DE4331656A1 - Binder mixture - Google Patents

Abstract

The invention relates to a binder mixture for materials based on wood and/or cellulose which contains methylol group-modified lignin, resol and a di- or polyisocyanate. The accelerators used are esters, in particular triacetin.

Description

The invention relates to a binder mixture for Materials based on wood and / or cellulose, the contains lignin as an essential component.

Lignins are by-products of Pulp production from wood and at Wood saccharification. Because of their compulsive Seizures from natural, renewable raw materials and Their polymeric structure makes them an interesting one Building block variant for polymers and binders. Es are a variety of attempts to lignin as to use inexpensive polymeric building block and thus to dispose of, e.g. B. by incorporating lignin in Phenol-formaldehyde condensation products Condensation with formaldehyde, by combination with Isocyanates or by various chemical Modifications (see Encyclopedia of Polymer Science and Engineering, 2nd edition, vol. 8 (1987) pages 795 to 852). The large-scale utilization of the found Solutions failed because of the low reactivity the lignins, which have either low strengths of the received products or too long curing times conditional.  

It is therefore an object of the invention, another Possibility of using lignin as a building block in Provide binders in which these binders sufficient storage stability at room temperature and a short curing time at curing temperature show and in which the end products obtained good Have strength values.

The task is solved by a Binder mixture according to claims 1 to 5 and a Process for its production according to claims 6 and 7. The binder mixture is suitable as Binder for materials based on wood and / or Cellulose, in particular for the production of particle board and textile fleece according to claims 8 to 9. Das anhydrous binder mixture is also suitable excellent as a reinforcing resin for rubber and Rubber mixtures according to claim 10.

It has been found that reactivity and therefore the economic applicability of lignin in can be easily increased by lignin through Treatment with formaldehyde methylolated and so with Lignin modified with a resol and methylol groups combined a di- or polyisocyanate becomes. With such a mixture of binders, containing 45 to 85% by weight of methylolated lignin, 5 to 25% by weight of resol, 10 to 30% by weight of a di- or Polyisocyanate and 0 to 15% by weight Accelerators are e.g. B. with chipboard Curing times are achieved, as has been the case up to now used urea resins were reserved. in the Contrary to boards bound with urea resins but when using the invention Binder mixture according to the strength of the boards  Water storage improved significantly, so that a Classification of bound chipboard in the Group V 100 (water-resistant) is attached.

The binder mixture is in the simplest case Mixture of the three in solid powdered form present components: with methylol groups modified lignin, resol and di- or polyisocyanate.

A major simplification is, however, the modified lignin and the resol not as To isolate solid, but directly to theirs Production of aqueous, alkaline solutions with each other and with a liquid di- or Polyisocyanate and possibly a curing accelerator mix and the binder mixture within its Processing time of up to 7 hours (at Room temperature).

Surprisingly, none occurs during this time Separation and the reaction of the isocyanate groups with water is negligible. Even with the Hardening of the binder mixture at higher The reaction preferably takes place at the temperature Binder components together so that the Presence of water does not bother.

Modified with methylol groups, so-called methylolated, Lignin is obtained by the known one Implementation of lignin with formaldehyde in alkaline aqueous solution, the pH in the range from 8 to 14, preferably in the range from 9 to 11.

Any lignin can be used as lignin, regardless of the raw material source and the  Production method. As is known different lignins different Molecular sizes and reactivities, it is of the different methylolated lignins expect. So z. B. methylolated bagasse lignin or methylolated lignin from the Organosolv process more reactive than methylolated Kraft lignin.

Lignin is a polymeric product with an average molecular weight of 5,000 to 10,000. A molar amount is therefore not appropriate. However, since lignin generally consists of phenylpropane units with occasional methoxy groups, structural units of the general formula C ₉ H ₇ O ₂ .H ₂ O. (OCH ₃ ) _0.94 can be defined. The quantitative ratio of formaldehyde to lignin used is therefore based on this structural unit. It is (structural unit lignin: mol-formaldehyde) in the range from 1: 0.7 to 1: 1.5, the reactivity of the modified lignin generally increasing with an increasing degree of methylolation.

