CA2158636C - 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

2158636 '~

FAST CURE AMD PRE--CURE ~ I ~ CRDSS-LINKED PHENOL-FCRMALDEHYDE
ADHESIVES AMD MF~ nfi OF M~XING SAME

Field of Invention S m e pr~ t inNention relates to a new and useful fast curing thermosetting adhesive comprised of cross-linked bLnary phenol-formaldehyde and lignin and additionally, an adhesive ~hich can be rend=rel "Fear~alrc" resistant, as well as the mRthods of preparing same. ~he fast curing and "pra-cure" resistant adhesive may be used in the preparation of nE~nufactured lignocellulosic Fl~xhJcts such as b~ards and panels employing ~--~t, wood chips, wood wafers and the like.

Backgxound of Invention Phenol-formaldehyde (PF) adhesive resins have long been used as th~rmn~etting binders in the ~ a~Lian of manufactured boards or panels. NhmY~nOU6 attempts have been made to develop suitable substitute adhesives, which utilize wood waste, in order to not only meet growlng envi~u.~ U~ s~ but to also red~ce the de ~ ~ ~e upon petroleum hased constituents, the av~ hility and cost of which is increasLngly uncertain.

These att~Fts have included efforts to develop suitable adhesive binders by using PF to cro6s-link other possible adhesive constituents, including one or ~ re waste pr~duK ts of wccd ~ ~Yssing.
Uhfortunately, to date thRse efforts have n~t with only limited s~c~s .

Ihe ~ e of w~od waste Frxr~ s which have been successfully cross-linked is limlted, and the m~x~ds used to produce these adhesive binders have been slow and lakorious, often rlc~ulrLng ~u~leatment of the waste product constituent. Furthermore, the cure time and adhesion characteristics of th~se adhesive binders have been such that widespread use or aoc~an ~ of these sub6titutes by the manufactured b~ard in~ustry has not cxxlunn3d. For example, it is often the case that the adhesive binder must be used under acidic conditions. However, board and panel manufactI~rs prefer to operate in an alkaline envil~a~nent, since less wear and tear is encountered by pGIduLtion e~ m~nt.

Ih U.S. Patent No. 2,786,008 j~l on Mbrch 19, 1957 -Herschler, an adhesive binder consisting of Fhenol-formaldehyde (PF) and ammonium b~sed spent sulFhite liquor (NHlSSL) is ~i~rlosed. In addition to p~oducing an acidic adhesive which is slow curing, the methcd ~i~clo~e~ by Herschler is laborious and tiDY~Ionsuming, as it is ne~;s~ry to make the alk21ine PF "acid tolerant" in order to avoid precipitation of the PF resin upon mixing of same with the acidic spent sulphite liquor.

Anokher example of using PF to cro6s-link a wood waste product is that disclosed in U.S. Patent no. 4,113,675 i~sued on September 12, 1978 - Clar~e et al., wherein methylolated lignin was cro6s-linked by an acid catalyzed low molecular weiqht PF resin. It was c~6~~d that kraft lignin was itself not sufficiently reactive to 215863~ --under significant cross-li ~ with PF, and that it was thus nçQ~s~ry to pre-react the lignin with a methylolating agent, such as formaldehyde, so as to intlxx~ooe methylol group6 to the lignin molecule. M~reover, it was indicated that in order to achieve S satisfactory cross-lin ~ on curing, the pH of the binder must be acidic. Finally, the adhesive disclosed in Clar~e et al. was fcund to be relatively slow curing.

In Can~dian patent 1,214,293 i~e~ on Nove~ber 18, 1986 -Calve et al., an adhesive oonsisting of am~nium based spent sulphite liquor (N~ r ) cross-linlc~ ~y a camr~rcial PF is ~ ~. It was fa~ that while PF normally precipitates when in acidic solutian with N~I,S5L, a useful adhesive could ~e obtain~ if the ~I,S~PF were n~int~ in dispersion thr~ rigorous stirring or agitatical.
h~ain, acidic co~2ditions, of pH 3 to 7, were required to E~vide acceptable m~ulus of rupture (M~R) test results on wafer~oard and particle~oard manufactured with the adhesive.

