Miranda-Mendoza, Félix G.

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    Processing and characterization of nematic co-polymer Phba/Pet nanocomposite films via hot-melt extrusion
    (2011) Miranda-Mendoza, Félix G.; Acevedo Rullán, Aldo; College of Engineering; Briano, Julio G.; Martínez Iñesta, María M.; Córdova Figueroa, Ubaldo M.; Department of Chemical Engineering; Suárez, O. Marcelo
    In this research work, the effect of particle shape (i.e. rod-like, spherical and platellet) and concentration on the liquid crystalline structure of poly (4-benzoic acidco-ethylene terephthalate) (PHBA/PET) was evaluated by studying the composites thermal transitions and structure. Composite films were produced by direct melt blending of the polymer with up to 1.5 v% loadings of four different kinds of commercial fillers, which are: silica, multiwalled carbon nanotubes (MWCNT), halloysite nanoclays (HNC) and montmorillonite nanoclays (MNC). Mixture and processing was carried out in a Thermo-Haake MiniLab2 twin-screw extruder. Thermal transitions were determined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and polarized optical microscopy (POM). Structure and morphology were analyzed by a combination of small angle X-ray scattering (SAXS), and scanning electron microscopy (SEM). No significant changes were observed on the glass and melting transitions since all the values are within the experimental error independent of particle type. An exception was the melting of MNC composites since from medium to high values (0.5 v%-1.5 v %) the melting temperature decreased but remained independent of particle loading. The isotropic-to-nematic transition temperature was diminished with the addition of particles for all cases, but was independent of concentration. This represented a decrease in the liquid crystalline region. Thermal degradation was also studied by 5 and 10 % of weight loss and at the maximum rate of degradation. All particles showed to produce a positive increment in composite thermal stability, except for MWCNT where temperatures remained almost constant. This behavior could be explained by the molecular confinement due to the increment in particle concentration of the MWCNT in PET rich region. The highly anisotropic nanoparticles (i.e. rods & plates) had a similar effect on the morphology, showing a fibrilar behavior at the fracture plane, as observed by the SEM, while silica showed no fibrillar structures. This was attributed to the nonpreferential arrangement of the silica spheres. No significant changes were observed on the SAXS patterns for HNC or MWCNT, while silica and MNC composites showed a slightly wider SAXS pattern. The latter can be attributed to the presence of a broader domain distribution. Addition of this kind of nanoparticles at the low concentrations studied did not showed any significant effect on the LC polymer thermal transitions. Also, no change is observed on the liquid crystalline structure for the rod-like particles while silica and clay particles promote large crystal domains distributions as evidenced by SAXS. In the case of thermal stability it seems that particles intrinsic properties are the factor that promotes the enhancement on temperature resistance rather than their shape or concentration.