Pulse blow method for forming container with enhanced thermal stability

A method of making a container having an enhanced thermal stability comprising the steps of:

• (a) providing a heated preform of an orientable and crystallizable polymer at a temperature in the orientation temperature range of the polymer, the preform being substantially transparent and amorphous, the preform having an elongated body-forming portion and a base-forming portion;
• (b) performing at least one pulse-blow step in a cavity of a blow mold to form a substantially transparent intermediate article, the pulse-blow step comprising:
• i) expanding at least the body-forming portion axially and radially at a first high-strain expansion rate to form crystal nucleation sites in the expanded body-forming portion;
• ii) holding the expanded body-forming portion under pressure to allow crystalline growth and relaxation of amorphous orientation, the expanded body-forming portion being smaller than and spaced from the cavity defining surface of the blow mold;
• iii) reducing the pressure and at least partially deflating the expanded body-forming portion to allow further relaxation of amorphous orientation;
• and
• (c) performing a final expansion step to form a final container having a substantially transparent and partially crystalline body with enhanced thermal stability, the final expansion step comprising expanding the at least partially deflated body-forming portion to fill the blow mold cavity at a second low-strain expansion rate to minimize the amorphous orientation.