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Considerable work has been done on the stimulation of pine IN RESINACID FRACTIORS oleoresin flow by treating a newly cut streak on the pine tree TABLE 1. l-PIMARIC ACID PRESENT OF PINEOLEORESINA N D SCRAPE with acids ( 2 ) , Inasmuch as the mineral acids used are known -7% I-Pirnaiic Acidto isomerize I-pimaric acid rapidly into I-abietic acid, deterMonth of 1941 Longleaf Slash minations of I-pimaric acid content of oleoresin obtained in Pine Oleoresin this manner were made to determine to what extent, if any, April 31 2 24 5 isomerization has taken place. Analysis of pine oleoresin ob31 3 24 3 tained from streaks treated with 10 per cent sulfuric acid June 33 5 23 1 showed the presence of 22.6 per cent I-pimaric acid from slash 33.4 23 3 pine and 31.9 per cent from longleaf pine. August 33.6 23.7 33.7 23.3 These results are in contrast to those of Sandermann (3) who found no I-pimaric acid in the oleoresin from European November 32.1 24.5 32.5 24.1 Pinus sylvestris when the streaks were treated with 25 per cent hydrochloric acid. From untreated streaks of this same Pine Scrape specie of pine, 40 to 48 per cent of I-pimaric acid was found. June 39.5 32.2 39.9 32.2 The reason for this difference is not clear, but it seems safe h'ovember to conclude that as far as the 10 per cent sulfuric acid treat38.0 29.4 38.0 29.7 ment is concerned, little or no change has been effected on the composition of the oleoresin obtained. ent is undoubtedly due to oxidized resin acids not eliminated by the n-pentane when the scrape samples were putinto solntion for analysis.
Literature Cited (1) Fleck and Palkin. IND. ENG.CHEM.,ANAL.ED.,14, 146 (1942). (2) Liefield, Am. Turpentine Farm. J.,4(6), 14 (1942). (3) Sandermann, Be?., 71,2005 (1938).
Fatigue Resistance oz Flexible Plastic Sheetings F. W. DUGGAN AND K. K. FLIGOR Carbide and Carbon Chemicals Corporation, New York, N. Y.
I
N MANY of the uses to which flexible plastic sheetings are being applied, the fatigue resistance of a sheeting is an important factor in the serviceability of the material. Because of its importance, the study and control of this characteristic were desirable, and for this purpose a flex-fatigue test procedure was developed. The type of test employed in this laboratory involves simple flexing of a flat or folded sheeting. For some uses the machine is adjusted to provide alternate tension and flexing. At the flexing end of the cycle the test sheeting is bent upon itself rather sharply to a controlled radius a t the mease. This feature, the sharp creasing of the sheeting a t each cycle, provides a severe test, the severity being controlled by the tightness of creasing. Some of the flexible elastomeric sheetings included in this study possess a high degree of fatigue resistance, and a particularly severe test was required in order that fatigue failures would be obtained within a reasonable period. This test has provided useful information regarding the effects of various factors on the fatigue resistance of certain flexible vinyl resin sheetings.
Method of Test The fatigue test machine incorporates the essential features of the A. S.T. M. De Mattia flexing machine used on rubber (D430-35T). A stationary head holds one end of the,test specimen and a reciprocating head holds the other end. The heads are adjustable for the clearance between them a t the
closed end of the cycle and for the stroke or total displacement during the cycle. The clearance setting controls the radius of crease during flexing, while the stroke setting controls the degree of stretch imposed. The standard fatigue test in this laboratory is carried out on a 0.040 X 2.5 X 5 inch sample of press-polished sheeting, folded longitudinally before insertion in the grips. The motion of the reciprocating head bends the folded sample transversely during flexing. The head clearance a t the closed end of the cycle is set a t 0.090 inch plus the total thickness of sheeting. I n the bent position there are four thicknesses of sheeting between the heads so that the clearance ~ 0 . 0 9 0 (4) (0.040) = 0.250 inch. This provides a radius of 0.045 inch a t the crease. The stroke is adjusted to draw the specimen taut a t the open position but not to apply any stretch. This standard test setup is known as the fold flex a t 0.045-inch radius. Tests ordinarily are run a t 26" and 0" C.; 0" is particularly useful for accelerated testing. Figures 1, 2 , and 3 show the details of the test setup. The machine tests twenty specimens a t a time and operates at 115 cycles per minute. This speed was chosen because much of the early work on the machine was for evaluating flexible sheetings for shoes, and 115 cycles per minute simulates the flexing which occurs when walking a t a brisk rate. This relatively low rate of flexing is desirable also because it minimizes the heating of the test piece due to the intcrnal friction of flexing.
