CDB 4423 Polymer Process Engineering
May 2017
EXPERIMENT 3
: COMPOSITE
GROUP
: 3
GROUP MEMBERS
: KOI ZI KANG
18868
NORANISAH BINTI JAMIAN
19339
SADADINE MAHAMAT YOUSSOUF
17839
LECTURER
: DR WAN ZAIREEN NISA YAHYA
DATE OF EXPERIMENT
: 15th JUNE 2017
Table of Contents
Chapter 1: Introduction 1.1 Abstract .................................................................................................................... 1 1.2 Problem Statement ................................................................................................... 1 1.3 Objectives ................................................................................................................ 1
Chapter 2: Literature Review 2.1 Composites............................................................................................................... 2 2.2 Polymer-Matrix Composites .................................................................................2-3 2.3 Rule of Mixtures ...................................................................................................... 3
Chapter 3: Methodology .........................................................................................................4-5
Chapter 4: Results and Discussions 4.1 Results ................................................................................................................... 6-7 4.2 Discussions .........................................................................................................7-10
Chapter 5: Conclusion ............................................................................................................. 11
References ........................................................................................................................... 11-12
CHAPTER 1: INTRODUCTION 1.1 Abstract Composites are largely produced due to its resulted superior properties from the combination of two or more different materials. Composite is also referred as fiber-reinforced polymer (FRP) which consists of a polymer resin matrix and a fiber as reinforcement. In this experiment, reinforcement of epoxy resin with fiber glass was studied by measuring the theoretical Young’s modulus of the composite. Also, effect of curing temperatures on mechanical properties of the composite was investigated. In terms of theoretical Young’s modulus, it was found that the fiber glass-reinforced epoxy with less hardener has higher Young’s modulus as compared to that with more hardener which might be due to a better distribution of fiber glass in the less hardener system. Moreover, the results from the experiment of effect of curing temperatures on mechanical properties of the composite contradicted the theoretical prediction.
1.2 Problem Statement What is the effect of curing temperatures on mechanical properties of composite?
1.3 Objectives The experiment is designed to improve understanding on composite material. The objectives of the experiment are: •
To understand the concept of composite material
•
To acquire knowledge on the formation of composite material
•
To relate the effect of curing temperatures on mechanical properties of composite.
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CHAPTER 2: LITERATURE REVIEW 2.1 Composites Composite is a material artificially made up of two or more different materials and its resulting material properties are better than its individual materials that make up the composite (Callister, 2007). Most of the composite materials contain two phases which are matrix phase and dispersed phase. Matrix phase is continuous and it wraps the dispersed phase. According to Callister (2007), the composite properties are influenced by the relative amounts of each phase as well as the geometry of the dispersed phase that encompasses particle size, distribution, shape, orientation and concentration. The schematic diagram of various geometrical and spatial characteristics of particles of dispersed phase is shown in Figure 2.1 (Callister, 2007).
Figure 2.1 Schematic representations of the various geometrical and spatial characteristics of particles of the dispersed phase that may influence the properties of composites: (a) concentration, (b) size, (c) shape, (d) distribution, and (e) orientation. In most industrial products, polyester resin for instance polyester, vinyl ester, epoxy or phenolic is the matrix phase and fiber is the dispersed phase (American Composites Manufacturers Association, n.d.). Fiber contributes in terms of strength and stiffness whereas resin with more flexibility provides shape and protects the fiber. Combination of both resin and fiber is called a polymer-matrix composite.
2.2 Polymer-Matrix Composites
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As mentioned earlier, polymer-matrix composites consist of a polymer resin as the matrix, with fibers as the reinforcement material. They receive the greatest attention due to their roomtemperature properties, ease of fabrication and cost (Callister, 2007). Three common types of fibers are glass fiber, carbon fiber and aramid fiber. Glass fiber is produced in bulk and is popular as the dispersed material as it can be easily drawn into high-strength fibers from the molten state and its incorporation into polymer matrix could produce a composite with high specific strength. Carbon fiber is mostly used in advanced polymer-matrix composites as it still possesses high tensile modulus and high strength even at elevated temperatures and not affected by moisture or a wide variety of solvents, acids, and bases at room temperature. Aramid fibers are materials with high strength and high modulus and they are popular due to their outstanding strength-to-weight ratios, which are superior to metals.
2.3 Rule of Mixtures Rule of mixtures is widely used to predict and to compare the strength properties of composites (Chawla, 1973). It is an operational tool that employs weighted volume average of the component properties as individual components to calculate value of the composite property. The schematic diagram of representation of rule of mixtures is shown in Figure 2.2 (University of Cambridge, n.d.).
