Continuous Filament

Continuous filaments can also be converted into other structural derivatives by deliberate entanglement or geometrical reconfiguration, using a process called texturizing for the purpose of producing stretchy or bulky yarns.

From: Engineering Textiles , 2009

Fiber Theory and Formation

Von Moody , Howard L. Needles Ph.D. , in Tufted Carpet, 2004

1.3.5 Staple Formation

Continuous filaments can be cut into staple by wet or dry cutting techniques. In wet cutting, the wet-spun fiber is cut to uniform lengths right after spinning, while dry cutting involves partial cutting, debonding, and shuffling of the dry tow to form a sliver.

Before the filament or staple is used in yarn spinning, spin finishes are added to give lubricity and antistatic characteristics to the fibers and to provide a greater degree of fiber cohesiveness. The finishes are usually mixtures including such materials as fatty acid esters, mineral oils, synthetic esters, silicones, cationic amines, phosphate esters, emulsifiers, and/or nonionic surfactants. Spin finishes are formulated to be oxidation resistant, to be easily removed by scouring, to give a controlled viscosity, to be stable to corrosion, to resist odor and color formation, and to be nonvolatile and readily emulsifiable.

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Reinforcements and General Theories of Composites

Hiroshi Ichikawa , Toshihiro Ishikawa , in Comprehensive Composite Materials II, 2018

1.6.1.2 Fabrication Processes of SiC Fibers

Table 1 shows a comparison of the properties of various SiC-based ceramic fibers. SiC fibers can be made by various fabrication processes: CVD, preceramic polymer pyrolysis, powder sintering, and chemical vapor reaction (CVR) processes.

Table 1. Properties of various SiC-based ceramic fibers

Property Manufacturer Nippon Carbon Ube Industries Textron Dow Corning Carborundum MER
Nicalon NL-200 Tyranno Lox-M SCS-6 HPZ
Process Polymer Polymer CVD Polymer Powder sinter CVR
Fiber diameter µm 14/12 11 140 10–12 17–20 7.5
Number of filaments fil./yarn 500 800 1 500 200–400 3000
Tex g/1000 m 210/105 200 100
Tensile strength GPa 3.0 3.3 4.0 2.8 1.5–1.75 1.5–1.7
Tensile modulus GPa 220 187 430 180 400 >400
Elongation % 1.4 1.8 0.9 1.6 0.4
Density g cm−3 2.55 2.48 3.0 2.48 3.15 –
Grain size nm 5 amorphous 100 amorphous 1.0 –
Specific resistivity ohm-cm 103–104 30 – 106 – –
Specific heat J g−1·K 0.71 0.80 – – – –
Thermal conductivity W m−1·K 2.97 1.14 – – – –
Coefficient of thermal Expansion 10−6 K−1 3.2 3.1 – – – –
Chemical composition Si (wt%) 56.6 55.4 β-SiC on C 60 α-SiC SiC-(C)
C 31.7 32.4 9
O 11.7 10.2 3–4
Ti2.0 N 27 B 0.5
C/Si (atomic) 1.31 1.37
References Nicalon Tech. Data Sheet Tyranno Fiber Catalog SCS Series Catalog 2 3 4

1.6.1.2.1 CVD SiC fiber

The SiC continuous filament SCS-6 (Textron specialty materials) is fabricated by the CVD process. It consists of a pure, stoichiometric SiC sheath and a carbon core. This SiC fiber exhibits high mechanical properties (strength and modulus). However, stiffness of the filament arising from its large diameter (140 µm) may sometimes limit the variety of applications.

1.6.1.2.2 Preceramic polymer pyrolysis

Several SiC fibers, including Nicalon (Nippon Carbon), Tyranno (Ube Industries), and HPZ (Dow Corning), are produced by the polymeric route. These fibers are fabricated by the sequence of (1) spinning the precursor polymer, (2) curing the precursor fiber to be infusible, and (3) pyrolysis into inorganic material. This process is fundamentally the same as that of carbon fibers from PAN or pitch. Polymer-derived SiC fibers are fine-diameter (8–15 µm), multifilament (400–1600 filaments) yarn. Therefore, they are flexible and weavable for a variety of cloths.

