SALTS OF RESIDUAL DIMERIZED FAT ACIDS A New Class of Resinous Substances
T .for some time. HE resinoua mtum of
.
J.
C. Cowan and H . M . Teeter r&mn d t s has. been -. ~.. NORTaERN REGIONAL RKSEARCR LABORATOUY. wcognized U. 9. DWARTMKNI OF AGPLCULNPB, P&o111*.ILL. For example. the calcium and zinc salts of ahictic acid have found aide ussqe in the paint and varnish cCat.in ulta, in pmrdoular the dnc, ddum, and magnssium .alu, of residual diin the lorn Of msrird fat .eid. are fouud to pomarked ruioolu pmpertiu; they are apable Limed rc-sio and sioc d o of formins Gbsn, &Irm. and 6-u. SOlUtioM. Thae pmpsltiea IM attributed to ionio ate Tbme and other aimid t i o n m of d i v l O n t mion. and catious into long ch.ins. Appmiinute mol& kr materiab, such an Lhe r*ht derslminstionm by vi-metric mothod. indicate a value of .bout 15,000 in Mphthenaka, d t U of fatty 10% wlutions i n pyridine. While Gbsn M apparently too r d to be of UW, the 6lmacids, and d t U of modiforming pmpertiu have been utilizad in the formulmtion of ahellac substitutes a n d 6ed glyoeml phthalatfa, runish, the httm h d q compared with zinc mainate and utm gum v u n i . b a . UB d ta of monobasic .ddsandarecharscten'sed by thir rerdy solubility in variolv organic aolvenk Their resinous or amarpboun nature potassium dimerate and zinc chloride were uaed in tbe p b p i t a is p r o w bent esphined by the inability of the relatively large tion metbod. The potesSium dimerate mlutioo m obtained llpgtiva ion to locate iteelf in a crystal lattice on account of tbe by dissolving residual dimeriaed acids in aqueous potaesium hydntance to ita motion (8.4). droxide, using a minimum amount of 2.3 to 2.5 moles of po& The question now srim an to tbe properties of divalent metal eium hydroxide (calculated an ioO% potassium hydroxide) per dtaof polybssio organic acid.% In these compounds the valence mole of dimerized acids. Use of leas potassium hydmxide rerehtim would permit sasoeistion into relatively long chains. a sult~io a soft, Lucky sina dimerato, appsreotly M a result of the m n d i t i o n w b i c b i c h n l d p r e p a i l i o t h e a ~ e e o f a ~ t e c r y e pksticiiing action of partially neutralired dimerized acid, tdline structure. It would be erpeeted, therefore, that such presumably formed by bydmlyaik On the other band, an exarmpounds ahodd exhibit to some degm the properties of d v e amount of SlLali c a w mutamination of the product by aioo bydmxide, which prevents tbe formation of clear mlutppiesl long-chsin polvmaa Fer paampled of such reaiDoua d t a of divalent metala and tions of zinc dimerate in 40 solvente; in other applicatiom polyhio .dds are recorded in the literature. IIsgedom (6) this cootaminstion muem no difficulty. hlso of prime imprepred d t U of poly.rrylic acid wbicb can be molded by heat portance am the concentration of the a~lutionsand the order of mixing. As much M 60% of the yield of sioc dimerate may be and pceesura A patent (8) M b e d dtm of acids obtained by p o l j n w i i mixtures of mdeic acid, fumaric acid. or methylImt by emulei6cation, wbicb is favored by ua of dilute s o l ~ t i o ~ and addition of xino chloride to potsasillin dimerate. EmuLai& k - n d o n i a acid with styrene or vinyl butyl ether. Bradley (1) prepared d t a of d k y d resins of high acid number wbicb cation in completely avoided by adding approxirmtaly 0.17 N likmim poeam properties in mme degm similar to long-chain potaesium dimerate mlution to 1.15 N sin0 chloride with vigorow polymerr and which have found use in impregnating and in stirrinp. Under these conditions, ai00 dimerate is obtained in quantitapink In these compounds, boweve& the negative ions am M v e a long-chain polymeric atructmm, 60 that i t in imtive yield Ma pale cream granular powder wbicb is beat r e c o d possible to attribute their properties solely to the poaSibility of by stminiw It wotains an extraordinarily large amount of ionic sasociatioa absorbed water. Drying may be aocomplisbed either by pmThia lsboratory haa been investigating the industrial u84 longed atamding in a desiccator or by fusion. the latter being fh of semidrying 0% such 88 corn and soybean. Residual the moat rapid method. Fusion is carried out in 8n oven at dimerked fat acids are thaw