Process for bonding water penetrable cellulosic particles

The preßent invention relates to a substitute for amino and phenolic resins in the polycondensation of such resins based on formaldehyde for bonding water penetrable cellulosic ^particles thus allowing lower amounts of resin solids to be used while at the same time reducing the free formaldehyde of the resulting board without imparting any loss in bond- in^g strength, without requiring any extra steps in the pro- ^duction, without changing the curing rate of the production, without causing any problem to the'boilers when burning particleboard sander dust or edges from cutting saws and without reducing the tack properties of the resin mixture.

The said substitute is comprised mainly of a solution of

• a) either an aldehyde together with an amide or together with a phenol, or a non-resinous condensation product of formaldehyde and urea, and
• b) a sugar or a sugar derivative or their by-products or a starch or a mixture thereof, and/or
• c) a raw and/or treated lignosulfonate or similar products.

The aldehyde is preferably formaldehyde, for example in the form of paraformaldehyde, or acetaldehyde. The amide is preferably mainly urea or thiourea or their homologues or melamine, benzoguanamine or dicyandiamide or their homologues. The phenol is preferably phenol itself or resorcinol.

Among the sugars, sugar derivatives, their by-products and mixtures thereof, molasses, dextrose, glucose, fructose or sucrose or mixtures thereof such as corn syrup are most preferred. Among the starches, wheat starch, modified starches, dextrin and the like are interesting.

Examples of raw lignosulfonates are black liquor and similar products, and examples of treated lignosulfonates are sodium, calcium and ammonium lignosulfonate.

The substitute of the invention preferably contains 40 to 52 % by weight of water.

The weight ratio of a) to b) and/or c) is preferably 0.1 to ₅₀.₀:1, most preferably 1.0 to 15.0:1. The combination of a) with b) and/or c) presents a synergistic behaviour. If the single components are added alone to the resin they do not give good boards, but if they are added in combination, they exhibit an improvement in the board properties obtained. The substitute according to the present invention (calculated as 100 % solids) may substitute as much as 30 % of the resin solids used. Said substitute is not added in quantities equal to the quantities substituted. It is added in quantities from 50 to 90 % of the amount of resin substituted (calculations referred to by weight and referring to all products as 100 % solids).

The substitute according to the present invention may therefore, because of its synergistic behaviour, substitute the resin in quantities from 110 % up to 200. % of its own weight. When added to lower amounts e.g. up to 15 % there is a considerable increase in the properties of the end product. When added to higher levels, i.e. up to 30 %, no difference is imparted to the properties of the end product but the free formaldehyde is considerably reduced and the amount of resin saved is considerably increased.

Bonding is effected by curing the resin mixture at elevated temperatures and pressures according to the me- ^thods well known in the art. The substitute may be used in all types of products where amino and phenolic resins are used for bonding lignocellulosic products, whether these are wood particles for p_arti_cleboard production using a flat press, or a calender or wood veneers such as in plywood production.

It is very interesting to note that the product has also good tack. This property otherwise called "green strength" is desired in some types of particleboard plants, specially the plants with multi opening press and in plywood factories, specially those having a pre-press.

The quality of boards produced was controlled weekly for a period of six months and no reduction in the properties was observed. This proves that no polymer degradation occurs and that the ageing properties of the boards are comparable to the ones normally produced.

The substitute of the invention can be prepared by plain mixing of the components. In order to obtain an acceptable shelf-life of the substitute, a base is preferably added to adjust the pH to a value in the range of 6 to 14.

Substitutes so far known in the art to substitute resin have not succeeded in substituting such high levels of resin by using lower amounts of the substitute and reducing simultaneously the free formaldehyde of the boards, without imparting any loss in bonding strength, without requiring any extra steps in the production, without changing the curing rate of the production, without causing any problems to the boilers when burning particleboard sander dust or edges from ; cutting saws and without reducing the tack of the resin mixture.

In particular, the known substituents are lignosulfonates, sodium chloride or mixtures of formaldehyde with urea and sodium chloride. It is well known that li^gnosulfo- ^nates may not be used for quantities higher than 10 %; otherwise, board properties will be reduced.

It is also known that the addition of halide salt alone succeeds in substituting part of the resin with the following limitations:

• -Hig^h substitutions, higher than 6 to 8 %, may not be obtained, otherwise the board properties will deteriorate.
• -Substitution is obtained in ratios 1:1, while in the case of the substitute according to the present invention it is 1.1 to 2.0:1.
• -When particleboard sander dust or edges from cutting saws are burnt in boilers, the latter are plugged within a few hours.
• -Tack is reduced when sodium chloride is added to the resin mixtures.

