UserCom44. Термический анализ

Safety is an important aspect in process development in the chemical industry. This article, describes how reaction calorimetry and DSC can be used to quickly assess the thermal hazard potential of chemicals and chemical reactions.

Introduction

In recent decades, numerous serious accidents have occurred in chemical production plants. Many of these accidents have resulted in serious injuries or even to the death of personnel and have often had a dramatic impact on the local environment. In many cases, the accidents are caused by processes that get out of control due to technical problems. Such so-called thermal runaways can result in disastrous explosions. This article illustrates how important information for assessing the thermal safety of chemicals and processes can be obtained using reaction calorimetry and DSC analysis.

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In many applications, such as in cables or seals, rubber blends must possess both excellent mechanical properties and good flame-resistant properties. This article shows how flame resistance can be easily determined by TGA measurements and how the combination of mechanical and thermogravimetric measurements can be employed to optimize properties.

Introduction

In the development of flame-resistant rubber blends, many properties have to be optimized through the right choice and combination of constituents. In traditional compounding techniques, a high content of inactive fillers is used to improve flame-protection properties. This, however, always has a negative effect on mechanical properties.

In the following sections, we present a physically motivated concept that offers the possibility of specifically improving both flame protection and mechanical properties.

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Photopolymerization is nowadays a widely used process. Systems are used for medical applications, for example in dentistry, for adhesive applications, in coating technology, and quite recently for 3D printing [1]. This article describes how the curing behavior of a two-component UV-curing sample can be investigated.

Introduction

Photochemical polymerization is an alternative to thermal polymerization in which a sample is heated and then begins to polymerize or cure. In photochemical polymerization, a so-called photoinitiator is excited on exposure to radiation (UV and visible light). The initiator forms radicals or ions that then induce polymerization [2, 3].

This type of polymerization takes place at low temperatures and occurs rapidly. DMPA (2,2-dimethoxy-2-phenylacetophenone, Figure 1) is often used as photoinitiator for methacrylates.

This article describes the photopolymerization of a two-component sample (methacrylate) using DMPA. Figure 1 shows the structural formula of DMPA. The compound acts as a radical photoinitiator. As such, it decomposes under the action of light of a suitable wavelength into a methyl radical (·CH₃) that attacks the carbon-carbon double bonds in the material to be cured (in this example, the methacrylate molecule), and thereby starts the polymerization process. Polymerization is interrupted when two radicals react with each other. The process can also be interrupted or influenced if the radical chain starter is no longer formed, for example by switching off the UV lamp [3].

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References

[1] Wikipedia.
[2] Kunsstoffkompendium, Adolf Franck, Bernd Herr, Hans Ruse, Gerhard Schulz, Vogel Verlag.
[3] Photopolymerization kinetics of multifunctional monomers, Ewa Andrzejewska, Prog. Polym. Sci. 26 (2001), 605–665.

Many different sorts of lipstick and mascara are nowadays available. The most important characteristics of these products are that the effect lasts a long time, that the products are easy to apply and easy to remove, and that they are physically and chemically stable and do not irritate the skin. The waxes and oils in lipstick are responsible for ease of application; carbon black is often used as pigment in mascara. Thermal analysis techniques allow the quality of these types of cosmetic products to be easily checked.

Introduction

There is an ever increasing demand for lipsticks, mascara, hair colors and creams on the cosmetic market. Cosmetic products often have complex formulations, which is the reason why good analysis techniques are needed to monitor the quality of such products.

The following application examples show how DSC and TGA were used to analyze different types of lipstick and mascara.

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Tricalcium phosphate (TCP) is one of the main constituents of bone replacement materials which find wide use in medical and dental applications for bone grafting and for implants. This article shows how TGA/DSC and TMA can be used to investigate the synthesis of tricalcium phosphate and to determine the transition temperatures of different TCP polymorphs.

Introduction

From the chemical point of view, bones consist of 60% calcium phosphate. It therefore seems obvious to use synthetic calcium phosphate compounds as bone replacement material. Bone replacement materials are needed for the production of ceramic bone implants and to repair bone defects.

