ASTM D832-2007(2018) Standard Practice for Rubber Conditioning For Low Temperature Testing.pdf

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1、Designation: D832 07 (Reapproved 2018)Standard Practice forRubber Conditioning For Low Temperature Testing1This standard is issued under the fixed designation D832; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r

2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This practice covers the characteristi

3、c mechanical be-havior of rubbers at low temperatures, and outlines the condi-tioning procedure necessary for testing at these temperatures.1.2 One of the first stages in establishing a satisfactorytechnique for low temperature testing is the specification of thetime and temperature of exposure of t

4、he test specimen. It hasbeen demonstrated that any one or more of the followingdistinct changes, which are detailed in Table 1, may take placeon lowering the test temperature:1.2.1 Simple temperature effects,1.2.2 Glass transitions, and1.2.3 First order transitions (crystallization), and solubilitya

5、nd other effects associated with plasticizers.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applic

6、ability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by th

7、e World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D471 Test Method for Rubber PropertyEffect of LiquidsD1053 Test Methods for Rubber PropertyStiffening atLow Temperatures: Flexible Polymers and Coated FabricsD1329 Test Method for Evaluat

8、ing Rubber PropertyRetraction at Lower Temperatures (TR Test)D1566 Terminology Relating to RubberD2136 Test Method for Coated FabricsLow-TemperatureBend TestD5964 Practice for Rubber IRM 901, IRM 902, and IRM903 Replacement Oils for ASTM No. 1, ASTM No. 2,ASTM No. 3 Oils, and IRM 905 formerly ASTM N

9、o. 5Oil3. Significance and Use3.1 Low temperature testing of rubber can yield repeatableresults only if the preconditioning of the samples is consistent.Properties such as brittleness and modulus are greatly affectedby variations in time/temperature exposures. This practice isintended to provide uni

10、form conditioning for the various lowtemperature tests conducted on rubbers.4. General Conditioning4.1 At least 16 h should elapse between vulcanization andtesting of a sample.4.1.1 If the time between vulcanization and testing is lessthan 16 h, it shall be agreed upon between customer andsupplier a

11、nd noted in the report section of the test methodemployed.5. Simple Temperature Effects (Viscoelasticity)5.1 Most elastic properties of rubber change as the tempera-ture is changed.As the temperature is reduced toward the glasstransition temperature, Tg, the specimen becomes increasinglystiff, loses

12、 resilience, and increases in modulus and hardness.At some point, still above Tg, the resilience reaches a mini-mum. As the temperature is lowered beyond this point, theresilience then increases until a temperature just above Tgisreached.5.2 Viscoelastic changes are usually complete as soon as thesp

13、ecimen has reached thermal equilibrium. Longer exposuretime should be avoided to minimize crystallization orplasticizer-time effects that might influence the test results. Themagnitude of these changes depends on the composition of thematerial and the test temperature.1This practice is under the jur

14、isdiction ofASTM Committee D11 on Rubber andRubber-like Materials and is the direct responsibility of Subcommittee D11.10 onPhysical Testing.Current edition approved June 1, 2018. Published August 2018. Originallyapproved in 1945. Last previous edition approved in 2012 as D832 07 (2012).DOI: 10.1520

15、/D0832-07R18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Dr

16、ive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations i

17、ssued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.16. Glass Transition6.1 Glass transition is a reversible physical change in amaterial from a viscous or rubbery state to a brittle glassy state(refer to Terminology D1566: transition, glass; transitionsecond order). It

18、 does not involve a change in phase and is nota thermodynamic change. It generally occurs over a smalltemperature range. It is designated as Tg. The Tgof polymers,obtained from measurements of change of modulus withchange in temperature, depend upon both the rate of specimendeformation and the rate

19、of temperature change. Primaryproperties, such as hardness and ultimate elongation, andtemperature coefficients of properties such as volume andenthalpy, change rapidly near Tg. Thus, thermal expansivityand specific heat appear discontinuous at Tg.6.2 Some rubbers such as copolymers or polymer blend

20、smay show more than a single Tgbecause of separate contri-butions by their polymeric components. There may also bedamping peaks not directly attributable to glass transitions. Aglass transition occurs at a temperature below which thethermal energies of molecular segments are insufficient to freethem

