Hybrid Fibre Based Composites with Nano Particles

Hybrid composite materials bring a revolution in the real-life commercial applications such as biomedical, aerospace, shipping industry, automobile, biomedical, construction, drug delivery, wound dressing and gas filtration applications.

In recent years, many researchers have been showing an interest in the utilisation of natural fibres for the preparation of hybrid composites because of its abundance, low density, recyclability and great strength, Natural fibres received a great deal of consideration as a potential elective alternative for synthetic fibres as a support of different reinforcement for innovative applications due to their properties, for example, their availability in nature, low cost and they are environmentally friendly. Their resources do not emit any harm full gasses and absorb carbon dioxide, which reduces environmental pollution.

One of the primary drawbacks of using natural fibres as reinforcement in composites is the hydrophilic in nature, which makes them inconsistent with hydrophobic matrices. For refining the inconsistency, the surface treatment of natural fibre is required to advance the global properties of the composite. Apart from this, natural fibres are readily accessible to the flame, to overcome this drawback, various fire retardants have been added to them to advance its fire resistance. Surface modifications by using various chemical compounds tend to increase their mechanical and physical properties. And also, structure modification of the composite materials leads to extra stability.

Over the previous years, there has been an ever-expanding enthusiasm to fuse at least two fillers into a typical matrix. There has been a consistent increment in the quantity of distributed works that are identified with hybrid composites from the past ten years. in view of hybrid composites (between 2010 to 2020) found in the Web of Science and Scopus via looking for the words ‘hybrid composites’ with 26,450 research yields. The development came about because of one goal, to progress the properties of the subsequent composite material to accomplish the wanted properties and improved execution of such composites.

The total research outcomes on hybrid composites in recent years and the input was from the Web of Science have been determined. Most of the research articles are from China, followed by India. The hybridisation process intersects the most research articles, for example; material multi-disciplinary, chemical industry, polymeric science, nanoscience, nanotechnology, material science engineering, electrochemistry, mechanics and mechanical engineering so on.

The total research publications on natural fibre hybrid composites have been determined. The input was from the Web of Science by searching for “natural fibres and hybrid composites.” There is a total of 1460 research yields, with most of the researchers from material science and polymeric science engineering. The process of the hybridisation of natural fibre composites started in early 2008 and then the interest slightly increased. The main aim is to improve the composite properties by adding two or three different filler materials under the same matrix material. Many researchers proved that the orientation of filler material also plays a key role in the composite.

 Hybrid Composites are the materials that are made up of twofold or more constituent materials, namely matrix and reinforcement. A matrix is a coupling material which binds the reinforcement. Reinforcements are the materials which are embedded in the matrix. These give the additional strength to the composite. The significance of the composites is to provide the desired physical, chemical and mechanical properties in an improved manner, which differs from the individual constituents. Based on the matrix, composites are categorised as polymer, ceramic and polymer. Depending upon the reinforcement these are varied as laminate, fibrous and particulate composites. Depending upon the type of availability, reinforcements are classified as either natural or synthetic.

If the compound material is metal fibre then it is called a metal matrix composite, if it is a polymer matrix then it is called a polymer matrix material. The fibre reinforced polymers (FRP) consist of a polymer matrix and high-quality fibres joined with an unmistakable crossing point among them. In this shape, the two matrices and fibres hold their chemical and physical properties.

Natural hybrid fibre composites

Natural hybrid composite materials contained fibres of great quality and a modulus introduced in a matrix material. Along these lines, every one of the individual materials (fibre and matrix) holds its chemical and physical properties and they give a combination of properties which would not be conceivable if they were utilised alone. Here, the fibres act as the central load-carrying agents and the matrix material encompasses them in position alongside, acting as a load carrying part between them, protecting the fibres from the natural harms of raised temperature and humidity. Accordingly, it could be properly said that the fibre gives reinforcements to the matrix; thus, the name Fibre Reinforced Composite Materials (FRCM).

