Polymer-based composites are the materials that are attained by the combination of composites and that is why the properties and the characteristics which are exhibited by the polymer-based composites are impossible to be found anywhere else.

The uniqueness in the working mechanics of polymer-based composites makes them one of a kind and as a result, they exhibit applications that are highly authentic and exceptionally excellent in their performances.Their applications are so vast that they can be found in almost every field, for example, marine, civil, aerospace, biomedical, etc. As the times have progressed so have the researches in the said field which have been carried out over time and have shown a drastic change in terms of advancements. All the applications have been discussed in depth in the following paragraphs in this article which furthermore reflect upon the importance of polymer-based composites.

Introduction

Since the start, polymer materials are considered to be advantageous and beneficial for numerous applications but due to less understanding of polymer materials, they were not used to their potential. Although, now the other materials have been displaced gradually by the polymer materials rapidly in most of the applications. They are also considered as materials of the first choice now for various applications because of enhanced knowledge and research. The areas which were not suitable for considering polymers to be in back then are now showing suitability with polymers as there are developments of more advanced materials from polymers to be used on a daily basis. In applications, for instance, medical, automobiles, aerospace, and constructions, ceramics and metals are recently replaced by polymer. Polymer materials will stay at the top now because of the polymer material's sustainability potential and inherent characteristics.

In composite material’s formulation, almost all of the polymer’s limitations are being taken care of. Also, researchers and scientists are handling the adaptation to positive environmental influence. Therefore, in this review, the polymer-based composites, their best application areas, and their importance in the advancement of humanity are discussed in detail.

Evolution of various materials

Since the start of time, from Stone Age to the plastic age, there were different materials in order but now there is a need for enhanced and advanced materials so that the materials can meet the requirements and function at their best. The polymer has undoubtedly remarkable characteristics for applications in vast areas, making it a dominant and best material ever. No doubt, it is a 21st-century material. In order to perform best in various fields, the material needs to have properties of such level, which is done when other materials reinforce the polymers for forming composites. Therefore, one most efficient method for influencing the polymer’s characteristics is the production of polymer matrix-based composites (PMCs).

Thermoplastic and thermoset are the two matrix forms of these polymer composites. Because of high-temperature resistance, reprocessing flexibility, no curing, low moisture content, high strength, and lower manufacturing cost, huge attention is gained by the thermoplastic-matrix based composites, but the most common ones are the thermoset-matrix based composites

Polymer matrix composites

Polymer matrix composites are capable of having either inorganic or organic polymer as the matrix or continuous or short fiber, particles of the range of millimeters to nanometers as the reinforcing material. With the usage of the polymer matrix, the fibers are firmly bonded together, the load is transferred to the fibers, and the applied load is distributed uniformly between the fibers. Meanwhile, due to their higher modulus and strength, the fibers work as the significant load-bearing component. These constituents play a major role that’s why their separate characteristics are known before their selection and merging.

Properties of the polymer-based composites

When the polymer-based composites are together, they offer remarkable characteristics like the required thermal expansion features, economic efficiency, easy fabrication, resistance to corrosion and wear, good resistance towards fatigue, high specific strength, high stiffness, and lightweight. The polymer-matrix composites are of huge importance in various fields like household, construction, energy, military, industry, marine, sports, communications, electronics, civil, medical, aerospace, and the automobile because of their characteristics.

Because of the polymer matric composite’s comparatively low processing temperatures, the polymer matrix composites are easy to fabricate than the ceramic-matrix and metal-matrix composites. Engineers and researchers are propelled by the increased need for innovations, energy-efficient technology, and sustainability to start producing natural biodegradable polymer composites instead of synthetic ones for promoting sustainable development. Due to this, the natural fibers from animals and plants have attracted a huge amount of attention. Examples are silk, hair, keratin wool, Kevlar wool, coconut coir, sugarcane bagasse, abaca, ramie, rice husk, kenaf, sisal, bamboo, flax, jute, cotton, and hemp.

