Temperature-dependence of polymorphism in electrospun nanofibres of PA6 and PA6/clay nanocomposite

10 pags., fig. 7Polymorphism found in nanofibres of polyamide 6 (PA6) and PA6/clay nanocomposite (PA6–NC), prepared by an electrospinning process, was studied by transmission electron microscopy (TEM) and variable-temperature wide angle X-ray scattering (WAXS), and compared with the polymorphic changes occurring in the pre-electrospun bulk materials. TEM results, concerning morphology and dispersion of the nanoclays, reveal that the produced electrospun nanofibres have an average diameter of 50 nm, and nanoclays are much more uniformly dispersed in the electrospun PA6–NC fibres than in the pristine PA6–NC. According to WAXS measurements, both types of electrospun nanofibres predominantly consist of γ-form crystals of PA6. Upon heating, from room temperature to the melting point, a number of successive transitions are observed for both systems, namely, crystalline γ to α′, α′ to α and α to the “amorphous” δ-form due to breakage of hydrogen bonds. On subsequent cooling, it has been observed, for the first time, that the development of crystalline forms for both systems is quite different from each other. The molten electrospun pure PA6 fibres first crystallize in the high temperature α′-form, and then they show the room temperature α-form. For these nanofibres, during a temperature cycle of heating and cooling, the initial γ-form crystals completely turn into the α-form crystals as in bulk PA6. In contrast, for the electrospun nanofibres of the PA6–NC, the γ-form crystals are preserved after completing a thermal cycle down to room temperature. The present findings on the evolution of polymorphism in the electrospun nanofibres of both systems provide useful information regarding their use as reinforcing elements in polymer composites.Peer reviewe

Nanostructure evolution during thermal treatment of Polyimide-fullerene composites as revealed by WAXS and SAXS

The nanostructure formation in polyimide–fullerene composites during thermal treatment was investigated ‘‘in situ’’, by means of wide-angle (WAXS) and small-angle X-ray scattering techniques. The WAXS patterns of the PI composites do not reveal the presence of C60 reflections. However, the PI/C60 composite, obtained by adding the C60 solution to the diamines-solution during the first step of the reaction (preparation of the polyamic acid, PAA), shows a maximum at small X-ray scattering angles. Results show that this intensity maximum is markedly affected by thermal treatment of the PI/C60 composite, disappearing at high temperature. From ‘‘in situ’’ X-ray scattering experiments, the ‘‘manner’’ in which the C60 nanoparticles are added to the other reactants and influences the properties of the final polymer is discussed.Peer reviewe