-FRB..4... NCAR Facilities Report Strength Characteristics of DuPont "Surlyn A" Film/ National Center. for Atmospheric Research Boulder, Colorado i=,, : ' _ APRIL 1965... ^ 5 '"NCAR Library :I ' 1 I III IUWlII III 11111 IIII11 1 I IIIIII 111111111 5 0583 01037285 6
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STRENGTH CHARACTERISTICS OF DUPONT "SURLYN A" FILM NCAR Facilities Report FRB-4 A test program conducted for the National Center for Atmospheric Research, by the Hauser Research and Engineering Company, 2965 Peak Avenue, Boulder, Colorado (Hauser Report No. 5034-65-05) April 1965
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ii PREFACE This report is one of a series prepared for the Materials Research Project of the NCAR Scientific Balloon Facility. The Materials Research Project is one of several related efforts undertaken by the National Center for Atmospheric Research (NCAR) to increase the reliability, and to extend the capabilities, of scientific ballooning. NCAR was founded in 1960, to conduct basic research in the atmospheric sciences, and to foster such research on the part of the universities and research groups in the U.S.' and abroad. NCAR is operated by the University Corporation for Atmospheric Research (UCAR), and sponsored by the National Science Foundation. The present report covers certain investigations performed by Hauser Research and Engineering Company, Boulder, Colorado, under subcontract with UCAR. Other reports published in this balloon materials research series include: FRB-1-64, Tests of Balloon Materials; FRB-2-64, Standard Test Methods for Balloon Materials; and FRB-3-64, Non-Standard Tests for Balloon Materials.
iii SUMMARY A new plastic film of the ionomer class, developed by DuPont, and tradenamed Surlyn A, appeared to have possibilities as a balloon material. Samples of the film were subjected to standard tests for mechanical strength. The test data indicate that Surlyn A is comparable in many of its material properties to a good polyethylene. However, the samples tested carried high static charges which would make the material unsuitable for use in balloons. If current development programs succeed in eliminating the static charge, Surlyn A may become a good prospect for balloon use.
iv CONTENTS PREFACE.... ii SUMMARY... LIST OF TABLES... iii v Section I. INTRODUCTION...... 1 II. MANUFACTURER'S SPECIFICATIONS... 2 III. DESCRIPTION OF SAMPLES... 4 IV. TESTS AND RESULTS -- MECHANICAL PROPERTIES OF SURLYN A. 6 V. CONCLUSIONS.... 8 FIGURE AND TABLES.... 9 REFERENCES... 15
v LIST OF TABLES 1. Summary of Tests.... 10 2. Test Data, 1-Mil Surlyn A.... 11 3. Test Data, 2-Mil Surlyn A... 12 4. Comparisons of Films Tested at 25C..... 13 5. Comparisons of Films Tested at -80 C.... 14
1 I. INTRODUCTION In September 1964 E. I. DuPont de Nemours & Company announced the development of a new class of plastic films called "ionomers. " Only one form of ionomer film, tradenamed "Surlyn A," is commercially available at present. The trade literature on Surlyn A indicated it might have value as a balloon material. Under subcontract to the National Center for Atmospheric Research, an investigation was begun in December 1964 to determine the strength characteristics of this film. One- and two-mil thicknesses of the film were subjected to the standard tests used in earlier film test programs for NCAR. These consisted of 160 tests to determine Surlyn A properties of ultimate tensile strength, tensile yield strength, elongation at yield, ultimate elongation, tensile modulus of elasticity, tear initiation strength, and tear propagation strength.
2 II. MANUFACTURER'S SPECIFICATIONS DuPont classifies their ionomers as thermoplastics -- materials which soften when heated, harden when cooled, and can be reshaped many times by alternate heating and cooling. DuPont asserts(l) that Surlyn is stronger and tougher than unmodified polyethylene, and that it has the stiffness of a medium-density polyethylene with the high elongation and low-temperature flexibility of many polyolefins. Because its structure consists of oxidized polymer chains and inorganic cation groups, the attractive forces between oxidized chains and cations give a partial cross-linking effect, as in thermoset plastics. However, in thermosets such cross-linking is irreversible. The ionic linking of the ionomers, on the other hand, is thermally reversible. Thus, the ionomers can be worked like thermoplastics, but offer some attributes of thermoset plastics. The manufacturer claims that the incorporation of inorganic metallic ions, such as sodium and potassium, increases the material's modulus of elasticity and yield point, as well as its chemical resistance to oil and solvents. DuPont ascribes the following properties (at room temperature) to Surlyn A: ( Specific gravity 0.93 -- 0.94 Tensile strength 3500 -- 5500 psi Yield strength 2000 -- 2500 psi Elongation 300 -- 400% Modulus 28,000 -- 40,000 psi Tear strength Elmendorf 20 -- 80 g/mil
3 The resin in bulk quantities costs 50 /lb. Film of 1- or 2-mil thickness costs $0.85 to 1.00/lb. DuPont is continuing development on the ionomer family. They expect that other polymers, such as polypropylene, with various cation groups (sodium, potassium, magnesium, and zinc) will give ionomers with a wide range of properties. When additional ionomer films are developed, they will be considered as possible balloon materials.