Figure 2.2 Schematic Diagram of Representation of Rule of Mixtures For instance, Young’s modulus of a composite can be predicted by using rule of mixtures as shown in Equation 1. 𝐸𝑐 = 𝐸𝑚 𝑉𝑚 + 𝐸𝑓 𝑉𝑓 Where, Ec, Em, Ef = Young’s modulus of composite, matrix and fiber respectively Vm = Volume fraction of matrix Vf = Volume fraction of fiber 3
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CHAPTER 3: METHODOLOGY The simplified methodology of this experiment is as follows: a) Sample Preparation 1) The mold (glass) is waxed. 2) 2 pieces of fibre glass mat is being cut and placed on the mold. 3) Epoxy with molecular weight of 700 g/mol and diamine with molecular weight of 448 g/mol are mixed with ratio of epoxy/diamine being 20/6.4. 4) The epoxy resin is the being poured onto the fibre glass and the composite is flattened using a roller. 5) Two samples are allowed to react at room temperature for 24 hours while another two samples is reacted at 120°C for 2 hours in the oven. 6) On the next day, the composite is being cut into at least four 50mm × 50mm × 3mm size composites. 7) These samples will be used for water adsorption process later.
b) Water Adsorption Test 1) Initial weights of composite samples are obtained at room temperature. 2) The dimension, the average thickness, length and width of each sample are measured at room temperature before immersion. 3) Two samples from each curing temperature are then immersed in different water baths at room temperature and at 50 °C respectively. 4) The samples are then periodically removed from the water bath on a daily basis, wiped with tissue paper and weighed before being immersed in the water again. 5) Step 4 is repeated for another three days. 6) The amount of water absorbed by the samples is then calculated using Equation (2),
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𝑀𝑡 % =
𝑊𝑡 − 𝑊𝑜 ×100 𝑊0
Where, Mt = water content at any given time Wt = sample weight at the time of measurement Wo =initial sample weight 7) All results are tabulated in the next chapter.
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CHAPTER 4: RESULTS AND DISCUSSIONS 4.1 Results Table 4.1 Dimensions of Sample Ratio
Cure
(Epoxy/Hardener) Temperature
Room Temp 20/6.4 120 °C
Room Temp 20/10 120 °C
Temperature
Length
Width
Thickness
(mm)
(mm)
(mm)
Room Temp
50.38
48.16
2.35
50 °C
47.99
47.23
1.92
Room Temp
49.43
46.81
6.90
50 °C
48.52
46.38
7.23
Room Temp
51.88
47.63
2.34
50 °C
54.35
49.77
2.11
Room Temp
48.22
47.23
8.89
50 °C
50.06
47.23
6.82
of Water Bath (°C)
Table 4.2 Measured Sample Weight for a Period of 4 Days Ratio (Epoxy/Hardener)
Curing
Water bath
Day 0
Day 1
Day 2
Day 3
Temperature
Temperature
(oC)
(oC)
W0 (g)
W1 (g)
W2 (g)
W3 (g)
25
4.99
5.00
5.04
5.06
50
4.67
4.74
4.79
4.81
25
6.06
6.37
6.61
6.70
50
6.56
7.55
7.62
7.71
25
6.10
6.12
6.14
6.15
50
6.40
6.49
6.56
6.71
25
5.23
6.17
6.32
6.49
50
4.41
5.50
5.77
5.84
25 20/6.4 120
25 20/10 120
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Table 4.3 Percentage of Water Absorbed Ratio
Cure
(Epoxy/Hardener) Temperature Room Temp 20/6.4 120 °C
Room Temp 20/10 120 °C
Temperature of
Length
Width Thickness
Water Bath (°C)
(mm)
(mm)
(mm)
Room Temp
50.38
48.16
2.35
50 °C
47.99
47.23
1.92
Room Temp
49.43
46.81
6.90
50 °C
48.52
46.38
7.23
Room Temp
51.88
47.63
2.34
50 °C
54.35
49.77
2.11
Room Temp
48.22
47.23
8.89
50 °C
50.06
47.23
6.82
4.2 Discussions 1. Write down your observation. Explain how the curing temperature may affect the water absorption of epoxy resin. Theoretically, increase in curing temperature should decrease water absorption due to higher degree of crosslinking and reduced free volume. However, that is not the case as observed in the results for this experiment as shown in Table 2. This could be due to the irregular shapes of the samples tested. The samples cured at 120oC are significantly thicker than the samples cured at room temperature. The irregular shapes could be caused by the rapid curing reaction at high temperature with the presence of glass fiber that might affect crosslink formation. Also, it may be that the supposed optimum curing temperature of this epoxy resin is lower than 120°C which means that the epoxy resin might undergo decomposition which lowers its density.
