1.1 本实践旨在定义评估塑料长时间单独暴露于热空气时耐热性的暴露条件。仅规定了热暴露程序。高温对任何特定性能的影响通过为该性能选择适当的测试方法和测试样本来确定。 1.2 该实践可用作比较材料热老化特性的指南，这些特性是通过某些感兴趣特性的变化来测量的。在室温下测量感兴趣的性质。 1.3 本实践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升高的温度来确定材料的热老化特性的推荐程序，以估计在较低温度下达到规定的性能变化的耐久性；在这种情况下，假设阿伦尼乌斯关系对其他温度进行预测的适用性。 1.4 ●这种做法不能预测应力、环境、温度和时间控制失效之间相互作用的热老化特性。 1.5 一个 本标准并不旨在解决与其使用相关的所有安全性问题（如果有）。本标准的使用者有责任在使用前建立适当的安全、健康和环境实践并确定法规限制的适用性。 附注1: 一个 本标准和ISO-2578涉及相同的主题，但技术内容不同。 1.6 一个 本国际标准是根据世界贸易组织技术性贸易壁垒委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认的标准化原则制定的米特。 ======意义和用途====== 4.1 ●使用这种做法的前提是，为评估材料而选择的失效标准（即，作为暴露时间的函数而测量的一种或多种性能）和暴露持续时间可以证明与材料的预期用途相关。 4.2 ●受热的塑料材料会发生多种类型的物理和化学变化。时间和温度暴露的严重程度决定了发生变化的程度和类型。塑料材料不一定因暴露于高温而降解。然而，塑料长时间暴露在高温下通常会导致一些降解，物理性能逐渐变化。通常选择特定的性能和这些性能的失效（或寿命）标准来评估热耐久性。4.3 一般来说，在高温下短时间暴露会驱除水分、溶剂或增塑剂等挥发物，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或两者的颜色发生一些变化。通常，随着挥发物的损失或聚合的推进，应预期额外的收缩。 4.4 一些塑料材料由于暴露在高温下后增塑剂的损失而变脆。其他类型的塑料变得柔软和粘性，或者是由于挥发的增塑剂的吸附，或者是由于聚合物的分解。 4.5 观察到的变化程度将取决于测量的性质。不同的性质，机械或电学，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，对热降解敏感，并且可以以更快的速率变化。在大多数情况下，强度或伸长率等极限性能比模量等整体性能对降解更敏感。 4.6 所研究的材料可以随着温度的变化而改变固有行为，例如当穿过Îą、Îό和Îł转变时。在使用的老化温度范围内以及在生命线的外推中都应避免这些转变。只有在材料性质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，升高的温度可能会导致材料形态的显著变化，从而使该假设无效或受损。附注2: 一个 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非常重要。ISO 9080中给出的通过外推表征管道形式塑料材料寿命的指南表明，最高烘箱老化温度应比玻璃状无定形聚合物的维卡软化温度至少低15°C，比玻璃状无定形聚合物的维卡软化温度至少低15°C。半结晶聚合物的熔点。 4.7 ●暴露的影响可能变化很大，尤其是当标本长时间暴露时。影响数据再现性的因素是外壳的温度控制程度、烘箱的湿度、样品上的空气速度和暴露时间。暴露误差随时间累积。某些材料容易受到湿度的影响。 4.8 这并不意味着比较材料排名是不可取的或不可行的。相反，这种做法旨在提供可用于这种比较目的的数据。然而，从这种实践中获得的数据，因为它没有考虑大多数现实生活应用中涉及的应力或环境的影响，设计者必须谨慎使用，设计者必须不可避免地使用与特定应用要求一致的附加数据（例如蠕变和蠕变断裂）来做出材料选择。 4.9 可能存在许多CUT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阿伦尼乌斯图或方程来估计在较低温度下产生规定性质变化的时间时，可能会存在非常大的误差。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拥有最终使用中特定失效标准的信息，而许多因素不在该测试的范围内。优选使用诸如“终点”、“耐热时间”等术语。由于与这些计算相关的误差，该耐久性时间应被视为“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.”