Origin of the double melting peaks of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) with a high HV content as revealed by in situ synchrotron WAXD/SAXS analyses

Abstract

We here reported the dual melting behaviors with a large temperature difference more than 50 °C without discernible recrystallization endothermic peak in isomorphous poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (P(HB‐co‐HV)) with a high HV content of 36.2 mol %, and the structure evolution upon heating was monitored by in situ synchrotron wide‐angle X‐ray diffraction/small‐angle X‐ray scattering (WAXD/SAXS) to unveil the essence of such double endothermic phenomena. It illustrated that the thinner lamellae with the larger unit cell and the thicker crystals having the smaller unit cell were melted around the first low and second high melting ranges, respectively. By analyzing in situ WAXD/SAXS data, and then coupling the features of melting behavior, the evolution of the parameters of both crystal unit cell and lamellar crystals, we proposed that the thinner unstable lamellae possess a uniform structure with HV units total inclusion, and the thicker stable lamellae reflect the sandwich structure with HV units partial inclusion. It further affirmed that the thicker sandwich and thinner uniform lamellae formed during the cooling and subsequent isothermal crystallization processes, respectively. These findings fully verify that it is the change of structure of lamellae rather than the melting/recrystallization that is responsible for double melting peaks of isomorphous P(HB‐co‐36.2%HV), and enhance our understanding upon multiple endothermic behaviors of polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1453–1461

Exploiting the Physicochemical and Antimicrobial Properties of PHB/PEG and PHB/PEG/ALG-e Blends Loaded with Ag Nanoparticles

“…The results of the structural and morphological analysis of the films are presented in Figure 4 . It is known that PHB crystallizes in an orthorhombic-like structure [ 46 ] belonging to the P212121 space group [ 47 ]. In the XRD patterns shown in Figure 4 a, some of the main reflections associated with the PHB polymer matrix can be found.…”

“…Explicitly, all spectra display similar patterns, with reflections centered around 2θ angles of 13.95°, 16.84°, 20.5°, 22.7°, 25.9°, 27.7°, and 30.9°, which are due to the crystallographic planes (020), (110), (101), (111), (121), (040), and (002), respectively. Previous works have shown that these planes typically occur for the ordered orthorhombic structure of poly-β-hydroxybutyrate [ 46 , 48 , 49 ]. The patterns also exhibit a large halo positioned in the range of 35°–40°, which was also observed previously by D’Amico et al [ 50 ].…”

Elastic Marine Biodegradable Fibers Produced from Poly[(R)-3-hydroxybutylate-co-4-hydroxybutylate] and Evaluation of Their Biodegradability

“…The peak corresponding to the (110) plane shifted as a result of the thermal expansion of the crystal lattice. 45,46 The diffraction peaks associated with the (020) and (110) planes were observed up to 160 °C, meaning that they were also present at 130−150 °C, i.e., the temperature at which the melt-spinning was performed in this study. Therefore, the fact that melt-spinning is possible at temperatures lower than 170 °C in this work indicates that the amorphous portion is melt-flowed with the crystalline part, although some crystals remain.…”

Impact of Thermal Properties on Crystalline Structure, Polymorphism and Morphology of Polymer Matrices in Composites

“…For instance, PHB forms a compound with poly(3-hydroxyvalerate) (PHV) and, indeed, PHB-PHV copolymers show a lower melting temperature and crystallinity level [ 16 ]. Zhu et al also studied the melting behavior of a poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) having 36.2 mol% of hydroxyvalerate (HV) units by in situ synchrotron X-ray analyses [ 17 ]. The authors concluded that the low-temperature peak is due to melting of the thinner crystals with lower density because of the HV inclusion in the orthorhombic PHB cells, whereas the high-temperature peak is due to the fusion of the thicker PHB crystals with a small cell excluding HV units, which are confined in the amorphous phase.…”