GB2136008A

GB2136008A - Formaldehyde binder

Info

Publication number: GB2136008A
Application number: GB08401225A
Authority: GB
Inventors: Efthalia Vergopoulo Markessini
Original assignee: Enigma NV
Current assignee: Enigma NV
Priority date: 1983-02-07
Filing date: 1984-01-17
Publication date: 1984-09-12
Also published as: HU197591B; DE3403136C2; FR2540506A1; NZ206859A; SE8400509D0; FR2540506B1; NO169848C; AU570028B2; CA1225630A; PT78066B; IT8447647A0; DK165184B; PL144282B1; AU2381084A; GR79713B; RO88986A; DD232018A5; ES529473A0; GB2136008B; NO840403L

Abstract

A formaldehyde binder is described for use in lignocellulosic sheet materials such as particleboard, plywood or blockboard, in which a formaldehyde-based adhesive is used. The binder comprises a solution of (a) at least one organic hydroxy compound. with the exception of C1-4 monohydric aliphatic alcohols, and (b) at least one amide, in water, and optionally (c) an organic compound which acts as a solvent for (a) and (b) and also reacts with formaldehyde. e.g. a C1-4-aliphatic monohydric alcohol, and optionally (d) a water-soluble inorganic compound, e.g. an alkali metal or alkaline earth metal halide.

Description

SPECIFICATION Aformaldehyde binder Boards such as particleboard, chipboard and the like are prepared from lignocellulosic materials using adhesives. The preferred adhesives (orglues) are based on formaldehyde, such as urea-formaldehyde, melam ine-fo rmaldehyde, phenol-formaldehyde and resorcinol-formaldehyde resins or mixtures thereof. It isawell-known fact that boards prepared using these adhesives have a formaldehyde odourwhich is both harmful and unpleasant. Formaldehyde is emitted both during the production of such boards and during their storage and final use.

Many methods of avoiding the emission of formaldehyde have been proposed, but all of them are either ineffective or reduce the properties of the boards or require complicated application procedures. Some of these procedures involve spraying or spread coating the warm boards coming out of the press with various solutions, such as solutions of urea and/or ammonia or of ammonium salts. Generally,thesetypes of methods are not desirable for industrial application because they require additional process steps and anyway are not very efficient Other methods involve the use of very complicated mixtures of a large number of components, some of which are natural glues. These products also are not very efficient. One handicap thereof is the fact that the properties of natural products are not constant.

Another way of reducing the content of free formaldehyde involves the use of an aqueous suspension of urea prills coated with a special wax. This method, too, requires a separate feeding line, because the product is not added to the adhesive formulation itself.

An object ofthe present invention is to provide a formaldehyde binderwhich effectively reduces the formaldehyde odourwithout reducing the properties ofthe board, without changing the reactivity of the adhesiveformulationsandwithoutrequiringany additional steps in the production of particleboard, plywood or blockboard.

The invention provides a formaldehyde binder when for use in boards prepared from lignocellulosic materials using adhesives based on formaldehyde, which comprises a solution of (a) at least one organic hydroxy compound with the exception of Ca4 monohydric aliphaticalcohols and (b) at least one amide in water. The formaldehyde binder can also contain (c) an organic compound which acts as a solvent for (a) and (b) and also reacts with formaldehyde and/or (d) an inorganic compound soluble in water. The organic compound (c) is preferably a Ca4 monohydric aliphatic alcohol. The inorganic compound (d) is preferably a halide salt. Even if the individual components are not soluble in water, they may dissolve in water if a mixture thereof is heated in water to 70'C.

Preferably the organic hydroxy compounds [component (a)] are soluble in water or in lower monohy dricaliphaticalcohols. Examples of such preferred hydroxy compounds are the dihydric, trihydric and pentahydric alcohols containing up to 6 carbon atoms, the monosaccharides containing up to 6 carbon atoms, the disaccharides containing up to 12 carbon atoms and the polysaccharides having an Ostwald viscosity up to 200 mPas at 25 "C and a concentration corresponding to 37 % refraction.Other examples of preferred hydroxy compounds are the a romatic alco holland phenols, which preferably are used alone or in combination with one or more ofthe abovementioned dihydric, trihydric and/or pentahydric alcohols and/or monosaccharides, disaccharides and/or polysaccharides. The phenols and aromatic alcohols can be monohydric or polyhydric phenols and monohydric or polyhydric aromatic alcohols containing one benzene ring.

