CA1136793A - Methylolated kraft lignin adhesive - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method of manufacturing composite wood products such as waferboard, particleboard and lumber products containing wood strands is disclosed incor-porating adhesives derived from wood chemicals rather than from petrochemical sources. In the method wherein wood pieces are coated with an adhesive mixture followed by a simultaneous pressure and heating step, the improve-ment comprises the steps of applying a water soluble phenol formaldehyde resole resin (PF) in a liquid form, powder form or a combination of liquid and powder form to the wood pieces, the PF in powder form having a pH
of at least about 9 when one part by weight is mixed in ten parts water. Applying to the wood pieces, either before, after or at the same time as the application of the PF, methylolated kraft-lignin (MKL) organic solids in a liquid form, powder form or a combination of liquid and powder form. The MKL organic solids are up to about 70% by weight of the total organic solids in the ad-hesive mixture, and the adhesive mixture in liquid form has a pH of at least about 10. Liquid and powder adhesives formed from PF and MKL are also disclosed.

Description

~L~36~93 This invention relates to a methylolated kraft lignin adhesive suitable for composite wood products such as waferboard, particleboard and lumber products containing wood strands. More particularly, the invention relates to an adhesive formed from a water soluble phenol ~ormaldehyde resole resin and lignin formaldehyde, referred to as methylolated kraft lignin (MKL).
The most common bonding agent used in the preparation of waferboard, exterior grade particleboard and other composite lumber products and the like is phenol formaldehyde resin. This resin is derived from non renewable petrochemical sources and is day by day becoming more expensive. Adhesives derived from wood chemicals have been considered as a replacement for phenol formaldehyde and other petrochemical adhesives. However, no satisfactory adhesives have yet been produced from wood chemicals which have the same properties as phenol formaldehyde resin and which can be used at the same low organic solids content for ~va~erboard and the like.
Many attempts have been made with kraft or soda black liquor to ~orm adhesives as substitutes in place of the normal phenol formaldehyde resin. In general the adhesives produced by these attempts have been limited because in order to obtain the ~nme adhesive properties as phenol formaldehyde it has been neces-sa~y to use larger quantities of lignin-containing organic solids hich reduces the advantages of this type of adhesive. Attempts have ~een made to modify kraft lignin with phenol formaldehyde to cause crosslinking of the lignin molecules. One such example dis~losed by Herrick et al in U.S. Patent 3,454,508 relates to a thermosetting phenolic resin in which an alcohol soluble poly-methylol phenol was condensed with an acid precipitated alkali lignin in a fugitive base such as ammonia. In another example, Ball et al in U.S. Patent 3,185,654 suggested a phenolic resin in which an A stage resole was reacted in methanol with an alkali - 1 - ~

~L~3~ 3 lignin. Neither Herrick nor Ball showed sufficient crossllnking between free methylol groups of the resole and hydroxyl groups in the lignin. These methods ~ailed to produce satisfactory water resistance and wet strength properties in the bonded produc-t.
Marton et al in a publication entitled "Lignin Structure and Reactions", Advances in Chemistry Series 59, American Chemical Society, Washington, D.C., pages 125 to 144, (1~66), reported a method of improving the reactivity of kraft lignin by introducing methylol groups into the lignin structure via an alkali catalyzed condensation with formaldehyde. Abe in a publication of the Hokkaido Forest Products Institute, No. 55 (1970) also extensively examined the mechanism of the lignin formaldehyde reaction in alkaline media and prepared plywood and particleboard adhesives based on the co-condensation o~
lignin with phenol and formaldehyde. Both these adhesives pro~
duced poor water resistance and wet strength properties in the bonded product. Enkvist in U.S. Patent 3,86~,291 describes a process for manufacture of an adhesive in which kraft or soda black liquor was methylolated with formaldehyde in the presence o* alkali and subsequently condensed with phenol or cresol form-aldehyde. However, plywood panels glued with this adhesive showed unsatisfactory wet strength after boiling.
Dolenko and Clarke in a published article entitled "~esin Binders from Kraft Lignin", Forest Products Journal No.8, p.41, August 1978, disclose MKL and phenol ~ormaldehyde mixtures which are prepared under acidic conditions. Such an adhesive cannot be prepared as an aqueous solution because MKL is insol~
uble in water under acidic conditions. Furthermore, when making wa*erboard having a thickness of 7/16" the article states that the press time has to be for seven minutes or more which is unsatisfactory in normal production facilities.

