What is DSC?

DSC enables a range of characteristics to be measured to benchmark materials. These include quality control, material and process development activities, failure investigations and material identification activities.

A small sample of the material (typically <10mg) is heated and compared against an inert reference material. Any endothermic or exothermic reactions are then recorded to get a detailed picture of polymer performance.

DSC Testing Explores the Following Material Properties:

Glass transition temperature (Tg)

The material Tg is the temperature where the material transitions from a rigid glassy state to a rubbery state. This may limit the temperature performance of the material.

Melt point temperature
In conjunction with infrared analysis, melting point can be used to differentiate different types of the same generic polymer type (copolymer, homopolymer etc.).
Purity
The presence of multiple melt points and/or wavy heat flow traces can be used to detect the presence of contamination in recycled materials e.g. PE in PP.
Crystallinity level
Crystallinity is determined from the melting enthalpy compared against the theoretical enthalpy for a 100% crystalline reference sample. To fully understand material and product performance, the amount of crystallinity is very important as it influences the level of shrinkage, material properties and chemical resistance. It is controlled by the processing parameters (cooling from the melt). 
Cure state
For cross-linked materials, the presence of any residual exothermic reaction may indicate that the material is not fully cured.  
Specific heat capacity (cp)
This is the quantity of heat necessary to raise the temperature of unit mass of material by 1 K at constant pressure.
Isothermal tests can also be carried out to determine:
Oxidation Induction temperature (OIT) 
This test measures the time for oxidative decomposition. It is widely used for polyethylene pipes but can also be used for material development programs and as part of failure investigations to assess the residual life of materials taken from service. 
Reaction studies
Evaluation of the reaction times to optimise processing conditions.

Smithers DSC Testing Labs

Smithers in-house polymer testing laboratories have DSC testing instruments with a calibrated temperature range of between -80°C and 600°C, and heating rates from 0.01°C to 300°C /min. They utilize the power compensated principle; sample and reference materials are each held in a separate, self-contained furnace with its own heater element. Auto-sampling technology provides an automated means of loading and unloading samples, allowing the ability to run many samples in a shorter period of time for larger projects.

Common Standards for DSC Testing

  • BS EN ISO 11357 Plastics. Differential scanning calorimetry (DSC). 
    • Part 1 General principles
    • Part 2 Determination of glass transition temperature and glass transition step height
    • Part 3 Determination of temperature and enthalpy of melting and crystallization
    • Part 4 Determination of specific heat capacity
    • Part 5 Determination of characteristic reaction-curve temperatures and times, enthalpy of reaction and degree of conversion
    • Part 6 Determination of oxidation induction time (isothermal OIT) and oxidation induction temperature (dynamic OIT)
    • Part 7 Determination of crystallization kinetics
  •  ASTM D3418 Standard Test Method for Transition Temperatures and Enthalpies of Fusion and Crystallization of Polymers by Differential Scanning Calorimetry
  • ASTM D3895 Standard Test Method for Oxidative-Induction Time of Polyolefins by Differential Scanning Calorimetry
  • ASTM D7426 Standard Test Method for Assignment of the DSC Procedure for Determining Tg of a Polymer or an Elastomeric Compound
  • ASTM E793 Standard Test Method for Enthalpies of Fusion and Crystallization by Differential Scanning Calorimetry
  • ASTM E1269 Standard Test Method for Determining Specific Heat Capacity by Differential Scanning Calorimetry
  • ASTM E1356 Standard Test Method for Assignment of the Glass Transition Temperatures by Differential Scanning Calorimetry
  • ASTM E2160 Standard Test Method for Heat of Reaction of Thermally Reactive Materials by Differential Scanning Calorimetry

Smithers Thermal Analysis Support

Our team of material experts can help with the thermal analysis of polymers, using a variety of techniques. This includes DMA, TGA and DSC for the characterisation of film structures.
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