Swelling Index Analysis of Thermoset Elastomer PDF

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EXPERIMENT 6 DETERMINATION OF SWELLING INDEX 1. OBJECTVE 1.1 To determine the effect of crosslink density on swelling index of vulcanized rubber 2. INTRODUCTION Crosslinking is when the different polymer chains are forming of covalent links between them and it is joining them all into a single netwo...

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Swelling Index Analysis of Thermoset Elastomer Ian Widi Perdana

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EXPERIMENT 6 DETERMINATION OF SWELLING INDEX 1. OBJECTVE 1.1

To determine the effect of crosslink density on swelling index of vulcanized rubber

2. INTRODUCTION Crosslinking is when the different polymer chains are forming of covalent links between them and it is joining them all into a single networked molecule. It also formed bridges that tied all the polymer chains in the rubber together [1]. Crosslink has major factor that greatly affects the mechanical properties of polymers. More crosslink occupy inside polymer chains, the more polymer becomes stiffer (figure 5.1). On the thermal resistance, crosslink also lend its capabilities to tie all the polymer molecules together when heat applied [2]. Hence, it provides a very excessive ability in the mechanical properties of the polymer itself. As with many other polymer

molecular characteristic, we cannot precisely

determine and describe the molecular structure on crosslinked polymers. In practice, we can measure crosslinked polymer’s gel contenr and its average crosslink density. These analysis provides a value that represent the complex situation [2]. Crosslink density analysis is used to determine a sample’s crosslink from the degree to which it swells when immersed in a suitable solvent (in this experiment is using toluene) [2]. We immersed a weighed sample of a crosslinked polymer in a suitable solvent and allow it to swell for up to 24 hours (usually 48 hours needed). After 48 hours passed, we will get the swollen weight and from this value we will also get the swelling index for each specimen we have observed. However, elastomers is a materials that are formed of polymers that are joined by chemical bonds, acquiring a final slightly crosslink structure. The characteristic of elastomer is it has ability to stretch twice or more of their original dimension when stress is applied and immediate release of stress will return quickly to their original length [3]. On the other hand, Vulcanized rubber is one of natural elastomers that formed by process of curing which increase its durability. Vulcanized rubber would not melt and get sticky when it was heated, or get brittle when left it outside in cold temperature.

According

to

[4,

5],

Vulcanization itself is

a chemical

process for

converting natural rubber or related polymers into more durable materials via the addition of sulfur or other equivalent "curatives." These additives modify the polymer by forming crosslinks between individual polymer chains. The curing agent is combined with latex and heated under pressure during vulcanization, which create rubbers with higher tensile strength and resistance of swelling and abrasion. In the other words, the important role in enhancing the physical properties of the vulcanized rubber is the blending of

two

rubbers

Fig 2.1: Crosslink in elastomer

Fig 2.2: Vulcanization of natural rubber (polyisoprene) with sulfur bridges

or

more

3. COMPONENT AND EQUIPMENT

Fig 3.1: pure SBR immersed in toluene

Fig 3.2: 100 SBR/0 CR/20 CB immersed in toluene

Fig 3.3: 95SBR/5 CR/20 CB immersed in toluene

Fig 3.4: 85 SBR/15 CR/20CB immersed in toluene

Fig 3.5:75 SBR/25CR/20 CB immersed in toluene

Fig 3.5: 65SBR/35 CR/20CB immersed in toluene

4. METHODOLOGY By accordimg to ASTM D471, determination of swelling index of the blends were carried out

Using an electrical balance the test piece of the blends with dimension 30 mm x 5 mm x 1.5 mm were weighted and this was considered the specimen original weight

The test pieces were immersed in toluene at a room temperature for 72 hours, respectively. Then, the test piece were removed from the toluene, wiped with tissue paper to remove excess toluene from the surface, and weighted which known as swollen weight

The swelling index of the blends was calculated for each specimen as follows �

��

=

��

��

5.

