DUPAPILITY OF PLYWOOD JOINTS MADE
WITI-I ONE MRAMIME-, ONE UM-, AND
FIVE RESORCINOL.-RESIN GLUES
October 1947
This Report is One of a Series
Issued In Cooperation with the
ARMY-NAVY-CIVIL COMMITTEE
on
AIRCRAFT DESIGN CRITERIA
Under the Supervision of the
AERONAUTICAL DOAN)
No) 1568
UNITED STATES DEPARTMENT OF AGRICULTURE
01'0
ST SERVICE
FORE Sr–PRODUCTS LABORATORY
L—
Madison 5, Wisconsin
In Cooperation with the University of Wisconsin
DURAXILITT_OF PLYWOOD JOINTS MADE WITH .ONE MELAMINE-,
1
ONE URFA-, AND FITE_WORCINOL-RESIN GLUES-
By W. Z. OLSON, Technologist
and R. F. BLOMQUIST, Chemist
Forest Products Laboratory Report No. 1530 (revised December 1946) summarizes durability data obtained at the Laboratory on several types of glues.
That report includes data on onJ.y two resorcinol-resin glues and no data on
acid-catalyzed melamine-resin glues or noncrazing urea-resin glues. The Laboratory was requested by the Army-Navy-Civil Committee on Aircraft Design
Criteria to augment the information on resorcinol glues and also to obtain
data on the durability of catalyzed melamine-resin glue and of noncrazing
urea-resin glue.
Seven glues were selected for this study. Five of these were resorcinol-resin glues; one, an acid-catalyzed melamine-resin glue; and one, a
urea-resin glue which was reportedly formulated to impart craze resistance
to the glue joint. Six controlled exposure conditions were used, in addition
to outdoor exposure. This report describes the preparation of test specimens
and includes test data obtained over an exposure period of 18 months. The
study is scheduled to continue for an additional 42 months.
Preparation and Exposure of Birch Plywood Test Specimens
Six, three-ply, 25- by 25-inch panels were prepared with each of the
seven glues, using 1/16-inch yellow birch veneers. The veneers contained about
12 percent moisture at the time of gluing and were glued under the conditions
given in table 1. After conditioning for at least 7 days at 80° F. and 65 percent relative humidity, 140 standard plywood shear test specimens were cut from
each panel, producing 840 specimens for each glue. Sixty specimens with each
glue representing all 6 panels were tested as controls, 30 dry and 30 wet after
soaking for 48 hours in water at room temperatures. The remaining specimens
were placed in the following exposures, to be tested at intervals of 2, 4, 6,
9, 12, 18, 24, 30, 36, 42, 48, 54, and 60 months.
1. Continuously in
2. Continuously in
3. Continuously in
4. Continuously in
air at 80° F. and 65 percent relative humidity.
air at 80° F. and 97 percent relative humidity.
air at 1589 F. and 20 percent relative humidity,
water at room temperatures.
1
-This is one of a series of progress reports prepared by the Forest Products
Laboratory relating to the use of wood in aircraft. Results here reported
are preliminary and may be revised as additional data become available.
Report No, 1568
-1-
5.
6.
A repeating cycle consisting of 2 weeks in air at 80° F.
and 97 percent relative humidity, followed by 2 weeks
in air at 80° F. and 30 percent relative humidity.
A repeating cycle consisting of 2 days in water at room
temperatures followed by 12 days in air at 80° F. and
30 percent relative humidity.
After each exposure interval, five specimens were tested immediately and
after exposures 1, 3, and 5, five additional specimens were tested wet after
48 hours soaking in water at room temperature. The specimens from exposure
6 were tested wet after the soaking part of the cycle.
Preparation and Exposure of Test Fence. Panels
Five-ply, yellow birch and Douglas-fir plywood panels were prepared
from veneer 1/8- by 25- by 25 inches in size. The veneers contained about
12 percent moisture at the time of gluing and were glued under the same conditions as were the panels made for the plywood specimens. Two panels of
each species were prepared with each glue. After conditioning for at least
7 days at 80° F. and 65 percent relative humidity, the panels were trimmed
to 18 by 18 inches in area and placed on outdoor exposure racks near Madison.
