I,VDUSTRIAL AiYD Eh'GILVICERING CHEMISTRY -
1214
Vol. 23, No. 11
Paint Thinners 11-Results of Accelerated Weathering Tests of White House Paints Reduced with Different Types of Thinners' H. K. Salzberg, F. L. Browne,2and I. H. Odel13 MELLON INSTITUTE OF INDUSTRIAL RESEARCH, UNIVERSITY OF PITTSEURGH, PITTSEURGH. PA.
A diversity of opinion exists among paint manufacA I N T manufacturers The physical constants of turers, paint technologists, and painters concerning the have been compelled to the t h i n n e r s are given in effect on the properties of paint of substituting pereplace turpentine Table I. The thinners pass troleum thinners for turpentine. This is particularly largely with petroleum prodthe specifications of the Fedtrue when durability is the property under consideraucts because the demand for eral Specifications Board for tion. In this paper the authors describe a test made paint thinners has outstripped gum spirits and s t e a m - d i s with acceIerated weathering apparatus of white house the available supply of turtilled wood turpentine (11) paints reduced with different types of turpentine and pentine. Naval stores, howand for mineral spirits (IO), petroleum thinners and applied to white- and yellowever, unlike petroleum, is a reand of the American Society pine panels. Careful analysis of the results with special newable natural resource, t,he for Testing Materials for deconsideration given to the effect of wood properties supply of which promises to structively distilled wood turon the deterioration of paint leads to the conclusion increase greatly in the future pentine (1) and for mineral that the substitution of the petroleum type for the through r e f o r e s t a t i o n and spirits ( 2 ) . turpentine type of thinner diminishes to a slight more enlightened methods of The two m i n e r a l spirits degree the durability of the paint. More turpentine harvesting and processing . were analyzed for content of than petroleum thinners can be added in producing As time passes, therefore, the unsaturated and a r o m a t i c the same degree of thinning. choice be tween turpentine hvdrocarbons bv the method and petroleum products for oiEgloff and Mirrell (8), with thinning paint can be based increasingly on their relative the following results in percentage by volume: merits rather than on their availability. Turpentine is generMINERAL U N sA T D . TOTAL AROMATIC SPIRITS ALIPHATIC UNSATD. ally considered, especially by painters, to be a better thinner BRAND HYDROCARBONSHYDROCARBONS HYDROCARBONS for paints than petroleum products because it is thought that 10.15 4.60 14.75 W 14.40 18.95 4.55 H turpentine makes paint more durable. Theories that have been advanced in support of this view were summarized in These two brands were chosen after analyzing a number of the first paper in this series (6). commercial brands, because brand W contained the least The first paper in this series described a test of the com- and brand H the most total unsaturated hydrocarbons. parative effect of turpentine. petroleum thinners, and coalTable I-Physical C o n s t a n t s of Thinners tar naphtha on the durability of white lead and of a lead-zincTURPENTINES inert pigment paint applied on matched panels of southern STEAMDESTRUCDIS TIVELY yellow pine and exposed out of doors a t five widely separated TILLED DISTILLED GUM WOOD WOOD testing stations. Two groups of these panels, one group for Specific gravity (15.5'/15.5') 0.869 0.862 0.867 each type of paint, were also prepared a t Madison, Wis., Refractive index at 20' C. 1.4665 1.4652 1.4734 after polymerization, % 2.0 2.2 1.6 for the accelerated weathering tests reported in the present Residue 157 157 152.4 Initial b. p. C. at 760 a m . paper. The details of preparation and painting of these Per cent dishled at 170' C. 97 93 56 91 cent distilled a t 180' C. panels and the nature of the thinners are recorded in the first Per Color pass Pass Pass paper (6). Besides the tests on southern yellow pine a series MINERAL SPIRITS BRANDW BRANDH of panels of northern white pine was prepared a t Pittsburgh, 143.0 152.0 Initial b. p., * C. at 760 mm. Pa,, for test by accelerated weathering and by outdoor ex226.3 218.3 End b. p., ' C. at 760 mm. Negative Negative Spot test posure a t Pittsburgh only. Details of the preparation of Negative Negative Sulfur test these panels and of the results of the accelerated test are reVery slight None Acidity Pass Pass Color ported here. Results of the outdoor exposures of white-pine panels will be reported in a third paper in this series. PAINTS-Three paste paints, designated c, D, and N, respectively, were supplied by paint manufacturers; each Preparation of the Tests on White Pine paste contained a combination of pigments widely used in THINNERS-8iX thinners were compared in the experiments commercial house paints. The compositions of the three paste paints in percentage by weight were as follows: on white pine:
