Blanka Tomkova

Optimized preparation of activated carbon nanoparticles from acrylic fibrous wastes

In present study, activated carbon is prepared by controlled pyrolysis of acrylic fibrous waste under the layer of charcoal using physical activation in high temperature furnace. The main objective is to study the effect of four factors (i.e. final pyrolysis temperature, holding time at final temperature, heating rate per hour, and number of steps) on carbonization behavior of acrylic fibrous waste. The Box-Behnken design and response surface modeling was performed to get higher specific surface area and higher electrical conductivity. The development of porous morphology having higher surface area is found to increase with increase in pyrolysis temperature, increase in number of steps, decrease in holding time and decrease in heating rate till some optimum value. This behavior is attributed to gradual reaction of atmospheric oxygen with carbonized acrylic fibrous waste, which resulted into the opening of previously inaccessible pores through the removal of tars and disorganised carbon. Moreover, these four factors also found to have significant effect on the development of electrical conductivity of activated carbon. Later on, the carbonized acrylic fibrous waste was pulverized in dry conditions by high energy planetary ball milling to get activated carbon nanoparticles. In addition to refinement of size, the specific surface area and electrical conductivity of pulverized carbon particles was found to increase with increase in milling time. The activated carbon particles obtained after three hours of dry milling revealed the particle size of 521 nm, the electrical conductivity of 21.78 s/m for 0.5 wt % concentration of aqueous dispersion and the specific surface area of 432 m2/g.

Evaluation of Effective Thermal Conductivities of Porous Textile Composites

An uncoupled multi-scale homogenization approach is used to estimate the effective thermal conductivities of plain weave C/C composites with a high degree of porosity. The geometrical complexity of the material system on individual scales is taken into account through the construction of a suitable representative volume element (RVE), a periodic unit cell, exploiting the information provided by the image analysis of a real composite system on every scale. Two different solution procedures are examined. The first one draws on the classical first order homogenization technique assuming steady state conditions and periodic distribution of the fluctuation part of the temperature field. The second approach is concerned with the solution of a transient flow problem. Although more complex, the latter approach allows for a detailed simulation of heat transfer in the porous system. Effective thermal conductivities of the laminate derived from both approaches through a consistent homogenization on individual scales are then compared with those obtained experimentally. A reasonably close agreement between individual results then promotes the use of the proposed multi-scale computational approach combined with the image analysis of real material systems.

Morphological, Thermal, and Mechanical Characterization of Sansevieria trifasciata Fibers

Sansevieria trifasciata is a common perennial plant which freely grows and widely found in homes, parks, and woodlands. In this research, we studied the morphology using Scanning Electron Microscope and Fourier Transform Infrared (FTIR); thermal properties using Thermogravimetric (TGA) and Differential Scanning Calorimetric (DSC) analyses; mechanical behavior through tensile tests of Sansevieria trifasciata fiber (STF) obtained from Butaleja in Eastern Uganda. Findings show that the fiber has an irregular cross-sectional shape with lumens in the center, the fiber diameter was between 80 and 120 μm. TGA tests showed that the fiber is stable below 200°C with maximum cellulose decomposition temperature of 315°C. DSC showed that the fiber’s crystallization temperature was 310.5°C and lignin decomposition temperature of 372.7°C. The surface functional groups were majorly of cellulose, hemicelluloses, and lignin in direct correlation with research elsewhere on natural fibers.

Thermo-physiological and comfort properties of Ugandan barkcloth from Ficus natalensis

The United Nations Educational, Scientific and Cultural Organization in 2005 proclaimed that Ugandan barkcloth largely produced from mutuba tree (Ficus natalensis) as a “Masterpiece of the Oral and Intangible Heritage of Humanity”. An exploratory investigation of thermo-physiological and comfort properties of barkcloth, a nonwoven material produced through a series of pummeling processes from mutuba tree in Uganda, is fronted. Barkcloth was extracted from the F. natalensis tree in Nsangwa village, Buyijja parish in Mpigi district, Central Uganda. Thermal conductivity, thermal diffusivity, thermal absorptivity, thermal resistance, fabric thickness, and peak heat flow density were measured using an Alambeta device, whereas a Permetest device was used for the measurement of the moisture vapour permeability and evaporation resistance. The study was carried out under relative humidity of 40% and at a laboratory room temperature of 24°C and the results show that the thermal conductivity is in the range of cotton fabrics rendering barkcloth from F. natalensis, a comfortable fabric. The lower value of thermal absorptivity of barkcloth compared to the value of cotton renders the fabric a warm feeling when in contact with the skin. Barkcloth had a higher moisture vapor permeability compared to cotton and other fabrics, meaning its clothing comfort properties are reasonable.

Investigation Of Sound Absorption Properties Of Bark Cloth Nonwoven Fabric And Composites

Abstract The quest for sound-absorbing materials that are not only environmentally friendly, but also sustainable is the foremost reason for natural fibre-acoustic materials. Bark cloth is a natural non-woven fabric that is largely produced from Ficus trees. An exploratory investigation of bark cloth a non-woven material and its reinforcement in epoxy polymer composites has been fabricated and investigated for the sound absorption properties so as to find the most suitable applications and also to see whether bark cloth can be used in some applications in place of man-made fibres. Three types of material species were investigated with their respective composites. The fibre morphology showed bark cloth to be a porous fabric that showed promising sound absorption properties at higher frequencies. The sound absorption results of four-layer material selections of Ficus natalensis, Ficus brachypoda and Antiaris toxicaria bark cloth showed sound absorption coefficient of 0.7; 0.71 and 0.91 at f > 6400 Hz, respectively. The bark cloth reinforced laminar epoxy composites had reduced sound absorption coefficients, which ranged from 0.1 to 0.35, which was attributed to decreased porosity and vibration in the bark cloth fibre network.

