FI20175363A1 - Phenol-free impregnation resin - Google Patents

Abstract

The present invention encompasses a process for producing a substantially phenolic-free impregnation resin as well as a resin composition prepared by this process or otherwise equivalent, and the end use thereof. The process uses as the starting material with phenolic OH groups essentially only lignin, which is condensed with formaldehyde in the presence of a catalyst at an elevated temperature.

Description

Background of the Invention

Field of the Invention

The present invention relates to a process for the preparation of a substantially phenol-free impregnation resin, and to a resin prepared by this process or otherwise having a resin composition and end-uses for the resin.

State of the art

Commonly used resin impregnation resins are either phenolic resins or melamine resins, depending on the application of the impregnated paper. In many applications, phenolic resins are a viable option, but melamine resins are used for improved water resistance and similar properties. Some applications require the properties of both resins, so a mixture of melamine and phenolic resin is used. Melamine resins are more expensive than phenolic resins in terms of their raw materials, but they are safer because they do not contain free phenol, which is toxic.

The structure and properties of the final resin depend on the reaction conditions used in the preparation, such as condensation temperature, condensation time, catalyst system, solvent system, and formaldehyde / phenol molar ratio. The choice of reaction conditions will depend on the end application for which the resin is made.

The availability of petrochemical raw materials such as phenol is limited and hence it would be important to replace them in the future with renewable natural raw materials such as wood-derived polyphenolic lignin. At the same time, avoiding e.g. environmental damage caused by phenol.

Phenol-formaldehyde-resin phenol substitution with renewable natural raw materials is already known.

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WO2014080033 discloses a process for preparing a phenol-formaldehyde impregnation resin, wherein the phenol is replaced by 60-100% lignin. According to the publication, mixtures of water and tetrahydrofuran, water and ammonia, and water and ethyl acetate are used for dissolving lignin.

In U.S. Pat. No. 5,177,169, an organic solvent, typically polar and at least partially immiscible with water, such as ethyl acetate, is added to the lignin-containing aqueous solution. The mixture is oxidized to provide an aqueous layer and an organic solvent layer containing demethylated lignin. The demethylated lignin is dissolved in a basic solution to which an aldehyde source has been added to make a resin. For example, formaldehyde in the solution step may be used as the aldehyde source.

According to known solutions, there is a risk that the temperature of the reaction mixture rises uncontrollably, which affects the quality of the final product. At the same time, the consumption of formaldehyde 15 will increase significantly.

Summary of the Invention

The object of the present invention is to eliminate at least some of the problems associated with the prior art and to provide an improved process for the preparation of a phenol-free impregnation resin.

The present invention encompasses a process for making a substantially phenol-free impregnation resin using essentially only 25 lignins as the phenolic OH-containing agent, and a resin prepared by this process or otherwise having a similar composition. In the process, formaldehyde is condensed with lignin in the presence of a catalyst at elevated temperature.

The invention is based on the idea that the lignin is first brought into the liquid phase by dissolving it in a solvent or solvent mixture, and then formaldehyde is added to the resulting mixture in the presence of an alkaline catalyst to effect a condensation reaction between formaldehyde and lignin.

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The alkali is then fed into the liquid phase gradually so that the reaction of the formaldehyde with the phenolic groups can be completed.

The invention thus provides a substantially phenol-free impregnation resin comprising a condensation product of formaldehyde and lignin having a content of up to 5% by weight of free formaldehyde, in particular up to 1% by weight, for example 0.1-1.0% by weight. Preferably, the finished impregnation resin is in the form of an aqueous mixture having a dry solids content of greater than about 20% by weight and usually no more than about 70% by weight, typically between 30 and 40% by weight.

More specifically, the solution according to the invention is essentially characterized by what is disclosed in the independent claims.

The present invention achieves significant advantages. In the invention, the phenol of the phenol-formaldehyde impregnation resin is substantially replaced by lignin, whereby the use of toxic phenol in the resin can alternatively be completely avoided.