acids obtained by heat polynwiaii 110' C. After water is completely removed, sin0 dimerate is the methyl ffltera of d d r y i n g oils, ranoving unpolymerired obtained M a transparent orange resin melting at 130' C., M monomer, m d saponifying the residual eatera They cowkt determined in a Parr melting point apparatus. largely of a mixture of polymers of linoleic acid; about 75% is Zinc dimerate wan slao prepared by cooking together eqUr dilineoleio acid. 20% is trilinoleic acid, and 6% is made up of d e n t quantitiea of zinc oxide and residual dimerized acids. The compounds of undatermined constitution (3). This mixture hss product in thin oaee in almoat black, h u c b 88 temperstures 8n avacid d u e of 190-200 and a mole& weight of 560in exof 200' c. are,requiredto raw resction. This method of prepsrstion is b e i i investigated further. 500. calculated 88 dibasic acid. It wan noted that &salts.in particular the calcium, zinc. 0th dimer acid salts utilized in thin research were prepared d u m . and atrontluah dta were bard and resinoun in by the D~UDihtiOllmethod outlined above. The calcium and nut& and rapable of being drawn into fibers and of pmducing n&nesikxn &ta were obtained 88 hard resinous granules with melting points in exof 2 0 0 O C. durable films, either alone or compounded into vzunkhea E+ cam of ita peater BUY) of b a d h ~ the ~ , sino salt is considered PROPEPTIES OF ZINC DWEBATB pvimsrily in thin p a p , dthongh examples of the properti- of other d t a are included. One of the pronound properties of sin0 dimerate ia ita ~~
PBWkBATION OW DWEB ACID SALTS
For the SaLS of brevity. a Balt of residual dimerised fat acids is here O ~ ~ IaWW J -G. %a dimerate WM prepared both by precipitation and fusion methoda Aqueow solotiins of
-
ability to form fibera. '&ee am obtained by warming the min to approximately 120' C.. w i n g with forceps, and drawing. Tbe StmntiUm. calcium. and maxneaium d t a Wrewiae ahow this promy, but. becausa. of tbe i& melting point of these ma( o w 2 0 0 O C.) it in wmewhat di6icnlt to demnmtmta
148
February, 1944
INDUSTRIAL AND ENGINEERING CHEMISTRY
Zinc dimerate fibers and those of the other salts are, unfortunately, weak and very brittle. Attempts to plasticize the fibers were unsuccessful because they are too wcak to tolerate the relatively large amounts of plasticizcr required to overcome the brittlencas. Also tlic fibers become sticky on incorporation of plasticizcr. Tho brittleness and weakness of these fibers are probably due to the existence of ionic linkages in zinc dimerato, as opposed to covalent bonds in ordinary high polymers. Even in an orientcd filamcnt no improvement would be anticipated since any pfrrnes of ions in the oriented structure would serve as planes of cleavagc, as in ionic inorganic crystals. The fibers show strong birefringcncc when inspectcd between crossed Nicol prisms. Figure 1 shows a fibcr as viewed in ordinary and in polarizcd light. The 45" orientation of the fiber to the plane of polarizcd light as indicated by the cross hairs should be noted, as maximum birefringence in this position is typical of synthetic fibers in which greatly elongated molecules arc oriented parallcl to the fiber axis. The orientation of these fibers is more pronounccd, the lower the temperature a t which they are drawn. A critical temperature has bcen observed for these fibers. If they are drawn above this temperature, birefringence is relatively weak and disappears within a few hours. On the other hand, if fibers are drawn below this temperature, bircfringcnce is pronounced and permanent. This critical temperature is about 125" C. for zinc dimerate. An x-ray diffraction pattern of these oriented fibers clearly indicated the low order of oricntation obtained in zinc dimerate filaments. No superiority in the physical properties of zinc dimerate fibers was observed when dilinoleic acid, purified by molecular distillation, was substituted for the residual acids. The divalent metal salts of residual dimerized acids are essentially insoluble substances, dissolving to the extent of only 1 or 2% i n common solvents. No satisfactory solvent has yet been found for the calcium and magnesium dimerates. Zinc dimerate, however, is soluble in amines, such as