Thermal Characterization of Silicone

Introduction

We encounter silicones, also called polysiloxanes, every day without even noticing them. For example, silicone rubbers protect car electronics from moisture and contamination, in washing machines they prevent the suds from foaming over, in shampoos they give hair a silky shine, and as silicone resin paints they keep masonry water-repellent while at the same time being permeable to water vapor and carbon dioxide from the interior. But silicones are also found in other applications that require high resistance, such as in medical technology as a pure material in medical tubes, wound pads or orthopedic products, and in electrical equipment as safe sealing and insulation materials. 

Silicone are long-chained molecules containing O-Si bonds. Dependent on their molecular mass and their degree of curing, they can be found as liquids, gels or elastomers [1, 2]. This wide variety of polysiloxanes is associated with very different properties, so it is important to characterize them.

DSC Measurement Parameters

DSC is particularly appropriate for analyzing the behavior of silicones at low temperatures. In the following the thermal properties of a silicone material are determined. To this end, a DSC measurement is carried out, as described in table 1.

Table 1: Measurement Conditions

DeviceDSC 300 Caliris®, P-Module
Sample mass8.75 mg
CrucibleConcavus® (aluminum) with pierced lid
Temperature range-170°C to 100°C
Heating rate10 K/min
AtmosphereNitrogen (40 ml/min)

Measurement Results

Figure 1 depicts the resulting DSC curve. The endothermic step detected at -117.6°C (mid-point) is due to the Temperatura di transizione vetrosaLa transizione vetrosa è una delle più importanti proprietà chimico-fisiche dei materiali amorfi e semi-cristallini, come, ad esempio, vetri, metalli (amorfi), polimeri, ingredienti farmaceutici e alimentari e definisce l’intervallo di temperatura in cui le proprietà meccaniche die materiali variano da duro e fragile a più morbido, malleabile o gommoso.glass transition of the material. It is associated with a change in Specific Heat Capacity (cp)Heat capacity is a material-specific physical quantity, determined by the amount of heat supplied to specimen, divided by the resulting temperature increase. The specific heat capacity is related to a unit mass of the specimen.specific heat capacity of 0.24 J/(g·K). Between -100°C and -30°C, two different effects take place. Firstly, the EsotermicoUna transizione o reazione è esotermica se il materiale genera calore exothermal peak occurs at -85.0°C, which is a Post Crystallization (Cold Crystallization)The post crystallization of semi-crystalline plastics occurs primarily at elevated temperatures and increased molecular mobility above the glass transition.post-crystallization effect. This occurs above the glass transition temperature, when the polymer chains are capable of moving freely and can therefore crystallize. Secondly, with increasing temperature, the endothermic peak detected at -46.4°C represents melting of the crystalline phase.

1) DSC measurement on silicone

Summary

Silicone can withstand high temperatures well due to its material properties. Therefore, it can also be used for different applications in a wider temperature range. However, the DSC investigation shows that these results are crucial for the application range of this material at low temperatures: It will behave very differently at room temperature as compared to a temperature below the melting effect or glass transition.

Literature

  1. [1]
    Biomedical polymers, ROBERT G. HILL, Biomaterials, Artificial Organs and Tissue Engineering, 2005
  2. [2]