Method for producing paper from waste wood, and paper produced therefrom

Abstract

The invention relates to a method for producing paper from a cellulose pulp, wherein waste wood is used as a starting material in a wood pulping method. The waste wood, selected from at least one of the classes A I, A II, and A III according to the German Waste Wood Ordinance for chipping or pulverizing, is comminuted to chips of one of the size classes including classes smaller than # 3, # 3, # 7, and # 13 according to SCAN CM 40:01; the formed waste wood chips are pre-steamed with saturated steam at temperatures between 85 °C and 120 °C at a pressure between atmospheric pressure and approximately 5 bar for a period of time between 1 and 90 minutes; the pre-steamed chips are pulped at a pressure between atmospheric pressure and 15 bar for a period of time of at least 20 minutes and are impregnated with an anionic or non-anionic organic additive in quantities ranging from 0.01 to 10 wt.% per ton of absolutely dried biomass; the chips are subsequently cooked at a pressure between atmospheric pressure and 15 bar; and the formed pulp is discharged and optionally mixed with additives such as starches, fixing agents, and / or flocculants and is subjected to a dewatering process and a subsequent drying process.

Description

[0001] Process for producing paper from waste wood and paper produced therefrom

[0002] The present invention relates to a process for producing paper from a cellulose pulp in which waste wood is used as starting material in a wood pulping process, and to a paper produced by this process.

[0003] Due to the increasing frequency of extreme weather events, which often damage large areas of forest and require felling, large quantities of wood have to be stored for long periods before they can be used, for example, in paper production. This wood, known as waste wood, has a lower moisture content than new wood and is therefore more difficult to impregnate in a digester, which leads to higher energy consumption in paper production and larger quantities of organic residues, such as resin acids, remaining in the paper made from it. Furthermore, due to the increasing scarcity of resources of good quality new wood and rising prices, the paper industry has also been trying for several years to at least partially replace new wood with the recycling of old materials, such as waste paper. Foreign fibers such as bagasse, straw, reeds, etc.were considered as a starting material for paper production in the past. However, these materials have only limited applications because they often contain high levels of inorganic contaminants, such as a high silicon content. The use of waste wood of classes AI to IV in accordance with the German Waste Wood Ordinance "Waste Wood Ordinance of August 15, 2002, Federal Law Gazette I, page 3302, in the version of June 19, 2020 (Federal Law Gazette I, page 1328), hereinafter referred to as the German Waste Wood Ordinance," in paper production has also been tested. However, it has been shown that since waste wood very often contains large amounts of organic contaminants, such as adhesive residues contained in wood products such as chipboard, plywood, or chipboard, only very low-quality paper can be produced from this waste wood.Waste wood and contaminated lumber have already been successfully used for research purposes in various cooking processes. For example, H. Rautkoski et al., "Recycling of Contaminated Construction and Demolition Wood Waste," Waste Biomass Valor (2016), 7:615 ff, describe experiments on the production of foam wood panels from waste and demolition wood. In this article, the author concludes that these materials can be easily processed and digested using conventional cooking processes, such as TMP or kraft processes, and that their mechanical properties are roughly comparable to those of fresh wood. However, despite the feasibility of the wood digestion process, it is to be expected that there are limitations to the use of such waste wood raw materials due to various contaminants.

[0004] US Pat. No. 6,325,888 B1 describes a process for digesting sawdust from new wood. A slurry prepared from sawdust is steamed and fed to a boiling kettle under elevated pressure, where it is boiled. The slurry is then discharged under elevated pressure and allowed to cool. This process solved the mechanical problems associated with the use of very fine sawdust, but did not address any problems associated with the content of residual materials, such as adhesives, resins, and the like, that arise from the manufacture of wood products such as particleboard.

[0005] EP 0 697 941 A describes the reactivation of wood from, for example, OSB or particleboard for subsequent recycling. This involves mild activation with caustic soda at temperatures up to 120 °C.

