**3. Reinforcements**

Composite reinforcements can be in various forms such as fibres, flakes, or particles. Each of these has its own properties which can be contributed to the composites, and therefore, each has its own area of applications. Among the forms, fibres are the most commonly used in composite applications, and they have the most influence on the properties of the composite materials. These reasons are that the fibres have the high aspect ratio between length and diameter, which can provide effective shear stress transfer between the matrix and the fibres, and the ability to process and manufacture the composites part in various shapes using different techniques.

However, frequent fluctuation in raw material prices acts as one of the major factors inhibiting the market growth. Asia-Pacific accounts for the biggest market for thermosets owing to the growth of the automobile market, primarily in China and India. Japan is a mature market and is expected to remain stagnant over the next years. China is the biggest automobile market in the world, and India also lists itself in the top five automobile markets in the world. Asia, along with being the largest market, is also the fastest-growing market for thermosets. The North American market for thermosets is primarily driven by the regulatory initiative to reduce automobile weight by 50% by 2020 in the USA in order to cut fuel consumption. Polyester resins and polyurethane account for the two most popular types of thermosets in the global market. The global market for thermosets is dominated by big multinational corporations which are present across the value chain. Some of the major companies operating in the thermosets market include Arkema, BASF, Asahi Kasei Chemical Corp, Bayer AG, Chevron Phillips Chemical Company LLC, Sinopec, Dow Chemical Company, Eastman Chemical Company, and Lyondell Basell Industries, among others [13]. To date, thermosets have been used predominantly in the industry. Thermosets are generally favoured for a variety of reasons, especially on commercial aircraft. Thermoset composites have been used for 30–40 years in aerospace. For example, the fuselage of the Boeing 787 is an

**Thermoset Thermoplastic**

*Composite and Nanocomposite Materials - From Knowledge to Industrial Applications*

Pellets soften when heated and become more fluid as additional heat is applied. This characteristic allows thermoplastics to be remoulded and recycled without negatively affecting the material's physical

• There is multiple thermoplastic that offer various performance benefits • Commonly offer high strength, shrinkresistance, and easy bendability. Depending on the polymers, thermoplastics can serve low-stress applications such as plastic bags or high-

stress mechanical parts • Highly recyclable

fibres and fillers • High-impact resistance • Chemical resistant

options

thermoset

• Can melt if heated, remoulding/ reshaping capabilities

• More difficult to wet the reinforcing

• Hard crystalline or rubbery surface

• Aesthetically superior finishes • Ecofriendly manufacturing • Generally, more expensive than

properties

Processing Contain monomers that cross-link together during the curing process to form an irreversible chemical bond. The cross-linking process eliminates the risk of the product remelting when heat is applied, making thermosets ideal for high-heat applications such as electronics and appliances

> deformation • Cannot be recycled

> > melt if heat)

thermoplastics • Highly flexible design • Thick to thin wall capabilities • Excellent aesthetic appearance • High levels of dimensional stability • More difficult to surface finish

• Cost-effective

fillers

• There are multiple thermoset resins that offer various performance benefits • Significantly improve the material's mechanical properties, providing enhances chemical resistance, heat resistance, and structural integrity. Thermoset are often used for sealed products due to their resistance to

• Cannot be remoulded or reshaped (not

• Easy to wet the reinforcing fibres and

• More resistant to high temperatures than

Features and benefits

**Table 1.**

*Thermoset vs. thermoplastic.*

On the other hand, the use of thermoplastic polymers (acrylic, polyolefin, acrylonitrile butadiene styrene (ABS), etc.), the more easily moldable and resettable

epoxy-based polymer [14].

**6**


Various types of fibres have been utilised to reinforce polymer matrix composites. The most common are carbon fibres (AS4, IM7, etc.), glass fibre (E-glass, S-glass, etc.), aramid fibres (Kevlar® and Twaron®), and boron fibres. Glass fibres have been used as reinforcement for centuries, notably by Renaissance Venetian glass workers. Commercially important continuous-glass fibre filaments were manufactured in 1937 by a joint venture between Owens-Illinois and Corning Glass.