Reinforced hybrid materials are made by joining at least two distinct varieties of fibres in a distinctive matrix material. Hybridisation of two sorts of filaments with particular lengths and widths offers a couple of central focuses over the use of both of the strands alone in a lone polymer lattice. Most studies are on the hybridisation of regular filaments with glass strands to upgrade the properties. They have average calorific regard and cause little stress, similar to prosperity, wellbeing and protecting Also, they show amazing mechanical properties, have a low thickness and are modest. The benefits of composite materials by confessional materials, such as greater rigidity and durability, make them more flexible to use. The availability and cost of these natural fibres attract researchers and also have promising results of composite fabrication for real-life applications. Composite materials are comprised of at least two materials with physically detachable phases.

The following aspects have been considered

• Characterisation of Composites
• Metal Matrix Composites (MMCs)
• Ceramic Matrix Composites (CMCs)
• Organic Matrix Composites (OMCs)
• Fibre Reinforced Polymer Composites (FRCs)

Natural fibres: Natural fibres are produced from animal (protein is the main component), plant (cellulose is the main component) and mineral based resources. Natural fibres have advanced physical and mechanical characteristics when compared to the other fibres. They are readily available in nature and also biodegradable. Because of its lightweight, high strength, low cost and corrosion resistance properties it is drawing attention for use in industrial applications. On the other side, natural fibres have few disadvantages, like high water absorption, high anisotropy, less homogeneity when compared to the synthetic fibres, development of stresses among the fibres in a composite.

Natural fibres has lightweight, high strength, low cost and corrosion resistance properties.

The chemical composition plays a significant role in fibre materials and it depends on the fibre source. It varies from fibre to fibre and also within the family. Their performance is mainly dependent on the aspect/ratio and cellulose crystallinity of the fibres. Previous studies stated that these fibres are biodegradable because of their chemical constitutes. For example, UV degradation because of lignin and hemicellulose is accountable for thermal and biodegradation and also water absorption. The physical and mechanical properties of the natural fibres have been determined. Cellulose, hemicellulose and lignin are the main components in the natural fibres. Due to the nature of development conditions, the percentage of these components varies accordingly. To consider the behavior of these fibres, it is important to consider the structure of the components. Cellulose is one of the major building blocks of the natural fibres, it makes up around 50 per cent of plants. The presence of cellulose in the plant fibres has an impact on moisture absorption. Hemicellulose is the second major component followed by cellulose and it is less remarkable as a filler material. Phenylpropane derivatives is comprised of lignin and it is a formless normal polymeric material that controls the transaction of fluid and also combines the hard cells in the plant. Lignin acts as a cementing material and it influences the structure, properties and morphology.  Some of the advantages and disadvantages of natural fibres are explained in Table 1 below.

Synthetic Fibres: There are various man-made or synthetic fibres that have been brought into recent research networks with respect to their remarkable properties. The mechanical properties of synthetic fibres have been determined. Among all synthetic fibres, glass and carbon fibres are the most used filler materials in the hybrid composites. These fibres are manufactured by using the polymerisation concepts, which includes joining monomers to form a great chain. The merits and demerits of synthetic fibres have been explained.

Among all synthetic fibres, glass and carbon fibres are the most used filler materials in the hybrid composites

Chemical treatment of natural fibres: Natural fibres are not defect-free materials even though they have great qualities when compared to the other advanced fibres. They have strong polar bonds, which may affect the bonding capability in the polymer matrix. To avoid this, some sort of chemical treatment is required to improve it. Chemical treatment is one that gives additional strength to the composite material to develop a relationship between fibre and matrix material during the curing process. It also improves the surface quality and decreases the amount of water absorbed (Moisture content) by the composite material.

Chemical treatment is one that gives additional strength to the composite material to develop a relationship between fibre and matrix material

Selection of matrix materials for fabrication: A matrix material is one which plays an adverse role in the composite material. The shape, durability and surface properties depend on matrix (resin) material. Based on processing techniques, resin materials are classified into two types, such as thermosets and thermoplastics. A matrix is used as a load distributer among the reinforcement material when external pressure is applied. Thermoplastics are widely used resin material over thermosets because of its ready pick-up shape to the required mold (moldability). Thermosets are not recyclable because it does not come back to its original state when the resin is converted from liquid state to solid state after the curing process. Only a heating process is required for the thermoplastics to form a new shape.

