3 '86010 0
U. S. Department of Agriculture, Forest Servic e
FOREST PRODUCTS LABORATOR Y
In cooperation with the University of Wisconsin
MADISON, WISCONSI N
R 7
DEVELOPMENT OF WOOD ADHESIVES AND GLUING TECHNI C
By T . R. TRUA X
Senior Wood Technologist
Published in Transactions of A . S . M. E.
February 28, 1932
DEVELOPMENT OF WOOD ADHESIVES AND GLUING TECHNIC *
(Published in Transactions of the A.S.M .E., February 28, 1932 )
By T . R TRUAXl, Senior Wood Technologis t
Furniture and other relics of earlier civilizations attes t
the gluing of wood (9)2 as an art of long standing, but they furnish
little authentic information that is of practical value to the crafts man of today as to kinds and quality of adhesives used or of method s
or processes . Because of mechanical and chemical progress, it i s
doubtful that even reliable and complete historical records woul d
add much of practical value to present-day gluing operations . Consequentlyy this paper will discuss only the more recent development s
in glues and in the technic of using'them .
Developmentof Glue s
It is a common assumption that the joints in chests an d
other articles recovered in recent times from ancient tombs wer e
glued with adhesives that were superior to modern glues . The fact
that the joints have endured for many centuries is, however, no posi tive evidence that the adhesives were superior to present glues . On
the other hand, the fact that the wood in these particular article s
was not damaged leads us to believe that the surrounding condition s
were not extremely severe . In other articles recovered there ha s
been more or less damage, presumably to both glue and wood . Adhesive s
are available today that might reasonably be expected to withstand permanent exposure to conditions where wood is not deteriorated .
Animal, and fish glues were undoubtedly of ancient origin an d
may have been used by the craftsmen of 20 or 30 centuries ago . Certainly they were the best known and most extensively used a few
*Presented at the Sixth Annual Wood-Industries Meeting, Winston-Salem ,
N . C ., Oct . 15-16, 1931, of The American Society of Mechanical
Engineers .
1 he author has spent 13 years in research and investigational work o n
glues and gluing problems at the Forest Products Laboratory .
%Umbers in parentheses apply to references cited at the end of th e
paper .
R947
centuries ago . Blood-albumin glues are reputed by some to have had an
early origin and perhaps casein glues were also known to the ancients .
Large-scale production of glues under efficient and refined methods ,
however, is a development of modern times . Manufacturing under mor e
precise, controlled methods has resulted in glues that are probably o f
higher and more uniform quality than the ancient glues from the sam e
sources . Coincident with better manufacture, improvements have occurre d
in the testing and grading of adhesives and better technic has bee n
developed in their use .
the •
it has been only within the last 2 0
years tiat' animal an
g ues have had serious competitors in th e
woodworking field . Starch glues, suitable for wood joints, were devel oped about 1912, and during the World War casein glues came into use o n
a commercial scale in the ',_ .odworking trade . Both starch and casei n
glues have grown in iuser • ce during intervening years . Vegetable a
subsequent to the World War ,
• ial
..and th
1 too,
ugh the protei n
get
cu
41.19*-
ot
t or proposed
7es for wood .
ably, and othos may eventually b e
ive tests over have been
esives . Samples o f
orest Products Labora
itabi
ester-- si n
been used to some
as been used conas i s
or
- 't of
going
m, however, have bee n
er to obtain some ide a
is in wood . The result s
anding proper the miscellane o
oanand Asiat i
use appears to be dimin een used principally i n
ar to be taking their plac e
er resistance is the most
so papers on these four classes of glues presented at the Sixt h
Annual Meeting of the Wood-Ynd .ustries Division of The American Soci ety of Mechanical Engineers .
valuable property of blood-albumin glues ; the necessity for hot-press ing is the chief disadvantage . Because the cheaper cold-press metho d
of gluing prevails in the United States, the blood-albumin glues hav e
been used here only in a few plants . Attempts to produce a cold-pres s
blood-albumin glue have met with only partial success .4
Phenol-Aldehyde Adhesives .--By heating a phenol with a n
aldehyde it is possible to produce hard, strong adhesive substance s
that appear to be unaffected by moisture in any form . Adhesives o f
this type that have been produced commercially have yielded joint s
in wood of high strength when tested both dry and wet . Phenol-alde hyde adhesives are apparently more water resistant than any of th e
glues now in common use . They are, however, several times as costl y
as the common woodworking glues, and the necessity for hot-pressin g
in order to produce the characteristic bakelite reaction is a disa dvantage particularly under prevailing methods of manufacture i n
American factories . Unless the phenol-aldehyde adhesives can be .pro duced more cheaply, they will be restricted to special uses . Test s
made in Germany indicated that similar adhesives of this class (8 )
became brittle in wood joints when dry, but this characteristic wa s
not found to be objectionalbe in the tests at the Forest Product s
Laboratory .
