It’s A Wrap“Best Buy” Science Experiments

Dr. Marialice Curran, EDUC 555/Fall 2012

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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 www.answers.com, 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.

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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 categories of plastics: polyethylene (PE), polyvinylidene (PVDC) and polyvinyl chloride (PVC).” (www.edusite.com/science/products.htm). 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 (www.bestcovery.com), it doesn’t keep food quite as fresh as Glad Cling Wrap, but testers named it tops in toughness and 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

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Sealing Ability: How well does plastic wrap prevent moisture evaporation, keeping food 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 three major categories of plastics -- polyethylene (PE); polyvinylidene (PVDC, now LDPE); and polyvinyl chloride (revised PVC). According to studies by Cook’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)

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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 oz Kitchen 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 (3 sheets x 8 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) 72 plastic 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:

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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 S for Saran with black marker; 3 with blue dot/labeled G for 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 for Each 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 G for 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.

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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.

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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 2nd paper 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.

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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 2nd plastic 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:

(3a) how well does it keep food “fresh”?

Procedure Instructions for Each Team:

No specific safety concerns if teacher uses knife to cut apple slices One apple is cut into 12 equal slices Label 9 (15 mm) squares (3 with red dot/labeled S for Saran with black marker; 3 with

blue dot/labeled G for Glad; 3 with yellow dot/labeled S&S for Stop & Shop) and adhere labels to plastic wrap.

On foil baking sheet line up: 3 unwrapped apple slices (control group); 3 slices wrapped tightly with Saran; 3 slices wrapped tightly with Glad; 3 slices wrapped tightly with Stop & Shop.

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Check color/condition of apples after one hour; after one day. Record results.

(3b) how well does the plastic wrap trap water vapor (which preserves freshness in food).

Procedure Instructions for Each Team:

No specific safety concerns Label 9 (15 mm) squares (3 with red dot/labeled S for Saran with black marker; 3 with

blue dot/labeled G for Glad; 3 with yellow dot/labeled S&S for Stop & Shop) and adhere labels to plastic wrap.

On foil baking sheet line up nine cups. Measure and pour ¼ cup of water into each cup. Cover 3 with Saran; 3 with Glad; 3 with Stop & Shop. Place rubber band around rim of

each cup to secure. Mark water line on each plastic cup with marker. Check for water vapor droplets on plastic cover or sides of glass after one hour; after

one day. Record results. After one day, observe water line on each cup. Record results.

DATA/OBSERVATIONS

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Test #1– Weight Resistance/Strength – measured by number of 28g /1 oz. washers added until plastic breaks, rips or pops

Trial Test #

SARAN WRAP

GLAD WRAP STOP & SHOP WRAP

#1 236 188 240

#2 240 204 230

#3 238 220 246

# of Washers: 714 612 716

Observations: We had a difficult time determining what type of weighted object to use for this test – small, flat and heavy. Research online proved that this is a problem for professional and Science Fair scientists worldwide! Marbles rolled off the top of the plastic film after a medium number were added; heavy bolts with grooves tore the plastic; coins were considered but would have been needed in a very large quantity. The biggest problem was finding any object in large enough quantities. My eldest son, a carpenter, solved the problem by providing us with boxes of flat metal washers.

In our testing, we were surprised to discover that plastic wrap stretched taut over a bowl and secured with a rubber proved to have a great amount of tensile strength. Therefore, a second problem that arose and needed to be solved before testing, was how to hold the great number of small objects in contact with the plastic film top. For this we used a tall, paper gift bag, which sat on top of the plastic-covered bowl. Washers were dropped into the bag, one at a time.

Test #2 – Stickability –

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How does the plastic wrap adhere to the three 3 different surfaces of glass, paper and plastic?

How does the plastic wrap hold M&M milk chocolates: ¼ cup/2 oz./56.699046g ½ cup/4 oz./113.39809g

1 cup/8 oz./226.79618g

Trial #1:

Saran Wrap

Container Material Holds: ¼ cup Holds: ½ cup Holds: 1 cupglass yes yes yespaper no no noplastic yes yes no

Glad Wrap

Container Material Holds: ¼ cup Holds: ½ cup Holds: 1 cupglass yes yes yespaper no no noplastic no no no

Stop & Shop

Container Material Holds: ¼ cup Holds: ½ cup Holds: 1 cupglass yes yes yespaper no no noplastic yes yes yes

Trial #2: Same result

Trial #3: Same result

Observations: We had purchased and planned to use plastic, paper and glass bowls of the same size and shape for this test, but discovered that there was no way to hold the bowl upside down, as necessary for this test, and not interfere with the plastic wrap that overlapped the sides of the bowl. For example, we seemed to either give unfair advantage by holding onto the plastic wrap, or put the plastic wrap at a disadvantage by breaking its seal with our fingers. This was solved by switching to drinking cups made of the three specified materials, which had enough room to seal with plastic at the top and hold near the middle or bottom of the glass.

