Profile-extruded poly(vinyl chloride) articles and method of making same
View Patent ↗A profile-extruded article is disclosed, made of a fiber-reinforced polymer of vinyl-chloride monomer, wherein the article has a ratio of actual specific gravity to theoretical specific gravity of nearly unity. A method of making the article is also disclosed.
1. A method of making a fiber-reinforced poly(vinyl chloride)-containing article, comprising the steps of:
(a) feeding granules of poly(vinyl chloride) reinforced with fibers into a two-stage, single-screw extrusion apparatus that has mixing pins at the end of the first stage and a vent only at the beginning of the second stage for devolatilization of outgasses during extrusion; and
(b) extruding the fiber-reinforced poly(vinyl chloride) through a profile extrusion die, wherein the granules contain fibers in an amount up to about 30 percent by weight of the article,
wherein between step (a) and step (b) the following steps occur in rapid succession:
(1) compression of the fed granules in a transition zone of the first stage of the screw along with melting of the compressed material at a barrel/material interface,
(2) continued melting without decompression or devolatilization along with dispersive mixing in a metering/mixing zone in the first stage of the screw,
(3) decompression for the first time of compressed and melted/partially melted material at the beginning of the second stage of the screw,
(4) devolatilization of the decompressed material for the first time through the only vent to remove volatiles including moisture, and
(5) build-up of melt pressure and conveying of the devolatilized melt to the die,
and wherein the fiber-reinforced poly(vinyl chloride) extruded through the profile die has a ratio of actual specific gravity to theoretical specific gravity that ranges from about 0.90 to about 0.99.
2. The method of claim 1 , wherein the extrusion apparatus has a L/D ratio ranging from 20:1 to 40:1.
3. The method of claim 2 , wherein screw configurations are selected from the group consisting of increasing pitch, standard, decreasing pitch, double flighted, and combinations thereof.
4. The method of claim 3 , wherein the screw also includes slotted disks.
5. The method of claim 1 , wherein the decompression is in the range of from 2 to 95 kilopascals.
6. The method of claim 1 , wherein the ratio of actual specific gravity to theoretical specific gravity ranges from about 0.95 to about 0.99.
7. The method of claim 1 , wherein the ratio of actual specific gravity to theoretical specific gravity ranges from about 0.97 to about 0.99.
8. The method of claim 1 , wherein the fiber is glass.