g~ '793 ~ ne purpose of the present invention is to provide a waferboard adhesive formed from isolated lignin that may be used at the same levels commonly used with phenol formaldehyde ad-hesives to provide strength properties that meet the requirements of CSA standards for waferboard. CSA 018~ (1975) lays down that the average static bending strength of waferboard test specimens taken from a single panel must be a minimum of 2,000 psi modulus of rupture (MOR), 400,000 psi modulus of elasticity (MOE), 40 psi internal bond (IB) and 1,000 psi MOR tested wet after boiling.
A waferboard adhesive is applied to wood wafers either by spraying when the adhesive is in a liquid form or alterna-tively, is mixed with the wafers when the adhesive is in a powder form. In some cases, the adhesive is applied to the wood wafers in both powder and liquid form.
Particleboard panels are generally prepared by spray-ing wood particles, referred to as furnish, with an adhesive mixture prior to a simultaneous pressure and heating step~
Composite lumber products, such as those disclosed in Barnes U.S. Patent 4,061,819 issued December 6, 1977, are made ~0 by coating straight wood strands with an adhesive mi~ture, generally by dipping, followed by a simultaneous pressure and henting step.
In the present invention methylolated kraft lignin (MKL) is prepared from black liquor, first by methylolation ~herein formaldehyde is added to strong black liquor followed by the addition of acid to the methylolated liquor. Suspension, dilution and filtration of the precipitate produces a filter ca~e of MKL organic solids. This filter cake may be dried and powdered, or alternatively an aqueous alkaline solution of MKL
may be prepared from the filter cake.
A commercially available water soluble phenol formalde-hyde resole resin (hereinafter referred to as PF) was used with ~36~93 the MKL. The PY was formed into an alkaline aqueous solution having a pH of at least about 7, or if in powder form had a pH
of at least about 9 ~hen one part mixed in ten parts water.
The quantity of adhesive in a waferboard, particleboard, composite lumber and the like, is generally measured in terms of percentage by weight of the total adhesive solids in the finished article. In the case of phenol formaldehyde the -total adhesive solids includes the resin solids which is the porti~n of the ad-hesive taking part in the condensation o~ the adhesive during the curing step. The term organic solids is used throughout the te~t especially in association with MKL. In a simple system, such as phenol formaldehyde, the organic solids are the same as the resin solids, howèver, in the case of MKL the organic solids may include other organic matter co-precipitated with the MKL.
The method of manufacturing composite wood products such as waferboard, particleboard, and lumber products containing ~vood strands includes coating wood pieces with an adhesive mi~ture followed by a simultaneous pressure and heating step. The improvement comprises the steps of applying water soluble phenol ~0 ormaldehyde resole resin (PF) in a liquid form, powder form or n combination o~ liquid and powder form to the wood pieces, the PF in powder orm having a pH of at least about 9 when one part ~y weight is mixed in ten parts water, and applying methylolated ~ra~t lignin (MKL) organic solids in a liquid form, powder form or combination of liquid and powder form to the wood pieces, wherein the MKL organic solids are up to about 70% by weight of the total organic solids in the adhesive mixture and wherein the adhesive mixture in liquid form has a pH of at least about 10 In a pre~erred embodiment an alkaline aqueous solution of PF
3Q having a pH of at least about 7 is mi~ed ~ith an alkaline aqu~ous solution of MKL having a pH of at least about 10. In another embodiment, an adhesive mixture in powder form is prepared by ~3~3 mixing PF in powder form having a pH of at least about 9 when one part mixed in ten parts water, with MKL in powder form such that the MKL organic solids are up to about 70~0 by weight of the total organic solids in the adhesive mixture, and blending the mixed powders with the wood wafers A still further embodiment provides an adhesive mixture in liquid form comprising a PF with up to about 70% by weight of the total organic solids in the ad-hesive mixture derived from an alkaline aqueous solution of MKL
organic solids, wherein the adhesive mixture has a pH of at least about 10.
In yet a further embodiment of a method for producing waferboard, MKL organic solids in powder form is first blended with the wood wafers followed by an application of an alkaline aqueous solution of PF having a pH of at least about 9 sprayed on the wafers. This method may also be carried out by applying the PF in powder form, such that the PF has a pH of at least about 9 when one part is mixed in ten parts water and then spraying the wafers with an alkaline aqueous solution of MKL having a p~ of at least about 10. Alternatively, a mixture of PF in powder form ~O Wit]l a pH of at least about 9 when one part is mixed in ten parts wnter and MKL in powder form may be blended with the wood wafers :followed by spraying the wafers with a mixture of an alkaline aque-ous solution o~ PF and an alkaline aqueous solution of MKL, the mixture having a pH of at least about 10. In all cases the MKL
organic solids may be up to about 70~0 by weight of the total or-ganic solids in the adhesive mixture deposited on the wafers.
One method of preparing MKL is from strong hlack liquor from the kraft process Kraft lignin in the strong black liquor is reacted with formaldehyde to produce MKL sometimes referred to as lignin formaldehyde. MKL is then separated from the black liquor by precipitation with sulfuric acid followed by filtration and ~vashing. The filter cake is dried and powdered or alternatively, the filter cake is mixed with water and an alkali metal base ~367~

