CA2042476C - Fast cure and pre-cure resistant cross-linked phenol-formaldehyde adhesives and methods of making same - Google Patents

Abstract

Fast cure and "pre-cure" resistant thermosetting adhesives and methods for their production useful for binding lignocellulosic materials together, are disclosed.
A fast curing adhesive is obtained by cross-linking binary phenol-formaldehyde consisting of high average molecular weight phenol-formaldehyde (PF) resin and low average molecular weight PF resin with lignin. A
"pre-cure" resistant adhesive is obtained by cross-linking a PF resin, such as binary phenol-formaldehyde, with a lignin with the addition of ammonia preferably in the form of an ammonium salt. The lignin may be obtained from different wood pulping waste materials including that recovered from the sulphite, kraft, organic extract or steam hydrolysed wood pulping processes. The adhesive can be produced as an aqueous solution or dispersion, and used in either a basic or acidic environment. The quick setting and "pre-cure" resistant adhesives are inexpensive to produce and both display improved adhesion characteristics when compared with existing adhesives prepared from wood waste products. The adhesives also compare advantageously to a variety of existing commercial phenolic resin presently being used in the manufacture of wood composite products such as waferboards. These adhesives are capable of being spray dried more easily and produce higher yields, when compared with existing wood waste products which have been cross-linked with commercial PF resin or to a variety of existing commercial phenolic resins.

Description

1 2o~2~~s FAST CURE AND PRE-CURE RESISTANT CROSS-LINKED PHENOL-FORMALDEHYDE
ADHESIVES AND METHODS OF SAME
Field of Invention The present irnrention relates to a new and useful fast curing thermosetting adhesive comprised of cross-linked binary phenol-formaldehyde and lignin and additionally, an adhesive which can be rendered "pre-cure" resistant, as well as the methods of preparing same. The fast curing axxi "pre-cwre" resistant adhesive may be used in the preparation of manufactured lignocellulosic products such as boards and panels employing sawdust, wood chips, wood wafers and the like.
Back~of Invention Phenol-formaldehyde (PF) adhesive resins have long been used as thexmosetting binders in the preparation of manufactured boards or panels. Ntmiero~zs attempts have been made to develop suitable substitute adhesives, which utilize wood waste, in order to not only meet growing envirormuental concerns, but to also reduce the dependence upon petroleum based constituents, the availability and cost of which is ir~reasingly uncertain.
These attempts have incl~ied efforts to develop suitable adhesive binders l~r using PF to cross-link other possible adhesive constituents, including one or more waste products of wood processing.
Unfortunately, to date these efforts have met with only limited success.

The range of wood waste products which have been sua:~sfully cross-linked is limited, and the methods used to produce these adhesive binders have been slow and laborious, often requiring pretreatment of the waste product constituent. Furthermore, the cure time and adhesion characteristics of these adhesive binders have been such that widespread use or acceptance of these substitutes by the manufactured board industry has not occurred. For example, it is often the case that the adhesive binder must be used under acidic conditions. However, board and panel manufacturers prefer to operate in an alkaline environment, since less wear and tear is encountered by production equipment.
In U.S. Patent No. 2,786,008 issued on March 19, 1957 -Herschler, an adhesive binder consisting of phenol-formaldehyde (PF) and ammonium based spent sulphite liquor (NH,SSL) is disclosed. In addition to producing an acidic adhesive which is slow curing, the method disclosed by HexsCnler is laborious and time-cons, as it is necessary to make the alkaline PF "acid tolerant" in order to avoid precipitation of the PF resin upon mixing of same with the acidic spent sulphite liquor.
Another example of using PF to cross-link a wood waste product is that disclosed in U.S. Patent no. 4,113,675 issued on September 12, 1978 - Clarke et al. , wherein methylolated lignin was cross-linked by an acid catalyzed low molecular weight PF resin. It was observed that kraft lignin was itself not sufficiently reactive to under significant cross-linking with PF, and that it was thus necessary to pre-react the lignin with a methylolating agent, such as formaldehyde, so as to introduce methylol groups to the lignin molecule. Moreover, it was indicated that in order to achieve satisfactory cross-linking on curing, the pH of the binder must be acidic. Finally, the adhesive disclosed in Clarke et al. was found to be relatively slag curing.
In Canadian patent 1,214,293 issued on November 18, 1986 -Calve et al., an adhesive consisting of ammonium based spent sulphite liquor (NH,SSL) cross-linked by a co~m~ercial PF is disclosed. It was found that while PF r~rmally precipitates when in acidic solution with NfI,SSL, a useful adhesive could be obtained if the NI-~SSL-PF were maintained in dispersion through rigorous stirring or agitation.
Again, acidic conditions, of pH 3 to 7, were required to provide acceptable modulus of rupture (NR~R) test results on waferboard and particleboard manufactured with the adhesive.
In U.S. patent 4,127,544 issued on November 28, 1978 -Allan, a process for the partial substitution of ammonium lignosulfonate for phenol in alkaline p~henolic-aldehyde resin adhesives is described. However, the NHaSSL is first pre-reacted with phenol at a temperature range of 150-300'C under autogenous pressure prior to condensation with formaldehyde under alkaline conditions. The reaction at high temperature and pressure is expensive. Also, no wood adhesive bond test data were provided.

