PHB is a thermoplastic - meaning it softens and melts when heated. It is insoluble in water, but has poor resistance to acids and bases and dissolves in chlorinated solvents. Apart from the high production cost, the main problem with using PHB to make consumer goods is its relatively poor mechanical properties.
This causes the chains to form helical structures, with the side groups all pointing away from the centre of the helix to minimise steric hindrance. The chains therefore pack together easily to form crystals, and the crystalline nature of the polymer makes it brittle and stiff. Another drawback is that it is difficult to process in a molten state because it starts to degrade at temperatures not much higher than the melting temperature of 175°C.