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Use of dynamic mechanical thermal analysis (DMTA)

Glass transitions of a cracker and its dough

Journal of Thermal Analysis and Calorimetry
Authors: A. Nikolaidis and T. P. Labuza

A Mark III DMTA (Polymer Laboratories, Loughborough, U.K.) was used to measure the glass transition temperatures (T g) of a commercial cracker and its dough, each equilibrated to various water activities covering a range of 0.11–0.75 for the cracker and 0.11–0.90 for the cracker dough. DMTA measures the change in the elastic modulus (E′) and loss modulus (E″), as well as that in tanδ (E″/E′), with temperature. The change in the elastic modulus with temperature for the two systems followed a pattern similar to that found for complex food polymers (gluten, amylopectin), withT g decreasing as moisture content increased. Baking did not change the location of the glass transition curve (T g vs. moisture content); i.e. the curves for raw dough and baked finished product were somewhat superimposable, and similar to the published gluten curve, indicating that for this type of cracker containing ∼5% sugars, the protein fraction is most responsible for theT g curve.

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Journal of Thermal Analysis and Calorimetry
Authors: R. Artiaga, A. Garcia, L. Garcia, A. Varela, J. Mier, S. Naya, and M. Grana

Abstract  

The nickel-titanium alloys are usually known as Shape Memory alloys because of their ability to return to some previously defined shape or size when subjected to the appropriate thermal procedure. Mechanical properties of a nickel titanium wire were investigated by DMTA using cylindrical tension mode. The Young"s modulus, the maximum strain and residual deformation have been calculated. Recovery of previously deformed samples was observed in constant stress temperature ramp tests. Relaxation stress behaviour at temperatures above the austenitic transformation has been studied. The strain and frequency ranges of linear response have been determined by dynamic experiments. Strain amplitude of 0.1% and frequency of 1 Hz have been chosen for the temperature ramp dynamic experiments. A big change between 65 and 95C is observed in the storage modulus. The values of E' at temperatures below and above the transition are essentially constant. Finally, the effects of the frequency at different temperatures have been examined.

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Journal of Thermal Analysis and Calorimetry
Authors: S. Ľalíková, M. Pajtášová, M. Chromčíková, M. Liška, V. Šutinská, M. Olšovský, D. Ondrušová, and S. C. Mojumdar

describes in detail DMTA that is very useful in studying composite structure and performance. DMTA can provide a complete description of the viscoelastic properties by dynamic experiments conducted over a range of time, temperature or frequency. This method

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analysis (DMTA) was performed with a DMTA V Rheometrics Scientific Instrument. These samples were submitted at frequencies of 1, 10, and 50 Hz in the temperature range from −110 to 180 °C in the double cantilever mode. The heating rate was 3 °C min −1 . The

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Abstract  

The correlation of linear data from dynamic-mechanical testing (DMTA) to nonlinear data from standard mechanical testing was attempted for a number of quite different polypropylene-based compositions. For limited composition ranges, correlations between storage modulus and stiffness as well as between loss angle integrals and impact strength could be achieved. Challenges in trying to correlate DMTA tests to standard mechanics clearly result from morphology effects at different scales, both in crystallinity and flow-induced superstructures (orientation) and in multiphase impact copolymers or composites. While a relative scaling turned out to be easy, absolute prediction is difficult.

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Abstract  

A sensitive method to characterize the thermomechanical behaviour of fiber reinforced composites is the dynamic mechanical thermoanalysis (DMTA) method. A Round-Robin-test with five different institutes was conducted to determine the role of the fiber orientation, processing conditions, test apparatus, the mode of loading, and the matrix materials on the determination of the glass transition temperature (Tg). The result shows that the DMTA is a suitable method to analyze Tg of long fiber composites. However, some major problems have to be taken into consideration: - A direct comparison of results from different DMTA-systems is not possible - The real temperatures in the specimens deviate from the temperatures displayed by the DMTA measuring system - There is no clear and common evaluation method for the glass transition temperature.

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Abstract  

In the present work, gelation and vitrification experimental data are obtained by TMA and DMTA techniques using the same thermoset based on an epoxy-amine system. The results show that the times obtained are not equivalent and depend on the technique used. An attempt has been made to compare both determinations using the degree of cure obtained by means of DSC technique. The principal conclusion that we want to emphasize is that it is the conversion degree and not the time of the phenomenological changes that take place during cure, that is the link to connect and interrelate the results obtained with different techniques. A method is also described for constructing the TTT diagram with only DSC and TMA or DMTA data.

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Abstract  

The temperature dependence investigated by means of DMTA of dynamic storage modulusE′, dynamic loss modulus E″ and loss tangent tgδ of blends obtained from polyamide 6 and poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (Biopol D600G) indicated, that the dynamic mechanical properties of the blends containing up to 40% Biopol D600G are governed by the properties of polyamide 6. First at the 50% Biopol D600G content in the blend the transitions of the Biopol phase become visible and dominant. The shifts of the loss modulus maxima of the blends might indicate some interactions between the blend components in the amorphous phase.

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Abstract  

Blends obtained from polyamide 6 and polyester or polyether polyurethanes were investigated by means of DMTA. The blends were prepared by compounding in a twin-screw Brabender —Plasticorder. Changes in composition did not influence the glass temperature of the amorphous fraction of the polyamide, but also no distinct transition for separated polyurethane soft segment was visible. Therefore the blends seem to be multiphase systems, where the elastomeric polyurethane phase is dispersed in a continuous polyamide phase. From changes in the β relaxation region of the polyamide better miscibility of polyester polyurethanes comparing to polyether polyurethanes was explained by hydrogen bonding in the common amorphous phase.

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