It’s A Wrap

“Best Buy” Science Experiments Dr. Marialice Curran, EDUC 555/Fall 2012

Which Plastic Wrap is the“Best Buy”?

PURPOSE:

The objective of this investigation is to compare, through scientific testing,which of three plastic wraps performs best overall.

RATIONALE:

My 12-year old daughter and I frequently cook and bake together. In the process, we are always in need of plastic wrap to keep our food products fresh. As I don’t always buy the same brand of plastic wrap, we have used several products and discovered that different brands of plastic wrap perform differently under certain conditions and circumstances. For example, some plastic wraps seem to adhere well to certain surfaces; some are stronger and can hold the weight of other food items stacked directly on top of them; and finally, some seem to form a better seal and keep food fresher. The following experiments were designed to investigate which of three different brands of plastic wrap performed “best” in three specific tests. All three brands were purchased from the Stop & Shop in Enfield, CT.

My daughter and I investigated the following:

  • Saran Wrap – best-selling brand, also most expensive of the three
  • Glad Wrap– well-known brand; second most expensive
  • Stop & Shop – “house brand”, least expensive

GENERAL BACKGROUND ON PLASTIC WRAP:

According to plastic wrap is a form of food packaging consisting of a thin film of flexible, transparent polymer that clings to itself and to food containers to form a tight seal. The plastic keeps food fresh by protecting it from air and by preventing either the loss, or the absorption of moisture in foods.

In scientific terms, plastics are artificial polymers made by humans, not nature. They consist of gigantic molecules formed by combining thousands of small molecules (monomers) of the same kind into a long chain. This process is called polymerization. (Natural polymers also exist and include silk, rubber, and cotton.)

Plastic wrap is made when granules of plastic are heated and forced through a die to form a tube of stretchable plastic in a process known as extrusion. Air is blown onto the moving plastic to stretch the plastic to the desired thinness and metal rollers roll the plastic into a film.

Concerns about using plastic wrap to protect food are that it is difficult to recycle and is seldom reused, and that certain plasticizers used as additives can be harmful, especially the wrap is used to heat food in the microwave.

BACKGROUND ON 3 SPECIFIC PRODUCTS TO BE TESTED:

“Consumer plastic wraps are made from three major categoriesof plastics: polyethylene (PE), polyvinylidene (PVDC) and polyvinyl chloride (PVC).” ( The three products we chose to test represent each of these categories:

Saran Wrap –Originally made of Polyvinyliden chloride (PVDC)which was discovered at Dow Chemical in Michigan in 1933 by mistake in the process of developing a dry cleaning product. It was initially developed into a spray to protect US fighter planes and automobile upholstery from the elements. In 1942 Dow’s PVDC was woven into ventilated mesh for use in soldiers’ combat boots. It was formed into a thin clingy film and introduced as Saran (the combination of the first names - Sarah and Anne - of the principal investigator’s wife and daughter) in 1949. It quickly became popular for its ability to preserve the flavor and aroma of food items stored in the refrigerator. Principal advantages were: low permeability to water vapor, flavor and aroma molecules as compared with other plastics; slowed food spoilage and locked in flavor. PVDC is not naturally flexible and must have plasticizers added or it is hard and rigid. Interestingly, today’s Saran Wrap is no longer composed of PVDC, but is made of low density polyethylene (LDPE) which is cheaper, easier to manufacture and recycle, and safer, due to fewer plasticizer additives. LDPE is impermeable but has far less cling than before.

Glad Wrap –Made from polyethylene (PE) which is naturally flexible, with a stickifier added for extra hold. It was invented in Australia by a Union Carbide Corporation’s chief research chemist there and introduced to the US market in 1963 as a competing food wrap. It contains no plasticizers. It is considered impermeable but not very clingy.

