1.1 本规程说明了如何测试塑料的氧化降解特性，这些塑料仅在没有任何选定的处理环境（如土壤、垃圾填埋场或堆肥）的情况下，在大气压力和热湿模拟的环境中降解。本规程并不通过扩展或外推数据或产生的结果表明此类塑料适用于或在这些环境中处置时会降解。特别值得注意的是，在实际环境中，如土壤、堆肥和垃圾填埋场，如果发生氧化，则主要是在存在其他干扰成分的条件下，如果是垃圾填埋场，则主要是在亚大气氧浓度下。因此，这种做法只能使塑料材料在测试条件下的氧化电位相对有序，而这些条件并不总是反映其在特定实际处理系统中的行为。 在实际处理条件下预测塑料的氧化是对适当方法（如测试方法）进行进一步测试的必要步骤 D5338 用于堆肥。基于这种做法，不能对现实世界中的行为提出任何索赔。 1.2 本规程仅旨在定义塑料在不同温度、大气压、受控湿度水平下长时间暴露在空气中的条件。湿度水平和温度范围应选择在丢弃此类塑料的处置场中通常观察到的可变记录季节范围（上限和下限）内。例如:土壤（15%至40%的水分）；垃圾填埋场（含水量35%至60%）和堆肥（含水量45%至70%）。 如果需要与指定的湿度范围进行比较，则可以选择在零湿度下暴露塑料。仅规定了热和湿度暴露的程序，而不是评估热和湿度暴露影响所需的试验方法或样本。通过选择适当的试验方法和试样，确定热和湿度对任何特定性能的影响；然而，建议实践 D3826 用于确定脆化终点，定义为75时材料历史中的点 % 试验样品的拉伸断裂伸长率为5 % 或更小，初始应变率为0.1 mm/mm min。 1.3 本规程用于通过选择适当的试验方法和试样，比较任何选定温度下的热和湿度对特定塑料降解的影响，例如在上述处理环境中发现的热和湿度。 1.4 当比较塑料材料在受控湿度水平下的热老化特性时，使用本规程是为了应用选定的暴露条件，该湿度水平通过某些相关特性的变化来测量（即通过伸长率损失、分子量、崩解等方式脆化）。这与实践非常相似 D3045 但用于评估使用后容易氧化的塑料。本练习中使用的暴露时间将显著短于练习中使用的暴露时间 D3045 1.5 使用的烤箱类型可能会影响从该实践中获得的结果。用户可以使用两种方法之一进行烤箱暴露。不要将基于一种方法的结果与基于另一种方法的结果混合。 1.6 程序A:重力对流烘箱- 推荐用于标称厚度不大于0.25 mm（0.010 in.）的薄膜试样。 1.7 程序B:强制通风烤箱- 建议用于标称厚度大于0.25 mm（0.010 in.）的试样。 1.8 本规程推荐了在干燥或选定湿度条件下，在单一温度下比较材料热老化和湿老化特性的程序。还描述了确定材料在一系列温度和湿度条件下的热老化特性的推荐程序，以估计在某些较低温度下达到规定性能变化的时间。在应力、环境、温度和时间控制之间的相互作用失效的情况下，本规程不会预测热老化特性。 1.9 以国际单位制表示的数值应视为标准。 1.10 以英寸-磅为单位的数值应视为标准值。括号中给出的值是到国际单位制的数学转换，仅供参考，不被视为标准值。 注1: 没有已知的ISO等效于本标准。 1.11 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 由于本规程中规定的条件与实际处置环境（例如堆肥、土壤或填埋场）之间的相关性尚未确定或确立，因此试验结果仅用于实验室中的比较和排序目的。 不得根据该程序获得的结果推断实际处置预期或预测。这种说法需要真实世界的评估和相关性。 4.2 暴露在湿热环境中的可降解塑料会发生多种物理和化学变化。暴露在时间、温度和湿度水平上的严重程度决定了发生变化的程度和类型。例如，高温下的短暴露时间通常有助于缩短氧化降解塑料的诱导期，在此期间抗氧化剂和稳定剂会耗尽。物理性能，例如拉伸和冲击强度以及伸长率和模量，在该诱导期内有时会发生变化； 然而，这些变化通常不是由于分子量降解引起的，而仅仅是温度依赖性响应，例如结晶度增加或挥发性物质损失，或两者兼而有之。湿度的影响不太清楚，更难预测，并且取决于可降解塑料的特性，如亲水性、极性和组成。 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；消除成型应力；促进热固性塑料的固化；增加结晶度；并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过程的推进，预计会出现额外收缩。 4.4 一些塑料材料，如PVC，由于增塑剂的损失或聚合物的分子分解而变得易碎。聚丙烯及其共聚物在发生分子降解时往往变得非常脆，而聚乙烯在脆化之前往往变得柔软和脆弱，从而导致拉伸强度和伸长率损失。 4.5 材料的脆化不一定与分子量的减少相称。 4.6 观察到的变化程度将取决于测量的特性。不同的属性不会以相同的速率变化。在大多数情况下，极限性能（如断裂强度或断裂伸长率）比体积性能（如模量）更容易退化。 4.7 暴露的影响可能相当多变，尤其是当样品长时间暴露时。 影响数据再现性的因素包括外壳的温度控制程度、烘箱的湿度水平、样本上的空气速度以及本规程评估的暴露期。暴露误差随时间累积；例如，在长期试验中，由于湿度而不是氧化的影响，某些材料可能会降解，从而产生误导性结果。易水解的材料（即可水解降解塑料）在进行长期热试验时会因水分而不是氧化而发生降解。 4.8 不要推断比较材料排名不可取或不可行。相反，本规程旨在提供在暴露后进行适当物理性能测试后可用于此类比较目的的信息。 然而，由于它没有考虑大多数实际应用中所涉及的应力或环境的影响，设计师必须谨慎使用从该实践中获得的信息，他们必须不可避免地使用额外信息进行材料选择，例如水分、土壤类型和成分，以及符合特定应用要求的机械作用效果。 4.9 可能存在许多温度指数，事实上，每个故障标准都有一个温度指数（达到故障的时间取决于暴露温度和湿度）。因此，为了使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暴露条件。 如果塑料材料在最终使用中以老化程序中未评估的方式暴露，则由此得出的温度指数不适用于塑料材料的使用。 4.10 在某些情况下，材料可以暴露在一个温度和湿度下一段特定时间，然后暴露在相同湿度下的另一个温度下一段特定时间。这种做法可用于此类应用。推导了第一个温度和湿度的热老化曲线，然后推导了样品暴露于第一个温度和湿度后，相同湿度下第二个温度的热老化曲线。 4.11 当使用基于一系列温度和湿度下实验数据的Arrhenius图或方程来估计在某些较低温度下产生规定特性变化的时间时，可能会出现很大的误差。 产生性能变化或故障的估计时间必须始终伴随95 % 基于计算或估计的可能时间范围的置信区间。

1.1 This practice indicates how to test the oxidative degradation characteristics of plastics that degrade in the environment under atmospheric pressure and thermal and humidity simulations, only, in the absence of any selected disposal environment such as soil, landfill, or compost. This practice does not by any extension or extrapolation of data or results generated indicate that such plastics are suitable for or will degrade on disposal in these said environments. It is particularly noted that in real world environments such as soil, compost and landfill oxidations, if they occur, will predominantly be under conditions where other interfering ingredients are present and, in the case of landfill, at sub-atmospheric oxygen concentrations. This practice, therefore, can only result in a relative ordering of the potential for oxidation of plastic materials under the conditions tested, which are not always reflective of their behavior in a particular real world disposal systems. Prediction of the oxidation of a plastic under real world disposal conditions is an essential further testing in appropriate methodologies, such as Test Method D5338 for composting. No claims can be made for real world behavior based on this practice. 