But to the original question...

The maximum pressure a cylindrical vessel can hold is given by:

stress = (pressure * diameter)/2* (wall thickness)

Looks pretty simple. These bottles are made of PET, so let's just assume a tensile strength 7,977 psi. Diameter is about 4.3 inches. Wall thickness is about .017 inches. (I'm pulling numbers out of the air here).

Solving for burst pressure:

(7,977psi)*2*.017 inches/4.3 inches = 63 psig.

You get the idea...

The problem is that under a constant load, plastics tend to increase in length or "creep". Different polymers vary in how much they creep. Teflon is one of the worst! Eventually, the bottle will burst just because it keeps growing. Wall thickness reduces and OD increases. A recipie for disaster in the pressure vessel business!