N,N′-Substituted p-phenylenediamines (PPDs) are widely utilized as rubber antioxidants and emitted into the environment with their transformation products (TPs) including the highly toxic 6PPD-quinone. However, the occurrence of PPDs and TPs in inconspicuous rubber products and their oxidation kinetics under natural aging conditions remains unclear. Herein, we performed a field survey of these compounds in crumb rubbers from 40 school artificial turfs. Twelve PPDs and TPs were frequently detected in rubber particles, dominated by the well-known N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) and N-isopropyl-N′-phenyl-1,4-phenylenediamine (IPPD), as well as their PPD-Qs. One pristine rubber material was chosen to simulate the aging process and examine the oxidation kinetics. The concentrations of all antioxidants in rubber powder decreased > 50% within 4 days under natural aging, much faster than that in particles, suggesting the size effect on oxidation. Different PPDs had distinct oxidation degrees under both field and simulated experiments. Besides ozone, we found that high temperature could induce a significantly faster decay of PPDs within rubber particles than UV exposure. In sum, our field and simulated investigations reveal that the transformation of PPDs to PPD-Qs is ubiquitous and chemically specific in artificial turf, which could be affected by particle size and temperature as key factors in controlling oxidation kinetics.

中文翻译：

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人造草坪再生橡胶颗粒中抗氧化剂对苯二胺及其醌的存在和氧化动力学

N,N'-取代的对苯二胺（PPD）被广泛用作橡胶抗氧化剂，并以其转化产物（TP）（包括剧毒的6PPD-醌）排放到环境中。然而，PPDs和TPs在不显眼的橡胶制品中的出现情况及其在自然老化条件下的氧化动力学仍不清楚。在此，我们对 40 个学校人造草坪的粒状橡胶中的这些化合物进行了实地调查。橡胶颗粒中经常检测到 12 种 PPD 和 TP，主要是众所周知的N -(1,3-二甲基丁基) -N'-苯基-对苯二胺 (6PPD) 和N -异丙基-N'-苯基-1， 4-苯二胺 (IPPD) 及其 PPD-Q。选择一种原始橡胶材料来模拟老化过程并检查氧化动力学。在自然老化下，橡胶粉中所有抗氧化剂的浓度在 4 天内下降了 > 50%，比颗粒中的下降速度快得多，这表明尺寸对氧化的影响。不同的PPD在现场和模拟实验中都具有不同的氧化程度。除了臭氧之外，我们发现高温会导致橡胶颗粒内 PPD 的衰减速度明显快于紫外线照射。总之，我们的现场和模拟研究表明，PPD 到 PPD-Q 的转化在人造草坪中是普遍存在的且具有化学特异性，这可能会受到颗粒尺寸和温度的影响，而这些是控制氧化动力学的关键因素。