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Any article about biodegradable plastics should start with advantages over cellophane/cellulose. People have figured out how to make it a hundred years ago, it

Any article about biodegradable plastics should start with advantages over cellophane/cellulose. People have figured out how to make it a hundred years ago, it's already used for food packaging, known properties, abundant and cheap - made from trees / other plants. The article starts as if it's some breakthrough miracle which is unheard of. I can literally just buy compostable bags for organic waste made of corn starch on Amazon. It's already a product. Journalist demonstrate less awareness than 8B LLM. Scientist tells you about a new plastic? Ask them how it's better than what's already on the market.

coryrc 7mo ago
> I can literally just buy compostable bags for organic waste made of corn starch on Amazon. They compost, but they don't biodegrade. The difference is whether it breaks into microplastics or dissolves/is digested in the ocean.
- jacobolus 7mo ago
  My understanding is that cellophane generally does biodegrade in most settings. Polylactic acid (those cornstarch-derived bags) mostly biodegrades in hot enough compost or (after several years) in ambient-temperature soil, but not very well in cooler water (One study: "The half-life period of degradation [of polylactic acid in artificial seawater] is 12 [days at 90° C] or 468 days [at 60° C]").
  - toss1 7mo ago
    >> 12 [days at 90° C] or 468 days [at 60° C] Those temperatures are certainly hard to find in nature, outside of hot springs! Even if this is an error and we are talking about 90°F/60°F, the higher temperature is pretty much constrained to the tropics, so we're talking a year+ to degrade in real conditions. It is better than centuries, but not exactly rapid?
    - jacobolus 7mo ago
      Yeah, I imagine it's considerably slower at ambient ocean temperature. Don't throw your PLA bags in the ocean or a river. Here's a different paper: > For example, PLA is not biodegradable in freshwater and seawater at low temperatures [32,36–39]. There are two primary reasons for this: (i) The hydrophobic nature of PLA, which does not easily absorb water [40–42]. In aqueous environments, the lack of hydrophilicity diminishes the hydrolysis process, which is crucial for the initial breakdown of PLA into smaller, more degradable fragments. (ii) Resistance to enzymatic attack; the enzymes that degrade PLA are not prevalent or active under typical freshwater and seawater conditions [39,43,44]. The microbial communities in these environments may not produce the necessary enzymes in sufficient quantities or at the required activity levels to effectively breakdown PLA. Additionally, the relatively stable and crystalline domains of PLA can further resist enzymatic degradation. Also: > It should be emphasized that neat PLA cannot be classified as a completely biodegradable polymer, as it generates microplastics (MPs) during biodegradation.
  - IAmBroom 7mo ago
    That can't be right - even 60 C is 140 F. No normal water bodies are near that hot. If it's actually 60/90 FAHRENHEIT, very few water bodies are (currently) 90 F. That's above even most equatorial temps.
    - jacobolus 7mo ago
      Yes, that's the point. It will only break down in water when the water is hot. Here's the paper https://link.springer.com/article/10.1007/s11696-022-02286-x https://link.springer.com/article/10.1007/s11696-022-02286-x
crystal_revenge 7mo ago
> Story Source: > Materials provided by Flinders University. It's not that the "journalist" didn't think to ask, it's that this is a PR piece sent out to media outlets from the university that did the research. Nearly all universities have a PR team that sets fluff pieces out to the media to promote the work of the university. The person who wrote this is being paid not to ask tough and important questions around this research.
marcosdumay 7mo ago
> Any article about biodegradable plastics should start with advantages over cellophane/cellulose. Well, I guess it starts with the plastic being thermoplastic.

coryrc 7mo ago

> I can literally just buy compostable bags for organic waste made of corn starch on Amazon. They compost, but they don't biodegrade. The difference is whether it breaks into microplastics or dissolves/is digested in the ocean.

jacobolus 7mo ago
My understanding is that cellophane generally does biodegrade in most settings. Polylactic acid (those cornstarch-derived bags) mostly biodegrades in hot enough compost or (after several years) in ambient-temperature soil, but not very well in cooler water (One study: "The half-life period of degradation [of polylactic acid in artificial seawater] is 12 [days at 90° C] or 468 days [at 60° C]").
- toss1 7mo ago
  >> 12 [days at 90° C] or 468 days [at 60° C] Those temperatures are certainly hard to find in nature, outside of hot springs! Even if this is an error and we are talking about 90°F/60°F, the higher temperature is pretty much constrained to the tropics, so we're talking a year+ to degrade in real conditions. It is better than centuries, but not exactly rapid?
  - jacobolus 7mo ago
    Yeah, I imagine it's considerably slower at ambient ocean temperature. Don't throw your PLA bags in the ocean or a river. Here's a different paper: > For example, PLA is not biodegradable in freshwater and seawater at low temperatures [32,36–39]. There are two primary reasons for this: (i) The hydrophobic nature of PLA, which does not easily absorb water [40–42]. In aqueous environments, the lack of hydrophilicity diminishes the hydrolysis process, which is crucial for the initial breakdown of PLA into smaller, more degradable fragments. (ii) Resistance to enzymatic attack; the enzymes that degrade PLA are not prevalent or active under typical freshwater and seawater conditions [39,43,44]. The microbial communities in these environments may not produce the necessary enzymes in sufficient quantities or at the required activity levels to effectively breakdown PLA. Additionally, the relatively stable and crystalline domains of PLA can further resist enzymatic degradation. Also: > It should be emphasized that neat PLA cannot be classified as a completely biodegradable polymer, as it generates microplastics (MPs) during biodegradation.
- IAmBroom 7mo ago
  That can't be right - even 60 C is 140 F. No normal water bodies are near that hot. If it's actually 60/90 FAHRENHEIT, very few water bodies are (currently) 90 F. That's above even most equatorial temps.
  - jacobolus 7mo ago
    Yes, that's the point. It will only break down in water when the water is hot. Here's the paper https://link.springer.com/article/10.1007/s11696-022-02286-x https://link.springer.com/article/10.1007/s11696-022-02286-x

crystal_revenge 7mo ago

> Story Source: > Materials provided by Flinders University. It's not that the "journalist" didn't think to ask, it's that this is a PR piece sent out to media outlets from the university that did the research. Nearly all universities have a PR team that sets fluff pieces out to the media to promote the work of the university. The person who wrote this is being paid not to ask tough and important questions around this research.

marcosdumay 7mo ago

> Any article about biodegradable plastics should start with advantages over cellophane/cellulose. Well, I guess it starts with the plastic being thermoplastic.