1.6.1.2.3 Powder sintering

The powder sintering technique to make SiC fiber has been developed by Carborundum. A mixture of submicrometer SiC powder and binder polymer is extruded through a spinnerette, and the green fiber is sintered continuously at 2100–2200°C into polycrystalline SiC fiber. This SiC fiber consists of relatively large SiC grains (approximately 1 µm) because of the high processing temperature; it is quite thermally stable and creep resistant, as well as monolithic. However, at present, a rather large diameter (17–20 or 30 µm) and low strength (1.5–1.75 GPa) are drawbacks.

1.6.1.2.4 CVR process

MER has a unique technology to make fine-diameter SiC fiber. Carbon fiber is converted to SiC fiber with silicon monoxide (SiO) vapor. This process has the potential to make a cheap SiC fiber because of relatively cheap raw materials and a simple process. This SiC fiber has high creep resistance, however, and suffers from a rather low strength (1.5–1.7 GPa).

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Fabric Finishing

P. Hauser , in Textiles and Fashion, 2015

18.3.2.3 Scouring silk

Silk is a continuous filament fiber produced by silk worms. The raw fiber consists of two filaments glued together with a substance called sericin. Silk filaments are not sized before weaving, since the sericin protects the filaments during the weaving process ( Peters, 1967, p. 323). After the silk fabric is woven, the sericin is removed in a process called degumming. Treatments with mild alkali, detergents, and enzymes are employed (Gowda, Padaki, & Sudhakar, 2004; Holds, 2007; Karmakar, 1999, p. 115).

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Advanced testing of silk fibers, yarns, and fabrics

P. Bhat , A. Basu , in Advances in Silk Science and Technology, 2015

7.2.1.3 Non-breakable filament length (NBFL)

This parameter represents the continuous filament length that can be unwound continuously without any breaks. This parameter gives information on the number of castings needed during reeling operation. The higher the non-breakable filament length, the better the quality of raw silk produced and the easier the reeling operation is, by way of a lower number of castings. Twenty randomly drawn cocoons are considered for this test. The cocoons are cooked to optimum level and used for the assessment.

N o n - breakable filament length = Total length of first - drawn filaments m Number of cocoons considered f o r the test

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The sewing of textiles

S. Hayes , J. Mcloughlin , in Joining Textiles, 2013

Twisted multifilament thread

Twisted multifilament threads are continuous filaments of polyester or nylon twisted together into a cohesive bundle and then plied to make a thread. They are then dyed, stretched and heat set to achieve the desired physical characteristics. Twisted multifilament threads are exceptionally strong for their size with three-ply threads demonstrating higher seam strength compared to two-ply threads. The strength of the thread increases with the increase in twist in the plied structure. A higher degree of twist also helps to gain circularity in the cross section of the thread, thus reducing the contact area between thread and needle, resulting in lower strength loss during sewing. Twisted multifilament threads are used for a variety of purposes, from swimming suits, to applications in the automobile industry.

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Air jet intermingling in yarn texturing

C. Atkinson , in False Twist Textured Yarns, 2012

7.1 The concept of air jet intermingling

Draw textured yarns comprise continuous filaments with crimp, which lack inter-filament cohesion. Filament separation from the yarn in some instances can be problematic in downstream processing due to:

•

Filament snagging on adjacent wind layers during package off-wind. This can create yarn tension peaks, broken filaments and sometimes yarn breaks. Depending on the yarn property, tension peaking can cause bands in circular knitting, and weft stripes in weaving during high speed off-wind where yarn feed accumulations are not used. Broken filaments can also lead to 'slubs' in fabric.

•

Filament trapping during needle penetration/yarn release in knitting.

•

Filament snagging (warp-weft contact) during passage of the weft yarn through the warp shed in weaving.

To overcome these tendencies, inter-filament cohesion is imparted to the draw textured yarn by the following processes:

•

A subsequent twisting process, which is a slow-speed, high-cost operation but provides a smoother better handle fabric depending on the twist insertion level applied.

