Poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)]/layered double hydroxide nanocomposites

BACKGROUND: The thermomechanical performance of poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] (PHBV) is associated with its crystallization. Enhanced nucleation using a stearate-functionalized synthetic layered double hydroxide (LDH) presents a potential solution. RESULTS: PHBV crystallization varied with concentration of LDH. At lower LDH concentration, thermal history-induced cold crystallization was present. The extent of this order-disorder transition decreased with increasing LDH concentration and was completely eliminated at 7 wt% LOH. PHBV did not have a melt recrystallization peak but the introduction of LDH resulted in an increasingly pronounced melt recrystallization with increasing LDH concentration. Polarized optical microscopy coupled with differential scanning calorimetry and wide angle X-ray diffraction (WAXD) analysis indicated increased lamella thickness in the nanocomposites compared to pure PHBV. WAXD and transmission electron microscopy showed that the nanocomposites had an intercalated but aggregated dispersion. CONCLUSION: The concentration of nanofiller provides unique effects in PHBV. Mechanical performance was found to scale with composition as determined using dynamic mechanical analysis and tensile testing. (C) 2008 Society of Chemical Industry58213314

Layer double hydroxides for enhanced poly(3-hydroxybutyrate-co-3-hydroxyvalerate) crystallization

Enabling the widespread utilization of poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] (PHBV) is strongly associated with enhancing its crystallization kinetics. In this article, we utilize a highly surface active (one reactive group per nanometer square) anion exchanged layered-double hydroxide (LDH) functionalized by stearic acid to probe the crystallization kinetics of PHBV. Our prior work has shown that the addition of LDH decreases the cold crystallization and induces a melt recrystallization peak in PHBV. Since the melt-recrystallization temperature shifted to higher temperature and its corresponding enthalpy increased with increasing LDH loading, this article is focused on understanding the effect of LDH on kinetics and energetics of PHBV crystallization. Both Avrami and LauritzenHoffman modeling are utilized to develop a comprehensive understanding of thermal history effects through differential scanning calorimetry and polarized optical microscopy measurements. Five concentrations by weight of LDH are used: 1, 3, 5, and 7%. The results show that the addition of LDH promoted both primary and secondary nucleation at low concentrations but additional LDH resulted in primary nucleation alone. The crystallization rate and activation energy show a significant increase, which is accompanied by a decrease in the nucleation constant, the surface energy and the work of chain folding for PHBV crystallization. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 201312753395340

Moisture-responsive films of cellulose stearoyl esters showing reversible shape transitions

Moisture-responsive materials are gaining greater interest for their potentially wide applications and the readily access to moisture. In this study, we show the fabrication of moisture-responsive, self-standing films using sustainable cellulose as starting material. Cellulose was modified by stearoyl moieties at first, leading to cellulose stearoyl esters (CSEs) with diverse degrees of substitution (DSs). The films of CSE with a low DS of 0.3 (CSE(0.3)) exhibited moisture-responsive properties, while CSEs with higher DSs of 1.3 or 3 (CSE(1.3) and CSE(3)) not. The CSE(0.3) films could reversibly fold and unfold as rhythmical bending motions within a local moisture gradient due to the ab- and desorption of water molecules at the film surface. By spray-coating CSE(3) nanoparticles (NPs) onto CSE(0.3) films, moisture-responsive films with non-wetting surface were obtained, which can perform quick reversible bending movements and continuous shape transition on water. Furthermore, bilayer films containing one layer of CSE(0.3) at one side and one layer of CSE(3) at the other side exhibited combined responsiveness to moisture and temperature. By varying the thickness of CSE(0.3) films, the minimal bending extent can be adjusted due to altered mechanical resistances, which allows a bending movement preferentially beginning with the thinner side