Determination of crystalline melting behaviour by differential scanning calorimetry (DSC). DSC analysis is a technique in which the heat flow rate (power) to the sample is monitored against time or temperature, whilst the temperature rise of the sample is programmed. When the sample undergoes a transition, such as melting, a much greater heat flow is recorded.
To erase the effects of the previous thermal history of the specimen (in order to obtain an unambiguous material identification), a second thermal cycle is performed.
Smithers Pira uses a Netzsch Polyma DSC214 instrument covering the temperature range -70°C to +600°C. Typical DSC applications include the determination of polymer melting points, glass transition point and crystallinity. It is one of a suite of test methods used by Smithers Pira to analyse plastic film structures.
Applicable standards are detailed in BS EN ISO 11357.
Oxidative Induction Time (OIT)
OIT provides information about the oxidative stability of mainly polymer materials.
The test specimen is heated to a specific temperature in an inert nitrogen atmosphere. After a holding period at a set isothermal temperature, the gas is switched to an oxygen, or air purge.
The time taken from the O2 gas switching to the onset of oxidation reaction is taken as the OIT.
OIT is used to assess polymers used at elevated temperatures under an oxygen atmosphere such as polyolefin tubes or vapour-barrier-films. It can be used to compare the aging resistance of different plastics, to detect the effectiveness of antioxidants.
Applicable International Standards include ISO 11357-6 and ASTM D3895.