Advanced composites

The huge enhancement in their tri-biological, structural, and mechanical characteristics makes these advanced composites, mainly of biodegradable sources, a better alternative than the conventional materials. The material’s characteristics like their wear resistance, electrical conductivity, thermal stability, fracture toughness, stiffness, and strength improve drastically when the natural fibers are utilized as reinforcements specifically in the nanometer range, resulting in them being very appropriate for applications in different and various fields, for instance, military, aerospace, marine, biomedical, automobile, and construction.

For analyzing the material’s wear resistance characteristics, flexural strength, compressive strength, and tensile strength, Singha and Thakur formed a polymer composite by synthesizing Hibiscus Sabdariffa’s natural fibers with a phenol-formaldehyde resin matrix. According to the results, the wear resistance and mechanical characteristics improved up to 30% with the fiber reinforcement building it appropriate for the automotive and other such industries. Arjmandi et al. researched the usage of the rice husk's (RH) natural fiber with diverse polymer matrices like polylactic acid (PLA), polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE) for forming polymer composites. This work was reported by Prabhakar et al.

Outcomes of the research

The work’s findings assured that the utilization of Rice husk in polyethylene enhanced the mechanical characteristics significantly, resulting in it being an appropriate composite material for construction and building. For reinforcing resorcinol-formaldehyde, natural cellulosic fiber was used by Thakur et al. The resulting polymer composite is appropriate for various industrial applications because of their enhanced mechanical and wears resistance characteristics.

Natural fillers, for instance, cellulose, animal fibers, and seed shells reinforce the polymer bio-composites, making them good for applications in biomedicine because of their resorbability and biocompatibility. In polymeric organic matrix composites, Kevlar (an aramid fiber) is utilized as a reinforcement and has attracted a lot of attention from scientists because of its thermal stability, stiffness, lightweight, and high tensile strength.

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Use of Kevlar in the composites

In composites, the utilization of Kevlar allows for the development of high-performance materials and resource efficiency, making it appropriate for applications in numerous fields, for instance, brake pads, chassis, vehicle's different body parts, cables, ropes, bicycle tires, propellers in aircraft, landing gear doors, radomes, helicopter’s rotor blades, bulletproof vest for defense, ballistic face masks, and combat helmets.

In the field of biomedicine, for delivery of the drug, healing of the wound, and tissue engineering, these keratin-based biomaterials have enormous usages because of their excellent biocompatibility and intrinsic biological characteristics. Keratin makes up the significant structural constituent of horn, wool, hooves, feather, and hair, as it is a fibrous protein. It is available in an abundant amount as a by-product from slaughterhouses and poultry.

Due to their characteristics like being eco-friendly, cheap, lightweight, thermal, and acoustic insulating, the usage of natural fibers as reinforcement has attracted a lot of researchers. Here, we are talking about natural fibers of cotton, keratin, coir, banana, jute, and sisal. Their characteristics make them good and beneficial for applications in several industries, for example, civil, and military structures, consumer goods, transportation industry, and biomedical industry.

Advanced research for better sustainability

There is now more research going on the available polymer resources, for instance, waste plastics, for sustaining the demand of light-weight materials for applications in automobile and other commercial purposes. Right now, the efforts are on promoting the usage of secondary materials instead of producing new ones in response to the demand of the globe for the new materials. Other than the improvement of the polymer composite’s properties, there are some natural fillers that are assumed of enhancing the degradation and mechanical characteristics of synthetic polymers, and because of the accelerated degradation, it is advantageous to the environment. In this paper, the focus is on the advantages given by the fiber-reinforced polymer composites for applications in several fields as compared to the advantages given by conventional materials.                            

The recent finding of hybrid composites

Due to improved mechanical characteristics, hybrid composites are being used because their characteristics are most suitable for aerospace applications. Aircraft's rain erosion resistance and specific strength are improved by using the hybrid kenaf/glass fiber reinforced polymer composites, whereas, when carbon fiber is utilized to form the aircraft bakes for an enduring temperature of almost 1200 C, silicon carbide is reinforced by the carbon fiber. In A-series aircraft’s several components, the hybrid FRP composites are used broadly. In A320 aircraft, by utilizing the FRP composites, we save 800 kilograms of weight.