The preparation of the alkaline reaction mixture Lignin and formaldehyde take place at elevated temperature, preferably at a temperature in the range from 50 to 90 ° C. The reaction time depends on the pH value the solution and the reactivity of the used Lignins. It is in the range of 3 to 10 hours. The The reaction product is a methylolated lignin in alkaline, aqueous solution. It can e.g. B. by Spray drying in the form of a solid powder and with solid resole and solid isocyanate into one Powder resin mixture can be mixed. But preferred  the reaction solution is not worked up, but after cooling with an aqueous resole solution, preferably with a cooled, no further processed reaction solution from the alkaline Condensation of a phenolic compound with a Aldehyde and with a di- or polyisocyanate mixed.

Decisive for the appropriate mixing ratio are the solutions of methylolated lignin in the solutions and resol, d. that is, it will be 45 to 85 parts by weight modified reaction solution containing lignin the methylolation reaction with a 5 to 25 parts by weight of resol containing reaction solution the resol condensation reaction is mixed. Subsequently or at the same time 10 up to 30 parts by weight of a liquid di- or Polyisocyanate and optionally 1 to 15 parts by weight of one Accelerator, preferably an ester mixed.

The resols and their building blocks are not subject to any Restrictions. All resolves can be used on and off polyhydric phenols with one or more aromatic kernels and various aldehydes including glyoxal or furfural in use various alkaline catalysts such as these e.g. B. from Knop and Pilato, Phenolic Resins, Springer Verlag 1985 are known. The resols can in themselves known way with urea or other aminic Connections must be modified. Resoles are preferred, which by condensing phenol with formaldehyde under catalytic effect of alkali or Alkaline earth metal hydroxides were produced, the Water resistance of the hardened binders and those with the materials they manufacture is improved if  both the resols and the methylolated lignins under the catalytic action of alkaline earth metal hydroxides were made instead of alkali hydroxides.

As di- and polyisocyanates are used for solid Binder mixtures solid at room temperature and for liquid binder mixtures liquid Isocyanate compounds used. Examples of fixed Isocyanates are diisocyanatonaphthalene, 4,4 ', 4' '- triisocyanato-triphenylmethane or Tris (4-isocyanatophenyl) thiophosphate. examples for liquid isocyanates are isophorone diisocyanate, Toluene diisocyanate or hexamethylene diisocyanate. The isomer mixture of is preferably used Diisocyanato-diphenylmethane (MDI), which is both a sufficient processing time as well as fast Curing time of the invention Binder mixture enables.

Although the binder mixture according to the invention at elevated temperature (120 to 200 ° C) even without Accelerator has a good curing speed owns, is common, especially when using less reactive strength lignin or to achieve particularly short pressing and hardening times, one additional acceleration desirable.

It has been found that such an acceleration in simply by adding 1 to 1.5% by weight of one Esters can be reached. All esters can be used aliphatic mono-, di- or polycarboxylic acids with 1 up to 6 carbon atoms with mono- or polyhydric alcohols 1 to 5 carbon atoms, but also lactones.  

Examples are esters of ants, vinegars, propions, Oxal, γ-chlorine butter, milk, wine or ε-oxycaproic acid with alcohols such as methanol, Ethanol, propanol, glycol or glycerin.

The preferred esters are γ-butyrolactone, triacetin and propylene carbonate.

Examples example 1

30 parts by weight of bagasse lignin (powder with 95% Solid) with stirring to 60 parts by weight of water given and slowly with 8 parts by weight of 30% Sodium hydroxide solution added. The pH is 13 a. This solution is heated to 60 ° C and with 3.5 parts by weight of paraformaldehyde (96% strength) were added (Molar ratio structural unit lignin Formaldehyde 1: 0.71).

The solution is stirred for 8 hours at 60 ° C and then cooled down.

Example 2

Analog to Example 1, Kraft lignin is methylolated.

