Franci Sluga

Modifying the UV Blocking Effect of Polyester Fabric

The influence of conventional acid and alkaline high temperature dyeing procedures on fabric construction is investigated. The effects of weave construction, orange, red, and blue disperse dyes, double layers of fabrics, and UV absorber on the ultraviolet protection factors (UPF) of polyester fabrics are the topics of this research. A spectrophotometer with an integrating sphere is used to measure the uv transmittance of polyester fabrics according to an AATCC test. Small differences in the weight of fabrics after blind dyeing procedures already influence the uv transmittance of fabrics. Pale orange and blue dyed fabrics show a high enough UPF, while a pale red dyed fabric does not reach such values. Deep dyed and double layered fabrics and fabrics aftertreated with a UV absorber reach high UPF values.

Evaluation of the Structure of Monofilament PET Woven Fabrics and Their UV Protection Properties

The importance of protection against ultraviolet radiation (UV) is increasing daily. The dependence of the UV protection level on different clothes is determined by the shape and design of fabrics, and especially by their construction parameters. The fabric structure represents an important factor which is in most cases the only condition for good protection. Other possibilities to ensure good or even excellent protection, mainly by finishing treatments, can be efficient only if the fabric structure is closed enough. To determine the key parameters which contribute to the closeness of the structure and offer suitable UV protection, an analysis of monofilament woven fabric structure was made. Monofilament fabric samples used in the production of high-module screen-printing meshes, which are characterized by the excellent dimension stability of the structure, the properties of which change with varying diameters of the monofilaments and the fabric density, were chosen for this research. A broad spectrum of similar but structurally different fabrics assures referential samples are available for the evaluation of UV protection properties. In all the samples tested, the parameters of transmission and reflection were measured. Moreover, the values of absorption and the ultraviolet protection factor (UPF) were calculated. The values calculated on the basis of a determined mathematical model matched well with the measured values and they can together represent the basis for successful planning of fabrics with suitable UV protection properties.

Impact of material, structure and relaxation process parameters of elasticized single-knitted fabrics on loop length

The development of knitted fabrics with incorporated elastane has increased in recent decades. Knitting with these elasticized yarns usually results in a very compact structure. Loop length is considered to be the primary parameter for knitted structures. Consequently, knowledge of all factors influencing loop length is vital for planning yarn consumption, comfort fit, quality, performance and aesthetic properties of knitted fabrics made from elasticized yarns. The objective of this research was to study the impact of material, knitted structure and relaxation process parameters on loop length. In addition, the objective was to examine the differences in loop length of single weft knitted fabrics, produced from different types of elasticized and non-elasticized yarns. For both groups of knitted fabrics, elasticized and non-elasticized, knitted fabric density and relaxation process influence the loop length most of all. Loop length decreases during the process of consolidation, but this decrease is not substantial. Addition of elastane does not significantly influence the loop length.

Shock in the Yarn during Unwinding from Packages

Tension in the yarn and its oscillations during the over-end unwinding of the yarn from stationary packages depend on the unwinding speed, the shape and the winding type of the package, the air drag coefficient, and also the coefficient of friction between the yarn and the package. The yarn does not leave the surface package immediately at the unwinding point. Instead, it first slides on the surface and then lifts off to form the balloon. The problem of simulating the unwinding process can be split into two smaller subproblems: the first task is to describe the motion of the yarn in the balloon; the second one is to solve the sliding motion. In spite of the seemingly complex form of the equations, they can be partially analytically solved as we show in the paper.

Measuring loop lengths of elasticised knitted fabrics

The methods for loop length measurement have mostly been developed for knitted fabrics made from conventional yarns. When measuring the loop lengths of knitted structures made from highly extensible staple yarns, problems arise because of an uncontrolled yarn extension at the low stresses. The present study proposes a test method for knitted loop length determination in which variable preloads are applied. In the study, the loop lengths measured on an INSTRON dynamometer using variable preloads and a HATRA Course Length Tester using a fixed preload were compared. The results demonstrated that knitted structures made from elasticised yarns exhibit only small changes in loop length after relaxation. The addition of elastane does not significantly influence loop lengths for fabrics knitted using the same machine, the same cam setting and relaxed by the same process. The loop lengths measured on an INSTRON dynamometer exceed the loop lengths measured on a HATRA Course Length Tester.

Yarn motion during unwinding from packages

We study the motion of yarn modelled as a one-dimensional inelastic string. In textile production, the yarn is being withdrawn from cross-wound packages in warping and weft insertion. During unwinding, there appear forces in the yarn that are approximately proportional to the square of the unwinding velocity. The yarn tension is not constant, but it oscillates within some interval. This is especially noticeable in over-end unwinding from a static cross-wound package. Even when the yarn is not strongly stressed, so that the tension never exceeds a few percent of the breaking strength, the yarn can still break sometimes. The production process requires as large warping and weaving speeds as possible; therefore, it is necessary to improve our understanding of the cross-wound package unwinding and to find the necessary modifications of the yarn unwinding process. In addition to empirical tests, it has proved useful to study yarn unwinding by mathematical modelling and computer simulations. We state the equations of motion that describe the yarn unwinding and develop a mathematical model that permits to simulate the process of unwinding.

Mathematical Model for Yarn Unwinding Part Ι: Cylindrical Packages

Stability of the yarn unwinding directly affects the efficiency of the textile production process and the quality of the final product. A package with an optimal shape will result in an optimal shape of the balloon. In addition, the yarn tension will be small and steady even at high unwinding velocity. Computer modeling is a valuable tool in the search for the optimal package shape. We demonstrate a mathematical model for simulating the unwinding from cylindrical and conic packages. We show how the winding angle and the apex angle influence the angular velocity of the yarn during the unwinding. Since the centrifugal forces on the yarn in the balloon depend on the angular velocity, this velocity has a large influence on the tension that we wish to reduce.

Mathematical Model for Yarn Unwinding Part ΙΙ: Conic Packages

Mathematical modeling can be used to simulate the unwinding of yarn from packages of different shapes. This method can be applied to design packages that can sustain high unwinding velocities at low and steady tension in the yarn. In the case of conic packages the angular velocity of unwinding depends not only on the winding angle as is the case for cylindric packages, but also on the apex angle. We will show that the dimensionless angular velocity depends very little on the apex angle. The apex angle, however, also determines the effective radius of the package at the lift-off point, therefore the angular velocity can be proportionally higher. We will compare unwinding from a cylindrical and a conic package with equal smallest radius and show that unwinding from the conic package is faster due to higher average radius of the package at the lift-off point.