The Structure And Behavior Of Filament/Staple Composite Yarns

The research of yarn structure and behavior is an important project in textile material field. It is due to the close relationship between the yarn structure and behavior and its fabrication or products. Twist structure and twist determining methods, tensile behavior and its composite principle have been mainly studied in this theme. The objects of this study are polyester (PET), polyamide 6 (PA6) filament and wool/PET staple composite yarns (Plyfil and Sirofil), and other yarns, such as spun cotton, worsted, ramie yarns.Which we mainly study on include the comparison of blend and composite concepts, the means and characteristics of composite spinning, twist structure and twist determining methods, fiber component and its content and composite ratio, diameter, mass of unit volume and linear density, cross structure of composite yarn, strengths and stretches and their distributions of single fiber and fiber bundle, the tensile curves and strengths and stretches of non-twisted or twisted composite filament yarn, filament/staple yarn composite thread (Plyfil), filament/staple composite yarn (Sirofil), the relationship between yarn strength or extension and composite ratio, and major factors influence the strength and stretch of composite yarn, etc.Some reviews are made before beginning the study about the research of cross structures, twist structures, tensile behavior, breakage mechanism of continuous filament yarn and staple yarn, structure and performance of blend yarn, blend filaments and filament/staple composite yarn. Then the concepts of blend or mixture, composite for different fibers, means and characteristics of filament/staple composite process are discussed. On the basis of these, the research project is determined.Twist structure is almost the most important characteristics for textile yarns. On the basis of yarn contraction theory by Hearle et al., contraction factor and retraction for composite yarns and their components, the relationship between stretch and untwisted factor of composite yarn are measured or educed. For different composite ratio polyester filament (PETF) and wool/PET staple Sirofil yarns and worsted, PET filament yarns, the untwisted processes, i.e. the relationships between stretch and untwisted factor are measured and analyzed. Then the results of twist measurement by three different methods, i.e. the longest method, untwist method and untwist-twist method, are compared and discussed. Some conclusions are as following. As same as worsted yarn, the results of twist measurement for Sirofil yarn by untwist-twist method are influenced in evidence by the pre-tension of yarn. As less pre-tension, twist factor by the longest method measurement is evidently greater than the untwist-twist method and slightly smaller than untwist method. As larger pre-tension, results of twist measurement by different methods are closer.After analysis, corresponding to blend ratio of blend yarn, composite ratio and composite component content are proposed to evaluate the composite structure. The relationship between them and fiber content, the relationship between yarn official regain, linear density and composite components are analyzed and measured. Diameters and mass of unit volume of some Plyfil, Sirofil and fascinated yarns are determined and compared. The author also discusses the lengthways and cross form and structure of composite yarns, and their influences to yarn tensile performances.Chapter 4 briefly shows and discusses some former proposed theoretical models for predicting the strength of blended fibrous structures. On the basis of theoretically analyzing the strength of two-constituents parallel non-twisted filament yarn, two strength predicting models are proposed, in which one is parallel composite strength predicting model (R0M2), another is parallel composite strength predicting model when considering the change of fiber number within a bundle (R0M3), and they are validated with PET and PA6DTY filaments parallel non-twisted composite yarn. These models are further predigested as a more simple model finally, which is proposed for predicting the strength of parallel non-twisted composite yarn.It is determined and discussed in chapter 5 that tensile curves, strengths and extensions of parallel composite yarns such as spun cotton, worsted yarn combine with PET or PA6DTY filament yarn etc., especially the tensile curves, strengths and extensions and their distributions, the relationships between strength, extension and composite ratio of wool/PET blend yarn and PET or PA6DTY filaments parallel composite yarns. The author proposes to evaluate the composite effect of composite yarn with composite yarn strength ratio and extension ratio, and then analyzes the composite effect and mechanism of different constituents parallel non-twisted or twisted composite yarns. Some conclusions are gained. The breakages of parallel non-twisted composite yarn and twisted composite thread (Plyfil) are not sharp. They break in steps (i.e. not same time breakage) up to much higher breaking extensions. The distributions of yarn strength and extension show two-modal or multi-modal characteristics. The relationship curve of strength and composite ratio for wool/PET blend yarn and PA6DTY filaments parallel composite yarn is concave, but the relationships of wool/PET blend yarn and PA6DTY filaments twisted composite yarn and wool/PET blend yarn and PET filaments non-twisted or twisted composite yarn are almost accorded with the simple rule of mixtures (R0M1).Some experimental samples which constitute with PET filaments and wool/PET staple fiber are produced in laboratory with Sirofil spinning process. Then the load-extension curve, strength and extension and their distributions, the relationships between strength or extension and composite ratio, and the composite principles of load-extension curve and strength are measured or established. Through experiment and analysis some conclusions are obtained, they are: Sirofil composite yarn does not break in steps in general, the distribution of strength and extension of Sirofil yarn is relatively concentrated, and the composite strength of Sirofil yarn commendably accords with the ROM1, the load-extension relationship of Sirofil yarn can be described by the formula (6-13).Chapter 7 discusses the major factors influence the tensile performances of composite yarns. The followings are concluded through experiment and analysis. Pre-tensions or spinning tensions for constituents of composite yarn affect the performance of composite yarn in different extent due to the different properties of constituents. Along with shortening the gauge length of tensile experiment, the strength and extension reduce in a sort way, and that the strength and extension of Plyfil composite thread reduce even more. The influence for tensile velocity to strength and extension is relatively light, however the composite twist factor is one of the most important factor to the behaviors. Along with the increase of twist factor, strength of composite yarn increases first then decreases. A critical twist aiso exists on this relationship. Generally, the critical twist for Plyfil composite thread is smaller than that for Sirofil yarn.Breaking mechanisms of Plyfil and Sirofil yarns are compared and analyzed, starting with the analysis for the form of fractures. The experimental results show that the breakage of Sirofil yarn is not sharper than Plyfil thread. There are some breakage phenomena such as breaking at same time and same place, at different time or different place for two constituents within Plyfil thread. However, the breakage of Sirofil yarn shows partial breakage and other part fibers being taken out characteristics, because off having much contact and inteaction between two constituents.Brief conclusions, some problems in this study and some prospects are given out in the last of this theme.