[0006] The disadvantage of all methods known to date is that, although the products manufactured from waste wood are essentially equivalent to those made from new or old wood, especially when their mechanical properties are measured or the kappa numbers, which essentially reflect the lignin content, are compared, all of these methods overlook the fact that organic compounds used as adhesives or composite materials in wood-based products, such as glued wood panels, melamine panels, and the like, introduce large quantities of organic resins, such as melamine-formaldehyde resins, isocyanates, and phenolic resins.These chemicals cannot be separated from lignin, which is also originally contained in the wood, during cooking, which is why either almost all of the lignin and almost all of the phenolic resins, isocyanates or melamine-formaldehyde resins are separated with the lignin after cooking, which in turn is detrimental to paper made from the pulp, or they are at least partially incorporated into the paper made from it, which is why paper made from waste wood is not suitable or only very conditionally suitable for various purposes, as it does not meet the standard for food use or packaging use, for example.

[0007] The invention now aims to provide a process for producing a pulp or paper, with which it is possible to separate the undesirable organic residual materials from the waste wood, such as phenolic resins, isocyanates, melamine resins and the like, from the lignin, so that the pulp used for paper production essentially only contains lignin or hemicelluloses and cellulose and digested wood fibers.

[0008] To achieve this object, the invention is essentially characterized in that waste wood selected from at least one of the classes AI and A 11 and A III according to the German Waste Wood Ordinance is subjected to chipping or grinding to chips of one of the size classes smaller than # 3 (fines), # 3 (pin chips), # 7 (small accepts) and # 13 (large accepts) according to SCAN CM 40:01, that the waste wood chips formed are pre-steamed with saturated steam at temperatures between 85 °C and 120 °C, preferably about 100 °C for a period of between 1 and 90 minutes, preferably between 10 and 60 minutes at a pressure between atmospheric pressure and about 5 bar, that the pre-steamed chips are digested under a pressure between atmospheric pressure and 15 bar for a period of at least 20 minutes and with an anionic or non-ionic organic additive, in amounts between 0.01 and 10 wt.-% per ton of absolutely dry biomass, in particular 1.0 and 6.0 wt.% per ton of absolutely dry biomass, and then boiled, and that a pulp formed is discharged and, if necessary, mixed with auxiliary materials such as starch, fixing agents and / or flocculation aids and subjected to dewatering and subsequent drying. By conducting the process in such a way that the waste wood, which can comprise any of the waste wood classes AI, A II and A III, is shredded or ground to one of the size classes smaller than # 3, # 3, # 7 and # 13 according to SCAN CM 40:01 in a first step, the subsequent impregnation succeeds in impregnating the chips completely and deep into their interior, thus optimally preparing them for pulping.By subsequently digesting the chips at a pressure between atmospheric pressure and an overpressure of approximately 15 bar for a period of at least 20 minutes and impregnating them with an anionic or non-ionic organic additive in quantities between 0.01 and 10 wt.% per ton of absolutely dry biomass, in particular 1.0 and 6.0 wt.% per ton of absolutely dry biomass, it is possible to keep the dissolved resins originating from the waste wood products in solution and prevent their renewed deposition or precipitation on the impregnated fibers. By optionally adding an additive to the impregnated and digested chips from waste wood, the organic resins originating from the waste wood or recycled products, which have always been separated together with the lignin in previously known processes, can be separated even more completely from the lignin contained in the wood and removed from the process.