P
(1) (2) (3) (4) (5) (6)
Gum turpentine Steam-distilled wood turpentine Destructively distilled wood turpentine Mineral spirits, brand W Mineral spirits, brand H A mixture of 3 volumes of thinner 1 with 1 volume of thinner 5
Received August 3, 1931. Presented before the Division of Paint and Varnish Chemistry at the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 31 to April 4, 1931. 2 Forest Products Laboratory, Madison, Wis. Formerly of Mellon Institute of Industrial Research, University Of Pittsburgh, Pittsburgh, Pa.
COMPOSITION Grinding vehicle Total pigment Pigment composed of: Basic carbonate white lead Zinc oxide (lead free) Lithopone Asbestine Silica
PAINTDESIGNATION C D ' h 18 18 17 82 82 83 60 30
..
..
10
75 25
.. .. ..
..
40 40 10 10
2
The paste paints were mixed with raw linseed oil, thinner, and paint drier according to the formulas given in Table 11. Pastes C and D were each mixed according to two sets of formulas, designated C1 and C2, and D1 and D2, respectively,
in which the ratio of linseed oil to thinner in tho first- and third-coat paints varied. Paste N was mixed according to one set of formulas only. Each set of formulas was repeated with each of the six thinners, making thirty sets of paint formulas. Four test panels were painted with tliree coats of paint aceording to each of the thirty sets of formulas, of which two pancls painted by each set of formulas were exposed in an accelerated weathering machine and two were exposed out of doors. Thus, in the accelerated test there were fire groups of twelve panels. Each group was painted a-ith one paint, using a different thinner for each pair of panels in the group.
Fipure I-Liaht
pared. On the other liand, the comparisons that are made are as nearly free from the disturbing effect of variation in characteristics of the wood as it is possible to make them. Accelerated Weathering Apparatus and Cycle
The three-unit accelerated weatliering apparatus and the cycle developed by Nelson and his caworkers (19, 14) were used as models in building the apparatus and selecting the cycle for this test. Figures 1 and 2 show the light and refrigeration units; I'iyres 3, 4, aiid 5 show the interior of the amter-spray, light, and refrigeration units. Two features of this apparatus warrant special mention, inasmuch as they were added t,o the units as originally built on the Kelson plan. One is tlie revolvable framework in the light chaniber that is driven by a I-horsepower motor and carries the panels around the chamber once in 10 minutes. The efit.ct of possible horizontal gradients of temperature and huniidity is thus elimiiiated. The effect of possihle vertical gradients is destroyed by changing the position of the panels from one ro?v to the nest before each exposure in the eliamhcr. A second added feature consists of a gravel arid sand waterfiltcring dev-ice attached t.o the water-spray unit. The installatiun of this filter reduces t l i e total iron content of the city aater, as it strikes tlie panels, from 3 p. p. m. to 0.05 p. p. in. so that at no time during the test are the paints coated
Chamber
TESTPnzsr.s--'l'Iir test panels of white pine were rereived from t,hc planing riiill alrendy cut to t,hc finished dirne~~sionsnamely, 0.75 hy 5.6 by 12 inclies (1.9 by 14 by 30.5 em.). The panels m r e distributed among the groups in a random manner, no effort heing made to bring together within each group panels of the same >mod properties. The defectiveness of this met,hod vas later recognized, and at the conclusion of the accelerated exposure the panels were examined carefully for density and for width and curvature of annual growth Fiewe +-Ice Mechine and Bor rings. These observations revealed the fact that the panels with red iron oxide deposited from the water. The water had hceii cut from a few long hoards and made it possible to tell which panels had bern cut from the same boards. Before passed through the spray in the light chamber also runs making comparisons between thinners, therefore, each group through the fiIter.
