Simultaneous Synchrotron SAXS/WAXD Study of Composition Fluctuations, Cold-Crystallization, and Melting in Biodegradable Polymer Blends of Cellulose Acetate Butyrate and Poly(3-hydroxybutyrate)

Abstract

Self-assembly of poly­(3-hydroxybutyrate) (PHB) and cellulose acetate butyrate (CAB) blends prepared by solvent casting was investigated by simultaneous synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction as a function of temperature in a heating process of the blends. The results revealed different elemental processes occurring in three characteristic temperature regions: (1) low-T region, where cold crystallization (CC) of PHB into one-dimensional (1D) assemblies of PHB lamellar crystals occurs in the temperature (T) range T cc,PHB ≤ T ≤ T cc,CAB, where T cc,PHB and T cc,CAB are the onset temperature for CC in PHB and CAB, respectively; (2) crossover-T region, where partial melting/recrystallization of PHB occurs concurrently with CC of CAB in the interstitial amorphous matrix among the 1D PHB lamellar assemblies at T cc,CAB < T ≤ T*, where T* is a characteristic temperature close to the T at the higher melting endothermic peak of differential scanning calorimetry (DSC), T m,DSC; and (3) high-T region, where PHB crystals melt and CAB partially melts/recrystallizes at T > T*. The study also elucidated for the first time in this blend systems, to our best knowledge, the following points: (a) the existence of two glass transition temperatures (T g’s) in the amorphous matrix, with a lower T g (T g,l) determined by DSC and a higher T g (T g,h) determined from the SAXS intensity at low q (magnitude of the scattering vector) values as a function of T; (b) the evolution of the large length-scale composition fluctuations in the amorphous matrix of the blend at T g,h ≤ T ≤ T cc,CAB; (c) crystallization of CAB at T > T cc,CAB and a melting temperature for CAB crystals higher than 183 °C. The roles of intermolecular hydrogen bondings (HBs) between PHB and CAB, intramolecular HBs within PHB, and those within CAB as well as roles of the exchanges of those HBs on the self-assembling process, the composition fluctuations, and the miscibility of the blends in the amorphous phase were also clarified in the text.

PHBV/CNC bionanocomposites processed by extrusion: Structural characterization and properties

“…WAXS pattern for CNC was presented in our previous work where it was shown that CNC did not have any effect on the shape and location of the peaks in the WAXS pattern of PHBV . WAXS diffractograms of both PHBV and PHBV/CNC6 samples at room temperature contains the main characteristics diffraction peaks of orthorhombic α– type crystalline structure . On increasing temperature until 200°C amorphous peaks centered nearly at 2θ = 14° for both samples were detected.…”

Novel Self‐Reinforced Films Based on Poly (3‐Hydroxybutyrate‐Co‐3‐Hydroxyvalerate) (PHBV) and PHBV Microparticles

“…At room temperature, all the main features of the diffraction peaks of orthorhombic α‐type crystalline structure of PHBV can be observed . Unchanged peaks positions also confirmed the orthorhombic crystalline structure of the srPHBV‐6 sample.…”

“…This can affect the electron density fluctuations between amorphous and crystalline layers, which are considered to go in a vertical direction to the lamellae planes . In a similar study for PHB, a decrement in the s max due to the growth of crystalline lamellar and thickening of the average lamellar spacing, was reported . In order to study the effect of filler loading on the crystalline features of PHBV more accurately, Lorentz‐corrected SAXS diffractograms ( Is 2 versus s ) at room temperature were used to calculate long spacing parameter and the results are shown in Table , indicating nearly the same long spacing for both samples.…”

Identification of optically clear regions of ternary polymer blends using a novel rapid screening method

“…CAB shows a weak amorphous halo at 3.0–5.5 Å, indicating an absence of crystallinity. This is typical for CAB and it is only recently that partially crystalline forms of CAB have been identified, following elevated temperature treatment at >180 °C …”