Example 3

94 parts by weight of phenol are mixed with stirring 40 parts by weight of a methanol-water mixture (20/80) and 55 parts by weight of paraformaldehyde (96%) mixed.  

The mixture is heated to the boiling point. In four 15 minute intervals will be a total of 20 parts by weight 30% sodium hydroxide solution added, the reaction mixture held under reflux for a further 60 minutes and then cooled down.

Example 4

The aqueous solution of the methylolated lignin Example 1 (MBL) as well as example 2 (MKL) is also used Resol solution from Example 3 (PF) and Diisocyanato-diphenylmethane (mixture of isomers) (MDI) mixed. The time to process the mixture Room temperature is more than 5 hours. The Mixtures have a pH of 12 to 12.5.

The mixtures are mixed with wood chips (pinus radiata) and pressed at 190 ° C and a pressure of 2.3 N / mm ² to chipboard of dimensions 400 × 350 × 12 mm.

The density and the transverse tensile strength are determined of plates a. dry and b. after water storage (2 hours in boiling water, then 16 hours at 105 ° C dried), varying the Mixing ratios of the binder component, the Amount of binder and the pressing time.

The values obtained can be found in the following Tables 1 to 3.  

Table 1

Different mixing ratios of the binder components (binder content 11%, pressing time 7.5 minutes at 190 ° C)

Table 2

Different binder content (mixing ratio MBL / PF / MDI = 46/24/30, pressing time 7.5 minutes at 190 ° C

a. methylolated bagasse lignin

b. methylolated kraft lignin (MKL / PF / MDI = 46/24/30)

Table 3

Different pressing times (binder content: 11%, MBL / PF / MDI ratio = 46/24/30)

a. methylolated bagasse lignin

b. methylolated kraft lignin (MKL / PF / MDI = 46/24/30)

Example 5

Chipboard is produced analogously to Example 4 and tested. However, methylolated Kraft lignin used and the hardening of the binder mixture (pH 10.5 to 11) by adding ester accelerates.

Table 4 shows the values obtained different proportions of each Binder components: (pressing time 7.5 minutes at 190 ° C):

Table 5 shows the strength values for different pressing times:

Claims (10)

1. Containing binder mixture
45 to 85% by weight of lignin modified with methylol groups
5 to 25 wt% resol
10 to 30 wt .-% of a di- or polyisocyanate. 2. Binder mixture according to claim 1, characterized characterized in that with methylol groups modified lignin and the resol in aqueous Solution. 3. Binder mixture according to claims 1 and 2, characterized in that it is 1 to 15 wt .-% Contains esters as accelerators. 4. Binder mixture according to claim 3, characterized characterized in that the ester is triacetin. 5. Process for the preparation of binder mixture according to claims 1 to 4, characterized characterized in that 45 to 80 wt .-% methylolated Lignin, 10 to 25% by weight resol, 10 to 30% by weight a di- or polyisocyanate and optionally  1 to 15% by weight of ester mixed together become. 6. Process for the preparation of binder mixture according to claims 1 to 4, characterized characterized in that lignin and formaldehyde in Ratio (structural unit lignin: mol-aldehyde) from 1: 0.7 to 1: 1.5 in aqueous alkaline Solution at a pH in the range of 9 to 14 for several hours at temperatures in the range be treated from 50 to 90 ° C that after Cool this reaction solution 45 to Containing 85 parts by weight of modified lignin Reaction solution with a 5 to 25 parts by weight Resol containing aqueous alkaline Resole solution and with 10 to 30 parts by weight of one liquid di- or polyisocyanate and if necessary with 1 up to 15 parts by weight of an ester are mixed. 7. Use of the binder mixture according to the Claims 1 to 4 as binders for materials based on wood and / or cellulose. 8. Use of the binder mixture according to the Claims 1 to 4 for the production of chipboard. 9. Use of the binder mixture according to the Claims 1 to 4 for the production of textile fleece. 10. Use of the binder mixture according to the Claims 1 to 4 as reinforcing resin for rubber and Rubber compounds.