视频: Differential Scanning Calorimetry of Polymers

Differential Scanning Calorimetry

Overview

Source: Danielle N. Beatty and Taylor D. Sparks, Department of Materials Science and Engineering, The University of Utah, Salt Lake City, UT

Differential scanning calorimetry (DSC) is an important measurement to characterize thermal properties of materials. DSC is used primarily to calculate the amount of heat stored in a material as it heats up (heat capacity) as well as the heat absorbed or released during chemical reactions or phase changes. However, measurement of this heat can also lead to the calculation of other important properties such as glassy transition temperature, polymer crystallinity, and more.

Due to the long, chain-like nature of polymers it is not uncommon for polymer strands to be entangled and disordered. As a result, most polymers are only partially crystalline with the remainder of the polymer being amorphous. In this experiment we will utilize DSC to determine polymer crystallinity.

Procedure

Turn on the machine and allow it to warm up for about an hour.
Check to ensure the compressed nitrogen tank and liquid nitrogen tank are both full and the valve connecting them is open. The compressed nitrogen pressure flow is set at 10 psi by the adjustment knobs on the regulator.
Prepare two empty pans. Poke a small hole in the lid of each and seal by using the crimping press. Remove the three furnace lids and place the pans on the two circular sensors within the furnace. Replace all three lids.
Click o

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Results

Figure 3 shows the result of a DSC percent crystallinity sample scan on a polybutylene terephthalate (PBT) polymer sample. The result is displayed as a DSC power reading (in milliwatts per milligram of sample) verses time. The power reading, the blue trace in Figure 3, indicates how much additional power was required to change the temperature of the sample pan in comparison to the empty reference pan. The temperature program is a

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Application and Summary

Differential scanning calorimetry is a technique used to determine many thermal properties of materials, such as heat of melting, heat of crystallization, heat capacity, and phase changes. DSC measurements can also be used to calculate additional material properties including glassy transition temperature and polymer percent crystallinity. The DSC requires very small samples that must conform to the size and shape of the pans used in the machine and is based on a differential heat comparison between an empty reference an

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Tags

Differential Scanning Calorimetry DSC Thermal Properties Materials Polymers Measurement Technique Sample Pan Reference Pan Temperature Sensors Heaters Energy Flow Phase Change Reaction Polymer Phase Transitions Percent Crystallinity Crystalline Polymers Amorphous Polymers Melting Glass Transition

Turn on the machine and allow it to warm up for about an hour.
Check to ensure the compressed nitrogen tank and liquid nitrogen tank are both full and the valve connecting them is open. The compressed nitrogen pressure flow is set at 10 psi by the adjustment knobs on the regulator.
Prepare two empty pans. Poke a small hole in the lid of each and seal by using the crimping press. Remove the three furnace lids and place the pans on the two circular sensors within the furnace. Replace all three lids.
Click on the icon labeled DSC 3500 Sirius to launch the machine's software.
Select File → New. The Measurement Definition window will open; four tabs are included that ask for information input. The first tab is the Setup tab. It contains information about the instrument and does not need to be altered for running a measurement using standard procedure.
Click on the second tab, labeled Header. Select Correction under Measurement Type. This will save the baseline measurement as a correction file, which will later be subtracted from the sample measurement by the software.
Input Baseline with the date as the sample Identity and Name under the Sample section.
Under Temperature Calibration, click Select. This will open a separate window; find the most recent temperature calibration file saved to the computer and select it.
For a percent crystallinity measurement, click Select under Sensitivity Calibration and select the most recent sensitivity calibration file saved to the computer.
Select the third tab, labeled Temperature Program.
Check the Purge 2 and Protective boxes listed under Step Conditions. This turns the nitrogen purge gas on for all temperature steps.
Select Initial under Step Category and input 20 °C as the Start Temperature.
Select Dynamic under Step Category and input a temperature for the End Temperature. This end temperature should be approximately 30 °C higher than the reported melting temperature of the polymer sample. The maximum temperature allowed by the aluminum pans is 600 °C; as a precaution do not go higher than 550 °C. Enter 10 K/min as the Heating Rate.
Select Dynamic under Step Category and input 20 °C for the End Temperature.
At the top of the screen, click on the drop-down arrow under LN2 for the second cooling step, which brings the furnace back to room temperature. Select Auto. This tells the temperature program to automatically turn on the liquid nitrogen to cool the furnace after the heating step has finished.
Select Final under Step Category. Input 20 °C as the End Temperature.
The program will ask for an Emergency Reset temperature. Input a temperature 10 °C higher than the highest temperature set in the temperature program. This is a protective setting, which stops the machine from heating higher than a set temperature in case of machine malfunction. This protects the furnace from heating to a temperature that could vaporize the sample and damage the machine.
The program will then ask for Final Standby information. This information will hold the furnace at the final temperature for up to 2 hours to keep it equilibrated but has no effect on the data collected. Input 20 °C for the Standby Temperature, 40 K/min as the Heating Rate, and a Max Standby Time of 2 hours.
Select the Fourth Tab, labeled Last Items.
To the right of File Name click Select. Choose a location on the computer to save the scan and name it Baseline with the date (same name as listed under the Header tab).
Click Forward at the bottom right hand corner of the Measurement Definition Window. A new, smaller window will appear, listing the Initial temperature as defined in the temperature program and the current furnace temperature. To start the program, the current furnace temperature must be within 5 degrees of the initial temperature.
If the furnace temperature is within 5 degrees of the initial program temperature, click Start and the measurement will begin. If the furnace temperature is too low, click start and the machine will do a heating and equilibration step prior to beginning the measurement. If the furnace is too hot, select Diagnosis → Gases and Switches. Check the box for LN2 and allow the liquid nitrogen to flow until the temperature reaches within 5 degrees of the initial. Then uncheck the LN2 box and press Start to start the measurement.
After the Baseline scan has run, remove the empty baseline pan and replace it with the pan containing the sample. The pans are approximately 6 millimeters in diameter with a volume of 25 microliters, and so require a very small amount of sample. Cut the sample into small pieces that fit into the pan. To ensure even heat flow and accurate DSC readings, a thin layer of the sample pieces are placed so the entire bottom of the pan is covered.
Select File → Open. Click Okay when the program asks to delete current configuration and find and open the Baseline scan.
The Measurement Definition Window will open to a Fast Definition page. Select Correction plus Sample under Measurement Type.
Under the Sample section, input the sample name under Identity and Name and input the sample mass in milligrams.
At the bottom of the window, click Select. Choose a place to name and save the scan.
Select Forward. Press Start when the smaller window appears.
After the measurement has finished, close the program, turn off the compressed nitrogen tank and turn off the machine.
Find the saved measurement for the sample scan and double click on it. This will open the scan in the Proteus Analysis software.
Use the software to find the area under the melting and recrystallization curves. These values are the heat of melting and heat of cold crystallization of the polymer sample in Joules per gram.
The percent crystallinity can be calculated using the equation listed above:
Crystallinity =

跳至...

0:08

Overview

1:26

Principles of DSC Analysis of Polymers

3:51

DSC Baseline Measurement

6:52

DSC Sample Measurement

8:21

Analysis of the DSC Data

9:33

Applications

11:29

Summary

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