RESULT AND DISCUSSION

Table 5.1: Weight the samples before swollen Sample Weight (mg)

Specimen (SBR/CR/CB)

Average

Std

(mg)

Deviation

1

2

3

4

5

100/0/0

332.5

368.3

356.3

454.2

466.7

395.6

54.33334151

100/0/20

434.9

484.8

435.8

429.9

425

442.08

21.70303205

95/5/20

383.7

347.5

388.0

354.5

368.3

368.38

15.80220238

85/15/20

469.5

395.8

453.1

359.9

359.9

417.6

39.5494627

75/25/20

339.8

321.8

366.2

329.5

329.5

350.92

19.21949242

65/35/20

297.8

289.8

341.7

351.3

351.3

312.74

28.24603335

Chart 5.1: Average weight from each sample before swollen 500 450 400

442.08 407.64

395.6 368.4

338.76

Weight (mg)

350

312.7

300

100/0/0 100/0/20

250

95/5/20

200

85/15/20

150

75/25/20

100

65/35/20

50 0 Type of specimens (SBR/CR/CB)

Table 5.1 and chart 5.1 are showing the weight of each specimen before it swollen. It can be seen that each type of sample have vary weight for each specimen. From the chart 5.1

the highest average weight is sample SBR100 PHR : CR 0 PHR : CB 20 PHR with 442.08 mg, followed with sample SBR85 PHR : CR 15 PHR : CB 20 PHR with 407.64 mg. The variance of these reading may indicates that there were errors occurred in measurement of their dimensions. However, these samples were measured before it involved in toluene for 72 hours.

Table 5.2: Weight the samples after swollen Sample Weight (mg)

Specimen (SBR/CR/CB)

Average

Std

(mg)

Deviation

1

2

3

4

5

100/0/0

1310.5

1500.1

1498.2

1890.2

1821.7

1604.14

217.9149981

100/0/20

1201.6

1211.7

1204.9

1205.8

1200.8

1204.96

3.866057423

95/5/20

1004.3

996.5

1000.6

1009.8

995.8

1001.4

5.195767508

85/15/20

1273.2

1073.3

1224.7

969.5

1064.0

1120.94

111.7094911

75/25/20

884.6

880.8

982

878.2

886.5

902.42

39.89488188

65/35/20

695.2

676.8

812.7

816.5

631.9

726.62

74.73862188

Chart 5.2: Average weight from each sample after swollen 1800

1604.14

1600 1400 1204.96

1120.94

100/0/0

Weight (mg)

1200 1001.4

1000

100/0/20

902.42 726.62

800

95/5/20 85/15/20

600

75/25/20

400

65/35/20

200 0 Type of specimens (SBR/CR/CB)

Table 5.2 and chart 5.2 shows the weight of each specimen after immersed in toluene for 72 hours. It can be seen that almost all specimens are getting some weight interpolation. For pure SBR the increasing of weight is obtained at 1604.14 mg (average weight). On the other words, it increases 4 times more than its weight before swollen. For 100 SBR/0 CR/20 CB, 95 SBR/5 CR/20 CB, 85 SBR/15 CR/20CB, their weight are getting 3 times higher with 1204.96 mg, 1001.4 mg, 1120.94 mg respectively. Last but not least, 75 SBR/25CR/20 CB, 65SBR/35 CR/20CB, is getting an increasing weight with less than 3times higher than their with before swollen with 902.42 mg and 726.62 mg respectively. The difference of these readings indicate that each sample have difference ability to swelling. Since pure SBR have greater results than other sample, it shows that pure SBR is have higher ability to swell than others. It can be seen on its swelling index for each specimen at table 5.3 below. Table 5.3: The swollen index from each sample Sample Weight Specimen (SBR/CR/CB)

Average

Std Deviation

1

2

3

4

5

100/0/0

3.9414

4.0730

4.2049

4.1616

3.9034

4.0568

0.1184

100/0/20

2.7629

2.4994

2.7648

2.8048

2.8254

2.7315

0.1185

95/5/20

2.6174

2.8676

2.5789

2.8485

2.7038

2.7232

0.1174

85/15/20

2.7118

2.7117

2.7029

2.6938

2.9564

2.7553

0.1007

75/25/20

2.6033

2.7371

2.6816

2.6653

2.6345

2.6643

0.0452

65/35/20

2.3345

2.3354

2.3784

2.3242

2.2337

2.3212

0.0476

Chart 5.3: The swollen index from each sample 4.5000 4.0568 4.0000 3.5000

Swollen Index

3.0000

2.7315

2.7232

2.7553

100/0/0

2.6643 2.3212

2.5000

100/0/20 95/5/20

2.0000

85/15/20

1.5000

75/25/20 65/35/20

1.0000 0.5000 0.0000 Type of specimens (SBR/CR/CB)