pyridine, substituted pyridines, quinoline, piperidine, morpholine, and aliphatic amines such as butyl and amyl amines. These solvents exert an extraordinary solubilizing effect in the presence of nonsolvents. Thus, as little as 5% of butyl amine will cause zinc dimerate to dissolve in a Skellysolve C-ethanol mixture, whcreas this mixture is without effect in the absence of the amine. Zinc dimerate is also soluble in methylcyclohexanone (but not cyclohexanone). This solution is quite tolerant to addition of nonsolvents such as toluene and xylene. Unfortunately, hard, nonsticky films cannot be obtained by evaporation, owing to the great tenacity with which the zinc dimerate retains methylcyclohexanone. Zinc, calcium, magnesium, and strontium dimerates dissolve in vegetable oils a t 300" C . After cooling and standing, however, separation occurs. On the other hand, cooking t h e oil a n d dimer acid salt together a t 300" C . until the oil is bodied results in compatible mixtures which show considerable tolerance
149
to nonsolvents and may be reduced with xylene or mineral spirits. An interesting peculiarity in the solubility behavior of zinc dimerate was also observed. If zinc resinate is present, zinc dimerate is rendered soluble in what ordinarily are nonsolvents. For example, zinc dimerate will dissolvc in a xylene solution containing zinc resinate in an amount equal to 60% or more of the .weight of zinc dimerate. MOLECULAR SIZE OF ZINC DIMERATE
In view of the polymeric propgrties shown by zinc dimerate, it was thought desirable to ascertain the extent of the ionic association which presumably was responsible for these properties. Analyses of the material indicated a somewhat variable composition. I n general, zinc was present in quantities from 12 to 15%, and chlorine, derived from the zinc chloridc, from 0.01 to 0.40%. The calculated value for zinc dimerate is 10.5% zinc. No simple correlation between composition and conditions of preparation was observed. Analyses of materials prepared under supposedly constant conditions were found to vary. Likewise, no correlation was found between composition and the ability of zinc dimerate to yield clear solutions in basic solvents. A probable cause is the fact that zinc dimerate cannot be readily purified and apparently contains small amounts of zinc chloride, hydroxide, or basic zinc dimerate, the proportions of which vary with minor experimental conditions such as speed of stirring, total time of mixing of reagents, etc. The variability of analyses prccluded attempts to ascertain molecular size by end group estimation. Such attempts would, in this case, be theoretically unsound since analytical data pointing toward a certain molecular size could alternatively be duplicated by assuming a different molecular weight and a small percentage of zinc hydroxide or chloride as impurity. Cryoscopic and ebullioscopicmethods of determining molecular weight appeared impractical, since solvents for zinc dimerate are not suitable for such purposes. Furthermore, since ionic association is postulated, a large temperature effect would be expected. Attention was next turned to viscometric methods. Since independent means of evaluating molecular weight were not available for zinc dimerate, it was necessary to obtain an approximation by comparison with a substance of known molecular weight. Zinc stearate was chosen for this purpose because it is chemically similar and has almost the same molecular weight as a zinc dimerate unit; it differs principally in its inability to associate into chains. The viscosities of solutions of zinc stearate (which had been purified by extraction with boiling benzene) in pyridine were
150
Vol. 36, No. 2
INDUSTRIAL AND ENGINEERING CHEMISTRY
/i
0.q-
of 15,600 is calculated for zinc dimerate, representing association of twenty-five zinc ion-dimerate ion combinations. Data obtained for other polymers (8) demonstrate that the value of K varies with the molecular weight of the polymer. However,
values of K for a given series of polymers are always of the same order of magnitude; therefore conservatively, the apparent molecular weight of zinc dimerate in 10% solutions may be placed between 10,000 and 20,000.
0 O.6a 7 i SHELLAC SUBSTITUTE
0
0.025
Figure 2.