of twelve panels, painted with the same paint but thinned successively with the six thinners, was regrouped according to the long boards from a-hich the panels had been cut. I n this paper, comparisons between thinners are reported only for those portions of the original groups of panels that could be regrouped in this way. The number of comparisons possible on t.hat ba.sis is severely limited; in no case could a complete series Ire set, up on which all six thinners could he com-
The cycle of extreme weatliering conditions to which these panels were exposed is essentially the same as that derived by Nelson, Schrnutz, and Gamble (f4)as the most effective. Essentially it consists of a series of short-time exposures (2 to 27 hours) to refrigeration a t 0" li: (-17.8' C.), nmter+pF8y a t 90" F. (32.2' C.), and light from a quartz mercury arc lamp at 140" F. (BO" C.), tlie latter exposure being made at both loa, and high humidities. The panels were exposed con-
I ‘ V I ~ ~ S T ~ IAND ~ 4 LIClV(
12lti
tinuouslj- for a period of 21 weeks, when the final inspection of the paints was made. Effect of Thinner on Consistency and Spreading Rate
Measuremcnt~sc t f the consistency of the paints were made by the Gardncr cylinder-glaus plat,e method (12). I n general, the paints containing mineral spirits flowed slightly farther in a givcir time than the paints containing t.urpentine. Rhodes and Wells (15), after studying the effect of thinners on the yield value and mobility of paint, report that mineral spirits reduces paint pastes faster than dow turpentine. In other words, to reduce paint pastes to a certain definite consistency, slightly inore turpentine than mineral spirits must be added. Tlic cffect. of diirercrrt thimlcrs on the opacity of paint has not yet heeo studied.
after application, but before exposure to the accelerated weathering, is recorded under 0 weeks in the fourth column of Table 111. The observed dzerences in gloss between paint thinned with turpentine or with mineral spirits lie within the limits of experimental error. Table III-Decrease KEN”OF WOO0
White pine
in Gloss of Paint8 during AcCelerated Weatheringa G L I S M B T ~ BSCILRRBADINCS Tup. ow 0 1 2 3 1 2 THINNaR weeks week weeks weeks weeks
46.2 32.4 26.1 4 5 . 9 36.4 2 9 . 0 4 6 . 5 35.3 2 8 . 3 4 5 . 0 37.8 2 8 . 9 White pine 46.1 43.3 35.0 47.8 34.8 2 5 . 1 W‘hiir pine 44.7 3 8 . 4 2 4 . 9 4 4 . 7 3 8 . 4 26.8 IVhetemiinations of the resin content of the boards from which the yellowpine panels were cut has been reported by Rrowne (7); that of the white pine was not determined. The number of resin spots observed increased rapidly with the resin content of the board 8s follows: 87 Averrir ieiin c o o t e a t , ‘;b by w c ~ i ~ i i l Numlxr resin spots observed
2.39 392
IN
BOARD No.