1.2 This practice is only intended to define the exposure conditions of plastics at various temperatures in air at atmospheric pressure under controlled humidity levels for extended periods of time. The humidity levels and temperature ranges are selected to be within the variable recorded seasonal ranges (upper and lower levels) generally observed in disposal sites where such plastics are discarded. For example: soil (15 to 40 percent moisture); landfill (35 to 60 percent moisture), and compost (45 to 70 percent moisture). It is optional to expose the plastic at zero humidity, if comparison with specified humidity ranges is of interest. Only the procedures for heat and humidity exposures are specified, not the test method or specimen, necessary for the evaluation of the heat and humidity exposure effects. The effect of heat and humidity on any particular property is determined by selection of the appropriate test method and specimen; however, it is recommended that Practice D3826 be used to determine the embrittlement endpoint, which is defined as that point in the history of a material when 75 % of the specimens tested have a tensile elongation at break of 5 % or less at an initial strain rate of 0.1 mm/mm min. 1.3 This practice is used to compare the effects of heat and humidity at any selected temperature, such as those found in the mentioned disposal environments, on the degradation of a particular plastic by selection of an appropriate test method and specimen. 1.4 This practice is to be used in order to apply selected exposure conditions when comparing the thermal-aging characteristics at controlled humidity levels of plastic materials as measured by the change in some property of interest (that is, embrittlement by means of loss of elongation, molecular weight, disintegration, etc.). It is very similar to Practice D3045 but is intended for use in evaluating plastics designed to be oxidized easily after use. The exposure times used for this practice will be significantly shorter than those used for Practice D3045 1.5 The type of oven used can affect the results obtained from this practice. The user can use one of two methods for oven exposure. Do not mix the results based on one method with those based on the other one. 1.6 Procedure A: Gravity-Convection Oven— Recommended for film specimens having a nominal thickness not greater than 0.25 mm (0.010 in.). 1.7 Procedure B: Forced-Ventilation Oven— Recommended for specimens having a nominal thickness greater than 0.25 mm (0.010 in.). 1.8 This practice recommends procedures for comparing the thermal and humidity aging characteristics of materials at a single temperature under dry or selected humidity conditions. Recommended procedures for determining the thermal aging characteristics of a material at a series of temperatures and humidity conditions for the purpose of estimating time to a defined property change at some lower temperature are also described. This practice does not predict thermal aging characteristics where interactions between stress, environment, temperature, and time control failure. 1.9 The values stated in SI units are to be regarded as the standard. 1.10 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard. Note 1: There is no known ISO equivalent to this standard. 1.11 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 Since the correlation between the conditions specified in this practice and actual disposal environments (for example, composting, soil or landfill) has not been determined or established, the test results are to be used only for comparative and ranking purposes in the laboratory. No extrapolation to real world disposal expectations or predictions are to be made from results obtained by this procedure. Real world evaluations and correlations are needed for such claims. 4.2 Degradable plastics exposed to heat and humidity are subject to many types of physical and chemical changes. The severity of the exposures in both time, temperature and humidity level, determines the extent and type of change that occurs. For example, short exposure times at elevated temperatures generally serve to shorten the induction period of oxidatively degradable plastics during which the depletion of antioxidants and stabilizers occurs. Physical properties, such as tensile and impact strength and elongation and modulus, sometimes change during this induction period; however, these changes are generally not due to molecular-weight degradation, but are merely a temperature-dependent response, such as increased crystallinity or loss of volatile material, or both. The effects of humidity are less well understood and are more difficult to predict and depend on the degradable plastics characteristics such as hydrophilicity, polarity and composition. 