0.05 0.075 0.1 0.125 CONC. BASE-MOLES/LITER
0.150 0.175
Relative Viscosities of Zinc Salts in Pyridine
Inasmuch as zinc dimerate films when free of solvent are quite hard, attempts were made t o devise a shellac substitute. For this purpose a solvent mixture was made up containing 60 ml. of Skcllysolve C, 40 ml. of absolute ethanol, and 5 ml. of monon-butylamine. Zinc dimerate was dissolved in this mixture to produce a solution containing 20% solids by weight and having a viscosity a t 25" C. of approximately 16.8 centipoises. Films poured on glass set to touch within 0.5 hour, but were not tackfree for over 100 hours. By warming a film, which had set to touch, for 1 hour a t 80" in a current of air, a tack-free film could be obtained which had a hardness of 26 (Sward rocker), or about half that of a good shellac film. Immersion of the film in water for 18 hours resulted in bad blushing which, however, cleared up within 2 hours and left the film somewhat dulled. Because of the chemical nature of zinc dimerate and its melting point, films showed no resistance to 5% alkali or boiling water. When films were poured on thin metal sheets, dried thoroughly, and bent over a small rod, no cracking was obscrved.
TABLE 11. HARDNESS O F ZINC DIMERATE-ZINC RESINATE FILMS
measured over a range of &lo% in a Hoeppler viscometer. Similar measurements for zinc dimerate were made, and relevant data are given in Table I. Plots of log qr against concentration in base moles per liter, as suggested by Kemp and Peters ( 7 ) ,were made (Figure 3). The data for zinc stearate fall on a straight line from which K ( 7 ) in the equation
..
logqr/C = KM is found to be 0.0162. The data for zinc dimerate lie upon a curve which, a t zero concentration, approaches asymptotically the line for zinc stearate but becomes increasingly steeper as the concentration increases. Since the slope of this curve should be proportional to the molecular weight, it appears that in very dilute solution the molecular weight of zinc dimcrate approaches that of zinc stearate; association of one zinc ion and one dimcrate ion is thus indicated. In more concentrated solutions, more and more of these fundamental zinc ion-dimerate ion combinations associate, leading to greater apparent molecular weight. At concentrations near 10% the curve for zinc dimerate becomes essentially linear. If the value of K obtained for zinc stearate is considered applicable, an apparent molecular weight
TABLE I. VISCOSITYDATAFOR SOLUTIONS OF ZINC SALTSIN PYRIDINE ,---ConcentrationBase %.by weight moles/liter 0.00 0.998 2.98 4.99 6.95 9.95 1 .oo 3.00 5.00 7.00 10.00
Density (30' C . )
Viscosity (304 e.,), Centipoises
Relative Viscosity
0.0158 0.0470 0.0803 0.110 0.158
Zinc Dimerate 0,978 0.981 0.984 0.986 0.988 0.992
0.783 0.828 1.014 1.438 2.242 5.160
1.29 1.84 2.86 6.59
0.0155 0.0465 0.0776 0.1086 0.155
Zinc Stearate 0.980 0.980 0.980 0.981 0.982
0.810 0.882 0.956 1.016 1.13
1.03 1.13 1.22 1.30 1.44
0.00
1.00 1.06
Zinc Zjnc Hardness at End of Dimerate, Resinate, Film No. Grams" Grams" 24 hr. 48 hr. 1 0.00 2.00 84 2 0.25 1.75 72 76 3 0.50 1.50 76 78 4 0.75 1.25 64 66 5 1 .oo 1.00 58 62 6 1.25 0.75 58 62 (7) b (2.00) (0.00) (22) (26) Xylene sufficient to give a solution containing 20% solids by weight. Skellysolve C-ethanol-butylamine solvent.
a
Several solutions in xylene of mixtures of zinc resinate and zinc dimerate were prepared, utilizing the solubilizing effect of zinc resinate. The solutions contained 20% solids by weight. In contrast t o films prepared entirely of zinc dimerate, those containing zinc resinate dried hard and tack-free in half an hour. The Sward rocker hardness of these films when cast in 0.003-inch thickness on glass is shown in Table 11. Zinc dimerate is not completely soluble in xylene in the presence of less zinc resinate than the minimum amount shown. When films were cast on metal, dried and subjected to bending, cracking occurred in every case. Adhesion to mota1 was greatly improved by the presence of zinc dimerate. Films of zinc resinate alone could easily be scraped from the metal with the fmgernail, whereas films containing a mixture of zinc resinate and zinc dimerate (particularly No. 6) showed only slight surface marring under the same treatment. Viscosity of the solutions increases with the amount of zinc dimerate present, a viscosity at 25" of A (Gardner-Holt) being reached with solution 6. It appears from these results that zinc dimerate should be useful as a shellac substitute in many applications, particularly as an undercoat where its lack of chemical resistance would be minimized by subsequent treatment with more durable finishes. VARNISHES
The hard resinous properties of zinc dimerate and its analogs, together with their solubility when cooked with a vegetable oil,
INDUSTRIAL A N D ENGINEERING CHEMISTRY
February, 1944
TABLB 111. PREPARATION OF VARNISmS Varnish No.
