THERMOSETTING POLYMER COMPOSITIONS

This invention relates to a method for preparing a specially formulated oligomer aqueous solution, by using condensation products of an aldehyde such as formaldehyde, glyoxal, acetaldehyde and furfural, an amide such as urea, its mono- and 1,2 di- substituted derivatives, diurea and thiourea, and an aminotriazine derivative such as melamine, benzoguanamine and acetoguanamine as raw materials. It specifically relates to the synthesis of such products under controlled conditions, as well as to its application either as a raw material for the production of melamine thermosetting resins (melamine-urea-formaldehyde (MUF), urea-melamine-formaldehyde (UMF) and meϊamine-urea-phenoϊ-formaϊdehyde (MUPF) resins) or as a performance-enhancing additive for formaldehyde-based resins (urea-formaldehyde (UF), urea-melamine- formaldehyde (UMF), meϊamine-urea-formaϊdefiyde (MUF), melamine-formaϊdehyde (MF), melamine-urea-phenol-formaldehyde (MUPF), tannin-formaldehyde (TF) resins) or even for other binders such as polymeric diphenyl-methane diisocyanate (PMDI).

The above resin types are prepared in large quantities worldwide for a variety of uses, their application as adhesives in the formation of composite wood panels

(particleboards, fibreboards, oriented strand boards, plywood) being one important use.

In the latter application area, the simple urea-formaldehyde resins still play a dominant part. Around 1978, health concerns for the formaldehyde emission connected with the application of straight urea-formaldehyde resins, imposed lower formaldehyde to urea (F:U) mole ratios (~ Y) that led to more complicated resin synthesis procedures. New generation UF resins combine acceptable bonding performance with low formaldehyde emissions. Despite the significant advances, there is an important disadvantage of UF resins, namely their susceptibility to hydrolysis, which results in gradual deterioration (in both dimensional stability and integrity) of the finished boards when exposed to humid environment. The production of moisture resistant boards requires the presence of resin bonds that are more stable and resistant to hydrolysis like in the case of the melamine-

formaldehyde bonds. However, due to the high cost of melamine., pure melamine- formaldehyde resins are seldom used in board manufacture. The less costly (but still more expensive as compared to simple UF resins) melamine-urea-formaldehyde (MUF) or urea-melamine-formaldehyde (UMF) resins are preferred instead.

Increasing the melamine amount in MUF resins improves the adhesive performance but at an increased resin cost. One way to decrease the cost is to utilize melamine more effectively so that lower amounts are needed. Over the years, a common sense is that melamine incorporation in MUF/UMF resins is not done in an optimum way. That is, the melamine is underutilized. The possible cause of this is the synthesis conditions of the resins. Typically polymerization takes place at alkaline or near neutral conditions (Shiau D.W. and Smith E., US 4,536,245; Druet B. and Hopin D., US 4,997,905). However, literature seriously debates whether under such conditions real copolymerization of urea and melamine takes place in appreciable amounts.

It is known that, melamine copolymerizes with formaldehyde throughout the pH range, whereas urea copolymerizes at pH values in the acidic region. At a higher pH value, urea may also polymerize to a small extent through ether linkages. Therefore, under the conditions prevailing during MUF and UMF resins preparation, the homopolymerization of melamine (through methylene or ether linkages) is favoured considerably. This leads to a structure of long melamine chains connected together by long urea segments, which are labile to hydrolytic attack especially since they are expected to contain a significant portion of ether groups. Needless to say, this is not the best way to incorporate melamine in the resin structure. The preferred way is: (a) to distribute melamine molecules as uniformly as possible throughout the polymeric network avoiding clusters

(b) to connect melamine and urea molecules through hydrolytically stable methylene linkages and

(c) to create UF segments with as many methylene linkages as possible.

The latter two conditions imply an acidic environment during melamine-urea- formaldehyde copolymerization. Unfortunately, direct copolymerization of melamine urea and formaldehyde under these conditions is not readily controllable due to the combination of high melamine reactivity and functionality (6 versus 3 of urea).

One possible way to circumvent this problem is by using a precursor based on melamine or other aminotriazine derivatives bearing some appropriate amido containing end- groups which are capable of more controlled reaction with formaldehyde. Such a product could replace part or all the melamine needed in UMF ₃ MUF and even MUPF resin synthesis.

