Type of publicationArticle (peer-reviewed) The electrical conductivity of a composite model system formed by highly structured carbon black ͑CB͒ filled, within an amorphous polymer, poly͑ethylene terephtalate͒ composite is studied. The dc conductivity as a function of CB content follows a scaling law of the type ϰ(pϪp c ) t yielding for the percolation concentration, p c ϭ0.011 and for the exponent, tϭ2.17. The analysis of the temperature dependence of the conductivity suggests that for temperatures larger than 45 K, conduction can be ascribed to thermal fluctuation induced tunneling of the charge carriers through the insulating layer of polymer separating two CB aggregates. At lower temperatures, conductivity becomes temperature independent, which is typical of conventional tunneling. The frequency dependence of the conductivity is also studied between dc and 10 9 Hz. By the introduction of a shift factor a p , a procedure for the construction of a master curve based on a ''time-length equivalence principle'' is proposed. Finally, a model is introduced to describe the frequency dependence of the conductivity of CB-filled composites based on the behavior of charge carriers placed in a fractal object.
In
the present paper, four fully biobased homopolyesters of 2,5-furandicarboxylic
acid (2,5-FDCA) with a high molecular weight have been successfully
synthesized by two-stage melt polycondensation, starting from the
dimethyl ester of 2,5-FDCA and glycols of different lengths (the number
of methylene groups ranged from 3 to 6). The synthesized polyesters
have been first subjected to an accurate molecular characterization
by NMR and gel-permeation chromatography. Afterward, the samples have
been successfully processed into free-standing thin films (thickness
comprised between 150 to 180 μm) by compression molding. Such
films have been characterized from the structural (by wide-angle X-ray
scattering and small-angle X-ray scattering), thermal (by differential
scanning calorimetry and thermogravimetric analysis), mechanical (by
tensile test), and gas barrier (by permeability measurements) point
of view. The glycol subunit length was revealed to be the key parameter
in determining the kind and fraction of ordered phases developed by
the sample during compression molding and subsequent cooling. After
storage at room temperature for one month, only the homopolymers containing
the glycol subunit with an even number of −CH
2
–
groups (poly(butylene 2,5-furanoate) (PBF) and poly(hexamethylene
2,5-furanoate) (PHF)) were able to develop a three-dimensional ordered
crystalline phase in addition to the amorphous one, the other two
appearing completely amorphous (poly(propylene 2,5-furanoate (PPF)
and poly(pentamethylene 2,5-furanoate) (PPeF)). From X-ray scattering
experiments using synchrotron radiation, it was possible to evidence
a third phase characterized by a lower degree of order (one- or two-dimensional),
called a mesophase, in all the samples under study, its fraction being
strictly related to the glycol subunit length: PPeF was found to be
the sample with the highest fraction of mesophase followed by PHF.
Such a mesophase, together with the amorphous and the eventually present
crystalline phase, significantly impacted the mechanical and barrier
properties, these last being particularly outstanding for PPeF, the
polyester with the highest fraction of mesophase among those synthesized
in the present work.
Article title: Evidence of a 2D-ordered structure in biobased poly(pentamethylene furanoate) responsible for its outstanding barrier and mechanical properties 5 Pages 6 Figures S2 Figure S1. dP vs. time for O 2 Figure S2. dP vs. time for CO 2 Sample Data Sample No. Order No. Sample Type Sample Name Received Tested by Request°C % Rel. Humidity Pre-conditioning Hrs.°C % Rel. Humidity Room Conditions Test Temperature°C mm³ Volume Device Number cm³/min % Rel. Humidity Gas Stream cm² Layer Sample Area Mask Test Gas Solubility cm³/cm³ bar Diff. Coeff.
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