Resin
Total Time Min- Color of era1 Garb- Na hthenate Cook, S irits, ner 6rier* % Min. %l. Scale Cobalt Lead
Source of Salt
151
on tin plate and bending sharply over a thin rod. Both baked and air-dried films passed this test. FILMPREPARATION. Films were poured on plate glass panels. Baked films were prepared by heating films (air-dried 72 hours) for 45 minutes a t 150" C. Only zinc resinate failed to give a satisfactory baked film under these conditions. EVALUATION OF DIMER ACID SALTS AS VARNISH RESINS
gum-Zn di-
.....
rn.=rmtn
I"-
Zn resinate Zn dimerate $ Cadimerate 9 Mndimerate 10 Znldimerate 6
7
Commercial spec. Oxide and acid Oxideandacid Oxideandacid Precipitation ( c p tained Zn oxide)
65 40 70 63 62
120 410 485 516 500
16 13 11 12 12
0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06
...
a Unbodied alkali-refined linseed oil used.
suggested possible applications in the formulation of varnishes. k series of varnishes was therefore prepared from zinc, calcium, and magnesium dimerates, and from ester gum and zinc resinate for comparison. Thirty-gallon oil-length varnishes with finseed oil as vehicle were decided upon as standard. No attempt was made to propare the best possible varnish from each rosinous material. Rather it was desired to effect a comparison among various resins with other factors constant. In this way the dimerates could be placed in their proper relative positions. PREPARATION. 41 grams of resin and 100 grams of Linseed oil were used. The resinous materials wcre zinc, calcium, and magnesium dimerates, ester gum, zinc resinate, and a 1:1 mixture of zinc dimerate and ester gum. The linseed oil was a commercially bodied 70-second oil unless otherwise indicated. The oil was heated over a period of 10 minutes to 300" C. and held a t that temperature for 30 minutes. The resin was added, and the mixture held a t 300' until an 8-inch string was obtained. When the mixture had cooled sufficiently, mineral spirits was added to obtain a viscosity of G on the Gardner-Holt scale. Driers (naphthenate type) were added the next day. To varnishes containing zinc dimerate or resinates, only cobalt was added in view of the thorough drying promoted by zinc. A variation in this procedure consisted in the addition of residual dimerized acids to the linseed oil, heating to 300' C., adding the calculated amount of zinc, calcium, or magnesium oxide, and completing the cook (varnishes 7, 8, 9, and 10, Table 111). This process is analogous to the preparation of limed rosin varnishes. It yields varnishes which are, in general, equivalent to those prepared from the precipitated salts, and has the advantage of being more convenient, more rapid, and less expensive. Complete data covering the preparation of the varnishes and their drying times are given in Tables I11 and IV. The varnishes were tested for hardness (Table IV) and cold and boiling-water resistance of unbaked and baked films (Table V). None of the films, whether air-dried or baked, withstood 6% aqueous alkali. Flexibility was determined by casting films
The data in Tables 111, IV, and V give an excellent idea of the potentialities of the dimer acid salts as varnish resins. The following generalizations may be drawn from these data: 1. Zinc and calcium dimerate varnishes are superior to varnishes from ester gum and from ester gum-zinc dimerate combination in drying time, through-drying properties, and hardness of baked films, and superior to zinc resinate in drying time and baking properties. 2. Ma nesium dimerate is inferior to the other resins in drying time, %ut yields a baked film practically equivalent to zinc and calcium dunerates. 3. Unbaked dimerate varnish films are definitely inferior to ester gum and slightly inferior to zinc resinate in hot- and coldwater resistance. 4. The baked dimerate films, especially those from calcium dimerate, are comparable to ester gum films. Zinc resinate gave only sticky, mottled films after baking.
