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Table of Contents:
TA Tip
- Heat capacity determination at high temperatures by TGA/DSC; Part 2: Applications
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- QUANTOS automatic powder dosing for small sample sizes
Applications
- The characterization of olive oils by DSC
- Tips for method development in 3-point bending DMA measurements
- Elastomer seals: Creep behavior and glass transition by TMA Tips and hints
- Temperature and enthalpy adjustment of the high pressure DSC827e
The characterization of olive oils by DSC
Can olive oils be used for frying? What are the optimal storage conditions for these products? These questions are discussed in the following article based on the results from different DSC experiments. OIT and OOT measurements were performed to characterize oxidation stability. Crystallization and melting behavior was also investigated.
Introduction
Oxidation stability is an important criterion for assessing the shelf life and quality of different products. Oxidation stability can be characterized by the OIT (Oxidation Induction Time) [1] or the OOT (Oxidation Onset Temperature) [2]. The OIT of a material is measured in an oxygen atmosphere at a particular isothermal temperature. It is the time from when the material is first exposed to oxygen up until the onset of oxidation. In contrast, OOT experiments can be performed more rapidly. The OOT of a material is measured in a dynamic measurement in oxygen. The OOT is defined as the temperature at which oxidation of the material begins, i.e. the onset temperature of oxidation.
The advantage of OIT is that it offers better reproducibility than OOT. Furthermore, the values obtained at particular temperatures can be more meaningfully compared. High-pressure DSC can be used to increase the oxygen concentration. This allows reactions to be performed more rapidly at lower temperatures. OIT and OOT measurements can however be quite easily performed with standard DSC instruments.
In this article, OIT and OOT measurements of edible oils used in the food industry (olive oils) were performed. The crystallization and melting behavior of the oils was also characterized.
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Literature
[1] ASTM E-1858 Standard Method for Determining Oxidation Induction Time of Hydrocarbons by DSC.
[2] ASTM E-2009 Standard Test Method for Oxidation Onset Temperature of Hydrocarbons by DSC
Tips on method development for DMA measurements in 3-point bending
In the 3-point bending mode, an offset force has to be specified in the method in addition to the maximum displacement and force amplitudes. In this article, we describe a possible procedure for determining the offset force and the other measurement parameters. We also estimate the uncertainty of the resulting 3-point bending modulus values.
Introduction
Ceramics, metals and composite materials are usually measured in DMA in the 3-point bending mode (see Figure 1). In this mode, the sample is held in position in the clamping assembly by an offset force (preload force) applied to the sample. The offset force must be greater than the amplitude of the force applied to the sample otherwise the sample will lose contact with the clamping assembly. In 3-point bending measurements, the offset force is usually provided as a “constant current offset force” (details are given in the next section).
In this article, we explain how measurement parameters can be determined for 3-point bending experiments. We also estimate the uncertainty of the resulting 3-point bending modulus values.
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Figure 1. In the 3-point bending mode, the sample is held in the clamping assembly by the offset force, Fs. Above: Without the offset force, there are times when no force is exerted on the sample. Below: The sample is only held in the clamping assembly when Fs > FA |
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Elastomer seals: Creep behavior and glass transition by TMA
This article describes how thermomechanical analysis (TMA) can be used to characterize the creep and viscous flow behavior of two different types of elastomers. This was done by means of different isothermal creep and recovery measurements and thermally stimulated creep (TSC) experiments. These methods allow the glass transition and other relaxation processes (e.g. reversible flow relaxation) to be measured with high sensitivity. Elastic deformation and the viscous flow of elastomers can also be determined. The elastomers studied were SBR (styrene-butadiene rubber) with different degrees of vulcanization and EPDM (ethylene-propylene-diene rubber) containing different amounts of carbon black.
Introduction
Hardness, glass transition, creep and the viscous flow component are some of the more important properties that have to be taken into account when elastomers are used for sealing applications.
The hardness of a material is determined by its elasticity and modulus and predicts the deformation capacity under pressure or load. The determination of the glass transition and the temperature retraction method (ASTM D1329) are often used to characterize the low-temperature sealing performance of such elastomers.
The term “creep” refers to the time- and temperature-dependent elastic and plastic deformation of a material when it is subjected to a load or stress. Creep deformation consists of two components: reversible creep relaxation and irreversible viscous flow. The time-independent elastic deformation that also occurs under load is not considered as being part of creep deformation. The creep deformation caused by reversible creep relaxation recovers over time when the stress is reduced or removed. This is a positive factor in sealing applications. Viscous flow however causes permanent deformation and geometry change and often leads to product failure.
These properties can be readily investigated using thermal mechanical analysis (TMA) by performing isothermal creep and recovery experiments and thermally stimulated creep (TSC) measurements. The results obtained from SBR (styrene- butadiene rubber) with different degrees of vulcanization and from EPDM (ethylene-propylene-diene rubber) containing different amounts of carbon black are discussed in detail.
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