Extra-tough, new-generation LLDPE said to mimic LDPE processability.

New film resins said to be tougher and more processable than anything comparable on the market are being developed by Union Carbide Chemicals and Plastics Co., Inc., Danbury, Conn. The new LLDPE materials will be made by a next-generation "Unipol II" process, using new high-activity catalysts that reportedly can make a full range of HDPE and LLDPE. The experimental LLDPEs aren't available for sampling yet and won't be commercially produced for another two years. The first two groups of Unipol II resins, referred to as Ultra-Tuflin and Easy-Flow, have controlled molecular weight and molecular-weight distribution.

Ultra-Tuflin is the more unusual, with twice the tear and puncture strength of current butene- or hexene-copolymer LLDPEs, Carbide says. It has Elmendorf tear properties of around 825 psi in both machine and transverse directions. That's 30-50% better TD strength than today's butene or hexene copolymers and 50-75% better MD properties. Dart impact strength is around 470 psi--more than double that of hexene copolymers and triple that of butene copolymers, Carbide says. Density of initial experimental grades ranges from 0.92 to 0.93. Ultra-Tuflin is a family of high-molecular-weight grades that can be processed on existing LLDPE or HDPE film lines, according to Carbide. They're aimed at stretch/shrink wrap, heavy-duty shipping sacks, and ice bags.

The second group of new LLDPE grades, Easy-Flow, has some improved properties (see New Products section), but primarily shows greater processability than other LLDPEs. Easy-Flow materials reportedly can be "drop-in" substitutes for high-pressure LDPE that runs on unmodified conventional extrusion equipment. Traditionally, this equipment couldn't run LLDPE resins without costly and extensive machinery modifications.

Easy Flow materials are further along in commercial development than the Ultra-Tuflin type, but both have been made on a semi-works plant, Carbide says. Easy-Flow was also processed in customer trials last fall under secrecy agreements and at Carbide film plants in Canada. Technical people say developmental grade "1349" ran back-to-back in extrusion equipment dedicated to high-pressure LDPE with no machinery modification. They say it even makes a more stable bubble than conventional LDPE. Easy-Flow materials target industrial liners, trash bags, and construction and agricultural film, rather than high-clarity products. (These resins show around 30% haze, with correspondingly low surface gloss.) Eventually, there will also be blow molding grades, Carbide says.

Easy-Flow resins will be priced competitively with LDPE, while Ultra-Tuflin resins are intended to be a premium high-performance product.

SHROUDED IN SECRECY

Carbide announced that it plans to build a new 650-million-lb/yr Unipol II plant in Taft, La., that will be the biggest fluidized-bed, gas-phase reactor in the world (about 35% bigger than the next largest). The new plant is expected to start up by the first quarter of 1995 or sooner. "The Unipol II process is designed to use new super-high-activity Ziegler catalysts as well as emerging new single-site systems," says Polyolefins Div. president Roger Staub.

Carbide won't say anything about the Unipol II process itself, except that it can control the level of chain branching and specific location of branches along the polymer chain (which is also said to be a prime characteristic of new "single-site" metallocene catalysts). If Carbide chooses to license Unipol II eventually, it could be retrofitted for Unipol (I) licensees, Carbide says.

Although Carbide isn't saying, Unipol II is widely speculated to be a linked two-reactor series with the flexibility to make conventional Unipol-type resins or bimodal material with a controlled mixture of short and long carbon chains. If indeed a multi-reactor plant is planned, it's only the third two-reactor Unipol plant in the world to make PE. One at Mitsubishi Petrochemical Co. in Japan started up last year, and Carbide previously retrofitted a two-reactor series at Seadrift, Texas, to make bimodal HMW-HDPE materials.