CA1059699A - Rapidly-foamable, fast-setting phenolic resin plywood glue - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE A rapidly-foamable, fast setting phenolic resin liquid ply-wood glue for use particularly in a plywood production line includ-ing an in-line continuous foaming unit comprises an aqueous alkaline solution of a fast setting, highly advanced, phenol aldehyde resin and a dried animal blood foaming agent. Glyoxal or other aldehyde is included to control the viscosity of the glue, Upon agitation in air or other gas the resulting glue is uniformly foamable to a den-sity of the order of 0.2 gm/cc in a time of the order of two seconds.

Description

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RAPIDLY-FOAMABLE, ~ST-SETTING
PHENOLIC RESIN PLY~OOD GLUE
This invention relates to liquid glues of the class used in the manufacture of plywood. It pertains particularly to liquid glues comprising phenolic resins and dried animal blood, which are rapidly foamable and fast setting and which accordingly in the manu~acture of plywood are applicable to the in-line application of foamed glues to wood veneers.
The application of phenolic resin glues in foamed condition is well known and has been practiced commercially from time to time over a period of several years. Their application has been attended by many significant advantages, including more uniform coverage per unit weight of glue; satisfactory coverage of rough surfaces with less glue; minimum penetration into the substrate; faster drying;
the use of lower viscosity glues; the elimination of the necessity of using solid extenders; and, in some instances, lower unit glue i:
weight and therefore lower glue costs while still producing satis-factory bonding.
This application of the phenolic resin glues prçsupposes,of course, that they are foamable. In the past, it has been possible to foam such glues adequately since relatively low molecular weight ~;
phenolic resins were used in their manufacture. However, the use of phenolic resins o~ low molecular weight created an economic problem in that a relatively long press time was required to cure them in the plywood hot presses. This in turn delayed production and increas-ed costs.
In an effort to overcome this problem, the plywood industry has turned to the use of more highly advanced resins which cure fast~
er in the press. Such resins, being less soluble in alkaline solu-tions than are the less highly advanced resins, presently are sup- :-plied to the market in aqueous alkaline solutions containing about ~o% by weight resin solids, as opposed to the solutions containing about 50% resin solids, formerly used extensively.
A serious problem attending the use of the present day more ~L, ,~ .`

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highly advanaed phenolic resin glues is that using conventional foaming techniques, they are not foamable at all, or at least `
with sufficient speed to be useful in the commercial production of plywood using foamed glue.
In accordance with the Cone procedure, phenolic resin glue is passed continuously from a reservoir to an in-line foamer where it is converted to foam. The resulting foam then is passed continuously to an applicator head which applies it to wood veneer surfaces in the plywood production line. Since the volume requirements of foam are high and the capacity of an in-line foamer necessariiy is restricted, it is essential, ~;~
~ for the successful application of this procedure, that the foaming of the liquid phenolic resin glue occur very rapidly, i.e. in a few seconds. Up to the present time this has not been possible, using the highly advanced phenolic resin glues of present day commerce.
A possible soiution to the problem is the inclusion in the glue mix of a suitable foaming agent for phenolic resin glues.
Menger et al, U.S. Patent 2,323,831, for example, suggests a large number of foaming agents which may be used to assist in the foaming of phenolic resin glues.
Listed as foaming agents in this patent are such materials as casein, hide glue, bone glue, blood, blood albumen r ~',i saponins, the salts of diisopropyl naphthalene sulfonic acid, the salts of sulfonated tar oils or of sulfonated fatty acids, the ammonium salts of high molecular weight aliphatic carboxylic acids such as fatty acids, wax acids, rosin acids and montanic acid. This reference does not indicate, however, the applicability of these foaming agents to the foaming of highly advanced phenolic resin glues, nor could it, since such glues were not commercially available nor in use at the time the Menger et al work was done.