Prior to beginning our experiment, we had researched online about the fact that plastic wrap molecules are long and tightly coiled, but when pulled, their molecules stretch. Friction created allows plastic wrap to absorb an electric charge. Electrons scatter, causing a negative charge.

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The surface covered with the wrap is positively charged, thus the “CLING”…opposites attract! However, cling depends on the amount of charge in the container and its covering; some materials cling, some do not.

Our most obvious observation was that paper does not create enough of a charge to cling to any of the three brands of plastic wrap that we tested. It would be interesting to research this more and find out if paper product can ever effectively seal with plastic wrap.

Test # 3 - Permeability:

(3a) How well does the plastic wrap trap water vapor. ¼ cup/2 oz./56.699046g added to each of nine glasses and marked with marker on side. Checked after 1 day.

Change in water level:

Discernible change Very slight change No change

##1

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Saran Wrap (3 trials) Glad Wrap (3 trials) Stop & Shop (3 trials)

(3b) How well does it keep food “fresh”, keep moisture in and prevent apple from turning brown? Results checked after 1 day.

Trial #1

Control Group (no plastic wrap): overall brown with slight withering around edges – 80% browning Saran Wrap: overall brown—no change in apple shape 60% browning,

Glad Wrap: lightest color change –, no change in apple shape 20% browning

Stop & Shop Wrap: medium color change –, no change in apple shape 40% browning

Trial #2

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Heavy water beading on inside top & sides

No water seen on inside top or on sides

Light water beading on inside top & sides

Control Group (no plastic wrap): overall brown with slight withering around edges – 60% browning Saran Wrap: overall brown— 40% browning

Glad Wrap: lightest color change – 10% browning

Stop & Shop Wrap: medium color change –

30% browning

Trial #3

Control Group (no plastic wrap): overall brown with slight withering around edges – 80% browning Saran Wrap: overall brown— 40% browning

Glad Wrap: lightest color change – 20% browning

Stop & Shop Wrap: medium color change – 30% browning

Observations: Both these tests seemed to agree that the polymer that best prevents evaporation, being the least permeable to air or oxygen, keeps food “freshest”. We measured water loss by observing it trapped in a bowl covered with each brand of plastic wrap. We measured freshness as best we could by comparing the color and shape change of sliced apples. Ideally, both these tests would be conducted over a longer period of time (than the one day we allowed) in order to be able to measure change with instruments. We were limited to visual, subjective observation for both tests.

CALCULATIONS & RESULTS: (Quantitative)

Test #1: Strength: How strong is the plastic wrap? How many 28 g metal washers can it hold on its surface until it rips?

Best: Stop & Shop (at 716 washers)

2nd Best: Saran was within 2 washers (at 714)

Least Best: Glad (at 612 washers)

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Trial #1 Trial #2 Trial #30

50

100

150

200

250

300

GLADSARANS&S

Test #2: Stickability: How well does the plastic wrap adhere to the 3 different surfaces of glass, paper, and plastic?

Best: Stop & Shop

2nd Best: Saran

Least Best: Glad

Note: None of the three brands adhered to paper.

SARAN: “Stuck” in 5/9 tests

Container Material Holds: ¼ cup Holds: ½ cup Holds: 1 cupglass yes yes yespaper no no noplastic yes yes no

Glad Wrap: “Stuck” in 3/9 tests

Container Material Holds: ¼ cup Holds: ½ cup Holds: 1 cupglass yes yes yes

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paper no no noplastic no no no

Stop & Shop: “Stuck” in 6/9 tests

Container Material Holds: ¼ cup Holds: ½ cup Holds: 1 cupglass yes yes yespaper no no noplastic yes yes yes

Test # 3: Permeability:

(3a) How well does the plastic wrap trap water vapor.

Best: Stop & Shop

2nd Best: Glad

Least Best: Saran

Change in water level:

Discernible change Very slight change No change

##1

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Saran Wrap (3 trials) Glad Wrap (3 trials) Stop & Shop (3 trials)

(3b) How well does it keep food “fresh”, keep moisture in and prevent apple from turning brown? Results checked after 1 day, based on amount of browning.

Best: Glad

2nd Best: Stop & Shop

Least Best: Saran

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Heavy water beading on inside top & sides

No water seen on inside top or on sides

Light water beading on inside top & sides

AMOUNT OF BROWNING

GladSaranStop & Shop

CONCLUSION: According to our investigations, we give the overall “Best Buy” Designation to Stop & Shop’s generic plastic wrap, which scored highest in three of the four testing situations. This was in direct variance with what my daughter and I had predicted. We had thought that the cheapest, least known brand would not be out performed in any test by the two better known plastic wrap brands.