. 4 2042476 In U.S. patent 4,324,747 issued on April 13, 1982 - fudan et al, a resin where an alkaline phenol-formaldehyde resin is simply mixed with a kraft pulping liquor and use to bond waferboard is disclosed. The p~henolic resin is prepared by refluxing phenol and formaldehyde in the presence of zinc acetate or heating at lowpx t~per~ature in the presence of calcium oxide. No reference to adjt>stment of molecular weight distribution of the phenolic resin or example of addition of ammonium salt is provided. This type of resin is slow curing and not "pre-cure" resistant.
To be acceptable for industrial use, a new adhesive mast meet certain criteria. For example, it must be available as a spray dried powder or stable liquid; be quick setting if it is employed as a core adhesive for thick multi-layer panels where the resin is far frrnn the heating source, or be "pre-cure" resistant if it is employed for boaxling a monolayer panel or the face of a arnzlti-layer panel. If the resin cures prematurely while the mat is resting on a hat Gaul plate before pressing or at first contact with the press platens before sufficient pressure is applied to consolidate the mat, a poor bond will ensue.
In the aforementioned examples and elsewhere, it has not been suggested or contemplated that the PF onent of the adhesive be modified or specially constituted to enhance the cross-linking of the wood waste product component of the adhesive.

Inlhile a two component or "binary PF" resin, comprised of a mixture of high average molecular weight PF and low average molecular weight PF components, has long been used in the manufacture of board, heretofore, the low molecular weight PF has been added to enhance resin 5 flora with mininann dry-out. Its unique reactivity to produce a quick setting resin when used in oarnbination with wood waste, especially polydisperse lignin, has not been recognized and its use in ooanbination with wood waste product not contemplated.
For example, in U.S. patent no. 4,269,949 issued on May 26, 1981 - Iiickson et al, there is disclosed a binary PF resin comprised of a mixture of high and low molecular weight resins, particularly suitable for use in hardboard applications, acing to the minimum dry-out exhibited by the adhesive.
In U.S. patent rte. 4,433,120 issued on February 21, 1984 -Chiu, it was demonstrated that a liquid binary PF resin having low viscosity and laa surface tension could be used for efficient spray application as fine droplets in waferboard manufacture. The liquid binary PF resin has limited pre-cure resistance due to the presence of the slower curing laa molecular weight phenolic resin which is however not sufficient for a surface resin. Although the liquid binary PF
resin exhibited some pre-cure resistance, this resin is relatively expensive to produce, and displayed only limited pre-cure resistance.
It is also difficult to spray-dry without advancing the resin and reducing its pre-cure resistance.

