Date of Award
12-2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Materials Science and Engineering
Committee Chair/Advisor
Dr. Igor Luzinov and Dr. Philip J Brown
Committee Member
Dr. Rajendra K. Bordia
Committee Member
Dr. Mark A. Johnson
Abstract
Polyolefin materials, polypropylene (PP) and polyethylene (PE), are widely used in day-to-day life both commercially and industrially, offering versatile applications due to their mechanical and chemical properties. The high consumption rate of these materials makes them important targets for recycling efforts. However, there are multiple contributing factors leading to low recycling of PP and PE, chiefly sorting factors: chemical similarity, changed properties after multiple rounds of processing, and the use of processing aids. It is necessary to point out that, because of multiple melt processing cycles, recycled PP has decreased molecular weight due to chain scission. Conversely, recycled PE molecular weight increases with multiple melt processing cycles since branching and crosslinking occur. To this end, we aim to better understand the PP/PE blend system and its recycling potential by forming blends of a low-viscosity PP with various sources of higher viscosity PE. We propose this blending methodology for use as a means of expanding the recycling of polyolefin materials.
Within this work, we report on the blends made with a target of 25wt% low-viscosity PP and 75wt% high-viscosity PE which is then referred to as an asymmetric viscosity blend. This designation refers strictly to the viscosity of the components not being of similar values. Commercial virgin sources of PE of both low-density polyethylene (LDPE) and high-density polyethylene (HDPE) are employed to generate blends guided by the PP as the basis of bulk mechanical properties. In the first part of this work, the PP material remained constant, whereas the melt viscosity of the LDPE and HDPE sources were varied. The produced materials were made through melt blending utilizing a melt extrusion process and were immiscible systems, in which the PP forms the matrix phase and PE the dispersed. This is made possible due to the blend morphology being dependent upon both the fractional material amount and the viscosity of the components.
The latter part of this work pushes the limitations of the utilized principle by expanding on the factors of the source components. The low viscosity PP is retained as the intended matrix material, but consumer sources of PE and other materials are utilized as the high viscosity material. The viability of the blend composition/viscosity principle in generating usable material blends with good mechanical and thermal properties reported properties, is expanded. Through this work, various modeling techniques are used to predict the expected behavior of the blends. This is important to the general scope of this work as it informs us of the broader ability to use this principle in real-world situations.
This work provides insights into a better understanding of PP and PE blends with asymmetric viscosity and the ability to generate usable blend material for real-life applications. We utilize a commonly known viscosity composition principle to generate predictable materials upon which the low viscosity PP component forms a matrix, and the higher viscosity PE forms the matrix, thus highlighting the ability to maximize the recycled material to virgin material for future product use.
Recommended Citation
Daichendt, Bernadine, "Polypropylene/Polyethylene Blends With Asymmetric Viscosity: Fabrication, Characterization, and Recycling Potential" (2025). All Dissertations. 4108.
https://open.clemson.edu/all_dissertations/4108