[0009] Such a pulp from waste wood, depleted of organic resins, adhesives, and the like, is subsequently subjected to a conventional cooking process, bleaching, dewatering, the addition of additives, and drying to produce paper or board. The lignin content of paper or board produced in this way is essentially in the range of that of paper made from new or waste wood and depends largely on the type of wood used. Furthermore, however, it has surprisingly been shown that paper or board produced using this process has a significantly reduced organic nitrogen content compared to paper produced from waste wood according to the prior art, which essentially makes paper produced according to the invention also suitable for use in the food sector.In connection with this application, the usual classification of waste wood is used. Group AI includes seasoned, natural, and only mechanically processed waste wood; Group A II includes pre-glued, painted, coated, varnished, or otherwise treated waste wood without organic halogen compounds in the coating; Group A III includes waste wood with organic halogen compounds in the coating; and Group A IV includes waste wood treated with wood preservatives that cannot be assigned to categories AI to A III due to its pollutant load. All groups are defined in accordance with the German Waste Wood Ordinance.According to a further development of the invention, the process is carried out such that waste wood with a fiber length between 0.01 and 5 mm length-weighted average fiber length according to ISO 16065-2:2014, preferably between 0.9 and 2.5 mm length-weighted average fiber length according to ISO 16065-2:2014, is used as the starting material. In connection with the process according to the invention, the fiber length of the waste wood used covers a wide range, which results from the previous use of the wood or the different wood species used here. In general, it should be noted that fiber lengths in the lower limit range of 0.01 mm refer to fines, which are inevitably entrained even in the process according to the invention, fiber lengths in the middle range refer essentially to hardwood fibers, and those in the upper limit range refer to softwood fibers.Advantageously, and in particular to achieve the best paper properties, hardwood waste and / or waste wood chips are used in processes which are particularly suitable for processes in which hardwood or predominantly hardwood proportions are usually used, such as the NSSC process. To ensure reproducibility of the process, the length-weighted average of the fiber lengths according to ISO 16065-2:2014 is used in the process. In order to enable optimal adjustment of the cellulose pulp to the requirements of a paper or board subsequently produced therefrom, the process according to the invention is essentially further developed by adding wood chips from non-waste wood classes, such as sawdust, new wood, waste wood, wood chips or rejects from the cooking process, as well as optionally other fibrous materials such as hemp, reeds, grass, in amounts between 15 and 90 wt.% to the starting material.By adding other wood materials or wood-like materials such as wood chips from non-waste wood classes, sawdust, planer nicks, and the like, or even waste from a conventional cooking process, as well as, if necessary, other fibrous materials such as hemp, reed, or grass in quantities between 15% and 90% by weight to the starting material consisting of waste wood, and by selecting alternative fiber materials that can be used in addition to the waste wood starting material, it is possible, for example, to adjust the mechanical properties of the paper or cardboard produced from it. With this type of process, virtually any paper quality can be produced using waste wood and other wood-like materials.

[0010] According to a further development of the invention, the process is carried out in such a way that an additive is introduced into the retention container before, during, or after delignification. Surprisingly, the introduction of an additive after delignification has shown that, since at this point in time during delignification the majority of the organic resins or adhesives as well as the lignin are in solution, adding the additive enables optimal and, in particular, almost complete separation of the organic resins or adhesive residues from the lignin, since the additive prevents them from precipitating out of the solution, while the lignin can attach itself unhindered to the pulp fibers and be carried away with them.Surprisingly, it has been shown that when anionic or non-ionic surfactants are added to the impregnation prior to cooking, they act as impregnation aids, transporting the lye more quickly into the interior of the waste wood. This effect is not observed when dispersants such as polyacrylic acids, lignosulfonates, or chelating agents such as EDTA, DTPA, etc. are added before, during, or after impregnation.