Specific examples of suitable organic hydroxy compounds are monoethyleneglycol, diethyleneglycol, glycerine, pentaerythritol, fructose, man nose, sorbitol, dextrose, sucrose, maltose, lactose, dextrin, phenol, resorcinol, hydroquinone and the like.

Preferablythe amides [component (b)] used in the formaldehyde binderofthe invention are likewise soluble in water or in lower monohydric aliphatic alcohols. Particularly preferred arethe aliphatic amides containing up to 6 carbon atoms and the aromatic amides containing one benzene ring.

Suitable examples of amides are urea, thiourea, formamide, acetamide, benzamide, oxamide, succinamide, malonamide and the like.

If desired, to enhance solubility, the formaldehyde binderofthe invention can additionally contain additives [component (c)] which are lower monohydric aliphatic alcohols such as methanol, ethanol, isopropanol and the like, Acheaperand more efficient formaldehyde binder is obtained if inorganic compounds [component (d)] which are preferably halide salts, more preferably halides of alkali metals oralkaline earth metals, such as sodium chloride, potassium chloride and calcium chloride, are added.

The ratio of organic hydroxy compound [component (a) and component (c), if present] and inorganic compound [component (d), if present] to amide [component (b)] is preferably 10:100 to 400:100, particularly 10:100to 200:100, byweight. Theformal- dehyde binder ofthe invention can be added to the usual glue formulations in quantities varying from 1 to 10%, preferably 3 to 7 %, of formaldehyde binder solids, based on the weight of the liquid resin containing 65 % by weight of resin solids.

The formaldehyde binder of the invention may contain 20 to 80 % by weight, preferably 50 to 70 % by weight, of the active ingredients [components (a) and (b) and components (c) and/or (d), if present]. The water content of the formaldehyde binder depends on the solubility of the active ingredients and the amount of waterwhich can be tolerated in the glue formulations.

The formaldehyde binder of the invention can be produced by simply adding the active ingredients and water to a mixer and mixing until the active ingre- dients are dissolved. This can be done at room temperature or at an elevated temperature up to 70 "C.

The formaldehyde binder of the invention may be used whenever boards are prepared from lignocellulosic materials using adhesives based on formaldehy de, such as urea-formaldehyde, melamine-formaldehyde, phenol-formaldehyde or resorcinol-formaldehyde resins or mixturesthereof.

When using the formaldehyde binder ofthe invention, it is possible to produce boards actuallycontain- ing less than 10 mg offreeformaldehyde per 100 g of the dry board, as determined by the F.E.S.Y.P.

(Federation Européenne des Syndicats des Fabricants de Panneaux de Particules) perforator method No. EN 120.

The amount of the free formaldehyde reduction depends on manyfactors and, therefore, can vary widely. If the emission offreeformaldehyde is high (higherthan 50 mg offormaldehyde per 100 grams of dry board), the reduction can be as high as upto 60to 85 %. If emission offreeformaldehyde is relatively low, i.e. 20 to 50 mg offreeformaldehyde per 100 g of the dry board,the maximum reduction is usually 50 to 60 %. The amount of reduction obtained also depends on the amount of formaldehyde binder used: The moreformaldehyde binder is used, the lower is the amount offree formaldehyde.

When the active ingredients oftheformaldehyde binder are used in combination with each other, the free formaldehyde reduction is surprisingly much higher than the sum ofthe effects of the separate components, and they have no adverse effect on the reactivity of the glue formulation orthe properties of the boards.

The following examples illustrate the invention. Part and percents are by weight.

Example? In this example the organic compound containing hydroxyl groups is glycerine and the amide is urea.