21、 from the force field of their immediate neighbors withinthe experimental time scale.6.3 Values determined for Tgare higher for test methods thatrequire high frequency distortions of the specimen than forthose that require low frequency distortions. The latter seem tohave the greater resolving power

22、 for multiple peaks. For thosemethods in which the test temperature is changed at a con-trolled rate, Tgdepends upon the rate that is chosen. Therefore,Tgis not a true material property since it depends upon the testmethod used to obtain it. The method used should always bestated.7. First Order Tran

23、sitions (Crystallization)7.1 Afirst order transition is a reversible change in phase ofa material; in the case of polymers, it is usually crystallizationor melting of crystals (refer to Terminology D1566: transition,first order). When a specimen is equilibrated at a temperatureat which crystallizati

24、on is possible, changes in propertiesresulting from the crystallization may begin immediately orafter an induction period of up to several weeks. The time toreach an equilibrium state of crystallization is likewise widelyvariable. Both times are dependent on the material being testedand the temperat

25、ure. Crystallization increases the hardness andmodulus.Aspecimen that has crystallized once may crystallizemuch more rapidly on subsequent tests, unless, in themeantime, it has been heated sufficiently to destroy the crystalnuclei.7.2 Examples of materials that crystallize relatively rapidlyin certa

26、in temperature ranges include Thiokol A3polysulfiderubber, chloroprenes (excepting the RT types), natural rubber,and some butadiene copolymers cured without sulfur or withlow sulfur. Materials that may require much longer times forcrystallization effects to become evident include butyl rubber,high s

27、ulfur cures of natural rubber, most silicone rubbers, somepolyurethane rubbers, RT types of chloroprene, and rubberscontaining fluorine.7.3 The temperature at which crystallization proceeds mostrapidly is specific to the polymer involved. For natural rubber,3The sole source of supply of this materia

28、l known to the committee at this timeis Thiokol Chemical Corp, Newtown-Yardly Rd., Newtown, PA 18940. If you areaware of alternative suppliers, please provide this information to ASTM Interna-tional Headquarters. Your comments will receive careful consideration at a meetingof the responsible technic

29、al committee,1which you may attend.TABLE 1 Differentiation Between Crystallization and Glass TransitionProperty Crystallization Glass TransitionPhysical effects(1,2,4,6,7)ABecomes stiff (hard) but not necessarily brittle Becomes stiff and brittleTemperature-volume relation(1,2,3,4,5,8)Significant de

30、crease in volume No change in volume, butdefinite change in coefficient ofthermal expansionLatent heat effect (4,5,8) Heat evolved on crystallization Usually no heat effect, butdefinite change in specific heatRate (2,4,6,7,8) Minutes, hours, days, or even months may be required. In general, astemper

31、ature is lowered, rate increases to a maximum and thendecreases with increase in deformation. Rate also varies withcomposition, state of cure, and nuclei remaining from previouscrystallizations, or from compounding materials such as carbon black.Usually rapid; takes place withina definite narrow tem

32、peraturerange regardless of thermalhistory of specimen. May belimited rate effect (2)Temperature of occurrence(4,5,7,8Optimum temperature is specific to the polymer involved. Very wide limits, depending oncompositionEffect on molecular structure(1,2,5,6,8)Orientation of molecular segments; random if

33、 unstrained, approachingparrallelism under strainChange in type of motion ofsegments of moleculeMaterials exhibitingproperties (5,7,8)Unstretched polymers including natural rubber (low sulfur vulcanizates),chloroprene, Thiokol A polysulfide rubber, butadiene copolymers withhigh butadiene content, mo

34、st silicones, some polyurethanes. Butylrubbers crystallize when strained. Straining increases rate ofcrystallization of all of the above materials.AllAThe numbers in parentheses refer to the following references:(1) Juve, A. E., Whitby, G. S., Davis, C. C., and Dunbrook, R. F., Synthetic Rubber, Joh

35、n Wiley for chloroprenes, 10C; for butadienecopolymers, 45C; for dimethyl silicones, 55C; forpolyester-type polyurethanes, 10C; and for butyl rubber,35C. Both above and below these temperatures, crystalliza-tion is slower. Accordingly, any attempt to compare materials(particularly those subject to c