[0011] A particularly advantageous and complete separation of the organic resins, gum residues, melamine resins, isocyanate resins and the like is achieved by using as an additive at least one from the group of anionic or non-ionic surface-active agents, such as saturated or unsaturated alcohol ethoxylates, alkyl polyglucosides, polyalkylene glycols, fatty alcohol ether sulfates, fatty alcohol sulfates, alkyl benzosulfonates, oleic acid sulfonates, emulsifiers and solubilizers such as modified saturated or unsaturated oils with optionally chemically bound ethoxylates, fatty alcohol ethoxylates or epoxidized vegetable oils or low-foam surfactants, such as EO-PO block polymers, polyglycol ethers of an aliphatic diol, C10 - C13 alkyl derivatives, anionic or non-ionic dispersants, such as carboxymethylcellulose and salts thereof, Polyacrylic acid and salts thereof, maleic acid-olefin copolymers and salts thereof,Lignosulfonic acids and salts thereof, as well as other sulfonic acid condensation products and salts such as benzenesulfonic acid, polyphosphates, alginic acid and salts thereof, or anionic chelating agents such as EDTA or DTPA, or tall oil or salts thereof such as sodium salt as tall oil soap are used. Most of these additives are well known in papermaking and are often used at another stage of the papermaking process, for example, as flocculation aids, fixatives, and the like. Their use at an early stage of the process, for example, during or after delignification, does not alter the composition of the resulting paper. However, this addition successfully enables the organic resins and adhesives derived from waste wood to be optimally stabilized and separated in the lye.

[0012] The Kraft or NSS C process has proven particularly suitable for digesting waste wood as a starting material. It is known to those skilled in the art that the NSSC process is usually carried out using hardwood or predominantly hardwood, while the Kraft process can employ mixtures of softwood and hardwood in any ratio. In both processes, the process according to the invention reliably prevents the precipitation of isocyanate resins, phenol-formaldehyde resins, melamine resins, and the like from the cooking liquor, thus achieving an optimized result with regard to the removal of organic resin contamination from the pulp.

[0013] According to a further development of the invention, the process is conducted such that the paper contains at least 10% by weight, preferably at least 50% by weight, and particularly preferably at least 85% by weight of waste wood fibers, additives, and optionally residual amounts of fibers originating from new or old wood, and optionally at least one auxiliary agent selected from starch, fixing agents, and / or flocculation aids, and that the paper has 0.1 to 22% by weight of lignin, preferably 5 to 20% by weight, and a total amount of bound nitrogen of between 0.2 and 1.0 kg / t of paper. This applies in particular to the mechanical properties and kappa numbers, as well as the nitrogen content of the paper. The kappa numbers of a pulp emerging from the digester in the process according to the present invention are essentially between 15 and 170.In the finished paper, the lignin content is up to 21%, depending on whether subsequent bleaching was carried out, whereby these high percentages are only achievable in papers produced using the NSSC process.

[0014] To reduce the lignin content in paper produced from the pulp according to the invention and to obtain a white paper, the process can be conducted by bleaching the pulp, preferably with chlorine-containing or chlorine-free bleaching agents. In this context, however, it should not be overlooked that bleaching weakens the cellulose fibers and makes them softer, so bleaching is only used for applications requiring relatively soft fibers.

[0015] In order to be able to control or influence the properties of paper or board produced from the cellulose pulp according to the invention even better, the process according to the invention is carried out in such a way that the pulp is mixed with 10 to 90 wt.% of another kraft or NSSC pulp, in particular a kraft or NSSC pulp from new wood or waste wood. With such a process, it is particularly suitable to produce papers or boards which have high lignin contents and low nitrogen contents as well as excellent mechanical properties, so that they appear particularly suitable for packaging purposes. The invention further relates to a paper produced according to the process of the invention, which is essentially characterized in that the paper contains at least 10 wt.%, preferably at least 50 wt.% and particularly preferably at least 85 wt.-% waste wood fibers, additives and optionally residual amounts of fibers originating from new wood and / or waste wood and optionally at least one auxiliary material selected from starch, fixing agents and / or flocculation aids and that the paper has 0.1 to 22 wt.% lignin, preferably 5 to 20 wt.% and a total amount of bound nitrogen between 0.2 and 1.0 kg / t of paper. Such papers surprisingly have almost identical strength properties such as elongation at break, TEA index or tensile strength to paper made from new wood or waste wood and, due to their extremely low content of bound nitrogen, are suitable for almost all applications for which paper made from new wood or waste wood, for example kraft paper, NSSC paper or even thermomechanically produced paper, can and may be used.This is particularly surprising because papers made from waste wood have previously had a significantly higher total nitrogen content, which originated from organic resins used for coating materials or adhesives. According to a further development of the invention, such papers can have a basis weight according to ISO 536 between 20 and 450 g / m². 2 and a density between 0.3 and 0.9 g / m 3 It goes without saying that such rapiers can also be subjected to conventional post-treatment steps such as calendering, micro-creping in a Clupak system or an Expanda, and the like, without their properties differing from papers made from new or old wood using an identical process and from the same wood species.

