ASTM D832-07(R2018) pdf free download

ASTM D832-07(R2018) pdf free download.Standard Practice for Rubber Conditioning For Low Temperature Testing
1. Scope
1.1 This practice covers the characteristic 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 satisfactory technique for low temperature testing is the specification ofthe time and temperature of exposure of the test specimen. It has been demonstrated that any one or more of the following distinct changes, which are detailed in Table 1, may take place on lowering the test temperature: 1.2.1 Simple temperature effects, 1.2.2 Glass transitions, and 1.2.3 First order transitions (crystallization), and solubility and other effects associated with plasticizers. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory 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 the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
6. Glass Transition
6.1 Glass transition is a reversible physical change in a material from a viscous or rubbery state to a brittle glassy state (refer to Terminology D1566: transition, glass; transition second order). It does not involve a change in phase and is not a thermodynamic change. It generally occurs over a small temperature range. It is designated as T g . The T g of polymers, obtained from measurements of change of modulus with change in temperature, depend upon both the rate of specimen deformation and the rate of temperature change. Primary properties, such as hardness and ultimate elongation, and temperature coefficients of properties such as volume and enthalpy, change rapidly near T g . Thus, thermal expansivity and specific heat appear discontinuous at T g . 6.2 Some rubbers such as copolymers or polymer blends may show more than a single T g because of separate contri- butions by their polymeric components. There may also be damping peaks not directly attributable to glass transitions. A glass transition occurs at a temperature below which the thermal energies of molecular segments are insufficient to free them from the force field of their immediate neighbors within the experimental time scale. 6.3 Values determined for T g are higher for test methods that require high frequency distortions of the specimen than for those that require low frequency distortions. The latter seem to have the greater resolving power for multiple peaks. For those methods in which the test temperature is changed at a con- trolled rate, T g depends upon the rate that is chosen. Therefore, T g is not a true material property since it depends upon the test method used to obtain it. The method used should always be stated.
7. First Order Transitions (Crystallization)
7.1 A first order transition is a reversible change in phase of a material; in the case of polymers, it is usually crystallization or melting of crystals (refer to Terminology D1566: transition, first order). When a specimen is equilibrated at a temperature at which crystallization is possible, changes in properties resulting from the crystallization may begin immediately or after an induction period of up to several weeks. The time to reach an equilibrium state of crystallization is likewise widely variable. Both times are dependent on the material being tested and the temperature. Crystallization increases the hardness and modulus. A specimen that has crystallized once may crystallize much more rapidly on subsequent tests, unless, in the meantime, it has been heated sufficiently to destroy the crystal nuclei. 7.2 Examples of materials that crystallize relatively rapidly in certain temperature ranges include Thiokol A 3 polysulfide rubber, chloroprenes (excepting the RT types), natural rubber, and some butadiene copolymers cured without sulfur or with low sulfur. Materials that may require much longer times for crystallization effects to become evident include butyl rubber, high sulfur cures ofnatural rubber, most silicone rubbers, some polyurethane rubbers, RT types of chloroprene, and rubbers containing fluorine.