The main goal of the presented study was to develop new multi-layered weft-knitted structure for thermal insulation and to investigate the dynamic of the heat transfer through this fabric. For knitting of outer and inner layers of this structure, different raw materials of yarns were used, i.e. wool, cotton, polyester and acrylic yarns. All the newly developed multi-layered weft-knitted fabrics show thermal insulation as, after 1 h of observation, temperature on the outer layer of all tested fabrics does not reach 40℃, i.e. the temperature of a heated plate. The results of this research showed that the nature of the yarns has a significant influence on the air permeability and dynamic of the heat exchange through the multi-layered structure, as it influences porosity of the knitted fabric. The results showed that the best fabric was the one where the outer layers are knitted from woollen yarns and the inner layer from polyester filament yarns.

Newly designed knits of highly eco-friendly peat fibers and their combination with widely used cotton and wool fibers have been analyzed in this study. The present investigation is focused on the thermal and mechanical properties of weft knits made of peat fiber yarns and their combinations (in various percentages) with other natural fiber yarns, such as cotton and woolen yarns, as well as with elastomeric yarn, as newly developed knits are designed for clothing. It was found that newly developed knitted fabrics with peat fibers have an optimal structure for use. The renewable peat fiber yarns, spun from two kinds of natural cellulose fibers -decomposed Eriophorum vaginatum (cotton grass) sedge stems and cotton -have intermediate strength and elongation values between cotton and flax yarns, and thus are fit for knitting. All the newly designed knitted fabrics have high abrasion resistance and can be used for clothing manufacture. It was found that the nature of the yarn's raw material and the number of different yarns in one stitch influence the heat transfer dynamic. The heat transfer dynamic through the peat fiber knit is slower than that through the cotton fabric, but it is faster than through the woolen fabric. When the heat transfer process through knitted fabric is faster, this structure may be recommended for warmer seasons.

A study of altering the conductive properties of wool fibers by applying copper selenide is presented. The researched modification of wool fibers was based on a two-stage adsorption-diffusion process. X-ray diffraction, scanning electron microscope, energy-dispersive X-ray spectrum, and Fourier transform infrared spectroscopy were performed to evaluate the morphological and physical characteristics of all CuxSe-coated wool fibers. X-ray diffraction (XRD) data showed a single, Cu0.87Se (klockmannite), crystalline phase present, while Atomic Absorption Spectroscopy (AAS) and Energy Dispersive X-ray (EDX) analyses showed that the concentrations of Cu and Se in copper selenide coatings depend on the number of wool fiber treatment cycles. It was determined that a dense layer of CuxSe grows through a nucleation mechanism followed by particle growth to fill out the complete surface. It was found that the conductivity of the coated wool fibers depends on the quality and density of the copper selenide coating, thus the resistance of electrically impermeable wool fibers can be reduced to 100 Ω by increasing the number of treatment cycles.

In this work the effects of different crystallographic modifications of calcium carbonate (CaCO₃) filler on the melt flow, mechanical properties, hydrolytic degradation, and shape memory behaviour of recycled low-temperature poly(e-caprolactone)-based polyurethane (rTPU) were evaluated. Composites were prepared by two-roll milling varying filler content from 2 wt % to 6 wt %. It was found that at temperature range from 20 °C to 50 °C CaCO₃ fillers do not change Young’s modulus, they decrease tensile stress and deformation of rTPU, but improve its mechanical properties at elevated temperatures (up to 65 °C). rTPU melt flow index increases due to chain scission during the recycling and filler mixing with mill. Therefore, destruction temperature of rTPU is 20 °C lower than that of TPU. The CaCO₃ does not change shape memory properties independently of filler type and transition from secondary shape to the primary shape at 70 °C temperature is completed within 17 s for both filled and unfilled rTPU. The investigation of hydrolytic degradation shows that CaCO₃ only slightly increases degradation rate of rTPU.

DOI: http://dx.doi.org/10.5755/j01.ms.18.3.2433

Purpose The purpose of this paper is to investigate the influence of geometrical microstructure of items obtained by applying a three-dimensional (3D) printing technology on their mechanical strength. Design/methodology/approach Three-dimensional printed items (3DPI) are composite structures of complex internal constitution. The buildup of the finite element (FE) computational models of 3DPI is based on a multi-scale approach. At the micro-scale, the FE models of representative volume elements corresponding to different additive layer heights and different thicknesses of extruded fibers are investigated to obtain the equivalent non-linear nominal stress–strain curves. The obtained results are used for the creation of macro-scale FE models, which enable to simulate the overall structural response of 3D printed samples subjected to tensile and bending loads. Findings The validation of the models was performed by comparing the computed results against the experimental ones, where satisfactory agreement has been demonstrated within a marked range of thicknesses of additive layers. Certain inadequacies between computed against experimental results were observed in cases of thinnest and thickest additive layers. The principle explanation of the reasons of inadequacies takes into account the poorer quality of mutual adhesion in case of very thin extruded fibers and too-early solidification effect. Originality/value Flexural and tensile experiments are simulated by FE models that are created with consideration to microstructure of 3D printed samples.