such as sodium hydroxide is added to form an alkaline aqueous solutio~, In one embodiment, a satisfactory adhesive in liquid form was prepared based on a 60 to 40 ratio of MKL to PF based on the weight of the organic solids in the adhesive mixture.
The PF is preferably a commercially available resin with a pH
of at least about 7 when in liquid orm and preferably in the p~
range of about 9 to 11.
The MKL aqueous solution was first prepared by taking the ~ilter cake of MKL and dissolving it in an alkaline aqueous solution. The total solids content in the solution was approxi-mately 35% by weight which gave an organic solids content of 25 by weight. After mixing, the pH of the MKL solution was greater than 10. Next, an alkaline aqueous solution of PF with a pH of at least about 7 and having a total solids content of from 40%
to 55% was also prepared. The MKL and PF solutions were mixed to~ether into an adhesive mixture having MKL/PF 60/40 ratio based on the weight o-~ the organic solids and a pH at least about 10.
Wood wafers were initially sprayed in a drum blender ~0 with 2% molten wax to improve the water resistance of the wafers.
The ~dhesive mixture was then sprayed onto the wood wafers to ~ive an organic solids content of 2%. Here and throughout the d~sclosuxe organic or other solids contents are based on the oven dry ~eight of the wood wafers. It was found that ~afers bonded ~ith the 2% organic solids content MKL/PF adhesive mixture exhibited superior mechanical strength compared to waferboards glued with an organic solids content of 0.8% PF alone. The presence of MKL substantially improved dry and wet bending strength and internal bond. These results confirm that MKL possesses adhesive properties and is providing an active addition for the PF.
Mats of wafers were manually felted onto steel caul plates to a size of 20" x 24" (~08,0 mm x 60g.6 mm). Mats were ~36~93 then passed to a press which was heated to a platen temperature of 210C ~ 3 with a closing pressure of between 400-500 lbs/sq.
inch and pressed between 5 and 6 minutes at a constant thickness to produce test panels appro~imately 7/16" (11.1 mm) thick.
Boards were homogeneous in wa~er thickness, moisture content and adhesive content, and the density ranged between 40 and 42.5 lbs/cu.ft. MOR, MOE, IB and accelerated aging tests as specified in CSA 0188 (1975) were used to evaluate the mechanical strength and durability of the boards.
MKL/PF powder adhesives were formulated by combining MKL in powder form which had been dried to about 95% total solids (i.e. about 5% moisture) at 50~C with a commercially available resole in powder form having a pH of at least about 9 when one part is mixed with ten parts water, The dry powders were mechanically blended in a rolling ball mill or mixed in an elec-tric blender to form an adhesive powder mixture having an MKL/PF
ratio of 50:50 based on the weight of the organic solids. Pre-ferably at least 80~ of the mixed powders passed through a 325 mesh screen. Wood wafers were initially sprayed in a drum blender ~0 with 2% molten wax followed by 2% of the adhesive powder mixture based on the oven dry weight of the wafers. The adhesive powder mixture was either put on as a blend of the MKL/PF or alternatively as put on in two stages, either the MKL first or the PF first.
MKL/PF powder adhesives were also prepared by taking a liquid adhesive mixture of MKL and PF, having a pH of at least about 10, and spray drying the liquid to a solid cake, then ball milling the cake to a powder. The liquid mixture is prepared ~rom an alkaline aqueous solution of MKL having an alkali metal such as sodium hydroxide therein. In all cases the MKL organic solids are up to about 70% by weight of the total organic solids in the adhesiveO

Mats of wafers were manually felted onto steel caul ~3~i7~3 plates, boards were homogeneous in wa~er thickness, moisture content and adhesive content, and the density ranged between 40 and 42.5 lbs/cu~t. Panels were then passed to the press which was heated to a platen temperature of 210C + 3 with a closing pressure of between 400-500 lbs/sq.inch. The panels were pressed to a constant thickness to produce test specimens of 7/16" thick.
The panels showed superior bond qualities to panels bonded with 1% PF resin alone or to panels bonded with 1% PF and 1% of a clay extender.
It was found the mechanical strength of waferboard panels was dependent on the ratio of MKL to PF in the formulation.
Satisfactory panel properties were achieved at PF replacement levels between 25 and 60~o. I f the level of PF substitution exceeded 50%, the accelerated aging MOR and IB strength decreased ~0 ~ 4 q~7~