+
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
February, 1943
Plasticizer
D93' % 20 25 30 35
--
0.020-in. radius 30 300 2,500 20,000
173 Fold-Flex at 0' C -. 0.045-111. radius (standard) 150
1,300 11,000 90,000
0.085-in. radius 300 2,700 20,000
170,000
DEGREEOF STRETCH. A sheeting which is alternately flexed and stretched will have a lower fatigue life than the same sheeting under flexing only. The decrease in fatigue life is roughly proportional to the degree of stretch imposed, by the following data on Resin W : c
Plasticizer
n7 70
No stretch (standard) 7
30 35 25 30
10,000 90,000 80,000 550,000
Fold-Flex 10% stretch A t 0' C. 1,400 23,000 A t 25' C.
.... *. ..
25% stretch 200 6,000
--.
12,000 150,000
As Figure 5 shows, the percentage decrease in fatigue life with stretching is greatest in the case of the stiff sheetings (low plasticizer concentrations). FLEXING OF FLAT OR FOLDED SHEETINQS. TEST F I G U R E 1. SAMPLES MOVSTEDFOR T%-IST-FLEX If a 0.045-inch or greater radius a t the bend is maintained, the manner of mounting samples of sheeting in the machine apparently does not affect fatigue results. The following variations were Correlations of laboratory fatigue data with shoe wear investigated: simple flexing of flat sheeting (flat-flex), transtests show that from 5000 to 15,000 cycles in the 25" C. verse flexing of sheeting folded longitudinally (fold-flex), and laboratory test approximate one day's wear in shoes. This transverse flexing of sheeting folded and twisted longicorrelation proved useful in the commercial development of tudinally. In this series of tests the machine settings were flexible sheetings for use in shoe uppers. adjusted to provide 0.045-inch radius a t the bend, and practically identical fatigue values were obtained with all three Effect of Physical Factors on Fatigue Values mountings. A number of physical factors (test conditions arid machine adjustments) have important influences on the fatigue values obtained for various sheetings. Those factors which are important should either be fixed (as test constants) or specified when the test data are reported. The various factors are discussed below in the approximate order of their importance. Of the resins used in the tests, S and W were vinyl chlorideacetate type; X was a vinyl butyral resin. The plasticizers employed are designated by the following letters: D, dioctyl phthalate; G, triglycol dioctoate; K, butoxyglycol phthalate; S, dibutyl sebacate. The fatigue life of flexible vinyl sheetings is shorter a t lower temperatures. As the temperature is lowered, the percentage decrease in fatigue life is greatest for those sheetings which stiffen most a t low temperature. The extent of decrease in fatigue life, for some of the vinyl resin compounds, is shown in the following table: Resin W
S X
Plasticizer, % D, 35 D 32 G,'28
-Fatigue 25' C.
4,000,000 100,000 50,000
Life, Cycles00
c.
90,000 1,500 180
Thus, when compared in equal flexibilities a t room temperature, sheeting from resin X has the lowest fatigue life. If these same sheetings are cooled to 0" C., the resin X material will be the stiffest of the three, and as the table shows, its percentage decrease in fatigue life is greatest. TIGHTNESS OF BENDING.Bending a sheeting more tightly upon itself a t the "closed" end of the flexing cycle (thus decreasing the radius a t the crease) reduces the fatigue life of the material. The following data on resin W (from Figure 4) illustrate the important effect of changing the radius of bending from 0.020 to 0.085 inch:
FIGURE 2. F A T I G TEST ~ E MACHINE
However, when the radius a t the bend was reduced-to 0.020 inch, the folded sheetings were found to have shorter fatigue life than that of the samples flexed flat. These relations follow as determined a t 0" C. on resin W: Fatigue Cycles at 0" C. 0.020-in. radius at bend Standard value Folded Flat at 0.045-in. radius 150 30 75 1,300 300 800 2,500 9,000 11,000
7 -
Plasticizer D, '% 20 25 30
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FIGURE 3. MOUNTINGOF S A M P L EFSO R S T A N D A R D FOLD-FLEX TEST
is applied, and flexible sheetings fall in line with fatigue trends on rigid materials in this respect. It should be pointed out that the data in this report were obtained on sheetings which had been annealed under pressure and fairly high temperature (150' C.) and thus contained very little residual etrain. However, it is possible, by improper adjustment of calendering or forming conditions, to produce flexible sheetings which contain an excessive amount of residual strain. The effect of such strain on the fatigue life of the sheeting has not been investigated, but from correlations with other physical properties, an appreciable reduction in fatigue life would be expected, For that reason the levels of fatigue resistance described in this report should not be expected unless the sheetings are properly fabricated.