The following have been considered

• Thermoplastics
• Thermosets
• Bio-Based Resins

Integration of Nano particles in natural fibre hybrid composites: Hybrid composites are not defected free materials because of the fabrication errors, voids in the composite, weak bonding between matrix and reinforcement, environmental conditions, errors during the development and curing period, scratches on the fibre materials, impurities, unbalanced proportion of matrix and reinforcement affect the total performance of the composite materials. Limiting the reasons for corrupting components can assist with keeping the presentation of composite materials. The addition of new constituents and material advancement quality control techniques is necessary to progress the performance of the hybrid composites. One of the best ways to overcome these problems is the integration of nanoparticles or nano constituents. Recent reports state that the addition of nanofillers in the composite materials showed greater improvement in mechanical properties such as tensile strength, flexural strength, creep strength, tensile strain, shear modulus, impact strength and also thermal properties than individual polymer-based hybrid composites.

Nowadays researchers are using three types of nano fillers to improve the performance of the composite material. They are classified into three main groups such as nanotubes, nanoparticles and nano layers. Nano fillers are used based on the particle sizes—one dimensional, two dimensional and three dimensional. Nanomaterials are larger than macro-level particles, individual atoms and also have a huge surface area per unit volume. Most of them are produced from metals, carbon, polymers and metal oxides. Nano clay, carbon nanotubes, carbon black and graphene are the best example of metal-based nano fillers and also widely used nanomaterials.

Pappu et al. worked on unused materials, like fly ash and sisal fibres, to prepare the micro and nanocomposites for multifunctional applications. The hand layup technique along with compression molding used for the preparation of composites, fly ash and sisal fibres were used as reinforcement and epoxy used as a matrix material. They prepared a total of two composites fabricated for comparison purposes. Results indicated that the presence of natural fibre and nano filler boost the performance of the composite, particularly the cellulose content in the sisal fibre and silica along with alumina in fly ash leads to the potential growth of mechanical properties. Majeed et al. reported on food packaging materials from natural fibre hybrid composites, which have nano filler as nano clay and developed a new method to enhance the bonding between matrix and reinforcement. The addition of nano clay to the hybrid, composite showed good progress in mechanical and thermal properties. But these are not suitable for all types of packaging applications because of higher biodegradability and moisture absorption properties than that of synthetic fibres. Essabir et al. investigated the mechanical and thermal properties of clay and palm fibre hybrid composites. They reported that the hybridisation of oil-palm incorporated with clay particles showed improved tensile and young’s modulus properties. Similar tests were reported by Arrakhiz et al. In this work, they reported the effect of mechanical and thermal properties of pine fibre reinforced with clay particles hybrid composites; the results were similar to those of the previous research. The addition of clay particles leads to the elimination the voids in the composite surface and adversely affect the surface properties and overall performance of the composite.

Nano clay particles are one of the most commonly used filler materials due to its availability and inexpensiveness. It comes under the silicate group nanomaterials. Nano clay particles in the composite material can increase the mechanical, physical and chemical properties. The size and shape of the particles also plays an important role in the composite material for the strength and bonding between reinforcement and matrix material. Toyota automobile industries first started using the nano clay particles in the polymer composite fabrication; in this research work, the author has shown the importance of clay particles as a filler material to create the interfacial bond between the matrix and reinforcement and an improvement in the physical and fracture toughness of the composite material. Due to advancements in the material properties by using the nano clay particles, the materials have been used in several functional and structural applications. The microstructure of the nanoparticles present in the material plays a key role in the improvement of mechanical properties.

Generally, nano clays are available in several forms such as nano clay platelets, calcined nano clay and natural montmorillonite (CB). Assaedi et al. investigated the effect of nano clay platelets (also called cloisite 30B) on the thermal and mechanical properties of fly ash geo polymer. In this study, the platelets are added by varying the weight percentages such as 1 per cent, 2 per cent and 3 per cent loadings. Results showed that adding the nano clay platelets to the geo polymer shows a slight increase in mechanical properties. Flexural strength and flexural modulus were increased significantly with an increase in nano clay loading up to 2 per cent weight loading. After 2 per cent weight, the properties of the materials slightly decreased due to porosity and poor dispersion. It is evident that continuous adding of the filler materials to the geo polymers does not increases its mechanical properties. On the other hand, Assaedi also stated the conditions for the temperature variant; he studied this by using the thermo-gravimetric analysis in terms of weight. It was observed that most of the weight loss occurred at 3 per cent nano clay loading due to extra friction.