A variety of glass fibre compositions are available for different purposes as

**Polymers Density**

Rigid thermoset polyurethane (RPU)

**(g/cm<sup>3</sup> )**

Melamine formaldehyde (MF) 1.5–1.6 0.6 65.0 12.0 Phenol formaldehyde (PF) 1.2 1.2 45.0–60.0 4.0–7.0

Unsaturated polyester (UPE) 1.1 2.0 34.0–105.0 2.1–3.5 Urea formaldehyde (UF) 1.5–1.6 0.8 65.0 9.0

Thermoset Epoxy (EP) 1.2–1.3 1.3 55.0–130.0 2.7–4.1

Polyurethane rubber 1.2–1.3 300.0–

**Elongation (%)**

580.0

Vinyl ester (VE) 1.23 2.0–12.0 73.0–81.0 3.0–3.5

**Tensile strength (MPa)**

1.2 90.0 60.0 2.2

**Young's modulus (GPa)**

39.0 2.0–10.0

• Grade A is high alkali grade glass, originally made from window glass.

for composite materials.

*Properties of some polymers.*

*Introduction to Composite Materials*

*DOI: http://dx.doi.org/10.5772/intechopen.91285*

**Table 2.**

grade.

composite materials.

**9**

• Grade M is high modulus grade glass.

significantly more expensive.

presented below. **Table 3** shows compositions of some commonly used glass fibres

• Grade C is chemical-resistant grade glass for acid environments or corrosion.

• Grade D is low dielectric grade glass, good transparency to radar (quartz glass).

• Grade E is electrical insulation grade; this is the most common reinforcement

• Grade R is reinforcement grade glass; this is the European equivalent of S-glass.

• Grade S is high strength grade glass, a common variant is S2-glass. This fibre has higher Young's modulus and temperature resistance than E-glass. It is also

**Table 4** presents the mechanical properties of the main grades of glass fibre for

Carbon fibre was first invented near Cleveland, Ohio, in 1958. It wasn't until a new manufacturing process was developed at a British research centre in 1963 that carbon fibre's strength potential was realised [27]. The principle precursors for carbon fibres are polyacrylonitrile (PAN), pitch, cellulose (Rayon), and some other

potential precursors such as lignin and polyethylene. Carbon fibres are

#### *Composite and Nanocomposite Materials - From Knowledge to Industrial Applications*



#### **Table 2.**

**Polymers Density**

*Composite and Nanocomposite Materials - From Knowledge to Industrial Applications*

Perfluoroalkoxy (vinyl ether) 2.15 260.0–

Thermoplastic Acrylonitrile styrene acrylate

(ASA)

Acrylonitrile butadiene styrene (ABS)

High-density polyethylene (HDPE)

High-impact polystyrene (HIPS)

Low-density polyethylene (LDPE)

Polyethylene cross-linked (PEX)

Polyethylene terephthalate (PET)

Poly-3-hydroxybutyrate (P-3-HB)

Poly-3-hydroxybutyrate-co-3 hydroxyvalerate (P-3-HB-3 HV)

Poly-3-hydroxybutyrate (P-3-HB)

Poly(methyl methacrylate) (PMMA)

Rigid thermoplastic Polyurethane (RTPU, PUR-RT)

**8**

**(g/cm<sup>3</sup> )**

Cross-linked polyethylene (PE) 0.9 350.0 18.0 0.5 Ethylene vinyl acetate (EVA) 0.9–1.0 750.0 17.0 0.02

Nylon 6 (PA 6) 1.1 60.0 81.4 2.8 Nylon 66 (PA 66) 1.1 60.0 82.7 2.8

Polybutylene (PB) 0.95 220–300 29.0–35.0 0.29–0.30 Polylactic acid (PLA) 1.2–1.3 2.1–30.7 5.9–72.0 1.1–3.6 Polycarbonate (PC) 1.2 200.0 69.0 2.3 Polycaprolactone (PCL) 1.1 700.0 16.0–23.0 0.4