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Neither does the Menger et al disclosure recognize that, of all the foaming agents listed, dried blood when added to a phenolic resin glue will convert it to a product which can be foamed successfully in a matter of a few seconds in an in-line plywood plant glue foaming unit to produce a uniform, stable foamed glue which can be applied to advantage in the commercial manufacture of plywood.
Applicants have discovered that this is the case. In -accordance with the present invention rapidly foamable, fast setting phenolic resin plywood glue is made by forming an aqueous alkaline solution of a highly advanced resinous condensation product of a phenol and an aldehyde, particularly phenol and formaldehyde, having a resin solids content of from 30-45% by -~
weight. The degree of advancement of the resin is such as to impart to the aqueous resin solution a viscosity of from 3-30 poises.
Mixed with this is a dried, powdered animal blood product used in amount sufficient to render the liquid glue convertible upon agitation in a gas and in 12ss than 30 seconds preferably less than 15 seconds to a foam having a density of i: .
less than 0.5 and more preferably, in less than 15 seconds to a foam having a density of less than 0.3.

Water is included in the glue mix in amount sufficient o impart to the adhesive a viscosity of from 1-50 poises.

From 0.1 to 10% by weight, based on the dry weight of the ;
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blood, of glyoxal or other aldehyde may be included in the blend to lower its viscosity to working levels.
The resulting glue mix upon introduction into an in-line continuous foamer may be foamed in a few seconds to a uniform foam having a density of less than 0.5, specifically a~out 0.2 grams/cc., and accordingly is well adapted to continuous application to traveling plywood veneers in a plywood mill production line. ;

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~S~6~g In accordance with one broad aspect, the invention relates to a rapidly foamable, fast setting phenolic resin liquid plywood glue comprising: `
a) an aqueous alkalin~ solution of a resinous . :
condensation product of a phenol and an aldehyde having a resin solids content of from 30-45% by weight, the resinous condensation product having a degree of advancement such as to impart to the aqueous resin solution a viscosity of from 3-30 poises, ;
b) dried animal blood having a water solubility not exceeding 90% by weight used in amount sufficient to render the - liquid glue convertible upon agitation in a gas and in less than 30 seconds, to a foam having a density of less than 0.5 grams~cc~
. c) from 0.1 to 10% by weight, based on the dried weight of the blood, of an aldehyde glue viscosity lowering agent, and .
d) water used in amount sufficient to impart to the liquid glue a viscosity of from 1-50 poises.
20. The hereindescribed glue compositions when foamed ~;
are also characteri~ed by the following important advantages:
They are substantially faster curing than those not including blood. This decreases press time and increases production.

