Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 672-674
672
Effect of Low Temperatures on PVC-Coated Nylon Scrimst Rita M. Crow' and Malcolm M. Dewar Defence Research Establishment Ottawa, Department of National Defence, Ottawa, Ontario, Canada K7A 024
I n a previous study on the effect of low temperatures on a range of uncoated and coated fabrics, the authors found that the PVC-coated nylon scrims tested were the most sensitive to low temperatures, and for all practical purposes, inappropriate for use at temperatures below 0 "C. Further work has been carried out on three newly manufactured PVC-coated nylon scrims to determine if such materials are also low-temperature sensitive. This paper reports the results of this work and compares them with that found for the PVC-coated nylon scrims in the earlier study. I t was found that the "new" fabrics reacted similarly to those previously tested; however, some of them did have coatings which did not shatter at -40 O C as some of the previous series had done. Therefore, these would probably be suitable for use at low winter temperatures.
Introduction
The authors had carried out a study to determine the effect of low temperatures on the pertinent physical properties of a variety of coated and uncoated fabrics (Crow and Dewar, 1982). This was undertaken because some fabrics, especially coated ones, are known to become hard and brittle at low winter temperatures. Thus, their usefulness at low temperatures would be determined by their ability to retain their room-temperature physical properties at these temperatures. In this study, the fabrics were broken on a tensile tester at 20,0, -20, and -40 "C. The effect of low temperatures on the fabrics was characterized by changes in the basic shape of their loadelongation curves and in other mechanical properties such as initial modulus, breaking strength, percent elongationat-break, and work-to-rupture. It was found that all fabrics tested were affected at low temperatures, becoming stiffer as shown by an increase in initial modulus, an increase in breaking load, and a general decrease in percent elongation at break. Taking the change in the basic shape of the load-elongation curve into consideration, as well as the statistically significant differences in initial modulus, breaking load, and percent elongation and the magnitude of the changes, we found the cotton/synthetic blends to be the least sensitive to low temperatures; the nylon fabrics, whether they were coated with polyurethane or neoprene or uncoated, more sensitive; and the PVC-coated nylon scrims tested, the most sensitive and for all practical purposes inappropriate for use at temperatures below 0 "C. The changes in breaking load and percent elongation confirmed work by others, namely that the breaking load increased with a decrease in temperature, be it fibers (Instron Corp., 1965), yarns (Coplan and Singer, 19531, or fabrics (Bozov and Nikitin, 1975; Nikitin et al., 1975),and that there is a general but not consistent decrease in percent elongation with a decrease in temperature for a given group of fabrics or for the warp and weft of the same fabric (Bozov and Nikitin, 1975; Nikitin et al., 1975). However, for our set of fabrics, there was not the marked change in breaking load and percent elongation at -20 "C except for a polyurethane-coated nylon, as found by Nikitin et al. (1975). However, our study did confirm their finding that the inclusion of cotton in a fabric renders this fabric blend less sensitive to low temperatures. Subsequent to our study, further work was carried out on three newly manufactured PVC-coated nylon scrims to Issued as DREO Report No. 880.
Table I. Pertinent Physical Properties of PVC-Coated 1 X 1 Nylon Scrimsa
fabric A B C
D E F G
total mass,b g/mz
mass of PVC on scrim, %of total
warp
weft
thickness,d cm
61 8 757 599 330 571 661 586
70 70 70 85 80 85 70
9 9 8 9 6 6 9
8 9 9 9 5 6 8
0.23 0.25 0.22 0.30 0.64 0.74 0.53
count yarn/cm
a National Standard of Canada-Textile Test Methods (1977). CAN2-4.2-M77 Method 5A. CAN 2-4.2-M77 Method 6 . Measured at 0.16 kPa, CAN 2-4.2-M77 Method 37.
