1.1 本实施规程旨在定义在长时间单独暴露于热空气中时评估塑料耐热性的暴露条件。仅规定了热暴露程序。高温对任何特定性能的影响是通过选择适当的测试方法和该性能的试样来确定的。 1.2 本规程可作为比较材料热老化特性的指南，通过某些相关特性的变化来测量。感兴趣的特性是在室温下测量的。 1.3 本规程推荐了在单一温度下比较材料热老化特性的程序。还描述了使用一系列高温来确定材料热老化特性的推荐程序，以估计在较低温度下达到规定性能变化的耐受时间； 在这种情况下，假设阿伦尼乌斯关系适用于对其他温度进行预测。 1.4 在应力、环境、温度和时间控制失效之间发生相互作用的情况下，本规程不会预测热老化特性。 1.5 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 注1: 本标准和ISO-2578涉及相同的主题，但技术内容不同。 1.6 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 4.1 使用本规程的前提是，选择用于评估材料的失效标准（即，作为暴露时间函数测量的一个或多个性能）和暴露持续时间可以表明与材料的预期用途有关。 4.2 暴露在高温下的塑料材料会发生多种物理和化学变化。暴露在时间和温度上的严重程度决定了所发生变化的程度和类型。塑料材料不一定会因暴露在高温下而降解。然而，塑料长时间暴露在高温下通常会导致一些降解，物理性能会逐渐变化。这些特性的特定特性和失效（或寿命）标准通常用于评估耐热性。 4.3 通常，在高温下短时间暴露会排出挥发物，如水分、溶剂或增塑剂，缓解成型应力，促进热固性塑料的固化，并可能导致塑料或着色剂的颜色发生一些变化，或两者兼而有之。 通常，随着挥发物的损失或聚合过程的推进，预计会出现额外收缩。 4.4 一些塑料材料在高温下暴露后由于增塑剂的损失而变脆。由于挥发性增塑剂的吸附或聚合物的分解，其他类型的塑料变得柔软而粘稠。 4.5 观察到的变化程度将取决于测量的特性。不同的机械或电气性能可能不会以相同的速率变化。例如，热固性化合物的耐电弧性提高到材料的碳化点。机械性能，例如弯曲性能，对热降解很敏感，并且可能以更快的速度变化。在大多数情况下，极限性能（如强度或伸长率）比体积性能（如模量）更容易退化。 4.6 所研究的材料可以随着温度的变化而改变固有行为，例如当跨越α、β和γ跃迁时。 无论是在使用的老化温度范围内，还是在生命线的外推中，都应避免这些转变。只有在材料特性没有根本变化的情况下，阿伦尼乌斯原理才能用于加速化学机制。对于半结晶和高结晶聚合物，温度升高可能会导致材料形态发生重大变化，从而使该假设无效或受损。 注2: 使用阿伦尼乌斯关系时应谨慎，了解材料在高温下的物理变化很重要。ISO 9080中给出的通过外推表征管形塑料材料寿命的指南表明，对于玻璃态非晶态聚合物，最高烘箱老化温度应至少低于维卡软化温度15°C，并且至少低于半晶态聚合物的熔点15°C。 4.7 暴露的影响可能相当多变，尤其是当样本长时间暴露时。 影响数据再现性的因素包括外壳的温度控制程度、烘箱的湿度、样本上方的空气速度和暴露时间。曝光误差随时间累积。某些材料易受湿度的影响。 4.8 不能推断比较材料排序是不可取的或不可行的。相反，本实践旨在提供可用于此类比较目的的数据。然而，由于从该实践中获得的数据没有考虑大多数实际应用中所涉及的应力或环境的影响，因此设计者必须谨慎使用，他们必须不可避免地使用与特定应用要求一致的额外数据（如蠕变和蠕变破裂）进行材料选择。 4.9 可能存在许多切割和TI值。因此，为了使切割或TI（温度指数）的任何应用有效，热老化程序必须复制最终产品的预期热暴露条件，或者必须应用阿伦尼乌斯关系。 4.10 当使用基于一系列温度下实验数据的Arrhenius图或方程来估计在某个较低温度下产生规定性质变化的时间时，可能会出现很大的误差。这种在较低温度下产生性能变化或“故障”的时间估计通常称为“使用寿命”然而，应避免使用该术语，因为这意味着测试人员在最终使用中有关于特定故障标准的信息，而许多因素不在本测试的范围内。最好使用诸如“终点”、“耐热时间”等术语。由于与这些计算相关的误差，该持续时间应被视为“最大预期”而不是“典型”

1.1 This practice is intended to define the exposure conditions for evaluating the thermal endurance of plastics when exposed solely to hot air for extended periods of time. Only the procedure for heat exposure is specified. The effect of elevated temperature on any particular property is determined by selection of the appropriate test method and test specimens for that property. 1.2 This practice can be used as a guide to compare thermal aging characteristics of materials as measured by the change in some property of interest. The property of interest is measured at room temperature. 1.3 This practice recommends procedures for comparing the thermal aging characteristics of materials at a single temperature. Recommended procedures for determining the thermal aging characteristics of a material using a series of elevated temperatures for the purpose of estimating endurance time to a defined property change at a lower temperature are also described; the applicability of the Arrhenius relation for making predictions to other temperatures, is assumed in this case. 1.4 This practice does not predict thermal aging characteristics where interactions between stress, environment, temperature, and time control failure occur. 1.5 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 appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Note 1: This standard and ISO-2578 address the same subject matter but differ in technical content. 1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 4.1 The use of this practice presupposes that the failure criteria selected to evaluate materials (that is, the property or properties being measured as a function of exposure time) and the duration of the exposure can be shown to relate to the intended use of the materials. 4.2 Plastic materials exposed to heat are subject to many types of physical and chemical changes. The severity of the exposures in both time and temperature determines the extent and type of change that takes place. A plastic material is not necessarily degraded by exposure to elevated temperatures. However, extended periods of exposure of plastics to elevated temperatures will generally cause some degradation, with progressive changes in physical properties. Specific properties and failure (or lifetime) criteria for these properties are typically chosen for the evaluation of thermal endurance. 