while the MOR and MOE remained constant Nevertheless, up t~ about 70% of the PF resin solids used in the manu-facture of waferboard panels may be replaced by MKL while still meeting the specifications o~ CSA 01~8 (1975) accelerated aging test for waferboard.
Separate (two part) addition of the PF and MKL powders to the flakes yielded waferboard panels exhibiting weaker dry and wet strengths than panels glued with pre-mixed and ball milled powders at the corresponding MKL/PF formulation, When the adhesive components were applied separately, satisfactory properties were nevertheless obtained for the waferboard panels using up to 50% MKL. MKL/PF formulations which were blended in an electric mixer prior to use, gave results intermediate between the ball milled and two part adhesive systems.
Waferboard panels glued with 60/40 MKL~PF liquid formulations, in which the ratio of NaOH~MKL (organic solids~ for the alkaline aqueous solution of MKL ranged between about 0.3/1.0 (7.5% NaOH) and 0.15/1.0 (3.9% NaOH) exhibited satisfactory mechanical strength. Waferboard panels having satisfactory strength proper~ies were also manufactured by applying 1% MKL
powder followed by spraying the wood wafers with 1% PF liquid to give an overall 50/50 MKL/PF formulation. In another series of tests~ waferboard panels were produced by applying 1~ PF
powder to the wood wafers followed by spraying the wood wafers with a 1% bIKL liquid, the liquid being-an alkaline aqueous solution having a pH greater than 10. Waferboard panels may also be prepared by applying a mixed PF and MKL powder to the wood wafers followed by spraying with an alkaline aqueous solution o~ a mix-ture of MKL and PF.

In all cases in the preparation o~ waferboard panels of 7/16" thickness according to the present invention, it has been found that press times of not more than six minutes can be ~36~7~3 employed while still meeting the specifications of CSA ~188 (1975)-Particleboard panels were prepared with 50/50 MKL/PFliquid formulations with an organic solids content from 4 to 8%
based on the dry weight of the furnish. The panels met the specifications of CSA 0188 (1975) and were superior to panels glued with an equivalent amount of PF alone.
Discrete dimensioned structural lumber products were prepared with 50/50 MKL/PF liquid formulations with an organic solids content of approximately 5% based on the dry weight of straight wood strands. The products were compared with samples made using 5% PF resin solids and did not show any drop in strength properties.

~36~

1280 grams of ~ormaldehyde (37%) was stirred at room temperature for 72 hours with 8000 grams o~ kra~t strong black liquor having a pH between 12 and 13 containing 48.2% total solids and 16% kraft lignin solids as determined spectrophoto-metrically. 840 grams of concentrated sulfuric acid was then added to the methylolated black liquor with high speed mixing.
The resulting pH of the final mixture was between 4 and 6.
The suspension was diluted to twice its original volume, filter-ed using a fritted glass funnel, washed with several portions of water, and dried in a forced air oven at 30C for 18 hours, To increase the drying rate, the filter cake was periodically broken down into smaller particles during the drying operation.
Typical analysis of MKL filter cake Total solids 72,1%
Ash 13.0%
Lignin (spectrophotometric) 84.0%
Organic solids (100% less ash) 87.0%
All analyses except total soIids were based on oven dry (o,d.) ~O weight of total solids.

50/50 MKL/PF adhesives were prepared by combining MX~ powder, which had been further dried to ~95% total solids at 50C, with a PF powder on the basis of MKL organic solids to PF total solids. The PF powder had the following analysis.
Total solids 92.3%
Ash (o.d. basis) 4.9%
Resin solids 87.8%
pH (1 part in 10 parts water) 9.8 ~0 ~L3~i793 The dried MKL and PF p~wders were either directly applied to the flakes or mechanically blended in a rolling ball mill or electric mixer prior to application.
Waferboard panels were prepared with 50/50 MKL/PF
at an organic solids content of 2%. Control panels were made with the same phenolic powder at a content of 1% and 2%.
Another set of control panels was prepared with 1% PF and 1%
of a clay extender, Plygel* III. The Plygel/PF adhesive was formulated by mixing Plygel III with PF in an electric blender at a l:l ratio based on o.d, solids.
Four 7/16" ~llOl mm) waferboard panels were manu-factured with each binder at the following conditions:
Wax 2% (100% o.d. solids) Press Temperature 210C (410F) Pressure 2,760 kPa (400 psi) Press Time 6 minutes *Registered Trade Mark ~3~7~3 _ e W ~ ~ ~ 1 ' _ o~ ~ ~ ~ ~ u~ a ~; _~ Q, ~ ~
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As may be seen ~rom Table 1, wa~erboard panels b~nded with MKL/PF exhibited superior mechanical strengt'n compared to panels glued with either P~ alone or a combination o~
an inorganic extender and PF. The presence o~ MKL signi~i-cantly improved dry and wet bending strength and internal bond.
This result con~irmed that MKL is acting as an ad-hesive and is providing an active addition to the PF.

