CH 112 Special Assignment #4 Chemistry to Dye for: Part B PRE-LAB ASSIGNMENT: Make sure that you read this handout and bring the essentials to lab with you. Review ionic compounds (pp 34-38), polar covalent compounds (pp.43-46), and dipole forces/hydrogen bonding (pp. 91-93) in Adventures in Chemistry. Here are the pre-lab questions for this week. 1. Redraw the structure of methyl orange (Figure 3), and identify the groups in the dye that will bind to ionic and polar sites in a fabric. 2. Complete the following “If/then” hypothesis to explain how the structure of a fabric will influence the relative color intensity produced by methyl orange. “If a fabric contains more ionic and polar groups in its structure, then the intensity of the dye color due to methyl orange should (increase/decrease), because _________.” 3. Using this hypothesis, predict the relative color intensity that will be produced by methyl orange on the six fibers of the multifiber test fabric. Rank the fabrics from 1 = lightest color to 6 = darkest color. Wool Acrylic Polyester Nylon Cotton Acetate Figure 1. Composition of the multifiber test fabric. INTRODUCTION: Our work for Dyenomite continues this week with an investigation of several dyes. They would like to know the best fabric(s) to use with their line of dyes. They are also interested in developing a new line of dyes from natural sources. 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, Chemistry 112; Spring 2010; Experiment 4B were so rare that only emperors and kings could afford to wear purple—hence the term “royal purple.” The modern dye industry started about 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. 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 structures 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 2. Cotton and wool are natural fibers, while acrylic, polyester, and nylon are synthetic fibers made from petrochemicals. Acetate, also called cellulose acetate, is prepared by chemical modification of natural cellulose. All fabrics, both natural and synthetic, are polymers (see Chapter 18 in Adventures in Chemistry). Polymers are high molecular weight, long-chain molecules made up of multiple repeating units of small molecules. The structures of the repeating units of these fabrics are enclosed in brackets in Figure 2. The number of repeating units (n) varies depending on the fiber and how it is prepared. A brief description of the chemical nature of each of these fabrics follows. • Wool is an animal protein— a naturally occurring polymer made up of amino acid repeating units. Many of the amino acid units have acidic or basic groups that are charged. The presence of many charged groups in the structure of wool provides excellent binding sites for dye molecules, most of which are also charged. • Cotton is an animal polysaccharide composed of glucose units linked in a very rigid structure. The presence of three polar hydroxyl (-OH) groups per glucose repeating unit provides multiple sites for hydrogen bonding to ionic and polar groups in dye molecules. • Acetate is cellulose in which some of the –OH groups have been replaced by acetate groups (-OCOCH3). The presence of acetate side chains makes acetate softer and easier to work with than cotton but also provides fewer binding sites for dye molecules. • Nylon was the first completely synthetic fiber. It is a polyamide, made up of hydrocarbon repeating units joined together by highly polar amide (-CONH-) functional groups, which provide sites for hydrogen bonding to dye molecules. • Polyester is a family of synthetic polymers in which the subunits are joined together by ester (-COO-) functional groups. Ester linkages tend to be less polar than those described above. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate (PET), often known by its trade name, Dacron. • Acrylic, or poly(acrylonitrile), is also a synthetic fiber. Each repeating unit contains one nitrile (-C≡N) functional group, which also tends to be less polar than many of those described above. 