Here, there is illustrated the synergistic behaviour of these two compounds. Various glue formulations are prepared and each is used subsequently in order to produce particleboard.

The control does not include any of the components ofthe formaldehyde binder according to the invention. Sample 1 includes both glycerine and urea, sample 2 includes only glycerine and sample3 includes only urea.

ltisnoticedfromthetablesreported herebelowthat glycerine when used on its own (sample 2) is a very efficientformaldehyde binder, but urea (sample 3) gives a poorerformaldehyde reduction and lower mechanical values and water resistance, however, when urea is used in combination with glycerine (sample 1), it gives values that are equivalent to those of glycerine on its own.

We may therefore use a cheaper and less efficient product (urea) and make it react as effectively as a more expensive and more efficient product (glycerine). The efficiency refers to formaldehyde absorbing capacities as well as to maintaining good mechanical properties and water resistance without changing the reactivity of the glue formulation and withoutthe need to introduce any special apparatus for its use.

Formaldehyde reduction actually is in this case 46 %.

The formulations ofthe various samples used are as follows: 1 2 3 parts by parts by parts by weight weight weight Glycerine (100 %) 270 590 Urea (100 %) 320 - 590 Water blO 410 410 1000 1000 1000 % solids 59 59 59 The glue formulations used are as follows: Control 1 2 3 grams grams grams grams Urea-formaldehyde resin 65 % 3077 3077 3077 3077 (Molar ratio F::U 1.27.1) Hardener 400 400 400 400 (Ammonium chloride 15 %) Paraffin emulsion 250 250 250 250 50 % Ammonia 250 Baume 5 5 5 5 Sample 1 - 308 - Sample 2 - - 308 Sample 3 - - - 308 Water 268 - - Total 4 4 4 4 4 4 4 Gel time in secs. 68 68 71 62 Single-layer boards are prepared in the laboratory by spraying each oftheseformulations onto 25 kgs wood chips. Boards are pressed at 10, and 9 and 8 secs./mm. The thickness of the boards is 17.3 mms.

The temperature of the press is 200 "C and the pressure is 35kg/cm2. The dimensions ofthe boards produced are 40 x 56 cms.

The results obtained are reported inthefollowing table and are average values.

Control 1 2 3 Density (kg/m ) 683 669 663 657 Bending strength (N/mm2) 19.9 18.1 17.3 16.3 Tensile strength (N/mm2) 0.73 0.72 0.71 0.63 2 hr. thickness swelling (%) 5.2 4.9 4.5 5.4 24 hr. thickness swelling (%) 51.4 49.9 47.4 53.1 Free formaldehyde 15.8 8.5 8.7 11.7 (mg/100 g dry board) Example 2 This is another example illustrating the synergistic behaviour of glycerine and urea in reducing the free formaldehyde of particleboards while maintaining the mechanical properties of the boards and the water resistance as well.

The control does not include any of the components of the formaldehyde binder according to the invention. Sample 1 contains both components ofthe formaldehyde binder according to the invention and sample 2 contains only one ofthetwo components (the most efficient of the two components).

It is noticed here again that only sample 1 gives free formaldehyde that is below 10 mug/100 g. dry board (which is the desired level for El class) and is the only one to have absolutely equivalent mechanical properties and water resistance. Formaldehyde reduction actually is 34 % .

The formulations of the various samples used are as follows: 1 2 parts by weight parts by weight Glycerine (100 %) 128 128 Urea (100 S) 424 - Water 448 872 1000 1000 S solids 55.2 12.8 Theglueformulationsusedareasfollows: Control 1 2 grams grams grams Urea formaldehyde resin 65 S 3077 3077 3077 (Molar ratio F:U = 1.27::1) Hardener 'too 400 'too (Ammonium chloride 15 %) Paraffin emulsion 250 250 250 50 % Ammonia 250 BaumB 5 5 5 Sample 1 - 268 Sample 2 - - 268 Water 268 - Total 4000 4000 4000 Gel time in secs. 66 67 69 Single-layer boards are prepared in the laboratory byspraying each oftheseformulations onto 25 kgs wood chips. Boards are pressed at 10,9 and 8 secs./mm. The thickness of the boards is 17.3 mms.

