Upcycling of Polyolefins Through Functionalization

Plastics constitute an important component of a range of materials used in modern society. Polyolefins (PO), mainly low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP), constitute ~57% of global plastic production, taking an essential role in our every day. Yet, the versatility and convenience of these materials have also threatened the environment as less than 4% is being recycled (in the U.S), the rest is incinerated or leaked to the natural environment. Momentum has therefore shifted towards looking for a solution to address PO waste in order to move to a circular economy. Post-use modification (or functionalization) has shown promising results in upcycling polyolefins, removing limitations of inertness, and potentially improving the final physical properties of the recycled material while extending its useful lifetime. Specifically, the functionalization of POs with hydroxyl groups provides new opportunities in the development of thermoset polyurethanes (PUs), which have not yet been explored. Thermoset PUs, known for their long-lasting properties, are frequently used in foams, elastomers, and film production. This provides the opportunity to upcycle POs to durable, value-added products with long lifetimes. In this work, polypropylene (PP) was hydroxylated through various means and upcycled to a PU. On the first route, a PP-based polyol was synthesized through hydroxylation of maleic anhydride-grafted PP and subsequently cured with a diisocyanate to form a thermoset PU. The crystal structure (unit cell and lamellar structure) and crystallization and nucleation kinetics of the PP were preserved in the PU, indicating the formation of a urethane network did not impact the PP crystallization process. The presence of PP crystallization in the PU led to a higher modulus than that of traditional polyester or polyether PUs, with a trade-off in diminished ductility. The mechanical integrity of the PU was maintained through several reprocessing cycles due to the melt processability enabled by the presence of a urethane exchange catalyst. On the second route, PP was oxidated in a melt extruder using several flow conditions, extrusion time and additives. Several functionalities were obtained with the tradeoff of the decrease in molecular weight. The effect of functionalization and molecular weight to the thermal properties, crystal structure and crystallization kinetics were studied to fully understand these materials upon forming the PU. Additionally, in this work, the concepts of upcycling were extended beyond higher education contexts. We developed a series of hands-on activities showing the importance of the plastic sorting process for K-12 students. The activities effectively enhanced students’ awareness of the sorting process of recycled waste as studied through pre- and post- evaluations and open questions laying the foundation for future inquiry and outreach project design.

Name thesis:degree_name

Doctor of Philosophy

Discipline thesis:degree_discipline

Chemical Engineering

Grantor

University of Houston

Year dc:date.issued

2025

Author dc:creator

• Monegro, Ronard Herrera 1995-

Advisors dc:contributor.advisor

• Robertson, Megan L.
• Krishnamoorti, Ramanan

Committee members dc:contributor.committeemember

• Carrow, Bradley
• Rimer, Jeffrey
• Alamgir, Karim
• Do, Loi H.

• Chemical engineering

Language dc:language.iso

English

Handle dc:identifier.uri

https://hdl.handle.net/10657/19825

OAI identifier oai:identifier

oai:uh-ir.tdl.org:10657/19825