Months ago, I asked a PET packaging specialist for comments about the draft manuscript of my recent book on green plastics issues. This helpful reviewer’s comments included one very specific concern: I hadn’t emphasized enough that the barrier properties of polylactic acid are PLA’s main limitation that restricts it from being used in many PET-type packaging applications, such as beverage bottles.
Large bottle-making and -using companies have looked into using PLA for beverage bottles, but most, like Nestlé and PepsiCo, have rejected it. PLA’s poor gas barrier means it requires additional barrier layers and/or additives for it to be effective in service – making PLA bottles ultimately a poor “value proposition” in most cases. (And even PET bottles require barrier layers or additives such as oxygen-scavengers to maximize product shelf-life.)
PLA makers and compounders are looking for a breakthrough on the barrier issue -- though seemingly not with as much attention as they’ve displayed in developing additives that address PLA’s other limitations. Major PLA producer NatureWorks LLC offers a technical bulletin that explains the use of barrier polymer layers for improving PLA bottle gas-transmission properties. At the high-tech end of research and development, nanoclay fillers have been used to improve PLA properties, increasing PLA crystallinity and lowering its oxygen-transmission rate.
Despite the challenges, some PLA beverage bottles are being introduced into the market, at a cost. And PLA bottles face at least one other major hurdle – their incompatibility and contaminating effect in current recycling streams and systems – among other obstacles. But these perhaps are topics for future blog postings.
Mike Tolinski is the author of Plastics and Sustainability, published in Oct. 2011 by Wiley-Scrivener, and he is Contributing Editor for Plastics Engineering magazine of the Society of Plastics Engineers in the USA. His views have been shaped by his engineering, university, and journalism experience in the plastics and manufacturing industries over the past 21 years.