Natural Fiber Reinforced Vinyl Ester and Vinyl Polymer Composites

Development, Characterization and Applications

S. M. Sapuan, H. Ismail, E.S. Zainudin, S.M. Sapuan

• Publisher: Woodhead Publishing
• Year: 2018
• Print ISBN: 9780081021606
• eBook ISBN: 9780081021613
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Natural Fiber Reinforced Vinyl Ester and Vinyl Polymer Composites: Characterization, Properties and Applications discusses recent advances on the development, characterization and application of natural fiber vinyl ester and vinyl polymers composites. Various types of vinyl ester and vinyl based polymers, such as poly(vinyl chloride) (PVC), low and high density polyethylene (LDPE and HDPE), polypropylene (PP), polyvinyl alcohol (PVA) and polyvinyl acetate (PVAc) are discussed. Chapters focus on different composite fabrication processes, such as compression moulding, hand lay-up, and pultrusion processes. Key themes covered include the properties and characterization of vinyl ester and vinyl polymers composites reinforced by natural fibers.The effect of fiber treatment and coupling agents on mechanical and physical properties of these materials is also evaluated. In addition to a determination of physical and mechanical properties, studies on thermal, degradation, swelling behavior, and the morphological properties of natural fiber reinforced vinyl ester and vinyl polymer composites is also presented.- Presents the importance of vinyl ester and vinyl-based polymers as matrices in natural fiber composites- Provides a detailed and comprehensive review on the development, characterization and applications of natural fiber vinyl ester and vinyl polymers composites- Looks at recent fabrication techniques and the mechanical properties of materials- Contains contributions from leading experts in the field

1

Introduction to Natural Fiber Reinforced Vinyl Ester and Vinyl Polymer Composites

S.A.N. Mohamed¹, E.S. Zainudin¹, S.M. Sapuan², M.D. Azaman³ and A.M.T. Arifin⁴, ¹University Putra Malaysia, Serdang, Malaysia, ²Universiti Putra Malaysia, Serdang, Malaysia, ³Universiti Malaysia Perlis, Arau, Malaysia, ⁴Universiti Tun Hussein Onn Malaysia, Batu Pahat, Malaysia

Abstract

In recent years, the polymer industry has intensified its efforts to produce renewable material based polymer. Therefore, the use of natural fiber composites has been widely considered in various engineering sectors to replace conventional synthetic composite usage. This is because natural fiber composite properties are easily disposed and environmentally friendly in generating economic and sustainability societies. Vinyl polymer is a group of matrices comprising of thermosets and thermoplastics that are normally preferred as matrices with natural fibers. Both groups have their own unique features in benefiting their applications. The composite made of thermoset resin cannot be reprocessed or recycled. The composites of the thermoset matrix tend to provide good mechanical strength, are fragile and have low tensile effects. This is in contrast to the properties of the thermoplastic polymer that can be formed and diluted without changing its physical properties. Thermoplastic has excellent impact resistance and ductile. However, various approaches continue to be carried out by researchers to meet the requirements of natural fiber composites in different applications.

Keywords

Natural fiber; vinyl polymer; thermoset; thermoplastic; mechanical strength

Acknowledgments

The authors wish to acknowledge the financial support provided by research grant UPM/700-2/1/GP-IPS/2017/9538700 and Ministry of Higher Education (MyBrain15).

1.1 Background

Composites are a blend of various materials, in which each component preserves different characters. These components perform collectively to provide the composite essential mechanical properties and robustness. A composite material consists of two or more different phases (matrix section and dispersed section) having bulk properties that are significantly distinctive from one to another (Gupta and Kumar, 2012). The matrix section, which is usually more ductile, is the main phase that has a constant character. The matrix section, which is usually more ductile, is the main phase that has a constant character. It holds the secondary phase, i.e., dispersed phase and causes equal load distribution (Ku et al., 2012). The dispersed phase is embedded within the matrix in a discontinuous form. Moreover, this phase is normally stronger than the matrix; consequently, it is also referred to as the reinforcing phase. Based on matrix phase, composites can be categorized into metal matrix composites (MMCs), ceramic matrix composites (CMCs), and polymer matrix composites (PMCs). On the other hand, classification according to types of reinforcement are particulate composites (composed of particles), fibrous composites (composed of fibers), and laminate composites (composed of laminates) (Smith and Yeomans, 2009).