2. Explain how the arrangement of fiber can affect the modulus and strength of composite materials. The arrangement or orientation of the fibers relative to one another has a significant influence on the strength and modulus of fiber-reinforced composites. In terms of arrangement, two extremes are possible which are a parallel alignment of the longitudinal axis of the fibers in a single direction and a totally random alignment. Continuous fibers are normally aligned whereas discontinuous fibers may be aligned, randomly oriented or 7
partially oriented. Uniform fiber distribution contributes to better overall composite properties. The modulus and strength of the fiber increases when the fibers are arranged unidirectionally (Callister, 2007). Moreover, the reinforcement efficiency is higher for the continuous fibers than discontinuous fibers. However, the strength of the composites also depends on the direction of the applied stress. For unidirectional fibers, maximum strength is achieved when the stress is applied longitudinal to the fiber directions as it is dominated by fiber strength (Callister, 2007). Callister (2007) mentioned that the voids between fiber strands are the weakening factor of the composites. In the case of non-uniform or randomlyarranged fibers (discontinuous fibers), there is a more significant improvement in reinforcement strength when forces are applied at any direction relative to the plane of the fibers attributed to their randomly distributed fiber strands (Callister, 2007).
3. Explain how the curing temperature may affect the water absorption and other mechanical properties. As curing temperature increases, the molecules are highly mobilized due to increased kinetic energy, thus crosslinking density increases. When there are more crosslinks, there are more steric hindrances that reduce accessibility of absorption site (Aronhime, Peng, Gillham, & Small, 1986). In terms of mechanical properties, as cure temperature increases but below Tcure at which Tg∞ is obtained, strength and stiffness increases as there is more crosslinks and thus the free volume decreases. However, if the cure temperature increases above Tcure at which Tg∞ is obtained, the strength and stiffness decreases due to thermal degradation or oxidative crosslinking (Carbas, Marques, da Silva, & Lopes, 2014).
4. Using the literature values, obtain the density and modulus for DGEBA epoxy resin and fiber glass (E-Glass). Calculate the theoretical modulus of your composite sample. (using the known volume, and known density of epoxy, calculate the theoretical weight of epoxy without fibers.) Table 4.4: Density and modulus for epoxy and fiber glass Density
Young’s Modulus, E
(g/cm3)
(GPa)
DGEBA Epoxy
1.13
1.26
Fiber glass
2.55
80
Properties Compound
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Reference
Maiorana, Spinella, & Gross (2015) AZo Materials (2001)
Given Volume of Composite = 5 cm x 5 cm x 0.3 cm = 7.5 cm3 For epoxy/hardener ratio of 20/6.4, 𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑀𝑎𝑠𝑠 𝑜𝑓 𝐸𝑝𝑜𝑥𝑦 = 20 𝑔 + 6.4 𝑔 = 26.4 𝑔 𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑒𝑎𝑐ℎ 𝐸𝑝𝑜𝑥𝑦 𝑆𝑎𝑚𝑝𝑙𝑒 =
𝑉𝑜𝑙𝑢𝑚𝑒 𝐹𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝐸𝑝𝑜𝑥𝑦, 𝑉𝐸𝑝𝑜𝑥𝑦 =
26.4 𝑔 ÷ 4 = 5.84 𝑐𝑚3 1.13 𝑔/𝑐𝑚3
5.84 𝑐𝑚3 = 0.78 7.5 𝑐𝑚3
Using “rule of mixtures” approach, 𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑌𝑜𝑢𝑛𝑔′ 𝑠 𝑀𝑜𝑑𝑢𝑙𝑢𝑠 𝑜𝑓 𝐶𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒 = 𝑉𝐸𝑝𝑜𝑥𝑦 𝐸𝐸𝑝𝑜𝑥𝑦 + (1 − 𝑉𝐸𝑝𝑜𝑥𝑦 )𝐸𝐹𝑖𝑏𝑒𝑟 = (0.78)(1.26 𝐺𝑃𝑎) + (1 − 0.78)(80 𝐺𝑃𝑎) = 𝟏𝟖. 𝟓𝟖 𝑮𝑷𝒂
For epoxy/hardener ratio of 20/10, 𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑀𝑎𝑠𝑠 𝑜𝑓 𝐸𝑝𝑜𝑥𝑦 = 20 𝑔 + 10 𝑔 = 30 𝑔 𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑒𝑎𝑐ℎ 𝐸𝑝𝑜𝑥𝑦 𝑆𝑎𝑚𝑝𝑙𝑒 = 𝑉𝑜𝑙𝑢𝑚𝑒 𝐹𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝐸𝑝𝑜𝑥𝑦, 𝑉𝐸𝑝𝑜𝑥𝑦 =
30 𝑔 ÷ 4 = 6.64 𝑐𝑚3 1.13 𝑔/𝑐𝑚3
6.64 𝑐𝑚3 = 0.89 7.5 𝑐𝑚3
Using “rule of mixtures” approach, 𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑌𝑜𝑢𝑛𝑔′ 𝑠 𝑀𝑜𝑑𝑢𝑙𝑢𝑠 𝑜𝑓 𝐶𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒 = 𝑉𝐸𝑝𝑜𝑥𝑦 𝐸𝐸𝑝𝑜𝑥𝑦 + (1 − 𝑉𝐸𝑝𝑜𝑥𝑦 )𝐸𝐹𝑖𝑏𝑒𝑟 = (0.89)(1.26 𝐺𝑃𝑎) + (1 − 0.89)(80 𝐺𝑃𝑎) = 𝟗. 𝟗𝟐 𝑮𝑷𝒂
5. What are the advantages of using thermoset as matrix as compared to thermoplastic? Thermoset has better thermal and chemical resistance properties than thermoplastic. Also, thermoset has higher flexural and tensile strength due to the crosslinking within thermoset’s structure. Thermoset maintains strength and other physical properties even if it is exposed to extreme temperatures for a long period.