35 3.99 810
36
6.07 1458
38 6.64 2290
ISDUSTRIAL A N D ENGILVEERINGCHEMISTRY
h-oveniber, 1931
T a b l e IV-Influence
of T h i n n e r s on D u r a b i l i t y RANGE
COM-
RATIOOF LEADTO
PAINT DESIGNATION
ZINC
OF PAXELb
THINNER
GROUP^
Grams
OF
GRAIN^ Degrees
.\lOISTURE
BILITY
W E I G H T OF
SIDE PAIXTEDd
PAINT APPLIED'
BASED ORDERF L U C O N IxOF TVATEGRITY
Lb / l o 0 sq. f 1 . i
Weeks
5.47 5.35 5.35 5 29 5.65 5.47 5.35 5.29 5.29 5.59 5.59 5 , 11 5.17 4.99 6.20 5.11 5.17 6.25 5.54 Not determined
21 21 21 18 >213 >21 >21 21 21 >21 21 >21 >21 >21 >21 >21 >21 >21 20 >21 221 20 >21 20 221 >21 >21 >21 >21 >21 >21 >21 >21
MERIT/ T I O N g Grams
END CHECKSh Inches (C'm.)
P A I N T S APP1,IED T O W H I T E P I N E
c1
60 : 30
c2
60: 30
lI2
N
DURA-
OF
WEIGHT ANGLE
PARISON
1217
75:25 Lithoponezinc
.
1 Steam-distilled wood tur entine Mineral spirits (brand HP Mineral spirits (brand H) 2 Gum turpentine Mineral spirits (brand W) 3 Steam-distilled wood turpentine Destructively distilled wood turpentine 4 G u m turpentine Gum turpentine Steam-distilled wood turpentine Steam-distilled wood turpentine Destructively distilled wood turpentine Mineral spirits (brand W) Mineral spirits (hrand H) Mixture of gum turpentine and H Destructively distilled wood turpentine Mineral spirits (brand W) Gum turpentine Mineral spirits (brand W) Gum turpentine Steam-distilled wood turpentine Mineral spirits (brand W) 10 Destructively distilled wood turpentine Mineral spirits (brand H) 11 Steam-distilled wood turpentine Mineral spirits (brand W) Mixture of gum turpentine and H 12 Mineral spirits (brand W) Mineral spirits (brand W) 13 DestructiGely distilled wood turpentine Destructively distilled wood turpentine 14 Mixture of gum turpentine and H Mixture of gum turpentine and H
341 350 355 365 360 344 334 379 381 374 382 370 362 355 349 349 34 1 330 345 327 322 323 397 404 360 361 361 366 362 334 349 330 349
2-3 0-2 2 5-24 6-24 16-50 19-46 3-17 6-18 14-21 8-14 19 16-20 37-62 25-57 56-69 37-66 4-9 5-2 1 11-14 2-14 5-13 6-26 0-18 25-45 42-55 30-53 20-21 16-20 19-46 56-69 7-15 5-10
B B
B B B B B B B B
B P B P B B B P P P B B P P P P P B P P B
Not determined Not determined 5.65 5.17 5.35 5.11 5.59 6.20
3 1
2 2 1 2
1
3 2 1 2 1 2 2 1 1 2 1
2
1
2 3 1 2 2 3 1 1 2 2 1 2 1
220 248 243 265 168 135 132 183 182 184 180 131 148 125 122 124 131 104 202 114 122 246 42 169 90 92 101 132 148 132 124 132 220 ~~~
l(2.5) 0 0 0 0 0 0 0 0 0 4 (10.2) 0 0 0 0
0 0 2 (5.1) 2 (5.1) 0 0 0 0 0 0 5 (12 7)
0 0
0 0 0 0 2 (5.1)
P A I N T S A P P L I E D T O Y E L L O W PINE
50-82 B 7.50 3 15 Destructively distilled wood turpentine 543 21 228 0 7.74 69-81 B 2 139 Steam-distilled wood turpentine 0 542 >21 8.28 70-78 B 1 Gum turpentine 605 0 85 >21 7.47 2 Oxidized turpentine 542 99 76-80 B 0 >21 7.49 2 Mineral spirits (Midcontinent) 522 112 49-64 B 21 0 7.73 1 Varnish and paint makers' naphtha 516 99 59-68 P 0 >21 n 7.53 34-44 B 2 Mineral spirits (Pa.) 505 224 21 7.11 Solvent naohtha 40-64 B 509 3 0 165 >21 . 7.40 30-45 B 506 191 Mineral spirits (Calif.) 