I suspect they wouldn't degrade very quickly in a compost pile, either, but I wouldn't assume that's necessarily true. In any case, they do degrade, and In my experience as a gardener, the best compost piles made from n normal household waste should age for about 2 years or so before using them.
I agree, Ann. Two years sounds about right for a compost pile. I've found that a compost pile that is entirely yard scraps (leaves, cut grass) becomes available to plow into the soil much more quickly. One year seems to be fine (especially if you water the pile regularly). But maybe I only have to water because I live in a desert.
Rob, two years is about how long we aged our compost piles when we combined kitchen waste with yard waste for use in the vegetable garden. Although some kitchen waste items take longer to degrade, they are important for the soil. The goal of a compost pile isn't necessarily quick decomposing, but the balance of nutrients achieved.
Thanks for your comments, Ivan. Biodegradable plastics biodegrade into CO2 and water, the ingredients that they started as. That's what biodegradable generally means. Here are some definitions from the SPI:
I discovered during the reporting for this article that there's a lack of awareness of what biodegradable and compostable mean, especially in relation to plastics. So here are links to the ASTM standards descriptions:
ASTM 6400 Standard Specification for Compostable Plastics
ASTM 6868 Standard Specification for Labeling of End Items that Incorporate Plastics and Polymers as Coatings or Additives with Paper and Other Substrates Designed to be Aerobically Composted in Municipal or Industrial Facilities
ASTM D7081Standard Specification for Non Floating Biodegradable Plastics in the Marine Environment
Plastics ands elastomers, thanks for commenting, but I don't speak Asian languages or read their scripts, nor do most of our readers. Can you try writing again in English? We'd like to know what you wrote.
Ann, thanks for another great article. I think your article hit the nail on the head about the decision-making process. Most companies these days say that sustainability is important to them, but very few are willing to pay extra for it.
If Material A is more expensive than Material B, I can make a case to management for Material A if I can show that using Material A rather than Material B will lead to a marketable improvement in product performance, a reduction in warranty costs, or elimination of a manufacturing step. But I can't make a case to management that using Material A will reduce harm to the environment, because the environment doesn't directly affect the company's bottom line.
The only exceptions would be if costly regulations restricting the use of Material B are likely, or if it is a high profile application where the use of Material A could be taken advantage of for marketing purposes.
What this means is that bioplastics suppliers need to bring prices in line with petroleum-based plastics, or else offer convincing performance benefits. This article shows that the suppliers are aware of this, and are trying to make it a reality.
Dave, thanks for your comments. I hope to get some more detailed, targeted input on that decision-making process during design. The bioplastics performance is now equal to or better than petro-based plastics in many cases. Cost is also coming down. In some markets, mostly consumer-related, the sustainability argument is at least a starting point. For example, witness Ford's programs to incorporate an increasing proportion of recycled content in its materials from suppliers:
This was a great description of the spectrum of bio polymers available. The inclusion of big company players like Dupont and BASF is a good indication that bio polymers will become better and cheaper in time. The avaialability of engineering grade polyamides that use bio stock can open up the doors to companies to be green without sacrificing any product performance.
Thanks for your comments, Tim. I was surprised at how far engineering bioplastics have come, and encouraged at the performance gains they've continued to make, as well as the gradually decreasing price differential.
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