In a recent study Step and Kutscha (Wood and Fiber Science, 19(4), 1987, pp. 353-361) fractionated a phenol-formaldehyde resin into a high and low molecular weight resin by ultrafiltration and c~pared the adhesive properties of each fraction to the unfractionated PF resin. They found that: "the high molecular weight resin fraction performed nearly as well as the unfractionated resin". The presence of low molecular weight phenol-formaldehyde only slightly improve the characteristic of the PF resin, and is not essential to the process.
'SLy Qf Invention On the contrary to previous findings, it has been ford that a mixture of a binary PF and a polydisperse lignin, shows an unexpected high adhesive reactivity.
While in previous work, different types of phenolic resin were required, for example, with kraft or sulphite lignin which have different molecular weight distribution, in accordance with this invention results better than previous were obtained with a binary PF
resin cross-linker for the lignin and independently of the lignin origin. 4vlhile high molecular weight PF resin could be used alone as adhesive, with a wood waste product such as lignin, the presence of both high and low molecular weight pher~lic resin is needed to produce a fast curing adhesive composition and a strong weather resistance joint. The use of high or low molecular weight PF alone with a wood waste produce such as lignin, results in a weak bond, while a balance position of high molecular weight PF, low molecular weight PF and 2o~2~~s lignin has been found to result in an adhesive with curing and strength properties similar to a fast curing ocqrnnercial phenolic resin. Both high and low molecular weight PF cross-link the lignin which is itself a mixture of high and low molecular weight particles. The small phenolic molecules are also believed to link the high molecular weight lignin polymer as the resin is cured ~lhile the large phenolic molecules link the smaller lignin molecules. This system can also be used under acidic conditions, as a water solution or dispersion.
It has also been found that the lignin, as well as their uses as a water dispersion, improves the facility of spray drying of the phenolic system resulting in a higher yield. This is regarded as important since a resin which spray drys more easily can be produced at a higher rate, increasing productivity.
In acaordanGe with yet another aspect of this invention, the inexpensive resin can also be made to exhibit improved pre-cure resistance which is important when used as a liquid or spray-dried powder face adhesive for three-layer composite products, such as waferboard.
This was achieved by simple mixing a phenol-formaldehyde resin (one which Gould be used as core adhesive for a 3-layer panel, for example), a relatively large quantity of a lignin and an ammonium salt. The use of ammonium spent sulphite liquor is preferred as lignin source as it already contains the ammonium salt component. If kraft, steam hydrolysed, organic extract, SSL of other cooking base or glucose was employed, the resin flow and pre-cure resistance is capable of being controlled by addition of ammonium hydroxide and ammonium salt such as ammonium sulphate, ammonium p-tolenesulfonic acid or ammonium chloride. The use of low molecular weight lignin is often preferable as it will help to control the flow of the resin. Upon addition of sodium hydroxide or a strong base other than ammonium hydroxide, the resin was found to loose some of its pre-cure resistance. Although the presence of a lignin is much preferred, it was also found possible to slightly improve the pre-cure resistance of a phenolic resin by adding directly to it an ammonium salt.
The use of a binary PF resin is preferred for pre-cure resistance in the presence of lignin and ammonium salt.
As indicated above, the present invention contemplates using binary PF to cross-link wood waste lignin in order to provide a novel quick-curing thermosetting adhesive. By employing a binary PF, it is not necessary to include the additional step of pretreating (by methylolation) lignin as was the case in Clarke et al (supra.). Furthermore, contrary to the results indicated in Canadian Patent 1,214,293, it has been found that sodium based spent sulphite liquor (NaSSL) can be employed as an adhesive component where binary PF is utilized. Importantly, satisfactory results are obtainable where the adhesive is employed under alkaline, as well as acidic, conditions. Not only is the adhesive of the present invention relatively simple to produce, but it is also quick-curing, easy to spray-dry and demonstrates improved adhesion characteristics.
An adhesive having the foregoing quick or fast curing qualities is produced by reacting preferably by mixing the binary PF in solution with lignin which advantageously, can be obtained from wood, pulp, waste, such as that produced in the sulphite, kraft, organic extract or steam hydrolysed pulping process (of course mixing the various ingredients by powder to powder blending is also possible). As previously noted, the binary PF consists of a mixture of high average molecular weight PF (high MW PF) and low average molecular weight PF (low MW PF). As indicated herein, binary PF has been found to be an effective cross-linker for the aforementioned lignins to produce a quick-curing adhesive having improved adhesion characteristics.
Preferably, either the low MW PF is mixed with the lignin prior to mixing with the high MW PF, or, the high MW PF and the low MW PF are mixed concurrently with the lignin.
The adhesive system can be used as an alkaline water (aqueous) solution (pH 9-11) by simple mixing of the alkaline binary PF with the lignin copolymer and slight addition of a base such as sodium hydroxide if required to increase the resin solubility or by utilization of a binary PF having a concentration of low MW PF, for example, 85% low MW PF and 15% high MW PF. Excessive addition of sodium hydroxide will result in advancing the resin particularly during spray-drying, and reducing its adhesive properties. As well, the pH of the solution can be lowered to disperse the adhesive (pH 3-9), or the adhesive may be separated from the solution, or spray-dried. Slight improvement in lignin-PF reactivity has been observed if the lignin-PF mixture is heated at low t~perature (for example 2 hours at 50°C), prior to spray-drying.
5 The weight ratio of the high Nb~T PF to the low 1~5n~ PF can be from 1:1 to 9:1, and is preferably in the area of 7:3, but where an acid water solution is preferred, the ratio can be 1:9 to 1:4, preferably 15:85.
10 The average molecular weight of the high l~bv1 PF is preferably from 1,200 to 10,000, and the average molecular weight of the laa l~bd PF is frarn 200 to 1,200. The weight ratio of binary PF to lignin may be from 9:1 to 1:9, preferably 80:20.
The weight ratio of the binary PF to lignin can range fr~n 9:1 to 1:9 and is preferably 85:15 for the production of a quicJc setting adhesive.
The rendering of the adhesive "pre-cure" resistant contemplates the addition of an ammonium salt to a PF resin to provide a navel pre-cure resistant thermosetting adhesive. This type of adhesive is primarily intended for use as a face adhesive for three layer waferboards. Employing a binary PF for this type of resin is preferred. A face or a core PF resin (preferably core PF as more PF
could be replaced with lignin) presently used for the manufacture of waferboard can be used. The amount of lignin and/or a~onium salt, and 11 20 ~ 24 7 6 the choice of PF copolymer will determine the rate of curing of the adhesive and its pre--cure resistance. As before, the adhesive can be transformed into a useful adhesive powder by spray drying and is generally employed under alkaline conditions.
To produce the "pre-cure" resistant adhesive, as before, a PF in solution (and which preferably a binary PF) is mixed with a lignin which advantageously is in waste form and recovered frown one of the different pulping processes, and an ammonium salt. As previously noted, the ammonium salt may consist for example of ammonium lignosulfonate, ammonium sulphate, ammonium p-toluenesulfonic acid or ammonium chloride.
The ammonium salts are generally acidic and will cause precipitation of the alkaline phenalic resin upon mixing. This may be prevented by concurrent slight ackiition of ammar~ium hydroxide. Again excessive aoldition of strong base other than ammonium hydroxide such as sodium hydroxide will rthe flow and pre-cure resistance of the resin. The content of ammonium salt (salt other than ammonium spent sulphite liquor) in the resin mixture may vary fr~n 1 to 30% based on the total dry weight of the resin mixture and is preferably 2-6%.
In the case of NH,SSL, the salt being also the lignin copolymer, the PF to NEi,SSL weight ratio can vary frown 8:2 to 1:9 and is preferably 70:30. The preferred weight ratio is also 70:30 for lignin sources other than Ni~,SSL such as for example, sodium or calcium based SSL or steam hydrolysed lignin. If a strongly alkaline kraft lignin is being used, it has been found that by removing part of the sodium salt content of the kraft lignin by precipitation of the lignin in acidic solution and washing with a dilute acid water solution, may be preferable, in order to avoid formation of excess of sodium hydroxide in the final resin mixture. It is also possible to formulate a phenolic resin with less sodium hydroxide to accommodate this copolymer.
As for the quick setting adhesive, the pH of the resin solution can be lowered to disperse the adhesive ( phi 3-9 ) but it is preferably used as a water solution (pH 9-11). The resin may be spray dried into a stable powder or used as a liquid.
An important aspect of these findings is that the lignin as well as most ammionium salts are inexpensive in co~q~arison to phenol-formaldehyde. Also important is the increase in the quantity of material recovered if spray-dried into stable powder per hour employing existing equipment, a further reduction in the adhesive production cyst.
A further advantage of this fir~iing is that the lignin and amttanium salt in a bite panel, during thermosetting, will react with any free formaldehyde present in the resin formulation and thus act as a formaldehyde scavenger.

