Marc Renner

Warm-Cool Feeling Relative to Tribological Properties of Fabrics

When the human hand touches a garment that is at a different temperature than the skin, heat exchange occurs between the hand and the fabric, and the warm-cool feeling is the very first sensation. This transient transfer of energy depends on the contact interface between the skin and the fabric, and the contact interface depends on many morphological and structural parameters like fiber morphology or yarn and fabric structure. This paper describes a new experimental device for measuring heat absorption of textile materials in a transient state. The link between the transient thermal behavior and the tribological properties of fabrics is then made to show the influence of contact interface and therefore the influence of morphological and structural parameters on heat transfer. This investigation involves two cotton varieties (Pima of Morocco and Kaba S of Benin), two yarn structures (single and two-ply yarns), and three stitch lengths of jersey fabrics.

Influence of the shape of fiber cross section on fabric surface characteristics

Fiber cross sections for use in textiles and composites are becoming more and more complex. Shape impacts fiber or filaments properties and therefore the yarn and fabric characteristics. This paper presents the influence of the fiber cross section on the fabric surface characteristics. The material used was polyester staple fibers, of four different shapes: round, scalloped oval, cruciform and hexachannel. All fibers had the same cut length with different fineness. Yarns obtained from these fibers had nominally the same yarn count, torsion value and structure. Plain jersey fabrics were knitted from each of the yarns under identical conditions and then relaxed prior to testing. Friction behavior was evaluated and a roughness-friction criterion developed. An indirect measurement of the real area of contact was obtained in order to provide roughness and friction properties. The influence of fiber cross section on yarn bending rigidity and on the state of the knitted fabric surface was characterized.

Tribological investigation of textile fabrics

Abstract There are several processes in textile finishing to improve fabric touch: one of them is sanding (emerizing). There is no current control system for this process. This study describes a tribological method for the quantization of sanding. Textile fabric is rubbed with a probe; the signal obtained is studied in the frequency domain. The calculated autospectrum shows a peak (or several peaks with the multi-directional roughness meter) which corresponds to the kind of weave or knit and the fabric density. The peak height increases with the process intensity and decreases after sanding. This phenomenon is due to a modification of fabric roughness. A tribometer with a probe linear movement has been used and a multi-directional roughness meter has been developed. The roughness meter can give the fundamental directions of the fabric relief which depend on the kind of weave or knit.

Optical characterization of the state of fabric surfaces

This paper presents the implementation of two optical methods for characterizing the state of fabric surfaces: a multidirectional roughness meter and a hairiness meter. A textile fabric has a complicated texture in that the relevant components (fibers) are not very small (usually at least 10 ?m in diameter), but in the fabric are partly ordered (in the yarn) and partly disordered (in the superficial hairiness). Hairiness is important in giving a textile fabric a characteristic surface. It makes the effective surface three-dimensional with many hidden areas. Thus, characterizing the state of a fabric surface requires special devices. On the one hand, the presented roughness meter measures essentially the fabric-reflected rays in all surface directions, because the fabric is rotated in its plane during the measurement. A Fourier temporal analysis of the reflected beam scanned across the fabric surface allows the fabric structure periods to be determined, because these periods yield peaks in the frequency spectrum. Two examples are given that show that the peak heights characterize the state of the fabric surface. On the other hand, the hairiness meter measures the hairiness of the fabric surface by an edge extraction method, which separates hairiness and structural information. The two devices are complementary and allow the processes that modify the fabric surface to be understood and controlled.

INSTRUMENTAL MEASUREMENT AND MACROSCOPICAL STUDY OF SANDING AND RAISING

Comfort is a major selling point for clothes, and tactile comfort is essential; a fabric must be pleasant to the touch. Several textile finishing processes improve fabric touch: sanding (or emerizing) (for 30% of clothes) and raising (for polar fleece, a current popular product), for example. There is no current control system for these processes, which are very often used but not well understood. This study describes a tribological method for investigating sanding and raising, and brings to light the effects of these processes on the fabric surface. A textile fabric is rubbed with a probe of a multidirectional roughness meter, and the signal is studied in the frequency domain. The calculated autospectrum shows several peaks that correspond to the kind of weave or knit and the fabric density. The peak height changes with the process intensity and decreases after sanding or raising, due to a modification of the fabric profile. The multidirectional roughness meter provides information about the fabric surface state and the fundamental directions of fabric relief, which depend on the kind of weave or knit. Observations with a scanning electron microscope and edge extraction of hairs produced by sanding or raising are used to interpret this information.

