Altering an Epoxy-Amine Thermoset's Performance Through Varying Mix Ratios

• Main Author: Smith, Kiersten M
• Format: Others
• Published: DigitalCommons@CalPoly 2020
• Subjects: Materials Chemistry; Polymer Chemistry
• Online Access: https://digitalcommons.calpoly.edu/theses/2195; https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=3612&context=theses

Epoxy resins are used in a number of different industries and therefore have application-specific material requirements, from satellites that require materials that operate in space, to paints and coatings that require high scratch resistance and mechanical durability, to medical devices, designed to be in continuous contact with biological fluids. Commercial epoxy products come with manufacturer’s information explaining the epoxy properties and recommended preparation processing conditions, which may include epoxy resin to curing agent mix ratio (Part A : Part B), cure time, and cure temperature, for example. Due to proprietary reasons, it can be difficult to understand why these values are provided, and more importantly, the consequences when deviating from the prescribed recommendations. When manufacturing bioprocessing products for the medical field, a company is under a limited capacity to change materials of construct. Determining how to modify the processing conditions in order to control the material properties of an epoxy would benefit bioprocessing product manufacturers as it would allow them to use the same epoxy that meets the different application-specific requirements of different products. Five different epoxy systems that were designed for medical applications were characterized to determine how variations in preparation and processing conditions, such as mix ratio (by weight) and cure conditions, affect the final properties of the cured epoxy, including: glass transition temperature, chemical resistance, and coefficient of thermal expansion. For each system, it was found that one mix ratio would produce a material with a maximum glass transition temperature, while changing the mix ratio with either excess Part A epoxy resin or excess Part B amine curing agent would result in a decrease in the glass transition temperature. A higher glass transition temperature indicates higher crosslink density, as a more tightly crosslinked network requires more thermal energy to reach the “rubbery” phase. This mix ratio did not always coincide with the manufacturer’s specifications, suggesting that these recommendations are potentially application specific. While variations in the curing agent’s chemical composition impacted the final material properties of epoxy, as expected, it was also found that varying the mix ratio and annealing conditions resulted in changes in epoxy material properties. A wide range of experiments provided critical data that supported the idea that a single epoxy formulation can be used to produce epoxy materials with varied performance properties through modifications in the preparation and processing conditions, while still remaining usable to manufacture products.