Stop & Shop Plastic Wrap – Made of a “food-safe version” of PVC (closer to PVDC) a blending of special plastic resins with plasticizers to provide softness and cling to its naturally rigid nature.It is similar to Stretch-tite Premium Plastic Food Wrap which is used by many restaurants and professional food producers. The original formula of PVC was produced before World War II as a second-rate substitute for rubber, but not utilized as a protective film until the 1950’s.It was prized for its high clingability, but plasticizers and chlorine in these wraps held a risk of food contamination, so manufacturers came up with safer substitutes.According to ( it doesn’t keep food quite as fresh as Glad Cling Wrap, but testers named it tops in toughnessand clinginess. Some consumers are still wary that any form of PVC may not be as safe as other materials, but like that it is heavy duty and clings well.

VARIABLES/PRODUCT CHARACTERISTICS TO TEST:

Strength: How much weight/pressure can plastic wrap withstand before tearing?

Cling/Adhesion: How well does plastic wrap adhere to 3 materials: glass, plastic and paper

Sealing Ability: How well does plastic wrap prevent moisture evaporation, keepingfood fresh?

Although there are numerous other brands of plastic film readily available in grocery stores, we selected these three products because we wanted to test the two most popular, heavily advertised, and competing brands against each other, and against a cheaper, less known, generic brand. By gauging performance in the three qualities that define the purpose of plastic wrap (strength, stickiness, and sealing); we hope to identify the “Best Buy” for consumers.Price is an interesting factor, but not one of our test considerations.

HYPOTHESIS:

Prior to beginning experimentation, we did conduct some online research on the threemajor categories of plastics -- polyethylene (PE); polyvinylidene (PVDC, now LDPE); and polyvinyl chloride (revised PVC). According to studies byCook’s Country, the major difference between PVC/PVDC and LDPE is that the former (Stop & Shop) clings better. LDPE (Saran) is less permeable, which means that food should stay fresher with less odor transference, but doesn’t cling as well, even though polymers can be added to help “cling”. Polyethylene (Glad) is very safe as far as reheating and general food safety but not rated highest in tests comparing clinginess.

Given these facts, it is reasonable to suppose that the Stop & Shop brand should do well in the cling/adhesion test, Saran should be better in locking in moisture and freshness, and that Glad should be average in all areas. I am wondering that if popularity and price (you get what you pay for) are factored in, maybe I should conclude that Stop & Shop, the cheapest brand, cannot perform as well as its two, better known, more expensive, competitors.

PREDICTION:

Based on our research, my daughter and I predict that there may be split results based on the three tests, depending largely on the type of plastic that each brand is made of. However, we give an overall edge to Saran Wrap, which as the most established brand in the United States, must have built a reputation on earned results.

PROCEDURE:

Three experiments were designed for classroom use. Three trials were performed for each.

Test #1: Strength: How strong is the plastic wrap? Which brand holds the most weight until it rips? Test #2: Stickability: How well does the brand adhere to three 3 surfaces, commonly found in the home:glass, paper, and plastic?

Test #3: Permeability: (3a) how well does the plastic wrap trap water vapor; keeping moisture in? (3b) How well does it keep actual food“fresh”?

COMPLETE LIST OF MATERIALS: 25 students (8 groups of 3 and one group of 4)

Test #1: 8 glass 750 ml (3 cup) Pyrex bowls 8 paper “gift” bags (square-bottomed, 8 mm x 21 mm, 30 gram) 24(3 sheets x 8 teams) 20 mm or 8 inch squares of Saran Wrap (for 3 trials) 24 (3 sheets x 8 teams) 20 mm or 8 inch squares of Glad Plastic Wrap (for 3 trials) 24 (3 sheets x 8 teams) 20 mm or 8 inch squares of Stop & Shop Wrap (for 3 trials) Adhesive labels ( 3 color ½ in round dot) Black marker 8(0.25 in or¼ inch wide rubber bands 16 boxes (100 count) of ½ USS Flat Washers (Hot Tip Galvanized); each washer weighs 28g/1 ozKitchen or bathroom scale