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They have a substantially longer assembly time tolerance, corres-pondingly facilitating plant schedules. They require less heat for curing, thereby lowering required press temperatures and further decre~sing press times.
They do not require the presence of a filler such as clay, walnu~ shell flour, oat hull flour, wood ~lour, ground bark, or ground corn cobs, which normally are used with conventional plywood glues with accompanying well known pro~lems. Accordingly, it is pos~
sible to reduce the amount of water in the glue mix. This in turn 10 reduces the likelihood of blistering in the press.
Considering the foregoing in greater detail:
As noted above, the hereindescribed phenolic resin plywood glues comprise essentially an aqueous alkaline solution of a highly -~advanced resinous condensation product of a phenol and an aldehyde;
a quantity of dried animal blood foaming agent; water; and, option-ally, an aldehyde type viscosity-lowering agent.
The resinous condensation product of a phenol and an alde- i hyde used in the glues of the invention may comprise any of those -suitable for use in the production of plywood-type glue~. Typical 20 phenols employed in the manufacture of such products comprise phenol itself, the cresols, and resorcinol. Typi~al aldehydes employed in the manufacture of such products include formaldehyde, acetaldehyde, and furura1. The commonest of such products, and the one with re~er-ence to which the present invention is described, comprises the resinous condensation product of phenol and formaldehyde.
Whatever its identity, the phenolic resin adhesive employed ;
in the present formulation is characterized by having a relatively high degree of advancement so that it will set rapidly in the ply-wood press, i.e. in a matter of five minutes or so under the usual 30 press conditions, as compared with six or seven minutes for the for-merly used phenolic resins having a lesser degree of advancement The degree of advancement of such resins is a dif~icult property to characterize. However~ for the present purposes the phen-olic resins are contemplated which have a resin solids content of ." ~ I ' 1~ 5~from 30-45% by weight, but have a degree of advancemen't such as to impart to the aqueous resin solutions in which they are contain ed a viscosity of from 3-30 poises. When incorporated in a plywood glue the resulting glue is capable oE producing plywood association 'lexterior grade" quality glue bonds when two 7/16 inch three ply panels are pressed per plywood press opening for a period of 6 1/2 minutes with press plates at 300F.
Such phenolic resins normally are supplied to ~he plywood trade in the form of their aqueous alkaline solutions having a suf-ficient content of caustic soda or other alkaline material to im-part to them a pH of from 9-12.
The blood which is the second major component of the present-ly described plywood adhesives comprises the dried blood of com-merce available in powdered form. This product is manufactured by collecting beef, hog or sheep blood from the slaughter house floor and dehydrating it under controlled conditions to a dry powder form.
In one successfully operated commercial process, the blood `;
is sprayed into a cyclone separator containing hot air under care-fully controlled conditions of temperature and time to produce a spray dried blood product of desired properties. By controlling the operating variables the degree of water solubility of the dry blood may be varied over a range of from completely soluble to com-pletely insoluble iIl waterO
Although it is possible to use any of the solubility grades ~ i of blood, from completel~ soluble to completely insoluble, it is preferred to use a blood product having a water solubility of from 30-90% by weight. Blood products having a solubility of less than 30% are not quite as efficient as foaming agents as are those hav-ing a greater degree of water solubility. On the other hand, blood products having a water solubility of more than 90% tend to cause gelation of the compositions.
The third major component of the hereindescribed plywood glues is water. A certain content o water is introduced into ~he glue mix via the water content of the aqueous resin employed. Addi-5~ 6~ ~tional water may be added, however, in amount sufficient to produce a product viscosity of the desired value, broadly from 1-50 poises, preferably from 1-30 poises.
Under some conditions, combin:ing blood with highly advanced phenolic resin glue solutions creates a problem in that the result-ing mixture has a higher viscosity than either of its components.
Furthermore, this viscosity tends to increase rapidly with time to levels interfering with normal plant procedures.
The degree of viscosity increase may be controlled to some extent by minimizing the amount of added blood, maximizing the a-mount of added water, using blood of a lower degree of water solu-bility, and using a less highly advanced resin.
For practical purpose, it often is not possible to control -these variables sufficiently to produce the desired result. In such cases, advantage may be taken of our discovery that the vis-cosity of the phenolic resin plywood glues of the class described herein may be controlled rapidly and effectively by the inclusion ;- -in the compositions of a viscosity-controlling amount of an alipha-tic or aromatic aldehyde. ~ -Typical of materials of this class which may be employed are the lower aliphatic aldehydes including formaldehyde; ~he formalde-hyde donors, such as paraformaldehyde, sodium sulfite formaldehyde~
and oxyzolidine; glyoxal; glutaraldehyde; pyruvicaldehyde; and the lower molecular weight aromatic aldehydes such as benzaldehyde.
These aldehydes may be used singly or in combination with each other. They are used in amount suficient to reduce the viscosity of the glue to the desired level. Normally this will require from `~
O.YOto 10% by weight of aldehyde, based on the weight of the solid ;-blood content of the composition.
3~ The viscosity reducing effect of the aldehyde is surprising in view of the fact that normally aldehydes added to alkaline solu-tions of blood markedly increase, rather than decrease, the vis-cosities of the solutions. Furthermore, the addition of the alde-hydes to the presently described compositions does not impair ~ 59~ig9 either the foam inducing or the adhesion enhancing properties of the blood.
The glues of the invention are easily and simply prepared, usually in two stages.
In the first stage, the predetermined amount of water and solid dried blood are thoroughIy mixed in a suitable mixer.
From one to three minutes of mixing suffices. Next the selected phenolic resin is added to the mixture and the mixing continued for another period of from one to three minutes. The mixing may be carried out at room temperature and no special precautions such as cooling of the mix are required.
- In the event that an aldehyde anti-thickener is to be included, the foregoing procedure is modified by adding the selected aldehyde in the predetermined amount to the mixer in the first stage of mixing. To be effective, the aldehyde should be added to the blood-water mixture before the blood is mixed with the resin. t The compositions prepared as above are ready for use in the manufacture of plywood. Although they may be foamed ....
batchwise before application to the veneers, they are particularly suited or continuous in-line foaming at a high production rate. Their use is attended by the above noted advantages of rapid and uniform foaming, even when highly -`
advanced resins are used; long assembly time tolerance;
elimination of the need for filler use with attendant disadvantages; faster curing in the press; and less heat required ~ -for curing. `~
The process of the invention is illustrated by the following examples wherein parts are given in parts by weight ` ;
and percentages are given in percentages by weight.