Adhesives fromRubber .--Joints can also be made in wood b y
hot-pressing with adhesives made from rubber . Two commercial product s
of this type have been tested at the Forest Products Laboratory . The
joints were strong both dry and wet, but the adhesives are expensive .
They may find limited uses for special purposes .
CelluloseEsters .--Cellulose cements have been suggested a t
various times as adhesives for wood, and tests have been made on sev eral products . Most of them are too thin and require more than on e
application to make good joints in wood, When so used, they are slow '
drying, and they are also relatively expensive . It is reported tha t
joints of good strength and high water resistance have been made wit h
them in Germany (8) . Cellulose cements can be cold-pressed, but thei r
cost and difficulty of use appear to make them impractical at presen t
for general woodworking purposes .
Silicate of$oda .--Silicate of soda makes joints in wood o f
fairly high dry strength . It is cheap, easy to apply, and finds a
large use in fiber containers, but the joints are weak when wet . Silicate of soda changes in properties with age and is therefore not con sidered a permanent binder .
4A blood-albumin glue, which can be cold pressed and which is recom mended only for light-weight woods, has been developed at the For est Products Laboratory . See U . S . Department of Agricultur e
Technical Bulletin No . 205, page 54 ;
R947
-3-
Waxes, Gums, andAsphalts .--Waxes, gums, and asphalts hav e
been proposed as adhesives for wood . So far none of them has prove d
to be satisfactory.
Dry Glue Films
Attempts have been made from time to time to produce a dr y
film of glue that could be used in place of a liquid adhesive, Th e
advantages of such a process are obvious, especially in laying thi n
veneer, but as yet a material of this kind has not come into commer cial production in the United States . Some work was done in 1918 a t
the Forest Products Laboratory on a dry glue process, and a film wa s
produced experimentally using blood albumin as a base (1, 11) . So
far as is known, this material is not being produced commercially .
Recently published accounts of tests in Germany indicate that attempt s
are being made in the same direction abroad (8) . Films made fro m
cresol-formaldehyde and from cellulose esters are reported to giv e
good results . The dry-glue films, so far produced, require the us e
of a hot press . No information is available as to cost, but the dr y
films of these materials are undoubtedly more expensive than commo n
glue mixtures .
Testing Glue s
Progress and development in the manufacture of glue ar e
necessarily related to its testing . Some means of measuring qualit y
is essential to determine the value of new products and the improve ment of old ones . Not only is glue testing necessary to the manufacturer, but it is also important to the user . It is his means o f
determining whether he gets value received for his money, and stil l
more important, it helps to insure the value and quality of his ow n
products . A table, a chair, a door, or an airplane wing beam is n o
better than the joints it contains .
Manufacturers commonly have their own methods of checking
the quality of their raw materials and their manufactured glues . Consumers and others, likewise, use one form or another of test in an
effort to check the quality of glues and to determine their suitability for a particular job . This has led to many forms and kind s
of tests, all of which are aimed at essentially the same purpose .
Standardization of tests and testing methods is therefore importan t
to a common understanding . A considerable amount of work has bee n
done upon standardization, but much remains yet to be done .
The testing of animal glues has reached a higher degree o f
perfection than the testing of other types of adhesives . A number o f
workers have investigated the physical and chemical properties o f
animal glues and methods of measuring them, and, as a result, clearl y
R947
-4-
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n .
C
cif
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f
r4
tests of the g
=elves are ,
curers, compri s
Lion of Glue M
s adopted unifo r
imal-glue makers ,
S .1Pederal S cifications Board h a
fication for Govern* LJ• '
woodw• .king (6) . In
Society for Test Ge
ns with the object
''
of
or testing animal
hat
glues (7) .
triedare also
'
studying the testing of animal glue .
n_...
1
!
Ik
e
-
_ r
`"%' lf
There is general agreement among i 'search orkers that
ria or judgviscosity and jelly strength are the most reliable
are
;, '
ing the quality of an animal glue, and one or the othe - ` :
usually the basis for grading . In Germany viscosity i
as
d
the more reliable of the two properties (7), while in
en
States both are considered essential for defining the grade of a
glue (4) .
