No abstract

In this work, for the first time, we described the possibility of eliminating the brittle fracture of filled polymer nanocomposites in orientation stretching by preliminary compression deformation and small uni form shear deformation before stretching. After such a treatment, the polymer composite material becomes capable of experiencing larger deformation elonga tions in stretching.Orientation stretching is known to be an efficient way to improve the mechanical properties of polymer materials [1]. However, such stretching of polymer composite materials filled with various dispersed fillers is often accompanied by their brittle fracture even early in the deformation [2].We studied specimens of a polymer composite (PC) based on polypropylene (commercial polymer of HC101BF grade (Borealis, Vienna, Austria) with a melt flow rate of 3.2 g/10 min) containing 5 wt % of a standard nanodiamond blend produced by detonation synthesis (ZAO Almaznyi Tsentr, St. Petersburg, Rus sia). The nanodiamond soot is a finely dispersed filler of a new type, which is promising for using in polymer composites [3,4]. The mixing of the components (polymer and soot powders) and the homogenization of a polymer composite melt were performed in a dou ble screw micro mixer at 200°C. Polymer composite specimens shaped as 0.5 mm thick plates were pre pared by compacting the material at 200°C with sub sequent fast cooling (quenching) in water with ice. This ensured the formation of a "structureless" amor phous-crystalline polymer matrix, which itself is gen erally well deformable in stretching [5]. The reference specimens (RS) were made from the initial polypropy lene without nanodiamond soot, which was prepared by slowly cooling the melt. According to polarized light optical microscopy data, this propylene had a developed large spherolite supermolecular structure incapable of experiencing large deformation elonga tions in stretching [5].The pretreatment of test specimens was performed in a special setup (Fig. 1). It produced a combination of compression and uniform shear of a specimen placed between plates made of a plastic Pb-Sn alloy while extruding through a conical die of a certain diameter, which determined the preliminary strain in treated specimens (specimens PC tr and RS tr ).The subsequent orientation stretching and record ing of the stress-strain curves of the specimens PC, PC tr , RS, and RS tr were performed at room tempera ture in a Shimadzu AGS 10 universal testing machine in uniaxial stretching mode at a relative deformation rate of 1 min -1 .The large and small angle X ray scattering studies and also the determination of the change in the speci men thickness in the necking region by X ray nanog raphy in the nanography mode were carried out on a Bruker NANOSTAR system (CuK α radiation) equipped with an area detector. Isotropic specimen Pb-Sh alloyOriented specimen Fig. 1. Setup for uniform shear of a material.

No abstract

No abstract

Self-oscillating neck propagation of amorphous polybutylene succinate was studied. The neck propagated by regular neck front jumps at the stretching speeds from 0.05 to 1000 mm/min. Self-oscillations at extremely low stretching speeds contradicts to the theory of this phenomenon. The instability of the neck propagation was explained by the deformation softening of the polymer.

No abstract

No abstract

A series of aromatic polyimides based on the asymmetrical diamine 3,4ʹ-oxydianiline and various tetracarboxylic acid dianhydrides, both “rigid” and “flexible” structure, have been synthesized using the original method of one-pot high-temperature catalytic polycondensation in molten benzoic acid. The synthesized polyimides were investigated using fourier-transform infrared (FTIR) and 1H NMR spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), thermomechanical analysis (TMA) and wide-angle X-ray scattering (WAXS). It was found that the synthesized polyimides, depending on the used dianhydride, are characterized by different solubility in organic solvent and molten benzoic acid, molecular weight, glass transition temperature (Tg) from 198 to 270 °C, an amorphous or semi crystalline structure with the degree of crystallinity from 41 to 52%. The influence of the method of synthesis on the formation of the crystalline phase of polyimides was studied, and the obtained results were compared with the literature data. The effect of dianhydride chemical structure on the performance of polyimide in pervaporation more specifically, dehydratation of azeotropic isopropanol solution was investigated and compared with the commercially available polyetherimide Ultem 1000™. Membrane structure was studied using scanning electron microscopy. It was found that polyimide PI-DA is the most effective for separation of 88 wt.% isopropanol/12 wt.% water mixture compared to the polyimide PI-6FDA and commercial polyetherimide Ultem 1000™ demonstrating normalized permeation flux of 2.77 kg µm m−2 h−1 and separation factor of 264 (water content in permeate 97 wt.%).