Test #2: 8 (16 oz or 453.59237 g)clear/hard plastic drinking cups 8 (16 oz or 453.59237 g) paper drinking cups 8 (16 oz or 453.59237 g) glass drinking cups 24 (3 sheets x 8 teams) 15 mm or 6 inch squares of Saran Plastic Wrap (3 trials) 24 (3 sheets x 8 teams) 15 mm or 6 inch squares of Glad Plastic Wrap (3 trials) 24 (3sheets x8 teams) 15 mm or 6 inch squares of Stop & Shop Plastic Wrap (3 trials) 8 bags (12.60 oz or 357.2 g) M&M milk chocolate candies 8 sets measuring cups (1/4 cup or 2 oz. or 56.699046 g); ½ cup or 4 oz. or 113.39809 g; 1 cup or 8 oz. or 226.79618 g) 8 plastic or paper bowls Adhesive labels ( 3 color ½ in round dot) Black marker

Test #3(two tests): 3a) 8 apples (cut into 12 equal pieces) 24 (3 sheets x 8 teams) 15 mm squares of Saran Plastic Wrap 24 (3 sheets x 8 teams) 15 mm squares of Glad Plastic Wrap 24 (3 sheets x 8 teams) 15 mm squares of Stop & Shop Plastic Wrap Adhesive labels ( 3 color ½ in round dot) Black Marker 8 foil baking sheets (15 -3/32 x 10-15/16 inches or 383.38125 x 277.8125 mm)

3b)72plastic cups (9 glasses x 8 teams) ( 354.8 mil or 12 oz) 8 measuring cups (56.699046 g or 2 oz or ¼ cup) 24 (3 sheets x 8 teams) 15 mm or 6 inch squares of Saran Plastic Wrap 24 (3 sheets x 8 teams) 15 mm or 6 inch squares of Glad Plastic Wrap 24 (3 sheets x 8 teams) 15 mm or 6 inch squares of Stop & Shop Plastic Wrap Adhesive labels ( 3 color ½ in round dot) 8 foil baking sheets (15 -3/32 x 10-15/16 inches or 383.38125 x 277.8125 mm) Bottled Water

DATA/OBSERVATIONS:

Test #1 –Strength

Procedure Instructions For Each Team:

  • Safety Procedures: Closed toe shoes worn for protection from weighted objects.
  • 9 Squares of 20 mm plastic are gathered and labeled for three trials each of the three brands of plastic wrap. (3 with red dot/labeled Sfor Saran with black marker; 3 with blue dot/labeled Gfor Glad; 3 with yellow dot/labeled S&S for Stop & Shop)
  • One 750ml Pyrex bowl is the base for stretching the plastic wrap; used for all nine trials.
  • To begin, one 20mm square of Saran Wrap is tautly stretched over the top of the bowl and secured with the rubber band.
  • The paper gift bag is carefully placed on top of the stretched plastic wrap. (Note: the bag is necessary to hold a larger quantity of washers).
  • Washers (each weighs 28 g/1 oz) are added, one-at-a-time, to the bag and counted.
  • When enough weight from the washers in the bag forces the plastic film to burst or rip, the bag is removed and the washers are recounted for accuracy (if necessary).
  • Process is repeated for 2nd and 3rd trials of Saran Wrap and data recorded.
  • Process continues using the 3 squares of Glad Wrap (3 separate trials); results are recorded.
  • Process continues using the 3 squares of Stop & Shop Plastic Wrap (3 separate trials); results are recorded.
  • Weight recorded for each brand in its three trials subtracts the weight of the paper gift bag (30 grams/1 oz)

Test # 2: Stickability

Procedure Instructions forEach Team:

  • No specific safety concerns
  • 9 Squares of 20 mm plastic are gathered and labeled for three trials each of the three brands of plastic wrap. (3 with red dot/labeled S for Saran with black marker; 3 with blue dot/labeled Gfor Glad; 3 with yellow dot/labeled S&S for Stop & Shop)
  • Glass Test: 3 glasses (16 oz or 453.59237g) are lined up on work table.
  • Measure 1/4 cup or 2 oz. or 56.699046 g of M&M milk chocolate candies and place in first glass.
  • Place I square of Saran Wrap on glass (with M&Ms inside)and press down firmly all around rim and sides of glass.
  • Position a plastic or paper bowl under glass to catch candies when glass is inverted.
  • Invert glass for 5 seconds; record whether plastic holds M&Ms inside glass or releases them into bowl. Using the same first glass, repeat process two more times and record results.
  • Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same first glass. Use same Saran Wrap square as above (pressing down firmly all around rim and sides of glass). Position bowl and invert glass as before for 5 seconds. Record results. Repeat process two more times and record results.
  • Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same glass as above.Use same Saran Wrap square as above (pressing down firmly all around rim and sides of glass). Position bowl and invert glass as before for 5 seconds. Record results. Repeat process two more times and record results. (You are done with this first glass).
  • Take 2nd glass and place I square of Glad Wrap on glass (with M&Ms inside) and press down firmly all around rim and sides of glass.
  • Position a plastic or paper bowl under glass to catch candies when glass is inverted.
  • Invert glass for 5 seconds; record whether plastic holds M&Ms inside glass or releases them into bowl. Repeat process two more times and record results.
  • Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same second glass. Use same Glad Wrap square as above (pressing down firmly all around rim and sides of glass). Position bowl and invert glass as before for 5 seconds. Record results. Repeat process two more times and record results.
  • Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same glass as above.Use same Glad Wrap square as above (pressing down firmly all around rim and sides of glass). Position bowl and invert glass as before for 5 seconds. Record results. Repeat process two more times and record results. (You are done with the second glass).
  • Measure 1/4 cup or 2 oz. or 56.699046 g of M&M milk chocolate candies and place in third glass.
  • Place I square of Stop & Shop Wrap on third glass (with M&Ms inside) and press down firmly all around rim and sides of glass.
  • Position a plastic or paper bowl under glass to catch candies when glass is inverted.
  • Invert glass for 5 seconds; record whether plastic holds M&Ms inside glass or releases them into bowl. Repeat process two more times and record results.
  • Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same third glass. Use same Stop & Shop Wrap square as above (pressing down firmly all around rim and sides of glass). Position bowl and invert glass as before for 5 seconds. Record results. Repeat process two more times and record results.
  • Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same glass as above.Use same Stop & Shop Wrap square as above (pressing down firmly all around rim and sides of glass). Position bowl and invert glass as before for 5 seconds. Record results. Repeat process two more times and record results. (You are done with the glasses).
  • Paper Cup Test: 3 paper cups (16 oz or 453.59237g) are lined up on work table.
  • Measure 1/4 cup or 2 oz. or 56.699046 g of M&M milk chocolate candies and place in first paper cup.
  • Place I square of Saran Wrap on glass (with M&Ms inside) and press down firmly all around rim and sides of paper cup.
  • Position a plastic or paper bowl under paper cup to catch candies when inverted.
  • Invert paper cup for 5 seconds; record whether plastic holds M&Ms inside cup or releases them into bowl. Using the same paper cup, repeat process two more times and record results.
  • Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same first paper cup. Use same Saran Wrap square as above (pressing down firmly all around rim and sides of cup). Position bowl and invert as before for 5 seconds. Record results. Repeat process two more times and record results.
  • Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same paper cup as above.Use same Saran Wrap square as above (pressing down firmly all around rim and sides of cup). Position bowl and invert as before for 5 seconds. Record results. Repeat process two more times and record results. (You are done with this first paper cup).
  • Take 2ndpaper cup and place I square of Glad Wrap on cup (with M&Ms inside) and press down firmly all around rim and sides.
  • Position a plastic or paper bowl under glass to catch candies when cup is inverted.
