The vast majority of the bottles are conventional monolayer PET. However a number of products have higher-barrier requirements than can be met by conventional monolayer PET. Such products include ketchup, some fruit juices, spaghetti sauce, and barbecue sauce, just to name a few. In this article we review a few of the technologies available for manufacturing high-barrier PET bottles. By no means is our review exhaustive in terms of covering all available technologies. But these are technologies that we find to be particularly interesting.
Going back a number of years ago, co-injection/stretch blow-molded PET bottles were a major technology used for high oxygen barrier, typically incorporating EVOH. Over the years there has been a trend away from co-injection/stretch blow-molded barrier bottles to other technologies. A major concern about co-injection/stretch blow molding were difficulties in commingling these barrier containers, which are made of multiple resins, with conventional PET bottles in the recycling stream. It’s possible for these multi-layer barrier bottles to contaminate the recycled PET resin and reduce overall clarity.
Monolayer PET barrier bottles
There has definitely been a trend toward increased use of monolayer PET barrier bottles, away from co-injection/stretch blow-molded and coated PET containers over the last few years. Nylon MXD6 emerged as a barrier resin that, when blended with PET, produced significant enhancements in oxygen barrier. MonOxbar® and Amosorb® are two technologies that are used in the US market commercially that do contain MXD6 nylon.
However, one of the problems that arises when using MXD6 nylon is that it tends to yellow the recycled PET material when mixed with conventional PET bottles. This is a major concern in the industry and there is significant interest in developing barrier containers that do not cause the recycled PET resin to yellow.
DiamondClear’ is a technology that was developed by Constar. It is a monolayer technology that blends in a proprietary barrier material with PET. DiamondClear containers can be mixed with conventional PET bottles in the recycling stream, as can other monolayer technologies. However, the real advantage of this technology is that it does not use Nylon MXD6 nylon (or for that matter any nylon) and that it reduces the yellowing that can occur when recycling it with conventional PET containers. ConAgra Foods converted its 46-oz plastic Hunt’s Kethcup bottle to Constar’s DiamondClear technology and won the 3M 2007 Sustainable Packaging Award at the AmeriStar competition. Constar is actively promoting this technology commercially.
"Nylon-free" technologies may be the wave of the future
"A number of new technologies have recently been introduced that are used to produce nylon-free monolayer PET barrier bottles, and they may just be the wave of the future," according to Gordon Bockner, President of Business Development Associates.
Two such technologies, from Invista and from Valspar, were described in presentations delivered at Nova-Pack 2008. Invista is developing a new oxygen scavenger material called Active Barrier that is designed to be blended with PET for improved OTR (oxygen transmission rate). Invista claims that a 3% blend of Active Barrier with PET provides an oxygen ingress of <1 PPM in 9 months in empty 500 ml 24 g bottles. Invista states that this is still a developmental product, and it is pursuing FDA and regulatory clearance in Europe. Commercial quantities are expected in 2009.
Another new technology that was just introduced is Valspar’s valOR® Activ300 barrier resin, which is another nylon-free product. What is unique about this new Valspar product is that it is a two component system that does not start working until the two components are mixed together at the in-feed system of the injection molding machine, along with PET resin.
ColorMatrix is also at work on a new oxygen scavenging technology that it calls HyGuard. What is unique about this technology is that it has a triggering mechanism that initiates oxygen scavenging upon the filling of the bottles, which reduces the amount of scavenging additive required. This technology is not yet commercial but is expected to be commercialized shortly. Through this unique triggering mechanism, ColorMatrix believes that further light-weighing of PET containers will be possible.
At this point it is too early to determine which technologies will prove commercially successful. But with all of the developmental efforts now focused on barrier PET, it’s certainly a packaging sector that bears watching.