This example compares the application of the herein ' .. ..

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described rapidly foamable, fast setting phenolic resin glue .
containing a highly advanced phenolic resin, in both foamed and unfoamed condition, with a commercial phenolic resin glue ~:
containing phenolic '', ' ~ ~,' ' ' ~, ~, , , .
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- ~)596,~9 resin having a conventiona1 de~ree of advancement, in the manu-facture o plywood~
The adhesive composition o~ the invention wa~ prep~red as ~ollowsi:
240 Partis water and 50 parts blood having a water solubility at 72F. of 50% by weight were mixed in a mechanical ~ixer for t~o minutes. l,000 Parts of aqueou~ alkallne phenol formaldehyde resin *~"~orden W-166S") having a viscosity of 5 poises, a pH of about 11 and ~ resin solids content of 40% ~y weight were added and the mix-in~ continued for 2 minutes. The compo~ition then wa~ resdy ~or applic8tion.
The conventional phenolic reæin ~dhesive compositlon was pre- :
- pared as followQ:
220 Parts water at 70, lO0 parts alder bark filler, and 34 parts wheat flour filler were mixed for f1ve mlnutes. 75 P~ir~s of aqueous alksline highly advanced phenol form~ldeh~de liquld resin ~"Bord~n W-166S") h~ving a ViRco~ity of 5 poises, a pH o~ ~bou~
ll snd a ~olids content of about 40% wexe added and the mixin~ con~ ~:
tinued for two minute~.

2~ 30 P~rts 50% aqueous C8U8tiC soda then was added and ehe mix-~n8 con~inued for ~no~her two m~nuees..l5 Parts qoda ~sh wai~ iadded ~.
and ~he m~xing continued for~nother 20 min~tes. 540 P~rts of the ~sme phenol form~ldehyde resin w~ added and ~he mix~ng continued for 5 minutes. Thi~ gave the finii~hed ~onvention~l adhesive compo- ~;...
sition.
The two ~dhe~ive compo~itions prepared in the fore~o~ng man-ner then were ~pplied to the ma~ufscture of plywood.
In one te~t prodedure ~i portion of the fidhe~lve composition ~?
of the lnventio~ which cont~ined bl~od ~iS a foaming a8ent wa~ in-troduced into the in-line contlnuous fo~mer described above and thereb~ converted i~ a foaming time of ~bout three second~ to B
uniLform foam h~vLn~ a den~ of 0.2 grAm~ p~r c~. Thl~ ~æ e~
truded on~o the ~rfacea of wood vereer~ ~hi~ih then wer~ l~ld up lneo pl~wo~d asse~lie3.
Trademark , . - . . .,, ., ~ .; ~ .

~ss~s For purposes of comparison, another portion of the blood-resin glue o~ the invention was roller spread on wood veneers which then were laid up into plywood making assemblies in the usual man-ner.
The conventional phenol-forma:Ldehyde resin glue could not be foamed in the in-line foaming unit in the dwell time of the unit.
It was rolle~ spread on plywood veneers which then were laid up in-to plywood assemblies in the usual manner.
In all three cases the assemblies comprised three ply Douglas fir panels of 7/16" thickness pressed two per press opening in a hot press with plates at 300~F. for 5 l/4 minutes. Test pieces were cut from the resulting panels and subjected to the standard Plywood Association shear test. In each case groups of panels having assem~
bly times of 4, 14 and 32 minutes were tested. This spans the range of assembly times ordinarily used in the plywood mill. The test re-sults were averaged. -The glue spread rate for the blood-resin glues of the inven-tion was 26 pounds per thousand square ~eet of single glue line, that for the conventional phenolic resin glueg 34 pounds. The pounds ;
of resin applied per thousand s~uare feet thus was approximately the same in both cases.
The results of the test are given in Table I. l ;
TABLE I
PLYWOOD SXEAR TEST RESULTS - (AVERAGE) Load in % Wood Glue Procedure Lbs.Per Sq. In. Failure Blood Resin Foamed and Extruded246 - 97 Blood Resin Not Foamed, Roller Spread 202 - 65 Conventional Not Foamed, Roller Phenolic Resin Spread 34 - 02 30 ~lue The foregoing results clearly indicate several things. First, the hereindescribed blood resin glue is rapidly foamable under con-ditions in which the conventional phenolic resin glue is not foam-able a~ all, although both glues contain the same phenolic resin '.

