Band 5, Heft 3

Spider silk has attracted the interest of several researchers in recent years because it displays a unique combination of high tensile strength, high breaking strain and an ultra-low weight. Hitherto, the focus has always been on dragline and viscid silk, whereas research on spider cocoon silk is limited. In order to explain the structure-property relationship of spider silk, the stress-strain behaviour of cocoon and dragline silk is compared in this study. It is shown that both fibres have completely different stress-strain behaviours.In addition, the influence of the testing speed is investigated. For cocoon silk, lower testing speeds result in lower strength, stiffness and higher post-modulus. When the stress-strain curve is simulated by an extended Maxwell model, as testing speed increases, the level of the hardening region is higher, the yield region moves to higher strains and the hardening region in the stressstrain curve becomes more horizontal. However, a speed of 20 mm/min can be considered as a saturation point where the effect of the speed decreases. The influence of the testing speed on dragline silk is clearly less pronounced than for cocoon silk. However, a more detailed study of the stress-strain curves of dragline revealed different possible shapes for the stress-strain behaviour of dragline silk.

Reducing yarn hairiness during yarn winding by the use of air jets is a new approach, since the production rate of winding is very high and the process itself increases yarn hairiness. The Box & Behnken factorial design approach has been used to optimise the jet angle, the jet diameter, yarn linear density and the winding speed in order to reduce the yarn hairiness. A jet angle of 45 0 , a jet diameter of 2.2 mm, 10 tex yarn and a winding speed of 800 m/min give the optimal results in terms of reducing the hairiness. A CFD (computational fluid dynamics) model has been developed to simulate the airflow pattern inside the jets with the use of Fluent 6.1 software. The air velocity around the core of the jet is the influencing factor in wrapping the hairs on the yarn body.

We have examined the fabric-to-metal surface and fabric-to-fabric frictional characteristics (in both warp and weft directions) of a series of fabrics containing 100% polyester, 100% viscose, and P/C & P/V blends with different blend proportions. It has been observed that the normal load and the frictional force follow a logarithmic relationship for all the fabrics. The nature of fabric friction is characterised by different parameters such as the F/N ratio, and the values of n, k and k/n. Fabric-to-metal friction is found to be less sensitive to fabric morphology and rubbing direction, whereas fabric-to-fabric friction is highly sensitive to these factors. Fabric friction has been affected by many factors such as the type of fibre, type of blend, blend proportion, yarn structure, fabric structure, crimp and crimp height, compressibility, etc. In P/C and P/V blended fabrics, the frictional force increases as the cellulose fibre component increases.

In this paper, the degree of breakage of glass filament yarns during the weft knitting process is studied. A quantitative method used for assessing the degree of glass filament breakage is proposed, and the effects of different factors such as cam setting, knitted structures and yarn parameters are analysed. The experimental results show that an optimum cam setting exists at which the degree of filament breakage is minimum.

In this work, a method for indirectly determining the tensile force in yarn of twisted units is propounded on a tensile force-elongation diagram. The elongation occurs in the change of the screw line step of the twisted units. The screw-line step is calculated after multiple measurements of short-length areas in the work zone of the knitting needles. The measuring is possible for knitting in producing conditions and in real time.

An experimental plasma reactor has been developed that enables the study of aspects related to the flow of a gas around and into textile structures while they are treated in a plasma at reduced pressure. A selection of experiments draws attention to the fact that even at reduced pressure a textile forms a barrier for a gas containing plasma-created species, resulting in an ‘edge effect’. It is also shown how basic variations in the structure of a textile influence the penetration of the treatment effect. The ratio of textile thickness to its porosity is proposed as a simple rule of thumb for assessing the effect of penetration and etching efficiency.

The influence of three acid dyes upon some physico-mechanical indices of polyamide multifilament yarn has been studied as a consequence of the structure modifications which occur during the dyeing process. It has been established that, irrespective of the differences in the chemical composition of the dyes, the modifications in the properties of the samples used are quite similar. Some structural characteristics, tenacity and elongation at break, crease resistance and the critical time of dissolution, have been determined. The dependencies of the indices listed on the dye concentration are of a complex character, which reflects the gradual penetration of the dye molecules into the inter-fibrillar and intra-fibrillar amorphous areas of the structure which are different in solidity. The fluctuations in the course of the dependencies in the area of the lowest concentrations are the result of the combined influence of the processes of improvement of the crystal phase and the relaxation phenomena, occurring in the most accessible amorphous areas of the fibrous structure. With the increase in the dye concentration, the so-called .cross-linking effect. starts to appear, as a result of the formation of intermolecular links of the polymer-dye-polymer type, which influence the properties under investigation in a characteristic way. The increase in the dye presence in the substrate provokes the repeated alternation of the above-mentioned phenomena in the thicker amorphous areas of the samples, with a pronounced influence of the .cross-linking effect. in the highest concentrations.