By means of the invention, the reactivity of the condensation reaction between lignin and formaldehyde can be controlled and regulated. In the process, the resin can be condensed such that virtually all free formaldehyde is reacted. Thus, the cooking system of the invention achieves really low levels of free formaldehyde, allowing the solution to be used in many applications that require low levels of formaldehyde. At the same time, however, the viscosity of the resin is maintained at such a level that it can still be used in paper impregnation applications. Such impregnated fiber sheets can be used, for example, for manufacturing multilayer veneer products.

Thus, the resin prepared by the process of the invention or corresponding to its composition is generally suitable as a substitute for a conventional impregnation resin e.g. fdmi and frame papers. In addition to impregnating resin, possible applications include, for example, various fiber boards.

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Brief Description of the Drawings

Figure 1 shows photographs of the finished extrudates of the lignin impregnates, and a reference sample, and Figure 2 shows a schematic drawing of the structure of a compact laminate in the open.

embodiments

In the present context, percentages are by weight unless otherwise stated.

By "resin" is meant the reaction product of the phenolic OH-containing starting material and formaldehyde obtained by the polymerization reaction.

In one embodiment, the phenol-free resin is prepared using essentially only lignin as the agent containing the phenolic OH groups. In practice, at least 90% by weight, preferably at least 95% by weight, preferably at least 98% by weight, or even 100% by weight of the raw material containing phenolic OH groups is lignin.

In one embodiment, another biomass, such as tannin, is used as the substance containing phenolic OH groups in addition to lignin.

It is also possible to use small amounts (10% by weight, preferably up to 5% by weight, especially up to 2% by weight) of phenol, cresol or resorcinol or a mixture thereof in the process.

The lignin used in the present invention is particularly lignin derived from biomass such as wood or annual or perennial plants or lignocellulose, respectively. In particular, a material isolated from the spent cooking liquor obtained from the biomass cooking 30 is used as the lignin starting material.

Examples of lignin starting material used include alkaline cooking lignin isolated from biomass, such as kraft lignin (i.e., sulphate-cooked lignin) or soda-lignin (i.e., soda-soup lignin). The method can also be used

20175363 prh 21 -04-2017 organosolv lignin (i.e. organosolv lignin). Among the lignin starting materials used may be mentioned pyrolytic lignin, steamed lignin, dilute acid lignin and basic oxidative lignin.

Mixtures of the above-mentioned lignin starting materials may also be used as lignin starting materials.

The lignin starting material may contain, in addition to lignin, other substances such as extracts or carbohydrates such as cellulose or hemicellulose or their degradation products.

Generally, the lignin starting material contains at least 90% by weight, preferably at least 95% by weight, especially at least 98% by weight of lignin.

The lignin starting material may be in the form of a solid such as a powder. Such lignin starting materials are represented by commercially available lignin products. It is also possible to use the lignin in the liquid phase as further described below.

The preparation is accomplished by dissolving the lignin starting material in a solvent containing an alkaline substance as a catalyst. To the solution is added formaldehyde, especially aqueous formaldehyde, i.e. formalin. The lignin and formaldehyde are then condensed at elevated temperature until virtually all formaldehyde, i.e. at least 90% by weight, more preferably at least 95% by weight, preferably at least 99% by weight, is reacted with formaldehyde. The resin thus formed is recovered.

In particular, lignin and formaldehyde are condensed at about 50-90 ° C until all formaldehyde has reacted, after which the resin is recovered.

Most preferably, the lignin and formaldehyde are condensed in the liquid phase formed by the lignin solvent or mixture thereof.

According to a preferred embodiment, in the resin manufacturing process, the lignin is initially dissolved in a solvent mixture containing a solvent, water and an alkaline catalyst. The addition of solvent and water at the beginning of the resin soup enables viscosity

20175363 prh 21 -04- 2017 control during condensation so that the viscosity does not rise too high at any stage of the reaction.

Dosage of the catalyst can also be done in several batches, which also helps to control the smooth progression of condensation reactions. Due to the solvent, water, and catalyst dosing, as well as the dosing modes, the resin can be condensed to the point where the free formaldehyde is virtually completely reacted.

In a preferred embodiment, kraft lignin is used to replace the phenol. Such commercially available lignin is generally supplied as a powder with a dry solids content of more than 90% by weight, e.g., about 93% by weight. An aqueous slurry of lignin having a dry matter content of about 50% by weight or more can also be used in the process.