The temperature of the press is 200 "C and the pressure is 35 kg/cm2. The dimensions of the boards produced are 40 x 56 cms.

The results obtained are reported inthefollowing tables and are average values.

Control 1 2 Density (kg/m3) 685 684 687 Bending strength (N/mm2) 20.7 20.6 19.4 Tensile strength (N/mm2) 0.74 0.73 0.67 2 hr. thickness swelling (%) 11.0 7.9 8.6 24 hr. absorption (%) 23.5 23.2 23.7 Free formaldehyde 14.3 9.5 12.3 (mg/100 g dry board) Example 3 This example illustrates the efficiency of monoethyleneglycol together with urea as a formaldehyde binder.

Two formulations are prepared: the control withoutanyofthe ingredients oftheformaldehyde binder according to the invention and sample 1 which includes both monoethyleneglycol and urea.

Boards are produced from these two glue formulations and it is proved here, too, that with the formaldehyde binder according to our invention we obtain with a urea-formaldehyde resin that gives normally boards classified as E 2 (control), boards classified as E 1 (sample 1).

Theformaldehyde reduction is in this case 37 %.

The formulation of sample 1 used is as follows: Sample 1 parts by weight Monoethyleneglycol 100 % 360 Urea 100 % 365 Water 275 1000 % solids 72.5 The glue formulations used are as follows: Control 1 grams grams Urea formaldehyde resin 65 % 3077 3077 (Molar ratio F:U = 1.27:1) Hardener 'too 400 (Ammonium chloride 15 X) Paraffin emulsion 50 % 250 250 Ammonia 250 Baumé 5 5 Sample 1 - 268 Water 268 Total 4000 'tooo Gel time in secs. 66 60 Single-layer boards are prepared in the laboratory by spraying each of these formulations onto 25 kgs wood chips. Boards are pressed at 10,9 and 8 secs./mm.The thickness ofthe boards is 17.3 mms.

The temperature of the press is 200 "C and the pressure is 35 kg/cm2. The dimensions ofthe boards produced are 40 x 56 mms.

The results obtained are reported in the following table and are average values.

Control 1 Density (kg/m') 685 684 Bending strength (N/mm2) 20.7 20.2 Tensile strength (N/mm2) 0.74 0.74 2 hr.thickness swelling (%) 11.0 8.6 24 hr. absorption (%) 23.5 22.6 Free formaldehyde 14.3 9. o (mg/100 g dry board) Example 4 In this example we are illustrating the synergistic behaviourofmonoethyleneglycol and urea.

Boards are prepared from three different formulations: the control wherein no ingredients of the formaldehyde binder according to the invention are used, sample 1 wherein both ingredients of the formaldehyde binderofthe present invention are used and sample 2 wherein only one ingredient is used.

It is obvious from the results obtained and reported here in belowthat sample 1 containing both ingredients is much more effective than sample 2 containing only one ingredient (the most efficient of the two ingredients).

The formaldehyde reduction obtained in this case is 32 %.

The formulations ofthe various samples used are asfollows: 1 2 1 2 parts by weight parts by weight Monoethyleneglycol 100 % 230 580 Urea 100 % 350 Water 420 420 1000 1000 % solids 58 58 The glue formulations are as follows: Control 1 2 grams grams grams Urea formaldehyde 3077 3077 3077 resin 65 F (Molar ratio F:U = 1.27::1) Hardener 400 400 400 (Ammonium chloride 15 %) Paraffin emulsion 50 % 250 250 250 Ammonia 250 Baum 5 5 5 Sample 1 - 268 Sample 2 - - 268 Water 268 - Total 4 4 4 Gel time in secs. 70 71 76 Single-layer boards are prepared in the laboratory by spraying each of these formulations onto 25 kgs wood chips. Boards are pressed at 10,9 and 8 secsJrjm. The thickness of the boards is 17.3 mms.