4 III. DESCRIPTION OF SAMPLES The 1-mil sample of Surlyn A was shipped on two rolls designated as: Surlyn 'A' ER 1601 1 mil The rolls, each 24 in. wide and 50 ft long, were received in excellent condition in December 1964. (We do not presently know if this film is available in lay-flat tubing or other production widths.) The 2-mil sample was shipped later and bore a similar notation. It was also received in good condition. This roll was 24 in. wide; its length was not measured. Each of the three rolls of film had slight ripples parallel to the machine direction. These ripples may have collected as a result of uneven rolling following fabrication. The rippling seemed to have no effect, except in the transverse-direction tensile modulus tests. This effect, consisting of a small inflection, was virtually negligible. (An example of the effect can be discerned in Fig. 1, near the origin of the curve for the -80 C test of the Surlyn film.) Close inspection of the film revealed that it contained many gel granules. During examination of a few tensile specimens by polarized light, these particles were observed to serve as centers of stress concentration. In handling the film to prepare test specimens, a high static charge was noted on its surface, similar to that which can be observed on Saran
5 Wrap. We did not make a quantitative measure of this force. It was present to such a degree, however, that it may cause balloon manufacturing problems. It may also present considerable restraint in unfolding any large balloon made of Surlyn. We cannot at present ascertain whether buildup of high static charges might also cause perforations in this material. Surlyn is very resistant to corona degradation but perforation cannot be ruled out. DuPont engineers are working on the static problem and may develop more satisfactory materials in the near future. The film was weighed, and can be compared in this respect with films tested previously: Material Nominal Thickness Weight (lb/1000 (mil) sq ft) Surlyn A 1 5.2 Surlyn A 2 10.3 Consolidated GF19X 1 4.8 Consolidated GF19X 2 9.9 Visqueen 1.5 7.4 Film thickness was measured around 2 ft-square samples from 1- and 2-mil rolls, and was found to be quite uniform. The dial gage used was accurate to 0.0001 in., interpolating to.00001 in. Ten readings were taken on each sample. The 1-mil sample had as average thickness of 1.005 mil with a variation -+J 8%. The 2-mil sample had an average thickness of 2.068 mil, with extremes of 2.19 and 2.01 mil. Personal communication from J.P. Broussard, Industry Representative, Polyolefins Division, DuPont, 18 December 1964.
6 IV. TESTS AND RESULTS -- MECHANICAL PROPERTIES OF SURLYN A The tests were standard procedures, described in Refs. 3 and 4. They are summarized in Table 1. The tests were conducted under two temperature environments: 25-1 0 C (73.4-1.8 0 F) and -79-2 C (-110.2 + 3.6 0 F). The coldenvironment chamber used for the latter tests is described on p. 5 of Ref. 3. Humidity in the testing area varied from 20% to 50%. Samples were preconditioned in the 50% humidity chamber. DuPont's technical description of Surlyn indicates that moisture absorption should not be a problem with this type of film. The results of the tests are presented on Tables 2 and 3 (pp. 10 and 11). Tables 4 and 5 summarize these data and compare them with test results on other films. The methods used for deriving these test results and deviation coefficients are described on p. 24 of Ref. 5. For all tests, our data show lower strengths than those reported by DuPont. This is because our tests are run at slower rates (0.125 in./in./min) than are most commercial tests. In ultimate strength, Surlyn A film is slightly lower than Visqueen at 25 C, and comparable at -80 C. The rather large value (.220) of the deviation coefficient for I-mil Surlyn A at 25 C in the transverse direction is due to an average of two high and three low values for this series. We could assign no cause for this variation.
7 The test values at 25 C for tensile yield strength and tensile modulus are superior to those of any other film listed in Table 3. At -80 C these properties are comparable to, or slightly lower than, those of other films. Surlyn A thus appears to have better creep resistance than standard polyethylene balloon films. In Fig. 1, typical tensile modulus test curves are plotted for 1-mil Surlyn A, and for two other films, using data from Tables 4 and 5 and from Ref. 3. In tear initiation and propagation strengths, Surlyn is comparable 0 to, or (at -80 C) slightly inferior to, Visqueen.
8 V. CONCLUSIONS On the basis of the samples tested, Surlyn A is comparable in many of its material properties to a good polyethylene. At room temperature it is superior to most of the other films tested in tensile yield strength and modulus. At low temperature it appears slightly inferior in modulus and tear properties. The film should be evaluated for sealing qualities and brittleness at low temperature. No tests were made of these properties during the program reported here. Surlyn film may become a good prospect for balloon use if it can be treated to eliminate its static charge. We believe our data to be representative of the samples received. These same data may not be representative of commercial production.
