Doctoral Defense - Enoch Kofi Acquah

About the Event

The Department of Chemical Engineering and Materials Science

Michigan State University

Ph.D. Dissertation Defense

March 25, 2025, 10 – 12 pm

ChEMS Conference room, 2108 EB

SYNTHESIS OF LIQUID LIGNIN POLYOL DESIGNED FOR FLEXIBLE POLYURETHANE FOAMS

By: Enoch Kofi Acquah

Advisor: Dr. Mojgan Nejad

Abstract

Over the years, there has been a growing need for sustainable alternatives to replace petroleum-based polyols in the formulation of flexible polyurethane (PU) foams. Lignin, being the second most abundant natural polymer after cellulose, possesses various hydroxyl functionalities, making it a good polyol replacement. However, the incorporation of lignin in polyurethane flexible foams has been hampered by lignin’s rigid structure, high hydroxyl value, poor solubility in co-polyols, and low reactivity towards isocyanate. Therefore, it is important to overcome these limitations to fully harness lignin’s potential in flexible polyurethane foam applications. This study presents various modification strategies to synthesize liquid lignin polyols suitable for flexible PU formulations.

First, lignin was oxyalkylated with propylene carbonate (PC) and the produced liquid lignin polyols were used directly in flexible PU foam formulations. The results showed that while lignin polyols enhanced the biobased carbon content of the foams, excessive unreacted PC negatively impacted mechanical properties such as tensile strength, tear resistance, and compression force deflection (CFD) of the lignin-based foams. Fourier-transform infrared (FTIR) spectroscopy revealed that unreacted PC disrupted microphase separation, weakening intermolecular interactions and reducing the strength of lignin based-foams. The optimal lignin to propylene carbonate molar ratio, which balances processability and thermomechanical performance, was identified as 1:5.

Next, various co-polyols were used to minimize the amount of unreacted PC in oxyalkylated lignin polyols. The results indicated that high ethylene oxide (EO)-based polyols showed the best compatibility with lignin oxyalkylation reaction and promoted lignin’s phenolic hydroxyl group’s reactivity with propylene carbonate, while propylene oxide (PO)-based and biobased polyols (castor oil, soy polyols and cardanol-based polyols) exhibited poor compatibility with the lignin during the oxyalkylation reaction resulting in a two-phase mixture. After optimization, a foam formed by replacing 20% of petroleum-based polyols demonstrated improved mechanical properties in flexible PU foams, meeting the standard requirements for automotive seating applications.

Finally, high-performance novel lignin-based polycarbonate polyols were prepared via a two-step process involving oxyalkylation of lignin with propylene carbonate, followed by transesterification with dimethyl carbonate. The resulting polycarbonate lignin polyols exhibited hydroxyl values (111 to 179 mg KOH/g) and viscosities (11,660 to 25,950 mPa.s) suitable for flexible PU foam formulations. In-depth Nuclear Magnetic Resonance (NMR) analysis confirmed the grafting of long polyether chains onto lignin during the oxyalkylation step and the introduction of multiple carbonate linkages at the end of the transesterification step. Foams were formulated by replacing up to 40% of petroleum-based polyols with synthesized polycarbonate lignin polyols. Additionally, flexible PU foams were prepared by replacing 60% of conventional polyol with a combination of synthesized lignin polyol and soy polyol. Formulated foams demonstrated superior mechanical properties, including enhanced tensile strength, and load-bearing properties, compared to petroleum-based foams. Additionally, the foams exhibited improved thermal stability, shock absorption, and biodegradability.

Persons with disabilities have the right to request and receive reasonable accommodation. Please call the Department of Chemical Engineering and Materials Science at 355-5135 at least one day prior to the seminar; requests received after this date will be met when possible.

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