The present invention discloses a method for the production of amino triazine derivatives suitable for the preparation of melamine thermosetting resins (melamine- urea-formaldehyde (MUF), urea-melamine-formaldehyde (UMF) and melamine-urea- phenol-formaldehyde (MUPF) resins). The invention further discloses the production of such derivatives, which can be applied as performance-enhancing additives in formaldehyde-based resins (urea-formaldehyde (UF), urea-melamine-formaldehyde (UMF), melamine-urea-formaldehyde (MUF), melamine-formaldehyde (MF), melamine- urea-phenol-formaldehyde (MUPF), tannin-formaldehyde (TF) resins) and in other binder types such as polymeric diphenyl-methane diisocyanate (PMDI).

The proposed method is based on the use of an appropriate amide such as urea and its mono- and di-substituted derivatives, diurea and thiourea, as suitable aminotriazine- blocking agent, whereby controlled synthesis conditions enable the blocking of initial aminogroups of aminotriazine by amido segments.

An advantage of the invention is that when the said derivative is used in place of melamine (in MUF/UMF/MUPF resin synthesis) it permits a reaction of the aminotriazine compound in a more controlled way and leads to a resin with more uniform aminotriazine segments distribution where amino and amido groups are linked with each other through more moisture resistant groups.

The proposed product synthesis comprises two discrete steps:

I. Reaction of aminotriazine with an appropriate aldehyde

II. Addition of an appropriate amido containing compound and further reaction.

The synthesis procedure in detail is as follows:

1) Appropriate amounts of aqueous aldehyde solution are charged into the reactor. Such aldehydes could be one of the following: formaldehyde, glyoxal, acetaldehyde and furfural. 2) The pH is adjusted between 5-8.5 using an appropriate alkaline medium, which can be either of the following: sodium hydroxide solution, potassium hydroxide solution, triethanolamϊne solution or solid borax.

3) A calculated amount of aminotriazine is added to obtain a mole ratio of aldehyde to amino groups between 2-8. Appropriate ammotriazines could be one of the following: melamine, benzoguanamine and acetoguanamine.

4) The mixture is heated to a temperature between 50-75 ⁰ C and maintained at the chosen temperature for a time period of 0-60 min.

5) An amide compound is subsequently added at an amido to aldehyde groups mole ratio of at least 1.0. Appropriate amine compounds are urea and its mono- and 1,2 di- substituted derivatives, thiourea and diurea compounds.

6) The mixture is reacted at a temperature between 50-75°C and at a pH value adjusted to 5.0-6.5 using an appropriate acid solution until the desired viscosity is reached. The acid can be a strong inorganic acid such as hydrochloric, sulfuric and nitric acid or an organic acid such as formic, maleic or p-toluene-sulfonic acid.

7) When the desired viscosity is reached, the pH is raised to 8-10 using one of the alkaline mediums mentioned in step 2 to stop the reaction and the reaction mixture is cooled to room temperature.

In the case that the aldehyde used in step one is formaldehyde, normally formalin is employed but, alternatively other formaldehyde sources, such as paraformaldehyde or a urea-foπnaldehyde pre-condensate with formaldehyde to urea mole ratio (F :U) of from 4.0 to 6.O ₃ can also be used to replace partially or even totally the formalin.

5

The products obtained by the process of the invention can be used for partial or total melamine substitution in the production of MUF, UMF and MUPF resins with a mole ratio of formaldehyde to amino groups between 0.4-1.5 and a melamine/aminotriazine content of 0.1-30% on a weight basis, which provide panels with very low formaldehyde o emission and improved moisture resistance.

An advantage of the proposed invention is that it helps to better exploit the aminotriazine compound used for resin manufacture as to obtain a lower cost resin (low aminotriazine content) at no sacrifice of the adhesive performance (moisture resistant 5 panels with acceptable mechanical strength and very low formaldehyde emission are obtained).

When the products synthesized according to the invention are used as additives in formaldehyde-based thermosetting resins, the performance of the latter in producing o composite wood panels is enhanced. Mixing appropriate amounts of the resin and the proposed product, a range of mole ratios and melamine/aminotriazine contents (e.g. from 0.1-30% on a weight basis) can be achieved, depending on the desired application and end-use requirements.

5 The following examples further illustrate the embodiments of the invention without limiting its scope and field of application.

EXAMPLE !