The lignin solvent is typically a polar liquid miscible with water.

Examples of the solvent include aliphatic and aromatic alcohols, such as methanol, and aliphatic ketones, such as acetone. Sufficient solvent is used to maintain the dry solids content of the mixture, i.e. about 20-70% by weight, especially 30-70% by weight, for the further reaction.

Usually the solvent used is methanol or mixtures thereof.

In one embodiment, the lignin is dissolved in a mixture of the actual solvent and water.

For example, in the case of methanol, the concentration of methanol in water is usually about 1.5 to 15% by weight, such as 1.6 to 12% by weight. The solvent present in the cooking step allows the resin to be condensed for a longer period without increasing the viscosity too quickly and achieving a low formaldehyde content.

When lignin is dissolved in a water / methanol mixture, the resin remains soluble for a longer period of time and allows viscosity control during the condensation reaction. This, in turn, allows virtually all free formaldehyde to be reacted to:

After the reaction, the content of free formaldehyde is up to 5% by weight based on the weight of the resin, in particular up to 1% by weight, for example 0.1-1.0% by weight.

According to one embodiment, the reaction may employ as a catalyst sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia (NH ₃ ), particularly as ammonium hydroxide, or a mixed catalyst system thereof, such as a mixture of sodium hydroxide and ammonia or sodium hydroxide and potassium hydroxide. Other nitrogen bases, such as organic amines, may also be used as the catalyst. Preferably, the catalysts are added to the mixture as aqueous solutions, the concentration of which varies slightly depending on the catalyst. For example, according to one embodiment, the concentrations of sodium and potassium hydroxide are between 40 and 60% by weight, preferably about 50% by weight for sodium hydroxide and preferably about 46% by weight for potassium hydroxide.

An aqueous solution of sodium hydroxide is also referred to below as the "" lye ".

The catalysts can influence the formation of the polymerization chain during the reaction by accelerating the condensation reaction between formaldehyde and lignin. Catalysts allow virtually all formaldehyde to react within a reasonable time, alternatively at either normal or elevated pressure.

According to one embodiment, the reaction uses formaldehyde as an aqueous solution having a formaldehyde content of 30-60% by weight, typically 50-60% by weight.

According to one application, technical grade formaldehyde is used. Technical grade formaldehyde starting material may include e.g. metallic impurities and some, typically up to 12% by weight methanol. According to a preferred embodiment, the formaldehyde content of the technical grade used is preferably at least 95% by weight.

According to one embodiment, the process for producing the resin according to the present invention is a multi-step process comprising 2 to 10 steps. Typically, the process is 2-3 steps, preferably 3 steps, whereby the addition of the alkaline catalyst is carried out gradually in several steps during the process. The gradual addition of the alkaline catalyst keeps the solids content of the mixture low during the reaction, allowing effective control of the viscosity. This in turn allows

20175363 prh 21 -04- 2017 keeping the viscosity of the reaction mixture so low that the condensation reaction can be carried out efficiently.

By "incremental addition" is meant that it takes longer to complete the addition if the predetermined amount is added at once (i.e., "incremental increments") without interrupting the addition. Generally, the addition time is at least 2 times longer than the incremental increment would require, preferably 5-100 times longer, e.g. 10-50 times longer.

Usually, the catalyst is added in two or more batches, whereby after the addition of one batch of catalyst, the reaction is allowed to proceed before the addition of the next batch of catalyst.

In a preferred embodiment, in the first step of the process of the invention, lignin is dissolved in a mixture of a solvent, especially water and a solvent, and a catalyst, especially a water-soluble alkali catalyst (optionally a first part). Dissolution occurs by stirring the mixture at room temperature (about ° C) or at elevated temperature. Generally, the temperature is below 70 ° C, preferably below 65 ° C, for example up to 60 ° C. In one embodiment, it is operated at 30-50 ° C, usually at 30-35 ° C.

The dissolution time is influenced by the selected reaction conditions as well as by substances such as the lignin used, the solvent / solvent mixture, the catalyst and the dissolution temperature. The dissolution time ranges from 0.5 to 2 hours, typically about 1 hour.

