The glass transition temperature of polymethylmethacrylate ( PMMA, Perspex) is measured using static and dynamic method while the glass transition temperature of rubber of different size is measured using only dynamic method. The glass transition temperature Tg of Perspex is found to be 90°C using the static method and 160°c using the dynamic method. On the other hand, the Tg of rubber is found to be -30°C. Introduction
Perspex is a type of amorphous polymer and has the following repeat unit :
If the PMMA is heated , the side group of the polymer will start to rotate. As the temperature gradually increase and reach a certain temperature , the polymer would lose its stiffness and becomes elastic like a rubber. This temperature is also known as glass transition temperature ,Tg. The Tg is always lower than melting point of the polymer. By heating and cooling the polymer, and observing the changes in their physical properties we could identify Tg. (For static test method of Perspex)
Tg is determine by observing at which temperature does the coefficient of thermal expansion change. This is done by using a mercury dilatometer which contains about 25g of Perspex in the glass bulb. A thermocouple is placed between the glass bulb and heating coil to measure the temperature. Temperature is recorded everytime the height of Hg column change by 1 cm. When the temperature reach 120°C switch off the heat supply. Continue taking the readings as the temperature falls until 60°C.
Height of Hg column while heating (cm)| Temperature (°C)| Height of Hg column while cooling (cm)| Temperature (°C)| 19.1| 60.9| 35.4| 118.9|
20.1| 65.6| 34.4| 107.4|
21.1| 68.7| 33.4| 104.2|
22.1| 73.9| 32.4| 101.5|
23.1| 77.7| 31.4| 99.1|
24.1| 81.6| 30.4| 96.7|
25.1| 90.0| 29.4| 93.9|
26.1| 94.5| 28.4| 91.2|
27.1| 98.3| 27.4| 88.2|
28.1| 101.7 | 26.4| 84.9|
29.1| 103.5| 25.4|...