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Composite films of polyacrylonitrile (PAN) and multiwalled carbon nanotubes (MWNTs) have been prepared by gelation/crystallization from solution. The contents of MWNTs were 5–10 wt.‐%, measured against PAN. The electrical and mechanical properties have been studied in comparison with those of the homopolymer PAN films prepared from the same method. Furthermore, stabilization and the carbonization have been carried out by using the drawn PAN–MWNTs as a new precursor to prepare carbon films with a cross‐sectional area much larger than that of a commercial carbon fiber (> 3000 times). The MWNTs within the PAN matrix promote the formation of a condensed aromatic ladder structure during the stabilization process and play an important role in preparing PAN‐based carbon material with high carbon quality and high mechanical properties. When the stabilized composites with 10 wt.‐% MWNTs are carbonized at 1000 °C, the Young's modulus reaches 37.5 GPa, and the electrical conductivity reaches 102 S cm–1. The carbonized PAN homopolymer does not form an adequately robust bulk film for the mechanical properties to be measured.

An oxidative stabilization process to prepare carbon films was carried out for a new kind of precursor using the composite of polyacrylonitrile (PAN) and vaporgrown carbon fiber (VGCF) by a process of gelation/crystallization from dilute solutions. It was found that the new precursor has special features in the stabilization process different from those of the homopolymer in regard to thermal and morphological aspects. In the stabilization process under heat treatment at 180 -350°C in an oxidative atmosphere, it was inferred that, although the introduction of VGCF hinders the initiation and propagation step of the cyclization and dehydrogenation reactions, the precursor helps the oxidation and the additional aromatization and intermolecular crosslinking reactions in the stabilization process, thus promoting the formation of the later carbon product in film's shape with good performance. From characteristic works by wide-angle X-ray diffraction (WAXD), FTIR, Raman, and DSC, the changes of the precursors in structure, morphology, and mechanical property in terms of different heat-treat temperatures and tensions were studied. Through a series of experimental results, the effect of the VGCF's introduction on those changes was discussed.

ABSTRACT:A lattice model proposed before for uniaxial stretching of polyethylene films was applied to estimate the oriented crystallization of ultra-high molecular weight polyethylene (UHMWPE) dry gel films under simultaneous biaxially stretching. In this model system, the preferred axis associated with the preferred orientation of amorphous chain segments was chosen along the direction between two successive cross-linked points and the preferred axis was assumed to deform in an affine fashion with respect to the stretching direction. As the application of the proposed model, the orientation distribution function of crystallites was calculated on the basis of the lattice model and oriented crystallization model. The oriented crystallization model is based on the concept that a kinetically determined distribution of crystal chain axes as the normalized distribution of clusters found at the saddle point corresponding to a non-uniform orientation under conditions of a steady-state nucleation rate. Of course, the crystallites are oriented randomly with respect to the film normal direction. The parameter fitting for the formulated orientation distribution function of crystallites was done for the film which was prepared by the gelation/crystallization from solution with 0.9 g/ 100 mL concentration, the solvent being decalin, since the concentration assured the highest drawability under simultaneous biaxially stretching. The calculated orientation distribution functions 2q j ðcos j Þ of the reciprocal lattice vector of the crystal planes were in good agreement with the observed ones. Thus the numerical calculations indicate that the orientation of the c-axes depends on that of amorphous chain segments and the orientation behavior of crystallites is strongly affected by their rotation around the c-axis. [DOI 10.1295/polymj.37.192] KEY WORDS A Lattice Model / Simultaneous Biaxially Stretching / Preferred Orientation / A Steady-State Nucleation Rate / Orientation Distribution Function of Crystallites / Segmental orientation in uniaxially deformed elastomatic networks has been treated in terms of gas-like theories and liquid-like theories.1-4 In the gas-like theories, the chain vector and segment vector distributions have been estimated theoretically by using idealized models in which the effect of mutual interference between chain segments are neglected. On the other hand, in a liquid-like theory, 3,4 the effect of intermolecular interferences relating to orientation-dependent packing entropy was taken into consideration based on a lattice model. Erman et al. 5,6 have attempted to improve the liquid-like theory by considering the effect of chain stiffness on segmental orientation. For this purpose, they adopted the lattice theory of Flory 7,8 for chains with freely jointed rod-like segments and applied it to a thermotropic system with anisotropic polarizabilities. Namely, Erman et al. pointed out that a segment of polyethylene chains with 1-22 bonds may be viewed as a rod-like object on the basis of the concept of Flor...