No. 26 - PET and PBT

PET was invented in 1941 by ICI in the U.K. and played its first role as a fiber, and its second as film with DuPont’s introduction of Mylar in 1952. It took more than 20 years for PET molding grades to come onto the scene. When they did, they revolutionized the packaging industry with oriented bottles.

In 1973, DuPont’s Nathaniel Wyeth patented the oriented PET beverage bottle. Because DuPont lacked solid-state PET resin production, its initial efforts to produce bottle preforms were unsuccessful, owing to insufficient intrinsic viscosity (I.V., a measure of molecular weight). The first commercial production of PET resin suitable for injection molding preforms came from Goodyear in 1974, which had solid-state capability in place. Between 1976 and 1978, three other suppliers—Celanese, American Hoechst, and Eastman—brought on PET bottle-resin capacity

At NPE 1979, Eastman Chemical introduced “spruce green” bottle-grade PET resins so that plastic bottles could match the color of glass bottles. In the early 1980s, CPET (crystallized PET) arrived as a highly heat-resistant material for thermoformable, dual-ovenable food trays for prepackaged meals and entrees. At NPE 1991, amorphous PET (APET) resins for extrusion blow molding of handleware were introduced by Eastman, DuPont, and Goodyear. APET did not take off, as the market found it too costly because of the thicker walls required. More successful was a glycol-modified amorphous PET, called PETG, introduced by Eastman in 1977. It has been successful in injection and blow molded containers and extruded sheet and profiles.

The current U.S. PET resin market is approaching 7 billion lb/yr. PET dominates the soda and “premium” water bottle market for 2-liter and smaller bottles, where handles are not required.

 

Engineering PET compounds

Glass- or mineral-filled PET was introduced by DuPont in 1978. Rynite PET constituted the first “engineering” grade of PET for general-purpose injection molding. It overcame the limitations of previous reinforced PETs, which were difficult to mold and suffered poor surface quality, brittleness, and warpage. Many of the earliest applications were electrical parts, such as coil forms, automotive ignitions, transformer housings, terminal blocks, motor end brackets, fuse caps, and light housings. Some other applications in Rynite’s first decade were chair shells and arms, bicycle drive parts, and boat propellers. Within five years, Rynite had at least four domestic competitors and at least 15 by the end of the 1980s.

 

PBT was first in molding

PBT for injection molding was first brought to the market in 1969 by Celanese, with its Celanex 3300, a 30% glass-filled grade. In 1972, GE introduced both unreinforced Valox PBT and a 30% glass-filled grade. Not long after, GE launched flame-retardant grades. By 1977, Eastman, GAF, LNP, and Thermofil had entered the business, with Fiberfil and Mobay not far behind.

The earliest PBT applications were in the electrical/electronic connectors, switches, controls, and automotive high-energy ignition systems. PBT also played a major part in the development of plastic automotive bumper systems. GE alloyed PBT with PC to produce Xenoy, a material with high impact strength at low temperatures plus heat and chemical resistance that enabled all-plastic auto-bumper systems to replace steel. The 1984 Ford Taurus/Mercury Sable were the first cars to utilizes this system in both front and rear bumpers.