The panels were unprotected by any coatings and were mounted vertically in
an open space facing south. The panels were examined for delamination after
10 months of exposure.
The trimmings from the panels were cut into standard plywood shear
test specimens with saw cuts made to test the inner glue lines. Five specimens from each panel were tested dry, five tested wet after 48 hours soaking
in water at room temperature, and five tested wet after the soaking-drying
cycle prescribed for high moisture resistant bondage in "Commercial Standard
CS35-42 for Hardwood and Eastern Red Cedar Plywood." This test involved
soaking the specimens for 16 hours in water at room temperature and drying
for 8 hours at 145° F. (plus or minus 5° F.), repeating for a total of three
cycles, soaking the specimens for an additional 16 hours at room temperature,
and then testing while wet. Average results of these tests are given in
table 2.
Results
Average results of shear tests made on the plywood specimens that were
under controlled exposure c1ditions are given in table 3. The results were
obtained at 0, 2, 4, 6, 9,/ant 18 months of exposure.
Eighteen months of exposure was not long enough to permit drawing
final conclusions concerning ultimate durability, but the following trends
were evident in the data for the 18-month period.
Report No. 1568
-2-
The five resorcinol-resin glues generally showed similarity in
behavior. There appeared to be some superiority in Glues C and E in maintaining very high wood failures, hut there was no consistent difference in
shear strength between the resorcinol-resin glues.
Continuous exposure at 158° F, and 20 percent relative humidity
proved tole the most damaging condition for the plywood glued with
resorcinol resin. The shear strength might be expected to fall in this
exposure because of possible heat damage to the wood. The average wood
failure in the dry tests of the joints glued with three of the resorcinolresin glues, however, decreased appreciably,
In the other exposures, some of the joints made with resorcinol-resin
glue decreased in shear strength while maintaining relatively high percentages
of wood failure. It appeared, however, that this decrease in shear strength
resulted from'the effect of the exposure conditions on the strength properties of the wood rather than from deterioration of the glue itself. The data
on two resorcinol-resin glues given in Report No. 1530 agree closely with
that obtained on the five resorcinol-resin glues of this study.
Joints made with the acid-catalyzed melamine-resin glue generally
showed somewhat greater deterioration than those made with the resorcinolresin glues. Marked decreases in shear strength or wood failure, and
usually in both, were observed when the specimens were tested after exposure
to the more severe conditions. Slight decreases in shear strength and Wood
failure were also observed upon testing those specimens that were exposed
continuously for 18 months in air at 80° F. and 65 percent relative humidity.
Comparison with the data presented in Report No. 1530 tends to indicate this
acid-catalyzed melamine-resin glue to be less durable than the average more
neutral, hot-press melamine-resin glue.
Joints made with the urea-resin glue deteriorated to a much greater
extent than did joints made with the other glues used in this study.
Exposure to high temperature and to high humidity was particularly injurious
to the joints in specimens made with urea-resin glue. A marked decrease in
wood failure resulted even in the mild exposure of 80° F. and 65 percent
relative humidity. Of the plywood panels exposed to the weather, only the
birch panels glued with the urea-resin glue G developed visible delamination
in the first 10 months (table 2). Comparisons with the data presented in
Report No, 1530 show Glue G to be generally about as durable as the average
urea-resin glue which meets the requirements of Specification AN-G-8.
Report No. 1568
-3-
Table 1.--auln conditions used in = re aration of l_ywaod ane1s
Glue
: Average :Assembly: Pressure : Curing : Pressure
:
spread : time :
tem- : period
:(closed);
:perature:
Hours,
Grams per-:Elaatut ;Pounds per;
:square in
s quare foot: ,
A
25.6
:20 to 30:
Room175
(resorcinol-resin):
B
24.3
(resorcinol-resin):
:
:
1
:21 o . .30:
175.