In U. S . patent 4 ,127, 544 issued on N~vember 28, 1978 Allan, a p~oaess for the partial su ~ titlltion of a~nonium ligno6ulfonate for phenol in aIkaline phenolic-aldehyde resin adhesives is described. However, the N~S5L is first pre-reacted with phenol at a temperature range of 150-300'C under autogencus F~ re prior to cxYI~nsation with formaldehyde under alkaline oonditions. Ihe reaction at high temperature and pressNre is exFensive. Also, no w~od adhesive bond test data were provided.

In U.S. patent 4,324,747 i~ql on April 13, 1982 - S ~
et al, a resin where an alkaline phenol-formaldehyde resin is simply muxed wqth a kraft pulping liquor and use to bond waferboard is disclosed. m e phenolic resin is ~u~ 3l by refluxing phenol and forr~l~P~yde in the F~T~I~X~C of zinc acetate or heating at lower ten~x~ature m the presence of calcium oxide. No reference to ad~u~LL~ of molecular weight disdl-~bution of the phenolic resin or example of addition of a~ium salt is provided. mis type of resin is slow a~ring and not "pre~c" resistant.
Ib be aoceptAhle for ir~ial use, a new ~ive mllst meet certain criteria. For example, it must be available as a s~ray dried p~der or stable l;~ ; be qui~k setting if it is employed as a core adhesive for thiclc m~lti-layer panels where the resin is far fmm the heating s~ce, or be "pr~e" resistant if it is ~lo~ed for bonding a ~nolayer panel or the faoe of a multi-layer panel. If the resin c ~res ~L~L-~rely while the mat is r~~ting on a ho~t caul plate before pressing or at first contact with the press platens before sufficient pressure is applied to c~olidate the mat, a poor bond will ensue.

In the aforer~ntioned examples and el~e~re, it has not been suggested or conten~lated that the PF ~ ent of the adhesive be modified or ~peci~lly constituteld to ~k~e the cross-linking of the wo~d waste product ocsponent of the adhesive.

21536~

While a tw~ oomponcnt or '~binary PF" resin, oomprised of a ni~lme of high average molecular weight PF and low average molecular weight PF comp~lk~-~s, has long been used in the manufacture of board, heretofore, the low ~le2~1~r weight PF has been added to enhance resin flaw wqth nu~Lunum d~y-out. Its unique reactivity to produce a quick set~i~ng resin when used in oombination with w~od waste, especially polydi~e~e lignin, has not been ~e~x~ ized and its use in oo~bination with wxx~d waste product not contemplated.

~or example, in U.S. patent no. 4,269,949 issued on May 26, 1981 - Hickson et al, there is ~i~clofiPd a binary PF resin oomprised of a n~ re of high and low molecular weight resins, particularly suitable for use in hardboard applications, ow m g to the nuruu~lm dry-cut ~xhihited by the adhesive.
In U.S. patent no. 4,433,120 issued on February 21, 1984 -Chiu, it was der~x~Lla ed that a liquid binary PF resin having low viscosity and law surfa oe tension could be used for efficient spray application as fine droplets in waferboard n~nufacture. m e liquid binary PF resLn has limited F~e-clLre resistance d~e to the E~ oce of the slawer curing low molecular weight phenolic resin which is however not sufficient for a surface resin. Although thle liquid bin~ry PF
resin exhibited some pre-cure resistance, this resin is relatively expensive to produce, and displayed only limited Ere-cure resistanoe.
It is also difficult to spray-dry without advancing the resin and reducing its Ere-cure resistance.

In a reoent study Stephens and Kutscha (Wbod and Fiber Science, 19(4), 1987, pp. 353-361) fractionated a phenol-formaldehyde resin Lnto a high and low molecular weight resin by ultrafiltration and clD~YIngd the adhesive ~u~e~Lies of each fraction to the unfractionated PF resin. They found that: "the high ~ lecular weight resin fracticn performed nearly as well as the unfractionated resin". m e ~les~x~e of low molecular weight penol-formalde~yde only slighkly imQrove the characteristic of the PF resin, and is not essential to the ~YL~5S.

Sln~m~ry of T~vention an the c~nlLLc~ to previous findings, it has been fcund that a mixture of a bLnary PF and a polydisFY~is lignin, shows an ur~oq?ecte~ high adhesive reactivity.

