NO147722B - BINDING MATERIAL FOR MANUFACTURING OF VINERATED, CHIPPING AND FIBER PLATES AND SIMILAR PRODUCTS - Google Patents

Description

The present invention relates to a binder for the production of veneer, chipboard and fiber boards and similar products, consisting of phenol-formaldehyde resin and of alkali lignin or lignosulfonates which are fractionated according to molecular weight, as well as possibly 5-10 weight percent urea calculated from the dry matter content of the phenol-formaldehyde resin .

Adhesive substances which are made from lignin derivatives and phenol-formaldehyde resins, for the production of veneer, chipboard and fiber boards are known, among other things, from Danish patent document 100,984,

Finnish Patent Application 965/69, Finnish Patent Publication 52,226, Canadian Patent Publication 735,389, US Patent Publications 2,786,008 and 3,185,654

as well as the articles "Thermosetting adhesives from electrodialyzed lignosulfonates", TAPPI 5_0, 92-94 A ( 1967 ), and "Reactive Lignin-Derived Products in Phenolic High-Pressure Laminates", TAPPI

44, 828-830 (1961). Moreover, weather-resistant binders made from fractionated lignin derivatives and phenol-formaldehyde resin are known from Finnish patent documents 51,105 and 51,946. Of the lignin derivatives, lignosulfonates or alkali lignins that are used in the production of the binder according to the latter patents, more than 50% have a molecular weight of over 5000. Such binders that are produced from fractionated lignin derivatives have proven to be significantly better than previous binders that are produced from lignin derivatives, especially in terms of weather resistance properties, while their strength properties fully correspond to the strength properties of commercial phenol-formaldehyde resin adhesives.

The binders listed above, where more than 50% of the lignin derivatives have a higher molecular weight than 5,000, are produced from lignin derivatives which are fractionated according to molecular weight and which have been obtained by cellulose cooking. Fractionation is usually carried out by ultrafiltration of the effluent after boiling using a semi-permeable membrane. Other types of fractionation methods include known from Finnish patent application 3626/72.

In the attempts to make the above binders, which

is produced from fractionated lignin derivatives, suitable for industrial production on a large scale, the fraction that contains a lot of high molecular weight lignin derivatives and which is indispensable for the production of the binder constitutes a small part of the dry matter in the effluent from cellulose boiling, in that of the alkali lignins obtained by sulphate boiling usually only has 25-30% by weight a molecular weight of over 5,000. If the aim is that of the lignin derivatives used for the production of the binder, more than 50% by weight should have a molecular weight of over 5,000, only a small part of the original dry matter of the effluent is application, which of course reduces the importance of the invention in terms of the total application of waste liquor and work.

The binder is produced by mixing fractionated lignin derivatives and phenol-formaldehyde resin. The phenol-formaldehyde resin is usually made from phenol and formaldehyde. Abundant use of formaldehyde promotes the formation of methylol groups in the phenol-formaldehyde resin. Abundant occurrence of methylol groups in the phenol-formaldehyde resin is to the advantage of the binder which is made from fractionated lignin derivatives, as it is likely that precisely these groups react with the lignin derivatives. However, it should be observed that the abundant use of formaldehyde in the production of the phenol-formaldehyde means that the produced phenol-formaldehyde resin contains plenty of free formaldehyde, which is dangerous from a worker-safety point of view due to the volatility and toxicity of the formaldehyde. The use of such a phenol-formaldehyde resin which contains free formaldehyde as a component in a binder is therefore less recommendable and is prohibited in a number of countries.

The purpose of the present invention is to remedy

the above disadvantages. The characteristic features of the invention are stated in the following claims.

The invention is based on the surprising fact that has been observed in recent research, that from fractionated lignin derivatives, of which even only 35% by weight, preferably more than 40% by weight, has a molecular weight of over 5000, a weather-resistant binder with excellent firmness for use can be produced in the production of veneer, chipboard and fiber boards and similar products. In the production of the phenol-formaldehyde resin used in the binder, phenol and formaldehyde are preferably used in a molar ratio of between 1:1.8 and 1:3.

