Functionalization and Repurposing of Polypropylene to a Thermoset Polyurethane.

Area of Science:

• Polymer Science
• Materials Science
• Chemical Engineering

Background:

• Polyolefin waste presents a significant challenge for achieving a circular economy.
• Post-use modification offers a viable strategy for upcycling polyolefins, enhancing their properties and extending their lifespan.
• Grafting maleic anhydride onto polypropylene (PP) is an established method to increase its reactivity for further functionalization.

Purpose of the Study:

• To develop an effective recycling pathway for polypropylene waste.
• To create a melt-processable thermoset polymer from polypropylene.
• To investigate the potential for upcycling polypropylene into polyurethane.

Main Methods:

• Maleic anhydride grafted polypropylene was hydroxylated.
• The hydroxylated polypropylene was cured with a diisocyanate to form a thermoset polyurethane (PU).
• The structural and mechanical properties of the resulting PU were analyzed, including its crystal structure, modulus, glass transition temperature, and crystallinity.

Main Results:

• The crystal structure of the original polypropylene was preserved in the resulting polyurethane.
• The PU exhibited a high modulus at room temperature due to PP crystallization, transitioning to a rubbery plateau at higher temperatures.
• The PU demonstrated a higher glass transition temperature and lower crystallinity compared to the precursor PP, attributed to its crosslinked nature.
• The PU maintained mechanical integrity through multiple reprocessing cycles, facilitated by a urethane exchange catalyst.

Conclusions:

• The functionalization and upcycling of polypropylene waste into thermoset polyurethane is a promising route for waste repurposing.
• This method yields a melt-processable thermoset material, expanding the potential applications for recycled polypropylene.
• The preservation of PP's crystal structure and the creation of a crosslinked network contribute to the material's unique properties and reprocessing capability.