Fibers are hair-like continuous filament materials that act as the dissemination phase. They can be utilized as a component in composite materials. Besides that, fibers can be matted into sheets to make products such as paper and felt. There are a few types of fibers, namely, natural (animal and plant fibers) and man-made (synthetic and regenerated fibers) (Debnath et al., 2013). Usage of fibers by humans depends on what type is available at a particular region. For instance, straw along with clay, was the primary composite used to build walls in ancient Egypt (Ashori and Nourbakhsh, 2010). Furthermore, in China, natural fiber hemp was utilized for making the sails of boats. Other natural fibers were applied in a similar manner for numerous applications. Additionally, natural fibers have demonstrated satisfactory ability for use as reinforcement cloth due to their biodegradable and renewable characteristics in thermoset and thermoplastic matrices.

In the past few decades, polymers have replaced various traditional metals or materials in many applications. This occurred due to the benefits that polymers provide over conventional materials. Among significant advantages of polymers are convenience of processing, increased productivity, and reduced cost (Saheb and Jog, 1999). In most applications, properties of polymers change with the use of fillers and/or fibers to match the high strength or high modulus requirements (Omrani et al., 2016). A fiber reinforced polymer (FRP) is a composite material that consists of a polymer matrix embedded with high-strength fibers, such as glass, aramid, and carbon. Other than that, vinyl polymers are made from vinyl monomers, which are small molecules containing carbon-carbon double bonds (Mallakpour and Zadehnazari, 2013). They make up the largest family of polymers. In general, vinyl polymer can be classified into thermoplastic, thermosetting (vinyl ester), and elastomer (Saba et al., 2014).

Currently, thermoplastic materials predominate as matrices for biofibers. The most commonly used thermoplastics for this purpose are polypropylene (PP), polyethylene (PE), and polyvinyl chloride (PVC). Meanwhile, phenolic, epoxy, and polyester resins are regularly used as thermosetting matrices (Puglia et al., 2005). Fiber-reinforced polymers are more advantageous compared to conventional substances for certain properties. Therefore, significant attempts have been made to utilize polymers in different commercial applications. Moreover, various types of reinforcements consisting of fibers are integrated into polymers to increase their physical and mechanical properties. Hence, FRP matrix composites are extremely attractive because of their lightweight, biodegradability, high strength, high stiffness, good corrosion resistivity, and low coefficient of friction properties. These characteristics are important mechanical and tribological properties, for use in appliances to spacecraft applications. Moreover, nowadays, such substances are utilized in almost all areas of daily life.

1.2 Natural fibers

1.2.1 Types of natural fibers

Nonrenewable resources are becoming scarcer and thus a generalized awareness exists regarding renewable resources and merchandise. Hence, different natural fibers or species of plants that can provide natural reinforcement fibers are always appearing. There are three ways in which natural fibers can be used: in textiles, paper, and fabrics for biofuel; and as reinforcement material for composites (Habibi et al., 2008). As reinforcement material, natural fibers can eventually replace glass fibers in some applications such as providing composite parts for use in the automotive, construction, and packaging industries.

Natural fibers can be categorized according to their source namely lignocellulosic materials, animals, and minerals. Lignocellulosic fibers, likewise known as cellulose-based materials, can be divided into wood, which is more abundant, and nonwood or plant fibers. Plant fibers consist of cellulose, hemicellulose, lignin, and pectin compounds (Väisänen et al., 2016). Many fiber properties can be approximated by the relative content of these constituents. Besides that, nonwood lignocellulosic fibers are divided into seed, leaf, bast or stem, fruit, and stalk fibers. Most industrial fibers are sourced from bast (e.g., hemp, flax, kenaf, and jute). These fibers are gathered from the phloem that surrounds the stem and exist in plants of a certain required height; this enables fibers with high stiffness to retain stability. On the other hand, fibers from leaves (e.g., sisal) are also common raw materials but generally suffer from low stiffness. Fig. 1.1 shows some examples of natural fibers.

Figure 1.1 Classifications of natural fibers (Jusoh et al., 2016).