Effect of Compound Formulation on Fatigue Life By combining various resins and plasticizers in suitable proportions, it is possible to prepare a large number of flexible plastic sheetings which are alike in flexibility and outward appearance. However, these various combinations may differ greatly in fatigue life. The following discussion brings out the effects of various components on the fatigue life of a compound. TYPEOF RESIN. Of the various vinyl resins studied, resin W had the greatest resistance to fatigue, as shown in the first table which compared different resin types in compounds which had been adjusted t o the same flexibility a t room temperature. The fatigue life of the various compounds appears to be a function of their elasticity or rate of elastic recovery from strain. It was noticed that fatigue failures most often occurred on the inside of the bend, as if a compound which
At 25" C. the same trend in relations was obtained. Reducing the radius a t the bend from 0.045 to 0.020 inch reduced the fatigue life of the flat samples slightly and reduced the life of the folded samples considerably. SHEETINGSURFACE. Sharp irregularities in the surface of a flexible sheeting reduce the fatigue life of the material. This is illustrated by the following data on sheeting prepared from resin W with 35 per cent plasticizer D, compared in the presspolished and matte-finished forms :
FOLD
-
TE5TED
I
PLLX
AT O'C.//
RADIUS
l00,OC
O F BENDING
2o.ooQ
c u '0
k 10,WO
111
FOLD-FLEX
J
9
L5
UJ
0
10,0(
,020 .040 RADIUS OF
0
u-
.060 .OB0 BENDING, I N C H
.IW
J
Id 3
-Oh
G
DEGREE
kL
OF
STRETCH
F O L D - F L E X A T O'C. RESLN W + PLAZSICI'LCI?
-Fatigue Life itt 25' C.Surface Unstretohed 25% stretch Press-polished 4,000,000 1,500,000 iMatto-finished 1,700,000 600,000
Thus, perfection of surface is a factor even when no stretching
AT O'C.
302
30 20 > % PLASTICIZER
FIGURE
40
D
0
0
5
10
PER CENT
\!5
20
D
25
5IRETCH
EFFECT O F R h D I U s A T BEKDON FATIGUE LIFBO F SHEETINGS FROM RESINw
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INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1943
different plasticizers impart different low-temperature stiffening characteristics. The sheeting containing plasticizer S remains most flexible, and that containing plasticizer K, least flexible of the three at 0" C. As the table shows, fatigue life a t 0" C. parallels these flexibility differences, FILLERS. The effect of fillers on fatigue life depends on the type of base resin used in the compound. I n vinyl chloride-vinyl acetate copolymers (resins W, S, etc.), fillers reduce the fatigue life of the sheeting to an extent depending on the proportion of filler present. I n polyvinyl butyral resin (resin X), certain fillers appear to have reinforcing action. The degrading effect of fillers in copolymer vinyl chloride-acetate resins is shown by the following data (from Figure 7) on different fillers. All the compounds were plasticized to equal flexibility a t room temperature:
10,000
I ,ooc
100
I
20
40
30
PER C E N T
20 PLASTlClZER
30
40
D
FIQURE5. EFFECTOF STRETCHING ON FATIQUE LIFE OF SHEETINGS FROM RESINW
Resin W W
was slow to recover from bending stress would be torn by tensile stress as the flexing cycle progressed. I n a series CONCENTRATION AND ~ y OFp PLASTICIZER. ~ of flexible sheetings prepared from a given base resin, the fatigue life increases rapidly with increase in plasticizer concentration. Figure 6, with log of fatigue life plotted against plasticizer concentration, shows this trend. The following typical data, on effect of plasticizer concentration on fatigue life (of resin W), were taken from Figure 6 (left) : Ds % 20 25 30 35 40
--Fatigue 250
c.
10,000 70,000 500,000 4,000,000
......
Lif-
00
-Fatigue
Filler, %
250
c.
None
4,000,000 50.000 170,000
None
100,000
W W
Calcene 40 York Whiting, 40 Raven Black, 40
8
Calcene, 40
8
Plasticizer
175
.....
.....
Lit00
c.
