Green Chemistry Workshop #6: Polymers US – Thai Distance Learning Program March 17, 2010 Professor Kenneth M. Doxsee University of Oregon

The Principles of Green Chemistry 1.Prevention 2.Atom Economy 3.Less Hazardous Synthesis 4.Designing Safer Chemicals 5.Safer Solvents and Auxiliaries 6.Design for Energy Efficiency 7. Renewable Feedstocks 8. Reduce Derivatives 9. Catalysis 10. Design for Degradation 11. Real-time Analysis 12. Inherently Safer Chemistry

Polymer Packing “Peanuts” Premise Packing “peanuts,” made up of various polymers, can be used for simple and safe demonstrations of various chemical properties. Chemical Concepts Polymers; carbohydrates; solubility. Image:

Background Packing “peanuts,” used to protect fragile items during shipping, are available in a variety of compositions. Varying in chemical properties – polarity, solubility, etc. – these different types of packing peanuts can be used to demonstrate these properties in simple and safe ways.

Polystyrene styrenepolystyrene Pink: antistatic Green: recycled content Polystyrene image:

Polyurethanes toluene diisocyanatea polyurethane Alcohols react with isocyanates to form urethanes: Diols react with diisocyanates to form polyurethanes: Polyurethane image:

Starch Starch image: Bffffff/packing_peanuts/eco_packing_peanuts_shipping_supplies_zoom.jpg

Materials and Procedure Add a polystyrene peanut to water, observe. Repeat for a biodegradable, starch-based peanut. Repeat for the two types of peanuts in acetone. Polystyrene “peanuts Biodegradable “peanuts” Acetone (10 – 25 mL) Water (10 – 15 mL) Containers – beakers or jars

Laboratory Safety Accident: An unexpected and undesirable event, especially one resulting in damage or harm. Safety glasses image from:

LABORATORY SESSION Break for ….

Results “Like Dissolves Like” Lotus flower image from: Lotus with droplet image from: water%20droplet%20on%20lotus%20leaf%20NANOSURFACES.jpg Close-up image from:

Green Relevance Green Concepts Consider Green Principles – #1 (prevent waste) – #3 (less hazardous reagents) – #4 (safer chemicals) – #7 (renewable feedstocks) – #10 (design for degradation) Trash image:

Carbohydrates Premise Simple household materials can be used to explore concepts of polymer chemistry. Chemical Concepts Properties of covalent compounds; carbohydrates; food chemistry; polymers; acid/base; intermolecular interactions. Sugar image:

Background Pectin is the major binding component of the cell walls of plants and fruits. It is chemically a polysaccharide, consisting of a linear chain of linked molecules of galacturonic acid. Aqueous solutions of pectin become gelatinous when treated with carbohydrates (e.g., sucrose) under suitable conditions of concentration and pH. Image:

Chemistry Image:

Chemistry Gelation is not a chemical reaction. Enhanced strand-strand interaction caused by high sugar concentration (reduced water activity). Moderate acidity also required – too many carboxylates can prevent chain aggregation. Ca 2+ can induce gelation in ‘low methoxyl’ pectin. Role of Sucrose in Pectin Gelation: Static and Dynamic Light Scattering Experiments Macromolecules, 2002, 35 (21), pp 8147–8151 sucrose pectin

pH Adjustment Apple juice image: Polymer swelling schematic: fruit juice (apple or white grape) malic acid

Materials & Procedure Place water, pectin, and juice in 600 mL beaker. Stir and heat until just about to boil. Add sugar, heat to hard boil with constant stirring. After 1 minute, remove from heat. Allow to cool, removing any foam with a spoon.

Laboratory Safety Accident: An unexpected and undesirable event, especially one resulting in damage or harm. Image from: Hot image from:

LABORATORY SESSION Break for ….

Results

Other Approaches Polystyrene, other polymers - crosslinking. Styrene, divinylbenzene. Solvent-swollen polymers (e.g., rubber o-ring in THF)  Hazardous reagents.  Reagents derived from petroleum - nonrenewable resource.  Disposal of hazardous waste. Image from:

Green Relevance Green Concepts Consider Green Principles – #3 (prevent waste) – #4 (safer chemicals) – #5 (safer solvents) – #7 (renewable feedstocks) – #10 (design for degradation) Image from:

Analysis of Charge with Polymer Gels Premise The “superabsorbent” polymer used in disposable baby diapers can be used as an ion exchange resin. Chemical Concepts Properties of ionic and covalent compounds; cation analysis; solubility; polymers. Disposable diaper image:

Background Disposable baby diapers contain a small amount of a polymer that is able to absorb many times its own weight in water. Image:

Chemistry More highly-charged cations – e.g., Ca 2+ - interact with the carboxyl groups, causing the gel to collapse. Cations are attracted to the charged polymer chain, while anions are not.

Procedure Carefully take apart a clean disposable baby diaper, transferring the cotton (fluffy white) portion to a plastic bag. In the bag, tear apart the cotton, shaking to separate the superabsorbent polymer grains. Remove as much of the cotton as possible. Bag image:

Procedure Hydrate about 0.5 g of polymer. In each of six plastic cups, place water and a sample of a dye – e.g., 1 drop of food coloring (red, blue, green), methylene blue, malachite green, crystal violet. To each cup add a portion of the polymer gel. Let stand for 15 minutes. While waiting, use a hot paperclip to melt small holes into the bottoms of six plastic cups. Transfer the samples to these plastic cups, allowing liquid to drain out through the holes. Rinse with excess water, allowing to drain. Plastic cups image:

Laboratory Safety Accident: An unexpected and undesirable event, especially one resulting in damage or harm. Safety glasses image from:

LABORATORY SESSION Break for ….

Results Other things that can be explored (see packet): – Effect of salts on gel. – Effect of acids on gel. – Other dyes or colored ions. – Your students’ ideas.

Green Concepts Consider Green Principles – #1 (prevent waste) – #4 (safer chemicals) – #5 (safer solvents) – #10 (design for degradation) – #11 (real-time analysis) – #12 (inherently safer chemistry) Green Relevance Ion exchange image from:

Questions and Discussion Image from:

สวัสดีครับ ขอบคุณครับ