Brief Description of Drawing Figure 1 is a graphic representation of the relationship between the percentage yield and particle size of the adhesive in powder form obtained after spray drying, and the percentage of binary PF and/or Nf~SSL present in the adhesive mixture before spray drying.
It should be noted that the 100°s NH,SSL and PF were sprayed as a water solution while all the PF-HI~,SSL mixture were spray-dried as a dispersion at a phi of 5Ø It should be added that similar high yield (89~ powder recovery based on initial resin dry weight) obtained using a resin containing kraft lignin (270)-(~)ySDy(3~)-PF(70%). The resin was spray dried as a water solution at a phi of 9.8.
Detailed Description of Preferred Etnbodiment,~
In the following, the method of preparing the adhesives of the invention are described. As well, test results including assessments of the adhesion characteristics of various adhesive fornwl.ations are set forth.
The Binary PF Resins There are several examples in the literature of method of preparation of binary PF resins (Ex. U.S. Pat. 3,180,784; 3,267,188;
3,591,535; 3,927,140; 4,269,949; 4,345,054; 4,433,120). As already mentioned, the unique reactivity of binary phenolic resin to produce a quick setting resin when used in a~nbination with lignin has not been recognized. The intent is not to show haw to produce a binary PF since this art has already been described in the literature, but to provide examples of binary resin formulations which could be used to demonstrate their unique reactivity when employed with wood waste products such as lignin or Containing lignin.
Ele of Preparation of a Binary PF Resin For the preparation of high I~dn1 resin: P-formaldehyde ( 167 g) was suspended in water (378 g) and heated at 95° for 30 minutes.
The mixture was then cooled to 25'C and pal (210 g) was added followed by slag ackiition of sodium hydroxide ( 62 . 5 g at 50 percent solid) . The temperature of the reaction was raised to 90°C in a 60 minutes period and held until the resin reach~l a (Brookfield) viscosity of 50 cps (viscosity measured at 25°C). The resin was Cooled to 75°C and held at this tertq~erature until a viscosity of 300 cps was obtained. At this point the resin was cooled to roam t~per~ature and 10 g of sodium hydroxide was added. The resin had a weight average molecular weight (lea) of 4,000 and a rnm~ber average molecular weight of 1314 as measured by gel permeation chromatography (polyethylene glycol calibration).
For the preparation of the laa I~dnl resin: P-formaldehyde (148 g) was suspended in water (220'C) and heated at 95°C for 30 minutes. The mixture was then Cooled to 25°C and phenol (210 g) was added followed by slow addition of sodium hydroxide (30.8 g at 50 percent solid). The temperature was raised to 60°C and held at this temperature until a Brookfield viscosity of 35 cps was obtained. At this point the resin was cooled to roam t.~perature and sodium hydroxide (25 g) was add~l.
Obviously the preparation of a binary PF is not restricted to these examples. For example, a high molecular weight PF could be obtained by a using a gradient t.~perature starting at 60'C and increasing to reflux and the order of addition of the various ingredients may be changed. Alkaline catalyst other than sodium hydroxide may be employed.
It is also possible to produce a binary pnenolic resin in a single process instead of separately producing the low and high molecular weight comrponents and mixing. For example, an aqueous solution of phenol, formaldehyde and a catalyst such as soditun hydroxide can be treated at a temperature of about 9~C and for a time sufficient to produce the high molecular weight PF c~Onent.
Follaaing cooling, additional phenol, formaldehyde and catalyst is added to this oamponent and heated within a temperature range froqn about 40°C to about 65°C for a time sufficient to generate the low molecular weight PF ca~onent of the binary PF. It is also possible to reverse the two process steps by producing the laa N~nT PF component prior to the high Nbri PF component.
~,q of Binary PF and Lig~
An ac~esive solution may be prepared by first adding the low 1~ PF to the lignin, and then adding the high l~dnT PF to the mixture of laa Ngn1 PF and lignin, or the low l~ffn1 PF and high 1~b~1 PF may be added concurrently to the lignin. Adding high N~n1 PF directly to the lignin may result in precipitation. Following reacting the binary PF and lignin preferably by mixing, the p~I of the solution may be adjusted by adding hydrochloric acid or sodiwn hydroxide. C~tirmun adhesive properties for NH,SSL as the lignin ocm~onent were obtained when mixed with a weight ratio of 30~ low MW PF to 70~ high Nda PF and at a phi of 3 to 10.5.
It is also possible to add the lignin during the single process production of the high and low MW PF previously described with the lignin during the first or secorxl stage of the binary PF
production, or both. The cross-linking reaction between the lignin and binary PF is accelerated with the application of heat and thus it is possible to effect cross-linking when an aqueous solution of the binary PF and lignin is spray dried to create a dry adhesive powder.
M~.' xing of PF,, Lignin Oonol~mier and Ammoniwn Salt A pre-cure resistant adhesive solution is prepared by mixing ammonia, preferably ammonium salt, and more preferably an ammonium acid salt with lignin and then adding the PF resin while stirring vigorously. Addition of the ammonium acid salt directly to PF
will cause its precipitation into a gummy mass rendering it difficult to work with. The mixture of PF, lignin and ammonium salt can be used as an alkaline solution by adjusting to pH 9-11 with ammonium hydroxide. The pre-cure resistance can be adjusted by varying the solid weight ratio of PF, lignin and salt.
The single process technique of producing binary PF with or wittxrut the addition of lignin thereto as above described can also advantageously be modified if it is desired that the thermosetting resin also exhibit pre-cure resistance. For example, ammonia, preferably in the form of an ammonia salt can be added with the second stage addition of phenol, formaldehyde arxi catalyst necessary for the production of the low molecular weight component in the binary PF.
Moreover, the temperature gradients, quantities of addition and sequence of addition of the ingredients can also vary and depending upon the intended end use or characteristics of the adhesive (face or core applications and if it is to be made pre-cure resistant or not).
Fle 1 In this example, the adhesive properties of M~,SSLrPF
adhesives having either a high molecular weight or a laa molecular weight PF coamponent are compared with a resin prepared by mixing in a 1 to 1 weight ratio a binary PF resin and NH,SSL with the results being set forth in Table 1.

