The range of applications of plastics in the last 40 years has been broadened by the development of new polymers and by customizing polymers with property-altering or property-emhancing additives. The flammability of plastics is modified by the additives called FR agents. Polymers can be made more flexible by the addition of plasticizers.

FR agents are used to make materials "fire retardant," "fire resistant," flame retandant," and/or "flame resistant," but not fireproof. They can increase the resistance of a material to fire or slow the burning rate, but they cannot entirely prevent the material from burning if conditions are sever enough. Some FR agents increase resistance to fire by decreasing the rate of decomposition of the burning material. This results in the formation of an insulating "char" layer that protects the rest of the material. Other FR agents slow the oxidation process by capturing free radicals. Still others release water of hydration, which carries away heat. The first part of this experiment involves testing the flammability of a plastic with and without a FR agent, then the testing of some other common plastics, which may or may not contain FR agents.

A plastic film may also contain added plasticizer to modify the properties of the film. Plasticizers alter properties of a polymer by altering the structure of the polymer. A plasticizer can decrease the rigidity of the polymer and increase the toughness. The second part of this experiment involves testing changes in the tensile properties of a plastic film due to the presence of an added plasticizer. A chemical analysis is the best proof for the presence of a plasticizer; however, a plasticizer is probably present in a material if, after gentle heating (less than 130 ^oC) the following occur:

• The material loses mass
• After mass is lost, the material becomes less flexible and more rigid
• After mass is lost, the breaking characteristic of the material changes from ductile (gradual break with much stretching) to catastrophic (sudden break without warning)
• The material does not appear to have degraded (extreme discoloration or blistering)

Procedure:

Part 1. Effects of FR Agents:

Cut four pieces of aluminum foil, each about 12 cm x 15 cm. Place one of the pieces of foil on a hot plate and turn the plate on to medium, making adjustments later as needed. Put one FR-treated polystyrene pellet on the foil and occasionally probe the pellet with a stirring rood until it is softened on the top. Then add about 50 additional pellets on the foil and cover with a second piece of the foil. Carefully roll the "pellet sandwich" with a rolling pin. This should cause the softened pellets to fuse into a single mosaic sheet of polystyrene.

Use a pair of tongs to pick up the "sandwich" by a corner, cool it under running water, peel open the foil, and remove the sample.

Repeat the procedure with the untreated pellets.

Break off a piece of each polystyrene sample and prepare small pieces about the size of a postage stamp of the other plastics to be burned. Set up a Bunsen burner under the hood. Hold the sample of untreated polystyrene with the tongs and over the flame of the burner. Remove from the flame. Note observations while in and out of the flame.

Repeat with the untreated polystyrene and the other samples.

Part 2. Effect of Plasticizers:

A. Preheat the oven to a stable temperature between 100 ^oC and 120 ^oC. Determine the total mass of several strips of Handi-Wrap. Use enough pieces to register on the three-place Fisher balance. Place the strips in the oven, being careful not to stack or cover the strips. Determine the mass of the strips again each hour for the first 6 to 8 hours and then twice daily for at least 3 days.

Repeat the procedure with Reynolds plastic wrap.

B. Prepare baked and unbaked strips of each film by placing two marks, 5 cm apart, on each strip. Set up the strips as in the tensile strength test in Experiment 15. Carefully suspend a 50 gram mass from a strip and measure the distance between the marks. Increase the load in 50 gram increments, measuring the distance between the marks at each increase in the load. Note the appearance of the strip at break and the nature of the break.

Test each kind of film a two more times, being careful to cut identical sizes for all three tests.

Analysis:

Part A. Plot graphs of "percent loss of original mass" versus time for each film tested. Calculate the percent added plasticizer of the mass of the film for those films you determined to contain plasticizer.

Part B. Plot stress (load) versus strain (stretch) graphs for each film tested. (stress = force/area; strain = change in length/length). Carry out a t test to determine whether the breaking loads of different films are significantly different.

Discussion:

Summarize the differences in flammability characteristics of plastics with and without FR agents. Make a list of common plastics with FR agents and those without FR agents.

Dinonly adipate is the most common plasticizer for flexible PVC wraps. Write out the structural formula for dinonyl adipate. What type of organic compound is dinonyl adipate?

Explain in detail the reasons for the different tensile properties you observed for different films.