A binder was prepared by grinding MKL and PF powders in a rolling ball mill prior to blending with the wafers so that at least 80% of the mixed powder passed through a 3~5 mesh screen. The PF powder had a pH of at least about 9 when one part was mixed in ten parts water.
Four 7/16" (11.1 mm) waferhoard panels were manu-~actured with each binder at the following conditions:
Organic solids content 2%
Wax 2% (100% o.dO solids) Press temperature 210C (410F) Pressure 2760 kPa (400 psi) Press time 6 minutes ADHESIVE STRENGTH PROPERTIES
_ 3 Accelerated Aging MKL/P~ MOR psi MOE 10 psi IB psiMOR psi 60/40 2610 670 58 10~0 2590 557 ~0 1230 , ~367~3 As may be seen from the above Table 2, between 60%
and 70% of the PF used in the manufacture of wa~erboard panels may be replaced by MKL organic solids while still achiev-ing satis*actory strength properties.

An MKL~PF powder was prepared and used in the production of waferboard panels. Preparation of the powder was done in three separate methods.
Method A MKL powder and PF powder were ground two -hours in a rolling ball mill prior to blending with the wafers.
Method B PF powder was first blended with the wafers, ~lKL powder (92% passed through 325 mesh) was then added.
Method C PF powder was mixed with MKL powder in an electric blender before application to the wafers. In all cases, the PF powder had a pH of at least about 9 when one part was mixed in ten parts waterO
Four 7/16" (11.1 mm) waferboard panels were manu-factured for each set of conditions:
Organic solids content 2%
~0 ~Yax 2% (100% o.d. solids) Press Temperature 210C (410F) Pressure 2760 kPa (400 psi) Press time 6 minutes ~3~7~3 ADHESIVE STRENGTH PROPERTIES
_ _ MOE 103 Accelerated Aging MKL/PF METHOD MOR psi . psi IB psi MOR psi .

50/50 ~3090 622 681450 ~0/40 A2610 670 581040 ~2590 557 601230 BL ZOID ~J~ L 640 I

A - ball milled B - separate application C - mixed in electric blender As may be seen from Table 3, approximately 60% to 70%
o~ the PF po~der used in the manu~acture of waferboard panels may be replaced by MKL powderO Excellent mechanical strength properties were obtalned if the MKL and PF powders were mech~nically blended prior to application of the wafers. The intel~nal bond strength improved significantly if MKL and PF
powders were ground by ball milling before blending with the wafers. This preparative method produced the finest particle size and the most intimate mixing of the two materials resulting in excellent adhesive organic solids distribution on the flakes.

Waferboard panels were prepared with a series o~
30 60/40 MK1/PF liquid formulations at an organic solids content of

2%, based on the dry weight of the furnish.
The 60/40 ~KL~PF liquid was formulated by blending an _ 14 -~L~36~3 alkaline solution o~ MKL (35.1% o.d. solids, 25.0% organic solids, 7.5% NaOH) having a pH of 12.9 together with PF liquid on the basis o~ MKL organic solids to PF resin solids.
In the case o~ resin A, the MKL/PF liquid mixture had a pH o~
12.7, and in the case of resin C, the MKL/PF liquid mixture had a pH of 11.7. In each case the resulting mixture was sprayed onto the flakes. Control panels were made with the corresponding PF liquid at an organic solids content of 0.8% by leaving out the MKL component from the adhesive mix-ture. Other control panels were prepared to an organic solidscontent of 2%, in this case using the PF liquid composi-tions as indicated in Table 4.
Four 7/16" (11.1 mm) panels were prepared for three dif~erent adhesive ~ormulations under the following conditions:
Wax 2%
Press Temperature 210C (410F) Pressure 2760 kPa (400 psi) Press Time 6 minutes The PF ~ormulations were ~s foll~ws:

PF RESI~ A B
_ _ , TOTAL SOLIDS % 47.653.6 42.4 ASH, (o.d. basis) % 11.3 7.3 3.7 RESIN SOLIDS, % 42.249.7 40.8 pH 10.510.3 9.2 VISCOSITY AT 20C, CENTIPOISES75 140 _ 15 -~L367~3 ~ o o o o o C o o o ¢ ~ o ~ ~ o~ ~ o ~ ~ o ~ c~ o u~ O a) ~
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. . _ ~367~3 The results in Table 5 show that all panels bonded with the MKL/PF mixture meet the specifications of CSA 0188 (1975~, and are superior to panels glued with (0.8%) PF
alone. These results con~irm that MKL possesses adhesive properties and is providing an active addition to the PF.