TABLP~ IV. DRYING OF VARNISH FILMS Varnish NO. 1 2 3 4 5 6
7
8 0 10 11"
Set to Touch (Sanderson) Hr. 10 2 L/&
63 27 13
12s/a
7'/r
2 1/4 131/4 101/a 7'/4
-Sward Air-dried 16 hr. 10 12 10 18 10 14 8 8 10 10 12
HardnessBaked 45 min 150'C': 40 42 44 26 24
..
16 10 20 18 48
Condition after 96 HI. Air-Dry Not tacky. hard film Slightly ticky Slightly tacky Not tacky. aoft film Slightly tacky; soft film Nut tacky; soft film Not tacky Slightly tacky Slightly tacky Not tacky Not tacky
a Varnish 1 plus 3% turpentine.
With respect to those dimerate varnishes in which the salt was prepared by cooking residual dimerized acids with the metal oxide in the presence of linseed oil, the following generalieationp hold: They are superior to those varnishes prepared from precipitated salts in drying time and in hot and cold water resistance; they are equivalent in air-dried hardness but are inferior in hardness of baked films. Because of the chemical nature of dimer acid salts, it is not surprising to observe that their varnish films possess almost no resistance to alkali. This weakness is shared by the zinc resinate varnish. An improvement in alkali resistance would be expected in varnishes containing harder drying oil-drier combinations.
u
TABLE V. WATERRESISTANCE OF VARNISH FILMS Varnish No.
1 2 3 4 5 6
7 8 9
10 11
After Exposure for 18 Hr. in Water at 25' C. Baked Unbaked Some blush Bad blush Very slight blush Very bad blush Bad blush Very bad blush Very sli ht blush Slight blush Rad blush No blus8; B ad blush Bad blush No blush Very bad blush No blush Slight blush Very bad blush Bad blush Someblush
.......
.......
I
.
.......
Recovery from Cold Baked Slight dulling Complete Dulled, some blush Complete Complete
........
Complete Complete Complete
........
Complete
Water after 2 Hr. Unbaked Dulled Slight dulling Dulled, some blush Complete Complete Complete Dulled Complete Some dulling Dulled
........
After Exposure for 1 Ilr: in Boiling Water and Drying Baked Unbaked Blushed, loosened Destroyed No blush, small tear Destroyed Bad blush, very soft Destroyed No blush loosened Blushed, loosened No blush' loosened Destroyed Destro ye$ Destroyed No blush small tear Destroyed No chanie Bad blush and wrinkling
........
No blush loosened No blush: roughened but not dulled
........ ........
Blushed, sticky
INDUSTRIAL AND ENGINEERING CHEMISTRY
152
During the drying of the varnishes, irregularitias in the evaporation of solvent occ&iody prudueed wavy, w r i d e d , n corrected by utiliaor orange peel surfsoea These eflecte c ~ be ing a balsnced solvent for thhez. It WBB dm noted that these wrface -ties dieappearea during the bsldng p r m of the straight sino h m t e varnish, f&,,tly olmdy the 6hue were formed. This condition WBS readily avoided by addition of a 4 perceotege of turpentine. A definite dein drvingtime wea obtained in the preeence ofturpestine. It &odd be mphasl;ed again k t the -g&a described are not the bed obtainable with thw materials, nor was any attempt made to make them 80. The development of an OPtirrmm vsrnish combination is a major problem in itself; OUT pur% pose was to qdbtive comparisons to be bm. to W a n a n t h o u s comidmtion of dimer mid saka as varnish reainS. St& IUQ conternplated which have as objectives the hpmVement Of varnish 61ms laepared with
-
d d d dimerized acid salta.
Vol. 36, No. 2
ACKNOWLBDGMENT
The authors @atefully ~kmwledge their indebtednea to A. J. Lewis for aeaktance in formulating and testing the wmiahes pnepared, to R. W. Powers for carrying out portions of the experimental work, and to the Analytical and Physical chemical Division of t h ~Northern Regionsl Research Laborstory for the &Ym. lITERATuaECZTED (1) Bradlw, T.F.. U. 8. Patent 1.7W.375 (Nov. 4,1930). (2) Clark, G. L.. "Applied X-Rays". 3rd ed., p. 474. New YoFk, McGraw-Hill Co.. 1940. (8) Cowan, J. C.. FalLenburg, L.B..and Teeter. H.M.,unpnb. work. (4) H W . 0..J . Clrstn. PAW.. 3,42 (1936). (6) H d o r n , Max. U. 8.Patent 2,046,080 (JUW 23.1936). (6) I. 0.Farbenindustrie. A A . Brit. Pstant 420.633 (Den. 3.1934). (7) Kemp. A. 8..nnd Peterr. E..IND.m e . Cray.. S3.la8a-9 (1941) (8) IW., 34,1W7-1102 (1942). before the Di-on of Paint. vu&. and F%~timChomiatw at the 106th MwtiO. of tho h a x i r c r m Camnorc ~OCI-, Pitiaburgh. P..