The temperature of the press is2005Candthe pressure is 35 kg/cm2. The dimensions of the boards produced are 40 x 56 mms.

The results obtained are reported in thefollowing table and are average values.

Control 1 2 Density (kg/m3) 688 688 687 Bending strength (N/mm2) 17.6 17.6 17.5 Tensile strength (N/mm2) 0.55 0.60 0.56 2 hr. thickness swelling (%) 6.7 4.9 4.7 24 hr. absorption (%) 20.1 20.1 19.5 Free formaldehyde 15.0 10.3 12.3 (mg/100 g dry board) Example 5 In this example the use of a resin of different molar ratio is illustrated as well as various levels of addition oftheformaldehyde binder itself.

Theformaldehyde binder used has the following formulation: parts by weight Glycerine 100 g 270 Urea 100 % 318 Water 412 1000 % solids 58.8 Single-layer boards are prepared in the laboratory by spraying each of theseformulations onto 25 kgs wood chips. Boards are pressed at 10,9 and 8 secs./mm. The thickness of the boards is 17.3 mms.

The temperature of the press is 200 C andthe pressure is 35kg/cm2. The dimensions ofthe boards produced are 40x 56 cms.

The glueformulations used in the various samples are as follows: Control 1 2 3 grams grams grams grams Urea formaldehyde resin 65 % 3077 3077 3077 3077 (Molar ratio F:U = 1.4:1) Hardener 293 380 380 380 (Ammonium chloride 15 7) Paraffin emulsion 50 % 250 250 250 250 Ammonia 250 Baume' 5 5 5 5 Formaldehyde binder - 154 215 375 Water 375 134 73 - Total 4000 4000 4000 4087 Gel time in secs. 73 73 72 75 The results obtained are reported in the following table and are average values.

Control 1 2 3 Density (kg/m3) 680 687 685 688 Bending strength (N/mm2) 22.0 22.5 22.3 21.6 Tensile strength (N/mm2) 0.61 0.63 0.66 0.611 2 hr. thickness swelling (% 10.1 9.3 8.8 9.5 24 hr. thickness swelling (% 20.6 21.8 21.0 21.5 Free formaldehyde 22.2 13.0 10.1 9.5 (mg/100 g dry board) It is noticed that the mechanical properties and water resistance of the boards are equivalent and the formaldehyde reduction is 41 % in case of sample 1, 55 % in case of sample 2 and 57 % in case ofsample 3.

Example 6 In this example six differenttypes of polyalcohols are illustrated, two different types of amides, one additive and a variation in the ratio of alcohol to amidecoveringarangefrom 57.5/100 to 385/100.

The various types of formaldehyde binder used are as follows: 1 2 3 4 5 6 Dextrose 230 - - - - Diethyleneglycol - 330 - - - Monoethyleneglycol - - 260 - - 110 Glycerine - - - 500 - Sucrose - - - - - 110 Sorbitol - - - - 140 Methanol - - 200 - 140 80 Urea 400 300 - 130 350 330 Thiourea - - 170 - - Water 370 370 370 370 370 370 Total 1000 1000 1000 1000 1000 1000 % solids 63 63 63 63 63 63 Weight ratio of alcohol/amide 57.5/100 110/100 270/100 385/100 80/100 91/100 All above-mentioned figures are in parts by weight.

The glue formulations used in the various samples are as follows: Control 1 2 3 4 5 6 grams grams grams grams grams grams grams Urea-formaldehyde resin 65 % 3077 3077 3077 3077 3077 3077 3077 (Molar ratio F:U = 1.27:1) Hardener 400 500 500 500 500 500 500 (Ammonium chloride 15 S solution) Paraffin emulsion 50 % 250 250 250 250 250 250 250 Ammonia 250 Baumé 5 - - - - - Formaldehyde binder Sample 1 - 307 - - - - Sample 2 - - 307 - - - Sample 3 - - - 307 - - Sample 4 - - - - 307 - Sample 5 - - - - - 307 Sample 6 - - - - - - 307 Water 268 - - - - - - Total 4000 4134 4134 4134 4134 4134 4134 Gel time in secs. 65 66 65 67 66 62 69 Single-layer boards are prepared in the laboratory by spraying each oftheseformulations onto 25 kgs wood chips. Boards are pressed at 10,9 and 8 secs./m m.The thickness of the boards is 17.3 mms.

