Date of Award

2024

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Linda Schadler

Abstract

Semicrystalline polymers are widely used in applications ranging from automotive to medical and aerospace. The addition of small amounts of nanofillers to a polymer matrix has been shown to impart significant changes in mechanical, dielectric, and optical properties. A common challenge in creating these polymer nanocomposites (PNCs) is controlling the dispersion of the nanofillers. Recent work has demonstrated methods to control dispersion and organization of spherical nanoparticles (NPs) in compatible matrices. At sufficiently slow crystallization rates in semicrystalline polymers, spherical NPs organize into the amorphous regions to create sheet-like structures of NPs. The micromechanical behavior underpinning changes in bulk mechanical properties in these organized PNCs has not been fully explored. Raman spectroscopy is a robust method for characterization of molecular structures in materials and has been shown as a useful tool in describing micromechanical behavior of neat polyethylene in-situ.In this study, in-situ Raman spectroscopy was performed on semicrystalline polyethylene samples under tensile load to explore differences in micromechanical behavior between neat, filled but unorganized PNCs, and PNCs that have undergone crystallization-induced particle organization. Quenched PNC samples (blended 50k and 100k Mw polyethylene (PE) matrix with 5wt% bimodally grafted SiO2 NPs) show a greater decrease in frequency for peaks assigned to crystalline chains versus quenched neat matrix. Quenched PNC samples show only slight upward shift of amorphous bands, and combined with increased downward shift of crystalline bands, suggests load is transferred earlier to crystalline structures versus neat quenched. An analogy between amorphous phases of spherulites in neat PE and a fiber-matrix composite system is discussed, where the matrix (amorphous) takes much of the strain. In isothermally crystallized PNC tensile samples results support that NPs within interlamellar regions appear to reinforce the amorphous phase by transferring load to the crystalline phase at lower strains, even if large-scale organization was not achieved.

Language

en

Number of Pages

58 p.

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