Unusual resins, new additives starred at SPE polyolefins conference.

Nearly 800 persons attended the biennial SPE Polyolefins RETEC in Houston last month to hear details on new resins such as peroxide-curable ethylene-octene elastomers, syndiotactic PP, dyeable and printable propylene-based carpet fibers, and other new-generation PPs. They also heard about new applications for polybutylene blends in container lidstock.

Technical papers on additives were another key attraction of the meeting. New developments in antioxidants were an especially strong focus. Attendees also learned about a new processing aid that prevents extrusion die build-up.

NOVEL RESIN DEVELOPMENTS

Himont Inc., Wilmington, Del., described new developments in PP resins made with its Catalloy process. Two low-modulus grades have been designed to compete with LLDPE in injection molded food-storage container lids. As shown in the graph at right, both resins retain stiffness better than the LLDPE as temperatures exceed 175 F.

Himont also discussed new high-modulus Catalloy-process PP homo-polymers for food-storage containers, which are typically injection molded of PP random copolymer. Himont addressed container heat-resistance requirements for repeated microwave reheating and dishwasher cycles. The Catalloy-process resin is twice as stiff as a random copolymer at room temperature and four times as stiff at 212 F. The Catalloy resins also have a higher HDT - 265 F vs. 180 F for a typical random copolymer used in this application. In food-stain resistance tests, these resins exhibited only one-seventh the change in yellowness index shown by a typical random copolymer.

The potential of a new high-clarity/high-impact syndiotactic PP (sPP) in cast film and BOPP was presented by Fina Oil & Chemical Co., Dallas. Two variants of this resin were extruded into 8-mil monolayer cast films and compared with a three-layer film used commercially in medical bags. One sPP film exhibited tear resistance and seal performance comparable to the laminate; the other sPP film had lower tear resistance but much better heat-seal properties.

Dow Plastics, Midland, Mich., showed how its new metallocene-based Engage polyolefin elastomers (POEs) can compete with EPDM in peroxide-cured compounds designed for high-temperature applications like radiator hose and brake parts. A POE of 23 Mooney viscosity was compared with a blend of 55 and 60 Mooney EPDMs. The POE showed comparable mechanical properties despite its higher flow, thereby permitting molders to formulate faster-curing compounds to reduce cycle times. The POE also showed higher uv resistance and significantly better heat aging - i.e., very little change in elongation after 10 days at 350 F, whereas the EPDM compound embrittled.

NEW DYEABLE POLYOLEFIN FIBERS

Shaw Industries, Inc., Dalton, Ga., a leading North American producer of PP carpet fiber, is a partner with Lyondell Polymers, Houston, in commercializing a new advanced fiber technology for carpets. Lyondell recently launched a Kromalon propylene-based polyolefin that's said to produce fibers that are disperse dyeable and printable, yet retain the beneficial properties of PP, including superior stain and moisture resistance.

Kromalon is available with MI of 18 to 35. Compared with standard PP bulk continuous filament, Kromalon fiber has similar denier and tenacity but higher elongation, toughness, and energy at break. Dyeable carpet fibers made with Kromalon reportedly have better stain and bleach resistance, antimicrobial properties, and cleanability than nylon and polyester fibers. Colorfastness, wear/durability, and physical properties are generally comparable.

NEW USE FOR POLYBUTYLENE

A new application for polybutylene as a peelable heat-seal layer on lidstocks was presented by Shell Development Co., Houston. The company has developed several Duraflex PB-based compounds for use as lid sealants compatible with PE or PP. The new materials are solventless, melt-processable resins that could replace sealants traditionally applied to the lid-stock by solvent coating. PB can be processed via blown or cast film, extrusion coating, or laminating.

The compounds - melt blends of polybutylene and other polymers (i.e., PEs, EVA, EMA, EEA, EBA, and EAA) - are said to provide "easy-open" pealability, thanks to a unique cohesive type of failure that results from the incompatibility of the polymer blend components.

