Thermal Analysis

We help determine the thermal property and behavior of materials as it is being heated.

Thermal Analysis

We help determine the thermal property and behavior of materials as it is being heated.

Figure 1: FTIR spectrum and DSC curves of the High-Density Polyethylene (HDPE)

Determination of Type of Reaction (exothermic or endothermic) using Differential Scanning Calorimetry (DSC)

The FTIR spectrum of polyethylene is shown in Table 1 of Figure 1. However, the data obtained in the FTIR spectrum is not enough to differentiate whether the material is LDPE or HDPE since both of these materials are made from the polymerization of ethylene and are both thermoplastics. That is why in order to differentiate the two materials from each other, the analysis is partnered with Differential Scanning Calorimetry (DSC).

Table 2 shows the plot of the DSC curves for the High-Density Polyethylene (HDPE) and Low-Density Polyethylene (LDPE) polymer materials where they exhibited different melting points (Tm).

The main difference between HDPE and LDPE is found in their structural composition, wherein HDPE is more rigid and has less branching compared to LDPE, as shown in Figure 2. This makes HDPE have a higher tensile strength and stronger intermolecular forces than LDPE. As a result, its melting point is expected to be higher than that of LDPE. Thus, HDPE can be differentiated from LDPE through the differences in their melting points.

Figure 2: Structural composition of HDPE and LDPE

Determination of transition glass (Tg), melting (Tm), crystallization (Tc), and degradation (Td) temperatures of polymers and materials

For polymer materials, Differential Scanning Calorimetry (DSC) is a very useful technique used to investigate their response towards heating. It basically measures the rate of heat flow and compares differences between the heat flow rate of the test sample and known reference materials. The difference gives information on the material composition, crystallinity and oxidation.

Figure 3: DSC Curve of PLA-OCS-3NPCC-MA 5050 Sample during First heating

Figure 3 shows the DSC curve of a certain polymer material. From the plot, the following information was obtained: (1) Glass transition temperature (Tg), which is an endothermic process characterized by a downward curve. It is the temperature at which the polymer changes its state from being brittle to soft, which basically describes the mobility of the polymer chain. This is very important for identifying the flexible and rigid applications of a polymer (e.g., hardness and elasticity). (2) Melting point (Tm) of a polymer, which is also an endothermic process characterized by a downward curve. Determining the melting point (Tm) is very important since it gives manufacturers an idea of how the polymer should be processed or handled. (3) Crystallization Temperature (Tc) of a polymer is an exothermic process characterized by an upward curve. It is the temperature at which the polymer molecules rearrange themselves into ordered arrangements.

Figure 4: DSC Curve of Polymer Material with Varying Ratio of Composition

Change on thermal behavior due to modification in the composition

Furthermore, Figure 4 reflects the change in the thermal behavior of a sample due to a difference or modification of its composition. From the DSC curve, a shift in the melting temperatures of the polymers, as well as the peak intensities, were observed as the composition was varied.

Thermogravimetric Analysis (TGA) is a technique that determines the thermal stability of a sample by monitoring the change in weight loss as a function of the temperature. The composition can be determined through the various weight loss events which occurred in the sample.

Figure 5: Stacked TG-DTG Curves of TM9

Powdered concrete when heated reveals composition through various weight loss events

Figure 5 shows the stacked TG-DTG curves for a powdered concrete sample. The TG curve exhibited a three-step weight loss. The first weight loss is attributed to the loss of moisture in the sample, while the second weight loss is attributed to the several decomposition reactions that occurred in the sample, and the third weight loss is attributed to the degradation of the material itself. Moreover, it can be observed that a residue was obtained, which corresponds to the amount of inorganic materials (e.g., fillers) present in the powdered concrete.

Furthermore, the DTG curve shows the decomposition temperature range of the material as well as the temperature of the peaks where the degradation is very significant.

Detection and identification of substances released when a material is being heated

TGA coupled with FTIR is the most common type of evolved gas analysis (EGA). It is a hyphenated technology very useful for the characterization of complex multi-component materials wherein the quantitative compositional analysis capabilities of TGA is combined with the identification capabilities of FTIR.

Figure 6 shows the TG-DTG curve of a rubber tire sample due to the monitoring of the weight loss as a function of temperature was measured by TGA. The evolved gases formed as a result of heating were analyzed by FTIR and the resulting spectra are shown in Figures 7 and 8.