Non-Isothermal Crystallization Kinetics of Poly(4-Hydroxybutyrate) Biopolymer.

Ina Keridou,Lutz Funk,Luis J. del Valle,Lourdes Franco,Jordi Puiggalí,Pau Turon

doi:10.3390/molecules24152840

Abstract

The non-isothermal crystallization of the biodegradable poly(4-hydroxybutyrate) (P4HB) has been studied by means of differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). In the first case, Avrami, Ozawa, Mo, Cazé, and Friedman methodologies were applied. The isoconversional approach developed by Vyazovkin allowed also the determination of a secondary nucleation parameter of 2.10 × 105 K2 and estimating a temperature close to 10 °C for the maximum crystal growth rate. Similar values (i.e., 2.22 × 105 K2 and 9 °C) were evaluated from non-isothermal Avrami parameters. All experimental data corresponded to a limited region where the polymer crystallized according to a single regime. Negative and ringed spherulites were always obtained from the non-isothermal crystallization of P4HB from the melt. The texture of spherulites was dependent on the crystallization temperature, and specifically, the interring spacing decreased with the decrease of the crystallization temperature (Tc). Synchrotron data indicated that the thickness of the constitutive lamellae varied with the cooling rate, being deduced as a lamellar insertion mechanism that became more relevant when the cooling rate increased. POM non-isothermal measurements were also consistent with a single crystallization regime and provided direct measurements of the crystallization growth rate (G). Analysis of the POM data gave a secondary nucleation constant and a bell-shaped G-Tc dependence that was in relative agreement with DSC analysis. All non-isothermal data were finally compared with information derived from previous isothermal analyses.

Highlights

Poly(4-hydroxybutyrate) (P4HB) is a biodegradable, linear, and aliphatic polyester with interesting applications in the biomedical field
Crystallization under isothermal and non-isothermal conditions is obviously different and slight differences, such as those detected for the secondary nucleation constant and the temperature associated with the maximum crystallization rate, can be expected
Non-isothermal crystallization studies of P4HB were performed by calorimetric experiments and allowed the determination of crystallization parameters by considering both the classical Avrami analysis and isoconversional methods

Summary

Introduction

Poly(4-hydroxybutyrate) (P4HB) is a biodegradable, linear, and aliphatic polyester with interesting applications in the biomedical field. This is mainly associated with its use as a wound closure material [1]. This hydroxyalkanoate (HA) derivative can be produced from microorganisms (e.g., Escherichia coli K12) by recombinant fermentation under a deficit of nutrients or other stress limitations [2,3,4]. The polymer is employed by microorganisms (as other polyhydroxyalkanoates (PHAs), such as poly(3-hydroxybutyrate) (P3HB) and polyhydroxyvalerate (PHV), as an energy storage form produced by the carbon assimilation from glucose or starch sources. Biosynthesis is the only practical pathway to produce P4HB, since samples with a reasonable molecular weight cannot be obtained from conventional chemical synthesis (e.g., ring-opening polymerization of butyrolactone) [5,6].

Objectives

Methods

Results

Conclusion