292.3 g of a 38.8 % w/w aqueous formaldehyde solution and 156.1 g of water were added in 0 a 1 -liter, 4-neck round bottom flask, equipped with a mechanical stirrer, a thermometer and a pH meter. The pH of the solution was adjusted to 7.2 by adding 0.07 g of a 20 % w/w

sodium hydroxide solution. 176.9 g of benzoguanamine were charged and the reaction mixture was heated up to 75 ⁰ C, where it became clear, and was maintained at that temperature for 10 mύi. 374.7 g of N ₅ ISP dimethylurea were added and the pH of the solution was adjusted to 5.5 using 0.91 g of a 10 % w/w formic acid solution. The mixture was allowed to react at 67°C until a viscosity of 45 cP was reached. The pH was then raised to 9.5 by adding 0.1 g of a 20 % w/w sodium hydroxide solution and the reaction mixture was cooled to room temperature.

EXAMPLE 2 0 853.5 g of a 39.2 % w/w aqueous formaldehyde solution and 7.0 g of water were added in a 2-liter, 4-neck round bottom flask, equipped with a mechanical stirrer, a thermometer and a pH meter. The pH of the solution was adjusted to 8.5 by adding 0.75 g of a 20 % w/w sodium hydroxide solution. 340.0 g of melamine were charged and the reaction mixture was heated up to 6O ⁰ C. 595.6 g of urea were added and the pH of the solution was adjusted to 5 5.4 using 86.3 g of a 10 % w/w formic acid solution. The mixture was allowed to react at 6O ⁰ C until a viscosity of 150 cP was reached. The pH was then raised to 9.0 by adding 28.7 g of a 20 % w/w sodium hydroxide solution and the reaction mixture was cooled to room temperature.

0 EXAMPLE 3

161.3 g of a urea-formaldehyde pre-condensate of 22.7 % and 56.4 % w/w concentration in urea and formaldehyde respectively, 236.8 g of a 39.2 % w/w aqueous formaldehyde solution and 142.1 g of water were added in a 1-liter, 4-neck round bottom flask, equipped with a mechanical stirrer, a thermometer and a pH meter. The pH of the solution was 5 adjusted to 8.0 by adding 0.2 g of a 20 % w/w sodium hydroxide solution. 90.0 g of melamine were charged and the reaction mixture was heated up to 75 ⁰ C. 333.0 g of urea were ^' added and the pH of the solution was adjusted to 5.2 using 18.5 g of a 10 % w/w formic acid solution. The mixture was allowed to react at 65 ⁰ C until a viscosity of 150 cP was reached. The pH was then raised to 9.5 by adding 9.5 g of a 20 % w/w sodium o hydroxide solution and the reaction mixture was cooled to room temperature.

EXAMPLE 4

Two UMF resin samples were prepared in parallel, each with a mole ratio of formaldehyde to amino groups of 0.96. One sample was prepared according to conventional synthesis by using melamine at a content of 1.5% w/w (Resin A). The second UMF resin sample was prepared using the aminotriazine derivative of example 2 instead of using melamine, to obtain a resin with a total melamine content of 1.35% w/w (Resin B). Both resins were subsequently mixed with wood chips, which were then formed to mats and hot-pressed, to enable the production of 16mm lab scale particleboards. Each one of the resins was applied at two loadings: 9 and 11% w/w based on wood chips weight. The pressing temperature and time were 210 ⁰ C and 9s/mm respectively, while the specific press pressure was 35 kg/cm ² . The target board density was 710 kg/m . Replicate boards were produced in each case and their performance characteristics were subsequently determined according to European standard EN 13986. The average values of board properties are presented below:

Resin type Resin A Resin B Resin A Resin B

Resin loading, % w/w 9 9 11 11

IB, N/mm ^{2 (1)} 0.24 0.50 0.32 0.53

Density, kg/m ³ 754 751 751 741

24h swelling in thickness, % 41.4 25.1 37.4 25.2

M0R, N/mm ^{2 (2)} 11.2 12.1 11.1 12.6

Formaldehyde content, 2.8 2.8 3.0 3.0 mg/10Og board ⁽³⁾

internal Bond (tensile strength) ² Modulus of Rupture (bending strength) Perforator value, EN 120

As it can be seen from the above test, the strength properties of the boards as well as

their thickness swelling after 24h immersion in water were significantly improved, when the resin used had been prepared from the aminotriazine derivative of the proposed invention.