Alkaline solutions of kraft lignin (KL) and MKL were prepared as follows, from isolated KL which contained (95.0%
total solids, 1.7% ash).
Parts by Weight Constituents MKL
Kraft Lignin (93.5% organic solids) 107 107 Water 188 188 Sodium hydroxide (flake) 30 30 Formaldehyde (37%) 75 These mixtures were allowed to stand at room tempera-ture for approximately 96 hours. The KL solution was then diluted to 25.0% KL organic solids with 75 parts of either water or formaldehyde prior to blending with the PF. The alkaline solution of MKL was used as originally prepared.
Tnree waferboard adhesives were formulated by replac-ing 70% o~ PF resin solids with KL organic solids derived from MKL, KL water, or KL formaldehyde. The PF in liquid form had a pH of ~t least about 7 Four 7/16" (11.1 mm) waferboard panels were manu-factured with each adhesive at the following conditions:
Organic solids content 2%
Wax 2% (100% solids) Press 210 (410F) Pressure 2760 kPa (400 psi) Press Time 5 minutes ~36~7~3 _ h ~ O O O
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As shown in Table 6, the dry strength of waferboard bonded with PF formulations modified wlth KL containing free formaldehyde and MKL were similar and in both cases signi-ficantly better than the properties of panels glued with a mixture of unmodified KL and PF, This can be taken as evidence that the presence of formaldehyde either free or bound as in MKL increases the reactivity of lignin with respect to the PF.
The superior wet strength after accelerated aging and water resistance of MKL/PF panels confirms that the condensa-tion o* lignin with ~ormaldehyde is necessary, prior to blending with the PF so that a highly cross linked waterproo~
bond is obtained after hot-pressing.

Waferboard panels were glued with MKL/PF liquid *ormulations in which between 25 to 70% of the PF resin solids was replaced by MKL organic solids. The PF in liquid form had a pH of at least about 7.

Four 7/16" (11.1 mm) boards were manufactured with each adhesive at the following conditions:
Organic solids content 2%
Wax 2% (100% o.d. solids) Press Temperature 210C (410F) Pressure 2760 kPa (400 psi) Press Time 5 and 5~ minutes _ 19 --~L3~793 b~ U~ O O O O O O O O
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~36~7~3 As seen in Tables 7 and 8, the mechanical strength o~ waferboard panels bonded with MKL/PF liquid adhesive was dependent on the ratio of MKL/PF in the formulation. Equivalent dry bending strengths (MOR) were achieved at PF replacement levels between 25% and 60%, while the accelerated aging MOR and IB strengths decreased with decreasing PF content. Approxi-mately 60% to 70% of the PF used in the manufacture of wafer-board panels can be replaced by MKL, while still meeting the requirements of CSA 0188 (1975).

MKL liquid formulations were prepared in which the ratio of NaOH/MKL (organic solids) was varied, namely 0.30/1.0 (7.5% NaOH) to give a pH of 13.1, 0.23/1.0 (5.7% NaOH) to give a pH of 13.1 and 0.15/1.0 (3.9% NaOH) to give a pH of 11.7.
The resulting alkaline solutions containing approximately 25~
organic solids ~ere blended with PF liquid (Resin A) to give a 60/4~ MKL/PF adhesive and pH of 12.5, 11.5 and 10.9 respectively.
Four 7/16" (11.1 mm) waferboard panels were manu-factured with each adhesive at the following conditions:
Organic solids content 2%
~a~ 2% (100% o.d. solids) Press Temperature 210C (410F) Pressure 2760 kPa (400 psi) Press Time 5~ minutes ~36793 ~ .
sb~,ln bD~ O O O
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t _ 23 --~L~36~13 Waferboard panels bonded with these adhesives have equivalent mechanical strength properties, as shown in Table 9.

MKL was dried to ~95% total solids at 50C to give a free flowing powder. 1% MKL organic solids, based on the dry weight of the wafers, was applied to the wafers followed by spraying of 1% PF liquid having a pH of at least about 9.
In a second series an alkaline solution of MKL con-sisting of 35.1% total solids, 25.0% organic solids, 7.5% NaOH
was ~ormulated. 1% PF in powder form based on the dry weight of the wafers was applied to the wafers ~ollowed by spraying of 1% organic solids derived ~rom the alkaline solution of MKL. The PF in powder form had a pH ~f at least about 9 when one part is mixed in ten parts water.
Waferboard panels (7/16") were manufactured with each adhesive at the following conditions:
Organic solids content ~%
~rax 2% (100% o.d. solids) Press Temperature 210C (410F) Pressure 2760 kPa (400 psi) Press Time 6 minutes _ 24 -~3~

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~36'7~3 As seen in Table 10, waferboard panels glued with adhesive mixtures of either MKL powder and PF liquid or MKL liquid and PF powder ~ave satisfactory physical pro-perties. Ball milling the PF powder to reduce particle size resulted in a significant improvement in strength pro-perties. Since both MKL and PF can be used in either liquid or powder form, the composition of the adhesive mixture may be varied by changing the proportion of MKL to PF either of which may be in the form of liquid or powder or combination of liquid and po~vder.