Uses of Polymer Matrix Composites

Automobile Application

PMCs are consumed in a large amount in the automotive industry because of their lightweight and less cost. PMC's mechanical characteristics are very significant for designing vehicles to an extent that they meet all of the requirements, including a deduction in the automobile’s weight, therefore promoting the fuel efficiency, and also reducing the emission of exhaust, thus lessening the air pollution. According to the estimation, if there is a 25% reduction in the weight of the car, 250 million barrels of crude oil can be saved, while if there is a 10% reduction in car's weight, there can be a 6-8% increase in the fuel efficiency. Although, when trying to achieve this, the safety of the passengers should not be sacrificed. So, when the vehicle is being designed, the most significant factors are three, including, the safety of the passenger, fuel efficiency, and lightweight.

Because of their biodegradability, low cost of production, resistance to abrasion and corrosion, vibration and noise reduction, high impact energy absorption, design flexibility, high stiffness, high strength, and lightweight, the perfect materials for such applications are natural fiber polymer composites. PMCs are utilized at some of the various parts in the manufacturing of automobiles. Some of those parts are body stiffener, chassis, parcel shelves, fire engine, pedal box system, seatback, spoiler, dashboard, connecting rod, refrigerated truck linens, boot linen engine cover, bumper system, and door panel.

Natural fiber polymer composites

In some parts of automobiles, the usage of natural fiber polymer composites (NFPC) has some problems like high flammability and high moisture absorption, making it difficult to address these issues for preventing these complications to occur during service. Therefore, they combine with synthetic fibers via techniques of hybridization for making hybrid composites. These hybrid composites are comparatively more cost-effective and have more remarkable structural and mechanical characteristics. According to several analysts and researchers, the usage of hybrid polymer composites in the automobile can reduce weight to 20-40%, lasts 10 years longer as compared to the conventional vehicles, therefore resulting in a new trend in the selection of materials for applications in automobiles.

Recently, an investigation was done on the utilization of recycled waste plastics in automobiles for arresting the pollution problems that the waste plastics emanates. According to the research, the bio-filler-recycled waste plastic-based composites were best suited for most automobile interiors like floor panel or door sills, as there is a requirement of moderate water resistance, good wear, and mechanical characteristics. According to the work, the developed bio-composite will easily degrade after reuse because of the aging, after it is disposed off.

Aerospace Application

The aerospace industry uses advanced composites in huge amounts. In the United States, 50% of the total advanced composites are consumed by the aerospace industry. The reason for the aerospace industry using advanced composites this much is the same as the reason for the automotive industry to use it. In the aerospace industry, the three main concerns are radiation shielding, cost savings, and weight reduction. The most crucial concern is weight reduction as it affects various factors like increasing range, maneuverability, number of assembled parts, speed, and fuel efficiency. Fuel savings and weight reduction are the two biggest benefits given by lightweight polymers to the aerospace industry.

According to Koniuszewska and Kaczmar, a fleet of almost 600 planes is operated by American Airlines. If they lessen 1 pound from the weight of every aircraft then they can save almost 11,000 gallons of fuel per year. In the production of aircraft, the process can be made cheap by making some changes, for instance, lessen the tooling cost, instead of metal alloys the fiber-reinforced polymer composites should be used, lessen the number of assembled parts, therefore making it less expensive as there will be no need to join several parts together, and there will be no need of maintenance. Also, because of the variations in the condition of the environment in advanced PMCs, property variations can be obtained.

Marine Application

Because of the remarkable engineering characteristics of advanced composites, the marine industry has been using them extensively in recent times. The major drivers for its extensive usage in the marine industry are its environmental sustainability, cost savings, and weight. Manufacturers were forced to make and use new innovative processes and materials while also keeping in mind the product's life cycle for developing high-performance engineering components simultaneously, therefore ensuring an eco-friendly environment. It's because of such demands that the biodegradable polymer matrix composites' (eco-composites) incorporation was needed as they help in reducing the hazardous and toxic materials, helps in recycling of the materials and also helps in reducing the waste and polluting air emission, meanwhile giving excellent mechanical characteristics too.