90.000 12.000 15,000 23.000 2,000 400
The reinforcing action of certain fillers in polyvinyl butyral resin (X) is still under investigation, but the following data (from Figure 8) illustrate the trend: % Calcene
Fatigue Life at O o C.
None 20 40
180 280 450
COLORING AGE~VTS.Limited data on olastic comoounds containing coloring agents show that thesk materials,- in the
c.
..... 1,200
10.000 90,000 800,000
If different plasticizers are compared a t concentrations which provide equal flexibilities, the type of plasticizer has no appreciable effect on fatigue life. This comparison was made on commonly used plasticizers which are readily compatible in the resin. Typical data (taken from the right-hand graph of Figure 6 and other sources) are shown in the following table on resin W: Plasticizer,
%
D, 35 K, 33 9, 29
-Fatigue 250 c.
4,000.000 4,000,000 4,000,000
Life00
c.
90,000 60,000
150,000
The three sheetings have equal flexibilities and equal fatigue strengths at room temperature (25" C.). There is a difference in fatigue life a t the lower temperature, but this may be explained by the fact that the three sheetings do not have equal flexibility a t 0" C. The
PER CENT
PLASTICIZER
F I G U R6.~ EFFECTOF RESINTYPEAND TEMPERATURE AND OF PLASTICIZER ON FATIQUE LIFE AT 0.045-IKCHRADIUSOF BEND TYPEAND CONCENTRATION
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concentrations noimally used, have no appreciable effect on the fatigue life of the compound. Among the coloring agents checked and found essentially neutral in effect were the following: 1 per cent Excello 2 X Black, 1 Genoa Toner X-1180, 1 Blue Toner B-3, 1 Opaline Green G - l , 2 C. P. Deep Orange A-4337, 2 Cadmium Red 4333, 2 Titanox A, 2 Osaka Yellow Lake X-1630, and 1 per cent Hoover Brown 7764.
I
0
20 40 60 PER C E N T F \ L L E R
FIGURE8. EFFECTOF CALCENE FILLERON F.4TIGUE LIFEO F SHEETINGS, PLASTICIZED TO EQUAL FLEXIBILITY AT 25 C. O
045" R A D I U S
AT BEND
20 PER C E N T
40
60
FILLER
(BY WT>
FIGURE7 . EFFECTOF FILLERAND TEMPERATURE OK FATIGUE LIFE OF SHEETIKGS FROM RESIN W, PLASTICIZED TO EQUAL FLEXIBILITY AT 25"
c.
Conclusions The effects of physical test factors on the fatigue life of the resulting flexible sheetings are given in conclusions 1 t o 4: the effects on variations in compound formulation, in conclusions 5 to 9. 1. TEMPERATURE. The fatigue life of flexible vinyl sheeting is from thirty t o two hundred times longer a t room temperature (25" C.) than a t freezing temperature (0' C.).
2. TYPEOF FOLD.The flexing of folded samples is no more severe than simple flexing of flat sheetings, provided they are both bent t o the same radius a t the creare during flexing and that this radius is 0.045 inch or greater. 3. DEGREEOF STRETCH. The alternating of tension with flexing reduces the fatigue life of a sheeting in proportion to the degree of stretch imposed. 4. SHEETING SURFACE.Press-polished sheeting has two or three times the fatigue life of sheeting with a matte finish (sharp irregularities in the surface). 5 . TYPEOF RESIN used in a sheeting is an important determinant of its fatigue life. Of the vinyl resins studied, W (a high-molecular-weight copolymer of vinyl chloride and vinyl acetate) provided sheetings with the greatest resistance t o fatigue. 6. CONCENTRATION OF PLASTICIZER. I n a series of flexible vinyl sheetings prepared from a given base resin, the fatigue life increases rapidly with increase in plasticizer concentration. A compound containing 40 per cent plasticizer will have from two to twenty thousand times the fatigue life of a compound containing 20 per cent plasticizer. 7. TYPEOF PLASTICIZER. If we consider only those plasticizers which are readily compatible with the resins involved, and if we make comparisons on compounds of equal flexibility, the type of plasticizer used in a sheeting has little effect on fatigue life. 8. FILLERS greatly reduce the fatigue life of flexible sheetings prepared from copolymer vinyl chloride-acetate resins. However, sheetings prepared from polyvinyl butyral appear to be reinforced by the inclusion of certain fillers. 9. COLORING AGENTS, in the 1 or 2 per cent concentrations normally used, have no appreciable effect on the fatigue life of flexible plastic sheetings.
