Abstract: Process for the purification of an inert gas recycled from a solid state polycondensation (SSP) reactor of aromatic polyester resins, comprising the step of adding the gas with oxygen or gas containing oxygen in stoichiometric quantity or in such an excess that the gas at the outlet of the catalytic bed contains no more than 250 ppm of oxygen, circulating the gas on a catalytic bed comprising Pt or Pt and Pd heated at temperatures from 250.degree. to 600.degree. C. and recycling the gas to SSP reactor with previous drying to eliminate the water formed in the oxidation stage.

Abstract: Process for the production of polyester resins suitable for the manufacture of fibers including a phase of esterification of an aromatic dicarboxylic acid with an alkylenic glycol or of transesterification of a diester of the dicarboxylic acid with the alkylenic glycol, of polycondensation of diester obtained to form a prepolymer with intrinsic viscosity between 0.2 and 0.5 dl/g and, lastly, of polycondensation of the melt polymeric mass added with a dianhydride of a tetracarboxylic acid kept in agitation and on which an inert gas current is circulated.

Abstract: A foamed cellular material from polyester resins is obtained by extrusion foaming of polyester resins having melt strength higher than 8 centinewton, intrinsic viscosity greater than 0.8 dl/g and complex melt viscosity higher than 25,000 poises.

Abstract: A process for the production of polyester resins having an intrinsic viscosity higher than 0.57 dl/g from polyester resins having intrinsic viscosities of lower than 0.57 dl/g in which 1) a melt of the polyester resin having an intrinsic viscosity lower than 0.57 dl/g is mixed with a polyaddition additive containing at least two groups which react with the terminal OH and COOH groups of the resin, 2) the melted mixture is converted into solid particles which are subsequently crystallized at temperatures higher than the Tg of the polyester resin and lower than its melting point, and 3) the particles are heated at temperatures higher than 150.degree. C. but lower than the melting point of the resin to increase the intrinsic viscosity.

Abstract: A foamed cellular material from polyester resins is obtained by extrusion foaming of polyester resins having melt strength higher than 8 centinewton, intrinsic viscosity greater than 0.8 dl/g and complex melt viscosity higher than 25,000 poises.