A particularly important aspect of bone replacement materials is their absorbability by newly produced bone material in the body. A prerequisite for this is biocompatibility of the bone replacement material. The calcium phosphates used for bioceramics are mostly hydroxylapatite or hydroxyapatite (HA), alphatricalcium phosphate (α-TCP), beta-tricalcium phosphate (β-TCP) or biphasic calcium phosphate (HA+ β-TCP).

Hydroxylapatite is the slowest to be absorbed and exhibits the greatest mechanical stability. In contrast, α- and β-TCP are more soluble in the body’s bone material. This increases their absorption rate and shortens the healing process. For this reason, α-TCP and β-TCP are often the main constituents in bone replacement material used to fill bone defects that for example can occur in the insertion of dental implants [1] or in ceramic bone implants [2, 3].

This article shows how the synthesis and the phase behavior of TCP can be investigated by TGA/DSC and TMA.

The starting material for the production of TCP is a stoichiometric mixture of calcium hydrogen phosphate (CaHPO₄) and calcium carbonate (CaCO₃). The overall reaction is shown in eq 1.

2·CaHPO₄ + CaCO₃ → Ca₃(PO₄)₂ + (1) H₂O + CO₂

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References
[1] Constantz B. R., Ison I. C., Fulmer M. T., Poser R. D., Smith S. T., Wagoner M. V., Ross J., Goldstein S. A., Jupiter J. B., and Rosenthal D.I., Science 267, 1796 (1995).
[2] Langstaff S., Sayer M., Smith T. J. N., Pugh S. M., Hesp S. A. M., and Thompson W. T., Biomaterials 20, 1727 (1999).
[3] Wang J. X., Chen W. Q., Li Y. B., Fan S. J., Weng J., and Zhang X. D., Biomaterials 19, 1387 (1998).

When polymeric binders are used in paints with hydrophilic pigments such as titanium oxide, the pigments must be treated beforehand with polymers that are compatible with the binder. Otherwise, large agglomerates can form due to poor adhesion between the binder and the particles. This can lead to brittle films and fractures in the paint coating. This article shows how TGA and DSC can be used to determine important properties of the coating using titanium dioxide as an example.

Introduction

Paints consist mainly of pigments, a binder and a solvent. In addition, numerous additives are used in order to obtain a multitude of specific properties, for example drying time, flow behavior, UV stability, gloss, etc. The binder binds the pigments as a thin film on the substrate after the solvent has dried. Binders are usually polymers (e.g. acrylates, polyurethanes, polyesters, melamine, etc.).

If polymeric binders are used together with hydrophilic pigments such as titanium dioxide (TiO₂), large agglomerates of pigments can be formed due to poor adhesion between the binder and the particles. This can lead to brittle films and to fractures in the coating of the paint. To prevent this, the particles are coated beforehand with polymers that are compatible with the binder.

This article describes how TGA and DSC can be used to investigate important properties of the coating such as thermal stability, the influence of polymerization time on the thickness of the coating, and the glass transition temperature, using titanium dioxide as an example.

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For many practical applications, it is important to be able to quickly and reliably identify polymers. This article describes how semicrystalline polymers can be identified by measuring their melting points using DSC.

Introduction

Thermoplastics consist of macromolecules. In the melt, the molecules are randomly entangled. Amorphous polymers are solid at temperatures below the glass transition. The molecules are arranged similar to in a melt. Besides an amorphous phase, semicrystalline thermoplastics also have a crystalline phase in which the molecular segments are arranged almost parallel to one another.

Melting of the crystallites produces broad melting peaks in the DSC curves. The crystallites are relatively small and surrounded by amorphous regions. The corresponding structure is referred to as a rigid amorphous region due to the restricted mobility of the molecular segments near the surface of the folds of the crystals. The rigid amorphous parts are not directly identified in a DSC measurement curve. In addition to these amorphous regions, there are also mobile amorphous regions that exhibit a glass transition (Figure 1).

On heating, the crystalline regions do not melt at a fixed temperature but rather over a temperature range. The melting point of crystallites depends on their size. Small crystallites melt at lower temperatures than large crystallites. Since crystallites of different size are present, polymers always melt over a temperature range.

This is the reason for the relatively broad melting peak observed in their DSC curves. The peak can be characterized by the peak temperature and the peak width.

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