Thetemperature of the press is 200 5C and the pressure is kg/cm2. The dimensions of the boards produced are 40 x 56 cms.

Control 1 2 3 4 5 6 Density (kg/m3) 688 689 687 685 690 685 692 Bending strength (N/mm) 19.6 19.5 18.3 19.5 20.1 19.3 19.4 Tensile strength (N/mm2) 0.71 0.69 0.67 0.73 0.74 0.72 0.70 2 hr. thickness swelling (%) 7.0 6.5 5.0 5.5 6.1 6.5 6.2 24 hr. thickness swelling (f) 19.7 19.3 20.0 19.8 19.5 20.1 19.9 Free formaldehyde 16.1 8.9 8.6 ll.o g.o 9.8 8.5 (mg/lOO g dry board) Formaldehyde reduction % - 45 47 32 44 39 47 The above-mentioned results prove that all samples used have values equivalentto the control and thattheformaldehydereduction is of the order of 32 to47%.

Example 7 In this example three differenttypes of organic compounds containing hydroxyl groups are exemplified by means of dextrin, phenol and resorcinol.

One monohydric alcohol acting as an additive otherthan methanol is also illustrated, namely ethyl alcohol.

The various types offormaldehyde binder used are as follows: 1 2 3 4 Monethyleneglycol 230 - - Dextrin - 140 - Phenol - - 130 Resorcinol - - - 130 Methanol - 140 130 130 Ethanol 80 - - Urea 350 350 370 370 Water 340 370 370 370 1000 1000 1000 1000 % solids 66 63 63 63 All above-mentioned figures are in parts by weight.

The formaldehyde binder samples are used in this example to substitute a part of the resin used.

The glue formulations actually used are as follows: Control 1 2 3 4 grams grams grams grams grams Urea formaldehyde 3077 2770 2770 2770 2770 resin (Molar ratio F:U = 1.27:1) Hardener 400 500 400 450 400 (Ammonium chloride 15 % solution) Paraffin emulsion 50 % 250 250 250 250 250 Ammonia 250 BaumB 5 - - - Formaldehyde binder Sample 1 - 307 - - Sample 2 - - 307 - Sample 3 - - - 307 Sample 4 - - - - 307 Water 268 - - - Total 4000 3827 3727 3777 3727 Gel time in secs. 65 64 62 63 63 Single-layer boards are prepared in the laboratory by spraying each oftheseformulations onto 25 kgs wood chips. Boards are pressed at 10,9 and 8 secs./mm.Thethicknessofthe boards is 17.3 mms.

The temperature of the press is 200 C and the pressure is kg/cm2. The dimensions of the boards pressed are 40 x 56 cms.

Control 1 2 3 4 Density (kg/m3) 702 698 695 705 710 Bending strength (N/mm2) 20.1 19.5 19.7 20.0 20.8 Tensile strength (N/mm2) 0.75 0.70 0.75 0.73 0.72 2 hr. thickness swelling (%) 7.1 6.8 6.5 6.3 6.6 24 hr. thickness swelling (%) 20.3 21.5 21.3 21.8 21.3 Free formaldehyde 13.1 9.6 9.2 8.2 10 (mg/100 g dry board) Formaldehyde reduction (%) - 27 30 37 24 The above-mentioned results prove that all samples have values that are equivalent to the control sample that contains no formaldehyde binder even though the lattersubstitutes an equivalent amount of urea-formaldehyde resin in the formulation. The formaldehyde reduction varies in this example from 24to 37 %.

Example 8 In this example one type offormaldehyde binder is used and the resin is based on phenol-melamine-urea formaldehyde resin.