Room=.7 :
:20 to 29:
175
: ROO M- :
:25 to 34:
175
:
•
(resorcinol-resin);
D
•
18
18
17
Roomy- :
17
1
'
22.1
REoom
:20 to 30:
- :
175
(resorcinol-resin);
17
(resorcinol-resin):
F
•
(acid -catalyzed :
melamine-resin) :
27.1
26.2
:14 : to 20:
:15 to 24:
175
; 140 0 F.:
175
1
: Room-:
17
(noncrazing urea- :
resin)
1
-
,
The temperature of the rooMvaried between 75° and 90° F. during
the pressure period.
Report No. 1568
Table 2.--Average results of initial tests of specimens from panels prepared
for outdoor exposure and insp ection of panels after 10 months'
exposure to the weather
: Initial : Initial: Initial :Delamination around
' Test 3 .
Species:Test:Test*Te.edges
of panel
1 : No.2No.1: No.3- ; after 10 months of
:
: outdoor exposure
:
Glue
•
•
Percent
.5
. 5
A
:Yellow birch: -586-98 :-478-100: 5478 -98 :
(resorcinol-resin);Douglas-fir : 333-96 : 304-84 : 301-80 :
0
0
:Yellow birch:
(resorcinol-resin): Douglas-fir :
478-60 : 416-88 :
290-92 : 326-86 :
403-96 :
318-92 :
0
0
C
:Yellow birch:
(resorcinol-resin):Douglas-fir
570-82 : 494-97 1
274-96 : 239-76 :
512-100:
258-90 :
0
0
:Yellow birch:
D
(resorcinol-resin):Douglas-fir :
435-92 :
488-76
338-94 : 278-94 :
455-92 :
298-92 :
0
0
:fellow birch:
(resorcinol-resin):Dauglas-fir :
534-60 : 406-92 :
330-98 : 362-70 :
415-92 :
316-95 :
0
0
:Yellow birch:
:Douglas-fir :
464-98 : 428-100:
287-90 : 264-100:
409-90 :
258-100:
0
0
232-24
99-1 :
2
(acid-catalyzed
melamine-resin)
•
•
:Yellow birch:
(noncrazing urea-:Douglas-fir :
resin)
•
•
•
•
•
•
467 - 80 : 436-92 :
262-88 : 259-30 :
0
-Tested dry.
arrested wet after soaking in water at room temperature for 48 hours.
gTested wet after soaking-drying cycle described for high moisture resistant
bondage in Commercial Standard 0S35-42 for Hardwood and Eastern Red Cedar
Plywood.
-The average for two panels.
-The value before the dash is the average shear strength in pounds per square
inch; the value after the dash is the average wood failure in percent. Each
value represents an average of 10 specimens, 5 from each of 2 panels.
Report No. 1568
Table
,
results of shear tests of yellow birch plywOodlepeeimene aade with seven glues
and subjected to six conditions of exposure
3.--Amerage
s Duration :Exposure lg:Exposure 21:
Exposure 31
:Exposure 45-s
:ixposure 61
Exposure 5§-
:
of
:-
:
:-- t: exposure :Tested dry:Tested wet:Tested dry :Tested dry:Tested wet:Test•d wet :Tested dry:Tested vet:Tested wet
Clue
-r -
-
r
: Months
A
.
(resoroinol-resin):
g
1
s
:
o
2
4
6
9
12
18
1
--
. .
.
1-
--- -t--
.
--t t
8
.
