PET & PETG Drive a 'Hard' Bargain

Despite a plethora of competing thermoplastics in the market, PET and PETG have made solid strides to become a popular choice for extruders and fabricators in the plastics industry.

BY KEVIN BASTIAN

In the food industry, presentation is often just as important as taste. To achieve an eye-catching appearance, PET and PETG are called to duty. Food storage and containers, among several other plastic products in such markets as electronics packaging and point-of-purchase displays, benefit from the thermoplastics' excellent properties.

PET, or polyethylene terephthalate, resins are thermoplastic polyester engineering resins. Numerous companies manufacture this resin, which is an inherently crystallizable polymer. However, by replacing some of the basic acid or glycol with secondary acids or glycols, the crystallization can be slowed down. With a sufficient amount of CHDM (1, 4-cyclohexanedimethanol) added, Eastman Chemical Co., for example, is able to produce PETG, an amorphous copolyester that will not crystallize. Eastman is considered to be the plastics industry's chief supplier of PETG resin.

"PET is a semi-crystalline product that will turn white when heated," said Randy Beavers, business market manager for Eastman in Kingsport, TN. "Polymer chains align themselves and the sheet or film turns opaque. PETG is amorphous and will not crystallize. You can heat bend it and it stays clear. Parts of PET are less tough in the crystallized areas and may break when force is applied."

PET and PETG have competed with acrylic and polycarbonate for many years in markets such as point-of-purchase displays and fixtures, food packaging, indoor/outdoor signage, and electronic and medical packaging markets. The resins possess some advantages over their competitors while lacking in other areas.

Seeking the expertise of company representatives, Plastics Machining & Fabricating asked leading manufacturers, distributors and fabricators about the following:

1. What advantages/disadvantages do PET/PETG have compared to other leading thermoplastics?

2. What are some of the most common and unique uses for PET/PETG?

3. What developments do you foresee in the next decade for PET/PETG?

PET/PETG Properties: Advantages/Disadvantages
On the topic of PET and PETG's properties as compared to other thermoplastics, a large number of manufacturers agreed as to their best characteristics. "Impact resistance is PETG's number one property -- without a doubt," said Daniel Rustin, marketing manager for Acrilex Inc. in Jersey City, NJ.

"When PETG is extruded in sheet, the sheet product is 15 to 20 times tougher than general-purpose acrylic and three to 10 times tougher than impact-modified acrylic," added Beavers. "It's 60 to 70 percent as tough as polycarbonate, but polycarbonate is sometimes over-engineered for its applications. They don't need the toughness."

Though tough, PETG still faces stiff competition in impact resistance, according to Scott Smith, executive manager for Repete Plastics in Geneva, IL. "The glycol used in the formulation makes PETG much less brittle than PET. Although it is not as strong as PVC in the same gauge comparison, you can compare a PETG in a gauge 2 to 3 mil (1 mil = 1/1000 of an inch) higher than PVC and you will realize the same strength," said Smith.

Clarity is also a property in which both PET and PETG could benefit from increased enhancement. While acrylic's clarity reigns supreme among thermoplastics, PET and PETG's optics rank about the same as polycarbonate sheet, according to Beavers.

PET's clarity is not as good as that of PETG mainly because of thermoforming, Beavers added. During this process, the polyester crystallizes, causing it to haze and become less clear than PETG, which is designed to avoid crystallization during forming. Sheets of PETG can have no color, resulting in a perfectly suited material for food packaging. The clarity allows for bar code reading through the package as well as accurate inspection of packaged components by manufacturing or customs personnel.

Besides non-crystallization, PETG's thermoformability is also an advantageous property because of the material's wide thermoforming window, reproducibility of products and ability to form at lower temperatures (300F to 320F) with shorter cycle times than acrylic or polycarbonate. According to Beavers, PET has a narrow forming window and will haze if formed at too hot or cold temperature.

Bob Crohan, product manager of Lustro Plastics Co. in Evanston, IL, adds, "PETG does not require pre-drying like polycarbonate and thermoformers benefit from lower initial cost and lower processing costs."

Fabricating sheet produced from PETG is also easy because of its toughness. Sawing, routing, die-cutting, drilling, bending and flame polishing are all made simple. "No challenges exist in regard to fabricating and machining," said Crohan. "Sheet extruded from PETG is easily fabricated and can be cold-bent without crease whitening at the bend."

In regards to the handful of fabricating possibilities with sheet material, Rustin added, "Polycarbonate and acrylic may have some of these capabilities, but not all. PETG has a broader range of properties."

"Polyesters inherently have good chemical resistance," said Beavers. "In heavy traffic areas (such as in grocery and department stores), fixtures need to be cleaned every day. Using a sheet of PETG, the products won't haze or craze."