2 Chemistry 112; Spring 2010; Experiment 4B Dyes are classified based on the structure of the dye and the way in which the dye is applied to the fabric. • Direct dyes are charged, water-soluble organic compounds that bind to ionic and polar sites on fabric molecules. Direct dye molecules contain both positively and negatively charged groups and are easily absorbed by fabrics in aqueous solution. • Substantive dyes interact with fabrics primarily via hydrogen bonding between electron-donating nitrogen atoms (-N:) in the dye and polar –OH or –CONH- groups in the fabric. • The ability of a dye to bond to a fabric may be improved by using an additive called a mordant. Mordant dyes are used in combination with salts of metal ions, typically aluminum, chromium, iron, and tin. The metal ions adhere to fabric and server as points of attachment for the dye molecules. HOH C OH HOH 2C O HO OH 2 O RO O O O O HO HO OH O OR O HOH 2C n HOH 2C n Cotton (cellulose) Cel lulose A cetate (R = CO CH3) O N N CH 2 CH2 O C C CH CH O C C H 2 H 2 n Acry lic (Orion ) O n Polyester (D acron) O H 2 H 2 H 2 H 2 H 2 H C C C C C C N C C C N C C C H 2 H 2 H H 2 H2 H 2 O n Nylon-6,6 CH 2CH2CO2 O CH 2OH O CH 3 O H H H CH N C CH N C CH N C H H H3N C C N C C N C C O H H H 2 O (CH 2)4NH 3 O CH2 O Wool (Protein) n S Figure 2. Chemical structuresF iofgu fabricre 1. C hmolecules.emical Stru ctures of Fabric Molecules 3 Chemistry 112; Spring 2010; Experiment 4B The goal of this experiment is to investigate the interaction of dyes with different fabrics. The dyes include methyl orange, malachite green, and crystal violet (direct dyes); congo red (a substantive dye); and alizarin (a mordant dye). See Figure 3 below for the structures of the dye molecules. You will also investigate some other dyes in a “raw” form directly from the source. The dyes will be tested on a multifiber test fabric that contains strips of six different fibers— wool, acrylic, polyester, nylon, cotton, and acetate (Figure 1). N(CH3)2 CH3 H O3S N N N CH3 Meth yl Orange O C X OH O O H N(CH3)2 Alizarin Malach ite Green (X = H) Crystal Violet [X = N(CH 3) 2] NH2 NH2 N N N N S O3Na Congo R ed SO3 Na Figure 3. Chemical structuresFigure of2. Cdyehem icmolecules.al Structures of Dye Molecules LEARNING GOALS: Be able to: • Investigate the interaction of dyes with different fabrics. • Identify ionic and polar groups in dyes and fabrics. • Identify the different types of bonding interactions between dyes and fabrics. 4 Chemistry 112; Spring 2010; Experiment 4B PROCEDURE: Part 1. Preparation of multifiber test strip 1. Cut the multifiber test fabric crosswise to obtain six 2-cm multifiber strips. 2. Each test strip should contain all six fabric samples. Notice that the wool fabric is cream-colored, not white. Use a pencil to mark the wool ends with a “W”. Label the strips with your and your partner’s initials. 3. Obtain a 12-inch square piece of aluminum foil. Using a permanent marker, write the names of the dyes to be tested (see dye baths listed in the chemical section) in separate locations on the aluminum foil. Label a sixth section “Alizarin + Alum” and another section “Raw dye.” All of the dyes are strong stains. Avoid getting any dye solution on your skin, clothes, or books. To avoid contamination, rinse tongs or forceps with water before inserting them into a new dye bath. Part 2. Direct Dyes (Crystal violet, malachite green, methyl orange) 1. Fold a multifiber test strip in half. 2. Using forceps or tongs, immerse the test strip into the crystal violet dye bath. CAUTION: The dye baths are very hot. Exercise care to avoid scalding or skin burns. 3. After ~5 minutes, remove the dyed test strip from the bath using forceps. Hold the fabric above the dye bath briefly to allow excess dye solution to drain back into the dye bath. 4. Pat the test strip with a paper towel and rinse the dyed test strip under running cold water from the faucet. Continue rinsing the test strip until all of the excess dye has been removed and the rinse water is colorless. 5. Blot the test strip with paper towels until most of the water has been absorbed. Place the rinsed, blotted test strip on the appropriately labeled section of the aluminum foil and allow it to air dry. 6. When the fabric is dry, record the color of each fabric type. 7. Repeat steps 1-6 with new test strips in the malachite green and methyl orange dye baths.