Paper making and fiber liberation – Processes and products – Non-fiber additive
Patent
1991-02-25
1992-05-05
Chin, Peter
Paper making and fiber liberation
Processes and products
Non-fiber additive
162 11, 162 12, 1621646, 1621682, D21H 1723
Patent
active
051104148
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a procedure for manufacturing lignocellulosic material products and for improving their strength and water resistance properties using high-molar mass lignin derivatives. Such products are e.g. those of the paper and cardboard industry and those of the industry manufacturing building materials, such as corrugated board, cardboard, kraft-liner, 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 of primary fibres but also to enable high-grade products to be made of lower grade raw materials such as reclaimed fibres.
BACKGROUND OF THE INVENTION
In cellulose manufacturing processes in which wood chips are heated in a cooking solution under pressure, about half of the wood is dissolved, forming the so-called waste liquor. One of the main organic components 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 lignosulphonates. In this form, lignin is soluble in water also in acid solutions. On the other hand, in alkaline cellulose manufacturing processes, such as the soda process (NaOH as digesting solution), in the kraft process (NaOH, Na.sub.2 S, NaHS as digesting solution) or in the oxygen/alkali process (with NaOH in the presence of oxygen), lignin is present in the form of an Na salt in the waste liquor, and it is water-soluble in alkaline solutions.
It is known in the art that the characteristics of e.g. paper, cardboard and fibre boards can be improved 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 24 (1975): 9, 269-70). 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 retention.
In the Canadian Patent CA 729,140 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 liquor only 26% by weight could be made to adhere to the fibres. All the same, the procedure was considered to be economically 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 (1984): 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, calculated on the dry matter of the fibres. In spite of poor retention, the breaking, punching and rigidity characteristics 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): 77-82) with the effect of phenol formaldehyde resin. Of the dry matter of the kraft lignin product used, 54.8% by weight was organic matter and 44% by weight was inorganic matter. When pH was adjusted with sulphuric acid to 4.5, only 15 g dry matter out of 100 g were precipitated. Precipitation could be somewhat improved by raising the precipitation temperature to 70.degree. C.; although 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 calculation analysis revealed that phenolic resin was somewhat more favourable in use than lignin owing to higher lignin addition and oxygen consumption, and to the heati
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patent: 2849314 (1958-08-01), Goss
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patent: 4357454 (1982-11-01), Holmberg
Forss Kaj G.
Fuhrmann Agneta G. M.
Toroi Martti
Chin Peter
Oy Keskuslaboratorio - Centrallaboratorium Ab
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