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.1 ..~ .1 z ro .a a o As the results in Table 1 indicate, the adhesive containing the binary PF yielded a better quality waferboard in ~arison to an adhesive having either only a low average molecular weight or high average molecular weight PF ~ponent. Both wet and dry NCR (modulus of rupture), and NEE (modules of elasticity) results were superior for the binary PF-NH,SSL adhesive under both acid and a7.kaline conditions and exhibited comparatively higher IB (internal bond strength) values.
Torsion shear test results also confirm the superiority of the binary PF-NH,SSL adhesive under both acid and alkaline conditions. 'Ibrsion shear test results also confirm the superiority of the binary PF-NH,SSL adhesive. Of particular note is that satisfactory adhesion characteristics are noted for the binary PF-NI~SSL adhesive under both acidic and alkaline conditions.
ale 2 In the following example, an assessment of the relative efficacy of a co~nmex~cial PF resin (not a binary PF) and a binary PF
resin as a cross-linker for methylolated kraft lignin (1~CL) was made with the results set forth in Table 2. As indicated by the superior 1~IDR and IB values, under both acid and alkaline c~r~litions I~CL was cross-lined with the binary PF to provide an adhesive yielding a waferboard having properties superior to waferboard prepared when a commercial PF was used as N~ cross-linker.