Polyether ether ketone (PEEK) 1.3–1.5 1.6–50.0 92.0–95.0 3.7–24.0 Polyether ketone (PEK) 1.2–1.4 20.0 100.0–110.0 3.5 Polyhydroxyalkanoates (PHA) 1.2–1.3 2.0–1200.0 10.0–39.0 0.3–3.8 Polyhydroxybutyrate (PHB) 1.2 1.56–6.0 24.0–40.0 3.5–7.7

Polypropylene (PP) 0.9–1.3 80.0 35.8 1.6 Polystyrene (PS) 1.04 1.6 34.0 3.0 Polytetrafluoroethylene (PTFE) 2.20 40.0–650.0 0.862–41.4 0.392–2.25 Polyvinyl chloride (PVC) 1.3–1.5 50.0–80.0 52.0–90.0 3.0–4.0 Polyvinylidene fluoride (PVDF) 1.8 50.0 43.0 2.0

300.0

0.92 20.0

1.5–1.6 300.0 55.0–159.0 2.3–9.0

1.3 0.4–6.0 40.0 3.5

0.2–0.3 1.6–20.0 23.0–40.0 3.5

1.2 1000.0 104.0 —

1.1–1.2 2.5 72.4 3.0

1.1 5.0 75.0 4.0

**Elongation (%)**

**Tensile strength (MPa)**

1.0–1.1 30.0 43.5 2.2

1.0–1.1 270.0 47.0 2.1

0.9–1.0 150.0 32.0–38.2 1.3

1.0 2.5 42.0 2.1

0.9 400.0 10.0–11.6 0.2–0.3

28.0–31.0 0.50–0.60

**Young's modulus (GPa)**

*Properties of some polymers.*

Various types of fibres have been utilised to reinforce polymer matrix composites. The most common are carbon fibres (AS4, IM7, etc.), glass fibre (E-glass, S-glass, etc.), aramid fibres (Kevlar® and Twaron®), and boron fibres. Glass fibres have been used as reinforcement for centuries, notably by Renaissance Venetian glass workers. Commercially important continuous-glass fibre filaments were manufactured in 1937 by a joint venture between Owens-Illinois and Corning Glass. A variety of glass fibre compositions are available for different purposes as presented below. **Table 3** shows compositions of some commonly used glass fibres for composite materials.


**Table 4** presents the mechanical properties of the main grades of glass fibre for composite materials.

Carbon fibre was first invented near Cleveland, Ohio, in 1958. It wasn't until a new manufacturing process was developed at a British research centre in 1963 that carbon fibre's strength potential was realised [27]. The principle precursors for carbon fibres are polyacrylonitrile (PAN), pitch, cellulose (Rayon), and some other potential precursors such as lignin and polyethylene. Carbon fibres are


above 99% (although their graphitic structure is still less than 75%), and have a tensile modulus above 350 GPa. High-modulus, high-strength carbon fibres have diameters of 7–8 μm and consist of small crystallites of "turbostratic" graphite. The layers have no regular stacking sequence, and the average spacing between the planes is 0.34 nm. To obtain high modulus and strength, the layer planes of the graphite must be aligned parallel to the fibre axis [29]. Carbon fibres have several advantages including high stiffness, high tensile strength, low weight, high chemical resistance, and high temperature. The carbon fibres can be utilised in various applications such as aerospace, automotive, sporting goods, and consumer goods.