While in previo~s w~r~, different types of phenolic resin were required, for example, with kraft or sulphite lignin which have different ~ lecular weight distribution, in ac~L~ ~ with this invention results better than previous were cl*ained with a binary PF
resin cross-linker for the lignin and inde ~ ~ ly of the lignin origin. While high molecular weight PF resin could be used alone as adhesive, with a w w d waste product such as lignin, the FQI#~nce of b~th high and low molecular weight phenolic resin is needed to pr~xhb3e a fast c~ring adhesive cnmrosition an~ a s ~ weather resi~L~i~e joint. The use of high or low molecular weight PF alcne with a wxxxl waste ~ e such as lig m n, results in a we3k bond, while a h~l~nce oomposition of high molecular weig~t PF, low molecular weig~t P~ and lignin has been found to result in an ~hp~ive with curing and strength ~uu~e~Lies similar to a fast curing cr~E~rcial phenolic resin. Both high and low molecular weight PF cross-link the lignln which is itself a mixture of high and low molecul ~ weight particles. m e small S phenolic molecules are also kelieved to link the high molecular weight lignin polymer as the resin is cured while the large phenolic mol ~ lles link the smaller lignin mol~les. Ihis sy~3m can also be used under acidic conditions, as a water solution or disFersion.

It has also been fo md that the lig m n, as ~ell as their uses as a water dispersion, lmpnoves the f~il;ty of ~u-ay drying of the phRnolic sy~tem resulting in a higher yield. This is re~arded as impo~ L since a resin which spray drys m~re o~cily can ~e pr~Y~ at a higher rate, increasing ErodLL*ivity.
In aoco~u~e with yet another ~pect of thiC inventicn, the incogp3nsive resin can also ke made to exhibit im~rov3d FrT~1~Ire resistance which is i~cuL~.~ when used as a liquid or spray-dried powder face adhesive for three-layer ccmposite Fr~ch~*s, such as wafer~x~rd.

This was achieved by simple n~cu~g a phenol-formaldehyde resin (one which could ~e used as core adhQsive for a 3-layer panel, for e~uy?le), a relatively large quantity of a lignin and an ammonium 2S salt. m e use of ammonium spent sulphite liquor is preferred as li~nin source as it already crnt~ins the ammonium salt corpcn~ft. 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 lose 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.

21~863~

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 MM 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 MM PF and 15% high MM 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 21586~
f lmprovement in lig m nrPF reactivity has b~en o~tl~roed if the ligninr PF mixture is heated at low temperat~re (for ex~ngple 2 hours at 50 C), prior to spray-drying.

The ~ h~ ratio of the high MW PF to the low MW PF can be fram 1:1 to 9:1, and is preferably in the area of 7:3, but where an acid water solution is prefe ~ , the ratio can be 1:9 to 1:4, preferably 15:85.

Ihe average molecular weight of the high MW PF is preferably from 1,200 to 10,000, and the average molex~llAr weight of the low MW PF is from 200 to 1,200. me weight ratio of binary PF to lignin may be from 9:1 to 1:9, preferably 80:20.

me weight ratio of the binary PF to li3nin can range fr~
9:1 to 1:9 and is preferably 85:15 for the pr~tion of a quic3c s~tting adhesive.

me rendering of the adhesive "~:ure" resistant co~plates the adrlition of an an~ ium salt to a PF resin to pr~vide a novel ~~e resistant then~et~ adhesive. I~is type of a~esive is primarily inter~ed for use as a face adh~ive for three layer wafeLL~a~3s. Employing a binary PF for this type of re~in is preferred. A face or a core PF resin (preferably core PF as m~re PF
2S could bP rP~l~l with lignin) ~ tly used for the ma~mfacture of waferboard can be used. The amcunt of lignin an~/or ammonium salt, and the choi oe of PF copolymer will determine the rate of curing of ,'h~
adhesive and its Fh~ re resistance. AS before, the adhesive can be transformed into a useful adhesive powder by spray drying and is generally employed under alkaline conditions.