  • Invert cup for 5 seconds; record whether plastic holds M&Ms inside or releases them into bowl. Repeat process two more times and record results.
  • Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same second paper cup. Use same Glad Wrap square as above (pressing down firmly all around rim and sides). Position bowl and invert as before for 5 seconds. Record results. Repeat process two more times and record results.
  • Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same paper cup as above.Use same Glad Wrap square (pressing down firmly all around rim and sides). Position bowl and invert cup as before for 5 seconds. Record results. Repeat process two more times and record results. (You are done with the second paper cup).
  • Measure 1/4 cup or 2 oz. or 56.699046 g of M&M milk chocolate candies and place in third paper cup.
  • Place I square of Stop & Shop Wrap on third cup (with M&Ms inside) and press down firmly all around rim and sides.
  • Position a plastic or paper bowl to catch candies when cup is inverted.
  • Invert cup for 5 seconds; record whether plastic wrap holds M&Ms inside cup or releases them into bowl. Repeat process two more times and record results.
  • Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same third cup. Use same Stop & Shop Wrap square as above (pressing down firmly all around rim and sides). Position bowl and invert as before for 5 seconds. Record results. Repeat process two more times and record results.
  • Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same cup as above.Use same Stop & Shop Wrap square as above (pressing down firmly all around rim and sides). Position bowl and invert cup as before for 5 seconds. Record results. Repeat process two more times and record results. (You are done with the paper cups).
  • Clear/Hard Plastic Cups: 3 plastic cups (16 oz or 453.59237g) are lined up on work table.
  • Measure 1/4 cup or 2 oz. or 56.699046 g of M&M milk chocolate candies and place in first plastic cup.
  • Place I square of Saran Wrap on plastic cup (with M&Ms inside) and press down firmly all around rim and sides.
  • Position a plastic or paper bowl to catch candies when inverted.
  • Invert plastic cup for 5 seconds; record whether plastic wrap holds M&Ms inside cup or releases them into bowl. Using the same cup, repeat process two more times and record results.
  • Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same first plastic cup. Use same Saran Wrap square as above (pressing down firmly all around rim and sides of cup). Position bowl and invert as before for 5 seconds. Record results. Repeat process two more times and record results.
  • Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same plastic cup as above.Use same Saran Wrap square as above (pressing down firmly all around rim and sides of cup). Position bowl and invert as before for 5 seconds. Record results. Repeat process two more times and record results. (You are done with this first plastic cup).
  • Take 2ndplastic cup and place I square of Glad Wrap on cup (with M&Ms inside) and press down firmly all around rim and sides.
  • Position a plastic or paper bowl to catch candies when cup is inverted.
  • Invert cup for 5 seconds; record whether plastic holds M&Ms inside or releases them into bowl. Repeat process two more times and record results.
  • Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same second plastic cup. Use same Glad Wrap square as above (pressing down firmly all around rim and sides). Position bowl and invert as before for 5 seconds. Record results. Repeat process two more times and record results.
  • Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same plastic cup as above.Use same Glad Wrap square (pressing down firmly all around rim and sides). Position bowl and invert cup as before for 5 seconds. Record results. Repeat process two more times and record results. (You are done with the second plastic cup).
  • Measure 1/4 cup or 2 oz. or 56.699046 g of M&M milk chocolate candies and place in third plastic cup.
  • Place I square of Stop & Shop Wrap on third cup (with M&Ms inside) and press down firmly all around rim and sides.
  • Position a plastic or paper bowl to catch candies when cup is inverted.
  • Invert cup for 5 seconds; record whether plastic wrap holds M&Ms inside cup or releases them into bowl. Repeat process two more times and record results.
  • Next, measure ½ cup or 4 oz. or 113.39809 g of M&M candies into same third cup. Use same Stop & Shop Wrap square as above (pressing down firmly all around rim and sides). Position bowl and invert as before for 5 seconds. Record results. Repeat process two more times and record results.
  • Measure 1 cup or 8 oz. or 226.79618 g of M&Ms into same cup as above.Use same Stop & Shop Wrap square as above (pressing down firmly all around rim and sides). Position bowl and invert cup as before for 5 seconds. Record results. Repeat process two more times and record results. (You are done with the plastic cups).

Test #3: Permeability: