I have been reading about thermoplastics, and in some publications they say that they can be melted, in fact, some people use the word "melt". But some other publications indicate, that due to the fact that thermoplastics polymers can't be 100% crystalline and therefore they always have and amorphous part there is no way to melt a thermoplastic polymer.
If thermoplastic polymers can't be melted, then How must be called that state in what the material flows? If it can't be melted, then it is not a liguid state.
I will aprecciate your help
Dear Estefano Ramos, being thermoplastics means they can be melted and remelted. The confusion you are getting in is the diference in melting of a amorphous and crystalline thermoplastics (or even semi-crystalline). The difference is that crystalline zones melt at precise and sharp temperature (same deltaH or CED), whereas, amorphous zones melt over a range/interval of temperatures because the irregular organization of chain result in different cohesion energies in the amorphous regions, so no precise or specific melting temperature. My Regards
Dear Estefano Ramos,
this is basically a terminology issue. Melting is the process of crystal destruction. Melt is the product of melting. Apparently, if the polymer is amorphous, it couldn't undergo melting because it has no crystals which could be decomposed. Instead, it undergoes "softening" (glass transition) until it turns into a liquid. This process is more gradual than genuine melting, as Abdelkader BOUAZIZ has explained. Nonetheless, the high-temperature polymer liquid produced by both processes is quite similar. For the lack of other terms, it is often called "melt" also for amorphous polymers, even though it is technically not accurate. Some authors are pickier about this term, while others don't really distinguish. That should explain your confusion.
Dear Estefano Ramos,
the state in which the material flows is the melt state. However, as you, Abdelkader BOUAZIZ and Petr Lepcio mentioned, you have to distinguish between crystalline and amorphous polymers or fractions of a polymer, respectively.
The term 'melting' describes the transition of a crystalline material with a long range order to a liquidlike material without any long range order.
Amorphous polymers do not have polymer chains arranged in crystals, thus the transition from a solid to a liquidlike behavior is not melting. However, in the liquidlike state these polymers are in the melt state. If the amorphous material is cooled, the polymer chains do not orient in crystals but their mobility is reduced (drastically at their glass transition temperature, Tg). These materials can be considered as a melt at T>Tg and as a frozen melt (= glass) at TTm>Tg) it is a polymer melt, but not all polymers can 'melt', because they can not make the transition between a (partly) crystalline material and this liquidlike state.
Additionally, the transition between the glass and the melt is a second ordertransition, whereas the transition between crystalites to a (frozen) melt is a first order transition. This can be seen in DSC measurements, in which a first order transition shows a peak, whereas a second order transition shows a step in the heat flow vs. temperature diagram.
Hi
Thermoplastics are melted and molded at their melting points.
Whereas thermosetting can not be melted they just degrade at higher temperatures.
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