Abstracts
Learn about student research from a variety of different topics
The effect of UV and thermal processing on the properties of a UV-curable polymer fabricated with 3D printing was studied. The polymers studied were proprietary methacrylate based resins (Formlabs) and samples were printed directly in test geometries. Uniaxial compression tests at room temperature were performed for Young’s modulus, Poisson’s ratio, and yield stress. Thermal tests using a Differential Scanning Calorimeter (DSC) described the glass transition temperature range, physical aging and (additional) high-temperature reactions of the samples. Post-processing consisted of either additional UV exposure time or high temperature “soak” time (or both). These indicated that post-processing has a pronounced effect on the mechanical and thermal properties. Both aspects of post-processing (UV and high-T soaks) increase the yield stress, the modulus and the glass transition. Combining high-T soaks with additional UV exposure is particularly effective.
Diglycidyl ether of bisphenol A (DGEBA) epoxy reacts with diethanolamine (DEA)
through a complex zwitterionic chain-growth reaction. This formulation has the advantages of
through a complex zwitterionic chain-growth reaction. This formulation has the advantages of
1) a ceiling temperature (reducing the risk of thermal runaway reactions);
2) reactants of relatively
low toxicity;
low toxicity;
3) a living polymerization that imparts a self-healing nature; and
4) an acceptably high Tg making it appropriate for engineering applications.
In the present paper, the time and extent of cure at the gel point is found over a wide
range of temperatures. This builds on previous studies that provide gel point values at only a few temperatures (65°C, 70°C and 90°C). Here, we extend this to 55°C to 160°C and find that the extent of cure at the gel point to be 0.40±0.05 for all cases. This agrees with theoretical predictions if proton transfer is prevalent during the reaction which result in a step-growth-like network structure. Finally, the gel point measurements are combined with prior glass transition temperatures to produce a time-temperature-transformation diagram. Techniques used are rheology, bubble viscometry, and micro-calorimetry. Theories used were those of Carothers and of Flory-Stockmayer. Analysis of the shear moduli after being reduced by their frequency power-law was found to give a better prediction of the gel point than analysis of the moduli themselves.
range of temperatures. This builds on previous studies that provide gel point values at only a few temperatures (65°C, 70°C and 90°C). Here, we extend this to 55°C to 160°C and find that the extent of cure at the gel point to be 0.40±0.05 for all cases. This agrees with theoretical predictions if proton transfer is prevalent during the reaction which result in a step-growth-like network structure. Finally, the gel point measurements are combined with prior glass transition temperatures to produce a time-temperature-transformation diagram. Techniques used are rheology, bubble viscometry, and micro-calorimetry. Theories used were those of Carothers and of Flory-Stockmayer. Analysis of the shear moduli after being reduced by their frequency power-law was found to give a better prediction of the gel point than analysis of the moduli themselves.