Four grades of lid-sealant compounds are commercially available. WBS747 is a blown film grade designed for dry laminating with adhesive onto PET, aluminum foil, or other substrate. WBS903 and WBS958 are two high-MI grades, and WBS879 is a low-MI grade, all designed for extrusion coating onto aluminum or PET using a primer or tie-layer adhesive such as LDPE, EEA, or a maleated polyolefin.

STABILIZER DEVELOPMENTS

A developmental phosphite antioxidant for polyolefins that boasts excellent hydrolytic stability and antioxidant properties at high temperatures was presented by Dover Chemical, Dover, Ohio. P92 is a type of pentaerythritol diphosphite with good thermal stability, as indicated by low weight loss at 660 F. It also has a high melting point and a relatively high phosphorus content compared with other phosphites. P92 is reported to perform excellently as a sole stabilizer - both in terms of melt-flow and color stability - in PP at 400 ppm use levels and extrusion temperatures up to 650 F. It also provides uv stability in PP fibers exposed to xenon-arc accelerated weathering, along with excellent thermal stability and gas-fade resistance.

Ciba-Geigy Corp., Hawthorne, N.Y., reported on its new high-performance organophosphite for high-temperature processing of polyolefins, polycarbonate, and nylon (see PT, Sept. '94, p. 13). CGA 12 reportedly provides excellent processing thermal stability and outstanding color control. It's said to be extraordinarily hydrolytically stable and to function as a catalyst deactivator.

Ciba also has developed a proprietary, experimental stabilizer that contributes both thermal and uv stability in filled systems. Stabilizer EXP-1 reportedly improves the thermal stability of a black, talc-filled PP at concentrations of 0.5 to 1.0%. It is effective as a light stabilizer in the same formulation, based on improvements in surface roughness and gloss retention during accelerated aging.

Uniroyal Chemical Co., Middlebury, Conn., reported on the synergistic effects of amine-type antioxidants with traditional hindered phenolic/phosphite combinations in LLDPE, HDPE and PP. One such ternary blend containing Uniroyal's Naugard 445 diphenylamine (typically used in ABS, nylon, and polyurethane) was reported to give much better color in LDPE than any binary phenolic/phosphite antioxidant combination. In both HDPE and PP, the ternary blend reportedly gives better melt stability.

New data on alpha-tocopherol, or vitamin E, as a polyolefin antioxidant were reported by Hoffmann-La Roche Inc., Nutley, N.J. The company cited studies of its Ronotec CF-120 phosphite-free proprietary blend in HDPE and PP. In HDPE, 400 ppm of CF-120 alone reportedly suffices as a replacement for traditional phenolic/phosphite combinations. CF-120 can also be combined with a phenolic if maximum stabilization is required. In PP, 1250 ppm of CF-120 not only functions well on its own, but adding phenolic or phosphite does not improve the performance. However, the company concluded that the most cost-effective solution for both resins is a blend of 250 ppm CF-120 with 500 ppm of an Irganox 1010-type phenolic. Such a package reportedly can cut total stabilizer cost by up to 50% in HDPE and 25-30% in PP, when compared to phenolic/phosphite systems.

ELIMINATE DIE BUILD-UP

Die build-up problems in blown film, extrusion coating, fiber spinning, wire and cable coating, and even blow molding reportedly can be reduced significantly by a proprietary fluoropolymer additive from DuPont Co., Wilmington, Del. Among the examples cited was high-speed tubing extrusion of an MDPE containing 2.5% carbon black. Within 5 min of start-up, excessive die build-up resulted. When 50 ppm of the fluoropolymer was added, extrusion proceeded indefinitely with no measurable die build-up.

In another case, an LLDPE film coextrusion line experienced sufficient die build-up to be shut down for cleaning every 8 hr. A fluoropolymer concentrate was metered into the external layer of the coextrusion at 100 ppm. The line then ran for 36-48 hr before the die had to be cleaned.