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6. Which one is more suitable for making aircraft body, epoxy/glass or epoxy/carbon fibers? Explain your answer. Epoxy/carbon fibers is more suitable for making aircraft than epoxy/glass due to its superiority in terms of stiffness and lightness, which are desired properties for manufacturing aircraft body (Gardner Business Media, Inc., 2014). Carbon fibers also have better tensile strength and compressive strength compared to glass.
7. Give ONE application of composite material based on glass, carbon and aramid fibers. Explain your answer. Fiber glass is widely used in transportation industries for instance manufacturing automotive and marine bodies, plastic pipes and storage containers. Carbon-reinforced polymer composites are currently being utilized in sports and recreational equipment such as fishing rods and golf equipment. Aramid fiber composites are widely used in ballistic products for instance bullet-proof vests and armor.
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CHAPTER 5: CONCLUSION In theory, increase in curing temperatures should decrease water absorption due to increase in the degree of crosslinking and reduction of free volume but the experimental results contradicted the theory. This discrepancy is possibly caused by the irregular shapes of cured epoxy resulted from the rapid curing reaction at high temperature with the presence of glass fiber that might affect crosslink formation. Also, it may be that the supposed optimum curing temperature of this epoxy resin is lower than 120°C which means that the epoxy resin might undergo decomposition which lowers its overall density. The theoretical Young’s modulus of the composite was determined using rule of mixtures which resulted in the values of 18.58 GPa and 9.92 GPa for both epoxy/amine ratios of 20/6.4 and 20/10 respectively.
REFERENCES Aronhime, M. T., Peng, X., Gillham, J. K., & Small, R. D. (1986). Effect of time-temperature path of cure on the water absorption of high Tg epoxy resins. Journal of Applied Polymer Science, 32(2), 3589-3626. doi:10.1002/app.1986.070320218 American Composites Manufacturers Association. (n.d.). Retrieved June 23, 2017 from http://compositeslab.com/composites-101/what-are-composites/ AZo Materials. (2001). E-Glass Fibre. Retrieved June 29, 2017 from http://www.azom.com/article.aspx?ArticleID=764 Callister, W. D. (2007). Materials Science And Engineering: An Introduction: John Wiley & Sons. Carbas, R. J. C., Marques, E. A. S., da Silva, L. F. M., & Lopes, A. M. (2014). Effect of Cure Temperature on the Glass Transition Temperature and Mechanical Properties of Epoxy Adhesives. The Journal of Adhesion, 90(1), 104-119. doi:10.1080/00218464.2013.779559 Chawla, K. K. (1973). On the Applicability of the "Rule-of-Mixtures" to the Strength Properties of Metal-Matrix Composites. Revista Brasileira de Física, 4 (3), 411-418. Gardner Business Media, Inc. (2014). The fiber. Retrieved June 23, 2017 from http://www.compositesworld.com/articles/the-fiber
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Jyoung. (n.d.). Carbon Fiber vs Fiberglass. Retrieved June 23, 2017 from http://blog.fibreglast.com/fiberglass/carbon-fiber-vs-fiberglass/ Maiorana, A., Spinella, S., & Gross, R. A. (2015). Bio-Based Alternative to the Diglycidyl Ether of Bisphenol A with Controlled Materials Properties. Biomacromolecules, 16(3), 1021-1031. doi:10.1021/acs.biomac.5b00014 University of Cambridge. (n.d.). Derivation of the rule of mixtures and inverse rule of mixtures. Retrieved June 23, 2017 from https://www.doitpoms.ac.uk/tlplib/bones/derivation_mixture_rules.php
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