Not familiar with the 'TPBI' product, but are biodegradable really as they advertise in the real world usage of:
"Biodegradable plastic bags
To put it simply, something is biodegradable when living things, like fungi or bacteria, can break it down. Biodegradable bags are made from plant-based materials like corn and wheat starch rather than petroleum. However when it comes to this kind of plastic, there are certain conditions required for the bag to begin to biodegrade.
Firstly, temperatures need to reach 50 degrees Celsius. Secondly, the bag needs to be exposed to UV light. In an oceanic environment, you'd be hard pressed to meet either of these criteria. Plus, if biodegradable bags are sent to landfill, they break down without oxygen to produce methane, a greenhouse gas with a warming capacity 21 times more powerful than carbon dioxide."
https://www.1millionwomen.com.au/blog/plastic-bags-whats-difference-between-degradable-compostable-and-biodegradable/