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Improved Melt Stable Polyester

IP.com Disclosure Number: IPCOM000009991D
Publication Date: 2002-Oct-07
Document File: 4 page(s) / 32K

Publishing Venue

The IP.com Prior Art Database

Abstract

A process for improving the melt stability of polyesters such as PET in melt extrusion process wherein additives such as epoxies are used. The extrusion process is improved by supplying solid polymer into the feed section and venting moisture extracted from the polymer during the conversion of the polymer from a solid to a melt into a vent area and through a rear vent positioned in the feed section. The additive is added after the moisture is extracted which results in improved reaction with PET resulting in enhanced melt stability.

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Improved Melt Stable Polyester

Abstract

A process for improving the melt stability of polyesters such as PET in melt extrusion process wherein additives such as epoxies are used.� The extrusion process is improved by supplying solid polymer into the feed section and venting moisture extracted from the polymer during the conversion of the polymer from a solid to a melt into a vent area and through a rear vent positioned in the feed section.� The additive is added after the moisture is extracted which results in improved reaction with PET resulting in enhanced melt stability.

BODY OF THE PAPER

Improved Melt Stable Polyester

This paper relates to processes for improving melt stability of polymers in twin-screw extruders, and more particularly to processes involving both removing of moisture from polymer pellets fed into twin-screw extruders to prevent hydrolytic degradation of polymers as well as improved reaction with additives.

DISCUSSION

Vented extrusion is a common means for removing volatiles from a polymer during processing. Typical volatiles include, but are not limited to, oligomers, residual solvents, and moisture. Conventional vented extruders have a vent located beyond the zone where the polymer has completely melted. The vent is typically located on the surface of the barrel, i.e. a vent port, with direct exposure to the atmosphere. Another venting option is to remove the volatiles through a screw having a hollow core connecting with lateral holes in the extraction zone.

However, since venting follows melting, the polymer experiences sufficient time and high temperatures with moisture in the melt that some hydrolysis occurs before the polymer reaches the vent area. The hydrolysis results in loss of molecular weight, surface imperfections, and poor overall properties of the polymer. The conventional vented extruder systems are thus incapable of removing sufficient levels of moisture in the polymer before hydrolytic degradation occurs. In particular, the removal of moisture is important for polyesters. Since conventional venting techniques are incapable of removing moisture, polyesters often undergo a drying process prior to extrusion. Drying is often cost prohibitive because additional equipment, space, and energy is required.

In twin-screw extrusion, multiple vents are commonly utilized including a rear vent located behind the feed hopper. Generally these rear vents are only considered effective for large-scale devolatilization when the feed material is liquid, slurry, or melt. The rear vents function similarly and are just as effective as standard vents in twin screws when the feed material is in a liquid form.

Rear venting has been used in single screw extruders, but only in cases where the feed material is already molten. Such is the case when a compounding extruder is fed into a devolatilization extruder or when the feed is a polymer-solvent solution. For many applications, the volatile involved does not degrade the polymer so...