Due to the invention, the lignin derivatives only need to be fractionated to the extent that at least 35% by weight, preferably more than 40% by weight, of the lignin derivatives have a molecular weight of over 5000. The production of the binder according to the invention is thereby significantly more advantageous and cheaper than the production of the binders according to the Finnish patent documents 51,105

and 51,946, as the lignin derivatives used according to these patents have had to be fractionated considerably longer, so that more than 50% by weight of the lignin derivatives have a molecular weight of

over 5000. The production of the binder according to the present invention is, due to the stated circumstances, significantly simpler and cheaper than the production of previously known binders of the same type.

The molecular weight distributions of the lignosulfonates and the alkali lignin can be determined using gel chromatographic methods,

as indicated by e.g. Whitaker, J.R., Anal. Chem. 5_3 ( 1963 ):

12, 1950-1953, Forss, K.G. and Stenlund, B.G., Paperi ja Puu £8

(1966):9, 565-574 and 11, 673-676, as well as Forss, K.G., Stenlund,

B. G. and Sågfors, P.-E., Applied Polymer Symposium No. 28 (1976), 1185-1194, John Wiley & Sons Inc. In these methods, the samples are eluted through a gel chromatography column. The molecular weight distributions are determined on the basis of the correlation between the molecular weights and corresponding retention volumes. This correlation can be established by determining the molecular weights of different fractions using the light scattering method or using osmometry or ultracentrifugation techniques. However, these methods are extremely laborious, and it is therefore more practical in terms of practice to calibrate the gel chromatograph column using readily available substances with known molecular weights. Such a substance is e.g. glucagon. According to this, more than 40% by weight, preferably more than 45% by weight, of the lignin derivatives used for the binder according to the present invention have a higher molecular weight than glucagon.

The water solution of the binder according to the invention has a pH

8-14. When producing the binder from acidic lignin derivatives, e.g. of lignosulfonates that are fractionated from effluent after

sulphite boiling, you can advantageously add to the binder e.g. alkali or alkaline earth hydroxide to raise the pH to 8-14. The lignin derivatives are most appropriately used in the form of alkali or alkaline earth salts, which possibly contain an excess of the respective alkali. The basicity of the binder is also advantageous because a basic binder causes less corrosion than an acidic binder. It should also be noted that by adding e.g. sodium hydroxide to the binder, the sodium hydroxide lowers the binder's viscosity, which simplifies the binder's production and further processing.

According to an advantageous embodiment of the invention, the binder contains 5-10 percent by weight, calculated from the dry matter content of the phenol-formaldehyde resin. When urea is added to the phenol-formaldehyde resin, the urea reacts with the excess formaldehyde and thus binds the excess formaldehyde in the mixture. The use of urea in the binder thus improves worker safety and enables the use of an excess of formaldehyde, which improves the firmness properties of the binder, in connection with the production of the phenol-formaldehyde resin. Together with the formaldehyde, urea forms a permanent polymer and thereby also increases the firmness of the binder.

Urea can advantageously also be used in such binders on a phenol-formaldehyde resin basis where more than 50% of the lignin derivatives, alkali lignins or lignin sulphonates have a molecular weight of over 5,000.

The lignin derivatives used to produce the binder according to the invention can e.g. be lignosulphonates from the sulphite cooking of the raw material containing lignocellulose (the cooking solution contains bisulphite and sulfur dioxide). Furthermore, alkali lignins from alkaline boiling of a raw material containing lignocellulose can be used to produce the binder, e.g. from the soda process (the boiling solution contains sodium hydroxide), the sulphate process (the boiling solution contains sodium hydroxide, sodium sulphide and hydrosulphide) or the oxygen-alkali process (the boiling is carried out with sodium hydroxide in the presence of oxygen).

The fractionation of the lignin derivatives can be carried out according to

an arbitrary in and of itself known fractionation method, such as

precipitation, extraction or ultrafiltration. Such fractionation methods are known from US patent 3,825,526 and from Finnish patent application 3 62 6/7 2.

