Effect of preliminary compression and uniform shear on the deformation behavior of a filled polymer nanocomposite in orientation stretching

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.

Strengthened electrically conductive composites based on ultra-high-molecular-weight polyethylene filled with fine graphite

“…It was previously established [2] that, if a similar "brittle" initial composite is subjected to uniform shear deformation, then its strength characteristics significantly increase, which was also observed in this work for the studied PENG specimens.…”

“…However, such stretching of polymer composites filled with various dispersed fillers is often accompanied by their brittle fracture even early in the deformation [2].In this work, for the first time, we described the possibility of producing strengthened oriented highly filled electrically conductive polymer nanocomposites under uniform shear conditions so that the rupture strength of these composites is an order of magnitude higher than that of non oriented composites of the same composition.We studied electrically conductive specimens of polymer composites of various compositions that were produced by filling a nascent reactor powder of ultra high molecular weight polyethylene (UHMWPE) of a nodular morphological structure (with a molecular weight of 5 × 10 6 and a bulk density of the reactor pow der of 0.058 g/cm 3 ) [1] with a commercial electrically conductive graphene nanopowder (GN) of grade AO 4 containing 60 nm thick flakes (Graphene Laborato ries) [3]. Our X ray powder diffraction studies showed that the filler is fine polycrystalline graphite with a coherent scattering length (stack height) in the crys tallographic direction [002] of ≈30 nm.…”

“…However, such stretching of polymer composites filled with various dispersed fillers is often accompanied by their brittle fracture even early in the deformation [2].…”

“…Uniaxial orientation of the specimens was carried out at room temperature in a special setup [2]. It pro duced a combination of compression and uniform shear of a specimen placed between plates made of a plastic Pb-Sn alloy.…”

“…However, the conductive non oriented specimens of various compositions that contained more than 2 vol % GN after subsequent orientation stretching under uniform shear conditions [2] to various stretch ing ratios become nonconductive after exceeding a certain critical ratio (l/l 0 )*. This critical stretching ratio increased with increasing filler content of the ini tial nonoriented conductive composite.…”