Optimum processing conditions for the maximum crystallization rate of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

Abstract

The effect of thermal and shear histories on the crystallization rate of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) was studied. As with other crystalline polymers, the shear history greatly affected the crystallization rate when the shear rate was beyond a critical value, i.e., the inverse of the Rouse relaxation time. Even after the formation of extended chain crystals, spherulite texture was clearly discernable. It grew from certain points on the extended chain crystals. Consequently, a row of spherulites appeared along the flow direction. The resin temperature in the molten state was also significant. When the sample was heated to 170 °C, which is beyond the main melting peak in the differential scanning calorimetry curve, unmolten crystals did not affect the linear viscoelastic properties. They acted as effective nucleating agents for the rest of the polymer during cooling. Therefore, the shear history hardly affected the crystallization rate and the number of spherulites.

Role of Shear Flow on Structure Development during Post-Processing Annealing for Poly(lactic acid)

“…Moreover, the alignment of shish to the flow direction led to the orientation of crystalline chains grown during annealing. Similar results were recently reported for isotactic polypropylene containing fibrous nucleating agents and polyhydroxyalcanoate [ 38 , 39 , 40 ], although the crystal growth did not occur during post-processing annealing in these studies. This anomalous growth of molecular orientation for PLA will be important for the dimensional control and mechanical properties, such as modulus and its anisotropy.…”

Effect of Monomers of 3-Hydroxyhexanoate on Properties of Copolymers Poly(3-Hydroxybutyrate-co 3-Hydroxyhexanoate)

“…The results obtained agree with the data of publications [81,98,99], which describe the regularities in the formation of spherulites during the isothermal crystallization of P(3HB-co-3HHx) copolymers. The authors of these works have shown that in P(3HB-co-3HHx) samples, the formation of banded spherulites similar to those obtained in this work, with a well-pronounced Maltese cross depending on the crystallization temperature of the melt, is possible.…”

Three/Four-Dimensional Printed PLA Nano/Microstructures: Crystallization Principles and Practical Applications

“…The kinetics of crystallization is an important consideration in polymer processing as it significantly affects the final thermal and mechanical properties of materials. The Avrami equation (Equation (5)) is the most widely used method for analyzing the crystallization kinetics of polymers [ 48 , 49 ]. However, the limitations of this model have been found; for example, it is only applicable to primary crystallization.…”