The invention will subsequently be described in detail with the help of exemplary embodiments and with reference to the accompanying drawings, in which: Fig. 1 and 2 show the elution of reference substances and internal standards through gel chromatography columns "Sephadex G-75" and "Sephadex G-50", determined by absorption at 280 nm. Figs 3 and 4 show the logarithms of the molecular weights of the reference substances as a function of relative retention volumes determined using the elution method and the light scattering method (LSA). Fig. 5a and 5b show unfractionated (A<1>) and fractionated (B<1>) lignosulfonates gel chromatograms and molecular weight distributions (sulphite boil of Western Hemlock). Fig. 6 shows the gel chromatogram of unfractionated (A) and fractionated (B,C,D,E,F) alkali lignins (sulphite boil of Scots Pine). Fig. 7 shows the cumulative molecular weight distributions, corresponding to the chromatogram in fig. 6.

The molecular weight distributions of the alkali lignins and lignosulfonates were determined in the execution examples by the following methods: The lignosulfonate and alkali lignin samples were analyzed gel-chromatographically using "Sephadex" columns (150 cm length, 1 cm diameter). The lignosulfonates were eluted through a column containing "Sephadex G-75", as eluent Tris/HCl buffer solution (pH 8.0, 0.1 M) containing NaCl (0.5 M), while the alkali lignins were dissolved in sodium hydroxide aqueous solution which was eluted through a "Sephadex G-50" column with NaOH (0.5 M) as eluent. The elution rate was 20 ml/h.

The lignin concentration in the eluent fractions was determined using absorbance measurements (280 nm). The retention volumes were determined by weighing the eluent fractions.

In order to achieve results that are independent of the gel filling density, a relative retention volume scale was introduced using two calibration substances as internal standards. The retention volume peak that appeared with Blue Dextran (M = 2.10 ) was assumed as the first reference point in the scale with the value 0. The second reference point, with the value 1, was found by determining the retention peak that appeared with sulfosalicylic acid

(M = 218) (Fig. 1 - "Sephadex G-75" and Fig. 2 - "Sephadex G-50").

Calibration of the columns took place by simultaneous determination of the ratio of the molecular weight logarithm and the relative retention volumes for easily accessible substances of known molecular weight. The "Sephadex G-75" column was calibrated with egg albumin (M = 45,000), chymotrypsinogen A (M = 25,000), cytochrome C (M = 12,500) and glucagon (M = 3483) as reference substances, as well as Tris/HCl buffer solution (pH 8.0, 0.1 M) containing NaCl (0.5 M) as eluent (Figs. 1 and 3). The "Sephadex G-50" column was calibrated using as reference substances cytochrome C, glucagon and baci-tractin (M = 1423) and NaOH (0.5 M) as eluent (Figs. 2 and 4).

Thereby, the lignin derivatives that are eluted faster than glucagon through the gel chromatography column (lower relative retention volume) consist of molecules with a higher molecular weight than 3483 (glucagon).

Example 1 (Comparison example)

Sulphate waste from pine sulphate cooking (Pinus silvestris) was evaporated to a dry matter content of 33%. The solution had a pH of 12.7. The molecular weight distribution was determined using the "Sephadex D-50" column according to the method described above.

The obtained chromatogram is reproduced in fig. 6 (A). The molecular weight distribution, fig. 7 (A), was calculated using the one in fig. 4 showed calibration curve. According to this, 25.3% by weight of the sulphate effluent's alkali lignins had a molecular weight of over 5000,

and 32.0% by weight had a molecular weight of over 3483 (glucagon).

In the production of the phenol-formaldehyde resin, a molar ratio of 1:2.5 between phenol and formaldehyde was used. The dry matter content of the resin was 4 6% and pH 11.1. The binder

was prepared by mixing 450 g of the prepared phenolic resin and 418 g of the evaporated sulfate liquor. The mixture was stirred for 10 minutes, and then 132 g of a filler mixture consisting of 13 g of wheat flour, 32 g of quebracho, 61 g of chalk and 26 g of wood flour were added. The binder had a viscosity of

24 0 mPa.s and pH 12.1.