•

Sizing of warp yarns for weaving application, which again is a high-cost process with environmental implications (the size has to be washed away from product).

•

Air intermingling, whereby a cold airstream is applied to the yarn on the draw texturing machine, imparting filament entanglements along the yarn axis.

The principle of air intermingling is also utilised for the assembly of yarn combinations in the draw texturing process; for example:

•

Textured yarns with elastomers (high elasticity yarn).

•

Differential yarn dye-uptakes to produce marle effects.

•

Differential yarn shrinkages to produce crepe fabric effects.

•

Simple combinations of yarns, typically two- to six-fold.

•

Pre-texturing zone filament entanglement for low dpf and microfilament yarns to promote filament migration within the twisting mechanism.

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Rope production

H.A. McKenna , ... N. O'Hear , in Handbook of Fibre Rope Technology, 2004

6.2.1 Assembling textile yarns

Whether the textile yarn is continuous filament or produced from staple, its size is too small for most rope manufacture. Rope yarns can be assembled either by twisting or by winding the yarns together to form a parallel roving. As a general rule, twisting is better since it gives the assembled rope yarn some structural integrity and preserves its strength. The outer helix angle of the rope yarn is generally around 5° to 10°, as shown in Fig. 6.8. Most commonly, the whole set of textile yarns is combined into a rope yarn in a single operation. However, sometimes it is carried out in two stages, first and second twist. For example, rope yarns for three-strand laid and eight-strand plaited ropes may be made by plying three first twist yarns together in a fly twister.

Fig. 6.8. Rope yarn showing outer helix angle

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Polymer Matrix Composites

K.J. NIDERÖST , M.H. WALTERS , in Comprehensive Composite Materials, 2000

2.03.3.2.1 Textile cord processing

After spinning the bundle of continuous filaments, these are brought together to form the yarn. This is then given a spin finish and a small amount of twist to aid processing and wound onto a cylindrical shaped center to form a cheese. At this spinning stage the yarn can also be given a surface coating to aid adhesion. The yarn is then twisted to form a singles yarn. Two or more of these singles yarns are twisted together in the opposite direction to the singles twist to form the cord. These cords are woven into a fabric at a fairly high density as the warp cords, i.e., those that run lengthways. The weft cords which run across the fabric are very openly spaced and just sufficient to hold the fabric together and keep the warp cords evenly spaced, which is very important for the quality of the final product. Typically the number of cords forming the warp is 70-120 ends per decimeter while the weft spacing is 7–10 ends per decimeter.

After weaving, the fabric is treated to give good adhesion to rubber, and in the case of thermoplastic fibers it is stretched and heat set to stabilize it and give it the required level of extensibility for tire manufacture and service performance. These two processes are usually carried out in one operation known as hot stretch and dip (HSD). The dip is an aqueous mixture of latex and resin through which the fabric is immersed and then dried to leave the bonding agents on the cord.

Most HSD lines have at least two ovens in which stretch or relaxation can be applied as well as two dipping baths, although today many adhesive systems only require one dipping operation.

For rayon, the HSD process is mainly one of applying the dip, drying, and then heating the dipped cord to a high enough temperature to activate the bonding reaction between the dip layer and the cord. However, with thermoplastic fibers the level of stretching and heat-treatment temperatures are important.

A typical sequence of operations in the HSD line for a thermoplastic fiber such as nylon would be dipping followed by a drying zone at about 170°C. In this zone the fabric is usually held to length or given a small amount of stretch or relaxation. The next zone is a heat stretching zone where a tension, the level depending on the required amount of stretch, is applied to the fabric at a temperature of 200–235°C depending on the fiber type. There is then a relaxation zone where the fabric is allowed to relax a few percent to stabilize the fabric. The relative levels of stretch, relaxation, and temperature are very important since they determine the modulus and thermal properties of the final cord in the tire which in turn determines the handling and other important characteristics of the tire.

