High-ESCR bottle resins may justify processing adjustments.
Blow molders of HDPE bottles for household and industrial chemicals (HIC) may find the time has come to learn how to handle the processing differences of some of the less familiar but higher stress-crack-resistant HDPEs on the market. Factors that may overcome prior resistance to these resins include the advent of a new supplier of these resins, bringing new grades that promise even higher performance than ever before, and the emerging need for such resins to upgrade the ESCR of recycled HDPE.
Phillips-type HDPE resins have dominated the extrusion blow molded bottle market in North America. Blow molding grades made by other HDPE processes, characterized by different profiles of properties and processability, have gained only limited acceptance so far in high-speed bottle making. Now as Houston-based Exxon Chemical Co. brings up its big new Mitsui-process reactor in Mont Belvieu, Texas, that could change.
This is not only Exxon's first pure-HDPE plant (it has "swing" capacity at two LLDPE sites), it's also the first Mitsui-process HDPE produced in North America (see PT, Sept. '90, p. 13). Exxon says this process yields resin with far higher ESCR at the same density, melt index and top-load strength, than conventional resins made by Phillips process (which Phillips licenses to a number of producers), or look-alike resins produced by other processes. The problem, Exxon readily concedes, is that the new resin's die swell is also different and requires a blow molder to make machinery adjustments before running it, especially in high-shear machines.
Exxon isn't the first to make such high-ESCR resin. Similar resins have been produced since 1984 with technology originally belonging to Du Pont/Conoco, then to Cain Chemical, and now to Occidental Chemical Corp. in Houston. Occidental uses Du Pont-developed technology with a Ziegler-type titanium catalyst, as does Exxon's Mitsui process. (Phillips' process uses a chromium catalyst.)
Oxy met a lot of initial resistance to its resins. "They were different, and different was unacceptable in many cases," recalls Oxy sales v.p. Thomas Williams. Eventually Oxy won film markets for HMW material (made by a second Ziegler process), but few blow molders, even though the resin's high ESCR properties acquired an excellent reputation. Oxy says its resin also didn't catch on big with bottle blowers because they were afraid of being single-sourced, especially after Phillips October '89 explosion tightened up HDPE supplies. "Now they have a second alternative, a second party selling lightweighting and high ESCR," says John Feick, in charge of developing blow molding markets for Oxy. "The processing problems (with Exxon and Oxy HDPE) are similar. Whatever modification works for one, works for the other."
Both Exxon and Oxy built big new capacity. Exxon expects to produce 100 million lb next year of one bottle resin, HD 9856 B, out of 265 million lb/yr total capacity (the rest will be two grades of HMW film). Exxon is following Mitsui's recipe slavishly at first, and will seek to modify it later on. Oxy, meantime, added 250 million lb to its bottle-resin capacity this year through debottle-necking.
WHY THEY'RE DIFFERENT
The key to the high ESCR properties and processing peculiarities of the Exxon and Oxy resins is their completely different type of catalyst. Exxon and Oxy sources say their processes leave less catalyst residue in the resin, and produce a characteristic "bimodal" molecular-weight distribution, with concetrations of long and short molecules making two peaks on a graph (chromatogram). Chromium catalysts used by Phillips and other Phillips-look-alike processes reportedly create a less saturated resin, which during extrusion generates molecules with long chain branching. This makes it more elastic, so a bottle parison drops and bounces back slightly, and also shows more die swell.
The high-ESCR bimodals are said to be hardest to run on high-shear blow molding machines, such as Uniloy reciprocating-screw blow molders. Graham Engineering's wheel, though lower shear, is also challenging because it extrudes parisons upwards at high speeds. Machines that run the bimodals most easily are said to be continuous-extrusion models like those from Bekum or Battenfeld-Fischer.
For blow molders, the key processing problem is that high-ESCR bimodal resins have low swell and don't "bounce," so parisons drop and extend, leaving thinner walls and more flash. Because the bimodal resins' ESCR and top-load strength are superior, thin-walled bottles reportedly are as strong as thicker bottles made of Phillips-type resin. But dies and secondary operations, like cutting and trimming, sometimes have to be adjusted. However, once adjusted for Exxon's resin, settings won't need to be changed, because Mitsui's process is totally consistent, says Exxon research associate John DeManuelle.
Oxy, based on its experience, thinks Exxon will have to modify its bimodal resins to improve processability. Oxy offered variations with improved processability almost immediately. Although still superior to chromium-based resins, Oxy gave up some ESCR benefits to create more "Phillips-like" resins, Alathon L 5850 for low-shear continuous-extrusion machines, and L 5840 for high-shear wheels. Both have 0.958 density and slightly less ESCR than Oxy's high-performance Alathon L 5440, with 0.954 density, which Oxy markets for blending with recycle (see PT, Sept. '90, p. 13).
Based on extensive sampling, however, Exxon thinks it can sell the Mitsui product as is, targeting monolayer motor-oil bottles with recycled content. For the past six months, Exxon has sampled comparable product from Mitsui licensees in Venezuela and Thailand, and says Sonoco Graham in York, Pa., can run it on its wheel machines after making die adjustments. Exxon also has monolayer detergent bottles lined up. And DeManuelle says his next developmental project will be a multilayer oil bottle.
Lightweighting is no real advantage to contract bottle makers like Graham, who sell by material weight not units. But on monolayer oil bottles, Exxon's resin, with its better ESCR properties has a strong advantage (see also recycling story on p.95). Exxon's HD 9856 B, blended with recycled homopolymer or copolymer, retained substantial ESCR with good top-load and drop-impact strengths in Exxon's tests. HD 9856 B/recycle blends greatly exceeded the ESCR ratings of recycle blends with standard Phillips-type resin, while top-load and drop-impact values were comparable.
Exxon's tests also show its new resin giving superior ESCR compared with a newer, improved ESCR Phillips-type resin from Soltex (see below). In a 52-g commercial bottle molded on a wheel machine and containing 15% recycled homopolymer, Exxon's resin showed ESCR of 140 hr to failure vs. 34 for the Soltex resin. (CIRCLE 7)
WHERE THE OTHERS STAND
To set the record straight, some non-Phillips-process resins from a number of producers have made significant penetration in the North American market--especially since the Phillips plant explosion--but those resins were designed for "drop-in" interchangeability with the standard Phillips types.
Meanwhile, some Phillips licensees have improved on the basic Phillips process and product. A major catalyst modification, for example, reportedly allows Soltex Polymer Corp., Houston, to make a higher ESCR resin than the Phillips standard, recently introduced as Fortiflex HP55-50-153 (see PT, Sept. `90, p. 13). Allied-Signal Inc., Baton Rouge, La., makes dairy-grade HDPE homopolymer considered even by competitors to have better organoleptic qualities than most. And a lot of R&D effort is reportedly continuing in catalyst improvements for the Phillips types.
However, Phillips 66 Co. itself, in Pasadena, Texas, says its first priority now is simply to replace the production it lost in last year's explosion, and that no catalyst changes are planned for now. The first stage of Phillips' recovery of production capacity was to bring on a 300-million-lb/yr unit last month, to be followed by a other 300 million lb this month. Another 600 million lb is due to start up in mid-'91, and a like amount a year later.
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|Title Annotation:||environmental stress-crack-resistance|
|Author:||Schut, Jan H.|
|Date:||Nov 1, 1990|
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