Wood adhesives for producing particle boards

Abstract

A composition based on phenolic resin comprising at least one phenolic resin, a vegetable protein hydrolysate, preferentially a wheat gluten hydrolysate, and an agent for accelerating curing, and also to the process for the production thereof.

Claims

1. A composition based on phenolic resin, characterized in that it comprises at least one phenolic resin, a wheat gluten hydrolysate, and an agent for accelerating curing selected from triacetin, butyrolactone, caprolactone and propylene carbonate; wherein the phenolic resin is a product of resinous reaction of a phenol with an aldehyde and wherein the phenol:aldehyde mole ratio is from 1:1.5 to 1:1.7.

2. The composition as claimed in claim 1, characterized in that the phenol and the wheat gluten hydrolysate are mixed in a phenol:wheat gluten hydrolysate ratio of 3.2:1 to 7.2:1 by weight.

3. The composition as claimed in claim 1, characterized in that the content of agent for accelerating curing is between 4% and 10% by weight of the resin solids.

4. The composition as claimed in claim 1, characterized in that the wheat gluten hydrolysate is obtained by acid or enzymatic hydrolysis.

5. The composition as claimed in claim 1, characterized in that the wheat gluten hydrolysate is obtained by enzymatic hydrolysis and has an average molecular weight of between 3 and 20 kDa.

6. The composition as claimed in claim 1, characterized in that the wheat gluten hydrolysate is also deamidated.

7. A process for the formation of a composition based on phenolic resin, said phenolic resin being a product of resinous reaction of a phenol with an aldehyde, characterized in that the process comprises the following steps: mixing phenol and a wheat gluten hydrolysate, in the presence of a base solution and of a molar excess of 10% of formaldehyde in a mixer; heating the mixture obtained to a temperature of between 90 and 98 C. and maintaining it at this temperature for approximately 15 minutes up to one hour; adding an additional amount of formaldehyde so as to achieve a phenol:formaldehyde ratio of 1:1.5 to 1:1.7; continuing the reaction until a resin with a viscosity of between 0.5 and 0.8 Pa.Math.s at 25 C. is obtained; mixing the resin obtained with an agent for accelerating curing selected from triacetin, butyrolactone, caprolactone and propylene carbonate.

8. A rigid phenolic foam board comprising a composition as claimed in claim 1.

9. A particle or fiber board comprising a composition as claimed in claim 1.

10. The composition as claimed in claim 3, characterized in that the content of agent for accelerating curing is between 6% and 8% by weight of the resin solids.

11. The composition as claimed in claim 5, characterized in that the wheat gluten hydrolysate is obtained by enzymatic hydrolysis and has an average molecular weight of between 4 and 15 kDa.

Description

DETAILED DESCRIPTION OF EMBODIMENTS

(1) Hereinafter, the invention will be illustrated by a certain number of examples concerning the production of the resins and the use thereof as bonding agent during the production of the particle board compositions. These examples can in no way be interpreted as a limitation of the scope of the invention or of the patent rights claimed in the claims.

Example 1: Production of a Phenolic Resin Containing a Protein Hydrolysate

(2) In a 500 ml glass reaction vessel, 105.75 g (0.9 mol) of, a solution of 80% of phenol 50 ml of 30% NaOH (0.35 mol) and a 100 ml solution of 37% formaldehyde (1.2 mol) are mixed together for 30 minutes at 30 C. 11.75 g of wheat protein hydrolysate are then added such that the reaction mixture is heated slowly to 94 C., and then maintained at this temperature for approximately 30 minutes. An additional amount of formaldehyde, which corresponds to 0.5 mol is then added. The reaction is then continued until a viscosity of between 0.5 and 0.8 Pa.Math.s at 25 C. is achieved. The final pH should be around 11.

(3) The resin thus obtained contains 10% of a protein hydrolysate. In order to increase the protein content by 20%, the proportion of phenol is reduced to 94 g (0.8 mol) and the proportion of proteins is increased by 11.75 g.

(4) Three types of wheat protein hydrolysates are used: SOLPRO 508 (product sold by TEREOS SYRAL): an enzymatic hydrolysate of wheat gluten; SOLPRO 050 (product sold by TEREOS SYRAL): an acid hydrolysate of wheat gluten; An experimental low-molecular-weight (LMW) wheat protein hydrolysate product having an average molecular weight of approximately 6000 Da.