After the HSD process the fabric is ready for calendering, which is the operation where the fabric is coated, or topped, with rubber compound. This rubber is usually known as a topping, skim, or bonding compound and of sufficient thickness to insure that in the tire making and molding process the cord material remains covered by it.

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Spinning of ultra-fine fibers

Miyoshi Okamoto , in Advanced Fiber Spinning Technology, 1994

9.2.2 Manufacturing processes for ultra-fine fibers 1−34

9.2.2.1 Continuous-filament type

Ultra-fine fiber of the continuous-filament type is now produced by a variety of methods including:

1

Direct spinning (conventional extrusion).

2

Conjugate spinning (extrusion of polymer components arranged alternately):

(a)

islands-in-a-sea type;

(b)

separation type or splitting type;

(c)

multi-layer type.

Various processes for ultra-fine filament production are illustrated in Fig. 9.2, where the upper part shows the fibers just after extrusion and the lower part shows them after conversion into ultra-fine fibers.

9.2. Spinning of ultra-fine fibers of continuous-filament type. The upper part shows the fibers just after extrusion and the lower part after splitting into ultra-fine fibers.

9.2.2.2 Random (staple) type

Ultra-fine fibers of the random type are produced by:

1

Melt-blowing or jet spinning.

2

Flash-spinning.

3

Polymer-blend spinning.

4

Centrifugal spinning.

5

Fibrillation or violent flexing.

6

Turbulent flow-moulding.

7

Bursting.

8

Other methods.

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Bioprinting of Biomimetic Tissue Models for Disease Modeling and Drug Screening

Min Tang , ... Shaochen Chen , in 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine (Second Edition), 2022

2.2.1.2 Extrusion-Based Bioprinting

Extrusion-based bioprinting systems deposit continuous filaments compared to the individual droplets of inkjet-based bioprinters ( Figure 2.1B). This technology uses a set of automated motors to control the stage or the printer nozzle and a dispensing system to deposit bioink at a precise time and location that is digitally controlled by a computer. Multiple approaches can be used to drive the dispensing system, including pressure-based control, mechanical control, or solenoid control (Murphy & Atala, 2014). In this case, acellular or cell-laden bioinks can be printed onto a receiving substrate in a layer-by-layer fashion.

For microscale nozzle printing, a more versatile selection of bioinks is compatible with this technology. These include cell spheroid suspension, decellularized extracellular matrix (dECM) solutions, and hydrogels with a wider range of viscosity such as poly(ethylene glycol) (PEG)-based hydrogels, gelatin, hyaluronic acid (HA), and alginate (Axpe & Oyen, 2016; Graham et al., 2017; Jia et al., 2016; Ozbolat & Hospodiuk, 2016). Printing of more viscous hydrogels can provide a stronger mechanical support in the final structure. Notably, the flexibility of using more biocompatible inks during extrusion-based printing also make it more suitable for building a variety of tissue models. In addition to the wider choice of printing materials, extrusion-based printing is also advantageous in terms of printing and deposition speed as well as upscaling potential. However, extrusion-based bioprinting has the lowest reported printing speed among the three types of printing approaches, in the range of 10–50   µm/s (Murphy & Atala, 2014; Zhu et al., 2016). Additionally, the resolution of the printed constructs is generally compromised to allow for 3D structures with a larger footprint. The reported minimal printed feature resolution can be 5   µm but it is generally over 100   µm (Murphy & Atala, 2014; Ozbolat & Hospodiuk, 2016; You, Eames, & Chen, 2017). Extrusion-based printing also suffers from shear induced cell death, which is similar to inkjet printing technology (Murphy & Atala, 2014; Ozbolat & Hospodiuk, 2016; You et al., 2017). Nevertheless, tissue models that lack microscale features such as bone, cartilage, and organoids can still be robustly built using extrusion-based bioprinting (Hung et al., 2016; Ozbolat & Hospodiuk, 2016; You et al., 2017). Furthermore, some biomaterials as well as tissues can be readily fabricated by modeling with customized molds that are prepared by extrusion-based 3D-printing technology (Hu et al., 2016; Tao et al., 2017).

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