The formaldehyde binder used has the following formulation: parts by weight Monoethyleneglycol 300 Urea 330 Water 370 1000 The glue formulations used are as follows: Control grams grams Phenol-melamine-urea-formal- dehyde resin 63 % 5600 5600 Hardener (solution in water of 15.5 d ammonium chloride) 840 840 Paraffin emulsion 50 7 150 150 Formaldehyde binder - 560 Total 6590 7150 Gel time in secs. 73 79 Single-layer boards are prepared in the laboratory by spraying each of these formulations onto 25 kgs wood chips. Boards are pressed at 10,9 and 8 secs./mm. The thickness ofthe boards is 17.3 mms.

The temperature of the press is 200 C and the pressure is 35kg/cm2. The dimensions of the boards produced are 40x56 cms.

Control 1 Density (kg/m3) 705 695 Bending strength (N/mm) 26.2 25.9 Tensile strength (N/mm2) 0.27 0.26 Tensile strength V100 (N/mm2) 2.7 2.6 2 hr. thickness swelling (fi) 7.1 6.2 ?4 hr. thickness swelling (%) 12.0 11.3 Free formaldehyde (mg/100 g dry board) 12.8 7 Formaldehyde reduction (%I - 45 The above-mentioned results prove that the for maldehyde binder according to the present invention can be used also for phenol-melamine-urea-formal- dehyde resins reducing considerably the free formal dehyde emission without adversely affecting the properties ofthe boards.

Example 9 In this example the formaldehyde binder used includes an inorganic compound [cornponent (d)], illustrated in this case by sodium chloride.

Theformaldehyde binder used has the following formulation: Parts bg weight Monoethyleneglycol 100 % 270 Urea 100 % 318 Sodium chloride 100 % 50 Water 362 Total 1000 % solids 63.8 The glue formulations used in the various samples are as follows: Control 1 grams grams Urea-formaldehyde resin (Molar ratio F:U=1.27::1) 3077 2770 Nardener (Ammonium chloride 15 S solution) 'too 450 Paraffin emulsion 50 S 250 250 Ammonia 25 Baumé 5 Formaldehyde binder - 307 Water 268 ~ Total 'tooD 3777 Gel time in secs. 65 64 Single-layer boards are prepared in the laboratory by spraying each of these formulations onto 25 kg wood chips. Boards are pressed at 10,9 and 8 secs/mm. The thickness ofthe boards is 17.3 mms.Thetemperature ofthe press is 200 C and the pressure is 35 kg/cm2.

The dimensions ofthe boards pressed are 40 x56 > cms.

The results obtained are reported in thefollowing table and are average values.

Control 1 Density (kg/m3) 695 699 Bending strength (N/mm2) 19.9 19.5 Tensile strength (N/mm2) 0.71 0.73 2 hr. thickness swelling (%) 7.0 6.6 24 hr. thickness swelling (S) 20.5 20.8 Free formaldehyde (mg/100 g dry board) 17 9.5 Formaldehyde reduction (S) - 44 The results prove thatthe sample including the formaldehyde binder gives values that are equivalent to the control sample in spite of the fact that the formaldehyde binder substitutes a part of the ureaformaldehyde resin in the formulation. The formaldehyde reduction is44 %.

Claims

1. Aformaldehyde binderwhen for use in boards prepared from lignocellulosic materials using adhesives based on formaldehyde, which comprises a solution of (a) at least one organic hydroxy compound with the exception of C14 monohydric aliphatic alcohols and (b) at least one amide in water.

2. The formaldehyde binder of claim 1 which, in addition, contains (c) an organic compound which acts as a solvent for (a) and (b) and also reacts with formaldehyde.

3. The formaldehyde binder of claim 2 wherein (c) is a C14 4 aliphatic monohydric alcohol.

4. The formaldehyde binder of any one of claims 1 to 3 which, in addition, contains (d) an inorganic compound soluble in water.

5. The formaldehyde binder of claim 4wherein (d) is a water-soluble halide salt.

6. The formaldehyde binder of claim wherein (d) is a water-soluble halide of an alkali metal or an alkaline earth metal.

7. Theformaldehyde binder of claim 6wherein (d) is sodium chloride, potassium chloride or calcium chloride.

8. The formaldehyde binder of any one of claims 1 to 7 wherein component (a) is soluble in water or in a C1 4 monohydric aliphatic alcohol.

