Bioplastic as carbon sink

1) Petroleum-derived plastic is an extremely stable form of carbon; it has essentially no decomposers.

2) Biomass-derived “plastic” does decompose, but only at high energy decomposing conditions, i.e. very hot regions in an industrial-scale compost pile (60 C).

This suggests to me that a way to dispose of plastic waste and simultaneously sink carbon in a semi-permanent form is to fuse it, preferably post-consumer, into large masses for use as building material (possibly coated in concrete), similarly to how much building is done on land-fill.

For traditional, petroleum-derived plastic, this simply avoids the problem of having lots of bits of it floating around killing marine life and strangling trees and whatnot, as well as returning it to the earth whence it came. However, for biomass-derived “plastic”, it could possibly be carbon-negative. It seems to me that it would be unlikely to biodegrade if placed in big blobs covered in concrete on the continental shelf or what-have-you. Instead, it would be a fairly stable form of solid-state carbon storage.

How stable, I’m not sure. That is an interesting question.

(Edited a minute later to add: In any case, we certainly shouldn’t be incinerating petroleum plastic! That’s a terrible idea. It’s much better off in a landfill.)