Phase Transition and Melt-Recrystallization Behavior of Poly(Butylene Adipate) Investigated by Simultaneous Measurements of Wide-Angle X-Ray Diffraction (WAXD) and Differential Scanning Calorimetry (DSC)

Simultaneous measurements of wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) were carried out to investigate the phase transition and melting behaviors of poly(butylene adipate) (PBA). Thermal expansion changes along the a and b axes of the β form unit cell are different from each other during the heating process. At the beginning of the β to α_H (high-temperature α phase) phase transition, the β phase melts very fast, while the recrystallization of the α_H phase is delayed and slowed. With the further increment of the temperature, the melting rate of the β phase slows down, while the recrystallization of the α_H phase accelerates. The diffraction peak intensity ratios of the β(020):β(110) and α_H(020):α_H(110) diffraction peaks during the first heating process have similar value. However, the above value is different from the value of α(020):α(110) during the following melt-crystallization process. This difference comes from the different orientations of the crystal lattices of the α and α_H(β) crystals to the substrate plane, which indicates that the α_H phase inherits the orientation of the β phase during phase transition and the orientation of α_H form crystals is different from the α form crystals that crystallized from the melt.

Sustainable Materials with Enhanced Mechanical Properties Based on Industrial Polyhydroxyalkanoates Reinforced with Organomodified Sepiolite and Montmorillonite

Microplastics have become one of the greatest environmental challenges worldwide. To turn this dramatic damage around, EU regulators now want to ensure that plastic itself is fully recyclable or biodegradable. The aim of the present work is to develop a biobased and biodegradable biocomposite based on commercial polyhydroxyalkanoates (PHAs) and nanoclays, with the objective of achieving a reduction of rancid odour while avoiding any loss in thermomechanical properties, thus tackling two key disadvantages of PHAs. This research aims at completely characterising the structural, thermal and mechanical behaviour of the formulations developed, understanding the compatibility mechanisms in order to be able to assess the best commercial combinations for industrial applications in the packaging and automotive sectors. We report the development of nine nanobiocomposite materials based on three types of commercial PHA matrices: a linear poly(3-hydroxybutyrate) (P3HB); two copolymers based on poly(3-hydroxybutyrate)-co-poly(4-hydroxybutyrate) (P3HB-co-P4HB); and nanoclays, which represent a different polar behaviour. Dispersion achieved is highly relevant compared with literature results. Our findings show impressive mechanical enhancements, in particular for P3HB reinforced with sepiolite modified via aminosilanes.

The dependence of the β-to-α phase transition behavior of poly(1,4-butylene adipate) on phase separated morphology in its blends with poly(vinylidene fluoride)

Two kinds of typical phase separated morphologies are prepared and they alter the stability of crystals.

Influence of polyethylene glycol on the phase transition of poly(butylene adipate) thin films: Polymorphic control

Control of the polymorphic crystals formation of poly(butylene adipate) (PBA) is crucial to tailor its performance. In the present study, we investigated the effect of polyethylene glycol (PEG) with molecular weight of 400 on the polymorphic crystal of PBA thin films using x-ray diffraction (XRD), temperature-dependent infrared-reflection absorbance spectroscopy (IRRAS) and two-dimensional correlation analysis (2DCOS). XRD and IRRAS results suggest that the PBA thin film tends to grow α-form crystal with addition of PEG at room temperature. Increasing the PEG contribution to 30wt%, the PBA thin film shows α-form crystal only. Temperature-dependent IRRAS spectra indicate that pure PBA thin film exhibited α/β mixed crystal and the β-to-α transition was observed during the heating process. After the incorporation of PEG, PEG not only inhibits the growth of β crystal but also suppresses the β-to-α transition during the heating process. In addition, we unexpectedly captured three different amorphous bands of CO stretching of pure PBA from the asynchronous 2D correlation spectrum. The band at 1740cm^-1 corresponded to the amorphous phase of PBA at room temperature, whereas 1746 and 1760cm^-1 respectively arose from the amorphous phase of PBA melting from α-form crystal and β-form crystal. This study demonstrated that the crystal form of PBA can be modified by blending with PEG, providing a new method to control the crystal modification and physical properties of polymorphic PBA in their blend system.

Regulating the polymorphism behaviour and crystal transformation of poly(butylene adipate) by incorporating butylene fumarate units into the crystal lattice

Copolymerized butylene fumarate units benefit the formation of β-form poly(butylene adipate) at high temperature by cocrystallizing into the crystal lattice.

Fractionated crystallization, polymorphism and crystal transformation of poly(butylene adipate) confined in electrospun immiscible blend fibers with polystyrene

Utilizing electrospun immiscible blend fibers of poly(butylene adipate) (PBA) and polystyrene (PS) and following coating by the high glass transition temperature poly(4-tert-butylstyrene) (P4tBS), confined PBA specimens in nanometer space were effectively prepared.

The phase transition behavior of poly(butylene adipate) in the nanoporous anodic alumina oxide

PBA nanotubes with different diameters have been prepared.

In situ study of the annealing process of a polyethylene cast film with a row-nucleated crystalline structure by SAXS

The secondary crystallization has more effect on polyethylene crystal thickening than melt recrystallization during the annealing process.