M. de Araújo

Application of warp-knitted spacer fabrics in car seats

Abstract Polyurethane foam is commonly used as padding in car seats despite some problems concerning comfort and recycling. Compared with polyurethane foam, textile seat padding is easier to recycle; so textile padding is a good candidate to substitute foam padding as regulations on recycling have become more stringent on car manufacturers. With the available textile option, warp-knitted spacer fabrics are likely a good substitute for polyurethane foam as padding in car seats. Warp-knitted spacer fabric structures can be designed to be quite flexible in a variety of thicknesses. Warp-knitted spacer fabrics can be very resilient and may display good breathing properties. The current work presents a study on the application of warp-knitted spacer fabrics as cushion in car seats. The results show that, relatively to polyurethane foam, warp-knitted spacer fabrics demonstrate better recovery to compression, thermal properties and breathability. Furthermore, warp-knitted spacer fabrics retain their original thickness for longer time and can be easily recycled.

Theoretical analysis of load-extension properties of plain weft knits made from high performance yarns for composite reinforcement

This paper presents a theoretical analysis of the tensile properties of plain weft-knitted fabric. Load-extension curves in the coursewise and walewise directions for fabrics made from glass fibers are theoretically calculated and compared with experimental results, and good agreement is obtained between them.

Studies on moisture transmission properties of PV-blended fabrics

Moisture transmission properties are most important for fabric comfort. We have studied the moisture transmission properties of the plain-woven fabric produced with polyester–viscose-(PV) blended yarns. PV-blended yarns of varying blend proportion, yarn count and twist levels have been used for fabric manufacture. A three-variable Box and Behnken factorial design technique has been used to study the interaction effects of the above variables on the aforesaid characteristics of fabrics. The interactive effect of these three variables on the air permeability, water vapour permeability, in-plane wicking and vertical wicking of PV-blended fabrics has been studied and the response surface equations for all the properties have been derived; also, the design variables have been optimized for all the moisture transmission-related properties. Most of the moisture transmission characteristics were found to be affected significantly by blend proportion, count and twist levels at 95% level of significance with the present variables.

Spirality of Knitted Fabrics Part II: The Effect of Yarn Spinning Technology on Spirality

We have studied the effect of yarn spinning technology of the spirality of jersey fabrics in the dry and fully relaxed states for 100% cotton and 50/50 cotton/polyester blend yarns. From this study, we have concluded that 50/50 blend yarns produce less spirality than 100% cotton yarns. Furthermore, it seems that each spinning technology influences the degree of spirality in fabrics. For all practical purposes, spirality was virtually eliminated for some of the 50/50 blend air jet and rotor spun yarns that were used.

Development of weft‐knitted and braided polypropylene stents for arterial implant

Textile biomedical materials have been used for various applications contributing considerably in improving quality of life. The current study aims at improving polypropylene fibre stents which may replace metallic ones. In order to produce the stents, weft‐knitting and braiding technologies were used. In the braiding technique, by varying the take‐up ratio (using gears with the appropriate number of teeth in the braiding machine), it was possible to manufacture regular braids with angles of 65°, 70° and 75° in order to obtain different covers. In the knitting technique, a circular machine was used and the tightness of the structure was adjusted by varying the loop length and thus the fabric loop density, resulting in variations of the sample diameter. The knitting machine had negative feed, and so loop length variations were achieved by varying the yarn input tension, the stitch cam settings and the fabric take‐down tension. The samples were heat set. Yarns were contracted by setting at 130°C and 140°C, and this led to increasing the loop density and the flexural rigidity of the samples. A high cover of the samples resulted in a greater stiffness of the structures. The stents were evaluated by undertaking the tests required for arterial support: rigidity to radial compression, resistance to tensile forces and bending rigidity. The best results were obtained with braided structures. Future work may concentrate in improving the stent design and using new biocompatible fibres.

6 – Weft-knitted structures for industrial applications

: The mechanical properties of weft-knitted fabrics are strongly related to fabric structure, yarn properties and fabric direction. These properties may be designed according to the needs of a particular application by choosing the fibres and yarns with the most appropriate properties and placing them in the most appropriate structure to obtain the required fibre architecture. The flexibility provided by weft-knitting technology enables the production of a wide range of structures with different properties. 3D structures and directionally oriented structures (DOS) are reviewed and represent types of textile fabrics developed for engineering applications, especially for the reinforcement of composite materials. In composite materials the ends of straight or nearly straight yarns are introduced to engineer the fabric characteristics and to enhance the fabric properties in the required directions, thus the fabric produced offers the ideal combination of excellent mechanical properties and cost-effective production. Simulation and modelling are reviewed, these being very important tools for engineering design. They may enable the development of new structures with particular properties and a significant reduction in time and costs of sample manufacturing and testing. The industrial applications of weft-knitted fabrics are reviewed.

Design and Marketing Innovation

Trends in global textile and clothing strategies are briefly reviewed to introduce the Portuguese context, and the development of Design & Marketing education and research at The University of Minho. The development of textile-oriented multimedia technologies is discussed with reference to the SME multimedia corporate and product presentation model and the interactive fabric library. New innovative design tools such as the use of fractal geometry in computer-aided textile printing design, the application of chromotropic pigments by a spraying technique, and the development of a CAD system for fancy yarn design are also discussed. The work conducted in developing novel weft-knitted structures for technical applications is reviewed with reference to 3-D structures, sandwich fabrics and a multiaxial technique.

Improving the stiffness of unidirectionally oriented weft-knitted structures for polymer matrix composite reinforcement

The use of weft-knitted structures in composite reinforcements is limited due to their poor mechanical properties. The tensile behaviour of weft-knitted fabrics is strongly restricted by its loop formation. When this type of structure is used as reinforcement, the mechanical properties of the composite material may be considerably hindered, as the resin may bear the initial load and fail before the load is transferred to the reinforcing fibres. However, weft-knitting is the most suitable technique for the production of 3D fabrics for complex shape composite reinforcements and so their stiffness must be improved. This paper reports on the progress that has been made to improving the modulus of elasticity of glass fibre fleece structures in the coursewise direction, in order to enable the production of tubular or flat preforms for composite materials with adequate stiffness.

Application of braided fibre reinforced composite rods in concrete reinforcement

This paper describes the work that is being done at the University of Minho concerning the development of braided rods for concrete reinforcement. A preliminary research study has been conducted to understand the mechanical behaviour of braided fabrics. Various samples have been produced varying the type of fiber (glass, polyester and aramid), the type of braided fabric (simple, hybrid and core reinforced) and in the latter case, the number of core reinforcing yarns. The tensile properties of these samples have been evaluated and the results presented. The influence of each factor on the tensile properties of braided fabrics has also been analysed and discussed. In order to produce braided reinforced composite rods to use as a concrete reinforcement, a special technique has been developed using a standard vertical braiding machine. The braided reinforced composite materials have been produced in rib structure to improve adhesion between them and the concrete. Special samples have been prepared and tested to evaluate the adherence between both materials involved. The tensile and bending properties of braided reinforced composite rods have been evaluated and the results obtained presented and discussed.

29—THE INFLUENCE OF RUN-IN RATIO ON THE DIMENSIONAL PROPERTIES OF SINGLE-JERSEY PIQUÉ FABRICS

An investigation is described in which the stable dimensional properties of cotton single-jersey pique fabrics of the Lacoste type were studied and found to depend on the yarn run-in ratio in such a way that it enabled considerable variations in fabric width, length, thickness, mass per unit area, and aesthetics to be made at constant structural-knitted-cell length.