Tb produce the "Fn~ Lre" resistant adhesive, as before, a PF in solution (and which preferably a binary PF) is mixed with a lignin which advan~ ly is in waste form and L~WVel~3~ f m m one of the different pulping ~ Y~ S, and an am~onium salt. As previously noted, the ammcnium salt may consist for example of am~Lnium lignosulfonate, a ~ nium s~ hAte, ammLnium p-toluenesulfonic acid or annonium chloride.

m e ammonium salts are generally acidic and wqll cause precipitation of the alkaline phenolic r~sin up~n mixing. m is may ke prevented by crr~llr~ent slight addition of ammonium h~nxxide. Again excessive addition of ~Ln~ ~ base cther than ammonium hydroxide such as sodium hydroxide will r~duce the flow and Fcl~clrre resistance of the resin. me oontent of amr~ni~n salt (salt other th_n an~ni~n spent sulphite liquor) in the resin mix~e may vary fmm 1 to 3096 ~sed on the total dry ~~ight of the resin mix~e and is prefer~bly 2-696.

In the case of NH,SSL, the salt being also the lignin co~olyn~r, the PF to ~,S5L weiqht ratio can vary fr~ 8:2 to 1:9 and is preferably 70:30. ~e preferred weight ratio is also 70:30 for lignin sa~rces other than ~,S5L su~h as for e~nnple, sodimn or calcium based ~CT~ or steam hydr~lysed lig m n. If a ~Ll~ ~ly alkaline kraft lignin is being used, it has been found that by rlqxrrLng part of the sodium salt oontent of the kraft lig m n by precipitation of the lig m n in acidic solution and w~L~ng 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 po~ihle to formulate a phenolic resin with less sodium hydroxide to acYxnml~date this copolymer.

As for the quick setting adhesive, the pH of the resin solution can be lowered to disperse the adhesive (pH 3-9) but it is preferably used as a water solution (pH 9-11). m e resin may be spray dried into a stable pcw~er or used as a liquid.

An impo~ ~ aspect of these findings is that the lignin as well as most ammonium salts are inexpensive in co~pariscn to phenol-form21dehyde. Also i~ L is the i~ se in the quantity of material reoovered if spray-dried into stable pawder per hour employing existing ~irm~nt, a further reduction in the adhQsive prodh~tion 006t.

A further a~lLaye of this finding is that the lignin and ammonium salt in a ocmposite panel, during thermLsetting, will react with any free for~ Phyde present in the resin formulation and thus act as a formaldehyde scavenger.

., Brief Descripkion of Drawl~g Figure 1 iS a graphic ~ ntation of the relationship between the ~e~ La~ yield and particle size of ths ~h~ive in pow~er form ob*ained after spray drying, and the ~e~ w .~Yye of binary PF and/or N~CT present in the ~hF~;ve mixture before spray drying.
It should bs noted that the 100% N~LSSL and PF were sprayed as a water soluticn while all the PF-Nn~SSL mixture were spray~dried as a dispersion at a pH of 5Ø It should be added that similar high yield (89% po~der recovery based on initial resin dry weight) ob~ained using a resin containing kraft lignLn (27%)-(N~ 30~(3%)-PF(70%). m e resin was spray dried as a water solution at a pH of 9.8.

Detailed Descri~tion of Preferred EhtxxL~cnts ~n the followlng, the L_ U ~d of ~u~ ~Lng the ~h~ives of the invention are described. As well, test results including ~csf~;~"~l~s of the a~P~ion cheQ~}cteristics of various adhesive formLlaticns are set forth.

m e Binary PF Re!sins m ere are several examples in the literature of methcd of preparation of binary PF resins (Ex. U.S. Pat. 3,180,784; 3,267,188;
3,S91,535; 3,927,140; 4,269,949; 4,345,054; 4,433,120). As a~ K~y mentioned, the unique reactivity of binary phenolic resLn to F~xx~x3e a quick setting resin when used in combinatiom with lignLn has not be~n reoognized. m e intent is not to show how to produce a binary PF since this art has already been described in the literature, but to provide 2158636 ~-e~les of bir~3ry resin f~lations ~ic~ ~~uld be used to d~x~ L ~Le their unique reactivity when emplcyed with wood waste products such as lignin or ccxd~l ming lignin.

EXample of ~ ation of a BLnary PF ~in For the ~Le~ Lion of high MW resm P~formalde~le (167 g) was SU~ K~3~ in water (378 g) and heated at 9~ for 30 n~inrtes.
m e ~ e was then ccoled to 25 C and phenol (210 g) was added followed by slow additicn of sodium hydroxide (62.5 g at 50 pe~cent solid). m e temperature of the reaction was raised to 90~C in a 60 minutes period and held until the resin reached a (Er~x~kfield) visooeity of 50 cps (visoosity ne##~i~ed at 25~C). Ihe resin was cooled to 75~C and held at this tL~r~L~e until a vqscosity of 300 c~s was ci*ained. At this point the resin was cooled to room temperature and 10 g of scdium hydro~ide was added. m e resin had a weight average molecular weight (M~) of 4,000 and a number average moleaular weight of 1314 as mE##~LD?d by gel permeation chrom~o~ hy (polyethylene glycol calibration).