2 >21 l(2.6) 7.00 50 1 Mineral spirits (Mexico) 3 46-51 B 0 193 >21 7.50 27-43 P White lead 16 Destructivelv distilled wood turoentine 667 1 21 295 4 (10.2) 7.74 1 67 1 21 Steam-distilled wood turpentine' 30-67 P 290 5 (12.7) 8.28 27-52 P 1 345 21 Gum turpentine 631 4 (10.2) 7.47 9-46 P 445 21 Oxidized turpentine 64 1 2 4 (10.2) 7.49 14-43 P 21 Mineral spirits (Midcontinent) 640 526 5 13 (33) 7.73 18-37 P 21 Varnish and paint makers' naphtha 64 1 4 528 19 (48) Mineral spirits (Pa.) 11-26 B 7.53 2 631 18 570 23 (58) 7.11 Solvent naphtha 3 616 19-30 P 21 559 26 (66) 7.40 Mineral spirits (Cali?.) 19-24 P 3 624 21 682 21 (53) 7.00 Mineral spirits (Mexico) 601 34-37 P 2 21 550 18 (46) 5.25 Lead .zinc 45340 17 Destructively distilled wood turpentine 564 67-69 B 1 0 20 276 602 Steam-distilled wood turpentine 5.75 58-68 B 2 200 20 0 n 5.09 20 Gum turpentine 605 65-78 B 228 ~. 4 5.31 Oxidized turpentine 67-80 B 595 1 320 20 i (2.5) 4.91 Mineral spirits (Midcontinent) 80-85 B 609 18 280 3 16 (41) 4.54 Varnish and paint makers' naphtha 76-78 P 588 282 3 18 15 (38) 4.96 Mineral spirits (Fa.) 72-73 B 612 3 12 (31) 18 308 4.62 Solvent naphtha 72-75 B 608 284 3 18 12 (31) 4.74 Mineral spirits (Calif.) 62-74 P 625 3 18 238 l(2.5) 4.52 Mineral spirits (Mexico) 675 43-69 B 14 2 217 2 (5.1) Lead -zinc 45:40 18 Destructively distilled wood turpentine 640 47-70 P 5.25 14 1 0 89 Steam-distilled wood turpentine 5.75 618 34-36 B 20 3 0 120 Gum turpentine 27-29 B 5.09 590 1 20 89 2 (5.1) Oxidized turpentine 5.31 580 50-69 P 1 20 99 Mineral spirits (Midcontinent) 4.91 597 28-66 B 99 18 0 Varnish and paint makers' naphtha 4.54 599 80-83 P 20 111 0 n Mineral spirits (Pa.) 4.96 59 1 64-69 P ' 20 79 Solvent naDhtha 4.62 79-84 62 1 P 101 0 >20 Mineral spirits (Calif., 4.74 618 69-88 B 20 88 3 (7.6) Mineral spirits 'Mexico; 4.52 579 61-89 B 18 0 110 a Each comparison group consisted of panels cut from same long board. f Order of integrity a t end of test, value 1 representing best integrity. b Determined when all panels were of approximately same moisture content. ISummation of ten fluctuations. C Angle a t which annual rings reached painted surface of panel. h Found to influence moisture-fluctuation values. d Pith (P) or bark (B) side. 1. One pound per 100 square feet equals 4.9 kg. per 10 square meters. e Average for each group of panels receiving same paint and hence not rigidly j Greater than 21 weeks: i. e., still sound at end of test. applicable to individual panel. Whit:e lead
~~~
~~
~~~~
The resin content within the boards was not sufficiently uniform to justify an attempt to trace an influence of thinners on exudation of resin. Yellowing of the paint oils (9) was observed after 8 weeks of exposure. The degree of yellowing was not affected by the nature of the thinner. The lithopone paints were discolored to a greater extent than the lead and zinc paints applied on white pine. EFFECTOF TYPEOF THINNER ON CHECKING OF PAINT FILM-By checking is meant the breaks in the film that presumably penetrate only the third, or the second and third coats of paint. The appearance of checks was detected by
observation a t a magnification of about 10 diameters, and the time a t which microscopic checking first appeared was recorded. Checks parallel to the grain were differentiated from checks transverse to the grain. The former appeared very much sooner and in greater abundance than the latter. The parallel checks appeared in all paints after 12 to 20 weeks of exposure. No effect of thinner on this phase of breakdown of the film was noticed, except in the white-lead paint thinned with oxidized turpentine. Checks in this paint first appeared several weeks after they had been observed in the other paints of this series. The same observation was made on the corresponding panel exposed outdoors at Madison (6).
