Comparative analysis of additive decomposition using one-dimensional and two-dimensional gas chromatography: Part I - Irganox 1010, Irganox 1076, and BHT.

Plastics incorporate diverse additives, including primary antioxidants with a typical amount between 0.05 to 3 wt.%, to enhance plastics functionality and durability, preventing their oxidation and maintaining their mechanical properties. While these antioxidants offer substantial benefits, their degradation can significantly impact plastic pyrolysis by changing the pyrolysis oil product distribution. Understanding the intricate distribution of decomposition products resulting from pyrolysis is essential yet often overlooked. This study delved into the analysis of the decomposition of common primary antioxidants, namely, Irganox 1010, Irganox 1076, and butylated hydroxytoluene (BHT), utilizing both one-dimensional gas chromatography coupled with a quadruple mass spectrometer (GC-MS) and two-dimensional gas chromatography equipped with flame ionization detector and time-of-flight mass spectrometer (GC×GC-FID/TOF-MS). This study showed that GC×GC-FID/TOF-MS provided a more detailed characterization of the pyrolysis product distribution of primary antioxidants used in plastics in comparison to GC-MS. For each of the antioxidants, using the GC×GC-FID/TOF-MS analytical approach enhanced the identification of degradation products at least fivefold. Furthermore, GC×GC-FID/TOF-MS identified products of more chemical classes than GC-MS. For instance, compounds from 14 chemical classes were identified from GC×GC-FID/TOF-MS in the pyrolysis of Irganox 1010, whereas only 9 chemical classes were identified in GC-MS. Olefins were the major chemical class for both Irganox 1010 and Irganox 1076 in the decomposition process, accounting for 23.25 wt.% and 20.76 wt.%, respectively. Ketones were the major chemical class in the case of BHT, having a 6.68 wt.% yield. This research enhanced the understanding of the decomposition of primary antioxidant and their product distribution during pyrolysis and shed light on the potential necessity for using two-dimensional gas chromatography.

Comparative analysis of additive decomposition using one-dimensional and two-dimensional gas chromatography: Part II - Irgafos 168 and zinc stearate.

Plastic production has experienced a significant increase in the last sixty years due to its cost-efficiency and adaptable characteristics, leading to the extensive use of additives to improve its performance and longevity. Due to the high demand for plastic, plastic waste production has increased, contaminating the environment and living beings by leaching additives, among other substances. Pyrolysis stands out among recycling techniques because it can handle mixed polymer waste feedstock. However, understanding the pyrolyzates distribution of additives is fundamental to assessing pyrolysis process of plastic waste. This study investigated the pyrolysis product distributions of two commonly used antioxidants, namely, Irgafos 168 and zinc stearate (ZnSt), using one-dimensional gas chromatography equipped with a quadruple mass spectrometer (GC-MS) and two-dimensional gas chromatography coupled to flame ionization detector and time-of-flight mass spectrometer (GC×GC-FID/TOF-MS). While GC separation technique provided limited information on product distribution, GC×GC offered enhanced resolution and identification of the decomposition products. In the pyrolysis of Irgafos 168 at 550 °C, GC identified 18 products, while GC×GC identified 198 products, representing an increase of approximately 11-fold. Similarly, for ZnSt, GC identified 67 products, while GC×GC identified 434 products, representing a 6-fold increase. GC×GC identified decomposition products from 15 different chemical classes for Irgafos 168 and 16 chemical classes for ZnSt, compared to 4 and 11 chemical classes identified by GC, respectively. Phenols and their derivatives were the major chemical class in the decomposition products of Irgafos 168 with a yield of 9.51 wt.%. In contrast, olefinic products were the dominant ones for ZnSt, with a yield of 9.73 wt.%. The major decomposition product of Irgafos 168 and ZnSt was 2­tert­butyl­methylphenol (C11H16O) and C6 olefin (C6H12) with yields of 3.88 wt.%, and 1.13 wt.%, respectively. Utilizing the GC×GC separation method improved the ability to identify decomposition products, which can ultimately lead to a better understanding of antioxidant degradation that occurs during the pyrolysis process. GC×GC also provided thorough characterization of minor and co-eluted products along with major antioxidant degradation products. Additionally, the decomposition product distribution of Irgafos 168 and ZnSt was also compared with the primary antioxidants, Irganox 1010, Irganox 1076, and BHT, studied in part 1. The analysis indicated that the olefinic chemical class was the predominant one in Irganox 1010, Irganox 1076, and ZnSt, while ketones were the major chemical class in the decomposition of BHT and phenolics had the highest yield in Irgafos 168.