Kwolek is a DuPont chemist who in 1965 invented an aramid fibre known as Kevlar, the lightweight, stronger-than-steel fibre used in bulletproof vests and other body armour around the world. The chemical structure of the materials is being alternated aromatic (aryl) benzene rings and the amide (CONH) group. The commercial name of the reinforcement's fibres is Kevlar from DuPont and Twaron from AkzoNobel, which are believed to be poly-(para-phenylene terephthalamide). The polymer is produced by the elimination of hydrogen chloride from terephthaloyl chloride and para-phenylene diamine. The polymer is washed and dissolved in sulphuric acid to form a partially oriented liquid crystal solution. The solution is spun through small die holes, orientation taking place in the spinnerette, and the solvent is evaporated. Hull suggests that the solution is maintained between 80°C and 50°C before spinning and is extruded into a hot-walled cylinder at 200°C. Kevlar was introduced for commercial products in 1971. There are three principal

Recently, with advantages of reasonable mechanical properties, low density, environmental benefits, renewability, and economic feasibility, natural fibres have been paid more attention to in composite applications. The natural fibres in simple definition are fibres that are not synthetic or man-made and are categorized based

**Precursor PAN PAN Pitch Pitch Rayon Pitch (K13D2U)** Modulus Low High Low High Low Ultrahigh Tensile modulus (GPa) 231 392 161 385 41 931 Tensile strength (GPa) 3.4 2.5 1.4 1.8 1.1 3.7 Strain to failure (%) 1.4 0.6 0.9 0.4 2.5 0.4 Relative density 1.8 1.9 1.9 2.0 1.6 2.2 Carbon assay (%) 94 100 97 99 99 >99

**Fibre type E (GPa) σ' (GPa) ε' (%)**

Kevlar 149 Ultra-high modulus recently introduced 186 3.4 2.0

83 3.6 4.0

131 3.6 2.8

**Table 5** shows properties for the different grades of carbon fibre.

types of Kevlar fibre as shown in **Table 6**.

*Introduction to Composite Materials*

*DOI: http://dx.doi.org/10.5772/intechopen.91285*

*Indicative properties for the different grades of carbon fibre [27].*

Kevlar 29 High-toughness, high-strength, intermediate

Kevlar 49 High modulus high-strength for composite

*Characteristics of the different grades of aramid fibre [27].*

modulus for tyre cord reinforcements

reinforcement

**Table 5.**

**Table 6.**

**11**

#### **Table 3.**

*Composition for some commonly used glass fibres [24–26].*


**Table 4.**

*Mechanical properties of the main grades of glass fibre [24].*

manufactured by stretching PAN polymer precursor, melt spinning of molten pitch, and graphitization under tensile stress [28].

The modulus of carbon fibres depends on the degree of perfection of the alignment. Imperfections in alignment results in complex shaped voids elongated parallel to the fibre axis, which act as stress raisers and points of weakness. The alignment varies considerably with the manufacturing route and conditions. Highmodulus fibres are those which have been subjected to heat treatment in excess of 1650°C, possess three-dimensional ordering of the atoms, have carbon contents

### *Introduction to Composite Materials DOI: http://dx.doi.org/10.5772/intechopen.91285*

above 99% (although their graphitic structure is still less than 75%), and have a tensile modulus above 350 GPa. High-modulus, high-strength carbon fibres have diameters of 7–8 μm and consist of small crystallites of "turbostratic" graphite. The layers have no regular stacking sequence, and the average spacing between the planes is 0.34 nm. To obtain high modulus and strength, the layer planes of the graphite must be aligned parallel to the fibre axis [29]. Carbon fibres have several advantages including high stiffness, high tensile strength, low weight, high chemical resistance, and high temperature. The carbon fibres can be utilised in various applications such as aerospace, automotive, sporting goods, and consumer goods. **Table 5** shows properties for the different grades of carbon fibre.

Kwolek is a DuPont chemist who in 1965 invented an aramid fibre known as Kevlar, the lightweight, stronger-than-steel fibre used in bulletproof vests and other body armour around the world. The chemical structure of the materials is being alternated aromatic (aryl) benzene rings and the amide (CONH) group. The commercial name of the reinforcement's fibres is Kevlar from DuPont and Twaron from AkzoNobel, which are believed to be poly-(para-phenylene terephthalamide). The polymer is produced by the elimination of hydrogen chloride from terephthaloyl chloride and para-phenylene diamine. The polymer is washed and dissolved in sulphuric acid to form a partially oriented liquid crystal solution. The solution is spun through small die holes, orientation taking place in the spinnerette, and the solvent is evaporated. Hull suggests that the solution is maintained between 80°C and 50°C before spinning and is extruded into a hot-walled cylinder at 200°C. Kevlar was introduced for commercial products in 1971. There are three principal types of Kevlar fibre as shown in **Table 6**.

