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Recycled plastics are considered as materials with physical, mechanical and aesthetic properties worse than the virgin ones. In fact, this is true because degradation during lifetime and during the recycling operations changes the structure and the morphology of the polymers and then the final properties of the secondary material. Several "strategies" are under investigation, and in some cases also applied, in order to avoid further degradation during recycling and, if possible, to repair the macromolecules broken during lifetime and then to restore or to improve the initial properties. In this paper the more important techniques, already used in industry or under investigation, according to this philosophy are shortly reviewed.

Filaments of two samples of polyethylene terephthalate-co-p-oxybenzoate) containing 30 (T2/30) and 60 (T2/60) mol % p-oxybenzoate were obtained by melt spinning at temperatures between 225 and 285 °C. As-spun filaments with varying degrees of orientation were obtained by altering the take-up velocity at constant outflow velocity. The as-spun filaments were further subjected to mechanical and thermal treatments. Determination of mechanical properties, wide-angle X-ray scattering, differential scanning calorimetry, and electrohydrodynamic instabilities was carried out. T2/30, which exhibited extensive poly (ethylene terephthalate) crystallinity and melted into an amorphous phase, yielded a maximum elastic modulus on the order of 3 GPa. T2/60 exhibited crystallinity due to short sequences of p-hydroxybenzoic acid residues which persisted up to about 240 °C. Electrohydrodynamic instabilities were observed for T2/60 only above 265 °C, at which temperature clear-cut evidence of a fluid nematic mesophase was exhibited. The elastic modulus of T2/60 spun at 225 and 245 °C, when some small degree of crystallinity likely persisted, reached ca. 32 GPa Considerably lower moduli were observed by spinning T2/60 above 260 °C. It is suggested that orientation and ultrahigh modulus in the present system are obtained by virtue of a superimposition of a small degree of crystallinity to the mesophase.