AGRICULTURE ROOAA
ARTIFICIAL RESIN GLUES MR R'EYWOO D
July 1939
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UNITED STATES DEPARTMENT OF AGRICULTUR E
`FOREST SERVIC E
FOREST PRODUCTS LABORATOR Y
Madison, Wisconsi n
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In Cooperation with the University of Wisconsi n
SCWiOL OF fORE TR
[ STATE
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ARTIFICIAL RESINGLUES FOR PLYWOO D
The term "artificial resins" was first used to describe syntheti c
chemical compounds that, in the intermediate phases of their production ,
resembled natural resins in general appearance . As new compounds wer e
developed, however, the term came to include many products bearing littl e
or no resemblance to natural resins, and at present It applies to a wid e
and heterogeneous group of products . Some of these have found wide practica l
application, while others are as yet mainly of theoretical interest .
Probably the best known artificial resins in manufacture and use ar e
those produced by a condensation of phenol (carbolic acid) and formaldehyde, ■
materials which have become available in increasing quantity wi4h the de- ,
velopment of modern chemical industry . Typical of such resins is the produc t
sold under the name of Bakelite . Other synthetics having considerable commercial importance are urea-formaldehyde resins, glycerol-phthalie anhydrid e
resins, polymerized vinyl esters, polymerized acrylic esters, cellulos e
esters, ketone resins, cumarone-indene resins, and sulphurphenol resins .
Of all these compounds only a few have thus far proved of practica l
value as woodworking adhesives, and those few belong to either tha phenol aldehyde or the urea-formaldehyde groups . The procedure in forming th e
phenol-aldehyde resins consists essentially in heating a mixture of pheno l
and formaldehyde, with or without the addition of small amounts of othe r
chemicals called catalysts . The products of the condensation reaction ar e
water and a resin-like mass that settles out . The water layer can be re moved and the resin can, by further action of heat and pressure, be converte d
into a hard, insoluble substance . The specific properties of the resin ar e
subject to control by the use of different catalysts and other modification s
of the process . For the production of woodworking glues the reaction i s
stopped at an intermediate stage at which the resin may be applied to th e
surfaces to be glued . By application of heat and pressure in the gluin g
operation itself the reaction, somewhat resembling a fusion, is carried t o
completion .
With most of the phenol-aldehyde resins this final stage of the reactio n
will require, for best results, temperatures in the neighborhood of 3000 F . ,
pressures as great as can be applied without crushing the wood, and a pressing time of some 3 to 5 minutes after the glue layer has reached full temperature . Such requirements, however, may be modified ven withixi a clas s
of resins . One phenol-aldehyde resin glue, for example- may be spread an d
pressed at room temperatures . After the glue has taken an initial set th e
condensation reaction is completed by heating to about 150 0 F . for some hours .
In the final form the phenolic resin is insoluble in hot and col d
water and, if the process is correctly controlled a it adheres well to woo d
surfaces . Thus a very water-resistant glue joint may be produced . Phenol aldehyde glues may be used in the form of films, dry lowders, or solutions ,
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all of which are readily available on the market . The powder is usually
brought into solution or suspension before spreading on the wood, .
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The urea-formaldehyde artificial resin glues are of more recent devel opment . At the present time (1939), they are on the market in the forms o f
dry powders and of solutions, but the film form is not available, at leas t
from domestic sources . The urea-formaldehyde glues set at somewhat lowe r
temperatures and at a ., sometiwhat more rapid rate than ..those of the phenol aldehyde type . As in the case of the latter group, the temperature requirements may be modifies within the group . Some of the urea-forlde'hyd e
modifications on the market may be used entirely at room temperature's . Whe n
the gluing process is properly controlled the urea : formaldehyde joints ar e
highly resistant to water at ordinary temperatures, but they will not wit h
s*wssl ■oaking in hot water .
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For most present commercial glues of the phenol-aldehyde ahd the .
urea-formaldehyde types, heat is an essential agent in causing ich:e final
reaction . The process of gluing with synthetic resins- lends itsself-, the4e,
fore, much better to plywood manufacture than to the gluing of th~k st.ook ,
t in which case the time required to bring the joint to the n e.'essary '^tei e a ture may be excessive from the standpoint of economy and quantity, p oduA q;.i4r i
The cost of the synthetic resin glues' may be reduced by the use or
"extenders" or "fillers" but unless the quantities added are very smal l
this "extend; n," results in a sacrifice of the water resista ee, mold re .sistance, and other desirable properties,
Theoretically, a wider range of glues with varying properties TAO ,
gluing requirements may be possible through the selection of other types o f
artificial resins . For example, vinyl esters are "thermoplastic" and d o
not undergo a permanent chemical change under the action of-heat alone : I f
they are to be used as . glues, a press is required that can be heated an d
cooled while the product is+ mmde* pressure . Filmsr .of vinyl esters an d
cellulose esters-have appeared at least on foreign markets but they hav e
not been used to any extent in the domestic plywood industry ,
The use of artificial resins as woodworking glues is still in the de velc
ata . stage with new products and modifications appearing frequently .
While service tests covering periods of 3 to 5 years have demonstrated a
high degree or resistance to severe conditions of exposure, judgment o f
quality and usefulness of a resin glue must, for the present, be based o n
characteristics and properties of the individual compounds for no genera l
statements can be made that apply with equal force to the entire field .
A PARTIAL LIST OF REFERENCES DEALING "TI L ARTIFICIAL PESIN GLUES '
Ciemistry_of
Chance, K . l
1935 .
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I~laterial s
Urea Plastics . Journal e2the Society of Chemical Industry .
54 : 102-4 .
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Dring, George .
1934 . Some Chemical Aspects of Phenol-formaldehyde Resins . Journa l
of the Society of Chemical Industry . 53 : 417-25 .
Ellis, Carleton .
1923 . Synthetic Resins and Their Plastics . 514 pp .,
illus .
New York .
Holmes, E . Leighton, and Megson, N . J . L .
1933 . Catalysts in Phenol-formaldehyde Condensations . Journal of th e
Society of Chemical Industry . 52 : 415T-18T .
ApElications as
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Brouse, Don .
1938 . Exposure Tests on Plywood . Mechanical Engineering . 60 :852-6 ,
Davidson, J . G ., and McClure, H . B .
1933, Applications of Vinyl Resins . Ind . and Eng . Chem, 25 : 645-52 .
Hovey, A, G .
1933 . Alkyd Resins for Bonding Materials . Ind . and Eng . Chem .
25 : 613-15 .
Morath, Edgar .
1937 . Properties and Uses of Synthetic Resin Glues . Holz als Roh m
and Werkstoffe . 1 : 21-26 .
Merritt, E . H .
1932 . Laminating with Phenolic Resins . Transactions of the A .S .M .E .
55 : (8), Paper No . WID-55-4 .
Ohl, Fritz .
1937 . Synthetic Materials as Adhesives . Gelatine, Leim, Klebstoffe .
5 : 35-43 .
Perry, T . D ., and Bretl, M . F .
1938 . Hot Pressing Technic for Plywood . Transactions of the A .S .M.E .
Sontag, L . A ., and Norton, A . J .
1935 . Phenolic Resin Adhesives in the Plywood Industry . Ind . an d
Eng . Chem . 27 : 1114-19 .
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Sorensen, Ray .
1933 . Dry Film Gluing in Plywood Manufacture . Presented at the 193 3
meeting of the Wood Industries Division of the A .S .M .E . (Copie s
available from the Resinous Products and Chemical Company ,
Philadelphia, Pa . )
1933 . Same (extract) .
Furniture Manufacturer . 46 : (7), 21-4 and 47 :
(6), 23 .
Stout, Lawrence E ., and Collins, R . G .
1935 . Use of Molded Plastics in Applying Wood Veneer . Modern Plastics .
12 : (10), 42 .
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