3 March 2013
Given the opportunity to conduct a research paper for design 40, our group chose fashion design evening/formal gowns as our topic. Not knowing where to start from, our group went to the library hoping to find information on contemporary evening dresses. As we continued our research we noticed that the information we acquired were too broad and vague. Therefore we narrowed our topic down to evening gowns that were designed by one exclusive designer. We decided to broadly research on Chanel and Versace Donatella’s recent haute courtre collection (Autumn/Winter collection 2012).
But again, we encountered two problems researching Coco Chanel and Versace Donatella. Both designers used a minimal amount of machinery and the clothes were mostly custom sewed. Also the clothes that were presented on the courtre collection were all exclusively custom and handmade costing from nineteen thousand to one hundred twenty five thousand dollars to create.
Moreover we attempted to find minimal information on the process of assembling the clothes and which raw materials were in use. With the consent from the professor, our group decided to completely change our research topic to spandex.
Spandex is a thermoplastic polyurethane elastomeric fiber made from a long polyglycol chainknown for its elastomeric behavior. Originally the research of spandex fibers emerged during 1930s and by 1940s IG company invented Perlon U but the fiber was non-elastic (not stretchable). Spandex or elastic polyurethane fiber was invented in 1959 by du Pont company as an alternative for rubber. It has elastomeric behavior far stronger than rubber stretching over five hundred percent of its length. Due to its flexibility and lightness, the use of spandex fibers spread immediately. The fibers are thin as fifteen to thirty denier, therefore it’s possible to create rubber threads ten times thinner than the ones created from latex.
According to the statistics from 2010, approximately eighty percent of clothing worn in the United States is produced out of spandex. Spandex fibers are applied to athletic/exercise wear and garments. Due to its elastic and light behavior, spandex fibers have become the main synthetic fiber used in the majority of swimsuits we wear today. Since spandex fiber doesn’t lose its characteristics even with mixed fiber, it is often mixed with both natural and synthetic fibers such as linen, cotton, wool, and polyester. Spandex fiber itself is a little comfortable, but a combination of the spandex fiber and other fibers result in lighter, body fitting, and comfortable swimwear.
Spandex is made of long chained polymers (substance created by natural/manmade macromolecules and is compiled of over fifty monomers) called polyurethane. The fibers are comprised of numerous polymer strands. These chains of polymers are composed of two repeated copolymers of soft and hard segments. The hard segments are typically urethanes that bond to urethane molecules in other chemical chains to form elastomeric fibers. On the other hand, the soft segments have a random molecule structure where the substance remains soft, rubbery, and amorphous. These soft segments allow the whole chain to stretch resulting spandex to have that elastomeric feature. But in order to produce these elastomeric features, force is applied which breaks the bonds between the hard segments allowing the soft segments to stretch out resulting in making the fiber longer in length.
Spandex fibers are composed from various raw materials. Spandex fiber is created with prepolymers made through a chemical reaction from polyol (macroglycol) and isocyanate. Prepolymers play the role of the back bone to the elastic fiber providing urethane linkage. Most of the urethane linkage found inside polyurethanes is from macroglycol. Prepolymer is composed of three raw materials flexible macroglycol, diisocyanate, and chain extenders.
Macroglycol is a molecule with relatively heavier weight (shorter soft segments). Macroglycol permits the formation of the long and stretchy characteristic of spandex fibers. Some macroglycol that can be used are poly tetramethyleneadiptate glycol, poly caprolactone glycol, poly hexamethylenecarbonate glycol, poly oxytetramethylene glycol, poly oxypropylene glycol, polyether, polyesterpolyestercarboxylate, and polycarbonate.The two substances that are usually used to synthesize polyurethanes are polyester and poly carbonates. Polyester and polycarbonate provide more stability against light, and more resistance towards thermal and hydrolysis degradation.
The next molecules used to create spandex fiber are polymeric diisocyanates (the longer hard segments). Diisocyanate is a term used to describe when two isocyanates are combined together. Diisocyanate substances are smaller molecular weight, but it plays three roles in building the chains of spandex fiber. First it acts as the coupling agent for the macroglycol component to produce the soft segments. Then it acts a coupling agent for the chain extender component to produce hard segments. Lastly, it creates the polyurethane chain by bonding with hard and soft segments. Recommended diisocyanate molecules for synthesizing are ones with cyclic and symmetrical nuclei. These molecules produce the urethane and hard segments reacting with different chemical groups resulting in enhancing the thermoplastic polyurethane elastomer chain.
The last molecules used are the chain extenders. Chain extenders are bi-functional compounds that influence the ends of the polyurethanes. There are two types of chain extenders, bi-functional compound consist of less molecular compounds (usually two or less) enabling the chain to stretch and expand, and high functional compound (more than two) which can cross link a bond to another. Bi-functional chain extenders are used in creation of polyurethanes elastomers. The chain extenders are a highly reactive material. Chain extenders react with macroglycol and form hydroxyl groups on both ends while forming isocyanate groups on both ends of polymeric di-isocyanate. Some of the chain extenders useful for creation of thermoplastic polyurethane elastomer are 1,4-butanediol, 1,4-cyclohexanedimethanol, p-xylylene glycol, aliphatic glycol, aliphatic ether-glycol, and 1,4-bis(2-hydroxyethoxy) benzene. The properties of polyurethanes elastomers can be affected depending on the ratio of the soft and hard segments and the type of chain extenders used so it’s important to use suitable substances and amounts.
