The disadvantages of polypropylene are that it tends to degrade from exposure to UV light, high temperatures or oxygen. It is hard to work with at high temperatures, and it is flammable and does not bond well with paint. Additives help offset these disadvantages.
Degradation in polypropylene products often results in the products becoming brittle and developing small cracks that enlarge with time. A UV-absorbing additive is introduced during manufacturing that prevents the plastic from absorbing the UV rays directly. Carbon black added to the polypropylene mix can also help protect against UV rays. To protect against oxidation, anti-oxidants are added to stop the oxygen molecules from bleeding off, making the material brittle. Additives tend to raise the price of polypropylene, and while they can slow degradation, they cannot prevent it entirely.
Another primary disadvantage of polypropylene is that it has a high thermal expansion coefficient, making it hard to work with at high temperatures. When exposed to high temperatures, the material tends to deform easily, thus limiting manufacturing methods primarily to injection molding, which can limit the sizes of objects created with the plastic.
There are several other more minor disadvantages, such as the material's high flammability when used in its natural state, along with its inability to bond well with paint. Additives have managed to lower flammability to safe levels, and techniques have been developed to allow painting of polypropylene surfaces. These modifications make the plastic a common choice as a manufacturing material for anything from containers to furnishings.