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 Publications

Abstract: Polyimide film is used for many advanced applications such as high-temperature adhesives, mechanical stress buffers, and insulation techniques due to its durability, strength, heat resistance, and dimensional stability. However, a complicated manufacturing process may result in different properties on the two sides (air and cast) of the film, affecting performance. Polyimide films with a 2 mm thickness were obtained from four manufacturers (A, B, C, and D) and investigated by an atomic force microscope (AFM). A 2 by 2-micrometer area was scanned at random locations five times on each side of the films to obtain their representative nanostructures. The AFM images suggest different morphology features on different sides. There often were small round bumps on the air side for all manufacturers, which could be from dust on the surface during the imidization process. Alternatively, scratches, round dents, and aggregates were likely to be on the cast side, possibly caused by the heating surface used in the manufacture. The roughness of both sides of the films (Rq and Ra values) was calculated from the AFM images. The t-tests confirmed the cast side was rougher than the air side for all manufacturers. ANOVA tests show that film from Manufacture D had higher roughness than other manufactures on both the air and cast sides. Manufacture B provided the smoothest film. Its roughness was lower than all manufacturers on the air side and lower than manufacturers C and D on the cast side.
Abstract: Although recycled plastics provide a low-cost and environmentally friendly alternative for many applications, their desirability is significantly limited by the presence of unpleasant odors from volatile organic compounds (VOCs). In this work, a headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) method was optimized to analyze volatile compounds from an odorous recycled plastic resin which was roughly composed of 85-90% polypropylene (PP) and 15-10% high-density polyethylene (HDPE). A large variety of aliphatic hydrocarbons and 13 additive residues were detected. Statistical tools were employed to screen the VOCs and successfully identified three components, i.e., 2,4-dimethyl-heptane, 4-methyl-octane and octamethylcyclotetrasiloxane (D4), which were significantly related to the odor intensity of the recycled plastic resin (p-values < 0.05). 2,4-Dimethyl-heptane has a strong, pungent plastic smell, which is very similar to the odor of the recycled resin.  It is identified as a major source of the odor. Past relevant research has not been able to establish a direct link between an odorous compound and the undesirable odor of recycled plastic until now. 4-Methyl-octane was highly corelated to 2,4-dimethyl-heptane and somewhat contributed to the odor. D4 does not have an odor, but it may serve as an indicator of some odorous residues from personal care products. 
Abstract: Although recycled plastics provide a low-cost and environmentally friendly alternative for a wide range of applications, several factors significantly limit their desirability. Most notably among these is thermal degradation of polymers during recycling process, which may compromise their mechanical performance and cause unpleasant odor. Previous studies mainly focus on polymer decomposition mechanisms and kinetics under high temperatures when quick reactions occur. However, polymer degradation behavior under processing temperatures for plastic recycling is essentially different, which attracts the most interest of the industry. In this work, degradations of low-density polyethylene (LDPE), high-density polyethylene (HDPE) and polypropylene (PP) was investigated under a typical recycling processing temperature (200°C). A headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) method was employed to detect representative volatile degradation products and monitor the degradation processes. The results show that each plastic had a unique volatile compound profile, their thermal stabilities varied notably, and they released different degradation products. LDPE had the lowest thermal stability among the three and gave out large amounts of n-alkanes with 12-16 carbons only after 20 min of heating. Accelerated degradation of PP was detected after 30 min of heating when it started to release 4-methyl-2-heptanone, heptadecane and octadecane. For HDPE, 1-tetradecene and 1-hexadecene were quickly released after 20 min of heating, but accelerated degradation was only observed when the amounts of 1-heptadecene and 1-nonadecene increased significantly after 40 min of heating. The volatile compound analysis method developed in this work is very sensitive to polymer degradation and could be used to distinguish plastic types. The results of this research may help the plastic recycling industry optimize processing conditions and improve product quality. 

Abstract: Polyethylene terephthalate (PET) accounts for 10.2% of the plastic produced worldwide and is nearly exclusively used for single use bottle packaging. Over the past few decades, recycling PET has become a major initiative around the world as result of increased pollution levels and climate change. Improvements in the reprocessing of recycled polyethylene terephthalate (rPET) for product applications will in turn diminish the demand for virgin PET and ultimately have a favorable impact on our environment. However, it has been challenging to reprocess the rPET because of its thermal degradation at elevated temperatures. The focus of this study is to address this issue and understand the effect that reprocessing has on the structure and the mechanical properties of rPET with different reprocessing conditions. The goal of this project is to develop an innovative fast processing method for compression molding rPET. Samples will be prepared from the molded rPET for thermal and mechanical testing, including differential scanning calorimetry (DSC), flexural, and impact testing.

Abstract: This paper will look at compounding recycled discontinuous carbon fiber with recycled LDPE pellets via extrusion compression molding. A novel in house metering unit will be used to compound recycled carbon fiber with recycled LDPE pellets. Differential Scanning Calorimetry (DCS) and Fourier Transform Infrared Spectroscopy (FTIR) will be conducted on the recycled LDPE to ascertain its thermal characteristics. Mechanical characterization will be conducted on the panels produced and optical Microscopy (SEM) images of the fractured surface will be done to analyze the composite failure mode. Successful demonstration of this process can be utilized to further evaluate the sustainability of thermoplastics via recycling.

Abstract: Although recycled plastics provide a low-cost and environmentally friendly alternative for a wide range of applications, there are several factors that significantly limit its desirability. Most notably among these is thermal degradation of polymers during their recycling process, which may compromise their mechanical performance and cause unpleasant odor. In this work, a headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) method was employed to help understand thermal degradation of low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) under a typical processing temperature (200°C) for plastic recycling. Volatile compounds from the three plastics before and after heating were monitored. The results show that each plastic has a unique volatile compound profile. They had notably differences in thermal stability and released different degradation products. LDPE had t he lowest thermal stability among the three materials studied in this work and gave out a lot of volatile compounds after 20 min of heating. Accelerated degradation of PP was detected after 30-min heating, while HDPE was still relatively stable after heated for 40 min. The volatile compound analysis carried out in this work could be used as an effective way to identify the type of plastics and evaluate their extent of thermal degradation. The results of this research may aid the plastic recycling industry in improving product quality.