Mechanical discrimination of hairy fabrics from neurosensorial criteria

Fabrics with more and more elaborate tactile properties are available on the textile market. However the specifications of the textile products do not feature their touch because this can not be measured precisely and objectively enough. Some measurement methods of the mechanical properties involved in tactile feeling have been developed. Nevertheless, a purely mechanical approach is not sufficient. Therefore, the human being was utilized as a touch sensor. The tactile afferent [i.e. conveyed to the central nervous system, centripetal] messages elicited by the mechanoreceptors of the skin in response to textile stimuli and which were propagated along the sensitive nervous fibers up to the brain were studied. These messages were recorded on conscious human individuals, by a method named microneurography. The aim of this study was to use the neurosensory results in order to improve the mechanical measurement methods for the characterization of the surface state of fabrics. The samples tested had undergone different emery finishing processes. The preliminary results of the microneurographic study highlight the importance of taking account of the effect along/against the main direction of the hairiness. In fact, the discrimination of different hairy fabrics by cutaneous mechanoreceptors is only achieved when the fabrics stroke the skin against the main direction of the hairiness. A friction device developed by the co-authors was modified in term of signal processing in order to measure the surface along and against the main direction of the hairiness separately. Moreover, the probe was improved in order to separate the mechanical behavior information on hairiness from the roughness information. The results obtained with this new method were compared with results obtained using the surface tester of the KES-F.

Characterization of roughness-friction : Example with nonwovens

In several technical applications, it is necessary to accurately determine the surface state of materials. In order to do so, a new method to evaluate the surface state of materials has been developed. This method gives roughness–friction criteria, based on the principle of a “blade-disc” type tribometer, where the analyzed surface is the disc. In this study we have demonstrated the effectiveness of the method in a study of two types of nonwovens. The first type of nonwoven is intended for use for female or baby hygiene and the second type for baby skincare wipes. The nonwovens compared have surfaces with different structures and different compositions. In addition it is shown that the method is able to distinguish fine modifications of the surface state.

Effect of grain size and abrasion duration on the state of textile fabric surfaces

During an abrasive wear process with emery paper, the influence of grain size and abrasion duration on the tribological behaviour of textile fabrics were studied with a rotative tribometer for fabrics and an optical hairiness meter, the latter measuring the hairiness quantity on the fabric surface. First of all, the effect of the abrasive material graining on the state of the worn fabric surface is shown. Using a fine grain size leads to a worn fabric at the microscopic scale (fibre). Using a coarse grain size shows that the state of the fabric surface is completely different, since the fibre surface is not worn. Actually, some fibres are partly pulled out from the fabric, then this is an abrasion at the mesoscopic scale (yarn). Afterwards, the results show a cyclic behaviour of the fabric friction relative to the time due to a cyclic change of the fabric surface. Thus, this study brings into light the non-linear surface wear of textile fabrics.

Contactless optical extensometer for textile materials

In this paper we present a contactless extensometer. For some flexible materials, with great displacements and deformations, contact during measurement is not acceptable. In fact, contact measurement can modify the tensile behavior, as is the case for fibrous materials. Contactless extensometers usually have to print or glue some marks on the sample, which may cause problems during measurement. These extensometers typically use digital image processingto obtain deformation data. The principle used in this study uses the natural periodicity or surface patterns inherent in most textile materials without any image processing. During deformation the distance between two periods or pattern elements changes, allowing this method to measure the real-time modification of this in-plane distance. The extensometer consists of two parts: an optical device and a signal processing unit performing a Fourier analysis. Some results obtained during a tensile test on woven fabrics and non-wovens are presented here.

Noncontact Measurements of Sanding and Raising Effects

The method presented in this paper pertains to an optical roughness meter that considers a fabric in all surface directions. A previous paper presented a tribological method for investigating textile fabrics, which used a roughness meter with a contact between the probe and the surface. However, a contact is not always acceptable, and sometimes a noncontact method is better. Thus, an optical multidirectional roughness meter with the same signal processing and sample movement of the earlier apparatus has been developed. The principle is to consider the reflection of a laser beam by a fabric. The reflected ray is converted into an electrical signal with a photomultiplier, and this signal is subjected to Fourier analysis. The power spectral density versus frequency presents some peaks that reveal the basic directions of the fabric structure, the function of the weave or knit, and the fabric density. The height of these frequency peaks decreases after sanding or raising, thus characterizing the state of the fabric surface.