For the ~pa~Lion of the low MW resin: P-formaldehyde (148 g) was suspended in water (220 C) and heated at 95~C for 30 minutes. me mixture was then cooled to 25C and phenol (210 g) was added followed by slow addition of sodium hydrcxide (30.8 g at 50 ~e~ .b solid). m e t~.~ re was raised to 6~C and held at this temperature until a E~obkfield viscosity of 35 cps was ob*~ined. At 215863~ '-this point the resin was cooled to room temperature and scc~.n~
hydroxide (25 g) was added.

Ob~iously the ~ c~Lion of a binary PF is not restricted to these examples. For example, a high ~ lecular weiqht PF could ke obtained by a using a gradient temperature starting at 60 C and increasing to reflux and the order of addition of the varicus ingredients may be ~ ~e~. Alkaline catalyst other than sodium hydroxide may be employed.
It is also po6sihl~ to produce a binary phenolic resin in a single ~u~oess instead of s~a1~ely producing the low and high mole~llAr weight cco~ ~ and nu~cLng- Far example, an A~Xy~YC
solution of phenol, for~AldPhyde and a catalyst such as sodium hydroxide can be treated at a temperature of about 95~C and for a tIme sufficient to produoe the hiqh mol~lAr weight PF cYxexx~3nt.
Following cooling, additional phRnol, formaldehyde and catalyst is added to this cYx$x>nent and heated within a tem~erature range from about 40~C to about 6~C for a time sufficient to ~ ~ e the lcw molecular weight PF comp~nent of the binary PF. It is also possible to reverse the two process step6 by producing the low MW PF c~lx~3n~-prior to the high MW PF ccmponcnt.

Mixing of Binary PF and r;gnin An adhesive solution may be prepared by first adding the low MW PF to the lignLn, and then adding the high MW PF to the ni~lrre of low MW PF and lignin, or the low MW PF and high MW PF may be added concurrcntly to the lignin. P~k~ng high MW PF directly to the lignin may result in precipitation. Following r(*K~=inq the binary PF and lign m preferably by nuuuLng, the pH of the solution may b adjusted by adding hydrochloric acid or sodium hydroxide. C~ um adhesive p4V~ ies for N~lSSL as the lignin CC~u~ were obtained when mixed with a weig~t ratio of 30% low MW PF to 70% high MW PF and at a pH of 3 to 10.5.

It is also po~cihle to add the lignLn during the single ~ ss pro~ n of the high and low MW PF previously described with the lignin during the first or seoond stage of the binary PF
prcduotion, or bath. m e cross-linking reaction b~tween the lignin and binary PF is ac~elerated with the application of heat and thus it is pn~;hle to effeot cross-linking when an aqueous solution of the binary PF and lignin is spray dried to create a dry adhesive pcw~er.

Mixing of PF, Lignin Ccpolymer and Ammonium Salt A pre-cure resistant adhesive solution is prepaled hy mixing ammonia, preferably amm~nium salt, and more preferably an ammonium acid salt with lignin and then ad~ing the PF resin while stirring vigorously. A~dition of the ammonium acid salt directly to PF
will cause its precipitation into a gummy mass rendering it difficult to work with. m e n~rbure of PF, lignin and amm~nium salt can be used as an alkaline solution by ad~usting to pH 9-11 with an~ m ium ide. m e ErT!1alre resistance can be ad~usted by varying the solid weight ratio of PF, lignin and salt.

