Finding Balance

“There are two reasons why commodity resins have moved up into what people used to consider engineering resins,” explains Eric Kelusky, vice-president, Advanced Sclairtech Development, NOVA Chemicals. “One reason is because of what molders and mold designers have done. They’ve found better ways to engineer products. The other reason is that people have found ways to make better polymers.”

In many cases, the defining technology shift has been the use of single-site catalysts. A long time in development, these catalysts are no longer in the realm of labs and theory. They have proven their mettle in the real world, showing tangible benefits in commercial applications. High performance styrenic co-polymers also show promise in areas such as freezer-to-microwave applications or clear, tough applications.

John Siegrist, vice-president, styrenic polymer sales, NOVA Chemicals, explains the dynamics of the economy have forced the market to seek alternatives to high-end engineering resins, and styrenic performance products are providing attractive, value solutions. “A few years ago there was a lot of talk about “down-engineering”. Then, in the last 3 to 4 years, many engineering resins have come under pricing pressure, and the whole dynamic has changed. Now, the market has tested functionality to a greater extent than ever before, in both packaging and durable goods.”

LOOK AT THE WHOLE PICTURE

Dow’s QUESTRA resins, for example, are syndiotactic polystyrene (SPS) manufactured using single-site catalysts. These easy-to-process crystalline polymers are often used in connectors and other electronics components, and have been known to replace PBT and glass-filled PPS.

In one case, engineers at Honeywell Consumer Products Ltd. (Hong Kong, China) were introduced to QUESTRA EA528 and EA540 as potential replacements for 30% glass-filled polybutylene terephthalate (PBT) and 40% glass-filled polyphenylene sulfide (PPS) for two heater fan applications.

The two QUESTRA resins outperformed the incumbent resins in testing and were selected to replace the PBT and PPS in this situation. The QUESTRA resins had superior or comparable heat resistance, improved processability and very good dimensional stability. As well, QUESTRA resins have low density, meaning they can produce more parts per pound, and reduce part weight.

Dow states that QUESTRA resins are often a “drop-in” replacement with only slight adjustments to processing parameters and minimal, if any, changes to molds. The SPS resins have minimal, consistent shrinkage between the crystalline and amorphous stages, which permits finished parts without the bowing and warping typical of PBT and other traditional solutions, states Dow.

“In comparison to competitive materials like nylon and PBT, QUESTRA resins are very easy to process,” says Chuck Schulthies, plastics manufacturing manager of Oberg Arizona (Chandler, AZ). Oberg chose QUESTRA for a connector housing to be used in LAN and telecommunications applications.

“Any company is always focussed on how to put more value in a product,” says Kelusky. “Value is more performance at lower cost. The trick is for designers and molders to find that balance of properties and value.”

THE END-USER IS MATERIAL NEUTRAL

Referring to NOVA Chemicals’ ARCEL polystyrene/polyethylene interpolymer for packaging applications, Siegrist says, “Our customers’ customers are material neutral. They care about value in use, and how it relates to an economical solution.”

In other words, the company using the packaging has no preconceptions about what resin it should be made from. They just look at the performance vs. economics equation.

Siegrist: “My belief is that the various packaging engineers have resin families that they think of, and that those resin families have a whole list of attributes. But because the industry is so competitive now, engineers are forced to look at value-in-use. They are more material neutral than ever before.”

NOVA has a sophisticated process model to demonstrate how their performance resins would work in existing applications.

“Once you get one success, then success breeds success,” says Siegrist.

Kelusky explains that NOVA’s Advanced Sclairtech technology has two features that allow the producer to tailor the architecture of the polymer. The fact that Advanced Sclairtech is a multi-reactor process, with each reactor forming a different part of the polymer, and the fact that it uses single-site catalysts, which create a consistent polymer each time, add up to a more “precise” polymer, he says.

POLYPROPYLENE’S POPULAR

Stiff, tough and economical, polypropylene is cost-effective for two reasons: the base material can be produced cost-effectively, and polypropylene has the lowest density of all plastics.

Basell’s proprietary Catalloy process has been a key factor in the growth of its polypropylene compounds in automotive markets. This process allows in-reactor alloying and grafting using multiple monomer inputs. The Catalloy process produces materials over a wide property specturm and with a high degree of consistency.

According to Basell, polypropylene is the most widely used thermoplastic in automobiles, with an average utilization of 50 kg per vehicle in mature markets. For example, Basell’s Hostacom advanced polyolefins can be used in under-the-hood applications. They have good dimensional stability and contribute as a sound barrier in some cases.

The company reports that filled polypropylene compounds are being replaced by high-crystallinity polypropylenes to achieve weight savings, particularly in parts such as heater housings. Basell’s new very high melt flow, high crystalline polypropylene grades allow for even more complex design of heater housings.