4.3 Generally, short exposures at elevated temperatures drive out volatiles such as moisture, solvents, or plasticizers, relieve molding stresses, advance the cure of thermosets, and may cause some change in color of the plastic or coloring agent, or both. Normally, additional shrinkage should be expected with loss of volatiles or advance in polymerization. 4.4 Some plastic materials become brittle due to loss of plasticizers after exposure at elevated temperatures. Other types of plastics become soft and sticky, either due to sorption of volatilized plasticizer or due to breakdown of the polymer. 4.5 The degree of change observed will depend on the property measured. Different properties, mechanical or electrical, may not change at the same rate. For instance, the arc resistance of thermosetting compounds improves up to the carbonization point of the material. Mechanical properties, such as flexural properties, are sensitive to heat degradation and may change at a more rapid rate. Ultimate properties such as strength or elongation are more sensitive to degradation than bulk properties such as modulus, in most cases. 4.6 The material studied can change inherent behavior with change in temperature as for example when crossing α, β, and γ transitions. These transitions should be avoided both in the range of aging temperatures used, as well as in extrapolation of the lifeline. Arrhenius principles may only be used to accelerate a chemical mechanism if there are no fundamental changes in the material properties. With semi-crystalline and highly crystalline polymers, elevated temperatures may cause significant changes to the morphology of the material, invalidating or compromising that assumption. Note 2: Caution should be exercised in using the Arrhenius relation and knowledge of physical changes in the material at elevated temperatures is important. Guidance given in ISO 9080 for characterizing lifetime of plastic materials in pipe form by extrapolation suggests that the highest oven aging temperature should be at least 15°C lower than the Vicat softening temperature for glassy amorphous polymers, and at least 15°C lower than the melting point for semi-crystalline polymers. 4.7 Effects of exposure can be quite variable, especially when specimens are exposed for long intervals of time. Factors that affect the reproducibility of data are the degree of temperature control of the enclosure, humidity of the oven, air velocity over the specimen, and period of exposure. Errors in exposure are cumulative with time. Certain materials are susceptible to the influence of humidity. 4.8 It is not to be inferred that comparative material ranking is undesirable or unworkable. On the contrary, this practice is designed to provide data which can be used for such comparative purposes. However, the data obtained from this practice, since it does not account for the influence of stress or environment that is involved in most real life applications, must be used cautiously by the designer, who must inevitably make material choices using additional data such as creep and creep rupture that are consistent with the requirements of the specific application. 4.9 It is possible for many CUT and TI values to exist. Therefore, for any application of the CUT or the TI (temperature index) to be valid, either the thermal aging program must duplicate the intended thermal exposure conditions of the end product, or the Arrhenius relation must apply. 4.10 There can be very large errors when Arrhenius plots or equations based on data from experiments at a series of temperatures are used to estimate time to produce a defined property change at some lower temperature. This estimate of time to produce the property change or “failure” at the lower temperature is often called the “service life;” however, using this term should be avoided as this implies the tester has information on specific failure criteria in end-use, while numerous factors are not under the scope of this test. It is preferable to use terms such as “end point,” “thermal endurance time,” and such. Because of the errors associated with these calculations, this endurance time should be considered as “maximum expected” rather than “typical.”