Can You Give Some Details Of The Melting Point And Crystalline Behaviour Of Nylon?


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A sharp melting point is common to all nylon homopolymers while some copolymers have broad melting point. Nylon 6 melts at about 150°C over glass transition point; it means about 428°F (22O°C). There is little softening of the resin until it actually melts. This provides the necessary strength at elevated temperatures and enables nylon to function in applications not suited to other thermoplastics. However, the sharp melting point of nylon must be considered from a processing standpoint. Screw design, barrel temperature profiles and melt temperatures are important variables in the production of a homogeneous melt.
In the melt state, nylon 6 is amorphous (no crystalline content). As nylon is cooled slowly from the melt state, crystallises and sometimes spherulites are formed. The quicker nylon 6 is quenched from the melt state to the Tg. (glass transition temperature), the lower will be the % crystallinity. The longer it takes to remove heat from a nylon- 6 film ,the higher will be the % crystallinity of the nylon. With increased % crystallinity, clarity will give way to opacity, ultimate tensile strength and stiffness will increase and % elongation will decrease.

Nylons are divided in two main types of stable crystal structures. These are denoted by alpha and gamma. In case of even nylons gamma can be converted in alpha. Alpha crystals are obtained from annealing or crystallization at higher temperatures where the Gamma crystals were obtained at low temperature.

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