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Unformatted text preview: Chemistry The Chemistry of Dyes Preparation: Each group wil turn in only ONE lab report, with one data sheet per group. You will need to write up an Objective, the Safety Precautions, Materials, and Procedure, as well as answer the Pre-lab and Post-lab questions. You will also need to prepare a data on a separate page. You will attach fabric samples to this page. You must read the procedure carefully to know how many columns and rows your data table must have. Introduction: The art of dyeing dates back thousands of years to the use of natural dyes extracted from plants and animals. Some dyes, such as Tyrian purple obtained from shellfish, were so rare that only emperors and kings could afford to wear purple – hence the term “royal purple”. The modern dye industry started 150 years ago with the discovery of “mauve”, the first synthetic dye. Since then, thousands of dyes have been developed to work with all types of fabrics. Concepts: Chemical bonding, ionic bonding, polar vs. nonpolar bonds, hydrogen bonding Background: Dyes are organic compounds that can be used to impart bright, permanent colors to fabrics. The affinity of a dye for a fabric depends on the chemical structure of the dye and fabric molecules and on the interactions between them. Chemical bonding thus plays an important role in how and why dyes work. The chemical structures of six common fabrics – wool, acrylic, polyester, nylon, cotton, and acetate – are shown in Figure 1. Cotton and wool are natural fibers obtained from plants and animals, while acrylic, polyester, and nylon are synthetic fibers make from petrochemicals. Acetate, also called cellulose acetate, is prepared by chemical modification of natural cellulose. All of the fabrics, whether natural or synthetic, are polymers. These are high molecular weight, long chain molecules made up of multiple repeating units of small molecules. The structures of the repeating units are enclosed in brackets in Figure 1. The number of repeating units (n) varies depending on the fiber and how it is prepared....
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- Spring '11