INUUS'I'RISL A.VD EN .GINEERlNL' CHE?/IIS1'IZY
1218
EFFECTOF TYPEOF TIIINNER ON DURABILITY OF PAINTSA dynamic method of evaluating paint service and two static methods of eomnarine nanels xvithin each moun have been . applied to the exa m i n a t i o n of both the whiteand yellow-pine panels. Kumeriea1 counts were made after each week of weatheringof thenumber of flaked a r e a s and cracks present in the area of the panel, disreg a r d i n g , however, those failures t h a t were obviously due to the presence of knots or long end c h e c k s in the panels. T h i s numerical, o r static, record of X'igurc 5-Inferior of Refrigerator flaking and crackingof the paint film has been converted into a dyiiar~iicevaluation in which the paints are rated in durability based upon integrity. When a panel had acquired more than one hundred bare areas of wood, made either by flaking of the film or loss of paint from the edges of a paint crack, it was arbitrarily corisidered poor enoughin integrity to be no longer serviceable. During one week of exposure to the cycle follou~imgthe last week of the test, and after application of fresh coats of paint to the backs and edges of the panels, the fluctuation in moisture content of the panels was measured by weighing the panels after exposure in the water-spray chamher or in the light chamber to alternately wet and dry conditions. This procedure was adopted to measure the extent to which the deteriorated paint film still protected the wood (3). It merely constitutes a static method of rating the deteriorated paints. R~llowingthe determination of moisture fluctuation, the panels were examined visually and given a final order-ofmerit rating, based upon hot.ti the number and distribution of areas of wood exposed. In general, tlie moisture fluctuation values substantiate the order-of-merit ratings. There are sonie pronounced discrepancies, however (see comparison group 1 of Table IV), which indicate that this method of evaluation udl not always rate panels in the same order as they are rated by visual examination. Provided there are no end checks in tlie panels and no roughness of surface, such as raised grain, moisture-fluctuation values should more definitely establish integrity ratings than visual examination. The ratings of the paints by the dynamic arid by Liotli of tlie static methods are shomi in Table IV. Considering the paints applied to white pine, the comparative effect of type of thiriner on tlie durability can be summed up after noting in eaclr comparison group involving difiereirt types of thinner (groups 1, 2, 5, 7, 8, 9, 10, and I l ) , the advantage one type of thinner has over the other. When this is done, it is seen that the turpentines have contributed more to the durability than have the mineral spirits.
-.
Turpentine proved superior , Minerd spirits proved supeiioi Both types had same rating
Y
5 2 1
.
