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 EEEECT Of BOILING fCR VARIOUS PERIODS Of TIMf 
 
 ON THE STRENGTH Of JOINTS IN DIRCH PLYWOOD 
 
 DONI 1 1 WITH URfA GLUE fORTIflED WITH VARYING 
 
 AMOUNTS Of MELAMINE AND RESORCINOL 
 
 December 1946 
 
 I 
 
 V 
 
 1348 ^ 
 
 TLAf 
 
 * m \NCH 
 i£ OR Qu 
 
 No. 1 343 
 
 UNITED STATES DEPARTMENT OF AGRICULTURE 
 
 FOREST SERVICE 
 
 FOREST PRODUCTS LABORATORY 
 
 Madison, Wisconsin 
 
 In Cooperation with the University of Wi»con»in 
 
EFFECT O F B OILING FOR VARIOUS PERIODS OF TIKE ON THE STRE NGTH OF JOINTS 
 IN BIRCK PLYWOOD BONDED 7TITH UREA GLUE FORTIFIED WITH 
 VARYING AMOUNTS OF MSLAMINE AND RESORCINOL- 
 
 By SYLVIA U, LECHER, Technologist 
 
 Boiling tests are commonly made on glued joints as a means of distinguishing 
 urea glues, which are weakened by boiling, from glues, such as phenol, mela- 
 mine, and resorcinol, that are not so affected. Because glues are on the 
 market that are mixtures of urea resins and either molamine or resorcinol 
 resins (commonly referred to as "fortified ureas"), information was desired 
 on the effect of boiling on the strength of joints made with uro% glues con- 
 taining varying amounts of these fortifiers. 
 
 The purpose of the work here reported was to ascertain the effect of boiling 
 for various periods of time on the strength of joints in birch plywood bonded 
 with urea glues fortified with varying amounts of melamine or resorcinol. 
 
 The procedure was to prepare plywood panels with urea- formaldehyde glues 
 containing various proportions of melamine-resin and resorcinol fortifiers, 
 to boil cheer specimens cut from these panels for various periods of time, 
 and to determine thy joint strengths of the boiled specimens by the standard 
 plywood shear tests. 
 
 Resorcinol-fortif ied Urea- formaldehyde Glues 
 
 The urea-formaldehyde glue employed in this phase of the work was a liquid 
 urea-resin solution containing 70 percent nonvolatile. To this solution was 
 added various amounts of a resorcinol fortifier and appropriate amounts of a 
 catalyst. The relative parts by weight of urea resin and resorcinol in the 
 six glues tested (all formulated to produce hot-setting glues) are given 
 in table 1. 
 
 The panels were made of three plies of l/l6-inch yellow birch hoartwood 
 veneer conditioned in an atmosphere of SO F. and 65 peroent relative 
 humidity, A ^— hour closed-assembly time was allowed, and the panels wore 
 pressed for k minutes at 2S0° F. under a pressure of 25O pounds per square 
 
 is study was made during the war period at the request of the Air Tech- 
 nical Service Command of the Army Air Forces with funds provided by them 
 for the purpose. 
 
 Report No. I5I+9 -1- 
 
inch. One 2k— by 2'!— inch panel was made with each glue* The specimens cut 
 therefrom were selected so that spocimens matched as nearly as possible were 
 subjected to each of six exposure conditions. The specimens were condi- 
 tioned for 1 week at SO F. and 65 percent relative humidity before boiling 
 and testing. 
 
 The results of the shear tests on these specimens before and after boiling 
 ore presented in table 1. 
 
 Mo lomine-resin- fortified Urea-fo r maldehyde Glues 
 
 The urea- formaldehyde glue employed in this phase of the work was a powdered 
 urea-formaldehyde resin. To this rosin were added various proportions of 
 molamine rosin and appropriate quantities of water. The relative propor- 
 tion:; by weight of urea resin and of melamine resin in the nine glues tested 
 ore given in table 2. 
 
 The plywood panels were made in the same manner as described for the experi- 
 ment with rosorcinol-fortif ied urea glue, except that a lb-hour closed- 
 assembly period was allowed and the panels wore held under pressuro at 
 2cS0° F."for g minutes. 
 
 The results of the shear tests on these specimens before and after boiling 
 are presented in table 2. 
 
 Conclusions 
 
 From the results of these experiments it appears that, except for rather 
 low concentrations of fortifiers, periods of boiling in excess of 12 hours 
 would bo required to reduce the joint strengths of fortified urea glues 
 below acceptable values. It would, therefore, be necessary to boil for 
 periods longer than 12 hours in order to differentiate between such forti- 
 fied urea glues and low- temperature phenol, melamine, or resorcinol glue. 
 