Particleboard panels were prepared with 50/50 MKL/PF
adhesive mixture formulated by blending an alkaline solution of MKL, having 35.1% oven dried solids, 25.0% organic solids and 7.5% NaOH. The solution had a pH of 12.9 and was mixed with an alkaline solution of PF. Panels were made with an organic solids content from 4 to 8% and were compared with panels made using PF resin alone.
The panels were prepared under the following conditions:
~0. Wax 1% (48% solids) Press temperature 210C
Pressure 450 psi Press time 12 minutes Particleboard furnish was sprayed with wax and adhesive mixture. The furnish was then classified according to particle si3e and hand felted. The finest particles were on the board surface, the coarsest near the centre. Panels were pressed to ~/8 inch thickness with a specific gravity of 0.75. Table 11 confirms that the adhesive mixture produces panels having strength properties approximately equal to the panels made with PF resin alone.

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~36~7~3 Blocks of a discrete dimensioned structural lumber product were made by pressing and simultaneously heating straight wood strands sprayed with an adhesive mixture in a mold. The adhesive mixture was 50/50 MKL/PF and approximately 5% organic solids of the mixture were used in the blocks. The pH of the ad-hesive mixture was at least about 10. Comparison block samples ~vere made using approximately 2.5 and 5% PF resin solids.
The strands were sprayed with the required weight of adhesive mixture and pressed under the following conditions:
Press temperature 170C
Pressure approximately 200 psi The finished blocks were cut into samples and tested for MOR and MOE. The results are shown in Table 12 which con-firms that 50% MKL organic solids does not result in any sig-nificant drop in strength properties.

ADHESIVE FORMULATION STRENGTH PROPERTIES
. . . _ _ _ Adhesive Specific MOR MOE
Solids % Gravity psi 106 psi ..
PF 4.8 0.568 9820 1.69 5.1 0.569 9560 1.74 50/50 MKL/PF 5.0 0.563 8i20 1.65 4.9 0.568 9430 1.70 PF 2.8 0.541 4260 1.44 2.5 0.543 4260 1.47 , _ 28 -

Claims (19)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method of manufacturing composite wood products selected from the group consisting of waferboard, particleboard and lumber products containing wood strands, where-in wood pieces are coated with an adhesive mixture followed by a simultaneous pressure and heating step, the improvement com-prising the steps of applying water soluble phenol formaldehyde resole resin (PF) in a liquid form, powder form or combination of liquid and powder form to the wood pieces, the PF in powder form having a pH of at least about 9 when one part by weight is mixed in ten parts water, and applying methylolated kraft lignin (MKL) organic solids in a liquid form, powder form or combination of liquid and powder form to the wood pieces, wherein the MKL
organic solids are not more than about 70% by weight of the total organic solids in the adhesive mixture, and wherein the adhesive mixture in liquid form has a pH of at least about 10, said adhesive mixture being substantially free of black liquor components other than lignin.

2. In a method of manufacturing a composite wood pro-duct selected from the group consisting of waferboard, particle-board and lumber products containing wood strands, wherein wood pieces are coated with an adhesive mixture followed by a simul-taneous pressure and heating step, the improvement comprising the steps of forming an adhesive mixture by mixing water soluble phenol formaldehyde resole resin (PF) with not more than about 70% by weight of the total organic solids in the adhesive mixture derived from an alkaline aqueous solution of methylolated kraft lignin (MKL), the adhesive mixture having a pH of at least about 10, said adhesive mixture being substantially free of black liquor components other than lignin and applying a layer of the adhesive mixture to the wood pieces.

3. The method according to claim 2 wherein the PF is in the form of an alkaline aqueous solution having a pH of at least about 7, and the alkaline aqueous solution of MKL has a pH
of at least about 10.

4. The method according to claim 3 wherein the alkaline aqueous solution of PF has a pH in the range of about 9 to 11.

5. The method according to claim 2 wherein the alkaline aqueous solution of MKL is produced by first reacting formalde-hyde with black liquor, precipitating MKL from the mixture by the addition of acid, diluting and filtering the precipitate and dissolving the precipitate in an aqueous solution containing an alkali metal base.

6. The method according to claim 5 wherein the alkali metal base is sodium hydroxide.

7. In a method of manufacturing waferboard wherein wood wafers are coated with an adhesive mixture followed by a simultaneous pressure and heating step, the improvement compris-ing the steps of forming a powdered adhesive mixture by mixing water soluble phenol formaldehyde resole resin (PF) in powder form with not more than about 70% by weight of the total organic solids in the adhesive mixture derived from methylolated kraft lignin (MKL) organic solids in powder form, said adhesive mixture being substantially free of black liquor components other than lignin, and blending the mixed powders with the wood wafers, wherein the PF has a pH of at least about 9 when one part mixed in ten parts water.

