Polymers In Textile

Fiber Production In The World. 

The Vast Majority Of Textile Fibers Both Natural And Synthetic Are Made Of Polymers 

This gives textile fibers some very unique and valuable properties. Polymers are large molecules that possess a chain like character. These chains consist of repeating groups of atoms that are covalently bonded to one another. The word polymer comes from the Greek in which poly means many and meros means part. Polyester is a polymer with a relatively simple repeat unit – your DNA is an example of a polymer with a very complex repeat unit. An exception: glass 

Synthetic Polymerization 

We take a collection of mers and take them from an unreactive to reactive state often by use of heat, pressure and a catalyst. Via this technique we can take ethylene gas and turn it into polyethylene plastic for example. As we change the elements composing the mer molecule so we change the attributes of the final fiber extruded. 

The Incorporation Of The Methyl Side Group Gives Polypropylene Some Important Differences From Polyethylene 

Polypropylene has a higher melting point, Polypropylene is more brittle than polyethylene, 9 g/d tenacity and 18% elongation at break for polypropylene vs. 3 g/d tenacity and 40% elongation at break for conventional polyethylene. Polypropylene can be made in 6 different isomers only one of which – head to tail isotactic is used in commerce to form fibers. Polyethylene is tougher than polypropylene rather like some nylons are tougher than some polyesters. 

Polyethylene And Polypropylene Share Some Things In Common 

Neither of these fiber types dye well as they are bereft of dye sites they are both in the olefin generic class. Both carry the same generic name: olefin. Both have low specific gravities as can be determined by AATCC Test Method 20 - of around 0.9 

Having Some Understanding Of Textile Fiber Polymers 

Provides a solid foundation for understanding how fibers behave. How they dye. How they burn and react to heat. How they shrink. How strong they are. How colorfast they are. 

Wallace Carothers And The Invention Of Nylon 

Wallace Carothers is credited with the invention of sythetic rubber and nylon around 1933 at Dupont. Fiber went commercial around 1938 and is still used extensively today. Dupont recouped all investment in nylon 6,6 within 30 days of plant startup as there had been nothing like it before. 

Fiber Properties And Polymer Chain Entanglement 

Due to the way in which polymer chains group themselves together in a fiber, fibers are endowed with unique characteristics in-between those of brittle plastics and rubber elastics. In a fiber we have a two phase system: Crystals contribute strength and amorphous regions give stretch. All other things being equal as we increase polymer chain length so we increase fiber strength. 

Comparison Of Conventional And Ultra High Molecular Weight Polyethylene 

Spectra® Ultra High Molecular Weight Polyethylene: 

Typical polymer repeat length in the tens of thousands. 3% elongation at break. Tenacity 38 g/denier. 

Conventional Polyethylene: 

Typical polymer repeat length in the thousands. 40 % elongation at break. Tenacity 3 g/denier. 

Pendant Groups, Side Groups or Functional Groups 

By adding various atoms or molecules along the polymer backbone, be it all carbon or otherwise we can radically effect fiber properties. We can add dye sites to impart specific dye affinity for example cationic and dyeable polyester. We can add flame resistance as seen in Treviera CS and similar fibers. If we take a carbon carbon backbone like we have in the olefins and add a particular pendant nitrogen containing group – what fiber do we end up with? 

Thermoplasticity 

The softening and melting behavior of textile fibers is a direct result of the way in which the polymer chains are interconnected. If the polymerchains are free to move when heated then they will soften and melt. If applied heat breaks up the chains before they are free to move then the fiber merely chars when heated rather than melting. In general those fibers which soften and melt can be heatset . This process in an extremely valuable finishing technique that can impart very high dimensional stability to fabrics so treated. 

What To Think About In Addition To Force Elongation Curves 

What is the fiber's ability to recover from repeated cyclic stress? What is the fiber's stress strain curve in solvents and in water? What is the relationship between toughness and tensile strength with respect to the force elongation curve? Our units of toughness (the area under the force elongation curve): joules or energy to break. 

The Relationship Between Fiber Bending Stiffness And Diameter 

Bending stiffness is proportional to diameter to the fourth power. So if we increase the diameter of a fiber threefold the bending stiffness increases 34 = 81 times. This is the reason why multi-strand copper wire is so much more flexible than single strand wire of the same thickness. 

Explaining The Behavior Of Microdenier Fibers Using The Bending Stiffness And Specific Area Rules

Microdenier fibers produce yarns and fabrics that are very soft due to the reduced bending stiffness explained by our bending stiffness diameter rule. Microdenier fibers require more dye per unit weight than do thicker fibers to achieve the same depth of shade, a phenomenon explained by the large additional surface area that must be dyed to a given color depth. 

Specialty Synthetic Fibers 

Specialty synthetic fibers are rather like specialty animal fibers. There are quite a few of them but not a huge amount of poundage is produced in any of them. They serve some very important end uses such as body armor. There are many of these, with special characteristics such as anti bacterial performance, high or low wicking, UV resistance flame resistance and high strength. 

Summary Of Generic Fiber To Polymer Type Relationships 

Generic Fiber Type »»»» Typical Polymeric Make Up 

Cotton »»»» Cellulose, 

Polyester »»»» Polyethyleneterephthalate, 

Rayon »»»» Cellulose, 

Nylon »»»» Polyamide,

Acrylic »»»» Polyacrylonitrile, 

Acetate »»»» Cellulose diacetate, 

Olefin »»»» Polyethylene or Polypropylene, 

Ramie »»»» Cellulose, 

Linen »»»» Cellulose, 

Wool »»»» Alpha Keratin, 

Cashmere »»»» Alpha Keratin, 

Silk »»»» Fibroin, 

There Are Three Main Systems For Extruding Synthetic Fibers 

Dry Spinning, Wet Spinning, Melt Spinning, The extrusion system can effect characteristics like fiber cross section.