The single ~L~ess technique of producing bin~ry PF with or S wit~out the addition of lignin thereto as above described c~n also ad~ 3e~l~1y be modified if it is desired that the then~x~tiLng resin also exhibit Fol~alro r~istanoe. For example, ammonia, preferably in the form of an ammLnia salt can be added with the seoond stage addition of phenol, formaldehyde and catalyst ~ c~y for the p~xx~;on of the low molecular weight ccDçxYK3nt in the binary PF.
, the temperature gradients, quantities of addition and sequerco of addition of ~he ingredients can also vary and deperx~mg upon the intcn~cd end use or ~a~l~ristics of the adhesive (face or core ~plic~tions and if it is to be made pre-cure resistant or not).
lS
Example 1 In this example, the adhesive ~*~Lies of NH~5LrPF
adhesives having either a high ~le~ r weight or a low m~leaular weight PF cc~xxKent are cc~FYred wi~h a resin prepared by mixing in a 1 to 1 weiqht ratio a binary PF resin and N~SSL with the re5ult~ being set forth in T'able 1.

215g63~

'D
:~
E
z I u~ O
Ll I .. .. ~ .
;

~ O O ~n o ~

J IOD Gg ~ 1~ -- O
o '- O O O O O O O
g O O ~ ' ' -- ~ O O O O -- _ Z ~ ~ ~ O

-E~ I' ~ O
D V~D ~ V
D

C U~
--I ~ U C C~
~ C~. t.J E ~
L V

O , _ ~, _~ . 5 U ~ ~ -- ~ V V
J _ ~ _ ~ ~ O ~ o V
~ o u- o u~ e o U -- _ "~
L C~ ~ _ C ~ I _ ~
o ~I O ~ O
.0 U

As the results in lable 1 indicate, the A~esive cc~dLuLin~
the binary PF yielded a better quality wafer~oard in comparison to an adhesive having either only a low dV~y~ ~ lecular weight or high average ~ lecular weight PF CXA~ K~I~. Both wet and dry MoR (modulus of rupture), and M~E (mcdulus of elasticity) results were superior for the binary PF-N~SSL adhesive under b~th acid and alkaline conditions and exhibited oo~çaratively higher IB (internal bond ~L~ ~ U~) vall~c.
Tbrsion shear test results also confirm the superiority of the binary PF-N~LS~L adhesive under b~th acid and alkaline oonditions. Tbrsion shear test results also oonfirm the superiority of the binary PF-N~lS~L adhesive. Of par~ia~l~r note is that satisfactory adhesion characteristics are noked for the binary PF-N~LSSL adhesive under both A~i~ic and alkaline conditions-Example 2 In the following e~ample, an A~e~ -L of the relative efficacy of a commercial PF resin (not a binary PF) and a binary PF
resin as a cro6s-linker for methylolated kraft lignin (MKL) was made with the results set forth in lable 2. As indicated by the superior M~R and IB values, under b~th acid and alkaline conditions MKL was cross-lined with the binary PF to prcvide an adhesive yieldLng a waferboard having prlperties superior to waferboard prepared when a cc~n~rcial PF was used as MKL cross-linker.

Comparison Between a Co~mercial PF and Experimental Binary Phenolic Resin a5 Crosslinker for Methylolated Kraft Lignin (MXl)1,2 Board Properties MOR
Resin Type pH Dry Wet IB
........... (Mpa) Co~mercial PF-MXl 11 4.B 0 9.5 16.1 8.6 0.28 3.0 23.5 11.4 0.30 Binary PF-MXL3 10.5 25.6 13.1 0.46 5.0 27.0 16.1 0.~2 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 215863~ ~

Fxam~le 3 Test results as set forth in Table 3 indicate that an N~S5LrPF adhesive having acceptable adhesion characteristics is ci*~L~Y~d where the weight ratio of high average ~ lecular weight PF to low average m~lecular weight PF is ke*~en 1:1 and 4:1, with optimal results being ci*lLLn3d where the weight ratio is 7:3. As also indicated by the results of Table 3, the pe~ w Laye yield of adhesive cl~ 3d upon spray drying is ~ where high MW PF mol ~ ~lAr weight PF is present in y~ea~ quantity, with accept~ble results be m g cL~zLi~3d for binary PF having at least 70% high MW PF.

, 215~636 ~able 3 0ptimi2ation of PF molecular weight dist~rit~ with relation to SSL (50~) - PF (50%) adhesive properties' and spray-drying yie~

PF MOR SPRAY-D~tlNG
- (MPa) ----- (%) 0 100 280 22.1 0 0 600 26.5 7.0 0 850 25.1 9.8 13 1300 25.5 14.0 76 ~350 27.1 12.3 82 100 0 1590 16.9 0 90 ; Waferboard of 11.1 mm thickness press 4 minutes at 210qC.
2 Spray dried with a laboratory spray-dryer nBowen EE 1031) at 165~~ inle~
9~ outlet temperature.
' Molecular weight ~eterm m ed by size exclusion ch~ Lography (SEC) relati~e to poly (ethylene glycol) stand3l~s.

