The first metallocene-catalyzed very low-density polyethylene (VLDPE) is a hexene-copolymer film resin of 0.912 g/cc and 1.0 MI, introduced by ExxonMobil Chemical Co., Houston. ECD-321, the new addition to the Exceed line of metallocene PE resins, is made by the Unipol gas-phase process. Samples are available now, and full commercialization is expected later this year.
The material is aimed chiefly at replacing conventional Ziegler-Natta VLDPEs, such as Mxsten XLDPE from Eastman Chemical Co., Kingsport, Tenn., and Attane ULDPE from Dow Plastics, Midland, Mich. ECD-321 is priced to be competitive with those materials.
PROPERTIES OF ECD-321 mVLDPE, (1.25-mil film) Haze, % 8 Gloss, 45° 58 Tensile Strength, psi @ Yield, MD 1080 TD 1080 @ Break,MD 11,230 TD 9200 Ult. Elongation, % MD 470 TD 620 1% Secant Mod., psi MD 253,000 TD 27,500 Elmendorf Tear, g MD 250 TD 490 Puncture, in.-lb 50 Dart Drop, g 1000
ExxonMobil marketing manager George Panagopoulos says the new metallocene VLDPE (mVLDPE) is designed primarily for flexible packaging of meat and dairy products, snacks and prepared convenience foods, frozen foods, and fresh fruits and vegetables. Non-food applications include industrial packaging, heavy-duty bags, and impact modification of other film resins.
Exceed mVLDPE has been shown to exhibit outstanding sealing properties (hot-tack and seal strength) compared with Ziegler-Natta VLDPEs. It reportedly allows fabricators to develop films with substantially lower sealing temperatures (down to 185 F), which results in faster seal-times and line speeds.
ECD-321 also boasts dart impact strength three times that of standard VLDPEs, along with exceptional puncture resistance, according to ExxonMobil. Thus, mVLDPE reportedly can be downgauged significantly to provide cost savings. It is also said to provide better low-temperature toughness for frozen-food packaging, as well as excellent optical properties and low extractables compared with conventional VLDPEs.
(Note: One family of Ziegler-Natta VLDPEs not included in ExxonMobil’s comparative data are the Flexomers from Union Carbide Corp., Danbury, Conn. Flexomers range in density from 0.800 to 0.915 g/cc, and film grades run 0.905 to 0.910 g/cc.)