10, 8 10-800C II/,8 0 0 C _ Surlyn A, I mil c, ^^ /. Visqueen, 1.5 mil _ /._. _ Consolidated GF 19X, 1.5mil - /,,~... Visqueen (adjusted to I mil) --» i /,, 4 (n I, (/) 25 C 04 1 S -- - - -' - - -1 ^ 0 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0. 16 0 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 Strain Fig. I--Typical Modulus Curves (machine direction)
Table 1 SUMMARY OF TESTS (5 samples each in machine and transverse directions, on Dillon Model M Tester) Test Method Sample Size Crosshead Rate or Type Strain Rate (in./min) Tensile ASTM D882 61T 1" x 6" 0.5a Strength method B (4" gage length) Ultimate Ultimatie l(determined from tensile strength test) Elongation b I Tensile ASTM D882 61T 1" x 12 ' (10" 1 o Modulus gage length) Yield ieldgh l(determined from tensile modulus test graphs) Strength Tear ASTM D1004 61 die-cut specimens 2 Initiation Graves tear test Tear ASTM D1004 die-cut specimens 2 Propagation Hauser-modified -- 1/16" slit 0. 1 2 5 in./in./min strain rate Autographic stress-strain curves made of load vs elongation. Pendulum-head travel corrected.
Table Z TEST DATA, 1-MIL SURLYN A Direction Ultimate Ultimate Tensile Tensile Elongation Tear Tear Tensile Elongation Modulus Yield at Yield Initiation Propagation Strength (%) (psi) Strength (%) Strength Strength (psi) (psi) (lb/in.) (lb/in.) -25 C Machine 2700 196 39,600 1640 8 460 320 3200 262 40,000 1670 8 490 380 3180 285 41,000 1500 8 470 350 2800 213 36,800 1480 8 450 370 2800 247 36,800 1610 8 410 350 average 2936 241 38,800 1580 8 456 354 Transverse 2400.292 30,900 1480 8 360 290 1600 177 32,000 1480 8 560 200 1500 168 31,400 1480 8 540 190 1700 198 33,700 1500 8 550 200 2300 320 33,400 1550 8 340 190 average 1900 231 32,300 1500 8 470 214-80 C Machine 8900 13 440,000 5310 3 850 450 7700 14 333,000 4400 3 640 470 9650 24 340,000 4300 3 740 430 9950 27 249,000 4960 3 750 480 9000 21 308,000 4960 3 800 410 average 9040 20 334,000 4760 3 756 448 Transverse 7200 18 203,000 4460 3 870 520 8800 25 229,000 4460 3 800 360 8600 15 234,000 4400 3 630 370 8050 18 229,000 4370 3 700 340 8600 17 187,000 4320 3 680 430 average 8340 19 216,400 4400 3 736 404
Table 3 TEST DATA, 2-MIL SURLYN A Direction Ultimate Ultimate ' Tensile Tensile Elongation Tear Tear Tensile Elongation Modulus Yield at Yield Initiation Propagation Strength (%) (psi) Strength (%) Strength Strength (psi) (psi) (lb/in.) (lb/in.) -+25 C Machine 3170 180 40,200 1850 8 502 365 3250 205 40,700 1750 8 501 355 3450 182 41,400 1700 8 495 345 3750 217 40,600 1750 8 502 370 3280 259 41,800 1850 8 506 400 average 3380 209 40,900 1780 8 501 367 Transverse 2750 352 36,800 1600 8 501 320 2100 237 39,600 1700 8 600 280 2900 345 41,600 1650 8 502 295 3150 370 43,000 1650 8 400 370 2750 324 42,300 10 08 603 295 average 2730 326 40,700 1640 8 521 312-800C Machine 12,400 67.5 238,000 5000 3 805 395 10,200 28.8 236,000 4450 3 870 385 10,850 38.8 208,000 4300 3 800 350 10,050 43.3 209,000 4500 3 980 505 12,000 70.0 227,000 4600 3 840 410 average 11,100 49.8 224,000 4570 3 859 409 Transverse 9050 47.0 197,000 4400 3 1105 510 8900 33.5 200,000 4600 3 995 380 9000 31.3 254,000 5050 3 1105 400 9000 27.5 200,000 4600 3 845 500 9450 33.0 222,000 4600 3 1000 400 average 9080 34.5 215,000 4650 3 1010 438