215863~ -Fx~m~le 4 In this example, a quick curing adhesive consisting by weight of 15% lignin of various origin and 85% binary PF resin (ccmprised 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 each of the various lignin copolymers identified in Table 4 to produce an adhesive having adhesion characteristics cso}~Lrable to a c~J~u~ ia PF adhesive.

(: 2l586~6 '~

Table 4 Effect of li~ ~e on binary PF (85%) - lignin (15%1 adhesive ~u~ ies for ~,~ous waferboards RE~IN RE~
CYCLE --MPa--Kraft Ligmn 10.3 3 28.0 13.7 Steam Hydrolyzed Lignin 9.5' 3 29.5 14.7 N~C~ 8.5 4 28.9 14.2 NaSSL 9.0 4 26.2 13.6 Commercial PF 3 28.8 14.8 ~ Panel 11.1 mm thickness press 3 minutes at 210-C with 2.0~ resLn.
' Li~-PF resLn heated 2 hours at 50 C prior to spray drying.

21~8636 Fx~le 5 A further a ~ age of u~ ;ng a binary PF resin to croes-link a lignin copolymer such as N~l~CT is that ~ ~Y~3~ yields may be ob*auned u~on spray drying. As graphically illustrated Ln Figure 1, S the yield on spray drying an N~LssLrbinary PF di~ rsion was greatest for a dispersion consisting of 50% ky weight N~LssL and 50% by weight binary PF. m is is imp~ L as it indicates that more kilogram per hour of a lignin-phenolic resin can be pr~Y~x~l in a commercial spray dryer, in comparison to spray dryLng of PF without lign m . m is 0 L~tS~ a higher prodbcti~n rate and impoiL~IL saving for a resi;n powder prDducsr.

m e followLng examples illustrate the ~uY~Lies of pre-cure resistant ~h~ives ob*dined from a mixture of a PF, a lignLn and an ammcnium salt. m e PF may be a s~rfa oe phenolic resin or a faster curing core phenolic resin. T~e core phenolic resin prodbces a faster curLng pre-cure resistant PF-lignin adhesive.

EXample 6 In a ~ill, a waferboard ~at may rest on a caul plate at 140 - 150 C for a few minutes before being transferred into the pre~s. In the p~ess, the mat may then rest on the hot press platen few seoands before pre~s closing to target panel thichless. If the resin is not pr~re resistant and cures prematurely, a poor band will result. One n~.U~d to ~differentiate be~een a face and ~re resin is th~3 s~ce cure test. Ihe test imrolved placing 0.75 g of resin an a hot platen ~ 215863~

set at a tempera~re of 150' and sE~read back and forth until hardened and cannot be spread furt~r. A fast core resin will generally have a short str~ke cure of 15-25 seconds, which co~qxl~es to 35-45 seoonds for a face pre~e resistant adhesive.

As sh~ in Table 5, a resin made frc~ ~I,S~iL (30%) and P~
(70%) had a str~e cure test of 42 se~, if an~nium sulF~ate salt was added, longer stroke c~re test cauld be d~Air~l. It was also po;sihle to ~tain a resin with stroke cure test ~ ~ arable to a commercial face r~sin (3S - 45 seconds) fram kraft lignin (27%), (N~), S~l (3%) and a ~ ~ ial PF (70%). Similar results were also ci~lL~ed with lign m other than kraft or N~S5L, such as N~.~CT. or o,~ku~olv lignin.