When the lignin is completely dissolved, i.e. at least 90%, preferably at least 95%, in the mixture, the temperature of the solution is typically raised to above 60 ° C, for example from about 60 to 100 ° C, preferably about 65 ° C. , and add water. Subsequently, a calculated amount of formaldehyde is added in a stepwise manner, with stirring, typically for about 0.1 to 2 hours, preferably for about 15 to 60 minutes. After the addition of formaldehyde, the temperature is raised to above 80 ° C, for example to about 80-100 ° C, preferably to about 85 ° C. At this temperature, the condensation reactions between lignin and formaldehyde take place. The reaction is continued for 0.1 to 2 hours, typically for about 15 to 45 minutes.

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In a multi-step embodiment, the second portion of the alkaline catalyst is then added, the mixture cooled to 80 ° C or less, e.g., in the temperature range of 20-80 ° C, and the condensation reaction is continued. The condensation reaction can thus be completed but, if necessary, the second part of the catalyst can be added in more, e.g.

2-5, typically in two steps. After the addition of the second catalyst moiety, the mixture is condensed. The condensation occurs for about 0.1 to about 2 hours, e.g., about 1 hour. A third portion of the catalyst is then added and condensed again for about 0.1-2 hours, e.g., about 1 hour. Similarly, if the catalyst is further subdivided, the same applies. When all the catalyst is added, the condensation reaction is completed.

Typically, when the condensation reaction is completed, the resulting resin is cooled to room temperature, i.e., about 20 ° C, which is its typical storage temperature.

According to one embodiment, the condensation reaction is continued until virtually all formaldehyde has reacted. As stated above, in the preferred embodiment this means that at least 95% by weight of the formaldehyde required for condensation has reacted, preferably at least 99% by weight, for example 99.0-99.9% by weight, of the formaldehyde required for condensation.

In the process, the resin can be cooked in a non-pressurized reaction vessel, i.e. a conventional reactor operated at normal pressure, or alternatively, a pressure boiler.

In both cases, the condensation reactor is preferably equipped with reactor heating and cooling devices, as well as temperature sensors and control. Further, the non-pressurized reaction vessel is preferably provided with a condenser, such as a vertical condenser, which can be used to condense any volatile solvent and return it to the reaction vessel. This ensures that the resin solvent is always present during the condensation reaction.

The catalyst system and dry matter affect the rate at which the resin viscosity develops.

By performing the condensation reaction as described above, in which a lignin solvent, such as methanol, is present during the reaction and the catalyst is gradually added to the reaction mixture, the solids content can be increased without excess viscosity, i.e., above 10,000 cP.

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As mentioned above, the reaction mixture typically has a dry solids content of about 20-70% by weight. If necessary, a solvent such as methanol, ethanol or acetone can be evaporated from the finished resin. This makes the resin more suitable for a variety of end uses where no solvent is present.

The solvent content of the finished resin is typically 0-15% by weight. Thus, the resin can also be recovered completely solvent-free.

In one embodiment, the finished resin has a Brookfield viscosity of 20-10,000 cP, especially 10-20-1000 cP, e.g. 20-300 cP or 50-300 cP.

The viscosity of the resin prepared according to one preferred embodiment is at the same level as the viscosity of normal impregnation resins. A resin having a Brookfield viscosity of 20-50 cP is particularly suitable for impregnating base paper. In particular, resin with a Brookfield viscosity of 100-300 cP is particularly suitable for impregnating film paper.

The solvents may also be added back to the resin after evaporation as needed, or the evaporated solvent such as methanol, ethanol or acetone may be replaced in whole or in part by, for example, water in applications where the solvent is not present at all or above % of total resin weight.

The resin prepared according to the process is itself thermosetting, i.e., the addition of additives is not necessary to formulate it as an adhesive. However, the composition of the resin can be further modified, for example, by mixing it with extenders and crosslinkers.

As extenders, compounds known per se such as amide or amine compounds such as urea or monomeric, oligomeric or polymeric carbohydrates such as sugars may be used.

Known compounds such as amine compounds such as hexamethylenetetra-amine or vinyl compounds such as divinylbenzene may be used as crosslinkers.

