Polymer Tensile Strength

Michelle Fong and Daniel MatthewsEngineering 45: Properties of MaterialsSanta Rosa Junior CollegeDecember 5, 2005

Polymers:

A polymer is a generic term used to describe a substantially long molecule with structural and repeating units called monomers.

In chemistry, a monomer is a small molecule that may become chemically bonded to other monomers to form a polymer.

The process of converting these units to a polymer is called polymerization. Polymerization is a process of reacting monomer molecules together in a

chemical reaction to form linear chains or a three-dimensional network of polymer chains. There are many forms of polymerization and different systems exist to categorize them.

The first ‘synthetic’ polymers of the 19th century were actually formed by modifying natural polymers. The first man-made polymer, the phenol-formaldehyde resin bakelite, was made in 1872. However, research into polymers and polymerization only really started to grow in the 1930s after the discovery of polyethylene by the chemical company ICI (Imperial Chemical Industries).

The mechanical properties of polymers can be described with much of the vocabulary introduced with metals. Tensile strength and modulus of elasticity are important design parameters for polymers as well as inorganic structural materials.

There are few natural polymers generally considered to be “plastics”.

History of the Plastic Bag1957 The first baggies and sandwich bags on a roll are introduced.

1958 Poly dry cleaning bags compete with traditional brown paper.

1966 Plastic bag use in bread packaging takes over 25 to 30 percent of the market. Plastic produce bags on a roll are introduced in grocery stores.

1969 The New York City Sanitation Department's "New York City Experiment" demonstrates that plastic refuse bag curbside pickup is cleaner, safer and quieter than metal trash can pick-up, beginning a shift to plastic can liners

among consumers.

1974/75 Retailing giants such as Sears, J.C. Penney, Montgomery Ward, Jordan Marsh, Allied, Federated and Hills make the switch to plastic merchandise bags.

1973 The first commercial system for manufacturing plastic grocery bags becomes operational.

1977 The plastic grocery bag is introduced to the supermarket industry as an alternative to paper sacks.

1982 Kroger and Safeway start to replace traditional craft sacks with polyethylene "t-shirt" bags.

1990 The first blue bag recycling program begins with curbside collection. Consumer plastic bag recycling begins through a supermarket collection-site network.

1992 Nearly half of U.S. supermarkets have recycling available for plastic bags.

1996 Four of five grocery bags used are plastic.

Has this ever happened to you?

Project Overview

Performed Tensile Tests on Kitchen/Trash/Grocery plastic bags to find:

Stress, σ Strain, ε Modulus of Elasticity, E Yield Strength, σY.S.

Tensile Strength, σT.S. Toughness Ductility Price Comparisions

Procedure: Cut a 2.54 cm x 30.48 cm strip vertically starting from the bottom crease and

cutting through both sides of the plastic bag.

Record the initial thickness with a micrometer.

Record the initial width with a metric ruler.

Clamp one end of the plastic strip to the top of the apparatus.

Record the mass of the clamp device that the hanger will be attached onto.

Record the mass of the hanger that masses will be added onto.

Clamp the other end of the plastic strip with the clamp device and record the initial length of the plastic strip before letting it hang.

Add a 20 gram mass and immediately record the new length.; Repeat until plastic strip breaks.

Calculate it’s stress ( = P/Ao) and strain ( = L/Lo) for each point recorded and graph Stress vs. Strain.

Experiment Samples:

13 Gallon Kitchen Bags: Safeway Costco Kirkland Glad Force Flex Hefty Ultra Flex

30 Gallon Trash Bags: Glad Force Flex Hefty Ultra Flex

Shopping Bags: Safeway Grocery Bag Longs Drugs Bag

Tensile Test for Safeway 13-Gal Kitchen Bag

0

2

4

6

8

10

12

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Strain, ε (m/m)

Str

ess,

σ (

MP

a) Modulus of Elasticity: 128.35 MPa

Yield Strength: 7.93 MPa

Tensile Strength: 10.47 MPa

Toughness: 8.69 MPa

Ductility: 89%

Tensile Test for Costco Kirkland 13-Gal Kitchen Bag

0

1

2

3

4

5

6

7

8

9

10

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Strain, ε (m/m)