1.2.2 Microstructure of natural fibers

Natural fibers have complex structures that are usually inflexible, with crystalline cellulose microfibril-reinforced amorphous lignin and/or with hemicellulosic matrix. Moreover, natural fibers (besides cotton) are generally composed of cellulose, hemicellulose, lignin, waxes, and a few water-soluble compounds, wherein cellulose, hemicellulose, and lignin are the principal elements. A typical microstructure of these compounds is presented in Fig. 1.2. Natural fibers are commonly comprised of 60%–80% cellulose, 5%–20% lignin, and moisture up to 20%. Cell wall surface of natural fibers will experience pyrolysis as processing temperature increases. Pyrolysis is a chemical decomposition process of organic materials at a high temperature in the absence of oxygen. This process involves chemical composition and physical phase changes. Furthermore, pyrolysis contributes a charred layer to assist in insulating lignocelluloses for similar thermal degradation.

Figure 1.2 Schematic structure of (A) cellulose, (B) hemicellulose, (C) pectin, and (D) lignin (Westman et al., 2010).

Cellulose is a linear glucose polymer consisting of β-1,4-linked glucose units that provide strength, stiffness, and structural stability. Thousands of glucose units with intramolecular hydrogen bonds form crystals, which produce stable hydrophobic polymers with high tensile strength. Microfibrils on plant cell walls cause the bonds structure to be strong. Various models have been proposed for packaging of microfibrils in which the cellulose area varies and partly forms more crystalline, noncrystalline, or lesser regions. This difference has an immense impact on the features and functions of the overall fibers. Besides that, the structure of cellulose results in a complicated situation for enzymatic degradation. In general, three celluloses are required to degrade cellulose, i.e., exocellulase (exocellobiose hydrolase), endocellulase, and cellobiase.

On the other hand, hemicelluloses are branched polymers containing five-and six-carbon sugars of varied chemical structure. Meanwhile, lignin is an amorphous, cross-linked polymer network consisting of an irregular array of diverse bonded hydroxy- and methoxy-substituted phenylpropane units. In addition, lignin is less polar than cellulose and acts as a chemical adhesive within and between fibers. Pectins are complex polysaccharides with main chains that consist of a modified glucuronic acid polymer and residues of rhamnose. Their side chains are rich in rhamnose, galactose, and arabinose sugars. Moreover, the chains are often cross-linked by calcium ions, thus, improving structural integrity in pectin-rich areas. Lignin, hemicellulose, and pectin collectively function as a matrix and adhesive to hold together the cellulosic framework structure of natural fiber composites.

1.2.3 Characterization and properties of natural fibers

Natural cellulosic fibers can originate from different parts of plants. Fibers are commonly categorized as seed (e.g., from cotton and kapok), stem or bast (e.g., from flax, jute, hemp, kenaf, and sugarcane), and leaf (e.g., from pineapple and banana) fibers (Namvar et al., 2014). These fibers can be acquired from plants grown principally for fibers (e.g., cotton, flax, hemp, and kenaf) or from plants in which fibers are basically a secondary product, such as from coconut (the strands are often referred to as “coir”), sugarcane, banana, and pineapple. Nonetheless, some fibers have not been broadly utilized due to restricted accessibility, trouble in extraction, lesser execution related properties, and constrained developing areas. Furthermore, some plants yield more than one type of fiber. For example, jute, flax, hemp, and kenaf have both bast and core fibers. On the other hand, agave, coconut, and oil palm have fruit and stem fibers while cereal grains have stem and hull fibers. Besides that, bast fibers obtained from inner bark or phloem of dicotyledonous plants contribute toward textural strength and stiffness of plants’ stem. These fibers are located under a thin bark and become fiber bundles or strands when the length of stem is parallel. In general, bast strands vary in length, however, are often up to 100 cm with widths of almost 1 mm.

1.2.3.1 Hemp

Early in the 20th century, cannabis was extensively planted. Its stagnation skin fiber is promoted as a raw textile fiber material, which can be employed for assembly of fiber merchandise, clothing, sails, rope, paper, and medical supplies. Nevertheless, hemp fiber has been solely used for manufacturing rope in ancient times. Since the 90s, in conjunction with the increase of worldwide environmental pollution, people’s eyes have turned toward a nonpolluting bactericide resource, which might be recycled and is referred to as green resources. Hence, cannabis has been reentering people’s mind, since it is the oldest textile crop. In addition, because of extended growth of fabric technology, excellence of hemp fiber continues to be enhanced. This has unearthed utilization of marijuana for comfort purposes. Nevertheless, hemp fiber and textile manufactured from it have shown a fantastic performance.