Hakamy et al. studied the effect of calcined nano clay (CNC) on mechanical and microstructural properties of hemp fibre reinforced Portland cement nanocomposites. Calcined nanoclay was prepared by using the heat treatment process of nanoclay particles at 800, 850 and 900 °C temperature for 2 h. It was found that nanoclay converted into a calcined state at 900 °C. Experimental results suggest that the mechanical properties, such as flexural strength and fracture toughness, were improved by adding the CNC to the composite material. Calcined nanoclay particles were added by varying its weight percentages such as 1 per cent, 2 per cent and 3 per cent. The optimum hemp fabric content was found as 6.9  per cent and CNC was found as 1 per cent.

Eesaee et al. worked on the effect of nanoclay particles in the reinforced glass/woven fibre composites with phenolic resins and mainly dealt with the natural montmorillonite (CN) and artificial montmorillonite (CB). The filler material improved the composite performance because of the proper dispersion of nanoclay particles on the composite surface, which lead to better interfacial bonding with the matrix and reinforcement. It was exposed that the amalgamation of 2.5 wt. per cent of the filler material boosts the elastic modulus up to 38 per cent for CN and 43 per cent for CB. On the other side, aging with water molecules and hydroxyl groups of the phenolic matrix leads to a decrease in the strength of the composite.

Avil et al. observed the effect of porosity and failure strength in the presence of nanoclay in glass fibre reinforced epoxy composites. The results showed that the additional filler material caused the reduction of porosity by 73.2 per cent at 10 wt. per cent. Binu et al. studied the effect of nanoclay, cloisite 15A, on the mechanical performance and thermal properties of polyester-based glass fibre composites. The results showed a maximum mechanical performance observed at 1 per cent loading of the filler materials to the composite. According to this study, the glass transmission temperature failed in between 95 and 110 °C. John et al. observed the dynamic mechanical and thermal properties of cyanate ester syntactic foams besides the nanoclay material. The studies showed that a significant improvement in mechanical properties like tensile, flexural strength moduli was detected for the foams on the integration of nanoclay particles. Nanoclay hikes the toughness of the overall composite and, on the other hand, thermal properties are not much prejudiced by the addition of filler materials.

Maharsia et al. studied mechanical properties in syntactic foams through nanoclay reinforcement. Results indicated that the presence of nanoclay (2 per cent and 5 per cent by weight) showed an improvement in mechanical properties though there was a reduction in modulus due to improper bonding between nanoclay particles and matrix material. Withers et al. observed the effect of cloisite 25A montmorillonite (MMT) nanoclay filler material in epoxy-based composites. The nanocomposites were fabricated by varying the weight percentages of nanoparticles in it. According to the results, the optimum mechanical properties are shown at 2 wt. per cent of MMT clay addition. The improved surface properties are observed at the low percentage loadings of MMT clay particles. Mo-lin Chan et al. studied the mechanism of reinforcement in nanoclay polymer composite. Different mechanical tests were conducted by varying the content of nanoparticles in the composite material. Interestingly the results are showed that tensile strength and modulus of the composite increased by 34 per cent and 25 per cent correspondingly. The establishment of limitations between the nanoclay clusters and epoxy resin can filter the matrix grains and additionally improve the strength of the composite.

Applications

Fibre-reinforced composites are better than pure polymer composites. There should be an occurrence of auxiliary applications on account of its high mechanical properties and lower expense. Due to an account of advanced properties, hybrid composites are a replacement for synthetic composites, particularly when it comes to the load-bearing and construction applications. A recent study stated that goods made up of natural fibre composites have been increased and used in several applications such as ward boards, windows, car door panels, tables, packing selves and lightweight goods. The utilisation of natural fibre composites in place of synthetic and petroleum-based fibre composites has increased drastically in various sectors such as sports equipment, aerospace, office machinery, automobile, and shipping industries are one of the main application sectors for lightweight composite materials. The researchers found interest in the replacement of bio fibre-based composites due to its abundance, cost-effectiveness, recyclability, ecofriendliness, low fabrication cost and biodegradability.

