Title

Rheology, structure, and properties of new phosphate glass/polymer hybrids

Date of Award

2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

First Advisor

Joshua Otaigbe

Advisor Department

Polymers and High Performance Materials

Abstract

Physical modification of structure and properties via polymer blending and reinforcement is a common practice in the plastics industry and has a large economic advantage over synthesizing new polymeric materials to fulfill new material needs. Despite the large amount of interest in polymer blends and composites, the currently available commercial materials cannot satisfy the growing need for new advanced materials. This need is being addressed in part by inorganic/organic hybrid materials. By blending low-TG phosphate glasses with polymeric materials, a new class of inorganic/organic hybrids can be created. These hybrids can be processed conventionally with glass loadings of up to 60% by volume or 90% by weight, making it possible to obtain significant improvements in properties that are impossible to achieve from classical polymer blends and composites. This class of inorganic/organic hybrids containing both the inorganic low-TG phosphate glass (Pglass) and the organic polymer are very unique materials because both hybrid components are fluid during processing. Thereby, providing the ability to tailor both the hybrid morphology and properties in unprecedented ways through carefully controlled processing. This dissertation discusses the continuing research into low-Tg tin fluorophosphate glass blended with commodity resins. The specific resins of interest are low density polyethylene (LDPE), polyamide 12, and polyamide 6. The shear rheology and the extensional flow characteristics of LDPE hybrids were studied to understand hybrid behavior under flow characteristics typical of many polymer processing techniques. The elongational flow was also utilized to generate unique morphologies, enhance crystallinity, and to alter polymer chain orientation. The extension of this field into interacting commodity resins like polyamide 12 and polyamide 6 yielded new hybrids with unprecedented properties. Polyamide 12 hybrids were used to build the first processing/structure/property relationships for hybrid materials. The effect of processing speed on the crystalline properties, as well as, the tensile mechanical properties was determined. Further studies of Pglass/polyamide 12 hybrids examined their rheological behavior under conditions that the materials are likely to encounter during processing and use. The application of a theoretical viscoelastic emulsion model pointed to a high degree of interaction between the Pglass and polymer phases at elevated temperatures. By changing the polymer to polyamide 6, the sites for potential interaction between the Pglass and the polymer chains was effectively doubled. This yielded the first evidence of melt-miscibility between the inorganic Pglass and an organic polymer. The high degree of interaction also yielded counter-intuitive mechanical properties and glass transition temperature effects described in this dissertation. The effect of Pglass on the glass transition temperature of polyamide 6 was further studied using advanced nuclear magnetic resonance spectroscopy and broadband dielectric spectroscopy, generating fundamental insights into the molecular origins of the unique properties observed for these hybrids. Overall, the experiments suggest that more complicated theories that explicitly take into account the Pglass/polymer interactions, shape factor, and size distributions of the dispersed Pglass phase may be necessary for more accurate modeling of these special hybrid systems with enhanced benefits. Additionally, the new knowledge gained should provide useful guidelines for future experimental studies and theory development of the little-studied phosphate glass/polymer hybrid systems.