Biomedical Application

One of the leading industries in using polymer composite materials is the medical field. They are being used in the applications of biomedicine because of their excellent characteristics, including their compactness, biomimicry, biocompatibility, bioresorbability, precise control, biodegradability, and compatible mechanical strength. Because of the bio-compatibility of the biopolymer materials, the living material’s morphological properties can be smartly imitated by the biopolymer materials. Some of their application areas are surgical implants, antimicrobial materials, blood vessels, ligament and bones application, regenerative medicine, drug delivery, protein immobilization, oral tissues, dental usage, tissue engineering, medical devices, and wound dressing.

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Use of natural polymers in the biomedical field

Synthetic polymers and natural polymers are used in the field of biomedicine. This field also uses fibers as its reinforcement's major form. Synthetic polymers that are included here, are polyester -amides (PEA), poly lactic-co-glycolic acid (PLGA), polycaprolactone (PCL), polylactic acid (PLA), polyglycolic acid (PGA), polyamide (PA). The included natural polymers are cellulose, starch, pullulan, psyllium, pectin, agar, alginates, guar gum, collagen, and chitosan. The polymer composites are also utilized widely in biomedical applications as soft (skin) and hard (bone) tissues.

Bones

Many constituents like the blood vessels, collagen fibers, mucopolysaccharides, bone cells, and hydroxyapatite (HA) nanocrystals form the bone. The animal’s waste bones can easily give off hydroxyapatites, which are utilized continuously for grafts and bone fillers. Their continuous usage is inclusive of their osteoconductivity characteristics which allow for the osteoprogenitor cell’s quick development. Therefore, serving as bone fillers to help in repairing the bone fracture, which is the most common sensitive disorder to bones.

For repairing the bone, both synthetic and natural degradable polymer composites are utilized as scaffolds in a broad range because of their remarkable biological and mechanical characteristics. Despite these materials being good for biomedicine, the environmental impact and sustainability were also measured, and therefore, for HA synthesis, environmentally sustainable processes are being developed and utilized for the formation of hydroxyapatite powders (HAp). Right now, all the manufacturing processes are being done to synthesize hydroxyapatite powders (HAps) from both animals and plants.

Skin

Being the body's first immune system organ, the skin is the body's one of the most major parts. The skin prevents the antigens and pathogens from entering the body as it has layers. Still, there are many conditions that they are exposed to. Some of them are necrosis, burns, and skin infections.

Researchers are very interested in using biocompatible and biodegradable polymer composites for skin regeneration. Polymeric materials are utilized as drug delivery materials as they are very appropriate and ideal for drug delivery systems. For example, the polymer-based hydrogels are utilized as carriers for the drug molecules like antifungal, antibiotic, and anticancer drugs. They are also utilized for providing a shield to the site of the wound and aid in quickening the process of healing as well as for tissue engineering so that the damaged or lost tissue can be reproduced by helping in the development of new cells.

All the other benefits

In aircraft, the usage of fiber-reinforced polymer (FRP) composites is very beneficial because of its tri-biological, electrical, and mechanical characteristics. Other commendable benefits in utilizing the fiber-reinforced polymer composites in aircraft are its resistance to fracture, characteristics of vibration-damping, decreased noise level, durability, improved impact and damage tolerance, resistance to heat and flame for interior panels, improved stiffness and strength, enhanced resistance to fatigue and corrosion, lessened scrap, and design flexibility. Such characteristics make the polymer composites suitable for the components like tail assemblies, food tray arms, vertical fins, fittings, airframe, aircraft wing boxes, fuselage, brackets, rotors, window frames, bulkheads, and aircraft brakes.

Conclusion

Polymer-based composites as discussed above hold great importance in almost every field due to the remarkability that is exhibited by them in terms of their properties and characteristics. A lot of researches have been carried out by various researchers in this said regard and all of them have reflected upon the in-depth importance of these polymer-based composites. The vast range of applications is evidence of the specificity that these polymer-based composites are capable of. 

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References:

https://www.hindawi.com/journals/ijps/2020/8834518/

https://novapublishers.com/shop/polymer-matrix-composites-types-applications-and-performance/

https://www.sciencedirect.com/topics/materials-science/polymer-composite

https://www.researchgate.net/publication/299613517_Application_of_Polymer_Based_Composite_Materials_in_Transportation#:~:text=Polymers%20and%20polymer%2Dbased%20composites,5%5D%5B6%5D%5B7%5D.