215~63fi ' ' Table S
Effect of lignin and ammonium sulphate additives on 5stroke cure test of ccmmercial core phenolic resin powder (sprayed at 200'C inlet and 90'C outlet) PF.l pFbl Kraft' N~LSSL (N~L)~30, Stroke Cure Tbst at 15C~C

(%) (%) (%) (%) (%) (sec. ) 94 o 0 0 6 36 1 PF. and PFb are core PF resin 2 Kraft lignin precipitated and washed to remove the free inorganic salts 2~5~636 FxamPle 7 In okher methods to test the resi ~ of an adhesive to "F~ alre", the caul plate was heated m an oven at 200 C and then pl~e~ on the waferboard mat (wafers blended with the adhesive being tested) for five munutes under 25 kg weight. Ihe mat was ~ n pressed in a normal manner. The panels were then tested for inberral band ~LL~ ~ U~ (IB). For the Erercmre resistant adhesives, it w3s found the hot caul plate treatment had no adverse effects on IB. m e tL~t~ re of the 1.6 mm thick metal caul plate at exit fru~ the oven was cb6erved to be l9~C. At ccntact w~ith the wood furnish, the caul plate cooled off gradually to aE~IxKLmately 80 C w~ithin the 5 munute ~LeaL

me results set forth in Table 6 below are for wafe~Lcau~
with the mat treated with a h~t caul plate prior to pressing. m e hot caul plate treatment had an adverse effect on IB and fa oe failure for the sample bonded with the cx~ rcial core PF and also the binary PF
copolymer. No ad~erse effect was noticed for the panels bonded w~ith N~LSSL-PF and kraft-PF-(N~L)~3o, resins as IB and fa oe failure test results were similar to those cl*lL~ned wqth panels bonded with the cc~Yercial face PF control.

2 1 ~8636 Table 6 Effect of caul plate heat treatment of mat~
5prior to pressing on ~ ical ~lopt~ies of three layer wafertlxmls' bonded with ocmmercial and experiment21 resins Fa oe Resin' Density IB Face' Failure (kg/h~) (MPa) (%) Commercial Fa oe PF 675 .467 8 P~ Cro6slinker 664 .390 42 N~LSSL (30%)-P~(70%) 652 .450 8 Kraft (27%)-F~(70%)- 650 .509 8 (N~ (3%) CX~ rcial Cbre PF 648 .179 100 ~ Caul plate heated in an oven at 200'C then placed on top of wafelL~al~ mat 5 minutes ~ r 55 kg weight ' Panel pressed 4 minutes at 220 C with 2.0% resLn ' Sample ~ nation (failure at surfa oe layers during test m g of 12 IB samples The core wafers were bcnded with a cx~ ial core PF for all the panels S Experimental resin cnrro6~A of high Mw PF (70%) and low M~ PF
(30%) resins

Claims (7)

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

1. A method of producing a pre-cure resistant surface adhesive having a stroke cure test time of about 35 to about 45 seconds comprising mixing a fast curing cross-linked thermosetting adhesive having a stroke cure test time of from about 15 to 35 seconds and having a pH of from 8 to 11 and which is useful for binding lignocellulosic materials together, products by the step of reacting at an elevated temperature 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 average molecular weight phenol-formaldehyde to said low average molecular 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, with an ammonium salt.

2. The method as claimed in claim 1, wherein said ammonium salt is mixed with said lignin prior to reacting said binary phenol-formaldehyde with said lignin.

3. The method as claimed in claim 1, 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 and said ammonium salt is added to at least one of said lignin and said binary phenol-formaldehyde prior to reacting said lignin and said binary phenol-formaldehyde.

4. The method as claimed in claim 1, wherein said ammonium salt is selected from the group consisting of ammonium based spent sulphite liquor, ammonium sulphate, and ammonium p-toluenesulfonic acid and said ammonium salt is added to said lignin and said binary phenol-formaldehyde, and the pH of the adhesive is adjusted from between 9 to 11 by the additional of ammonium hydroxide.

5. The method as claimed in claim 1, wherein said ammonium salt is added to said adhesive in an amount from 0.1 to 30% on a dry weight basis, and the pH of the adhesive is adjusted from between 7 and 11.

6. A pre-cure resistant thermosetting surface adhesive useful for binding lignocellulosic materials together, said adhesive having a pH from 7 to 11 and comprising cross-linked lignin, 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, and an ammonium salt selected from the group consisting of at least one of ammonium sulphate, ammonium p-toluenesulfonic acid and ammonium chloride.

7. A method of producing a pre-cure resistant cross-linked thermosetting surface adhesive which comprises admixing an ammonium salt selected from the group consisting of at least one ammonium sulphate, ammonium p-toluenesulfonic acid and ammonium chloride with lignin and 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 for a time and at a temperature sufficient to cross-link said lignin and said binary phenol-formaldehyde and adjusting the pH of said adhesive to a pH range from 7 to 11.