When mixtures of sodium chloride with urea and formaldehyde are used the following shortcomings are present :

• -The presence of salt in the mixture causes severe problems in the boilers when sander dust or cutting saw edges of boards are burnt. That is caused because the presence of salt reduces the melting point of the mixture and as a result a molten mass deposits in the boiler forming a glass like deposit which adheres on the boiler thus plugging it.
• -The other shortcoming of this product is the fact that tack is severely reduced, thus making it difficult to use in the plywood industry where there is a pre-press and in particleboard plants where a multi opening press is present requiring green strength of the mat.

The product according to the present invention overcomes all of the above shortcomings.

The substitute according to the present invention provides yet another advantage. Apart from substituting up to 3^{0 %} of the resin by adding only 50 to 90 % of the resin solids substituted, and reducing the free formaldehyde of boards, it reduces also the free formaldehyde in the production hall where workers are exposed to formaldehyde fumes.

The following Examples illustrate the invention and are not intended as limitations.

Example 1

Three samples were prepared according to the following formulations :

The above mentioned samples were prepared by plain mixing at room temperature until the solids were completely dissolved. The pH of the final products was adjusted to 7.5 to 8.0.

Glue formulations were then prepared as follows :

• No. ^0: Glue formulation is the blank and does hot include any of the above mentioned samples.
• No. 1: Glue formulation includes sample 1, whereby only formaldehyde and urea are included.
• No. 2: Glue formulation includes sample 2 whereby only molasses are included.
• No. 3: Glue formulation includes sample 3 whereby all three ingredients are added, namely, formaldehyde, urea and molasses. Sample 3 represents the product according to the present invention.

These glue formulations were used separately to spray a constant quantity of dried wood chips.

The sprayed wood chips were then formed into a mat having a normal thickness of 16 mm. These mats were then introduced into a hot press and boards were pressed at the following conditions :

Boards were then tested and the results are reported in the following table.

It can be noticed from the above mentioned table that while all three samples reduce the free formaldehyde of boards, only sample 3 including the components according to the present invention gives boards equivalent to the blank, without deterioration of the board properties.

Example 2

This example proves the synergistic behaviour existing between formaldehyde, urea and lignosulfonates.

For this purpose the following samples were prepared :

The above mentioned samples were prepared by plain mixing at room temperature until the solids were completely dissolved. The pH of the final products was adjusted to 7.5 to 8.0.

Glue formulations were then prepared as follows :

These glue formulations were used separately to spray a constant quantity of dried wood chips.

The sprayed wood chips were then formed into a mat having a nominal thickness of 16 mm. These mats were then introduced into a hot press and boards were pressed at the following conditions :

Boards were then tested and the results are reported in the following table :

It will be noticed from the above mentioned figures that boards produced with plain lignosulfonates, sample 2, have the worst results. Boards obtained with all three components according to our present invention, sample 3, have the best results. Actually boards of sample 3 are equivalent to the blank, 0, which is the resin mixture without any substitute, while giving at the same time a reduction in the free formaldehyde of the boards.

Example 3

. In this example two samples are illustrated whereby the ratio of formaldehyde to urea is different from the one used in the previous examples. Also the weight ratio between components a) and b) is different from the one of examples 1 and 2.

The following samples were prepared :

The above mentioned samples were prepared by plain mixing at room temperature until the solids were completely dissolved. The pH of the final products was adjusted to 7.5 to 8.0.

Glue formulations were then prepared as follows :

These glue formulations were used separately to spray a constant quantity of dried wood chips.

The sprayed wood chips werethen formed into a mat having a nominal thickness of 16 mm. These mats were then introduced into a hot press and boards were pressed at the following conditions :

Boards were then tested and the results are reported in the following table :

It can be noticed from the above mentioned table that samples 1 and 2 including the substitute according to the present invention give boards equivalent to the blank, sample 0, while giving a significant free formaldehyde reduction and resin saving.

Example 4

This is a laboratory test for plywood using a phenolic resin.

The following samples were prepared:

The samples were prepared by plain mixing at room temperature until the solids were completely dissolved. The pH of the final products was brought to 10.0 by means of addition of sodium hydroxide.

These samples were used in a glue formulation as follows:

The above mentioned glue formulations were used to spread both sides of the core veneer for 3 ply boards.

Boards were then introduced in a cold press where they were pressed under the following conditions:

• Press time 8 minutes
• Pressure _{10 k}p/_cm²

All boards gave very good tack properties.

