The Sweet Smell of Success, Resin Style
By Jim Anderton, technical editor
Last Sunday, I bought a bottle of water at my local gas station. There's nothing noteworthy about that, but the beautifully blow molded bottle, with re-sealable squirt cap, was crystal clear, extremely flexible and super lightweight. In other word...
Last Sunday, I bought a bottle of water at my local gas station. There’s nothing noteworthy about that, but the beautifully blow molded bottle, with re-sealable squirt cap, was crystal clear, extremely flexible and super lightweight. In other words, it was a beauty, better than the mundane product inside it.
The water was a different story. It had what my wife calls “that plastic taste”. Plastics can impart a taste or a smell, and that’s the point of this month’s rant: smell. Plastics smell because they’re organic compounds and as organics, they form an enormous pool of chemical compounds that can either stink, or literally smell like roses. A favourite of mine is 2-n-pentyl-3- (2-oxopropyl)-1-cyclopentanone. It’s the aroma of magnolia trees. Paramethylmercaptobenzaldehyde, however, is the rotten egg smell that suggests a natural gas leak. Both are organics, as are most resins. Just as unlucky for our industry is that Mother Nature has equipped us with an olfactory detection system (i.e. a nose) that can detect odoriferous molecules in parts per million concentrations. We’re so good at it that so far machines haven’t yet matched our ability, and panels of test sniffers are still a widely used Q.A. strategy in industries such as food and beverage.
How do you deal with odor? Since you rarely have the luxury of specifying the resin to substitute low odor grades, a possibility is to use fillers or additives that deal with the odor.
Bactericides are an obvious option if your molded parts support mold or mildew growth. The latex industry is a typical example, since it uses a liquid phase technology that can ferment like beer, producing foul odors.
If it’s the “plastic” smell you’re trying to kill, however, you have a couple of choices. One is to attack the problem at its source, by aerating the parts along with an absorber such as activated charcoal or a zeolite. It’s also possible to wash your parts post-mold with solutions that dissolve obnoxious additive residues or smelly leftover monomer. Then you rinse, just like your laundry. Cost prohibitive? Maybe the answer is to mask the odor, rather than eliminating it.
Fragrances are a viable option, but they need specific properties to work well in the polymer industry. They have to be physically and chemically compatible with the base resin, thermally stable enough to survive the trip through the barrel and they can’t interact negatively with the rest of the resin’s additive package. Assuming you can find a perfume that fulfils these tough criteria, how do you get it into your product? Anyone that’s experienced the headache of dry color knows what it’s like to try to disperse a powder effectively in your base resin. Ditto for liquids.
Fortunately for molders (and their compounders) there are easier ways. One is to use a filler that can adsorb the fragrance on its particle surface, and let it carry the scent for you. High specific surface silica is an example, and since you need to fill your resin anyway, cost should be reasonable. Or you can go the masterbatch route. One innovative technique is to use microporous polymer pellets of conventional commodity resins. The microporous structure lets each pellet carry several times its weight in liquid additives, while handling and flowing like dry resin. Additive loading of up to 75% by weight is possible, with good dispersion, too.
Then consider the marketing possibilities. Your product can smell like anything you want, from beef jerky to Johnny Walker Red. How about hard luggage that smells like fabric softener? And the possibilities for automotive interiors alone would be endless. Why not take new car smell to the next level?