Zp~2476 Comparison Between a Conanercial PF and Experimental Binary Phenolic Resin as Crosslinker for Methylolated Kraft Lignin (~,)l, 2 Board Properties MOR
Resin Type pH Dry Wet IB
...........(Mpa)............
Commercial PF-MKL 11 4.8 0 -9.5 . 16.1 8.6 0.28 3.0 23.5 11.4 0.30 Binary PF-MIQ.,3 10.5 25.6 13.1 0.46 5.0 27.0 16.1 0.52 1 Waferboards pressed 5 min. at 210°C
2 Resin containing 50% PF solid by weight 3 Binary PF-MKL3 resin formulated from the single two stage process 21 2p~~476 Fle 3 Test results as set forth in Table 3 indicate that an NI~,SSIrPF adhesive having acceptable adhesion characteristics is obtained where the weight ratio of high average molecular weight PF to laa average molecular weight PF is between l:l and 4:1, with optimal results being obtained where the weight ratio is 7:3. As also indicated by the results of Table 3, the percentage yield of adhesive obtained upon spray drying is enhanced where high I~T PF molecular weight PF is present in greater quantity, with acceptable results being obtained for binary PF having at least 70~ high l~b~ PF.

Table 3 Optimization of PF molecular weight distribution with relation to SSL (50~) - PF (50~) adhesive propez~iesl and spray-drying yield PF MoR SPRAY-DRYIT1G
HIGH MW LOW I~T ~T' DRY WET yg~
($) ($) _____ (papa)-____ ($) 0 100 280 22.1 0 p 30 70 600 26.5 7.0 p 50 50 850 25.1 9.8 13 70 30 1300 25.5 14.0 76 80 20 1350 27.1 12.3 82 100 0 1590 16.9 0 90 ' Waferboard of 11.1 mm thickness press 4 minutes at 210°C.
' Spray dried with a laboratory spray-dryer (Howen ~ 1031) at 165°C
inlet and 90° outlet te~erature.
' Molecular weight detezmined by size exclusion chroQnatography (SEC) relative to poly (ethylene glycol) standarr~s.

23 2 0 4~ 2 4 7 fi Fle 4 In this example, a quick curing adhesive consisting by weight of 15~ lignin of various origin and 85~ binary PF resin (ooa~~rised of a 1:1 by weight mixture of high and low average molecular weight PF) was prepared. As indicated by the test results as summarized in Table 4, the binary PF resin effectively cross-linked eaoh of the various lignin copolymers identified in Table 4 to produce an adhesive having adhesion oharacteristics ale to a coa~,m~xcial PF adhesive.