,, , _ ~596~9 o high degree of advancement. Second, the hereindesc~ibed blood resin glues can be cured adequately in the press at a press time of only 5 1/4 minutes. The usual press time required for the con-ventional phenolic resin glue descriked above is 6 1/4 minutes or longer. This represents a saving in press time of almost 20%. Third, the blood-resin composition of the invention foamed has a noti~eably faster cure than does the same blood-resin mixture unfoamed. This is unexpected and additionally indical~es the unique quality of the composition.
In a manner similar to the foregoing there are prepared and applied the glues of the invention using, in place of the phenol-formaldehyde resin: a cresol formaldehyde resin, a resorcinol or-maldehyde resin, a phenol acetaldehyde resin, or a phenol furfural resin.
EXAMPLE II
This example illustrates the unique suitability of dried ani~
mal blood as a rapid foaming agent for foaming phenolic resin solu- `~
tions containing phenolic resins of a high degree of advancem~
In the preparation of the test compositions, "x" parts of the 20 test agent was mixed with 300 parts of water for two minutes. The re-sulting mixture then was added to 1,000 parts of aqueous alkaline ;~
phenol-formaldehyde resin having a solids content of 40% by weight, a viscosity of about 5 poises and a pH of about 11 and mixed for another two minùtes. `, The resulting composition then was passed continuously through an in-line foamer where it was mixed with a stream oE air. In order to foam the mixture exhaustively, the streams were recirculated un~
til the liquid would take up no more air. This required a time of up to 3 minutes.
The stream when it emerged from the foamer contained large bubbles of incorporated air. These bubbles were separated from the stream and measured v~lume of the foamed material, free of large bubbles, was weighed to determine its density (grams per cubic ce~ti-meter).
The results are given ~ ~Table II.

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TABLE II
FOAMING AGENT
Foamed Density Tes~ No. Kind Amount ~.
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parts by .- 1 Blood-30% water weight) `:
- soluble 50 193 2 " ll 30. 320

3 B lood ~40% wa t er soluble 30 . 221

4 Blood-50% water ~oluble 50 .12 1 " " ~0. 172 ~
6 ~l 1. 30 .251 -7 " " 20.4~7 8 B loo d -7()% wa t er soluble 30 ,290 9 Bl~od-90% water soluble 3Q . 301 ~Q Blood-water insolubl e 30 . 484 11 .l Soybean f lour 100 . 834 2012 Animal glue 50 , 990 13 Alkyl aryl sulfon~te 30 o712 type foaming agent ~k( 'Ultra T~et 60L") 14 " " 60 . 5~4 -Sodium ~alt o:E an alkyl aryl 8ulfona~e type wet~ing a,~ent ::
( 'Ultra Wet SK ) 3n .780 .~::
16 Ole~:c acid l .
~ Neof~t 9bO4") 30 . 846 17 Stearic acid ~ :
Cheofat 854") 30 1.03 .. :
18 Aliph~t~c amine type ':
wetting a~ent ;::
~ ~"Armeen DM~") 30 1.08 19 Amine t~pe wetting ~gent*( 'Armflow 65") 30 1.05 `
Sodium alkyl aryrl poly-ether sulfate type wet'cillg agent~("Trlton 770") 30 .984 1 " " 30 . 9~5 ~`.
~(Triton X200"~
22 Palmc>llve soap 30 ,87fi The test resule.Q ~et forth in Table II clearly indicate ehe unique suitability of drled animal blood a9 a foaming agent Xor highly ~dvanced aqueous alkaline phenol formaldehyd~ resins. Even "~
when exhaustively foamed over a per~od o 8everal mlnute~ 7 the lise-ed non-blood foaming agen~, which all ~re of recog;nized potencr"