As we expected, the highest swelling index which is showed at table 5.3 and chart 5.3 is pure SBR. It has 4.0568 on average swelling index with others is having a small difference between their swelling index. According table 5.3, we can simply conclude that pure SBR have the smallest crosslink, since it more absorbs water compared to other samples. It reinforces by [4], when polymer absorbs water and get high amount of swelling index, it indicates the polymer is having a low crosslink inside its chains structure. Hence, based on this experiment, the vulcanized rubber which is having the highest crosslink is 85 SBR/15 CR/20CB with swelling index 2.7553. It is followed by 100 SBR/0 CR/20 CB, 95 SBR/5 CR/20 CB, 75 SBR/25 CR/20 CB, 65 SBR/35 CR/20CB with swelling index 2.7553, 2.7315, 2.7232, 2.6643, 2.3212 respectively. Nevertheless, one thing to be considered is the standard deviation on the measurement of their weights. Some of the specimens are showing high standard deviation which also indicates they are having high standard error on the measurement of weight. Pure PU, 85 SBR/15 CR/20CB, 65 SBR/35 CR/20CB are the most highest in standard deviation. Since some of them are having high standard deviation, we cannot consider these results as valid results. Hence, we need a further experiment to prove these results and also we need to have a precise dimensional for specimen that used in the experiment, due to precise dimension will give the precise reading. However, the addition of CB (carbon black) and CR (Chloroprene

rubber) is

affecting a lot on the SBR swelling index. Based on [6], CR has a unique balance properties

compared to other synthetic elastomers. It has good mechanical strength, high ozone and weather resistance, good aging resistance, low flammability, good resistance toward chemicals and moderate oil and fuel resistance. On the other hand, CB is one of the major fillers in tire industry, due to its extraordinary features. According to [7, 8, 9], the current investigation was found that, the increase in carbon black will drastically deduct the swelling percentage of elastomer (in this experiment is SBR). CB also increases the modulus of elasticity of most elastomers [7], which means it lends higher rigidity to the polymers. It reinforce by [10], that surface area of CB is one of the most critical parameters considered for degree of reinforcement, which supply necessary sites to polymer chains for wetting. Indeed, CB and CR which added to SBR samples give SBR more crosslinks since their swelling index is lower than pure SBR. 6.

CONCLUSION In brief, this experiment showed that the addition of CR and CB to the SBR is

reducing SBR’s swelling index. On the other words, these fillers involved on SBR’s capability to absorbs the solvent (toluene). Since it reduces the swelling index of SBR, we can simply conclude that SBR with fillers have higher crosslink than pure SBR. On this experiment, the highest crosslink which is interpreted by the result we obtained and based on theoretical understanding is the 65SBR/35/CR/20CB.

7.

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Mrs Marliza Mustafa Zakaria. Introduction to Polymers, Universiti Malaysia Perlis,

Perlis,

2014.

[Lectures].

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UniMAP

Portal,

http://portal.unimap.edu.my [accessed on 26 Nov. 2014]. [2]

A. Peacock and A. Calhoun. Polymer Chemistry Properties and Applications. Munich: Carl Henser Verlag, 1996.

[3]

Mrs Marliza Mustafa Zakaria. Polymers Categories, Universiti Malaysia Perlis, Perlis, 2014. [Lectures]. Available: UniMAP Portal, http://portal.unimap.edu.my [accessed on 26 Nov. 2014].

[4]

W. D. Callister and D. G. Rethwisch. Materials Science and Engineering, 8th, ed. Asia: Jonh Wiley & Sons Pte Ltd, 2011.

[5]

Princeton

education.

Vulcanization

[Online].

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[6]

Zorge. Rubber technology. 2012.

[7]

Mangaraj, D., Elastomer Blends. 1996.

[8]

Mostafa, A., et al., Effect of carbon black loading on the swelling and compression set behavior of SBR and NBR rubber compounds. 2009.

[9]

Zhang, J., et al., Evaluation of the improved properties of SBR/weathered coal modified bitumen containing carbon black. 2009.

[10]

Akovali, G. and I. Ulkem, Some performance characteristics of plasma surface modified carbon black in the (SBR) matrix. 1999....