VORTEX SPUN YARN VS. AIR-JET SPUN YARN
Vortex spinning can be viewed as a refinement of jet spinning, or a natural development in fasciated yarn technology. As in all other fasciated yarns, the structure of vortex yarn consists of a core of parallel fibres held together by wrapper fibres. This has been revealed by examining an untwisted vortex yarn sample under the Scanning Electron Microscope. Subsequently, the physical properties of vortex and air-jet yarns produced from different polyester cotton blends were compared. Results indicated that vortex yarns have tenacity advantages over air jet yarns, particularly at high cotton contents.
MODELLING THE STRUCTURAL BARRIER ABILITY OF WOVEN FABRICS
Woven fabrics with their full, systematically arranged and non-stochastic structure, are the subject of increasing interest as barriers to fluids, radiation, micro-particles, and micro-organisms. The structure of woven fabrics, which is characterised by inter-thread channels of predetermined shape and location, is especially important. Some procedures for designing channel shape and methods for sealing barrier woven fabrics are presented.
MODELLING AND SIMULATION OF THE MECHANICAL BEHAVIOUR OF WEFT-KNITTED FABRICS FOR TECHNICAL APPLICATIONS Part I: General considerations and experimental analyses
This paper is in four parts. The first is related to general considerations and experimental analyses, and each of the successive papers is related to different approaches to theoretical analyses of the mechanical behaviour of weft-knitted fabrics and weft-knitted reinforced composites made of glass fibre. The objective is to find ways of improving the mechanical properties and simulating the mechanical behaviour of knitted fabrics and knitted reinforced composites, so that the engineering design of such materials and structures may be improved.
In Part I, general considerations, experimental analyses and ways of improving the mechanical properties of weft-knitted fabrics and knitted reinforced composites are discussed.
In Part II the first model is presented, a 3D model based on the classic elastica theory, and it is used to calculate the load-extension curves of a plain weft-knitted fabric in coursewise and walewise directions. Good agreement is obtained between theoretical and experimental results.
In Part III the second model is presented, a 2D model based on FEA (finite element analyses). A plain weft knitted fabric, based on the simple loop structure, is simplified and represented by a 2D hexagonal structure constructed by non-linear truss elements. The characteristics of the truss elements for FEA simulation are obtained from experimental results through an analytical method when a loop is converted to a FEA model. The elongation deformation is simulated in one, two and many directions. The model can also be used to calculate a planar knitted fabric to be deformed to fit a 3D spherical mould.
In Part IV the technologies for the development of weft-knitted 3D complex shape preforms] are surveyed and a third model is presented, a 3D model based on FEA (finite element analyses). A solid representation of a 2D yarn is built up, and a MES (mechanical event simulation) is applied to obtain a 3D shaped loop. The final knitted fabric geometry is obtained by interacting this loop with the adjacent loops, according to the dimensional properties of the knitted fabrics and by using a MES. Finally, the geometry of the reinforcement inside the composite is built up, and the composite material is divided into small tetrahedric elements to obtain a mesh of finite tetrahedric elements (FEA). The average values of the mechanical properties are obtained with FEA and compared with the experimental ones.
NET-SHAPE KNITTED FABRICS AS CARRYING ELEMENTS IN TECHNICAL COMPOSITE PRODUCTS
This paper presents an experimental investigation aimed at broadening the range of knitwear application on composite products of non-conventional destination carried out at the TRICOTEXTIL Institute of Knitting Technology and Techniques. The research problems of these investigations, as solved by us, included the application of knitted fabrics as abrasive composite products for finishing activities in the building industry, filter materials, and upholstery constructions. An analysis of the structure of net-shaped knitted fabrics as applied for technical composite materials is presented, together with the fabric's parameters. In addition, an estimation of the composites manufactured with the use of net-shaped knitted fabrics also is presented.
INTENSIFICATION OF MASS TRANSFER IN WET TEXTILE PROCESSES BY POWER ULTRASOUND
In industrial textile pre-treatment and finishing processes, mass transfer and mass transport are often rate-limiting. As a result, these processes require a relatively long residence time, large amounts of water and chemicals, and are also energy-consuming. In most of these processes, diffusion and convection in the inter-yarn and intra-yarn pores of the fabric are the limiting mass transport mechanisms. Intensification of mass transport, preferentially in the intra yarn pores, is key to the improvement of the efficiency of wet textile processes. Power ultrasound is a promising technique for accelerating mass transport in textile materials. In this paper, the intensification of mass transfer in textiles under the influence of ultrasound on the basis of a total system approach is described. EMPA 101-test fabric was selected as a model for the cleaning process. This study focuses on two aspects, the mechanism of the ultrasound-assisted cleaning process and the effect of the presence of the cloth on the ultrasound wave field generated in a bath. It has been found that the dissolved gas content in the system plays a dominant role in the cleaning process. The cleaning effects observed are explained by two different mechanisms: small-amplitude acoustic bubble oscillations and micro-jets (resulting from the collapse of acoustic bubbles in the boundary layer between the fabric and the bulk fluid) that give rise to convective mass transfer in the intra-yarn pores. It has also been observed that the overall power consumption of the system varies with the position of the fabric in the acoustic field. This variation is explained on the basis of a model involving the specific flow resistance of the fabric and the physical properties of the standing waves.
EXAMINATION OF THE AGEING OF SELECTED SYNTHETIC FIBRES UNDER THE INFLUENCE OF UV RADIATION
An attempt has been undertaken to assess the effect of UV radiation on the molecular and supermolecular structure of polyamide and polypropylene fibres that are characterised by various macroscopic features, colours and additives. Based on the measurements performed, the general conclusion can be drawn that UV radiation under the exposure conditions used in our experiments causes changes in both the molecular and supermolecular structures of the investigated fibres. The extent of these changes is clearly dependent on the initial fibre structure, the modifiers added and the macroscopic features.
THE EFFECT OF NAFTA ON THE US SPINNING INDUSTRY
The purpose of the research presented in this paper has been to examine the effects of NAFTA on the US short staple spinning industry. Yarn, particularly cotton, plays a critical role in the apparel supply chain, and therefore the factors that affect yarn, in turn, also affect apparel. Since the inception of NAFTA in 1994, many changes have taken place in the US short staple spinning industry, as well as the entire textile and apparel industry. However, this paper will examine current trends, which have resulted primarily from NAFTA, but also the Asian financial crisis. Specific focus will be given to yarn production levels, price, imports, exports and labor.