Recently, with advantages of reasonable mechanical properties, low density, environmental benefits, renewability, and economic feasibility, natural fibres have been paid more attention to in composite applications. The natural fibres in simple definition are fibres that are not synthetic or man-made and are categorized based


#### **Table 5.**

*Indicative properties for the different grades of carbon fibre [27].*


#### **Table 6.**

*Characteristics of the different grades of aramid fibre [27].*

manufactured by stretching PAN polymer precursor, melt spinning of molten pitch,

The modulus of carbon fibres depends on the degree of perfection of the alignment. Imperfections in alignment results in complex shaped voids elongated paral-

alignment varies considerably with the manufacturing route and conditions. Highmodulus fibres are those which have been subjected to heat treatment in excess of 1650°C, possess three-dimensional ordering of the atoms, have carbon contents

lel to the fibre axis, which act as stress raisers and points of weakness. The

and graphitization under tensile stress [28].

*Mechanical properties of the main grades of glass fibre [24].*

**Fibre Density**

**Oxide E-glass with boron**

**E-glass without boron**

**ECRglass**

*Composite and Nanocomposite Materials - From Knowledge to Industrial Applications*

SiO2 52–56 59 54–62 64–66 60–65 Very low thermal expansion Al2O3 12–16 12.1–13.2 9–15 24–26 17–24 Improved chemical durability B2O3 5–10 — ——— Low thermal expansion CaO 16–25 22–23 17–25 — 5–11 Resistance to water, acids, and

MgO 0–5 3.1–3.4 0–5 8–12 6–12 Resistance to water, acids, and

ZnO — — 2.9 — — Chemical durability Na2O 0–1 0.6–0.9 1.0 0–0.1 0–2 High thermal expansion,

K2O Trace 0–0.2 0.2 — 0–2 High thermal expansion,

TiO2 0.2–0.5 0.5–1.5 2.5 — — Improved chemical durability

Li2O — — ——— High thermal expansion,

Fe2O3 0.2–0.4 0.2 0.1 0–0.1 — Green colouration F2 0.2–0.7 0–0.1 Trace — — —

Zr2O3 — —— 0–1 — —

**S-2 glass**

**Table 4.**

**10**

**Table 3.**

**(kg/m<sup>3</sup> )**

*Composition for some commonly used glass fibres [24–26].*

**Young's modulus (GPa)**

A (alkali) 2460 73 3100 2760 3.6 C (chemical) 2460 74 3100 2350 D (dielectric) 2140 55 2500 E (electrical) 2550 71 3400 2400 3.37 R (reinforcement) 2550 86 4400 3100 5.2 S (strength) 2500 85 4580 3910 4.6 S2 2460 90 3623 S3 2830 99 3283

**Virgin filament strength (MPa)**

**Roving strength (MPa)**

**R-glass Effect on fibre properties**

alkalis

alkalis

moisture sensitivity

moisture sensitivity

especially alkali resistance

moisture sensitivity

**Strain to failure (%)** on their origin from animals, mineral, or plant sources [30]. Natural fibres are one such proficient material which would be utilised to replace the synthetic materials and their related products for the applications requiring less weight and energy conservation. Natural plant fibres are entirely derived from vegetative sources and are fully biodegradable in nature. Fibre-reinforced polymer matrix got considerable attention in numerous applications because of its good properties. The current indicators are that interest in natural fibre composites by the industry will keep growing quickly around the world. The application of natural fibre-reinforced polymer composites and natural-based resins for replacing existing synthetic polymer or glass fibre-reinforced materials is huge. However, natural fibre quality is influenced significantly by the age of the plant, species, growing environment, harvesting, humidity, quality of soil, temperature, and processing steps, and there is a move to reduce the on-field processing to improve consistency and reduce costs. The properties of several natural fibres and commonly used synthetic fibres are shown in **Table 7** [31–35].


