Date of Award

Winter 2024

Project Type

Dissertation

Program or Major

Mechanical Engineering

Degree Name

Doctor of Philosophy

First Advisor

John Tsavalas

Second Advisor

Nate Oldenhuis

Third Advisor

Mrityunjay Kothari

Abstract

Bonding between two polymer films can be achieved through various heat- or chemical-based methods. Recently, our group has discovered the novel phenomenon of deformation-induced bonding (DIB) for solid-state glassy polymers in time on the scale of a fraction of a second at ambient temperatures substantially below the bulk glass transition temperatures (T_g). DIB is achieved by bulk plastic compression, which triggers the molecular mobility of polymer chains to cause interpenetration across the interface even in a glassy regime.

First, we performed a series of experiments to evaluate solid-state, deformation-induced bonding in organic polymer blends composed of films of hydroxypropyl methylcellulose (HPMC) and polyvinyl alcohol (PVA) products. Our findings (Chapter 4) suggest that the use of deformation-induced bonding could shorten welding durations and lower the temperature requirements for polymer adhesion.

Next, this thesis shows the possible mechanism of the new phenomenon of DIB at temperatures below T_g (Chapter 6). Large-scale molecular dynamics (MD) simulations show that active plastic deformation in glassy polymers causes segmental translations of macromolecules, resulting in interfacial interpenetrations and the formation of new entanglements at temperatures well below the bulk (and surface) glass transition temperatures T^b_g (and T^s_g). The molecular-scale dilatations (or densifications) during deformation-induced mobility are identified as the mechanistic basis for this new type of bonding.

Furthermore, MD simulations of bidisperse polymer blends (Chapter 7) examine the role of diluents in the thermophysical and mechanical properties of these systems, which affect the bonding strength of these samples during the DIB process. The results show that moderate concentrations (ϕ≤20%) of low-molecular-weight diluents enhance the number of host polymer chain-ends during deformation at the interfacial region compared to a pure glass sample (ϕ=0%), which improves the possibility of opposite side entanglement formation and bonding strength. In other parts of the thesis (Chapter 8), we compared the DIB to alternative bonding methods in terms of energy and cost. This thesis concludes with a brief summary and future outlook (Chapter 9).

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