Development of a Sensor for Polypropylene Degradation Products
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1174-V06-12
Development of a Sensor for Polypropylene Degradation Products Shawn M. Dirk,1 Patricia S. Sawyer,1 Robert Bernstein,1 James M. Hochrein,2 Cody M. Washburn,1 Stephen W. Howell,3 and Darin C. Graf4 1
Organic Materials Department, 2 Materials Reliability Department, 3 Rad Hard CMOS Technology Department, 4 Advanced Sensor Technologies Department, Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185. ABSTRACT This paper presents the development of a sensor to detect the oxidative and radiation induced degradation of polypropylene. Recently we have examined the use of crosslinked assemblies of nanoparticles as a chemiresistor-type sensor for the degradation products. We have developed a simple method that uses a siloxane matrix to fabricate a chemiresistor-type sensor that minimizes the swelling transduction mechanism while optimizing the change in dielectric response. These sensors were exposed with the use of a gas chromatography system to three previously identified polypropylene degradation products including 4-methyl-2-pentanone, acetone, and 2-pentanone. The limits of detection 210 ppb for 4-methy-2-pentanone, 575 ppb for 2-pentanone, and the LoD was unable to be determined for acetone due to incomplete separation from the carbon disulfide carrier. INTRODUCTION The aging of partially crystalline olefins, such as polypropylene, is particularly complex. Polypropylene has been exposed to thermal, radiation, and thermal combined with radiation accelerated aging environments. Isotopically labeled carbons (13C) have been selectively positioned at chemically distinct locations in the polymer and studies performed on materials containing enrichment at each position. Selective labeling, combined with 13C nuclear magnetic resonance (NMR) and mass spectroscopy, has provided the ability to follow each chemically distinct carbon throughout the degradation process.[1, 2] Some of these degradation products including 4-methyl-2-pentanone, acetone, and 2-pentanone were selected as targets for a newly developed chemiresistor sensor system that uses a siloxane matrix.[3] As an example, Scheme 1 shows the proposed degradation pathway of polypropylene resulting in 4-methyl-2-pentanone. Since isotopically labeled polypropylene was used with mass spectroscopy characterization, each of the three distinct atoms was followed with unprecedented detail. This resulted in the proposed mechanisms as well as extreme confidence in the assignment of the degradation products. [2]
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(4-methyl-2-Pentanone)
Scheme 1. Oxidative degradation mechanism of polypropylene producing 4-methyl-2-pentanone.[2] Chemiresistors may be a potenti
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