The finished resin can be impregnated into the paper as such or formulated with additives and then compressed into a laminate under the influence of heat and pressure.

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Paper impregnated with a resin impregnated with the process of the present invention or corresponding to its composition can be compressed into a laminate.

For example, a multiaxial press can be used for compression where the pressure is greater than 70 5 bar at about 140-150 ° C.

Alternatively, a high-speed press, a continuous press, or another method commonly used in the industry may be used. The fast speed press used is typically between 1-3 and has a processing temperature of 170-200 ° C.

Typical process parameters for a continuous press are 20-50 bar pressure and 170-180 ° C.

The following non-limiting examples represent applications of the present technology.

eXAMPLES

The resin was boiled in a standard reactor at normal pressure. The reaction was equipped with a reflux condenser to re-condense any volatile solvent into the reaction mixture. In the first step, water I, methanol and catalyst I, i.e. the first part of the catalyst comprising sodium hydroxide or sodium hydroxide together with either ammonia or potassium hydroxide, were charged to the reactor. At this point, the pH of the mixture was

7-8.5. To this mixture was added kraft lignin, after which the mixture was stirred for about 1 hour while maintaining the temperature below 50 ° C, generally between 30 and 35 ° C. After stirring, the temperature of the mixture was raised to about 65 ° C and water II was added. Next, formalin was added to the mixture at a constant rate for about 40 minutes. After the addition, the temperature of the mixture was raised to about 85 ° C and condensed for about 30 minutes. Thereafter, catalyst II, the second part of the catalyst, was added to the mixture and the mixture was cooled slightly to about 80 ° C. The mixture was condensed at this temperature for about 1 hour. Catalyst III, the third part of the catalyst, was added and the mixture was condensed for another hour. Finally, the resin was cooled.

The following examples illustrate the soups that were performed by the method described above:

Cooking Example 1

Kraft Lignin (75%) 25.16 Formalin (54%) 12.17 Alkaline (50%) 13.52 Water I 22.19 Water II 20.29 methanol 6.68 Rule 100.00

Cooking Example 2

Kraft Lignin (75%) 24,16 Formalin (54%) 11.69 Ammonia (25%) 5.19 Alkaline (50%) 5.19 Water I 21.29 Water II 19.48 methanol 12.99 Rule 100.00

Cooking Example 3

Kraft Lignin (75%) 31.26 Formalin (54%) 15.97 Alkaline (50%) 15.13 Water I 27.56 Water II 8.4 methanol 1.68 Rule 100.00

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Cooking Example 4

Kraft Lignin (75%) 27.46 Formalin (54%) 11.07 Potassium hydroxide (46%) 8.61 Alkaline (50%) 7.38 Water I 15.61 Water II 17.23 methanol 12.63 Rule 100.00

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Use Examples

The present process can be used for the preparation of a substantially phenol-free impregnation resin and the resin prepared according to the method or its composition is generally a substitute for a conventional impregnation resin.

The finished end product can be used as such for paper impregnation or as a blend with standard impregnation resins. The finished resin can be impregnated into film / backing paper (60-200 g / m ² ). The amount of resin in the paper ranges from 20-50% by weight, depending on 10 end uses. The amount of volatiles in the impregnate is between 5 and 10% by weight.

Fig. 1 shows, on the right, specimens (6) of ready-made extrudates of lignin impregnates with different catalyst systems. To the left is a reference sample made of phenol-formaldehyde resin 15.

In particular, the present method is suitable for the preparation of a base paper impregnating resin and its use in a compact laminate (Figure 2) as an adhesive.

In addition to impregnating resins, the following applications can be mentioned in particular: plywood, LVL, chipboard, MDF (medium-density fiberboard), HDF (high-density fiberboard). In addition to these, there is also the production of abrasive paper, beam glue and wool resins, especially mineral wool resins such as glass wool and rock wool resins.