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; increase crystallinity; and cause some change in color of the plastic or coloring agent, or both. Normally, additional shrinkage is expected with a loss of volatiles or advance in polymerization. 4.4 Some plastic materials such as PVC become brittle due to loss of plasticizers or to molecular breakdown of the polymer. Polypropylene and its copolymers tend to become very brittle as molecular degradation occurs, whereas polyethylene tends to become soft and weak before it embrittles with resultant loss in tensile strength and elongation. 4.5 Embrittlement of a material is not necessarily commensurate with a decrease in molecular weight. 4.6 The degree of change observed will depend on the property measured. Different properties do not change at the same rate. In most cases, ultimate properties, such as break strength or break elongation, are more sensitive to degradation than bulk properties such as modulus. 4.7 Effects of exposure can be quite variable, especially when samples are exposed for long intervals of time. Factors that affect the reproducibility of data are the degree of temperature control of the enclosure, humidity level of the oven, air velocity over the specimen, and exposure period which are evaluated by this practice. Errors in exposure are cumulative with time; for example certain materials have the potential to be degraded due to the influence of humidity rather than oxidation in long-term tests and thus give misleading results. Materials susceptible to hydrolysis (that is, hydrolytically degradable plastics) undergo degradation when subjected to long-term thermal tests due to the presence of moisture rather than oxidation. 4.8 Do not infer that comparative material ranking is undesirable or unworkable. On the contrary, this practice is designed to provide information that can be used for such comparative purposes after appropriate physical property tests are performed following exposure. However, since it does not account for the influence of stress or environment that is involved in most real life applications, the information obtained from this practice must be used cautiously by the designer, who must inevitably make material choices using additional information, such as moisture, soil-type and composition, and mechanical-action effects that are consistent with the requirements of the particular application. 4.9 It is possible for many temperature indices to exist, in fact, one for each failure criterion (time to reach failure is dependent on the exposure temperature and humidity). Therefore, for any application of the temperature index to be valid, the thermal-aging program must duplicate the intended exposure conditions of the end product. If the plastic material is exposed in the end use in a manner not evaluated in the aging program, the temperature index thus derived is not applicable to the use of the plastic material. 4.10 In some situations, a material can be exposed to one temperature and humidity, for a particular period of time, followed by exposure to another temperature at the same humidity, for a particular period of time. This practice can be used for such applications. The heat-aging curve of the first temperature and humidity is derived, followed by derivation of the heat-aging curve for the second temperature at the same humidity, after exposure of samples to the first temperature and humidity. 4.11 There can be very large errors when Arrhenius plots or equations based on data from experiments at a series of temperatures and humidity 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 must always be accompanied by a 95 % confidence interval for the range of times possible based on the calculation or estimate.