Polyester composition and method for preparing articles by extrusion blow molding
Polyester compositions described herein have properties which are particularly suitable for extrusion blow molding (EBM). These properties relate primarily to the rate of crystallization and melt strength or melt viscosity. Articles prepared from the polyester compositions exhibit good clarity, aesthetics, and other physical properties. The polyester compositions also exhibit broad molecular weight distribution (MWD), resulting in improved processability and melt strength. The crystallization rate allows for good drying characteristics while also enabling the use of regrind. In addition, the compositions exhibit improved recyclability, such as in existing PET recycling streams. In one aspect, articles are prepared in an extrusion blow molding method by combining a dry first polyester copolymer component, a dry second polyester component, and a chain extender to form a feed material suitable for extrusion blow molding. In another aspect, a single component co-polyester and a chain extender are combined to form a feed material.
1. A process of extrusion blow molding an article comprising:
providing a feed material suitable for extrusion blow molding, the feed material consisting essentially of a dry first polyester copolymer component, a dry second polyester component, a chain extender, and optionally a branching agent, wherein the chain extender is selected from the group consisting of trimellitic anhydride, pyromellitic dianhydride, trimellitic acid, or haloformyl derivatives thereof, and the second polyester comprises up to 100 wt % recycled polyethylene terephthalate;
feeding the feed material to an extrusion blow molding machine to form an extruded article; and
recovering excess material from the extrusion blow molding process as regrind material and combining the regrind material with the feed material.
2. The process of claim 1 wherein the regrind material is combined in an amount up to about 90 wt % based on the total weight of the feed material.
3. The process of claim 2 wherein the regrind material is combined in an amount up to about 50 wt % based on the total weight of the feed material.
4. The process of claim 1 wherein the first polyester copolymer comprises an unbranched or lightly branched polyethylene terephthalate copolymer of 1,4-cyclohexane-dicarboxylic acid, 1,4-cyclohexanedimethanol, isophthalic acid, or combinations thereof.
5. The process of claim 1 wherein the second polyester comprises polyethylene terephthalate.
6. The process of claim 1 further comprising adding a branching agent to the feed material.
7. The process of claim 6 wherein the branching agent is selected from the group consisting of pentaerythritol, trimethylolpropane, and combinations thereof.
8. The process of claim 1 wherein the feed material suitable for extrusion blow molding has a peak crystallization time of less than 60 minutes and at least 8% crystallinity.
9. The process of claim 1 wherein the feed material is produced by combining the dry first polyester copolymer component and a dry second polyester component in an extruder.
10. The process of claim 9 wherein the feed material suitable for extrusion blow molding has a moisture content of less than about 100 ppm.
11. The process of claim 9 wherein the extruder has at least two rotating screws.
12. The process of claim 11 wherein the at least two rotating screws are co-rotating screws, and wherein the extruder further comprises at least three sets of kneading blocks.
13. The process of claim 12 wherein the extruder has an L/D ratio of at least 20:1.
14. The process of claim 1 wherein the feed material suitable for extrusion blow molding has a zero shear viscosity of at least 4,000 Pa·s at a temperature of at least 490 ° F.
15. The process of claim 14 wherein the zero shear viscosity is at least 10,000 Pa·s at a temperature of at least 490 ° F.
16. The process of claim 15 wherein the zero shear viscosity is at least 20,000 Pa·s at a temperature of at least 490 ° F.