Morphology, Thermal, and Mechanical Characterization of Bark Cloth from Ficus natalensis

The United Nations Educational, Scientific and Cultural Organization (UNESCO) proclaimed in 2005 that Ugandan bark cloth is largely produced from mutuba tree (Ficus natalensis) as a “Masterpiece of the Oral and Intangible Heritage of Humanity.” An exploratory investigation of bark cloth a nonwoven material produced through a series of pummeling processes from mutuba tree in Uganda is fronted as a prospective engineering natural fabric. Bark cloth was obtained from Ficus natalensis trees in Nsangwa village, Buyijja parish in Mpigi district, Central Uganda. The morphology of the fabric was investigated using scanning electron microscope (SEM). thermal behavior of the fabric was studied using thermagravimetric analysis (TGA) and differential scanning calorimetry (DSC). Fourier transform infrared spectroscopy was used to evaluate the surface functional groups. The fabric was subjected to alkaline treatment for six hours at room temperature in order to study the change in fabric thermal properties so as to set a base for applications in biodegradable composites. Findings show that the natural nonwoven fleece is stable below 200°C; alkaline treatment positively influences the thermal behavior by increasing the onset of cellulose degradation temperature. The fabric morphology showed that it is made up of fairly ordered microfibers which can be beneficial for nanocomposites.

Effect of Layering Pattern on the Mechanical Properties of Bark Cloth (Ficus natalensis) Epoxy Composites

The quest for sustainable materials as a consequence of a global drive to mitigate climate change has led to a focus on natural fiber–reinforced composite materials. In this study, skillful ply angle arrangement of bark cloth–reinforced laminar epoxy composites was carried out for the first time using vacuum-assisted resin transfer molding, and the composites fabricated were characterized for the effect of the layering pattern on their static and dynamic mechanical properties. Tensile strength and flexural strength were shown to be dependent on the ply angle arrangement. Dynamic mechanical analysis of the composites showed a glass transition temperature of 70°C, and the storage modulus and mechanical damping properties showed that the developed composites can withstand considerable loads and have excellent fiber-to-matrix adhesion.

Development of Multilayered Nanocomposites for Applications in Personal Protection

The aim of the presented research was to study the influence of surface layer material on improvement of impact, dielectric, EMI shielding and sound absorption properties of sandwich composites. The sandwich composite structure consisted of Kevlar or Carbon woven fabric at the surface layer, recycled high loft nonwoven in the center and a mixture of carbon particles/epoxy matrix as a binder to hold the surface layer and core together. The carbon particles were incorporated in epoxy in order to improve failure mechanism and enhance dielectric properties or electromagnetic shielding of sandwich composites. The biggest improvements on impact properties of sandwich composites were obtained when Kevlar fabric was used as surface layer. However, surface layer of carbon fabric was found to provide better dielectric properties and improve EMI shielding of sandwich composites against Kevlar fabric surface layer.

Effect of enzyme and plasma treatments of bark cloth from Ficus natalensis: morphology and thermal behavior

Bark cloth fabric has been in production in Uganda since the thirteenth century. In a move to preserve its cultural heritage, the United Nations Educational, Scientific and Cultural Organization (UNESCO) proclaimed in 2005 that Ugandan bark cloth is a “Masterpiece of the Oral and Intangible Heritage of Humanity.” Plant fibers require surface treatment before aimed at impurity reduction and for enhancement of fiber to matrix adhesion in composites. An exploratory investigation of enzymatic and plasma treatment of bark cloth is reported. The morphology of the fabric was investigated using scanning electron microscope. Thermal behavior of the fabric was studied using thermogravimetric analysis and differential scanning calorimetry. Fourier transform infrared spectroscopy and ultraviolet–visible (UV–vis) spectrophotometer were used to evaluate the surface functional groups. Enzyme-treated fabrics were cleaner and thermally stable compared to plasma and untreated fabrics.

Static and Dynamic Mechanical Properties of Barkcloth (Ficus Natalensis)-Reinforced Epoxy Composite

The United Nations Educational, Scientific and Cultural Organization (UNESCO) proclaimed in 2005 that Ugandan barkcloth largely produced from mutuba tree (Ficus natalensis) as a “Masterpiece of the Oral and Intangible Heritage of Humanity.” An exploratory investigation of barkcloth a nonwoven material produced through a series of pummeling processes from mutuba tree in Uganda is fronted as reinforcement for epoxy composite laminates. The fabric and composite morphology was investigated using scanning electron microscopy (SEM). The composite response to loading against temperature, time, and frequency was investigated using dynamical mechanical analysis (DMA). The results show that the developed composites are stable with considerable tensile strength and bending rigidity thus providing material engineers with the possibility of applying the material for semi-structural applications.