Exploration of Dynamic Structure-Process-Property Relationships in Vitrimer-Like Materials and Multimodal Polymer-Clay Composites
| dc.contributor.author | Luster, Larry E. | en |
| dc.contributor.committeechair | Bortner, Michael J. | en |
| dc.contributor.committeemember | Martin, Stephen Michael | en |
| dc.contributor.committeemember | Harrison, William L. | en |
| dc.contributor.committeemember | Sarmah, Anubhav | en |
| dc.contributor.department | Chemical Engineering | en |
| dc.date.accessioned | 2026-08-13T08:00:23Z | en |
| dc.date.available | 2026-08-13T08:00:23Z | en |
| dc.date.issued | 2026-08-12 | en |
| dc.description.abstract | When designing and modeling composite materials, it is common to make simplifying assumptions regarding intermolecular interactions so that the composite can be considered as a homogeneous material with predictable behavior. This approach is acceptable for traditional composite processing and in any case where the components of the composite have uniform, static structures after they are incorporated into the bulk material; however, real materials for engineering applications rarely fit these idealized models and the components have specific, non-negligible interactions and transient topologies. This body of work examines two such materials: vitrimeric thermoplastic polymers and polymers reinforced with layered aluminosilicates; specifically, we 1) attempt to deconvolute contributions of bond exchange kinetics and segmental relaxation in a covalent adaptive network comprised of a poly(methyl-methacrylate)-poly(hydroxy-ethyl-methacrylate) copolymer (PMMA-PHEMA) crosslinked with dynamic aromatic disulfide bonds and 2) examine the role of in-situ dehydration on intercalation and exfoliation of montmorillonite agglomerates into nanoplatelets during melt-extrusion of a polyethylene terephthalate glycol (PETG)-montmorillonite-zeolite composite. In both studies, we challenge the fundamental assumptions used to simplify kinetic, thermodynamic, and transport properties of the material and utilize bulk rheological measurements to extrapolate mechanistic understandings of the material behavior that can be exploited in process design to yield desirable properties and morphologies in the end-use material. | en |
| dc.description.abstractgeneral | Dynamically crosslinked polymers (DCPs) have been the subject of increasing research interest in recent years as sustainable alternatives to thermosetting polymers. Covalent adaptable networks (CANs) are DCPs crosslinked by metastable covalent bonds that undergo dynamic exchange reactions. The frequency of these dynamic exchanges increases as CANs are exposed to appropriate stimulus (e.g., light, pressure, heat, or pH). By substituting permanent covalent crosslinks with dynamic bonds, a material that has the chemical resistance and mechanical properties of a thermoset, but can be recycled like a thermoplastic is created. Until recently, CANs derived from thermoset architectures have dominated the dynamically crosslinked polymer literature, but few of the materials generated are suitable for commodity-scale production or extended use for engineering applications—especially at elevated temperatures. Thermoplastic vitrimerics, whose dynamic bonds are introduced as reinforcements in a polymer that is not inherently chemically crosslinked, present scalable, creep-resistant alternatives to analogous thermosets. However, the challenge of deconvoluting overlapping thermal transitions has discouraged development and rigorous characterization of these materials. Similarly, aluminosilicate (clay) reinforced composites are targeted for various applications ranging from structural reinforcement, thermal management, and separation processes. The performance of these composites is heavily influenced by the degree to which the microscale clay aggregates are reduced to nanoscale platelets—a process known as exfoliation. Like vitrimers, the idealized clay composites designed for academic research do not reflect compositions or processing conditions realistic for engineering use-cases, resulting in the development of inefficient material systems and processes. One such example is the incessance of the community on completely dehydrating aluminosilicates prior to extruding incorporating them into a feedstock for melt-extrusion—a decision that ultimately leads to the formation of permanent aggregates that are undesirable for all applications. Here, we present a novel vitrimer-like thermoplastic composed of methacrylate copolymers (P(MMA-co-HEMA)) dynamically crosslinked by aromatic disulfides. This polymer exhibits improvements in thermal stability, mechanical properties, and chemical resistance relative to linear PMMA. By employing torsional rheometry to access a substantially broader temperature window than is typical in comparable studies, we resolve rheological behavior that is consistent with theoretical predictions of how dynamic polymers relax but has not been previously observed empirically. We also present a novel process for exfoliating layered clays during melt-extrusion by introducing—instead of removing—water via a second hydrated particle and controlling the depressurization of the extruder during compounding to prevent adverse effects on the binding polymer. Both of these studies utilize bulk material properties to validate component-level hypotheses of how the system will behave. These findings are then leveraged to develop advanced manufacturing processes that are efficient and scalable. | en |
| dc.description.degree | Doctor of Philosophy | en |
| dc.format.medium | ETD | en |
| dc.identifier.other | vt_gsexam:47447 | en |
| dc.identifier.uri | https://hdl.handle.net/10919/143715 | en |
| dc.language.iso | en | en |
| dc.publisher | Virginia Tech | en |
| dc.rights | Creative Commons Attribution-NonCommercial 4.0 International | en |
| dc.rights.uri | http://creativecommons.org/licenses/by-nc/4.0/ | en |
| dc.subject | CAN | en |
| dc.subject | montmorillonite | en |
| dc.subject | extrusion | en |
| dc.subject | LAOS | en |
| dc.subject | Sticky Rouse | en |
| dc.title | Exploration of Dynamic Structure-Process-Property Relationships in Vitrimer-Like Materials and Multimodal Polymer-Clay Composites | en |
| dc.type | Dissertation | en |
| thesis.degree.discipline | Chemical Engineering | en |
| thesis.degree.grantor | Virginia Polytechnic Institute and State University | en |
| thesis.degree.level | doctoral | en |
| thesis.degree.name | Doctor of Philosophy | en |