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The aim of this lab experiment was to prepare and analyze samples of poly(lactic acid) (PLA), methyl methacrylate (MMA), and epoxy resins using Differential Scanning Calorimetry (DSC). DSC is a powerful technique for characterizing thermal transitions in materials and polymers, including glass transitions, crystallization, and melting points. This report presents the results obtained from DSC analysis of the three materials and discusses the nature of the main phase transitions and processes occurring in them.
Differential Scanning Calorimetry (DSC) is a widely used technique in materials science to measure the heat changes associated with thermal transitions in materials and polymers.
It provides valuable information about the thermal behavior of materials, including their glass transitions, melting points, and phase transitions [1]. DSC analysis is based on measuring the heat capacity of a sample relative to a reference temperature and an empty aluminum sample pan. By analyzing the heat flow in and out of the sample, DSC can determine the amount of heat released or absorbed during various processes.
The experiment involved the analysis of three different samples: poly(lactic acid) (PLA), methyl methacrylate (MMA), and epoxy resins.
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The following procedure was followed:
For PLA, the temperature was raised to 220°C.
The DSC analysis produced distinct thermal traces for each of the three samples, reflecting their varying chemical structures and thermal behaviors. The area under the curves represented the heat released or absorbed during the processes. Below are the DSC traces for PLA, epoxy resins, and MMA (Figures 1.1, 1.2, and 1.3, respectively).
| Sample | Mass (mg) | Glass Transition (°C) | Crystallization (°C) | Melting Point (°C) | Enthalpy (J/g) | Crystallinity (%) |
| PLA | 15.185 | 68.7 | 112.5 | 177.9 | 93 | 45.7 |
| Epoxy Resins | 8.568 | N/A | 115.0 | 200.0 | N/A | N/A |
| MMA | 16.081 | N/A | N/A | N/A | N/A | N/A |
Figure 1.1: DSC trace for PLA (Heating Cycle 1)
Figure 1.2: DSC trace for Epoxy Resins (Heating Cycle 1)
Figure 1.3: DSC trace for MMA (Heating Cycle 1)
In Figure 1.1, the DSC trace for PLA shows the first heating process from 25°C to 220°C. PLA undergoes a glass transition (g) at approximately 68.7°C, followed by crystallization (cr) at 112.5°C, and finally, melting (mp) at 177.9°C. The linear arrangement of PLA molecules contributes to its flexibility during the glass transition.
Figure 1.2 illustrates the DSC trace for epoxy resins, which exhibits an exothermic peak during crystallization (cr) at around 115°C. The highest energy release occurs during this transition, followed by a significant drop as the sample melts at 200°C. The second heating cycle indicates the melting of the epoxy resin (cr m).
Figure 1.3 represents the DSC trace for MMA, displaying a sharp peak at 113.5°C during the first heating cycle. This peak corresponds to the polymerization of MMA, releasing energy. In the second heating cycle, there is no significant change, indicating the stability of poly(MMA) at this temperature.
The results obtained from the DSC analysis provide valuable insights into the thermal behavior of PLA, epoxy resins, and MMA.
For PLA, the glass transition (g) indicates the point at which the material becomes more flexible due to molecular rearrangements. The crystallization (cr) and melting (mp) points represent the transition from an amorphous state to a crystalline state and the subsequent melting of the crystalline regions, respectively. The calculated crystallinity of PLA is 45.7% based on the enthalpy of fusion (ΔHftot) and the enthalpy of crystallization (ΔHfcryst) using the formula:
Crystallinity (%) = (ΔHftot / ΔHfcryst) x 100
However, for epoxy resins and MMA, detailed crystallinity calculations were not possible due to the absence of specific phase transitions in the DSC traces. Epoxy resins exhibited an exothermic peak during crystallization, followed by a sharp drop during melting, indicative of their polymerization and subsequent melting during the first heating cycle. MMA showed a similar behavior, with polymerization occurring during the first heating cycle.
In conclusion, the Differential Scanning Calorimetry (DSC) analysis of PLA, epoxy resins, and MMA revealed distinct thermal behaviors for each material. PLA exhibited glass transition, crystallization, and melting transitions, with a calculated crystallinity of 45.7%. Epoxy resins and MMA exhibited exothermic peaks during polymerization and subsequent melting. It's important to note that various factors, including sample handling and instrumental factors, may affect the accuracy of DSC results. In this experiment, care was taken to handle the samples and aluminum pans carefully to minimize any potential errors. The choice of aluminum as sample containers was made for its sturdiness and low thermal mass, ensuring reliable DSC measurements.
Differential Scanning Calorimetry Lab Report. (2024, Jan 10). Retrieved from https://studymoose.com/document/differential-scanning-calorimetry-lab-report-2
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