The binder was used to produce three-layer birch veneer panels. The amount was 150 g/m 2 , the pressing pressure 0.7 MPa and the pressing time 6 minutes. The plates were hot-pressed at 135°C with a pressure of 1.7 MPa. The pressing times used were 2, 3 and 4 minutes. The properties of the boards were determined in the dry state and after boiling according to the Finnish plywood standard SFS 2416. The properties of the boards are given in table 1 where each number is the mean value of five test pieces.

Example 2 (Comparison example)

The sulfate effluent used in example 1 was ultrafiltered, whereby an alkali lignin product was obtained whose molecular weight distribution is shown in fig. 7, curve B (the gel chromatogram in Fig. 6, B). According to this, 3 0.9% by weight of the lignin derivatives had a molecular weight of over 5000 and 4 0.0% by weight had a molecular weight higher than 3483 (glucagon). The binder was prepared as in Example 1 using the same phenolic resin. The viscosity after filler addition was 320 mPa.s.

Using the binder, three-layer birch veneer boards were produced under the same conditions as in example 1. The board's properties are listed in table 1.

Example 3

An alkali lignin product was isolated by ultrafiltration of

a sulphate effluent. Its molecular weight distribution was determined gel chromatographically, the chromatogram is shown in fig. 6, C, and the molecular weight distribution in fig. 7, C. According to this, 36.0% of the sulfate lignins had a molecular weight of over 5000 and 46.5% by weight a molecular weight of over 3483 (glucagon). The binder was prepared as in Example 1. Its viscosity was 420 mPa.s and pH 12.0.

Using this binder, three-layer birch veneer boards were produced as in example 1. The board's properties are listed in table 1.

Example 4

By ultrafiltration, an alkali lignin fraction was produced whose gel chromatogram is shown in fig. 6, D, and the molecular weight distribution in fig. 7, D. According to this, 43.2% by weight of the alkali lignins had a molecular weight of over 5000 and 54.1% by weight had a higher molecular weight than 3483 (glucagon).

The binder was prepared as in Example 1. Its viscosity was 470 mPa.s and pH 12.0.

Using the binder, three-layer birch veneer boards were produced as in example 1. The board's properties are listed in table 1.

Example 5

The sulfate leachate used in example 1 was ultrafiltered, whereby an alkali lignin fraction was obtained whose gel chromatogram is shown in fig. 6, E. Its molecular weight distribution is given in fig. 7, E. According to this, 4 6.0% by weight of the lignin derivatives had a molecular weight of over 5000 and 57.7% by weight over 3483 (glucagon).

The alkali lignin fraction was used to produce binder as in example 1. The viscosity after filler addition was 560 mPa.s and pH 11.9.

Using the binder, three-layer veneer boards were produced as in example 1. The properties of the boards are listed in table 1.

Example 6

By ultrafiltration, a high-molecular alkali lignin fraction was isolated from the sulfate leachate used in example 1, whose gel chromatogram is shown in fig. 6, F, and the molecular weight distribution in fig. 7, F. According to this, 53.4% by weight of the alkali lignins had a molecular weight of more than 5000 and 64.7% by weight had a molecular weight of more than 3483 (glucagon).

The binder was prepared as in example 1. Dets

viscosity was 680 mPa.s at 25°C and pH 11.8.

The binder was used to produce three-layer birch veneer boards under the same conditions as in example 1. The board's properties are listed in table 1.

According to the Finnish plywood standard SFS 2415, the shear strength should

in a dry state be at least 2.10 N/mm 2, after boiling at least 1.40 N/mm 2, and if the values are lower, fracture must be through wood-

subject be at least 50%. In practice, however, significantly higher figures are required for breakage through the wooden blank. After boiling, the corresponding percentage must be above 80.

One observes when considering the properties of the plates, which

is indicated in table 1, that these conditions are met in examples 3-6 already with pressing times of 2 and 3 minutes. The binder according to example 2 needs a longer pressing time for the conditions to be met. In example 1, extending the pressing time does not help any more, the adhesive joint does not harden to water resistance.