8 32-100 r -532-loo
5
: IZ59-93 : 432-loo 1
t 111 59-93 : 1532-100 1 1532-100
9-93 : 1559-93 : -5
1 78-98 1 551-93 1
3-98 s 11-65 : 536-90 : 475-87 1 55-s6 t 563-91 r 506-95
t 5713-97 1 513-92 : 571-91 : 446-84 r 504-93 : 4182-56 1 49o-55 1 00-90 : 513-90
: 499-96 : 505-95 1 526-100 1 393-76 t 43o-99 1 484-98 : 465-55 t 502-93 : 465-97
t 518-97 : 503-95 , 499-98 : 365-98 : 417-99 : 441- 118 : 477-94 : 483-93 : 446..95
I 474-100 : 533-99 1 487-100 1 337-79 I 405-100 : 450-97 3 456-67 : 498-98 :
455-99
: 440. 58 t 483-100 : 468-100 : 31240 t 358-100: 467-99 : 452-76 1 1 160-100: 395-100
3
a
1 491-100: 504-84 : soar e 491-10o I 491-100 r 504-84: 491-100: 491-100
2
rir)11,4i^:146 1 500-91t : 514-91. t
69 : 466^95 I 484-53 I 457-84 : 472.-93 I 487-93
4
525-86 1 497-91
:
I 514-98 t 1s14-15 r 470-94 t 463-94 • 4, 5-85 5 491-91 t 479-92
: g 6 t 359-95
: 4 53-79 1 4 67-9 2c
: 501-96
396-98 1 491 .- 98 r 441-73 5 4 70-94 I 471'98
9,
1 4 55- 159 2 4 76-95 1 4 95-
•
: 341-75 t 339-99 : 4 33-99 1 444-69 : 471-91 1 423-95
:
12
1 446-97 • 512. 100: 471-'100 r 328-80 r 397-100 : 465-92 t 427-79 : 450-95 1 392-98
•
16
1 406-54 1 463-. 98 1 406-100 : 300-61 1 323-100: 437.-96 r 412-67 : 441-100 : 366..100
inol resin):
0
(resorcinol-resin):
0
(
C
.
I
1
1
1
1
D
(
2
4
6
9
12
16
inol resin):
0
t
4
6
9
t
;
t
I
2
12
18
3
(resorcinol-resin):
t
:
2
.
1
:
0
2
4
6
9
12
16
(acid catalyzed 1
melamine-r•sin) t
0
2
:
6
9
12
16
s
:
4
0
(nonerasing urea- :
t
resin)
t
a
:
0
2
4
6
9
12
18
I 526-98 : 536-93 : 526-98 : 526-98 : 536-93 r 536-93 : 526-98 : 536-93 I 536-93
t 485-98 : 495-57 : 522-96 : 427 .. 96 : 477-99 1 502-99 ; 457-52 s 499-95 2 512- 100
1 53 8-99 : 545 ,- 59 : 525-99 : 398- 99 : 492-99
510-97. 8 463-92 : 499-98 ; 502-96
: 530-91 : 52095
- : 482-99 : 370-96
- t 453- 100:t 511-97 1 427-95 ,: 527-99 1 48b99
t 511-100": 499-100 : 443-100 8 326-98 : 376-100: 455-93 t 466-95 1
98 : 437-100
: 477-99 1 526 .. 100 : 440-100 : 331-100: 397-100 I 456103 r 416-99 : 94-98 1 369..100
1 435-100 s 490-100 : 356-100 : 294-100 s 315-100: 451-99 s 422-100 : 426-100 t 3104..100
: 575-90
551-97 t 575-90 ; 575-9 0 r 551-97 : 551-97 :
90 1 551-97 1 551-97
t 50-76 :$ 523-96 : 577-98 I 43o-52 r 553-90 t 533-94 : 440 63 1 573-96 I542-99
_,
s 517-92 1 598-92 t 57o-96
: 397-81 1 531-94 / 54-96 ! 475-87 t 5524:92 1 550-ye
1 485-95 1 536-97 : 56o-94 I 359-95 : 474-loo 5 506-97 : 404-95 I 52' 4-97 : 505'97
t 507-98 : 529-99 t 54o-97
t 347-78
5
: 438-100 : 496-99 i 466- 82 s 516-99 : 503-99
t 486.. 84 : 5 8-100: 500-100 : 339-65 I 464-100 t 50r 99 2 427-64 : 524-9g a 481'99
t 428-89 t 525-99 : 496-98 t 325-38 a 365-100 I 456-100 : 437-43 1. 455-100 : 370-100
