Can You Explain What Is Melting Temperature And Melting Process?

The melting temperature also called fusion temperature characterizes the transition from a hard semi-crystalline structure into an amorphous liquid state. The process is endothermic, i.e. energy has to be supplied in order to melt the crystallites in addition to heating the material. The melting process covers a considerable temperature range. First the thinner and less perfect crystals melt, followed by the melting of the large mass of more or less uniform crystallites.

The latter, corresponding to the maximum determines the melting temperature. It is still an open question whether the  melting occurring after the maximum is de to even thicker lamellae or to a lag in the registration unit of the differential scanning calorimetery equipment, related to heating rate, sample size, or thermal conduction.
The differential scanning calorimetry curve of liner polyethylene sample shows, while it is first heated the beginning of melting and how the sample was affected by processing. These effects disappear upon heating well into the melting range.

If the material is then cooled at a constant rate, the sample crystallizes under almost ideal conditions. The degree of crystallinity, for example, increased from 60 to 72 %. If the sample is them heated for a second time, the melting curve is displaced towards higher temperature and shows greater peak area i.e. higher degrees of crystallinity.