Hemp is the common name for plants under the genus Cannabis. Besides that, hemp is noted as the oldest cultivated fiber plant by man. The plants grow to 4.5 m in height within 140 days with a stem diameter of 4–20 mm. Technically, hemp is the source of two natural fiber varieties: bast (used primarily in paper and textile industries) and woody core hurds. Hemp stem consists of roughly 20–40 wt% of bast fibers and 60–80 wt% of hurds. The hurds accommodate 40%–48% cellulose, 18%–24% hemicellulose, and 21%–24% lignin (Shahzad, 2012). Other than that, bast fibers contain higher amounts of polyose (57%–77%) while content of hemicellulose (9%–14%) and lignin (5%–9%) is lower compared to woody core fibers.

Furthermore, a cross section of hemp stem reveals its complicated structure consisting of various layers predetermined in the stem (Fig. 1.3). The external surface of the stem, covered with bark, denominates the epidermis. Within hemp stems are bast fibers and hurds. The bast fibers are connected by a middle lamella, primarily composed of pectin, and organized in bundles forming a ring around the outer part of stem. Additionally, every fiber bundle consists of single strands of fiber. There are two forms of fibers: useful primary fibers (5–55 mm long) and short secondary fibers (2 mm long). In distinction to top quality bast fibers, hurds are the least valuable part of a plant, with chemicals situated very near the wood.

Figure 1.3 Cross section of hemp stem (Stevulova et al., 2014).

Chemical composi...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• 1. Introduction to Natural Fiber Reinforced Vinyl Ester and Vinyl Polymer Composites
• 2. Natural fiber reinforced vinyl polymer composites
• 3. Recent Advances in Polyethylene-Based Biocomposites
• 4. Optimization Method of Injection Molding Parameters for Vinyl-Based Polymer Composites
• 5. Fabrication and Effect of Immersion in Various Solutions on Mechanical Properties of Pultruded Kenaf Fiber Composites: A Review
• 6. Properties of Betel Nut Husk Reinforced Vinyl Ester Composites
• 7. Sugarcane Bagasse-Filled Poly(Vinyl Chloride) Composites: A Review
• 8. Mechanical Properties and Morphological Analysis of Roselle/Sugar Palm Fiber Reinforced Vinyl Ester Hybrid Composites
• 9. Mechanical Properties of Mengkuang Leave Fiber Reinforced Low Density Polyethylene Composites
• 10. The Effect of Titanate Coupling Agent on Water Absorption and Mechanical Properties of Rice Husk Filled Poly(vinyl Chloride) Composites
• 11. Development of Sugar Palm Fiber Reinforced Vinyl Ester Composites
• 12. Taro Powder (Colocasia esculenta) Filler Reinforced Recycled High Density Polyethylene/Ethylene Vinyl Acetate Composites: Effect of Different Filler Loading and High Density Polyethylene Grafted Glycolic Acid as Compatibilizer
• 13. Physical, Mechanical and Ballistic Properties of Kenaf Fiber Reinforced Poly Vinyl Butyral and Its Hybrid Composites
• 14. Hybridization of Commercial Fillers With Kenaf Core Fibers on the Physical and Mechanical Properties of Low Density Polyethylene/Thermoplastic Sago Starch Composites
• 15. Poly(Vinyl Chloride)/Epoxidized Natural Rubber/Kenaf Powder Composites: Preparation and Properties
• 16. Characterization and Properties of Biodegradable Polymer Film Composites Based on Polyvinyl Alcohol and Tropical Fruit Waste Flour
• 17. Comparison of Processing and Mechanical Properties of Polypropylene/Recycled Acrylonitrile Butadiene Rubber/Rice Husk Powder Composites Modified With Silane and Acetic Anhydride Compound
• 18. Electrical–Based Applications of Natural Fiber Vinyl Polymer Composites
• Index