In power tools, Hostacom polypropylene is also making inroads. Housings for Black & Decker’s drills, sanders, jigsaws and its new Scorpion Saw have all been fabricated with the Hostacom D1250 grade, a 30% glass-coupled polypropylene. This material has a good balance of stiffness and toughness, and has a low density compared with engineering polymers.

Black & Decker performs demanding drop tests to ensure the selected materials conform to drop impact requirements, and also conducts screw retention tests and life cycle trials.

Basell has also been involved with a novel process involving polyolefins. Smoby, a toy manufacturing firm based in France, has used water-injection molding with a polyolefin material for the handlebars and front fork of a tricycle. The fork was particularly challenging because of its complex fill geometry and standards governing its behavior in crash tests. In addition to meeting the mechanical and rheological characteristics for water-injection molding, the material was colored to mimic pearlescent aluminum grey.

The project involved Basell, Smoby’s designers, the toolmaker Etd, machinery manufacturer Battenfeld and an engineering design company called Simplast.

SAME PROCESS, DIFFERENT RESULTS

One benefit of NOVA Chemicals’ styrenics performance product grades is that they can be run on the same equipment as lower performing grades because they share the styrenics “backbone” and have similar molecular structures. If you switch resin families to find better properties, you may need to invest in equipment modifications as well. If you simply upgrade to a more finely-tuned version of what you already use, you’re less likely to have to modify your processing equipment as well.

In food packaging, for microwave reheating, for example, DYLARK FG styrenic copolymer offers an alternative to polypropylenes and polyphenylene oxide-modified HIPS. Segrist notes that Dylark FG has very good low temperature performance, so it performs well in the freezer, plus it has good retention of its shape and rigidity when reheated in the microwave. It generally permits downgauging when compared with alternative materials. It can also be easily extruded into sheet and thermoformed by existing customers who run standard polystyrene.

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HIGH GROWTH FOR LONG-FIBRE REINFORCED GRADES

Long-fi
bre reinforced thermoplastics are an option when the application requires high strength at lower cost.

When Briggs & Stratton Corp. increased the impact strength requirements for a gas cap, Thermotech, which produces the cap, switched over to Celstran PP-GF40 long fibre-reinforced thermoplastic (LFRT). Celstran LFRT, which is made by Ticona, gave the best combination of strength, fuel resistance, appearance and economics versus the other resins evaluated. The alternatives included impact-modified nylon.

“The new impact test we had to meet called for dropping a two-pound (4.4 kg) ball on a cap from a height of 55 inches (40 cm) at -20F (-29C),” says Tim Hardwick, district sales manager at Thermotech.

The Celstran grade that was chosen has a polypropylene matrix reinforced with 40% long glass fibres. “This grade gave us the impact strength we needed at a cost that is at least 25% below that of most impact-modified engineering resins.”

A new report from Townsend Polymer Service & Information calls long-fibre reinforced thermoplastics (LFRT) one of the fastest growing materials in the industry. The group predicts global consumption of LFRT in 2003 will be 225 million lb., up from 133 million in 2001. The driving forces in this rapid growth are advances in technology, the development of in-line compounding and increased acceptance in the automotive market. Door modules and running boards are cited as two new applications. The report is available for purchase from Townsend PS&I.

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RAISING THE BAR IN ROTOMOLDING

Rod Gonzales, market manager, polyethylene molding products for NOVA Chemicals, is gung-ho about the growth possibilities for advanced polyethylenes in rotomolding applications. “What’s great is that rotomolders are entrepreneurs,” he says. “They think out of the box.”

One emerging application for large rotomolded parts is what Gonzales calls “plastic roads.” These are made of large, flat, interlocking panels. They are used to form a roadway on unstable surfaces such as muskeg. Cold temperature impact properties are especially important in this application.

In recreational products, such as boats, rotomolded PE parts are replacing FRP in consoles, fascia and even in boat bodies for canoes and kayaks. “Advanced polyethylenes offer the strength properties, increased density and higher impact strength,” he explains.

NOVA Chemicals offers two grades of Surpass resins, made with the Advanced Sclairtech process, for rotomolding. Surpass RMs529 is a high flow, super rigid grade for applications that require good processability. It has a melt index of 5.0 g/10 min., and density of 0.939 g/cm3.

For more industrial applications that require higher strength, there’s Surpass RMs244. It has melt index of 1.8 g/10 min., with 0.944 g/cm3 density.

Rhodia Engineering Plastics has also recognized the growth potential of rotomolding. Working with key players in the industry, Rhodia has developed polyamide 6 grades for rotomolding.