They were then pressed in a hot press under the following conditions:

These boards were tested as follows:

• They were immersed for 24 hours in water at 60°C. After this they were introduced in water at 20°C for one hour and then the knife test was carried out.

Results were as follows:

The knife test is carried out as follows:

• Plywood samples are placed in water under pressure for 30 minutes and then in vacuum for another 30 minutes. Samples are then scraped with a knife on the surface until the top veneer comes off and the core shows up. The grading depends on the amount of fibers showing in the core after the top veneer was scraped off.
• When gluing is satisfactory, the surface that appears after scraping with the knife must still be covered with fibers. When it is completely covered with fibers grading is 10 (excellent). As more clean spots appear and less fibers, grading is diminished. A grading of 8 is still satisfactory, ant it means that the surface is mainly covered with fibers with only a few clean spots .appearing. Lower grading is unsatisfactory.

Example 5

Two samples were prepared according to the following formulations:

The above mentioned samples were prepared by plain mixing at 25 to 30°C until the solids were completely dissolved. The pH of the final products was adjusted to 8.5 to 10.0.

Glue formulations were then prepared as follows:

These glue formulations were used separately to spray a constant quantity of dried wood chips with 12% dry glue/ dry wood.

The sprayed wood chips were then formed into a mat having a normal thickness of 16 mm. These mats were then introduced into a hot press and boards were pressed at the following conditions:

Boards were then tested and the results are reported in the following table.

The V-100 test is carried out as follows:

• The samples to be tested are placed in water at 20 + 5°C. This water is warmed u^p in 1 to 2 hours to 100°C. The water temperature is kept at 100°C for 2 hours. It is important that there is a space of at least 15 mm on all sides of every sample so as to make sure that water is freely introduced in the samples. The samples are then introduced for at least 1 hour in a refrigerator at 2 + 5°C. Water is then allowed to drip and the wet samples are tested again for internal bond.

Example 6

The following example will illustrate the fact that products according to our present invention may be produced by means of a variety of raw materials.

Samples were prepared according to the following formulations:

The above mentioned samples were prepared by plain mixing until the solids were completely dissolved. The pH of the final products was adjusted to 7.5 to 8.0. Glue formulations were then prepared as follows:

These glue formulations were used separately to spray a constant quantity of dried of wood chips.

The sprayed wood chips were then formed into a mat having a normal thickness of 16 mm. These mats were then introduced into a hot press and boards were pressed at the following conditions:

Boards were then tested and the results are reported in the following table:

Boards obtained with all glue formulations are equivalent.

Example 7

In this example four samples were prepared according to the following formulations:

The above mentioned samples were prepared by plain mixing at 40 to 50°C until the solids were completely dissolved. The pH of the final products was adjusted to 8.5 to 10.0.

Glue formulations were then prepared as follows:

These glue formulations were used separately to spray a constant quantity of dried wood chips.

The sprayed wood chips were then formed into a mat having a nominal thickness of 16 mm. These mats were then introduced into a hot press and boards were pressed at the following conditions:

Boards were then'tested and the results are reported in the following table:

It call be noticed from the above mentioned table that samples 1 to 4 including the substitute according to the present invention give boards equivalent to the blank, sample 0, while giving a significant free formaldehyde reduction and resin saving.

Example 8

Three samples were prepared according to the following formulations:

The above mentioned samples were prepared by plain mixing at 25 to 30°C until the solids were completely dissolved. The pH of the final products was adjusted to 8.5 to 10.0.

Glue formulations were then prepared as follows:

These glue formulations were used separately to spray a constant quantity of dried wood chips.

The sprayed wood chips were then formed into a mat having a nominal thickness of 16 mm. These mats were then introduced into a hot press and boards were pressed at the following conditions:

Boards were then tested and the results are reported in the following table:

Boardn obtained with all glue formulations are equivalent. Those however that include the substitute according to the present invention have lower free formaldehyde.

Example 9

Three samples were prepared according to the following formulations:

The above mentioned samples were prepared by plain mixing at 25 to 30°C until the solids were completely dissolved. The pH of the final products was adjusted to 8.5 to 10.0.

Glue formulations were then prepared as follows:

These glue formulations were used separately to spray a constant quantity of dried wood chips.

The sprayed wood chips were then formed into a mat having a nominal thickness of 16 mm. These mats were then introduced into a hot press and boards were pressed at the following conditions:

Boards were then tested and the results are reported in the following table:

Boards obtained with all glue formulations are equivalent. Those however that include the substitute according to the present invention have a very big formaldehyde reduction and resin cost saving.