Saran and Glad would be a tie for my 2nd and 3rd choice, based on their strengths in different areas. For example, Saran did well in both the strength and stickiness categories –two important factors in preparing and storing food. Before Saran changed it formulation from PVDC to the cheaper, “safer” LDPE, it was considered the top performer in these two areas.

Glad, invented and produced to rival Saran in the United States, has always been made of Polyethylene, which is good at locking in moisture and flavor, safe as far as reheating and general food safety, but not rated highest in clinginess. We predicted and were correct that this brand would not be the best in the clinginess test but it did surpassed the other two in keeping food (apple slices) fresh.

In short, Stop & Shop Plastic Wrap did best because it is closer to the old formulation of PVC wrap, which had always been considered the strongest and clingiest of wraps. Whether it is the safest for microwave reheating, as a result of the many plasticizers added, is not known to us at this time –something to research…

I will buy Stop & Shop (a good deal for the price). The following data summarizes the tests and results:

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Test #1: Strength Saran: 714** Glad: 612* Stop & Shop: 716 ***

Test #2: Stickability Price Notes: Saran: 5/9 ** Saran Wrap: $2.89 Glad: 3/9* Glad: $2.49 Stop & Shop: 6/9*** Stop & Shop: $1.89

Test # 3: Permeability: 3a) Trap water vapor Saran: * Glad: ** : Stop & Shop: ***

(3b) Keep food fresh *** best Saran: 46% browning* ** second Glad: 16% browning*** * third Stop & Shop: 33% browning**

Additional Experiments That Could Have Been Done

We found it difficult to quantify “freshness” with a real-world test (how brown was the apple?). According to the Cook’s Country website, a more scientific approach would be to purchase a bottle of Indicating Drierite (calcium sulfate), an absorbent used in packaging which turns from purple-blue to bright pink when exposed to moisture. Placing Drierite in bowls covered tightly with a sheet of each wrap, the change in color of the absorbent indicates which wraps were impermeable.

Standards:

CT Frameworks: Grades 6-8 Core Scientific Inquiry, Literacy and Numeracy How is scientific knowledge created and communicated?

Scientific Inquiry is a thoughtful and coordinated attempt to search out, describe, explain and predict natural phenomena. It progresses through a continuous process of questioning, data collection, analysis and interpretation. It requires the sharing of findings and ideas for critical review by colleagues and other scientists.

C INQ.1 Identify questions that can be answered through scientific investigation.

C INQ.2 Read, interpret and examine the credibility of scientific claims in different sources of information.

C INQ.3 Design and conduct appropriate types of scientific investigations to answer different questions.

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C INQ.4 Identify independent and dependent variable, and those variable that are kept constant, when designing an experiment.

C INQ.5 Use appropriate tools/techniques to make observations and gather data.

C INQ.6 Use mathematical operations to analyze and interpret data.

C INQ. 7 Identify and present relationships between variables in appropriate graphs.

C INQ.8 Draw conclusions and identify sources of error.

C INQ.9 Provide explanations to investigated problems/questions.

C INQ.10 Communicate about science in different formats, using relevant science vocabulary, supporting evidence and clear logic.

Processes of Science Involved:

a) Generally, there are 5 stages in an inquiry learning unit such as the “Best Buy” Testing described above:

Engagement: stimulate students’ interest, curiosity and preconceptions; Exploration: first-hand experiences with concepts without direct instruction; Explanation: students’ explanations followed by introduction of formal terms and

clarifications; Elaboration: applying knowledge to solve a problem. Students frequently develop and

complete their own well-designed investigations; Evaluation: students and teachers reflect on change in conceptual understanding and

identify ideas still “under development”.

b) Specific processes include: observation; making predictions; controlled inquiry processes; data collection; analysis of data; articulation of data; and drawing conclusions.

Resources:

www.metric-conversions.org.htm

www.answers.com/topic/plastic-wrap

www.edusite.com/science/products.htm

www.cookscountry.com

www.m.cooksillustrated.com

http://www.education.com/science-fair/article/determine-type-polymer-food-wrap/

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www.wiley.com “Relationship between kinds of plastic wraps and food dehydration.” Author: Janice VanCleave

www.sciencebuddies.org/science-fair-projects/project_ideas

Gait, A. J. and E. G. Hancock. Plastics and Synthetic Rubbers. Pergamon Press, 1970.

“Keeping Food Fresh.” Consumer Reports, March 1994, pp. 143-47.

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