Table 4 COMPARISONS OF FILMS TESTED AT 250C (elongation at yield, 8% for all samples; no deviation) Film Weight Direc- Ultimate Tensile Ultimate Tensile Tear Tear (lb/1000 tion Tensile Yield Elongation Modulus Initiation Propagation sq ft) Strength Strength average d.c? average d.c. average d.c. average d.c. average d.c. average d.c. (psi) (psi) () (psi) (lb/in.) (lb/in.) Surlyn M 2936.080 1580.054 241.149 38,800.034 456.063 354.062 A 5.2 1-mil T 1900.220 1500.020 231.302 32,300.039 470.074 214.201 Surlyn M 3380.068 1780.038 209.155 40,900.159 501.007 367.060 A 10.3 2 -mil T 2730.142 1640.026 326.160 40,700.061 521.162 312.114 Winzen Strato- M 2054.087 720.078 193.249 13,200.166 374.056 245.114 film 320 3,3 0.75-mil T 1734.109 848.090 285.233 16,300.117 360.086 240.05 Winzen Strato- M 1720.159 690.141 192.302 13,600.205 390.046 290.064 film 320 6.3 1.5-mil T 1890.078 820.079 290.146 16,900.150 400.083 290.042 Winzen Strato- M 1540.133 940.068 260.323 20,300.152 380.100 280.082 film 320 7.9 2-mil T 2600.084 970.103 380.121 23,200.067 448.087 330.127 Consolidated M 2140.016 1020.094 200.300 15,200.040 590.048 510.049 GF19X 4.8 I-mil T 1330.100 1000.059 236.320 17,200.070 510.087 360.110 Consolidated M 2080.150 1000.052 387.160 17,300.087 543.069 450.01 GF19X 9.9 2-mil T 2020.073 996.005 438.058 17,800.087 493.032 400.051 Visqueen M 3970.170 850.040 456.170 14,400.035 581.036 416.018 A 7.4 1.5-mil T 3510.180 800.027 442.110 13,500.130 440.037 388.036 deviation coefficient Source: Data from Hauser Research & Engineering testing programs
Table 5 COMPARISONS OF FILMS TESTED AT -80 C (elongation at yield, 3% for all samples; no deviation) Film Weight Direc- Ultimate Tensile Ultimate Tensile Tear Tear (lb/1000 tion Tensile Yield Elongation Modulus Initiation Propagation sq ft) Strength Stren th average d.c.* average d.c. average d.c. average d.c. average d.c. average d.c. (psi) (psi) (%) (psi) (lb/in.) (lb/in.) Surlyn M 9040.096 4790.028 20.308 334,000.200 756.102 448.064 A 5.2 1-mil T 8340.092 4400.013 19.196 216,000.094 736.161 404.165 Surlyn M 11,100.096 4570.057 49.8.366 224,000.064 859.085 409.143 A 10.3 2-mil T 9080.024 4650.051 34.5.214 215,000.112 1010.106 438.137 Winzen Strato- M 6984.041 4250.041 78.105 245,000.115 1134.016 962.155 film 320 3.3 0.75-mil T 7254.033 4900.028 22.264 304,000.049 1012.131 676.197 Winzen Strato- M 7440.161 5990.156 30.433 308,000.138 1050.068 630.185 film 320 6.3 1.5-mil T 7090.051 5802.078 23.413 279,000.105 1070.054 658.186 Winzen Strato- M 7070.161 5830.178 23.478 210,000.109 1160.149 700.050 film 320 7.9 2-mil T 9040.079 6610.046 48.854 224,000.061 1090.139 734.189 Consolidated M 10,300.200 5420.155 206.120 339,000.130 1400.064 1080.100 GF19X 4.8 1-mil T 7500.024 5470.127 22.2.530 468,000.095 970.035 750.130 Consolidated M 8560.072 5420.025 187.420 276,000.038 1210.100 950.088 GF19X 9.9 2-mil T 8160.066 5700.108 104.370 299,000.200 1120.120 760.029 Visqueen M 8490.026 5690.125 45.5.500 373,000.110 1190.140 740.170 A 7.4 1.5-mil T 7540.084 6500.081 7.3.420 403,000.076 1040.091 710.098 deviation coefficient Source: Data from Hauser Research & Engineering testing programs
15 REFERENCES 1. "New Tough Transparent Plastics," Materials in Design Engineering 60, No. 3, 106-107, September 1964. 2. Surlyn A Ionomer Resin, Brochure A-38352, Plastics Dept., Polyolefins Div. E. I. DuPont de Nemours & Co., Wilmington, Del., undated. 3. Tests of Balloon Materials, NCAR Facilities Report FRB-1-64, National Center for Atmospheric Research, Boulder, Colo., November 1964. 4. Standard Test Methods for Balloon Materials, NCAR Facilities Report FRB-2-64, National Center for Atmospheric Research, Boulder, Colo., November 1964. 5. Non-standard Tests for Balloon Materials, NCAR Facilities Report FRB-3-64, National Center for Atmospheric Research, Boulder, Colo., November 1964.
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