[0016] According to a further development of the invention, such paper can also be bleached. It goes without saying that bleaching weakens and softens the pulp fibers, and therefore bleaching is only used when the paper is used for a purpose whose strength properties do not need to be outstanding.

[0017] Finally, as also corresponds to a further development of the invention, the paper can also be formed in multiple layers or can also have individual layers of new wood or old wood and at least one layer of waste wood, without this having any adverse effects on the end product.

[0018] The invention is explained in more detail below using exemplary embodiments.

[0019] In an initial laboratory test, 12 different samples of waste wood, shredded to size classes #3 and #13 according to SCAN CM 40:01, were first subjected to pre-steaming, then impregnated, and finally boiled. Additives such as tall oil were added to some samples. The thus-processed waste wood samples were subjected to grinding at 8000 rpm in a PFI mill known to those skilled in the art, then dewatered and dried. Paper sheets with a basis weight of 75 to 80 g / m² were produced. 2 were prepared and analyzed, and the values ​​obtained were compared with those of an analogously treated new wood sample and a non-ground recycled pulp.

[0020] The test conditions are given in Table 1 below, and analysis results of the waste wood samples digested in the laboratory tests are summarized in Table 2 below, and the properties of the paper sheets formed are summarized in Table 3.

[0021] Table 2

[0022] Analysis of the digested wood samples

[0023] Table 1

[0024] Digestion of wood samples kA: not specified TÖ: = Tall oil Inf.: = Infinity is a trademark of Solenis SA and consists of a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-2H-isothiazol-3-one as main components

[0025] Nop.: = Nopcosperse is a trademark of Solenis SA and consists of a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-2H-isothiazol-3-one as main ingredients.

[0026] Table 3

[0027] Subsequently, in a further series of tests, blends of 25%, 50%, and 90% waste wood pulp and 75%, 50%, and 10% unrefined recycled paper, as well as blends of 75%, 50%, and 10% refined, never-dried softwood pulp from virgin wood, were produced. Paper sheets were then produced from the mixed pulps produced in accordance with the processing described above. The resulting paper sheets were compared with paper made from recycled cardboard and a paper made exclusively from virgin softwood fibers in terms of their tensile strength index, burst strength index, and tear index. The results are shown in Table 4.

[0028] Table 4

[0029] Papers made from mixed pulps

[0030] The results obtained show that the papers made from waste wood exhibit surprisingly good mechanical properties, which are significantly better than those of papers made exclusively from recycled paper, especially newsprint. These properties can be significantly improved by adding a pulp made from waste wood and, in particular, are not significantly worse than those obtained for pulps made from 100% fresh wood.

[0031] It follows that the processing of waste wood according to the invention can yield a valuable raw material for paper production, so that overall a resource-saving process is provided with which paper of surprisingly good quality can be produced.

Claims

Patent claims 1. A process for producing paper from a cellulose pulp, in which waste wood is used as starting material in a wood pulping process, characterized in that waste wood selected from at least one of the classes AI and A II as well as A ill according to the German Waste Wood Ordinance is subjected to chipping or grinding to chips of one of the size classes smaller than # 3, # 3, # 7 and # 13 according to SCAN CM 40:01, that the waste wood chips formed are pre-steamed with saturated steam at temperatures between 85 °C and 120 °C, preferably about 100 °C for a period of between 1 and 90 minutes, preferably between 10 and 60 minutes at a pressure between atmospheric pressure and about 5 bar, that the pre-steamed chips are digested at a pressure between atmospheric pressure and 15 bar, preferably 1.5 to 3.5 bar for a period of at least 20 minutes and with a anionic or non-ionic organic additive,in amounts between 0.01 and 10 wt.% per ton of absolutely dry biomass, in particular 1.0 and 6.0 wt.% per ton of absolutely dry biomass, and then cooked at a pressure between atmospheric pressure and 15 bar, preferably 4.5 to 6.5 bar, and that a formed pulp is discharged and optionally admixed with auxiliary substances such as starch, fixing agents and / or flocculation aids and that it is subjected to dewatering and subsequent drying.