Reference list

Patent letter in alli mouth:

Claims (5)

A process for the preparation of a phenol-free impregnation resin, comprising: - the formaldehyde is condensed with a substance containing phenolic OH groups 5 in the presence of an alkaline catalyst to form a resin, characterized in that - lignin is used as the substance containing phenolic OH groups, - lignin is dissolved to form a solution, - incorporation of a portion of the necessary alkaline catalyst in the lignin solution, Formaldehyde is added to the 10 - lignin solution, and - condensation of lignin and formaldehyde in the liquid phase until virtually all formaldehyde has reacted, after which recovering the resin thus formed. 15 Process according to Claim 1, characterized in that kraft lignin is used as lignin, either as an aqueous slurry or a corresponding lignin powder, wherein the lignin has a dry matter content of more than 50% by weight, in particular at least 90% by weight, e.g. Process according to claim 1 or 2, characterized in that the lignin For dissolving, a solvent is used which is a polar liquid miscible with water such as an aliphatic or aromatic alcohol such as methanol or ethanol or an aliphatic ketone such as acetone. Method according to one of the preceding claims, characterized in that Sufficient solvent is used to maintain the dry solids content of the mixture in the reaction, for example, in the case of methanol, the concentration of methanol in water is about 1.6 to 12% by weight. Method according to one of the preceding claims, characterized in that The catalyst used is NaOH or KOH or ammonia or an organic amine or a mixture of two or more substances. 20175363 prh 21 -04- 2017 Process according to any one of the preceding claims, characterized in that formaldehyde is used as an aqueous solution having a formaldehyde content of about 30 to 60% by weight. 5 Process according to any one of the preceding claims, characterized in that the lignin and the formaldehyde are condensed at a temperature of about 50-90 ° C until all the formaldehyde has reacted, after which the resin is recovered. Method according to one of the preceding claims, characterized in that The lignin and formaldehyde are condensed in the liquid phase formed by the lignin solvent or mixture thereof. A process according to any one of the preceding claims, characterized in that the preparation of the resin is multi-step, wherein the addition of the alkaline catalyst takes place 15 in several steps during the process to keep the viscosity of the reaction mixture so low that condensation can be effectively performed. The process according to any one of the preceding claims, characterized in that the lignin is first dissolved in water and solvent and in a water-soluble alkaline catalyst. 20 (first portion), by stirring at room temperature or slightly elevated temperature below 70 ° C. The process according to claim 10, characterized in that when the lignin is completely dissolved, the temperature of the solution is raised to above 60 ° C, for example to about 65 ° C, And water is added, followed by a stepwise addition of the calculated amount of formaldehyde with stirring. Process according to Claim 10, characterized in that after the addition of formaldehyde the temperature is raised above 80 ° C, for example to about 85 ° C, wherein At this temperature, a condensation reaction occurs between lignin and formaldehyde. 20175363 prh 21 -04- 2017 Process according to Claim 12, characterized in that the second part of the alkaline catalyst is added, the mixture is cooled to 80 ° C or the condensation reaction is continued. 5 Process according to one of the preceding claims, characterized in that the condensation reaction is continued until the resin has a formaldehyde content of not more than 5%, in particular not more than 1% by weight, e.g. 0.1-1.0%, and has a Brookfield viscosity of at least 20 cP and up to 10,000 cP. Process according to one of the preceding claims, characterized in that the condensation reaction is carried out in the presence of a solvent for lignin to keep the viscosity of the reaction mixture low enough. Process according to claim 15, characterized in that The condensation reaction is carried out in a non-pressurized reaction vessel or pressure boiler, the reactor being preferably equipped with reactor heating and cooling devices and temperature sensors and control. A method according to any one of the preceding claims, characterized in that The resin is recovered in solvent-free form or containing up to 15% by weight of solvent. A resin made by the process of any preceding claim. A phenol-free impregnation resin comprising formaldehyde and lignin 25 condensation products containing up to 5% by weight of free formaldehyde. Impregnation resin according to claim 18 or 19, characterized in that it is in the form of an aqueous mixture having a dry solids content of about 3070%. An impregnation resin according to any one of claims 18 to 20, obtained by evaporating off solvent residues contained in the resin in a separate evaporation step. Use of an impregnating resin according to any one of claims 18 to 21 for impregnating backing paper, impregnating film paper, plywood, LVL, particle board or fiber boards such as medium density fiberboard (MDF) or high density fiberboard (HDF). , for making abrasive paper, 5 as glue in wool resins, especially mineral wool such as glass wool or rock wool.