A recent survey stated that the fabrication of fibre-reinforced polymer composites has become more popular in commercial applications, especially in the aerospace industry. The utilisation of fibre-based composite caused a reduction in overall weight by 35 per cent of the aircraft, and shows a positive effect on fuel consumption and efficiency of the overall performance. Due to these properties, aircraft industries such as Boeing, Dreamliner and Airbus companies have started using the composites in the majority of their components. The main crucial factor in composite fabrication is weight reduction. Some of the natural fibres serve as a natural filler material in the composite fabrication in the presence of bio-based and biodegradable matrix material designed for the extrusion film blowing of thin packages.

Santos da luz et al. worked on natural fibre composites in the replacement of synthetic fibre composites for military applications. They compared natural fibre (pineapple) epoxy composite material and synthetic (aramid) fibre composite material in a hard armor. Results showed that the armor plate made from natural fibres has a stronger impact strength than synthetic fibre plates. Natural fibre hybrid nanocomposites are used in various industries because of its improvement in mechanical, thermal and moisture absorption along with light weight and less cost. Nowadays, these composites are in construction, biomedical, filtration, drug delivery, tissue template, wound dressing and cosmetics. Some of the potential applications are listed below.

1. Filter media: Liquid, gas and molecule filtration.
2. Nano-sensors: Biochemical, thermal and piezoelectric sensor.
3. Cosmetics: Skin cleaning and healing.
4. Life science: Drug delivery carrier and wound dressing.
5. Tissue engineering scaffolding: Porous membrane for skin, 3D scaffolds for bone and cartilage regeneration.
6. Industrial applications: Micro/nano electronic devices, electrostatic dissipation, LCD devices, lightweight space craft materials.

Conclusion and future perspectives

In this review paper, fibre-based hybrid composites have been evaluated, specifically on account of their properties such as surface morphology, thermal stability, dynamic mechanical, mechanical, moisture absorption, fire retardance and applications. Hybridisation became famous, not just because of the improved presentation of the subsequent items, but also due to the possibility of conquering the confinements that hamper the relevance of common filaments in specialised structures. There is an immense chance that a huge level of natural fibres can be consolidated in ordinary engineered fortified composites items, which is a major advance from biological and affordable perspectives. The quality natural fibres rely on the development conditions and development time affects the performance of the composite. Although there are so many advantages to using natural fibres in commercial applications, it is bounded to some of the applications because of its biodegradability and flammable properties compared to synthetic fibre composites. To overcome this problem, the researchers started to work on chemical treatment of natural fibres under various conditions. These modifications improved the fibre strength and also bonding capacity between matrix and reinforcement. On the other hand, the researchers found an interest in the integration of nanofillers into composite materials. The addition of nanoparticles to the hybrid composites played a crucial role in advancing their properties. The surface properties, fracture toughness, void elimination, amount of water absorbed is decreased and the dynamic mechanical properties are increased because of these nanofiller materials in the hybrid composite. It is worth saying that hybrid composite materials bring a revolution in the real-life commercial applications such as biomedical, aerospace, shipping industry, automobile, biomedical, construction, drug delivery, wound dressing and gas filtration applications. In the future, the alterations in fabrication techniques and the addition of nanofillers may lead to improvement as well as prediction of the results is possible, which attracts researchers to use it in multiple applications.

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About the author

• S Karthikeyan is from the Department of Petrochemical Engineering, SSM College of Engineering, Komarapalayam, Tamil Nadu.

• Dr N Gokarneshan is from the Department of Textile Chemistry, SSM College of Engineering, Komarapalayam, Tamil Nadu.

• M Manoj Prabagar is from the Department of Mechanical Engineering, SSM College of Engineering, Komarapalayam, Tamil Nadu.

• V Sathya is from the Department of Costume Design and Fashion, Vivekananda College of Arts and Science, Tiruchengode, Tamil Nadu.

• Department of Fashion Design, SRM Institute of Science and Technology, Ramapuram, Chennai, Tamil Nadu.

• Department of Textiles, Sardar Vallabhai International School of Textiles and Management, Coimbatore, Tamil Nadu.

• School of Fashion Design, Footwear Design and Development Institute, Chennai, Tamil Nadu.