Recrystallization strain induced

Reconstructive phase transitions occur when major changes are made in the topology, i.e. when the bond graph is reorganized. The transitions usually observed in structures with lattice-induced strain are displacive and often second order (no latent heat). Reconstructive transitions arise when two quite different structures with the same composition have similar free energies. Unlike the displacive transitions they involve the dissolution of one structure and the recrystallization of a quite different structure. These phase transitions possess a latent heat and often display hysteresis. 

Since PHB is a polyester it might have been expected that it could be drawn and oriented into fibres quite easily using similar techniques to those developed for poly (ethylene terephthalate). This is not the case. PET is normally melt-spun into a fibre which is then quenched and wound up as an amorphous, glassy material.In a separate stage it is then drawn over a hot pin at a temperature above its 7 and crystallized in this oriented state to produce the familiar strong polyester fibres. This type of stress-induced crystallization from the quenched amorphous state does not seem to be possible with PHB. Indeed, the application of strain to a supercooled PHB melt can inhibit recrystallization rather than promote it. 

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