 Report No. 1^9 -2- 
 
Table 1. — Average re sults of she ar tests on throe-ply 3/l6- inch birch plywood 
 specimens, glued -with a ur oa-formaldohy d o roc i a glu e fort ifie d 
 with resorcinol, before and after boiling in \mter 
 
 Glue: Relative parts 
 
 :Numbor 
 
 : Dryi 
 
 : Wet- 
 
 
 
 
 
 num- : by 
 
 wo ight 
 
 : of 
 
 s speci- 
 : mens 
 
 : Boiling poriod«2- 
 
 
 :Urca- 
 
 :Resorcinol 
 
 
 
 :3 hours: 6 hourr:- hours 
 
 :12 hours 
 
 iresin 
 
 
 [tested 
 
 
 
 
 
 
 
 1 :100 
 
 2 : 93 
 
 
 l 7 
 
 l 120 
 , 120 
 
 "^77-91 
 504-92 
 
 -573-96 
 I 635-99 
 
 ;-L50-l 
 . 344-0 
 
 1 -5^-1 
 271-1 i 
 
 '• 4 
 ^2-1 
 
 203-1 
 
 I h 
 
 : ~23-0 
 
 2<»- 
 
 3 : S7 : 
 
 4 20 ! 
 
 13 1 
 20 : 
 
 120 ! 
 120 : 
 
 523-gS 
 536-OS 
 
 6^7. 100 j 
 
 I 671-100 : 
 
 453-42 
 '+99-77 1 
 
 423-32 
 4Sl-9o: 
 
 1 394-11 1 
 
 391-7 
 
 1 465-65 
 
 5 : 73.5= 
 
 6 : 62 , 
 
 26.5 1 
 
 33 i 
 
 120 : 
 120 j 
 
 Rlo-94 : 
 
 443-99 1 
 
 601-100 ! 
 
 57 6- 100 : 
 
 536-91 1 
 
 549-95: 
 
 491-49 : 
 1 5OS-S5: 
 
 515-72 1 
 
 469-69 
 495-23 
 
 —Tested dry after conditioning at 60° F. and 65 percent relative humid J 
 "Tested v;et after soaking in water 46 hours. 
 
 ^Tested xrot after boiling for the period designated. 
 
 4 
 
 —The first figure is the shear strength in pounds per square inch; the 
 
 second figuro is the -wood failure in percent. 
 
 Report No. 1549 
 
Tabic 2. — Average res ults of s hear tests on th ree-ply '^/lG-inc\\ birch plywood 
 s poo imo ns, glued with a u r e a- formald ehyde resin gl u e fortified 
 with me 1 ami no resin bo f or o^ and after boiling in wa ter 
 
 Glue 
 
 ; Relative parts 
 
 : Number 
 
 
 ' p 
 
 
 
 
 
 num- 
 ber 
 
 i by 
 
 weight 
 
 : of 
 
 1 Dry- 
 
 : Wot— : Boiling poriod^- 
 
 :Uroa- 
 
 : Mel amine - 
 
 : mens 
 
 
 t :3 hours: 6 hours :9 hours 
 
 12 hours 
 
 
 :resin 
 
 : resin 
 
 :testcd 
 
 
 
 
 
 
 1 
 1 
 
 1 
 2 
 
 3 
 
 : 100 
 I 95 
 ! 90 
 
 : 
 
 5 i 
 10 : 
 
 ! 156 
 
 ! 36 
 
 36 
 
 IV33-9S . 
 
 : 462-97 
 
 teg-95 : 
 
 k 
 
 -430-99 
 
 396-IOO 
 434-94 
 
 ! -H3-3 
 : IS3-5 
 
 302-5 
 
 1 --3-0 
 
 1 133-3 
 : 212-0 
 
 : -0-0 
 : 33-0 
 . I96-O 
 
 ! -Vo 
 
 20-0 
 160-0 
 
 4 
 
 5 
 6 
 
 , S5 : 
 
 : SO i 
 
 60 , 
 
 15 i 
 20 : 
 
 4o i 
 
 36 < 
 120 ; 
 
 120 : 
 
 539-90 . 
 14.54-. 100 i 
 
 433-100: 
 
 495-95 1 
 
 51S- 100: 
 
 £54-99 
 
 332-42 
 
 421-73: 
 
 ^-25-96 
 
 ' 276-17 
 
 339-30 
 
 : 392-8 ; 5 
 
 ! 22R-6 
 . 302-21 
 : 370-63 
 
 215-1 
 330-32 
 
 363-75 
 
 7 ! 
 
 3 i 
 9 : 
 
 40 \ 
 
 20 : 
 
 : 
 
 6o 1 
 
 SO : 
 100 j 
 
 120 ; 
 120 : 
 120 i 
 
 ^72-95 I 
 
 ^55-54 ! 
 
 ^19-57 ' 
 
 493-100: 
 513-91 1 
 495-97 1 
 
 431-S9: 
 474-93 1 
 
 51S-95' 
 
 403-73 
 447-56: 
 
 449-S7 : 
 
 410-30 • 
 440-60 : 
 445-36 : 
 
 1 
 
 409-73 
 430-62 
 434-92 
 
 —Tested dry after conditioning at 30° F. and 65 percent relative humidity. 
 
 2 . . 
 
 ""Tested wet after soaking in water 4o hours. 
 
 Ip 
 
 k 
 
 Tested wet after boiling for the period designated. 
 
 "The first figure is the shear /in" pounds per square inch; the second figure 
 is the wood failure in percent. 
 
 Report No, 1549 
 
UN/vep< 
 
 !!l!((/iilf/ 
 
 3 1262 
 
 08 ^4 6606