542-91 : 499-94 I 542-91 : 54f:91 : 499-94 : 499. 54 : tii2li : 499-94 : 499.94
: 500-95 r 522-57 I 538-10o t 4 21-93 : 477-65 : 521-90 :
5, 505-91 1 515-92
1 511-93 1 545-95 I 575-96 t 390-91 r 494-9g I 524-ss 1 44"
, 513-97 : *463-95
1 496.19 1 522-96 : 516-95 t 397-91 : 423-54
465-96 : 11, 40 78 2 1 495-92 1 460-89
: 558-85 t 502-96 A 40-95 : 379-86 r 415-96 : 465-90
: 441-94 7 1123-90
I 451-67 I 519 . 100: 496-100 t 331-93 4
7..100
471-96 : 433-98 : 500-95 t
1 40-96 : 496-100: 465-l00 1 337-79 : •378-100 t 441-85 r 447-96 : 463-98 I 369..100
t
F
I
2`100:
: 449-76 I 435.. 92 I 449-76 : 449-76 s 435-92 t I11135-92: 449-76 : 435-92 I 435-92
s 456-73 1 440-63 : 436-52 : 368-52 t 355-65 8
2-82 t 401-80 t 393-65
$ 415-71 r 439-94 5 403-19 8 311-62 : 365 .. 60 t
50 t 3r67 : 388-65 1 gir719
1 45S-91 1 356-59 I 353-45 1 329-64 1 337-100 : gi;: 73 : 35 -52 1 g4:98 : 369.61
4
8 446 . 52 : 377-95 1 35&• 47 t 301-78 : 320-98 1 327-48 : 394-63 :
98 I 269'41
: 414-94 r 406-87 t 297-67 s 304-22 : 329.. 90 s 331-0
1 351:35 1
3-71 : 280410
3 352-62 : 356-7o : 285-50 : 263-52 s 251-100 1 330.. 52 : 377-42 1 352-32 : 298.15
5514-94 : 526-80 : 514-94
1 457-99 1 507-. 52 : 431-30
i 464.. 89 1 524-75 : 350-10
t 460-100 t 500-66 c 333-2
t 435-62 1 435-.51 : 315-6
1 417-65 : 465-61 : 296-5
3 391• 611 1 439-30 1 214-0
1
1 514-94 I 526-80 t 526-80 3 5114-1 : 526-80 z 526-80
: 338. 87 I 3872 t 468-86 t 401-.481..25 : 431-71
: 304.. 63 : 3991 t 506-47 8 359-40 t 434-45
425-20
: 204-16 : 267-100 : 45
7 : 380-55 : 432-75 : 416-32
.
e 223-4 t 250-100 1 423- . 60 t 330-12 s 364-6
: 358-22
1 207-0 t 245• 60 t 426-55 1 303-19 1 35436 I 350-43
: 187-37 : 196^62 t 411-56 : 298-14 1 330-2 : 299-53
LThrse-ply, 3/16-inch birch plywood.
bxpemed continuously in air at 80 0 1. and 65 percent relative humidity.
Zxposed continuously in air at 60 0 1. sad 97 percent relative humidity; tested Immediately upon realm' from this condition.
.—posed continuously in air at 158 0 7. and 20 percent relative humidity, tested at room temperature.
coed continuously in water at room temperature.
A repeating cycle of 2 weeks exposure in air at 80 0 7. and 97 percent relative humidity followed by 2 weeks exposure
• in air at 800 Y. and 30 percent relative humidity.
IA repeating cycle of 2 days exposure in water at room temperature, followed by 12 days exposure in air at 60° P. _aud
i
30 percent relative humidity.
-The value before the dash is the average shear streagth is pounds per square /net; the value after the dash is the
estimated wood failure is perceat. Each value is the average for 5 epee:Wens.
7 M 74104 F