Experimental Study on the Decomposition of Antioxidants and Interactions with Polypropylene Waste During Their Deconstruction
Restricted (Penn State Only)
- Author:
- Khan, Rowfi
- Graduate Program:
- Energy and Mineral Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- December 13, 2023
- Committee Members:
- Hilal Ezgi Toraman, Thesis Advisor/Co-Advisor
Semih Eser, Committee Member
Jeremy Gernand, Program Head/Chair
Bryan D Vogt, Committee Member - Keywords:
- Plastics
Additives
Antioxidants
Decomposition
Pyrolysis
Two-dimensioanl Gas Chromatography
Polypropylene - Abstract:
- Plastics are widely used in various consumer products and industrial applications in everyday life. Plastics commonly include different additives to improve their qualities and durability. Among different additives, antioxidants are a common choice to prevent or decelerate the oxidation process of plastic materials. Although antioxidants provide major advantages in product quality, their deterioration can lead to environmental and health risks and create challenges in recyclability. This study offers a detailed investigation of the decomposition of antioxidant additives commonly found in plastics and their effect on polypropylene (PP) deconstruction. Firstly, the decomposition products of common antioxidants, including Irganox 1010, Irganox 1076, Irgafos 168, butylated hydroxytoluene, and zinc stearate, have been investigated. By employing traditional one–dimensional gas chromatography coupled with mass spectrometry (GC–MS) and two–dimensional gas chromatography coupled with a flame ionization detector and time–of–flight mass spectrometer (GC×GC–FID/TOF–MS), this research identified the decomposition products of the investigated antioxidants at a typical pyrolysis temperature of 550°C. The results demonstrated the superior analytical capability of GC×GC–FID/TOF–MS over GC–MS. GC×GC–FID/TOF–MS identified more than five times the compounds that GC–MS has identified for all the antioxidants. Olefins were the major chemical class for antioxidants like Irganox 1010, Irganox 1076, and zinc stearate. Ketones were the major ones for BHT, and phenolic derivatives dominated the decomposition products of Irgafos 168. Additionally, GC×GC–FID/TOF–MS was able to identify more distinct chemical classes for all the antioxidants, and it was also instrumental in detecting minor and coeluting products during pyrolysis. A detailed list of decomposition products, along with their yields, was also provided in this thesis. Secondly, this research investigated the effect of these common antioxidants on polypropylene (PP) pyrolysis, a widely used polymer in industrial applications. Irganox 1010, Irganox 1076, Irgafos 168, butylated hydroxytoluene, and zinc stearate at a concentration of 3 wt.% were extruded along with PP and then subjected to pyrolysis temperature of 550°C. The addition of antioxidants reduced the overall yield for all the antioxidants other than Irganox 1010, varying between 4-9%. The inclusion of Irganox 1076 caused the largest decrease in yield, accounting for approximately 9% compared to PP. The decrease in yield was mainly contributed by carbon numbers ranging from C1 to C12. In the case of Irganox 1076, 2.6 wt.% yields decreased in this carbon range, accounting for approximately 67% of the total decrease in yield (3.91 wt.%). Aliphatic hydrocarbons represented over 95% of the products in all the antioxidants. Though the antioxidants had oxygen in their structure, the relative yield of oxygenated products was insignificant, accounting for approximately 0.1% of the total yield. Finally, Irganox 1076 showed a relatively negative impact on the overall yield, accounting for a 9% decrease compared with the pure PP sample, where the addition of Irganox 1010 did not lead to any change. Furthermore, ZnSt, Irganos 168, and BHT also have a moderate decrease in yield. The results obtained in this work provide insights into the decomposition products of commonly used antioxidants and the extent of their effect on PP pyrolysis in terms of product distribution and overall yield.