Other characteristics commonly considered of some importance in an animal glue for woodworking are moisture content ,
reaction (acidity or alkalinity), tendency to foam, and odor or keep ing gnality . Joint tests in glued wood blocks have been a part o f
most all glue-testing investigations, but they are less accurate an d
ss satisfactory for testing t quality of animal glues than ar e
.-w4og#4-' .. .(14) .
cepted physical and
getable methods, the
the water resistanc e
ble-protein glues are
therefore, constitut e
ermi14 suitabil
'A~rest Products Labo r
dun. the World
Wa r
_ worms o
ak
It in
1:
.--The
t Product s
of
tests for
n starch and othe r
hear and plywoodpublications (13) .
s and the plywood-shea r
en used in the same or slightl y
ti
(2, 5, 9, 10, 15) . Both
uipment and care can be quickl y
accuracy .
joinsts involve a gluing operation, an d
portant effect upon the results . Poor gluing
is with .
uality adhe
ul
ty
rly s
with
glues . Th'alladli'ion to She gluing o ration ) the writable properties
rroneo .u.s conclusions unof the wood are=f,qptors
U
al is ma . With proper care i n
_ less careful selOptiipn of
selecting and makTI40.1jotnii%4-hAever, the blodk and plywood test s
will ihow tacky lt!igdisterlt-4ifferences between weak and strong
glues, and w- it e*VIIS thei ' im"1, 4iotton of a glue or glues satisfactory
blood-albumin l casein, starch ,
for a part oulr' jai. Other Visitsfosesity
and
working life of the mixed
vegetable glues, .such . as the't1nTrmation
of
much value . It is to b e
glue, may gi;ve s4l)D ItOtaltY
sts. WifIlt6k
COmOletq
hoped, hOweVer, that in the cbliltbe af tittle
oitl$1.%eft:
4.
lieveloped for each of nets 01.1es 'that can be made,
glued joints.
..
.C
etails i
rincip
E
it us
handl i
changes win o e desc
y,
is
.and mel d, the s t
Lein, or albumin all
ture . It is also i
i.--e-a■am-m
,
glue for us e
and proper contely dissolved or dis-,
us must be all soft Aiiein ) vegetabl e
Duce a uniform
or conversion be done
.
Outside
the characte r
unts o air
tirring and the type of mixe r
chided . Suitable types o f
rig the different kinds of glues ,
eration good glue mixes can readil y
4 , i-'
1_1
.1- I -
met be boile d
tradition has been tha t
common practice t o
use . Furthermore, it ha s
oiling point during use .
glue boiling or near t
the glue and the wastefulnes s of such practice have been
investigators (13) . It is unnecessary to go any
ct than
t t that the most desirabl e
at commercial practice has been
d practice . Equipment manufacturer s
n bringing about this change by providing glue
automaticall y
but is nevertheless important . The gliality of a starch glue and th e
working life of casein and vegetable-protein glues depend. to some extent upon temperature . Manufacturers of starch adhesives usually recomrrend the temperature conditions most satisfactory in mixing, an d
temperature recommendations are also made by some manufacturers o f
casein and vegetable-protein glues. Heating blood-albumin glues an d
certain other adhesives during preparation above their coagulatin g
temperatures alters their adhesive properties .
Spreading .--To make a satisfactory joint it is important to
spread an adequate amount of glue evenly and quickly over the surface s
to be joined . Machine spreading is quicker, more uniform, cheaper ,
and more economical of glue than hand spreading and is recommended o n
work
toed is. essential in many operations in orde r
to get' r; r
re ., It is important tQ
- the right amoun t
of, glue e a jstrong joint, but
gent
f 3~
not ellNug$l Vet AO ,
emb s . The
re d
later to t'
amen g Oleesq
.
fai. r, 1 est
of 4loint uses
Ovt , #
du
ic
e
t+
.Atli
hnic has to do wilt*
development ilk .
,
Here
e consistency p t
mmtuzk
t .4 ,' •,
~ ~,
inmain with respAiN
imal gl~ge+e, .,= .ld
- tr
~I~' ,
t the glue mix ure muni'
ativ - ` thi n
;ivi
hr~ twit
, must be hot, and ,
t
lution mus t
'' ett"
a ce
to
,ac
tirmop.
vera$
s had been it upon
le .
re, that the suit s
rile deeply in o
tlG ,
ive better results
imal
gi' yap. unh ..