7
3
1 0
4
1
Yol. 23, s o . 11
Unfortunately no comparison groups could he formed that involved both types of mineral spirits. ki; a result, no comparison of the effect of high and low content of unsaturated hydrocarbons in mineral spirits can be made directly. However, both types of mineral spirits are represented in the comparison groups in which turpentine proved superior. Comparison groups 12, 13, and 14 indicate that variation in the proportions of oil and thinner with which the C1 and C2 paints were reduced failed to exert any appreciable influence on the serviceableness of the coatings. This conclusion agrees with the results of other tests reported by Urovne (5). Considering the paints applied to yellow pine, the turpentines again contributed more to the durability than did the mineral spirit.s:
G?e.W
Per *v%d
We'rcko
White lead
Cumlnrrciel turpentines
6
230
1.5
White lead
Mineral spirits
8
36S1
2.6
Lead-zinc
Commercial t ~ r p r u i i i i e i 6
107
2.0
Lesd-zinc
blineial spirits
8
177
2.5
Unusuuliy high moisture Aucluafiuii influenced t o ercrrrive end checking o i these p ~ m l rs,i indicated in Trbii
Oxidized turpentine, which proved superior to any other thinner in the outdoor test (G), appears in Table 1V to have
Figure 6-Corn ari*on Group 16 Shewine Paiiel SurfeceaafferRernmdiof Paint Coatings a t Conclusion of T a t Panels are laced in same order irom left t o right, ton to bottom. as they are liste8by thinners in Table IV. Rectangles msik acejls photamicrographed before removal of paint a d shown in Figure
S.
Xovernber, lYSl
IiVl~USTIzIA L AND ENGINEEltINC CHEMISl'RY
Figure 8.-Pbommicrogra hs ( x 10) of Resuicted Ares. of Comparison &oun 16 (see Fig61 0-D~rtructively distilled wood turpentine l--Stcrm-dirtiIICd Wood turpentine 2 .-Gum turpentine 8-Oxidized turpentine 4 -Minrr=l spirit3 (Midconlinenti
5-Vamish and paint makers' naphtha , %-Mineral spirit3 (Pa.) 7-%lvent naphtha 8-Mineral spirits (Calif.) 9 -Mineral spirits (Meaieol
of chalking could he ascribed to tlie effect of the type of thinner used. FiQure 7 4 o m p a r i s o n Group 16 a t Conctuaion of Test
iiilidc paint weather eitlier as well or better tlian paints con-
taining tlie ordinary turpentines. Varnish and paint makers' naplitlia, which in the outdoor tat was distinctly superior to any of the minrral spiritsj also ranks geiierally high in tliese tests. The panels of c(miparison group 16, Table IV, were examined in special detail, because the supcriority of the turpentincs is more outstanding in this than in any other group. The paint was cleaned from the panels and they m r e cxamined with regard to surface markings, which are shown in Figure 6. In grain the panels were ail intermediate between Rat grain and edge grain. The first four panels cut from the long hoard, ov vhich the thinners were turpentines, are heavier than tlie uthers and would therefore lie expected to give worse rather than better paint service (4). ,Figure 7, which is a view of the panels before removing the paint, shows how much more intact were the coatings on tlie four panels for which the thinners were turpentines than on tlie other panels. The rectangle uutlined on each panel marks an area of which a photomicrograph appears in Figure 8. These areas were selected because the wood bcneath them, as indicated in Figure A, was similar in width of annual rings and in ratio of sprinpood to summerwood. Clearly the turpentines have cont.rihuted more to the durability of the paint f i l m than have the other thinners. The degree of chalking of the paint film was estiruated dter each week of exposure hy drawing, with pressure of the fingers, a black relret strip of cloth from onc end of the panel to the other. All paints, except the white-lead paint, chalked heavily after 6 weeks of exposure. Eo differences in degree
Summary
