Thermal Analysis UserCom 6

Today's building materials such as tile adhesives not only comprise the classical ingredients such as cement and additives - sand, lime, etc. - but also a complex mixture of polymers in the form of dispersions. These polymer additives provide the building materials with the required properties in regard to elasticity, adhesive power, frost resistance, etc. Such complex formulas also require a corresponding number of quality controls during the production. In addition, the increasing competition in this sector necessitates pressing ahead with further development and comparing rival products with one's own.

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Summary

Today, most thermoanalytical measurements are performed with predefined constant heating rates. Despite the great success and wide application of this method, it has been known for forty years that concepts such as thermal effects of a sample exist which must be enlisted in the determination of the experimental conditions [1 - 4], i.e. particularly how the heating rate can be adapted during the analysis. This article describes the basic differences between these two methods with constant or effect-dependent heating rate, their specific advantages and disadvantages and offers tips on the selection of valid experimental parameters using the example of the MaxRes method in thermogravimetry [5].

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References

[1] L. Edrey, F. Paulik, and J. Paulik, Hungarian Patent No. 152 197 (1962)
[2] J. Rouquerol, Bull. Soc. Chim. Fr., (1964), pp 31-32
[3] F. Paulik, Special Trends in Thermal Analysis, John Wiley & Sons, Chichester (1995)
[4] H.G. Wiedemann, D. Nehring, Zeitschrift für anorganische und allgemeine Chemie, 304 (1960) 137
[5] USER COM 4, Information for users of Mettler Toledo thermal analysis systems December 1996, page 4

Summary

When a PE sample is exposed to temperature in the melting range of the crystalline fractions for a certain time, the crystal structure is changed. This phenomenon is known as the memory effect ("thermal memory capacity") and can be measured using DSC. The memory effect is manifested as a deviation in comparison with a DSC curve of a sample without a thermal prehistory. The aim of this article is to show that these deviations have a reproducible magnitude which depends on the temperature and the treatment time. As a result, it is possible to determine how long a sample has been subjected to a particular temperature.

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Introduction

This article investigates the influence of additives as well as the oxidative decomposition on the crystallization of copolymers. Copolymers are used frequently in industry as they are favorably priced and their properties can be very easily changed. In the shaping of thermoplastic, they are crystallized from the melt by cooling. This process induces nonisothermal crystallization which is of great interest for the processing, e.g. by injection molding. The investigated material is a PP-rich polypropylene-polyethylene (PP-PE) copolymer (95 % weight percent). The two samples called A and B contain REPSOL PPR 1042 (melting index 66.5, melting point temperature 162 ° C, density 0.903 g/cm 3 ). Various additives were used:

• Antioxidants (Tinuvin 327, Tinuvin 770, Tinuvin 770-DF, Kronos CL 220 and Irganox BZ15)
  
• UV stabilizers (Quimasorb 144 and Chimasorb 944)
  
• Dyestuffs (Iagacolor 10401, Elf Tex 415, Cromoftal A3R, Cromoftal DPP-BO and Cinquasia RRT 891D)

DSC is used to measure the heats of fusion and crystallization. The influence of additives on the kinetics of the crystallization and on the melting temperatures of copolymers was already investigated in earlier work [1].

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Referenzen

[1] J.J. Suñol, J. Saurina, D. Herreros, P. Pagès, F. Carrasco, „Análisis calorimétricø de copolímeros de base polipropileno-polietileno“ Afinidad 1996, submitted for puplication.

In addition to fats and carbohydrates, proteins, long chain molecules comprising amino acids, are one the most important food components. Depending on the process parameters used, their processing may involve denaturation. As the extent of this denaturation influences the subsequent properties such as water binding power, emulsifiability, etc., it is of great importance for the process control. As the following example shows, the denaturation can easily be measured using DSC.

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Many substances used in the pharmaceutical industry have the ability to form so-called hydrates or solvates. In these, water is not only present on the surface as moisture, but also bound permanently in the crystal. This property is known as pseudopolymorphism and usually leads to a really complex melting behavior being obeserved with such hydrates. A combination of DSC and TGA can be used for a complete characterization.

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In alternating differential scanning calorimetry (ADSC), the temperature is varied sinusoidally as a function of time and is superimposed on a constant underlying heating rate.

Schawe [1] has proposed that the data obtained using the technique may be best interpreted in terms of a complex heat capacity (C_p*) an in-phase heat capacity (C_p' ) and an out-of-phase heat capacity (C_p" ) which are defined as:

|C_p*| = A_HF / A_q (1)

In-phase heat capacity:

C_p' = |C_p*| cos φ (2)

Out-of-phase heat capacity:

C_p" = |C_p*| sin φ (3)

where A_HF is the amplitude of the heat flux modulations, A_q is the amplitude of the heating rate modulations and φ is the phase angle. The phase angle is defined as a negative quantity within the Mettler-Toledo STAR^e software, which is intuitively pleasing because it indicates that the heat flux modulations lag behind the heating rate modulations.

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[1] J. E. K. Schawe, Thermochim. Acta, 260 (1995) 1

The application of ADSC to the glass transition is now reasonably well understood in respect of the complex specific heat capacity C_p* , its in-phase and out-of-phase components, C_p’ and C_p’’ respectively, and the phase angle f between heating rate and heat flux [1-3]. For example, the “step-change” in |C_p*| and C_p’ occurs in a temperature range where the timescale for molecular motion is approximately equal to the period of the ADSC modulations. At lower temperatures, the molecular timescale is much longer than the period, so that the response is glassy, with the value of Cp corresponding to that of a glass; on the other hand, at higher temperatures, the molecular timescale is much shorter than the period, so that the response is liquid-like and gives a value of C_p corresponding to that of a liquid. Clearly, the temperature at which this “step-change” occurs will depend on the chosen period of the modulations; the shorter is the period, the higher the temperature at which this transition occurs.

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[1] J.M. Hutchinson and S. Montserrat, J. Thermal Anal, 47, 103 (1996)
[2] J.M. Hutchinson and S. Monserrat, Thermochim. Acta, 286, 263 (1996)
[3] J.M. Hutchinson and S. Monserrat, Thermochim. Acta, in press (1996)