Another material used to comprise spandex fiber is stabilizers such as antioxidants. Spandex fibers are vulnerable to damage from heat, choline, and exposure to light. Antioxidants such as monomeric/polymeric hindered phenols and hydroxybenzotriazoles are added to protect the fiber from these problems.
Spandex threads are produced in four different ways: melt extrusion, reaction spinning, solution dry spinning, and solution wet spinning. Spinning is a method used to twist synthetic fibers together to form yarn. The first step for every method listed above is to chemically react monomers to create a pre-polymer. This can be done by mixing the macroglycol and di-isocyanate monomer.
I’ll be introducing the two main spinning methods listed above. The first method is wet spinning, the oldest and most earth friendly process to extrude synthetic fibers. First of all, the polymer getting spun must be transformed to a fluid form. This can be done by dissolving the substance in a solvent to form thermoplastic or soluble derivatives. The polymer solution is then poured inside a tank moving to the spinning pump, filtered then into the spinneret. The spinneret is a machine that looks like a bathroom shower head consisting of numerous holes where the polymer solutions are pushed inside. The spinneret is placed inside a spin bath consisting of dilute solvent with water mixture. The polymer solution squeezes out from the spinneret in the form of filaments. Once out of the spin bath, the polymers are cooled down and converted to a rubbery state then to a solidified state.
After the coagulation (spin bath), the polymer solution is stretched. As it passes through, the solution is heated from solvent gas and nitrogen. This process causes a chemical reaction so the liquid polymers form solid strands. A particular amount of the solid strands are gathered together to form a desired thickness with a compressed air device. Next the fibers are applied with lubricant/fiber finish. This may be polydimethyl-siloxane or magnesium stearate. After the finish is applied, the fibers are placed on top of heated drum rolls to be completely dried. The finished fiber is wounded around a spindle and packaged to be shipped to customers.
The next method of manufacturing spandex fiber is by dry spinning. Nearly ninety percent of spandex fibers are produced through dry spinning. The polymer solutions are squeezed out into a bath filled with coagulants and through the spinneret. Once the polymer solutions are coagulated, they are passed down to a hot gaseous atmosphere inside a spinning tube where all the solvents are taken away. Now the filaments/fabrics are wounded up together to form yarn.
The interaction between the mixtures of the two prepolymers creates spandex fibers. During this process, the hydroxyl groups inside the macroglycol react with the isocyanate causing step growth/addition polymerization. In addition polymerization is the chemical reaction that occurs to form long chain polymers without by products. During the addition polymerization process, the high molecular weight diol is transformed into a prepolymer which contains an isocyanate group on each end. Depending on the ratio of component materials (macroglycol and dissocyanate) fibers with different characteristics are formed so the ratios are measured precisely.
The next process is the chain extension reaction. During this process, the prepolymer produced from the previous step is reacted with equal amounts of a chain propagation agent such asdiamine (typically hydrazine and ethylene) or other bi-functional active hydrogen compound like diol. Polyurethanes that were formed in this process now create hard segments resulting in creation of elastic fibers.
The finished product of spandex fiber is white so usually color dyes are added to increase visual appearance. The initial step for dyeing spandex fiber is by preparing a dye bath with organic acid (formic and acetic acid) and acid dye. The dye bath is heated from 3 degrees Fahrenheit up to two hundred fifty degrees Fahrenheit until the fabric is completely dyed and cooled afterward. In general there are two types of dyes, cold water fiber reactive dyes such as Procion MX and warm water fiber reactive dyes such as Rit all-purpose dyes. Different dyeing methods are used for spandex fibers interwoven with other synthetic/manmade fibers.
During the spinning process (preparation and application) of polyurethane fibers, it produces waste. Recycledpolytetrahydrofuran can be result from glycolysis waste through the spinning process. Studies have shown that the purity of recycled polytetrahydrofuran increases with the increase of the amount of catalyst and glycolysis contained inside the glycolysis.
There are two main methods of recycling polyurethane wastes which are mechanical recycling and chemical recycling. Mechanical recycling is where polyurethane wastes are reused by its natural form (polymer form). On the other hand, chemical recycling of polyurethane substances are reformed back to their chemical components.
Our research topic shifted from evening gowns to contemporary evening gown designs, and then finally to spandex. Through this research on spandex fibers, I found more information on the chemical and molecular structures of the spandex fiber than its physical structures. Studies have shown that depending on the prepolymers mixed during the initial steps of creating polyurethanes, fibers with better stretching characteristics are developed. Research and improvements on spandex fibers take place on a daily basis which make spandex fiber one of the most common synthetic fibers used today.
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