Ile regarded
cep.tNIt very ''-&
' W'the
princi .H es hair- •
bee-z ilssOICir..di
ied
~•# I■ de
active there : ' ' '
vets*
a
'
. 141 ,141httgk
the a. dse '
sUdl!ngth ,* a gl^ :
a result *!:'#Ii3,g4s
atious1y_ *
hibite,
seccy VA'of
unt
t] s .ttl1Oy 1g.l.408m• A
of tb
fig--■ce item
bows epdigrtakea . ' o
ire sults *vl4ftattjj
othekli
earO
lea (II i
ee
s ire being ve
1-5)e
eatwhat more - ,
rs tfiaaffect the
es were formulated
glue adheres tena-
1,ed -lb -'•'the
1
,
, ..104
• '
'
- . .~ .1
r
.i
e
c
-ii
~-
_
ii~'►'r~
ti? ,_y .'S
1
lation of factors for different glu Brent
species
of wood required the making o f
ons and
nds of t s and several years of work . The kind of glu e
on of water in the mixture, the quantity of glue spread ,
and the room and the wood, the lapse o f
ure of . ~_
thount of pressure, th e
ies of wood were all inh
tors is compl
ets .~ '
_
ints are made by the us e
gluing pressures . Thes e
surfaces of wood t o
nt, to spread t h
;
ntinuous film, to
not
;st
*pod subst .aice,
ct
ti
od ke e
ive warding of th
ing and favors starved joints~ ti 9
uous film ;Qf glue in th e
•
K' . .
and certain'
k clamping, sudiM-$'J
ck
or,
as
y
.
:'.~.
, the glue must- W mixed re]
vely
-' i
in the case of animal glue, permitted to come to the proper consist,
ency by cooling . Wood at 700 F . normally requires no further warmi 0
in operations where the pressure is applied within 1 minute afte r
spreading . Gluing pressures of 100 to 200 pounds per square inch o#lT , .' .'= ~
joint are best ; the lower pressures for lighter woods and the highe r
pressures for heavy woods . These recommended pressures are highe r
''
than those that still generally prevail in many operations .
Time-saving machinery and devices also have brought abou t
important changes in the gluing room, as related to the technic o f
gluing . Mechanical spreaders, rotary clamp carriers, and hydrauli c
presses have had a marked effect on the time element in gluing -. They have tended towardamostiprnfacoijtprducon
- .4 4 . . 1
higher gluing pressures, have made it inadvisable in many operations
d
to warm the wood, have brought about shorter clamping periods an
.- . .
the need for quick-setting glues, and have made it necessary to mix
glues relatively thick . These developments have generally contribute d
to a more uniform and higher standard in glue joints, but to take ful l
advantage of them the gluing operator must make certain that he con trols the details of the operation in harmony with the changed condi tions .
R947
-8-
(I) Akti*W48 . L, and Truax T . R "Glues Used in Airplane Parts, "
-0mv.. . Advisory dom. A00aut . ann. rpt . 5, pp . 387-407,
. 191'8 ( t.,iOthiv#06
(2) Bocharo;ff,
% .Ir-'11#01stigation of Gelatlt Joiners ! Glues ) "
UM:en of -SIp4t4ait'Soviet Republics, Scientific-Technical
ZAPt . rpt: IZ . J*actions of the Central Aerohydro dYnamicial'ImoitWte, l Xt . 27), 166,le *l 1926, Moscow .
fsion in th e
Bt-dWMy Y. L ., a44 :Truax, T . R., "the Placw . of
GIpEng Osf Wood," Colloid Symposium Monograph 4, pp . 2582-6S, 196.
(4) DeBeaut4laer, P . L., Rowell, J . R., an5 :Bah1man,
n, "Standard- ,Methods (revised) for Determining Viscosity and Jelly
.ngth 0'GluB," Indus . & Eng . Chem., Anal . Ed., 2, pp .
-51, NW.
Douglas * Wm. D.., and Pet.tif.or l d. B., "pie' Tesltilg of Adhesive s
fa t, Timbr l * Jpu . Roy, Aeronaut . ace ., vol ; 33, pp. 92-128, 1920, Ld tn.
(6) Federtl 3peoificaems Beard, ".F Loral Specifications for Animal
'
Glue for Wo.Wworking," No . C-G-451 .
(7) , Gerngveso,
" :G,1-te' and Gelatin," a paper fot the 6ongress o f
the now
, Pock Testing Materials in
19a1 l published in Zeitschrift f rlAngewandte Chgza@ % . vol .
42, pp . 968-97Z, 1929, Berlin .
(8) Gernoo. ss, O . * "Woodworking .Gluee and Their Ti6ting with Specll l
Poterente te,Glmimg'Waod wtIth4ahesive Films," Zeitschrif t
As. Ang4wilan4to'e1lem1e, vol . 414. P,a4l, 1931, Berlin .
(I, OWN; 1% I." -iiWO)IM-10t,, ., r wineeis ana Plywoodg .Wheir Craft**Ishii)!
aid Attistri"
37F pp ., 1927.
, .