2. Method according to claim 1, characterized in that waste wood with a fiber length between 0.01 and 5 mm length-weighted average fiber length according to ISO 16065-2:2014, preferably between 0.9 and 2.5 mm length-weighted average fiber length according to ISO 16065-2:2014 is used as starting material.

3. Process according to claim 1 or 2, characterized in that wood chips from non-waste wood classes, such as sawdust, new wood, waste wood, wood chips or waste from the cooking process and optionally other fibrous materials, such as hemp, reed, grass, are added to the starting material in amounts between 15 and 90 wt.%.

4. A method according to claim 1, 2 or 3, characterized in that an additive is introduced into a retention container before, during or after delignification.

5. Process according to one of claims 1 to 4, characterized in that at least one of the anionic or non-ionic surface-active agents, such as saturated or unsaturated alcohol ethoxylates, alkyl polyglucosides, polyalkylene glycols, fatty alcohol ether sulfates, fatty alcohol sulfates, alkyl benzosulfonates, oleic acid sulfonates, Emulsifiers and solubilizers such as modified saturated or unsaturated oils with optionally chemically bound ethoxylates, fatty alcohol ethoxylates or epoxidized vegetable oils or low-foam surfactants such as EO-PO block polymers, polyglycol ethers of an aliphatic diol, C10 - C13 alkyl derivatives, anionic or non-ionic dispersants such as carboxymethylcellulose and salts thereof, polyacrylic acid and salts thereof, maleic acid-olefin copolymers and salts thereof, lignosulfonic acids and salts thereof and other sulfonic acid condensation products and salts such as benzenesulfonic acid, polyphosphates, alginic acid and salts thereof or anionic chelating agents such as EDTA or DTPA, or tall oil or salts thereof such as sodium salt as tall soap.

6. Process according to one of claims 1 to 5, characterized in that the waste wood starting material is digested using a Kraft or NSSC process.

7. Process according to claim 6, characterized in that the pre-steaming is carried out in a slightly acidic to slightly alkaline atmosphere, in particular at pH values ​​of 4.5 to 10, and the subsequent cooking process is carried out at pH values ​​between 5 and 14.

8. Process according to one of claims 1 to 7, characterized in that the pulp is bleached, preferably with chlorine-containing or chlorine-free bleaching agents.

9. Process according to one of claims 1 to 8, characterized in that the pulp is mixed with 10 to 90 wt.% of another kraft or NSSC pulp, in particular a kraft or NSSC pulp from new wood or waste wood.

10. Paper produced according to the process according to one of claims 1 to 9, characterized in that the paper contains at least 10 wt.%, preferably at least 50 wt.% and particularly preferably at least 85 wt.% waste wood fibers, additives and optionally residual amounts of fibers originating from new wood or waste wood and optionally at least one auxiliary agent selected from starch, fixing agents and / or flocculation aids, and that the paper has 0.1 to 22 wt.% lignin, preferably 5 to 20 wt.% and a total amount of bound nitrogen between 0.2 and 1.0 kg / t of paper.

11. Paper according to claim 10, characterized in that it has a basis weight according to ISO 536 between 20 and 450 g / m 2 and a density between 0.3 and 0.9 g / m 3 has 12, Paper according to claim 10 or 11, characterized in that it is bleached.

13. Paper according to claim 10, 11 or 12, characterized in that the paper is formed in multiple layers.

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