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Resin for retort packaging trays increases rack/surge capacity

GE Advanced Materials : 03 May, 2004  (Application Story)
A new thermoplastic alloy, designed for use in large retort packaging sterilization trays, offers OEMs the ability to increase rack/surge capacity for higher output, double service life, and lower systems costs, helping to improve productivity for food processors.
Introduced by GE Advanced Materials, Noryl PPX 615 resin – an alloy of polyphenylene ether (PPE) and polypropylene (PP) – is targeted at the large trays used to handle retort pouches during sterilization and conveyance due to its special balance of broad chemical resistance, excellent thermal and hydrolytic stability, and stiffness with ductility. The new material also offers good surface appearance, a wide processing window, and fast cycle times, all of which can help moulders improve their bottom line.

Retort sterilisation, invented in the early 19th century, uses superheated steam to cook food while killing pathogens. Today, this food-preservation method is most commonly used for MREs – a military acronym that means Meals Ready to Eat. MREs are highly portable, compact, and easy to prepare – no dishes or water are needed. While the entree may be eaten cold when necessary, it can also be heated in a variety of ways, including submersion in hot water while still sealed in its individual entree package.

Each portioned meal is enclosed in retort packaging, which consists of a heavy-duty multilayer pouch of aluminium and plastic laminate designed to maintain food quality under harsh storage and shipping conditions. Originally developed for military food use, MREs are now used by police, search and rescue teams, outfitters and outdoor enthusiasts, and for disaster preparedness kits. Retort packaging is also used for consumer products such as pet foods, and in non-food institutional sectors such as healthcare. Moreover, the multi-billion dollar retort pouch industry is growing.

The technical challenges of retort sterilisation, however, can be sizeable. The process involves forcing steam at high pressure and temperatures up to 125C into a chamber containing rigid sterilization trays, stacked up to 13 high, in which the pouches sit for as long as 90 minutes. This requires that tray materials have excellent heat-distortion performance under load, as well as dimensional and hydrolytic stability, stiffness, and impact strength. Resistance to common foods and cleaning chemicals are also required properties since the trays must be cleaned after each use and may be exposed to cooking oils and other substances. Common tray materials are metals, wood, or plastics. However, metal trays are typically heavy and can oxidize; wood can be hard to clean and has a limited number of cycles; and, many plastics are limited in that they lack the sufficient mechanical properties needed to resist creep or warpage under the rigorous heat and humidity of retort conditions.

Noryl PPX 615 resin is GE Advanced Materials’ answer to these challenges and represents the newest addition to the company’s growing family of thermoplastic alloys characterized by their versatility, durability, cost-effectiveness, and new levels of design freedom. These products are available from the company in filled and unfilled resin grades and can replace materials such as olefins, ABS, nylon, wood, and metals in a variety of applications.

With Noryl PPX resin, GE Advanced Materials’ technologists have brought together two incompatible resins via a patent-pending alloying technology that incorporates PPE particles into a matrix of PP. The resulting material benefits from the low-temperature toughness, creep resistance, melt strength, aesthetics, and dimensional, hydrolytic, and thermal stability of the dispersed PPE phase. The alloy also gains broader chemical resistance, higher impact strength and flow, greater stiffness, and a lower specific gravity from the PP matrix. By varying the ratio of alloy constituents, new formulations can be tailored to meet different application requirements.

Versus competitive materials, the new GE resin can offer:
• Lower temperature toughness and better impact strength than most olefins;
• Higher thermal performance and mechanical property retention than most olefins;
• Better cleanability than wood with a significantly longer service life;
• Lower mass and generally lower systems costs than metals;
• Greater processing versatility so trays can be produced via injection moulding or thermoforming;
• Good thin-wall performance and living-hinge properties that can expand design flexibility further;
• Recyclability; and,
• Easy-to-clean, non-stick surfaces.

Noryl PPX 615 resin – which is available globally in grey and black – was selected by tray manufacturer, Allpax Products, Inc., for its retort sterilisation trays.

“Allpax had been experiencing challenges with both short- and long-glass-filled polypropylene, including sagging and breaking in the harsh retort environment,” said Vanessa Mirabile, GE Advanced Materials industry manager for Performance Packaging. “So we introduced them to Noryl PPX 615 resin and the material passed all the criteria they required, including rigorous 1,000-hour heat aging and two-foot drop tests. Even after 500 heat cycles, the trays made from Noryl PPX 615 resin experienced minimal warpage.”

Scott Williams, Allpax Products, Inc., business development manager, said, “Switching to Noryl PPX 615 resin has allowed us to increase the rack capacity in our ovens by 35%, which means we achieve higher food output per cycle. In addition, the service life of our trays has doubled, which is a major cost savings for us.”

GE Advanced Materials’ Global Product Manager, Dusty Majumdar, concurs, adding, “The trays made from Noryl PPX 615 resin have held up for one year of continuous production in spray retorts – at six cycles per day – in high-pressure environments, at 125C. We are very satisfied with the performance and utility of the trays.”

According to Thomas Hammoor, GE Advanced Materials’ general manager for Engineered Styrenics, “These new trays are just the tip of the proverbial iceberg in terms of Noryl PPX 615 resin’s capabilities. We’re doing some groundbreaking work with this amazingly rugged and versatile alloy that we expect will continue to offer great benefits to the packaging, food processing, and materials handing industries worldwide. We’re in the business of giving our customers new value-added ways to grow, and this product is a great example of that.”

In addition to food processing, Noryl PPX resins are also targeted at a variety of other applications including power tools, fluid-engineering components, and automobiles.

For more information on retort sterilisation trays, contact Allpax Products, Inc., 13510 Seymour Myers Boulevard, Covington, La. 70433, tel: +1 985 893 9277, fax +1 985 893 9477
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