determine if such materials are also low-temperature sensitive. This paper reports the results of this work and compares them with those found for the PVC-coated nylon scrims in the earlier study. M e thod Materials Used. The pertinent properties of the three
PVC-coated nylon scrims A, B, and C from the present study and D, E, F, and G from the previous study are given in Table I. Experimental Method. In our first study, the scrims were broken at 20, 0, -20, and -40 "C. For the second study, the scrims were broken only at 20 and -40 "C, since it was the sensitivity of the materials to low temperatures rather than the progressive reaction to low temperatures which was now of interest. Only the results obtained at 20 and -40 "C are give here for D, E, F, and G . The tests are carried out in accordance with CAN 24.2-M77, Method 9.1, Breaking Strength of Fabrics-Strip Method (Constant-Time-To-BreakPrinciple) (1977). The temperature and relative humidity in the room in which the tests were done were nominally 20 "C and 65%, respectively. The tests were carried out in M environmental chamber fitted onto an Instron, Model 1102. The chamber was cooled to -40 "C by solid carbon dioxide placed in the bottom of the chamber. For the 20 "C tests, the specimens were broken immediately. For the -40 "C tests, the specimens were cold-soaked for 15 min 'before being broken. It took approximately 5 min of the 15-min period for the chamber to return to this temperature after opening and closing the door to insert the specimen in the Instron
0196-4321/83/1222-0672$01.50/00 1983 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983 673 Table 11. Summary of Results of Load-Elongation Curve Parameters warp
weft % change from 20 to -40 "C
% change from 20 to -40 "C
breaking fabric load
%
elong
init modulus
yield point
A
+37
0
t331
B C D
+8 +17 +21
-16 -25 -48
t 63 t146 +SO0
J
E
+18
-27
+204
J
F
t31
-17
+I02
J
G
-1
-18
+175
J
None a t 20 'C, one a t -40 "C.
secondary yield pt.
breaking load
elong
init inodulus
yield point
secondary yield pt.
jagged trace a t -40 "C
+75
-4
+2124
a
-
+1 +27 +9
-15 -15 -37
J J
-
+14
-14
+ 64
-8
+17
-18
+ 485 + 174 + 671 + 691 + 270 + 448
-
b jagged trace a t -40 "C jagged trace a t -40 "C b jagged trace a t -40 "C
One a t 20 'C, none a t -40 "C Breaking Point
Secondary Yield
3000
25W
I I
Initial
1Modulus I
///
b jagged trace at -40 "C jagged trace at -40 "C jagged trace at + 20 "C
J
J
-
a
G Welt
- - - 200 c
/
-
-40' C
/:
/ /
I I
t
/
/
1500
I I I I
/
,/
I I
I
'Ybeld
I
I
I I
1.
I
2000
I I I
LOAC
%
I I
I
I I I
I!---'
I
O
ELONGATION
Figure 1. Idealized load-elongation curve for a woven textile fabric.
jaws. In order to reduce slippage, the jaws were lined with emery paper. Definition of Parameters. Figure 1 is an idealized load-elongation curve for a woven textile fabric. The "secondary yield point" has been added to the parameters which conventionally describe this curve because, for many fabrics, its presence or absence was temperature-dependent. Rennell (1978) calls the secondary yield point "a 'hardening' point". However, we think that the term "secondary yield point" describes this point more accurately, as hardening occurs before this point is reached and yielding after. In this study, the term "yield point" is used for yielding which occurs at low loads and low elongations while the term "secondary yield point" is used at high loads and high elongations. Results and Discussion The changes from 20 to -40 "C (expressed as a percent of the 20 "C value) in breaking load, percent elongation at break, and initial modulus are give in Table 11. The or absence (-) of a yield point and a secpresence (4 ondary yield point and breaks in the coating as shown by jagged traces on the load-elongation curves are noted. Except for G warp and B weft, all PVC-coated nylon scrims had statistically significant increases in breaking load when the temperature was decreased from 20 to -40 "C. Except for A warp, all percent elongations at break decreased significantly from 20 to -40 "C. All fabrics had substantial increses in initial moduli (+63 to +2124%) with decreasing temperature. The respective orders of magnitude of all three parameters were similar for the three "new" fabrics and the four previously tested.