Example 7

For the production of a binder, Na-lignosulfonates were used, of which the high molecular weight lignosulfonates, Mw over 5000, were 72%, and 61% by weight had a molecular weight that was higher than that of glucagon, i.e. over 3483. A 50% by weight water solution of these lignosulfonates had a viscosity of over 80,000 mPa.s, a water solution with 10% by weight had a pH of 6.4.

The phenol-formaldehyde resin used for the production of this binder was made from phenol and formaldehyde in a molar ratio of 1:3, and the resin contained 3.4% free formaldehyde.

To remove this, 8% by weight of urea was added to the phenol resin, calculated from the dry matter content of the phenol-formaldehyde resin. The mixture was stirred for 3 hours. After one day, the free formaldehyde was measured again. !The formaldehyde content was now 0.1%. 417 g of phenol-formaldehyde resin, which had been treated in this way oum uauuc c: i- J. o luj. in Xllllliu J.U yd. *± oh, JJ±t! LllbclLL i-X-L to water solution of the above-mentioned Na-lignosulfonates with a solids content of 32%. The mixture was stirred for 10 minutes, after which 26 g of sodium hydroxide solution with a 50% dry matter content by weight was added. Then 140 g of filler mixture containing 40% by weight wheat flour, 24% by weight quebracho, 20% by weight wood flour and 46% by weight chalk were added. The adhesive mixture had a viscosity of 800 mPa.s and a pH of 9.3.

The binder was used for the production of fifteen-layer veneer sheets. The quantity was 150 g/m 2 , the open time 45 min, the pressing time 6 minutes and the pressing pressure 0.7 MPa.

The plates were hot-pressed at 130°C with a pressure of 1.37 MPa, pressing time 18 minutes. The properties of the boards, which are listed in Table 2, were determined according to the Finnish plywood standard SFS 2416

in the dry state and after boiling and soaking. Each value is the mean of five samples.

The plates well met the requirements set in Finnish standard SFS 2415, that the shear strength in the dry state should be 2.10 2 '2 > 2 N/mm , after boiling 1.4 0 N/mm and after soaking 1.60 N/mm . If the shear strength values stated above are not achieved, breakage through the wood should amount to at least 50%.

Example 8

Sulphate lignin was used as raw material for the binder, where the high molecular weight (Mw> 5000) had a weight share of 40% by weight of all lignin derivatives, and 50% by weight had a molecular weight higher than glucagon.

As phenol-formaldehyde resin, a product was used which was made from phenol and formaldehyde in a molar ratio of 1:2.5 and contained 2.1% by weight of free formaldehyde. 3% by weight of urea was added to the solutions, calculated from the resin's dry matter f content. The mixture was heated to 30°C and stirred for 3 hours. The formaldehyde content was thereby lowered to 0.4%.

520 g of the treated, 46 percent phenol-formaldehyde resin was mixed with 340 g of the sulfate lignin solution which had a solids content of 30%. The pH of the glue was 11.8 and the viscosity 160 mPa.s. Then 140 g of filler mixture containing 14 g of wheat flour, 56 g of chalk, 35 g of quebracho and 35 g of wood flour were added. The viscosity after 30 minutes of mixing was 640 mPa.s.

The adhesive mixture was used for the production of three-layer birch veneer panels. The amount used was 150 g/m 2 , the pre-pressing time 6 minutes and the pre-pressing pressure 0.8 MPa. The plates were hot-pressed at 135°C at a pressure of 1.8 MPa. The pressing times were 2, 2\, 3 and 4 minutes. The properties of the plates were determined as dry and after boiling. In Table 3 below, each value is the mean value of five plates, i.e. 25 samples.

Good results were also achieved with this binder for pressing times that were shorter than normal (2 and 2\ minutes).

For the production of the binder, alkali lignin was used, where the high molecular (Mw> 5,000) weight share was 48% of all lignin derivatives, and 59% by weight had a molecular weight higher than glucagon.