Increasingly, the fibres have replaced parts formerly made of steel. The fibres used in composite materials appear at different forms and scales as shown in **Figure 1**.

There are several methods for fabricating composite materials. The selection of a method for a part will depend on the materials, the part design, the performance,

**4. Composite manufacturing techniques**

and the end-use or application.

*Introduction to Composite Materials*

*DOI: http://dx.doi.org/10.5772/intechopen.91285*

**Figure 1.** *Various fibre forms.*

**13**

#### **Table 7.** *Properties of several natural fibres and commonly used synthetic fibres.*

on their origin from animals, mineral, or plant sources [30]. Natural fibres are one such proficient material which would be utilised to replace the synthetic materials and their related products for the applications requiring less weight and energy conservation. Natural plant fibres are entirely derived from vegetative sources and are fully biodegradable in nature. Fibre-reinforced polymer matrix got considerable attention in numerous applications because of its good properties. The current indicators are that interest in natural fibre composites by the industry will keep growing quickly around the world. The application of natural fibre-reinforced polymer composites and natural-based resins for replacing existing synthetic polymer or glass fibre-reinforced materials is huge. However, natural fibre quality is influenced significantly by the age of the plant, species, growing environment, harvesting, humidity, quality of soil, temperature, and processing steps, and there is a move to reduce the on-field processing to improve consistency and reduce costs. The properties of several natural fibres and commonly used synthetic fibres are

*Composite and Nanocomposite Materials - From Knowledge to Industrial Applications*

shown in **Table 7** [31–35].

**Fibre Density**

Softwood Kraft

**Table 7.**

**12**

**(g/cm3 )** **Elongation (%)**

Abaca 1.5 — 511.0–1051.0 13.5–29.8 Alfa 0.89 — 350.0 22.0 Bagasse 1.2 1.1 20.0–290.0 19.7–27.1 Banana 1.3–1.4 2.0–7.0 54.0–789.0 3.4–32.0 Bamboo 1.5 — 575.0 27.0 Coconut 1.4–3.8 — 120.0–200.0 19.0–26.0 Coir 1.2 15.0–30.0 175.0–220.0 4.0–6.0 Cotton 1.5–1.6 3.0–10.0 287.0–597.0 5.5–12.6 Curaua 1.4 — 825.0 9.0 Flax 1.4–1.5 1.2–3.2 345.0–1500.0 27.6–80.0 Hemp 1.4–1.5 1.6 550.0–900.0 70.0 Henequen 1.4 3.0–4.7 430.0–580.0 — Isora 1.2 — 550.0 — Jute 1.3–1.5 1.5–1.8 393.0–800.0 10.0–30.0 Kapok 0.4 — 93.3 41.0 Kenaf 1.2 2.7–6.9 295.0 — Palf 1.4 3.0 170.0–635.0 6.2–24.6 Piassava 1.4 — 138.5 2.8 Pineapple 1.5 1.0–3.0 170.0–1672.0 82.0 Ramie 1.5 2.0–3.8 220.0–938.0 44.0–128.0 Silk 1.3–1.4 — 650.0–750.0 16.0 Sisal 1.3–1.5 2.0–14.0 400.0–700.0 9.0–38.0

**Tensile strength (MPa)**

1.5 — 1000.0 40.0

Wool 120.0–174.0 5.0–10.9

*Properties of several natural fibres and commonly used synthetic fibres.*

**Young's modulus (GPa)**

#### **Figure 1.** *Various fibre forms.*

Increasingly, the fibres have replaced parts formerly made of steel. The fibres used in composite materials appear at different forms and scales as shown in **Figure 1**.
