Measurement of Crystallinity:
A general application of DTA is the measurement of the mass fraction of crystalline material in semi crystalline polymers. The method is based upon the measurement of the polymer's heat of fusion , ?Hf, and the plausible assumption that this quantity is proportional to the crystalline content. If by some process of extrapolation the heat of fusion, ?Hf*, of a hypothetical crystalline sample is known then the mass fraction of a crystallinity is
Mass fraction =? H f/? H f *
Therefore, crystallinity of a polymer sample (X) can be determined by measuring the total energy absorbed by the sample per gram ( ? H ) and subtracting the amount of energy which would be absorbed by one gram of totally amorphous material [ ? H f (a) ] in the temperature interval, and then dividing by the heat of fusion of one gram of a perfectly crystalline sample [ ? H f (c) ], as expressed by following equation.
X = ?H - ?Hf (a)/ ?Hf(c)
Another method for the determination of polymer crystallinity is based upon the ability of the instrument to cool a molten sample rapidly and reproducibility to a selected temperature where isothermal crystallization is allowed to occur. A number of crystallization curves may be obtained at different temperatures. The difference in crystallinity may be caused by branching, molecular and nucleation effect.