Process for orienting partially crystallized 3-hydroxybutyrate polymers

A process for the production of an oriented shaped article from a polymer containing at least 40 mole % of 3-hydroxybutyrate residues in the polymer chain comprising uni- or bi-axially drawing a preform of said hydroxybutyrate polymer in a partially crystalline state at a temperature between the glass transition temperature, Tg, and the melting point of the hydroxybutyrate polymer into said shaped article, and then increasing the degree of crystallinity of the hydroxybutyrate polymer by subjecting the drawn preform, while in the drawn condition, to a temperature between the glass transition temperature and the drawing temperature until the drawn article is nonrubbery, the amount of said uni- or bi-axial drawing being such that, after said step of increasing the degree of crystallinity, at least one dimension of the preform has increased by at least 200%, said hydroxybutyrate polymer having a degree of crystallinity, at the time of drawing, such that the preform is not so brittle that it breaks before achieving said increase in said at least one dimension, and such that the drawn article does not break during the step of increasing the degree of crystallinity.