eco- nomically advantageous way.

Claims: CLAIMS 1. A procedure for manufacturing van;., ducts from lignocellulosic material and for _- their strength and water resistance characteris '. c h a r a c t e r i z e d in that to the lig^: losic material are added highmolar—mass lignin . tlves of which at least 35 7. by weight of f- = molar mass over 5000 In the form of aqueous sc . suspension or powder, and that the acidity is justed that the pH of the 1 ignocel lulose/1 ignlr- after addition Is in the range from pH 2 to pH ~~ 2. Procedure according to claim 1, c a c t e r i z e d in that at least 407. by weiq lignin derivatives have molar mass over 5000. 3. Procedure according to claim 1 or Ξ c h a r a c t e r i z e d In that in the aqueG--- tion of the lignin derivatives at least 707 . of the total dry matter is precipitated frc solution with 1 M hydrochloric acid at pH 3. 4. Procedure according to any one of - to 3, c h a r a c t e r i z e d in that the ; solution of the lignin derivatives is acidize; its pH is below 7 before its addition to the 11- lulosic material. 5. Procedure according to any one of - to 3, c h a r a c t e r i z e d in that the 1; lulosic material Is neutralized or acidize: adding lignin. 6. Procedure according to any one of r. to 5, c h a r a c t e r i z e d in that tr; quantity to be added to the lignocellulosic e 1 to 607- by weight, calculated as lignin u n ¬ rela ed to the dry matter of the lignocellul: terlal. 7. Procedure according to any one cla 6, c h a r a c t e r i z e d in that the c- content of the high-molecular lignin derivatives at addition to the lignocellulosic material is in the range 0.1 to 1007. by weight. 8. Procedure according to any one of claims 1 to 7, c h a r a c t e r i z e d in that the lignin derivatives are added to the lignocellulosic material so that the retention of the lignin derivatives is over 907.. 9. Procedure according to any one of claims 1 to 8, c h a r a c t e r i z e d in that the lignin de¬ rivatives originate from alkaline cellulose manufactur¬ ing processes. 10. Procedure according to any one of claims l to Θ, c h a r a c t e r i z e d in that the lignin derivatives originate from the kraft pulping process. 11. Procedure according to any one of claims l to 8, c h a r ' t e r i z e d in that the lignin derivatives originate from a cellulose bleaching pro¬ cess. 12. Procedure according to any one of claims 1 to 11, c h a r a c t e r i z e d in that to the lig¬ nocellulosic material are added, before or after lignin addition, bivalent or trivalent metal salts, such as alum, ferric or ferrous sulphate or ferric chloride, at 0.5 to 107. by weight, calculat- ed as dry matter related to the dry matter of the 1 ignin/1 ignocel lulose material. 13. Procedure according to any one of claims 1 to 12, c h a r a c t e r i z e d in that to the lig¬ nocellulosic material are. added, before or after the lignin addition, cationica. organic precipitation chemi¬ cals, such as polyethylene i ine, at 0.5 to 107. by weight, calculated as dry matter related to the dry matter of the 1 ignin/1 ignocel lulose material. 14. Procedure according to any one of claims 1 to 13, c h a r a c t e r i z e d in that the 1'ignin derivatives are chemically modified before being added to the lignocellulosic material. 15. Procedure according to any one of claims 1 to 13, c h a r a c t e r i z e d in that the lignin is chemically modified after being added to the ligno¬ cellulosic material.

Inventors: FORSS KAJ G, FUHRMANN AGNETA G M, TOROI MARTTI, FORSS, KAJ, G., FUHRMANN, AGNETA, G., M., TOROI, MARTTI
Applicants: KESKUSLABORATORIO, OY KESKUSLABORATORIO - CENTRALLABORATORIUM AB
Application year: 1988
Main classification: D21H3
IPC codes: C08L97, D21H17