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Abstract  

Polyaminobismaleimides (PAMBI) with diphenyl methane, diphenyl ether and hexamethylene segments were synthesized according to Michael type addition reaction. The modification of PAMBIs with 2-glycidyl-phenyl-ether (GPE) was performed in order to ameliorate the toughness of the products. Dynamic mechanical analysis allowed the study of the processes that concur in the material through curing by tracking the storage modulus (E′) and loss factor (tanδ) changes. The small drop of E′ with increasing temperature in the glass transition region argues for crosslinked structures. The viscoelastic behavior revealed complex processes, i.e., overlapping of glass transition temperature range with intra-and inter-crosslinking.

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. Dynamic mechanical analysis (DMA) is a sensitive technique that measures the mechanical response of materials by monitoring property changes with respect to temperature and/or frequency of oscillation. Studies of dynamic mechanical properties are important

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Dynamic mechanical analysis

Thermal degradation of a diglycidyl ether of bisphenol A and 1,3-bisaminomethylcyclohexane epoxy resin system

Journal of Thermal Analysis and Calorimetry
Authors: L. Barral, J. Cano, A. López, J. López, P. Nogueira, and C. Ramírez

Abstract  

Using dynamic mechanical analysis (DMA) we have studied thermal degradation for a system containing a diglycidyl ether of bisphenol A (DGEBA) and 1,3-bisaminomethylcylohexane (1,3-BAC). The changes of dynamic mechanical properties during thermal degradation indicated a shift of the glass transition temperature (T g) to higher temperatures and a decrease in the peak value of the dynamic loss factor (tan δ) with an increasing of aging time. The value of dynamic storage modulus (E′) at the rubbery state showed an increase with aging time, whiteE′ at the glassy state only underwent a moderate change with increased thermal degradation. From these results it can be argued that thermal degradation during the stage prior to the onset of the severe degradation involves structural changes in the epoxy system, as further crosslinking and loss of dangling chains in the crosslinked network.

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Abstract  

The glass transition of lyophilized materials is normally measured by conventional or temperature modulated differential scanning calorimetry (TMDSC). However, because of the weakness of these transitions when protein concentrations are high, these techniques are often unable to detect the glass transition (T g). High ramp rate DSC, where heating rates of 100 K per min and higher are used, has been shown to be able to detect weak transitions in a wide range of materials and has been applied to these materials in previous work. Dynamic mechanical analysis (DMA) is also known to be much more sensitive to the presence of relaxations in materials than other commonly used thermal techniques. The development of a method to handle powders in the DMA makes it now possible to apply this technique to protein and protein-excipient mixtures. HRR DSC, TMA and DMA were used to characterize the glass transition of lyophilized materials and the results correlated. DMA is shown to be a viable alternative to HRR DSC and TMA for lyophilized materials.

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Applications of the new 980 Dynamic mechanical analyser (DMA) to the study of thermoplastic polymers, thermosetting polymers and metal glasses have been discussed in this paper. This instrument has also been used to study impact modified thermoplastics [2] elastomers [3] and metals. DMA is one of the thermo-analytical thechniques available to the research or quality control chemist for evaluating the mechanical properties of materials. With the introduction of the 980 it is anticipated that the disadvantages due to long operation time and complexity inherent in older instrumentation will no longer hold back progress towards the full realisation of the technique.

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Abstract  

New cross-linked poly(esterurethanes) (PEU) based on unsaturated olygo(alkyleneester)diol (OAE), 4,4’-diphenylmethane diisocyanate (MDI) and styrene or methyl methacrylate as curing monomers were prepared. The synthesis of PEU was performed in two steps. In the first step OAE was obtained from adipic acid, maleic anhydride and ethylene glycol. In the second step a prepolymer was obtained in a reaction of OAE with different amounts of 4,4’-diphenylmethane diisocyanate followed by crosslinking using previously mentioned curing monomers. The influence of structure of the poly(esterurethanes) on thermal and dynamic mechanical properties is studied. Thermogravimetric analysis shows that cross-linked poly(esterurethanes) demonstrate high thermal stability. Moreover the dynamic mechanical thermal analysis shows that the presence of styrene cross-linking chains in polymers lead to the phase separation in cross-linked poly(esterurethanes).

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Journal of Thermal Analysis and Calorimetry
Authors: B. Ormsby, G. Foster, T. Learner, S. Ritchie, and M. Schilling

Abstract  

After improvements were made to a modified Polymer Labs MkIII DMTA instrument to facilitate repeatable controlled humidity (RH) experiments using isothermal and thermal scanning conditions, the viscoelastic properties of titanium white pigmented artists’ acrylic emulsion films were measured in tensile mode. The effects of temperature, relative humidity and accelerated ageing regimes on two brands of titanium white paints were explored. These paints are highly responsive to changes in temperature and relative humidity, formulation differences affect properties slightly, and while light ageing had a negligible effect, thermal ageing resulted in decreased storage modulus and increased film density.

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Abstract  

DMA and solid state 13C NMR techniques were used to measure historical parchment samples within the framework of the project (MAP) Micro Analysis of Parchment (EC contract No. SMT4-96-2101) in collaboration with the School of Conservation in Copenhagen. DMA was used in both thermal scan and creep modes. Thermal scans provided information on the transitions associated with the collagen polymer. Microthermal analysis was also used to obtain information on the topography and thermal conductivity of sample areas of 100 μm. Localised heating enabled measurements of softening transitions in the sample. This behaviour is influenced by the chemical composition of parchment. 13C NMR provided information on the carbon atoms associated with the polypeptide chains of the collagen in parchment. The behaviour of samples immersed in water and measured in DMA creep mode was used to measure the shrinkage behaviour of the parchment samples. The different but complementary techniques provided a means for characterising the physicochemical state of parchment samples.

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Abstract  

A description is given of modifications to a dynamic mechanical analyser (DMA) to allow controlled relative humidity (RH) experiments to be performed under isothermal or thermal scanning conditions. Free film samples of polyester melamine paints (under-cured, normal-cured and over-cured) were supplied and the viscoelastic properties measured in the tensile mode of the DMA. A reduction in the glass transition temperature (T g) of up to 10C was found as the controlled RH was increased.

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Abstract  

The aim of this paper is to describe how a dynamic mechanical analyser can be used together with the microwave coaxial line technique. This coupling enables the simultaneous recording of changes in the mechanical properties and moisture content of materials as a function of time or temperature at a selected frequency. The sample is placed either directly under the probe or clamped in the sample holder of the dynamic mechanical analyser. Sample positioning and heating is accurately controlled by the mechanical analyser and its temperature controller. Samples can be subjected to a constant static force, a frequency or both. A micro probe, recently designed for measurements on semi-rigid and rigid surfaces [1], and connected to a network analyser was used to monitor the moisture content of the samples.

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