24 2 p ~ 2 4 7 8 Table 4 Effect of lignin type on binary PF (85~) - lignin (15~) adhesive properties for harnogeneous waferboardsl RESIN RESIN PRESS ~tY WET

TYPE pH CYCLE --~a ---Kraft Lignin 10.3 3 28.0 13.7 Steam Hydrolyzed Lignin 9.52 3 29.5 14.7 NHsSSL 8.5 4 28.9 14.2 NaSSL 9.0 4 26.2 13.6 Co~m~ercial PF 3 28.8 14.8 1 Panel 11.1 mm thicJa~ss press 3 minutes at 210'C with 2.Oo resin.
a Lignin-PF resin heated 2 hours at 50'C prior to spray drying.

ale 5 A further advantage of utilizing a binary PF resin to cross-link a lignin copolymer such as I~i,SSL is that enhanced yields may be obtained upon spray drying. As grapni.cally illustrated in Figure 1, the yield on spray drying an NH,SS~binary PF dispersion was greatest for a dispersion consisting of 50% by weight 1~SSL and 50% by weight binary PF. This is important as i.t indicates that more kilogram per hour of a lignin-phenolic resin can be produced in a o~nercial spray dryer, in comparison to spray drying of PF without lignin. This repreVents a higher production rate and important saving for a resin powder producer.
The following examples illustrate the properties of pre-cure resistant adhesives obtained from a mixture of a PF, a lignin and an axrnnonium salt. The PF may be a surface phenolic resin or a faster curing core phenolic resin. The core phenolic resin produces a faster curing pre-cure resistant PF-lignin adhesive.
ale 6 In a mill, a waferboard mat may rest on a Gaul plate at 140 - 150°C for a few minutes before being transferred into the press. In the press, the mat may then rest on the hot press platen few se~r~ds before press closing to target panel thickness. If the resin is not pre-cure resistant and cures prematurely, a poor bond will result. One method to differentiate between a face and core resin is the stroke cure test. The test involved placing 0.75 g of resin on a hot platen 26 204~2~7~
set at a temperature of 150° and spread back and forth until hardened and cannot be spread further. A fast core resin will generally have a short stroke cure of 15-25 seconds, which oampares to 35-45 seconds for a face pre-cure resistant adhesive.
As shown in Table 5, a resin made frown NH,SSL (30%) and PF
(70%) had a stroke cure test of 42 seconds, if ammonitun sulphate salt was added, longer stroke cure test could be obtained. It was also possible to obtain a resin with stroke cure test ooanparable to a co~nercial face resin ( 35 - 45 seconds ) froqn kraft lignin ( 27% ) , (NH, ) a S04 (3%) and a co~m~ercial PF (70%). Similar results were also obtained with lignin other than kraft or NHdSSL, such as NaSSL or organosolv lignin.

Table 5 Effect and ammonium sulphate additives of on lignin stroke cure test of comnnercial core phenolic resin powder (sprayed 200'C inlet and 90'C outlet) at RESIN PdWDER
OO~OSITION

PFel PFbl Kraft2 NH,SSL ( NIA ),SO, Stroke Cure Test at 150C

( PFa and PFb are core PF resin Kraft lignin precipitated and washed to remove the free inorganic salts 2$ 202476 lle 7 In other methods to test the resistance of an adhesive to "pre-cure", the Gaul plate was heated in an oven at 200°C and then placed on the waferboard mat (wafers blended with the adhesive being tested) for five minutes under 25 kg weight. The mat was then pressed in a normal manner. The panels mere then tested for intezmal bond strength (IB). For the pre-cure resistant adhesives, it was found the hot Gaul plate treatment had no adverse effects an IB. The t~perature of the 1.6 irnn thick metal Gaul plate at exit frown the oven was observed to be 190°C. At contact with the wood furnish, the Gaul plate cooled off gradually to a~oximately 80°C within the 5 minute treatment.
The results set forth in Table 6 belay are for waferboard with the mat treated with a hot Gaul plate prior to pressing. The hot Gaul plate treatment had an adverse effect on IB and face failure for the sample banded with the ooarnmercial core PF and also the binary PF
copolymer. No adverse effect was noticed for the panels bonded with NEi,SSLrPF and kraft-PF-(NH,)zSO, resins as IB and face failure test results wpxe similar to those obtained with panels bonded with the oonmaercial face PF control.