9. The formaldehyde binder of claim 8, wherein component (a) is selected from dihydric, trihydric and pentahydric alcohols containing up to 6 carbon atoms, monosaccharides containing up to 6 carbon atoms, disaccharides containing up to 12 carbon atoms and polysaccharides having an Ostwald viscosity up to 200 mPas at 25 "C and a concentration corresponding to 37 % refraction.

10. The formaldehyde binder of claim 8, wherein component (a) is selected from aromatic alcohols and phenols.

11. Theformaldehyde binder of claim 10, wherein component (a) is selected from monohydric and polyhydric aromatic alcohols containing one benzene ring and monohydric and polyhydric phenols.

12. The formaldehyde binder of any one of claims 1 toll wherein component (b) is soluble inwateror in a C14 monohydric aliphatic alcohol.

13. The formaldehyde binder of claim 12, wherein component (b) is selected from aliphatic amides containing up to 6 carbon atoms and aromatic amides containing one benzene ring.

14. The formaldehyde binder of any one of claims 1 to 13, characterized in that the ratio by weight of component (a) plus components (c) and (d), if present, to component (b) is 10:100to 400:100.

15. The formaldehyde binder of any one ofclaims 1 to 14,characterized in that it contains 20to 80 % by weight of the active ingredients.

16. The formaldehyde binder as claimed in claim 1 substantially as hereinbefore described in any of the Examples.

17. A process for preparing the formaldehyde binder as claimed in claim 1,wherein (a) at least one organic hydroxy compound with the exception ofC1.4monohydric aliphatic alcohols, (b) at least one amide and (c) optionally at least one organic compound which acts as a solvent for (a) and (b) and also reacts with formaldehyde and (d) optionally an inorganic compound soluble in water and water are mixed at a temperature from room temperature to 70"C.

18. A process as claimed in claim 17 wherein (c) is a CIA monohydric aliphatic alcohol.

19. A process as claimed in claim 17 or 1 8wherein (d) is a water-soluble halide salt.

20. A process as claimed in claim 19 wherein (d) is a water-soluble halide of an alkali metal oran alkaline earth metal.

21. A process as claimed in claim 20wherein (d) is sodium chloride, potassium chloride or calcium chloride.

22. A process according to any one of claims 17 to 21 wherein component (a) is soluble in water or in a C1 4 monohydric aliphatic alcohol.

23. A process according to claim 22, wherein component (a) is selected from dihydric, trihydric and pentahydric alcohols containing up to 6 carbon atoms, monosaccharides containing up to 6 carbon atoms, disaccharides containing up to 12 carbon atoms and polysaccharides having an Ostwald viscosity upto 200 mPas at 25 "C and a concentration corresponding to 37% refraction.

24. A process according to claim 22, wherein component (a) is selected from aromatic alcohols and phenols.

25. A process according to claim 24, wherein component (a) is selected from monohydric and polyhydric aromatic alcohols containing one benzene ring and monohydric and polyhydric phenols.

26. A process according to any one of claims 17 to 25, wherein component (b) is soluble in water or in C1 4 monohydric aliphatic alcohols.

27. A process according to claim 26, wherein component (b) is selected from aliphatic amides containing up to 6 carbon atoms and aromatic amides containing one benzene ring.

28. A process according to any one of claims 17 to 27, characterized in thatthe ratio by weight of component (a) plus components (c) and (d), if present, to component (b) is 10:100 to 400:100.

29. A process according to any one of claims 17 to 28, characterized in thattheformaldehyde binder contains 20 to 80% byweightoftheactive ingredients.

30. A process for preparing boards from lignocellulosic materials using an adhesive based on formaldehyde, wherein aformaldehyde binder according to any one of claims 1 to 16 is added to the adhesive.

31. A process as claimed in claim 30 substantially as hereinbefore described in the Examples.

32. Boards when produced bya process as claimed in claim 30 or claim 31.