The phenol-formaldehyde resin was prepared in a molar ratio of 1:2.2 and contained 1.7% free formaldehyde. 5% urea was added to the resin, calculated from the resin's dry matter content. The mixture was stirred at room temperature for 5 hours. Subsequently, the amount of free formaldehyde had dropped to 0.08%. The resin-urea mixture was added to the alkali lignin solution with a dry matter content of 4 2% (43 2 g 51 percent resin/524 g lignin solution). 44 g of 50 percent sodium hydroxide solution were added. The mixture was stirred for 30 minutes, pH 11.8. The viscosity at 25°C was 320 mPa.s.

Chipboards were produced using the produced binder. To this was then added 10% paraffin emulsion, calculated as dry matter of the glue's dry matter content.

Using the binder, chipboards of 15, 20 and 30 mm thickness were produced, with a nominal volume weight of 7 50 g/m 2. The amount of binder injected into the chips was 10% by weight, calculated on dry matter content. For the hot pressing of the chipboards, combined contact and high-frequency heating was used. The temperature of the pressing plates was 18 0°C and the pressing pressure 2.65 N/mm 2. The pressing times and the properties of the plates appear in the table below.

The boards completely satisfied the requirements set by the German standard DIN 68761 for phenol-glued chipboards. The boards were completely formaldehyde-free after the hot pressing.

Example 10

For the binder, a phenol-formaldehyde resin was prepared with a phenol:formaldehyde molar ratio of 1:3. After production, it contained 4.8% free formaldehyde. 10% urea was added to the resin, and the mixture was stirred at 25°C for approx. 4 hours. The mixture was then allowed to stand for another day, after which the free formaldehyde was determined. This had dropped to 0.1%.

The alkali lignin fraction whose properties are stated in example 9 was used to prepare the binder. To 640 g of the alkali lignin solution with a dry matter content of 42% was added 360 g of the above-mentioned phenol-formaldehyde urea resin, which had a dry matter content of 50%. The ratio of lignin to phenol-formaldehyde resin was 60:40. The binder had a pH of 11.0.

The binder was used to produce formaldehyde-free chipboard.

The amount of binder was 8%, calculated as dry matter content

of the weight of the dry center chips and 10% of the weight of the surface chips. In addition, 50 percent paraffin emulsion, 1% dry matter by weight of the dry chips was injected into the chips. Using the binder, 15 mm three-layer chipboards with a volume weight of 750 kg/m² were produced. The temperature of the press plates was 215°C, the pressing pressure 2.94 MPa and the pressing time 20 s/mm. After the hot pressing, the plates were post-cured at 180°C.

The properties of the plates are shown in table 5.

The boards met the requirements set out in DIN 68761. No formaldehyde smell could be felt during production, and formaldehyde was not released from the boards afterwards.

The viscosity values stated in the design examples were measured with a Brookfield viscometer at 25°C and 50 rpm.

Thereby, the dry weight ratio between the lignin derivatives included in the binder and the phenol-formaldehyde resin can vary, e.g. within the limits of 90:10 and 20:10. Furthermore, the ratio of phenol:formaldehyde in the phenolic resin can vary, e.g. within the limits 1:1,4 and 1:3. In addition, glue produced with the binder can be added to fillers known per se, such as chalk, wood flour, quebracho, wheat flour etc.

Claims (4)

1. Binder for the production of veneer, chipboard and fiber boards and similar products, consisting of phenol-formaldehyde resin and alkali lignin or lignosulfonates that are fractionated according to molecular weight, as well as possibly 5-10 weight percent urea calculated from the dry matter content in phenol- the formaldehyde resin, characterized in that at least 35% by weight and less than 50% by weight of the alkali lignin or lignosulphonates have a molecular weight of over 5,000. 2. Binder in accordance with claim 1, characterized in that more than 40% by weight of the alkali lignin or lignosulfonates has a molecular weight of over 5,000. 3. Binder in accordance with claim 1 or 2, characterized in that more than 45% by weight of the alkali lignin or lignosulfonates has a higher molecular weight than glucagon. 4. Binder in accordance with one of claims 1-3, characterized in that it contains 5-10 weight percent urea.