15 I
25 I
20 I
10 90 ELONGATION
Figure 2. Load-elongation curves typical of A and G weft.
t 35mt
4000
n ' I
G Warp
3000
- --
-
-.
/'
20'C 40'C
'
I
/
I
z-
2500
I
-
I
I I
n
I I I
s 2000 -
I 1500
-
I I I
1000
-
I I /
I I
/'
/ /
I
I
,
I
I
I
674
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983
1
I I
,
I’
/ /
/
I
/ I
I 10
0
I
15 00
I
I 25
I 20
1 30
ELONGATION
Figure 4. Load-elongation curves typical of D and E warp and weft.
B Warp
_.
20”
c
40’
C
I
1 000-
I
I
/ 0
I 1 5
I 10
I 1
15
I
though the load-elongation curves of the uncoated nylon scrims were not determined, the previous study (Crow and Dewar, 1982) showed the uncoated nylon fabrics to be less sensitive to low temperatures than the PVC-coated nylon scrims and in general, to have load-elongation curves with no yield points but with secondary yield points. The shape of the curves in this study would indicate that it is the relatively inflexible PVC coating rather than the nylon scrims which determines the main shape of the loadelongation curve, especially at low temperatures, with the coating yielding slightly at low loads to accommodate elongation of the scrim and then both the coating and the scrim yielding at high loads to give the secondary yield point. A t 20 “C, A and G weft had concave load-elongation curves, indicating a “flowing” elastic-like PVC coating. However, at -40 “C, both materials had stiffened sufficiently to acquire a yield point, that of G being more pronounced than that of A. In fact, the curve of G weft at -40 “C is not typical of textile materials, but is rather similar to ones reported for plastics by Billmeyer (1971), who described such a curve as being characteristic of a “hard and tough” polymeric material. In the warp direction for A and G, breaks occurred in the coating, as shown by the jagged trace just before the specimen broke. These breaks were not as spectacular as those of D and E, where the PVC coatings became brittle, shattered, and flew off in many directions, coating the inside of the environmental chamber. The irregular breaks in the load-elongation curves of D and E show the sudden failures in the coating (Figure 3). From the curves of B, C, and F it may be concluded that although stiffening is occurring, their coatings stay intact and do not shatter at -40 “C. Thus for all practical purposes, these three PVC-coated scrims would probably be useful at low temperatures. It was noted that F had irregular breaks at 20 “C which were also present a t lower temperatures but to a lesser extent. A t 20 “C we could view the specimens as they broke and observe that the scrim and coating were breaking independently.
I
20
Conclusions The three %ew” fabrics reacted similarly to those previously tested and confirm that PVC-coated nylon scrims are sensitive to low temperatures. However, some of the materials had coatings which stayed intact and would therefore probably be suitable for use at low temperatures. Finally, observations of the change in shape of the loadelongation curve, as used in this study, are a quick and easy way of qualitatively determining the sensitivity of a fabric to low temperatures. Registry No. PVC,
9002-86-2.
Literature Cited Biilmeyer, F. W. “Textbook of Polymer Science”, 2nd ed.; Interscience Publishers: New York, 1971. Buzov, 8 . A.; Nikitin, A. V. Tekst. Prom. (Moscow) 1975, 35(11), 67-68. Coplan, M. A,; Singer, E. W.A.D.C. Technical Report 53-21 Part 2, 1953, United States Air Force. Crow. R. M.: Dewar. M. M. Defence Research Establishment Ottawa R e ~ o r t NO. 858. 1982. Nlkitln, 1E-2 A. 1 V.: Buzov, B. A.: Somova, T. I. Shveinaya Prom. 1975, 76(6), ._ Instron Application Series T-1. Instron Corporation, Canton, MA, 1965. Rennell. R. W. Textiles 1978, 7(1), 12-16. Textile Test Methods. National Standard of Canada. CAN2-4.2-M77. Published by Canadian Government Speciflcations Board, Ottawa, K I A 055. 1977.
Received for review March Accepted May
28, 1983 27, 1983