Table 6 Effect of Gaul plate heat treatment of maul prior to pressing on mechanical properties of three layer waferboardsz bonded with c~ercial and experimental resins Face Resin' Density IB Face' Failure ()cg/m') (~) (%) Co~miercial Face PF 675 .467 8 PFD Cmsslinker 664 .390 42 NH,SSL ( 30% ) -PFs ( 70 652 . 450 8 % ) Kraft (27%)-Pf~(70%)- 650 .509 8 (I'1H')Z~'(3%) Ooa~nercial Core PF 648 .179 100 1 Caul plate heated in an oven at 200°C then placed on top of waferboard mat 5 minutes under 55 kg weight Panel pressed 4 minutes at 220°C with 2.0% resin ' Sample delamination (failure at surface layers during testing of 12 IB samples ' The core wafers were bonded with a ccamnercial core PF for all the panels Experimental resin coed of hick I~n1 PF ( 70 % ) and low Nbo PF
(30%) resins

Claims (16)

1. A fast cure thermosetting adhesive useful in binding lignocellulosic materials together and having a stroke cure test time from about 15 to 25 seconds, said adhesive comprising a binary phenol-formaldehyde consisting of high average molecular weight phenol-formaldehyde and low average molecular weight phenol-formaldehyde and wherein the weight ratio on a dry weight basis of said high molecular weight phenol-formaldehyde to said low molecular weight phenol-formaldehyde is from 80:20 to 50:50, with lignin and wherein said lignin is a wood pulping waste lignin recovered from at least one of the Kraft, sodium sulphite, organic extract and steam hydrolysed wood pulping processes and wherein the pH of the adhesive is from 8 to 11.

2. The adhesive as claimed in claim 1, wherein the ratio of binary phenol-formaldehyde to lignin is from 10:90 on a dry weight basis.

3. The adhesive as claimed in claim 1, wherein the ratio of binary phenol-formaldehyde to lignin is from 90:10 to 60:40 on a dry weight basis.

4. The adhesive as claimed in claim 1, wherein the average molecular weight of said high average molecular weight phenol-formaldehyde is from 1,200 to 10,000 and the average molecular weight of said low average weight phenol-formaldehyde is from 200 to 1,200.

5. A pre-cure resistant surface adhesive having a stroke cure test time of from about 35 to about 45 seconds comprising the fast curing adhesive as claimed in claim 1 in combination with an ammonium salt.

6. A pre-cure resistant adhesive as claimed in claim 6, wherein said ammonium salt is selected from the group consisting of ammonium based spent sulphite liquor, ammonium sulphate, ammonium p-toluenesulfonic acid and ammonium chloride.

7. A pre-cure resistant adhesive as claimed in claim 1 or 5 when in dry powder or liquid form.

8. A method of producing a fast curing cross-linked thermosetting adhesive having a stroke cure test time of from about 15 to about 25 seconds and having a pH of from 8 to 11 and which is useful for binding lignocellulosic materials together, comprising the step of reacting at an elevated temperature binary phenol-formaldehyde consisting of high average weight phenol-formaldehyde and low average molecular weight phenol-formaldehyde and wherein the weight ratio on a dry weight basis of said high average weight phenol-formaldehyde to said low average weight phenol-formaldehyde is from 80:20 to 50:50, with lignin, and wherein the lignin is a wood pulping waste lignin recovered from at least one of the sodium sulphite, Kraft, organic extract and steam hydrolysed wood pulping processes.

9. The method as claimed in claim 8, wherein said binary phenol-formaldehyde is prepared by heating a first mixture of phenol, formaldehyde and a catalyst at a temperature and for a time sufficient to produce one of a high molecular weight and low molecular weight phenol-formaldehyde component and heating said component with a second mixture of phenol, formaldehyde and a catalyst to produce the other of said one of a high molecular weight and low molecular weight phenol-formaldehyde component.

10. The method as claimed in claim 9, wherein said lignin is added to at least one of said first and second mixtures.

11. The method as claimed in claim 8, 9 or 10, wherein the average molecular weight of said high and said low average weight phenol-formaldehyde is from 1,200 to 10,000 and from 200 to 1,200, respectively.

12. The method as claimed in claim 8, 9 or 10, wherein the weight ratio of binary phenol-formaldehyde to lignin is from 90:10 to 10:90 on a dry weight basis.

13. The method as claimed in claim 8, 9 or 10, wherein the weight ratio of said binary phenol-formaldehyde to said lignin is from 90:10 to 60:40 on a dry weight basis.

14. The method as claimed in claim 8 or 9, wherein said high and low average weight phenol-formaldehyde are mixed together prior to mixing said binary phenol-formaldehyde with said lignin.

15. The method as claimed in claim 8, 9 or 10, wherein said low average weight phenol-formaldehyde is reacted with said lignin prior to reacting said high average weight phenol-formaldehyde with said lignin.

16. The method as claimed in any one of claims 8, 9 or 10, wherein the adhesive is spray dried.