Aging of polymeric glasses continues to be an active field of investigation within the scientific community. Fundamental questions concerning structural rearrangement together with its related effects on the physical and mechanical properties associated with aging continue to be an intense area of study from both a fundamental and practical perspective. In particular, methods to accelerate the aging process as well as rejuvenate the glass continue to be areas of interest. In this work, we present results from a study to evaluate how pressure conditioning affects both basic physical and nonlinear mechanical properties of glassy networks with controlled crosslink densities. Specifically, we compare effects of pressure conditioning to thermal annealing. The pressure conditioning consisted of hydrostatically loading samples under pressures in the range 130 – 190 MPa followed by a pressure soak. Pressure conditioning was performed at temperatures both below and above the glass transitions of the samples studied. Thermal annealing consisted of heating samples 20°C above their glass transition temperatures and allowing to soak at this temperature for one hour followed by a slow cool to room temperature. Heating and cooling rates never exceeded 1°C/min. The samples studied were aliphatic crosslinked epoxies with controlled crosslink densities in the range 1.5 – 3.5 mol/kg and whose glass transitions were all greater than room temperature. After pressure conditioning was complete, samples were stored at negative 40°C until subsequent testing. Characterization of the pressure conditioned and thermally annealed samples consisted of compression tests and differential scanning calorimetry tests. The measured mechanical and thermal properties (Young’s modulus, yield stress, rejuvenated stress, strain hardening modulus, glass transition temperature) were used to analyze the influence of the mechanical and thermal histories that were imposed on the samples and ultimately how these histories influenced the structure of the polymeric glasses.

Comparative investigation between pressure conditioning and thermal annealing in aging studies of glassy thermosets

254th National Meeting (2017)

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