(5) The inventors demonstrated, by virtue of a preliminary study, that triacetin was more suitable in accelerating the curing of the phenolic compositions comprising a vegetable protein hydrolysate since it confers good curing acceleration for stability of the curing mixture allowing use of the obtained composition in an industrial environment, this being with low amounts. Thus, triacetin showed a mixture stability able to reach five hours for an amount of triacetin of 5% to 10% of the dry matter of the resin. Comparative tests were in particular carried out with esters such as propylene carbonate or methyl formate.

(6) The resins prepared in the following examples were used as such or combined with triacetin (7% of the dry matter of the resin).

Example 2: Production of Particle Boards

(7) Particle boards are produced using the phenolic resins obtained by means of the process described in example 1. The resins used are represented in table 1:

(8) TABLE-US-00001 TABLE 1 Resin Composition Reference 100% phenol R1 90% phenol-10% LMW R2 90% phenol-10% SOLPRO 050 R3 80% phenol-20% SOLPRO 050

(9) The particle boards are prepared by mixing 100 g of wood particles (moisture content of 2.5%) with 10 g of resin solids. The resin as such has a moisture content of approximately 50% to 55%. A series of boards is produced without addition of triacetin, and a second series is produced with addition of 7% of resin dry matter (therefore in this case 0.7 g).

(10) The mixtures are then pressed in a mold in order to obtain boards. The mold has the following dimensions: 14300350 mm. The processing conditions are the following: heating at 160 C. while applying three consecutive and decreasing pressures. This is represented in table 2:

(11) TABLE-US-00002 TABLE 2 Pressure (bar) 80 35 17 Time (min) 3 2 2.5

Example 3: Behavior with Respect to Swelling of the Boards Produced

(12) In this example, the behavior with respect to swelling was tested on boards manufactured with the resins prepared in example 1. The boards tested have a thickness of 13 mm. The behavior with respect to swelling is thus determined as described in standard NF B51-262.

(13) First, the thickness of the board is measured and then the board is cured for two hours. After curing, the boards are oven-dried at 103 C., for 24 hours.

(14) The dry swelling value G is then determined as follows:

(15) $G\left(\%\right)=\frac{\mathrm{dry}\mathrm{thickness}\mathrm{after}\mathrm{swelling}-\mathrm{dry}\mathrm{thickness}\mathrm{before}\mathrm{swelling}}{\mathrm{Dry}\mathrm{thickness}\mathrm{before}\mathrm{swelling}}100$

(16) The effect of the addition of triacetin to the phenolic resins containing the protein hydrolysate is clearly demonstrated in table 3, which shows swelling values which are much lower than those without triacetin.

(17) TABLE-US-00003 TABLE 3 Behavior with respect to swelling of the boards based on resins of table 1 G (%) without triacetin G (%) with triacetin Reference 9.9 7.8 R1 21.9 5.4 R2 10.7 6.2 R3 11.7 5.5

Example 4: Internal Cohesion of the Boards

(18) In this example, the internal cohesion before swelling (according to EN319) and after swelling (according to EN321) is determined. The values are expressed in N/mm.sup.2 in table 4. These values again show the effect of the presence of triacetin on the phenolic compositions containing proteins.

(19) TABLE-US-00004 TABLE 4 Effect of the presence of triacetin on the phenolic compositions containing proteins Internal cohesion Internal cohesion before swelling after swelling Without Without triacetin With triacetin triacetin With triacetin Reference 0.58 1.01 0.18 0.59 R1 0.28 0.60 0.00 0.21 R2 0.31 0.68 0.06 0.36 R3 0.68 0.86 0.17 0.50

Example 5: Formaldehyde Emission of the Particle Boards

(20) In order to be classified as class E1, the formaldehyde emission of the boards must be less than 6.5 mg/100 g on a dry board, according to EN312, as determined by the method described in EN717-3.

(21) In table 5 below, the formaldehyde emissions of the boards manufactured with adhesives according to the invention are presented.

(22) TABLE-US-00005 TABLE 5 Formaldehyde emissions Resins cont. 7% triacetin Formaldehyde emission (mg/100 g) Reference 3.88 R1 3.74 R2 4.62 R3 2.11

(23) The inventors observed that, compared with the boards not comprising gluten hydrolysate, the boards comprising gluten hydrolysate showed a lightening of the board visible to the naked eye. This characteristic of the boards obtained by using the compositions according to the invention makes it possible, for example, to reduce the thickness of the coating required to obtain colored boards and in particular white boards. Such a lightening is particularly advantageous in the principal use of these boards in the construction field.