Thermal Analysis UserCom 23
Thermal Analysis UserCom 23; Table of Contents:
- How to determine optimum experimental parameters for DMA measurements
- Evaluation and interpretation of peak temperatures of DSC curves. Part 1: Basic principles
- Photocalorimetric simulation of the light curing of adhesives
- Characterization of vegetable oils by DSC
- Influence of the chain structure of polymers on their flow behavior
Tips and hints
- Unusual sample properties as an origin of artifacts
- Influence of the heating rate: Melting and chemical reactions
Evaluation and interpretation of peak temperatures of DSC curves. Part 1: Basic principles
The peak temperature is an important experimental value in DSC measurements. Systematic differences in this quantity can occur depending on the measurement conditions and the origin of the peak. The article explains the reasons for these differences and discusses the possibilities for correcting them. If proper attention is paid to the points concerned, samples can be more reliably compared and more meaningful data is obtained.
Photocalorimetric simulation of the light curing of adhesives
Light-curing adhesives are nowadays widely used in the electronics industry to fix precision parts and electrical connections accurately in place. In the following article we will describe how such processes can be investigated using photocalorimetry.
Modern electronic components consist of a multitude of miniaturized parts and connections. In production processes, these have to be fixed accurately in place.
One way to do this is to use light-curing adhesives that cure within a few seconds. The technique has several important advantages: the components are not subjected to thermal or mechanical stresses and the actual fixing process takes place very quickly.
This article describes how we investigated the curing behavior of a technical adhesive used in the manufacture of access arms for the read/write heads of hard disk storage devices. The approach chosen was to simulate the production methods in a DSC-photocalorimeter system, and to analyze the cured samples with respect to their postcuring behavior. The results were then compared with measurements of real samples taken from different access arms.
Figure 1 shows a typical access arm. The comparison measurements were performed using small samples (approx. 0.4 mg) cut out from the region marked “sample”.
Figure 1. Access arm for moving the read/write head over the surface of a disk in a hard disk storage device. A small sample of about 0.4 mg was cut out from the position shown and analyzed by DSC.
Characterization of vegetable oils by DSC
Differential Scanning Calorimetry (DSC) is used to characterize very many different types of materials in research, product development and quality control.
The crystallization behavior of fats and oils has been studied by DSC methods for many years.
This article presents some interesting DSC measurements performed on vegetable oils. Vegetable oils (or fats, depending on their consistency) are plant constituents obtained from the seeds or fruit pulp by pressing and/or solvent extraction followed by evaporation of the solvent. Vegetable oils consist mainly of triglycerides. Chemically, triglycerides are tri-esters, formed by the esterification of glycerol with three long-chain carboxylic acids (fatty acids).
In natural oils, triglycerides contain many different fatty acids. A natural oil is therefore always a mixture of different triglycerides. In addition, the oil contains different amounts of partial glycerides (i.e. mono- and diglycerides) and other constituents (e.g. phospholipids, sterols, vitamins, etc.), depending on the origin of the oil and the type of processing.
The crystallization behavior of a fat or oil is very sensitive to its composition and can easily be measured by DSC. The DSC curve obtained from an oil sample is characteristic of the particular oil and serves as a “fingerprint”. DSC is in fact an excellent method for determining differences between oils, for example between refined and natural oils.
Influence of the chain structure of polymers on their flow behavior
The molecular architecture of polymers (molecular weight, molecular weight distribution, long chain branching, etc.) strongly impacts the processing behavior of elastomers as well as the vulcanizate properties. An efficient, specific optimization of the processing conditions and vulcanizate properties therefore requires a quantitative correlation between the technical properties and the molecular architecture of the polymer.
Since the molecular architecture of high molecular weight polymers such as EPDM is difficult to analyze using standard methods (e.g. GPC), alternative measurement techniques are necessary for a complete and accurate characterization.
Thimm and Maier [1, 2] have shown that dynamic mechanical analysis in the regime of viscous flow can be used for a quantitative characterization of the chain architecture. This article demonstrates how this is done in practice using measurements performed with a dynamic mechanical analyzer (DMA) and a rheometer.
 W. Thimm, C. Friedrich, M. Marth, J. Rheol 43,6 (1999)
 Maier et al., J. Rheol 42, 1153-1173 (1998)