Probably the most beneficial of PETG's properties in the long run is its cost-to-performance ratio. It is 15 to 25 percent more expensive than general purpose acrylic sheet, 2 to 10 percent lower than impact-modified acrylic sheet and 20 to 40 percent lower than polycarbonate sheet, Beavers said. Sheet and film manufactured from PET is somewhat cheaper than from PETG.

PET also offers users some profitable characteristics. According to Michael Oliveto, marketing manager of DSM Engineering Plastic Products, in Reading, PA, compared to nylon and acetal, PET has "better resistance to acidic solutions and chlorinated aqueous solutions commonly used to sanitize food processing equipment."

Oliveto also referred to its high wear and abrasion resistance, saying, "In both low load/high speed and high load/low speed conditions, PET provides three times greater wear life than acetal, based on a K factor, and up to 15 percent greater wear life than unfilled nylon. The high PV capabilities, low friction and wear rate of PET allow products made of this material to run fast and more efficiently and last longer." He also noted that PET stock shapes have very low residual stress and are porosity-free.

Dennis Magyar, business manager of the melinar PET container resin region, a business of DuPont Polyester in Wilmington, DE, also gave PET high marks. "It's self-limiting so that it can be produced by the injection stretch blow molding process, and environmentally friendly as far as low metals, high oxygen content and recyclability. And, of course, its low CO2 permeability makes it suitable for CSD packaging," Magyar said.

A.F. Leger, executive chairman of Vesco Plastics in Virginia, South Africa, agreed on PET's advantages concerning its wear, chemical resistance and loading strength, but also noted its downsides. According to Leger, PET has a much lower water absorption than nylon and a low resistance to alkalis and hot water.

PET also has a lower impact resistance than other thermoplastics and is more difficult to cut, according to Joe Rusinek, director of sales and marketing for PurePlast Inc. in Cambridge, Ontario. Problems with PETG's gluing and bondability capabilities also exist, added Rustin, but the "practice makes perfect" method can be put to use. "Once you've mastered the technique, it doesn't require any further efforts. It's once you know how -- that's the key," he said.

Beavers also noted that PET and PETG are not inherently UV-stable, meaning they will yellow and embrittle when exposed to the sun for long periods of time.

Applications
PET and PETG's broad range of advantages makes them suitable for a number of products in a number of different markets. PET's primary market is packaging for soft drinks, bottled water, fruit-based beverages and iced teas. PETG is chiefly utilized in food, medical and electronic packaging. It has also seen use in the display fixture industry.

"This represents a new standard in design freedom for displays," said Beavers. "Excellent clarity, impact strength -- even at thinner gauges and cold temperatures -- deep draw characteristics and ease of fabrication, have all contributed to the growth of this sheet in display and store fixture applications."

Smith sees PETG filling a more important role in a separate industry. "The most common applications for PETG in virgin form are medical and food packaging," he said. "Blisters, clamshells and trays are the most common medical packages for instruments and disposable trays. PETG is a good choice for this mainly because of its ability to stand up to gamma irradiation used to sterilize medical instruments within the package." Smith cites blue tint PETG as the most common medical packaging material used because it aids greatly in the inspection and assurance of the seal around the instrument packaged within. In food packaging, he finds clear lids as the most common use of PETG because of its favorable gas permeation properties for food and the great clarity it provides, making for an attractive food package.

Smith's company, Repete Plastics, produces only recycled PETG material, which cannot be used for either medical or food packaging. "There are a variety of non-durable consumer goods that are packaged in our material," he said. "PETG provides excellent clarity and toughness. Bottom line -- it makes for an attractive package."

Other applications using PET and PETG range from electronic packaging and signage to architectural glazing, game boards, graphic arts, and tub and shower surrounds.

Growing Trends
With more and more applications requiring materials that are stronger, clearer and more directed to their specific needs, manufacturers of thermoplastics are constantly working on new and improved developments and properties for their resins. Regarding the future of PET, PETG and copolymers, representative responses varied greatly due to the diverse focuses of their respective companies.

"We foresee improvement in impact strength, service life and resistance to hot water, as well as a broadening of the size range produced, leading to new applications," said Leger regarding the market for PET.

Mark Ballard, director of manufacturing for Kama Corp. in Hazleton, PA, said he also expects greater acceptance of PET by markets dominated by other clear resins as well as the utilization of secondary finishing techniques such as sonic and radio frequency sealing. Randy Deeley, process improvement coordinator for Vinyl Plastics Inc. in Sheboygan Falls, WI, adds, "PET and PETG will need to be blended with other clear resins for price and performance enhancements."

In addition to improvements in PETG's brightness and bondability, Beavers sees more advancements in UV protection being made in the material's future, especially with refrigerated vending machines. A current problem with the majority of materials now being used is from fading or yellowing due to overexposure to the sun.

Architectural building and construction markets, bus shelters, office partitions, glazing applications, taxi shields, machine guards and transparent golf cart tops are other areas in which Beavers sees more affiliation in the future of copolymers. "We're looking at market research and putting together strategies to go after those markets," he said.

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