Doctoral Dissertations

Date of Award

8-2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Mechanical Engineering

Major Professor

Uday Vaidya

Committee Members

Chad Duty, David Harper, Halil Tekinalp

Abstract

Natural fiber-reinforced composites (NFRCs) are increasingly being used in the automotive industry due to the growing push toward sustainability and vehicle lightweighting. NFRCs offer several advantages such as low density, low cost, and good thermal and vibration insulation. However, these also possess some key challenges such as poor compatibility with hydrophobic polymers, which limits their wide range of applications. This research is focused on addressing those challenges using different strategies.

The first strategy used in this study was fiber modification via alkali treatment and fiber sizing with the primary goal of improving the fiber properties and interfacial properties between fiber and matrix. Due to the wide variability within the fiber and fiber type, the effectiveness of alkali treatment varies. Therefore, the first objective was focused on determining the optimal alkali treatment condition and understanding the interplay between alkali treatment and fiber sizing. Among 2, 5 and 8 wt% NaOH treatment conditions, fibers treated at 5 wt% NaOH for 6 hrs showed maximum improvement in tensile and IFSS properties. Sizing treated fiber with commercial sizing agent PP201 at a concentration of 1.5 wt% further enhanced the IFSS properties without a significant reduction in the tensile properties of the fiber. For the second objective, the effect of different sizing approaches and sizing concentrations on the properties of composites was studied. Sizing discontinuous coir fibers during the nonwoven manufacturing process, also termed in-situ sizing throughout the study showed significant improvement in tensile strength compared to ex-situ sized or unsized composites. Furthermore, based on the mechanical and morphological properties, 1.5 wt% sizing concentration was found to be the optimal sizing concentration resulting in composites with a balance of tensile and impact properties.

The second strategy used in this study was – hybridization. For the third objective, coir fiber composites were hybridized by adding a fraction of glass fibers, to obtain the balance between mechanical properties, lightweighting, and environmental sustainability. Lastly, the cumulative energy demand (CED) and greenhouse gas (GHG) emissions related to material production, material transport, manufacturing, and use phase associated with coir fiber composite part were investigated and compared with glass fiber composite counterpart.

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