i\i:celerataci weatlwiiig tests of exterior white liouae paints, reduced with different types of volatile thinner and applied to groups of white-pine and of southern yellow-pine panels, shqw that ordinary turpcntincs contribute slightly more t o thc durability of paint coatings than do mineral spirits, rcgardless of the type of crude oil from which the mineral spirits is obtained or its eontent of saturated and aromatic hydrocarbons. In thinning paints of which oiric oxide is a component, slightly more turpentine tlian mineral spirits may be added to reach tile mine consistency. Cliecking of coatings of straight aliiblead paint on southern ycllow pine did not appear so soon when thc thinner was an oxidized turpentine as it did when the thinner was ordinary turpentine or a petroleum or coal-tar distillate. In these experiments the initial gloss of the coatings, the rate of loss in g1oss, discoloration by yellou~iiiyof paint oil, the rate of chalking, and exudation of resin were not affected by the choice of paint thinner. The ratio of oil to tliiiiner in the paint mixture can be varied within wide limits witliout appreciably affecting the durability of paint coatings on white pine. Acknowledgment
Acknowledpients are made to C. 1". Spell, of the Piire Institute of America, and to G. D. Ucal a i d W. U. Burnett, of Melion Institute, for advice during the progress of these experiments; to H. A. Xelson, of t,be New Jersey Zinc Go., for aid in constructing tlie accelerated weathering units; to C. E. I I r u l d q r , of the Forest Products Laboratory, for aidin preparing the yellow-pine panels for the test; and to the Nortliern Pine Manufacturers' Association, the New Jersey Zinc Co., and the Pittshiir& Plate Glass Co. for materials
I N D U S T R I A L A N D .ENGINEERING CHEMISTRY
1220
Literature Cited American Society for Testing Materials, Standard No. D236-27 (1930). American Society for Testing Tentative Standard No' D235-26T (1930). Browne, IND.ENG.CHEM.,19, 982 (1927). Browne, Federation of Paint and Varnish Production Clubs, O.@cial W e s t , 96, 106 (1930): Am. Paint J . , 14, 22 (April 7. 1930); Paint, Oil Chem. Rev., 89, 9 (March 20, 1930). Browne, IND. E N G . CHEM..12, 847 (1930). Browne, Ibid., 23, 868 (1931). Browne, Ibid.,as, 874 11931).
Vol. 23, xo. 11
( 8 ) Egloff and Morrell, Ibid., 18, 364 (1926). (9) Elm, Federation of Paint and Varnish Production Clubs, OBcial Digcsf, 105, 474 (1931). (10) Federal Specifications Board, Master Specification 16, Bur. Standards, Circ. 98 (1923). (11) Federal Specifications Board, Master Specification 7b, Bur. Standards, Circ. 86 (1926). (12) Gardner and Holdt, Mfrs. Assocn. u.s,, Tech. Circ. 199 (1923), (18) Nelson, Proc. Am. SOL.Testing Materials, 12, Pt. 2, 485 (lQZ2). (14) Nelson, Schmutz, and Gamble, Ibid.. 16, Pt. 2, 563 (1926). 21, 1273 (1929). (15) Rhodes and Wells, IND.E N O .CHRM.,
Formaldehyde and Its Polymers' Frederic Walker T H EROESSLBR & HASSLACHER CHBMIC.\L COXPANY, INC., PBRTKAMBOY,N. J .
LTHOUGH from a structural standpoint formaldehyde is the simplest member of the aldehyde group, its chemistry is exceedingly complicated. In general, the first member of any homologous series of organic compounds is the most unorthodox in its behavior and this is especially true in the case of formaldehyde. This compound shows many reactions that are peculiar to itself and does not take part in some of the standard aldehyde reactions. However, even disregarding its chemical reactions with compounds other than itself and water, volumes could be devoted to the chemistry of its polymers, hydrates, and solutions. Our knowledge concerning these things has been greatly clarified in recent years. At present, however, most of this information remains scattered through the literature, and much of the information that is easily available is confusing and in some cases incorrect. The object of this paper is to summarize briefly the present status of our knowledge of formaldehyde, its solutions and its polymers. Formaldehyde was first prepared by Butlerow (3) in 1859 in the form of one of its polymers by the action of silver oxide on methylene iodide. On the basis of this study he came to the conclusion that the compound thus obtained was dioxymethylene, an "isomer" of the unknown formaldehyde. He gave an account of its characteristic reactions, prepared aqueous formaldehyde solutions by heating it with water and also described
