Date of Award

Spring 5-2026

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Materials Science

First Advisor

Dr. Ram K. Gupta

Second Advisor

Dr. Serif Uran

Third Advisor

Dr. Tim Dawsey

Keywords

Schiff base diol, Polyurethane, Adhesive, Mechanical strength, Thermal property

Abstract

Recent advancements and trends in eco-efficient bio-based adhesives are explored in recent years. “Eco-efficient” refers to being effective both environmentally and economically. In this study, soy-based polyurethane (PU) adhesives were reinforced with vanillin-derived Schiff base diols (VB and VH) to improve mechanical strength and thermal stability. Two diols synthesized from vanillin and aliphatic diamines butanediamine (BDA) for VB, hexanediamine for VH were incorporated at 5, 10, and 15 weight percentages (wt.%) into a soy-based PU network cured with methylene diphenyl diisocyanate (MDI). Mechanical testing on bonded oak wood showed that adding these crosslinkers noticeably increased adhesive strength. Optimal performance occurred at 10 wt.% loading, yielding a higher tensile strength (approximately 5070 kPa for VH-10wt.%) compared to the control (approximately 1600 kPa). VB-10wt.% exhibited similarly high strength (approximately 4450 kPa), with VH slightly outperforming VB due to its longer flexible chain. At 15 wt.% loading, strength declined, indicating that excessive crosslinker can reduce network efficiency. Thermogravimetric analysis (TGA) showed an increased char yield with 15 wt.% diols, indicating improved thermal stability. Differential scanning calorimetry (DSC) revealed elevated glass transition temperatures (Tg), particularly for VH-10wt.% (Tg ~54 °C) versus ~30 °C for the CNT. The crosslinked adhesives also exhibited high gel content (GC) and negligible degree of swelling (DS) in water, reflecting excellent moisture resistance. Overall, incorporating VB and VH substantially enhanced the PU adhesive’s mechanical performance and thermal resilience, demonstrating an effective strategy for producing high-strength, bio-based adhesives.

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