Process for obtaining modified polyethylene terephthalate pilling-free fibres originating from the polymer thus modified

A pilling-free fiber capable of being employed in a mixture with at least one cotton fiber for weaving applications, based on polyethylene terephthalate modified with --SiO-- groups bonded chemically to the macromolecular chains in an amount of 300 to 700 ppm of silicon and having:

• an elongation at break greater than zero and less than 25%;
• a tenacity greater than or equal to 40 cN/tex;
• a boiling water shrinkage of between 1.5 and 6%;
• and
• a flex abrasion index after dyeing greater than zero and less than or equal to 6,500 at 130.degree. C. and under pressure;
• said modified polyethylene terephthalate being obtained by the process comprising the continuous reaction of direct esterification between terephthalic acid and ethylene glycol and modified by the introduction of methoxyethyl or propyl silicate in an amount of 300-700 ppm of silicon at a time when the prepolymer has a molecular mass of between 9,000 and 16,000, a polydispersity index of between 1.5 and 2, and when the temperature of the reaction is between 260.degree. and 290.degree. C. and at a pressure of between 1.5 and 2.5 bars, the silicate/prepolymer reaction time being at least 5 min,
• wherein after polycondensation, the polyester is drawn in the presence of steam.