Liquid thermoset samples

Hermetically sealed pans should be used for volatile (or liquid) samples. After the liquid sample is placed on the bottom of the DSC pan, it is covered with a lid, and the edges of the bottom and the lid are cold-welded together with a small instrument called a crimper. The process itself is called crimping. In addition to measurements on low-molecular-mass liquids, these sample pans should be used for liquid samples such as unreacted thermosets and when the sample contains volatile components such as residual solvent or low-mass additives whose evaporation one wishes to suppress (these pans are also used for polymers that can release degradation products). Evaporation of these materials is endothermic and may interfere with exothermic events such as... 

At constant conditions, different fluids will diffuse at different rates into a particular elastomer (with their rates raised proportionally by increasing the exposed area), and each will reach the far elastomer-sample surface proportionally more rapidly with decreasing specimen thickness. Small molecules usually diffuse through an elastomer more readily than larger molecules, so that, as viscosity rises, diffusion rate decreases. One fluid is likely to diffuse at different rates through different elastomers. Permeation rates are generally fast for gases and slow for liquids (and fast for elastomers and slow for thermoplastics and thermosets). 

The changes which occur in thermosetting resins undergoing cure have been studied by a variety of techniques. Supported sample methods have been used to monitor the relative changes modulus and damping behavior from the initial low viscosity liquid to the fully cured rubbery or glassy state. Torsional braid analysis (TBA) employs a resin sample impregnated on a... 

The preparation and characterization of the VR and ESR liquid rubbers and of the two-phase epoxy thermosets were described in detail previously (3-6). DGEBA is a solid epoxy resin (Epon 825) from Shell Chemical Company. ESO and ELO are commercial products from Atochem. Samples of VO and crambe oil were obtained from the U.S. Department of Agriculture. All other reagents and solvents were purchased from Aldrich Chemical Co. and Fisher Scientific Co. and used without additional purification. 

Gas chromatography (GC) is restricted in application, since only about 15% of materials are volatile and capable of analysis by GC. Gel permeation chromatography (GPC) is more versatile and is a mode of liquid chromatography (LC) in which soluble components of a complex sample can be separated according to molecular size, a characteristic that is closely associated with the molecular weight. However, only soluble fractions of a fully crosslinked thermoset can be evaluated. 

Other tests have been described by Mosle et al. [16] and Maelhammar [17]. The latter test is a combination of metal-liquid wear and corrosive wear. The apparatus was modified by Volz [18] for thermosets. The volatiles are extracted from the polymer melt, which has been prepared in an injection molding machine and has been sheared through a test gap. Through electrochemical measurements, Volz could prove that significant differences exist in the corrosive action of volatiles separated from injection molded samples of thermosetting polymers. 

Softening and cure are examined with the help of a torsional pendulum modifled with a braid (73), which supports thermosets such as phenolics and epoxies that change from a liquid to a solid on curing. Another method uses vibrating arms coupled to a scrim-supported sample to measure storage and loss moduli as a function of time and temperature. An isothermal analytical method for phenolic resins provides data regarding rate constants and activation energies and allows prediction of cure characteristics under conditions of commercial use (55). 

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