36、hange in properties resultingfrom crystallization or plasticizer time effects) on a basis ofexposure at a given temperature for a specified time is almostcertain to be misleading. Such specific temperature may benear the optimum rate of crystallization of one of the materialsand many degrees above o

37、r below the optimum of another.7.4 The only rubbers that may be expected to crystallizespontaneously are those that also develop crystallinity onstretching. Application of stress usually increases the crystal-lization rate, apparently by forming effective nuclei. Stressapplication may be used to acc

38、elerate tests of crystal growth,but may give misleading results regarding induction periods.7.5 Specimens to be tested for crystallization should bedecrystallized immediately before testing by heating them in anoven for 30 min at 70C. They should then be conditioned atstandard laboratory temperature

39、 for 45 min and no more than60 min before testing.8. Effects Associated with Plasticizers8.1 When the test material contains certain plasticizers, timeeffects not necessarily associated with crystallization may beobserved. These effects occur over a wide range of time,temperature, and composition. S

40、ome may be due to limited lowtemperature solubility of such plasticizers in the compound. Ifthe original plasticizer concentration is less than the amountcorresponding to saturation at the test temperature, no timeeffects will be observed.8.1.1 The effects consist of delayed stiffening that occursov

41、er a wide temperature range and, in some instances, anelevation of the brittle temperature that occurs over a narrowtemperature range. In the case of elevation of the brittletemperature, plasticized compositions may become brittle afteran extended exposure to temperatures slightly higher than theirn

42、ormal brittle temperatures.8.2 Low temperature serviceability of a plasticized rubberproduct may depend on whether or not the plasticizer remainsin the rubber.8.2.1 For example, the temperature at which a rubber oilseal retracts 10 % (TR10, Test Method D1329) may be 45Coriginally but only 35C after

43、exposure to IRM 903 (thereplacement for ASTM Oil No. 3; refer to Test Method D471and Practice D5964) for 70 h at 100C. Part of the liquidplasticizer has been extracted and replaced by the oil, which isa relatively poor plasticizer; hence the change in TR10.CONDITIONING PROCEDURES FORMECHANICAL TESTS

44、9. Tests for Simple Temperature Effects (ViscoelasticEffects) Only9.1 Make tests at 70, 55, 40, 25, 10, 0, and +23C,respectively. Hold the test specimen at each test temperatureuntil it reaches thermal equilibrium. Calculated times requiredfor thermal equilibrium are given in Table 2.9.2 In a flat s

45、heet specimen, the time required for thermalequilibrium may be taken as being directly proportional to thesheet thickness. Thus, for a 25-mm thick slab, the times givenin Table 2 for a 2.5 mm thick sheet should be multiplied by 10.9.2.1 If the air temperature is changed 100C, the tempera-ture differ

46、entials would be 10, 5, 2, and 1C, respectively, forthe respective time periods. For any temperature change, T, thetemperature differential in Table 2 should be multiplied byT/10.9.2.2 For example, if the test specimen described in TestMethods D1053, at a room temperature of 20C is placed in airat 7

47、0C, the temperature change would be 90C; and at theend of 510 s, the temperature differential between the center ofthe specimen and air would be 0.9C, making the temperatureof the center of the test specimen 69.1C.9.2.3 The above times can be reduced at least 50 % byproviding air circulation with ve

48、locities of 4.5 m/s past thespecimen, and by about 85 % by using a circulating liquid bath.9.2.4 The required measurements of modulus, hardness, orbrittleness should be made as soon as the specimen has reachedequilibrium temperature except for any conditioning timerequired by the method, while maint

49、aining the specimen at thesame temperature.10. Tests for Effects of First Order Transition(Crystallization) Only10.1 Test each material at the temperature at which itcrystallizes most rapidly, when this is known.10.1.1 For unstressed specimens, this temperature is near:10.1.1.1 25C for natural rubber,10.1.1.2 10C for chloroprenes,10.1.1.3 45C for butadiene copolymers,10.1.1.4 55C for silicones,10.1.1.5 56C for cis-1,4 butadiene, and10.1.1.6 10C for polyurethanes.10.2 When the temperature of maximum rate of crystalliza-tion is unknown, make