Анализ механических и термогравиметрических свойств композиционных материалов на основе ПВА/МУНТ и стирол-акриловый сополимер/МУНТ

Изучены механические и термогравиметрические свойства полимерных композиционных материалов с различной концентрацией многостенных углеродных нанотрубок, эффективно экранирующих излучение в радиочастотном (20 Гц – 1 МГц) и микроволновом (26–36 ГГц) частотных диапазонах. В качестве матрицы использовались широко доступные полимерные материалы, такие, как поливинилацетат и стирол-акрилат в виде дисперсий. Из анализа полученных экспериментальных данных было показано, что введение в полимерную матрицу углеродных нанотрубок позволяет повысить комплекс механических свойств и термическую устойчивость композиционных материалов

Chemical Composition and Mechanical Properties of Wood after Thermal Modification in Closed Process under Pressure in Nitrogen

In this study, silver birch (Betula pendula) and Scots pine (Pinus sylvestris) wood planks (1000 × 100 × 25 mm) were thermally modified in pilot-scale equipment. Research extended our knowledge of the thermal modification (TM) process in a closed system under nitrogen pressure, as well as how process parameters affect the chemical composition and mechanical strength of wood. Various TM regimes were selected—maximum temperature (150–180 °C), modification time (30–180 min), and initial nitrogen pressure (3–6 bar). Chemical analyses were performed to assess the amount of extractives, lignin, polysaccharides and acetyl group content following the TM process. The mechanical properties of TM wood were characterized using the modulus of rupture (MOR), modulus of elasticity (MOE), and Brinell hardness. The MOR of both studied wood species following TM in nitrogen was reduced, but MOE changes were insignificant. The Brinell hardness of TM birch wood’s tangential surface was much higher than that of the radial surface, although Scots pine wood showed the opposite pattern. TM birch and pine wood specimens with the highest mass loss, acetone soluble extractive amount, and the lowest xylan and acetyl group content had the lowest MOR and Brinell hardness

Dynamic Mechanical, Dielectrical, and Rheological Analysis of Polyethylene Terephthalate/Carbon Nanotube Nanocomposites Prepared by Melt Processing

The polyethylene terephthalate/carbon nanotube (PET/CNT) nanocomposites were prepared by melt mixing using a twin screw extruder. CNT content was varied up to 5 wt. %. Morphology as well as dynamic mechanical, calorimetric, and rheological properties of the PET/CNT nanocomposites was investigated. Morphological studies indicated that CNT bundles are regularly distributed within the polymer matrix creating a connected network structure which significantly affects the nanocomposite properties. Dynamic mechanical thermal analysis revealed increase in storage and loss modules of the investigated PET nanocomposites by increasing the content of CNTs. Differential scanning calorimetry results demonstrated increase in crystallinity of the investigated PET nanocomposites upon addition of the nanofiller. Rheological studies demonstrated that CNT addition up to 5 wt. % caused increment in complex viscosity and storage modulus. Rheological percolation threshold was observed to be 0.83 wt. % of CNT concentration, respectively

p-Type PVA/MWCNT-Sb₂Te₃ Composites for Application in Different Types of Flexible Thermoelectric Generators in Combination with n-Type PVA/MWCNT-Bi₂Se₃ Composites

This work is devoted to the fabrication of p-type polyvinyl alcohol (PVA)-based flexible thermoelectric composites using multiwall carbon nanotubes-antimony telluride (MWCNT-Sb2Te3) hybrid filler, the study of the thermoelectrical and mechanical properties of these composites, and the application of these composites in two types (planar and radial) of thermoelectric generators (TEG) in combination with the previously reported PVA/MWCNT-Bi2Se3 flexible thermoelectric composites. While the power factors of PVA/MWCNT-Sb2Te3 and PVA/MWCNT-Bi2Se3 composites with 15 wt.% filler were found to be similar, the PVA/MWCNT-Sb2Te3 composite with 25 wt.% filler showed a ~2 times higher power factor in comparison with the PVA/MWCNT-Bi2Se3 composites with 30 wt.% filler, which is attributed to its reduced electrical resistivity. In addition, developed PVA/MWCNT-Sb2Te3 composites showed a superior mechanical, electrical, and thermoelectric stability during 100 consequent bending cycles down to a 3 mm radius, with insignificant fluctuations of the resistance within 0.01% of the initial resistance value of the not bent sample. Demonstrated for the first time, 2-leg TEGs composed from p-type PVA/MWCNT-Sb2Te3 and n-type PVA/MWCNT-Bi2Se3 composites showed a stable performance under different external loads and showed their potential for applications involving low temperature gradients and power requirements in the range of nW

Positive and Negative Changes in the Electrical Conductance Related to Hybrid Filler Distribution Gradient in Composite Flexible Thermoelectric Films Subjected to Bending

P-type multiwalled carbon nanotubes (MWCNTs), as well as heterostructures fabricated by direct deposition of inorganic thermoelectric materials as antimony and bismuth chalcogenides on MWCNT networks are known as perspective materials for application in flexible thermoelectric polymer-based composites. In this work, the electrical response of three types of Sb2Te3-MWCNT heterostructures-based flexible films—free standing on a flexible substrate, encapsulated in polydimethylsiloxane (PDMS), and mixed in polyvinyl alcohol (PVA) is studied in comparison with the flexible films prepared by the same methods using bare MWCNTs. The electrical conductance of these films when each side of it was subsequently subjected to compressive and tensile stress during the film bending down to a 3 mm radius is investigated in relation to the distribution gradient of Sb2Te3-MWCNT heterostructures or bare MWCNTs within the film. It is found that all investigated Sb2Te3-MWCNT films exhibit a reversible increase in the conductance in response to the compressive stress of the film side with the highest filler concentration and its decrease in response to the tensile stress. In contrast, free-standing and encapsulated bare MWCNT networks with uniform distribution of nanotubes showed a decrease in the conductance irrelevant to the bending direction. In turn, the samples with the gradient distribution of the MWCNTs, prepared by mixing the MWCNTs with PVA, revealed behavior that is similar to the Sb2Te3-MWCNT heterostructures-based films. The analysis of the processes impacting the changes in the conductance of the Sb2Te3-MWCNT heterostructures and bare MWCNTs is performed. The proposed in this work bending method can be applied for the control of the uniformity of distribution of components in heterostructures and fillers in polymer-based composites

Nanostructured zinc oxide filler for modification of polymer-polymer composites: structure and tribological properties

Self-lubricating behaviour of materials is very demanded in industry. In this study we investigated the effect of anisometric nanostructured ZnO filler (tetrapod shaped particles with arm length of 70–100 nm and diameter of 10 nm) and ethylene-1-octene copolymer on structure and tribological properties of isotactic polypropylene (PP). It was observed that addition of EOC caused the increment of roughness as well as of the coefficient of friction (COF) of the investigated composites. Addition of ZnO, in its turn, caused decrement of the COF and improvement of surface quality at certain nanofiller contentsVytauto Didžiojo universitetasŽemės ūkio akademij