8. In a method of manufacturing waferboard wherein wood wafers are coated with an adhesive mixture followed by a simultaneous pressure and heating step, the improvement of apply-ing water soluble phenol formaldehyde resole resin (PF) in powder form to the wood wafers and blending the PF powder with the wood wafers, adding methylolated kraft lignin (MKL) organic solids in powder form to the wood wafers and blending the MKL
powder with the wood wafers, the MKL powder being not more than about 70% by weight of the total organic solids in the adhesive mixture and the PF having a pH of at least about 9 when one part mixed in ten parts water, said adhesive mixture being substantially free of black liquor components other than lignin.

9. In a method of manufacturing waferboard wherein wood wafers are coated with an adhesive mixture followed by a simultaneous pressure and heating step, the improvement of applying methylolated kraft lignin (MKL) organic solids in powder form to the wood wafers and blending the MKL powder with the wood wafers, adding a water soluble phenol formaldehyde resole resin (PF) in powder form to the wood wafers and blending the PF powder with the wood wafers, the MKL powder being not more than about 70% by weight of the total organic solids in the adhesive mixture, and the PF having a pH of at least about 9 when one part mixed in ten parts water, said adhesive mixture being substantially free of black liquor components other than lignin.

10. In a method of manufacturing waferboard wherein wood wafers are coated with an adhesive mixture followed by a simultaneous pressure and heating step, the improvement comprising the steps of applying methylolated kraft lignin (MKL) organic solids in powder form onto the wood wafers followed by spraying an alkaline aqueous solution of phenol formaldehyde resole resin (PF) having a pH of at least about 9, onto the wood wafers, the MKL organic solids content being not more than about 70% by weight of the total organic solids in the adhesive mixture applied to the wood wafers, said adhesive mixture being sub-stantially free of black liquor components other than lignin.

11. In a method of manufacturing waferboard wherein wood wafers are coated with an adhesive mixture followed by a simultaneous pressure and heating step, the improvement compris-ing the steps of applying water soluble phenol formaldehyde resole resin (PF) in powder form onto the wood wafers followed by spray-ing an alkaline aqueous solution of methylolated kraft lignin (MKL) having a pH of at least about 10, onto the wood wafers, the MKL organic solids content being not more than about 70% by weight of the total organic solids in the adhesive mixture applied to the wood wafers, and wherein the PF has a pH of at least about 9 when one part mixed with ten parts water, said adhesive mixture being substantially free of black liquor components other than lignin.

12. In a method of manufacturing waferboard wherein wood wafers are coated with an adhesive mixture followed by a simultaneous pressure and heating step, the improvement comprising the steps of applying a water soluble phenol formaldehyde resole resin (PF) and methylolated kraft lignin (MKL) organic solids powder mixture onto the wafers followed by spraying an alkaline aqueous solution of a mixture of PF and MKL onto the wood wafers the MKL organic solids content being not more than about 70%
by weight of the total organic solids in the adhesive mixture applied to the wood wafers and wherein the PF powder has a pH of at least about 9 when one part mixed with ten parts water, and the alkaline aqueous solution has a pH of at least about 10, said adhesive mixture being substantially free of black liquor com-ponents other than lignin.

13. In a method of manufacturing waferboard panels wherein wood wafers are coated with an adhesive mixture followed by a simultaneous pressure and heating step, the improvement com-prising the steps of forming an adhesive mixture by mixing phenol formaldehyde resole resin (PF) with not more than about 70% by weight of the total organic solids in the adhesive mixture derived from an alkaline aqueous solution of methylolated kraft lignin (MKL) the adhesive mixture having a pH of at least about 10, drying the adhesive mixture to a powder form and blending the adhesive mixture in powder form with the wood wafers, said adhesive mixture being substantially free of black liquor components other than lignin.

14. An adhesive mixture in powder form comprising water soluble phenol formaldehyde resole resin (PF) in powder form with not more than about 70% by weight of the total organic solids in the adhesive mixture derived from methylolated kraft lignin (MKL) organic solids in powder form and wherein the PF
has a pH of at least about 9 when one part mixed in ten parts water, said adhesive mixture being substantially free of black liquor components other than lignin.

15. An adhesive mixture in liquid form comprising a water soluble phenol formaldehyde resole resin (PF) with not more than about 50% by weight of the total organic solids in the adhesive mixture of an alkaline aqueous solution of methylolated kraft lignin (MKL) organic solids, wherein the adhesive mixture has a pH of at least about 10, said adhesive mixture being substantially free of black liquor components other than lignin.

16. The adhesive mixture according to claim 15 wherein the alkaline aqueous solution of MKL contains an alkali metal base.

17. The adhesive mixture according to claim 15 when dried into powder form.

18. The adhesive mixture according to claim 14 with not more than about 50% by weight of the total organic solids in the adhesive mixture derived from MKL organic solids.

19. The method according to claim 1 or claim 2 wherein the PF is mixed with not more than about 50% by weight of the total organic solids in the adhesive mixture derived from MKL
organic solids.