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~05~699 , did not produce a foam having the density of 0.5 or less necessary for successful application in the in-line application for foamed glue to plywood production.
The test results further indicate that animal bloods of all grades of water solubility, i.e. per cent soluble in water at 72F.
in 5 minutes, share this unique property. Thus even blood which has been heated until it is totally insoluble is a reasonably efficient foaming agent for the intended purpose. Bloods having solubility in the range of 30 to 90% by weight are preferred.
`10 EXAMPLE III ;;
This example illustrates the effectiveness of a minor pro-portion of an aldehyde in lowering the viscosity of the hereindes-cribed blood-resin adhesive compositions:
The procedure o~ Example I was followed with the exception -~
that the indicated amount of the indicated aldehyde was added to the water-dry blood mixture preliminary to mixing in the phenolic resin. The blood employed was dried animal blood having a water ,'J~
solubility of 40-50% by weight~ The resin employed was an aqueous alkaline solution having a pH of from 9-11, a viscosity of 5 poises, and a solids content of highly advanced phenol formaldehyde resin of 40%.
TABLE III
Amount 3 1/2 hr. 22 hr.
Aldehyde Addi~ive (Parts by weight)Viscosity Viscosity (~oises2 (Poises) None - (Control) 45.6 260 40% Aqueous Glyoxal 1 9.2 16.3 " " " 3 .5 7.3 37% Aqueous Formaldehyde 1 9 14 ;
" " " 3 4 4.3 ~;
25% Aqueous Glutaraldehyde 3 9 14 45% Aqueous Pyruvic 3 10.1 15.8 -Aldehyde 100% Benzaldehyde 3 14.8 27.7 Sodium Sulfite Formaldehyde 6 11.2 16 60% Aqueous Oxyzolidine 3 9.7 12.0 ~ .,`
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Thus the addition of even a small amount of a wide variety of aldehydes effectively controls the viscosity of the glues.

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Claims (17)

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

1. A rapidly foamable, fast setting phenolic resin liquid ply-wood glue comprising:
a) an aqueous alkaline solution of a resinous condensation pro-duct of a phenol and an aldehyde having a resin solids content of from 30-45% by weight, the resinous condensation product hav-ing a degree of advancement such as to impart to the aqueous resin solution a viscosity of from 3-30 poises, b) dried animal blood having a water solubility not exceeding 90%
by weight used in amount sufficient to render the liquid glue convertible upon agitation in a gas and in less than 30 seconds, to a foam having a density of less than 0.5 grams/cc, c) from 0.1 to 10% by weight, based on the dried weight of the blood, of an aldehyde glue viscosity lowering agent, and d) water used in amount sufficient to impart to the liquid glue a viscosity of from 1-50 poises.

2. The glue of claim 1 wherein the resinous condensation pro-duct comprises a resinous condensation product of phenol and for-maldehyde.

3. The glue of claim 2 wherein the dried animal blood comprises spray dried beef blood.

4. The glue of claim 2 wherein the dried animal blood has a water solubility of from 30-90% by weight.

5. The glue of claim 2 wherein the blood is used in amount suf-ficient to render the liquid adhesive convertible to a foam having a density of less than 0.3 upon agitation in a gas in less than 15 seconds.

6. The glue of claim 2 wherein water is used in amount suffi-cient to impart to the liquid adhesive a viscosity of from 1-30 poises.

7. The glue of claim 1 having a pH of from 9-12.

8. The glue of claim 2 wherein the dried animal blood is used in an amount of 5-30% by weight, based on the weight of the resin solids content of the adhesive.

9. The glue of claim 2 wherein the dried animal blood is used in an amount of 8-15% by weight, based on the weight of the resin solids content of the adhesive.

10. The glue of claim 1 wherein the viscosity lowering agent com-prises at least one member of the group consisting of formaldehyde, paraformaldehyde, sodium sulfite formaldehyde, oxyzolidine, acetal-dehyde, glyoxal, glutaraldehyde, pyruvicaldehyde and benzaldehyde.

11. The glue of claim 10 wherein the viscosity lowering agent comprises formaldehyde.

12. The glue of claim 10 wherein the viscosity lowering agent comprises acetaldehyde.

13. The glue of claim 10 wherein the viscosity lowering agent comprises glyoxal.

14. The glue of claim 10 wherein the viscosity lowering agent comprises glutaraldehyde.

15. The glue of claim 10 wherein the viscosity lowering agent comprises pyruvicaldehyde.

16. The glue of claim 2 wherein the blood comprises dried beef blood.

17. The glue of claim 2 wherein the blood has a water solubility of from 30-90% by weight, the blood is used in amount sufficient to render the liquid glue convertible to a foam having a density of less than 0.5 by agitation in a gas for less than 15 seconds, and the water is used in amount sufficient to impart to the liquid glue a viscosity of from 1-30 poises.