Pu-m
PLYWOOD BONDING Henry Grinqfeldet and M . R . Collins, nizsmous PRODUCTS The objmtive of thin work was to establiah a method for detenninii a minimum bonding t h e aehedde applicable to a wide ra.iety of plywood constructiom a d bonding conditions. E a t penetration measurements have beeol made in plywood of various thicknesses plreed betaheated ph-. The time neeennary to cure the resin adhdvehaabwtahIi&ed foroneparticulprplywoodconafilction and then faloulntd to m m t for the diSerenm between phtem temperature and actual resin temperatmi the rete of polymdzationof the -in adhesive at merent mnpmahrrais t h determined. ~ The reaction rate of the rrsin invemtigated apto double with e v a y 2 8 O F. rime in tempmature. The bonding time for a paaicular con-
T
HE demand . . for durable, . resin-bonded plywood has created
W UL the mechanism of bonding and the determination of plywood bonding time and temperature relations. The most generally used redins for the manufactwe of high quality plywood m the ec-dlcd thermosetting resins of the phenol-formaldehyde type. These resine are available in the form of &e&, ea watemluble powders, or ea solutions. Although tbeze resins sre described BS thermosetting, they posess a tbermoplsatic stage which determines their usefulnees. Wben a pack of veneers,either interlead with a film glue or apread with a p h o l i c resin solution, is made into plywood, the sequence of events producing a bond between adjacent veneers is a8 follows: a mwmg m
&ins of the adhesive t
~
.
__
S. Eventually the reain L m e s infusible and insoluble, and produces a strong durable union between the veneera.
The amonnt and auration of resin flow is determined by eharacie of the lesin, moishw content, temperature, rata of best input, and premnra. The &ta of experiments to il-
AND CHEMICAL COMPANY. PIIILADELPgu. PA.
stmction in obtained fmm heat-penetration and ratedfnsotian curyes hv a modifioation of the Bryant method. A stepped E W W developed &w the a c ~ u a lcurve, in whieh the temperature L MSUmed to remain constant at one temperature for the time necasary to increaw 10' F. Us* the curing time at various temperatin the midpoint of each step, the proportion or percentage of the total enre attained during each increment b dcuhted. When the s u m of the percantagem for the sucee(yILyeetap totab 100%. enre is assumed to be mmplete. The cotrespondiq time ie taken e% the minimum prmhsible bondtimc. Predug t h e e for a number of consrructiow can beplotted to rep-t a gemerdizd bonding schedule.
*
lwtmte tbia concept of resin flow are presented in Figure 1. These dnta were obtained in a study of the Bow character and curing rate of a relatively dry p o w d e d resin for use ea a plywood adbeaive. Other teste on powder conteining a higher moisture content indcate that resins of this type, which are water soluble, Bow to a W t e r extent when wet thsn when dry. The flow character tost is as follows: Flow out a film of the resin solution on a clean glass plate. Dry the resin film a t mom t e m p e r a h cr ea low a temperature as possible to d u c a polymerizationof the reain. h p e the dried film from the gbss plate with a m o r blade, snd grind the scrapinga to a uniform sise powder in a mortar. Prepare a pellet 01 the powdered rosin in a pill machine, and place the pcllet between electrically heated platena which are set at a definite and constant tampcrature; usually a piece of paper ia placed on both sides of the pellet to prevent sticking to the hot plates. Apply a known pressure to the pellet for a definite time interval. remove the pellet, and messwe the attained diameter. Calculate the corresponding flow in terms of aversge p r e m m m pounds per mure inch of avcrsge pellet ~ u e aand convert to k w at conatsnt area and M) pounds per square inch area Rep& with another pellet at another time of hest and pres$ure appliartion, etc. It ia d i 5 c d t to extrapolate the results plesented in Figure 1 to the bonding of plywood, but the graphs do indicate the approximate deptb of penetration possible with tbk resin at &ow
