Effect of Boron Nitride as a Nucleating Agent on the Crystallization of Bacterial Poly(3-hydroxybutyrate)

Journal of Applied Polymer Science (Impact Factor: 1.4). 06/2012; 128(2013):2586–2594. DOI: 10.1002/app.38182

ABSTRACT Different concentrations of boron nitride (BN) (0.2–0.8 wt %) are added to poly (3-hydroxybutyrate) (PHB) as a nucleat-ing agent. Polarized Optical Microscopy (POM) coupled to Differential Scanning Calorimetry (DSC) allow to monitor the isothermal and nonisothermal crystallization of neat and nucleated PHBs. It is found that the addition of BN to PHB modifies the mechanisms of crystallization without changing the crystallinity degree. DSC can replace POM whenever POM does not allow to estimate the spherulites growth rate. The Hoffman-Lauritzen theory is used to explain the role of BN. The nucleating agent allows polymer crystallization at lower supercooling degrees. The regime II of crystallization is observed for nucleated PHBs. A modification of the coupling effect between the amorphous and the crystalline phases is evidenced. It is shown that a concentration of 0.2 wt % BN is sufficient to decrease the glass transition temperature and modify the crystallization mechanisms of PHB.

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    ABSTRACT: Three different grades of Boron Nitride (BN) powder (BN NX1, BN NX5 and BN HCV) having different mean particle size (0.7 to 11 μm) and specific surface area (16 to 40 m2·g−1) were used as nucleating agents for poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) at a fixed concentration of 2 wt %. Polarized Optical Microscopy (POM) observations, coupled to Differential Scanning Calorimetric (DSC) measurements, allowed to monitor both the isothermal and non-isothermal crystallization of neat and nucleated PHBVs. It was found that the addition of BN to PHBV modifies the mechanisms of crystallization by starting it at lower supercooling degrees and reducing the half-crystallization time. This work proved that DSC can replace POM whenever POM does not allow to estimate directly the average linear growth rate of the spherulites during crystallization. The Hoffman-Lauritzen theory was used to explain the effects of the addition of different grades of BN on PHBV crystallization. As a result, a transition from growth regime III to the growth regime II could be observed for nucleated PHBVs, no matter the grade of BN added. It was evidenced that the coupling between the amorphous and the crystalline phase is modified by the presence of the BN particles. In particular, for a given concentration of nucleating agent, it is the mean size and the specific surface area of BN particles that affect PHBV crystallization.
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    ABSTRACT: Don't hesitate to ask me for a Full-Text version of this paper. Laurent Delbreilh. Two types of bacterial semi-crystalline copolyesters, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB) are studied neat or with 8 wt% of Cloisite® C30B (C30B) organoclays. Wide Angle X-ray Diffraction (WAXD) and Differential Scanning Calorimetry (DSC) reveal that the nanoclays are partially intercalated, exfoliated and agglomerated. With selected sample preparation, the crystalline phase is unaffected by the C30B presence. Broadband Dielectric Spectroscopy (BDS) measurements showed no influence of the nanoclays on the secondary local relaxations modes of both polymers and on the segmental relaxation of P3HB4HB. Nevertheless, a strong modification of the α relaxation of PHBV has been observed after incorporation of C30B. A strong decrease of the fragility index and of the glass transition temperature revealed an increase of the molecular mobility in the amorphous fraction influenced by the nanoclays.
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    ABSTRACT: Mechanical, thermal, and morphological properties of injection molded wood-plastic composites (WPCs) prepared from poplar wood flour (50 wt%), thermoplastics (high density polyethlyne or polypropylene) with coupling agent (3 wt%), and hexagonal boron nitride (h-BN) (2, 4, or 6 wt%) nanopowder were investigated. The flexural and tensile properties of WPCs significantly improved with increasing content of the h-BN. Unlike the tensile and flexural properties, the notched izod impact strength of WPCs decreased with increasing content of h-BN but it was higher than that of WPCs without the h-BN. The WPCs containing h-BN were stiffer than those without h-BN. The tensile elongation at break values of WPCs increased with the addition of h-BN. The differential scanning calorimetry (DSC) analysis showed that the crystallinity, melting enthalpy, and crystallization enthalpy of the WPCs increased with increasing content of the h-BN. The increase in the crystallization peak temperature of WPCs indicated that h-BN was the efficient nucleating agent for the thermoplastic composites to increase the crystallization rate. POLYM. COMPOS., 35:194–200, 2014. © 2013 Society of Plastics Engineers
    Polymer Composites 01/2014; 35(1). · 1.48 Impact Factor