subject: Process For Removing Moisture And Volatiles From Pellets In Single Screw Extruders [print this page] In a process for extruding a thermoplastic resin in a single screw extruder, a barrel of a single screw extruder has a channel, a feed section and a first melt seal located after the feed section. The 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. An unfilled area within the channel of the barrel between the rear vent and the first melt seal forms the vent area.
In a process for extruding a solid polyester resin in a single screw extruder, wherein the improvement comprises the steps of supplying the solid polyester pellets through a feeding device into a feed section of a barrel of a single screw extruder and venting a vent area of moisture volatilized from the polyester through a rear vent positioned behind the feeding device, wherein the vent area is defined by an unfilled area within a channel of the barrel between the rear vent and a first melt seal and wherein a portion of a screw between the rear vent and the feeding device has an increased pitch.
This invention relates to processes for melting polymers in single screw extruder, and more particularly to processes for removing moisture from polymer pellets fed into single screw extruders to prevent hydrolytic degradation of polymers.
Rear venting has been used in single screw extruder, 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 early extraction is not needed. Also, the volatile is typically distributed evenly throughout the pellet, thus feeding a polymer melt versus cold pellets would result in only a minor change of devolatilization efficiency.