Str

ess,

σ (

MP

a) Modulus of Elasticity: 132.83 MPa

Yield Strength: 6.64 MPa

Tensile Strength: 9.01 MPa

Toughness: 11.25 MPa

Ductility: 150%

Tensile Test for Glad Force Flex 13-Gal Kitchen Bag

0

1

2

3

4

5

6

7

8

9

10

0 0.2 0.4 0.6 0.8 1 1.2

Strain, ε (m/m)

Str

ess,

σ (

MP

a)

Modulus of Elasticity: 10.75 MPa

Yield Strength: 7.11 MPa

Tensile Strength: 8.97 MPa

Toughness: 40.53 MPa

Ductility: 108%

Glad 13-Gal Kitchen Bag

Tensile Test for Hefty Ultra Flex 13-Gal Kitchen Bag

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6

Strain, ε (m/m)

Str

ess,

σ (

MP

a)

Modulus of Elasticity: 149.22 MPa

Yield Strength: 8.3 MPa

Tensile Strength: ~8.99 MPa

Toughness: 40.53 MPa

Ductility: ~490%

Hefty 13-Gallon Kitchen Bag

Tensile Tests for 13-Gallon Kitchen Bags

0

2

4

6

8

10

12

0 1 2 3 4 5 6

Strain, ε (m/m)

Stre

ss, σ

(MPa

) Safeway

Glad Force Flex

Hefty Ultra Flex

Costco Kirkland

13-Gallon Kitchen BagsYield Strength, Y.S.

0

1

2

3

4

5

6

7

8

9

Yield Strength

(MP

a)

Safeway 13-Gal Kitchen

Glad 13-Gal Kitchen

Hefty 13-Gal Kitchen

Costco 13-Gal Kitchen

Modulus of Elasticity

0

20

40

60

80

100

120

140

160

Modulus of Elasticity, E

(MP

a)

Safeway 13-Gal Kitchen

Glad 13-Gal Kitchen

Hefty 13-Gal Kitchen

Costco 13-Gal Kitchen

Toughness

0

5

10

15

20

25

30

35

40

45

Toughness

(MP

a)

Safeway 13-Gal Kitchen

Glad 13-Gal Kitchen

Hefty 13-Gal Kitchen

Costco 13-Gal Kitchen

Tensile Strength, T.S.

8

8.5

9

9.5

10

10.5

11

Tensile Strength

(MP

a)

Safeway 13-Gal Kitchen

Glad 13-Gal Kitchen

Hefty 13-Gal Kitchen

Costco 13-Gal Kitchen

Tensile Test for Glad Force Flex 30-Gal Trash Bag

0

2

4

6

8

10

12

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

Strain, ε (m/m)

Str

ess, σ

(M

Pa)

Modulus of Elasticity: 14.57 MPa

Yield Strength: 8.56 MPa

Tensile Strength: 10.59 MPa

Toughness: 13.21 MPa

Ductility: 168%

Tensile Test for Hefty Ultra Flex 30-Gal Trash Bag

0

2

4

6

8

10

12

14

0 1 2 3 4 5 6

Strain, ε (m/m)

Str

ess,

σ (

MP

a)

Modulus of Elasticity: 169.46 MPa

Yield Strength: 8.91 MPa

Tensile Strength: ~11.96 MPa

Toughness: 53.95 MPa

Ductility: ~543%

Hefty 30-Gal Trash Bag

Tensile Tests for 30-Gallon Trash Bags

0

1

2

3

4

5

6

7

8

9

10

11

12

13

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Strain, ε (m/m)

Str

ess,

σ (M

Pa)

Glad 30-Gal Trash

Hefty 30-Gal Trash

30-Gallon Trash Bags

0

2

4

6

8

10

12

14

Yield Strength, sY.S. Tensile Strength, sT.S.

(MP

a) Glad 30-Gal Trash

Hefty 30-Gal Trash

0

20

40

60

80

100

120

140

160

180

Modulus of Elasticity, E Toughness

(MP

a) Glad 30-Gal Trash

Hefty 30-Gal Trash

Tensile Tests for Safeway Grocery Bags

0

5

10

15

20

25

30

35

40

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Strain, ε (m/m)

Str

ess,

σ (

MP

a)

Safeway Trial 1(InconclusiveResults)

Safeway Trial 2

For Trial 2:

Modulus of Elasticity: 476.28 MPa

Yield Strength: 21.5 MPa

Tensile Strength: 25.99 MPa

Toughness: 18.87 MPa

Ductility: 78%

Why Safeway Trial 1 was Inconclusive:

Tensile Test for Longs Drugs Grocery Bag

0

5

10

15

20

25

30

35

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Strain, ε (m/m)

Str

ess, σ

(M

Pa)

Modulus of Elasticity: 304.95 MPa

Yield Strength: 24.4 MPa

Tensile Strength: 28.95 MPa

Toughness: 39.16 MPa

Ductility: 150%

Longs Drugs Bag

Tensile Tests for Grocery Bags

0

5

10

15

20

25

30

35

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Strain, ε (m/m)

Stre

ss, σ

(MPa

)

Safeway

Longs Drugs

Grocery Bags

0

5

10

15

20

25

30

35

40

45

Yield Strength,sY.S.

Tensile Strength,sT.S.

Toughness

(MP

a) Safeway Grocery

Longs Drugs

0

100

200

300

400

500

600

Modulus of Elasticity, E

(MP

a) Safeway Grocery

Longs Drugs

Tensile Tests for Kitchen, Trash, & Grocery Bags

0

5

10

15

20

25

30

0 1 2 3 4 5 6

Strain, (m/m)

Str

ess,

(MP

a)

Safeway 13-Gal Kitchen Glad Force Flex 13-Gal Kitchen Hefty Ultra Flex 13-Gal Kitchen

Costco Kirkland 13-Gal Kitchen Glad Force Flex 30-Gal Trash Hefty Ultra Flex 30-Gal Trash

Safeway Grocery Longs Drugs Grocery

All BagsTensile Strength, T.S.

0

5

10

15

20

25

30

35

Tensil Strength

(MP

a)

Safeway 13-Gal Kitchen

Glad 13-Gal Kitchen

Hefty 13-Gal Kitchen

Costco 13-Gal Kitchen

Glad 30-Gal Trash

Hefty 30-Gal Trash

Safeway Grocery

Longs Drugs

Toughness

0

10

20

30

40

50

60

Toughness

(MP

a)

Safeway 13-Gal Kitchen

Glad 13-Gal Kitchen

Hefty 13-Gal Kitchen

Costco 13-Gal Kitchen

Glad 30-Gal Trash

Hefty 30-Gal Trash

Safeway Grocery

Longs Drugs

Yield Strength, Y.S.

0

5

10

15

20

25

30

Yield Strength, Y.S.

(Mp

a)

Safeway 13-Gal Kitchen

Glad 13-Gal Kitchen

Hefty 13-Gal Kitchen

Costco 13-Gal Kitchen

Glad 30-Gal Trash

Hefty 30-Gal Trash

Safeway Grocery

Longs Drugs

Modulus of Elasticity

0

100

200

300

400

500

600

Modulus of Elasticity, E

(MP

a)

Safeway 13-Gal Kitchen

Glad 13-Gal Kitchen

Hefty 13-Gal Kitchen

Costco 13-Gal Kitchen

Glad 30-Gal Trash

Hefty 30-Gal Trash

Safeway Grocery

Longs Drugs

Ductility

0%

100%

200%

300%

400%

500%

600%

Ductility

(%)

Safeway 13-Gal Kitchen

Glad 13-Gal Kitchen

Hefty 13-Gal Kitchen

Costco 13-Gal Kitchen

Glad 30-Gal Trash

Hefty 30-Gal Trash

Safeway Grocery

Longs Drugs

Recycled Plastic

What you get for your money!Prices for Each Material Property

$0.00

$0.01

$0.02

$0.03

$0.04

$0.05

$0.06

Price per Bagper YieldStrength

Price per Bagper TensileStrength

Price per Bagper Toughness

U.S

. D

oll

ars

Safeway 13-Gal Kitchen

Glad 13-Gal Kitchen

Hefty 13-Gal Kitchen

Costco 13-Gal Kitchen

Glad 30-Gal Trash

Hefty 30-Gal Trash

Safeway Grocery

Longs Drugs

References:

http://en.wikipedia.org

http://www.plasticbag.com/environmental/history.html

http://www.budgetpackaging.com/inofgaba.html

http://www.santarosa.edu/~yataiiya/E45/LAB/TENSILE%20TEST.pdf

http://www.americanplasticscouncil.org/s_apc/sec.asp?CID=313&DID=931