J Polym Eng 2021; 41(5): 339–355 Review Kawaljit Singh Randhawa* and Ashwin D. Patel A review on tribo-mechanical properties of micro- and nanoparticulate-filled nylon composites https://doi.org/10.1515/polyeng-2020-0302 MWNT Multiwalled carbon nanotube Received November 6, 2020; accepted February 20, 2021; PbS Lead sulfide published online March 15, 2021 PEEK Polyether ether ketone PTFE Polytetrafluoroethylene Abstract: Nylon composites are of evolving interest due to SiO2 Silicon dioxide their good strength, toughness, and low coefficient of fric- UHMWPE Ultra-high-molecular-weight polyethylene ZnF Zinc fluoride tion. Various fillers like micro- and nanoparticulates of 2 ZnO Zinc oxide metals and metal compounds were used to enhance the ZnS Zinc sulfide mechanical and tribological properties of nylons for many ZrP Zirconium phosphate years by researchers. In this paper, an overall understanding of composites, filler materials, especially particulate filler materials, application areas of polymer composites, wear of 1 Introduction polymers, and the effect of various fillers on tribo- mechanical properties of nylons have been discussed. The A composite is a material that consists of two or more detailed review is limited to micro- and nanoparticulate chemically different constituents that are combined at a fillers and their influence on the mechanical and tribological macroscopic level and are not soluble in each other to yield a properties of various nylon matrices. useful material. Composite materials have been widely Keywords: friction; mechanical properties; nylon applied in various applications like aeronautical industries, composite; tribological properties; wear. biomechanics, public infrastructure, automobile industries, furniture. Composites have unique advantages over many monolithic materials, such as high strength, high stiffness, Nomenclature longer fatigue life, low density, and adaptability to the intended functions of the structure [1–8]. ABS Acrylonitrile butadiene styrene A few examples of composites are shown in Table 1. Al2O3 Aluminum oxide CaF2 Calcium fluoride There are several benefits of composites mentioned as CaO Calcium oxide follows: COF Coefficient of friction – Light weight: composites can be made light in weight fl CuF Cuprous uoride to replace any heavier material. Their lightness is CuO Copper oxide CuS Copper sulfide important in automobiles and aircraft, for example, GRF Graphite fluoride where less weight means better fuel efficiency. People GRP Glass(fiber) reinforced plastic who design airplanes are greatly concerned with HDPE High-density polyethylene weight since reducing an air craft’s weight reduces the HNT Halloysite nanotubes amount of fuel it needs and increases the speeds it can LDPE Low-density polyethylene reach. MoS Molybdenum sulfide – High strength: composites can be designed stronger. MoS2 Molybdenum disulfide Metals are equally strong in all directions, but composites can be engineered and designed to be *Corresponding author: Kawaljit Singh Randhawa, Mechanical strong in a specific direction. Engineering Department, CSPIT, CHARUSAT University, Changa, – Strength to weight ratio: strength to weight ratio is a Anand 388421, Gujarat, India, ’ E-mail: [email protected]. https://orcid.org/ material s strength to how much it weighs. Some 0000-0002-2944-6714 materials are extraordinarily strong and heavy, such as Ashwin D. Patel, CSPIT, CHARUSAT, Changa 388421, Gujarat, India steel and other metals. Composite materials can be 340 K.S. Randhawa and A.D. Patel: Tribo-mechanical properties of nylon composites designed to be both strong and light. This property is Apart from all these, composites are also used in why composites are used to build airplanes, which consumer goods products, agriculture, computer hard- need a remarkably high strength material at the lowest ware, and many more places. possible weight. A composite can be made to resist Composites can be classified according to the: bending in one direction. – Matrix material used – Corrosion resistance: composites resist damage from – Reinforcing element used, and the weather and harsh chemicals. Composites can be – The orientation of fibers/particles and numbers of used where chemicals are handled or stored. Com- layers. posites can be used in humid areas. It can be used in an open rainy atmosphere. A few examples of available matrix materials are shown in – High-impact strength: composites can be made to Table 3. absorb impacts like the sudden force of a bullet, for Depending on the matrix material used, composites instance, or the blast from an explosion. Because of are classified as thermoplastic/thermoset matrix compos- this property, composites are used in bulletproof vests ite, metal matrix composite, and ceramic matrix and panels, and to shield airplanes, buildings, and composite. military vehicles from explosions. A few general properties of matrix materials are – Low thermal conductivity: composites are good mentioned in Table 4. insulators. They do not easily conduct heat or cold. Following are the functions of matrix materials: They are used in buildings for doors, panels, and – Holds the fillers windows where extra protection is needed from severe – Protects the reinforcing particles/fillers from weather. contamination – Durability: structures made of composites have a long – Helps to maintain the distribution of fillers life and need less maintenance. Composites can replace – Distributes the loads evenly other materials where durability is the main issue. – Enhances some of the properties of the resulting ma- – Nonconductivity: Most of the composites are non- terial and structural component (that filler alone is not conductive, meaning they do not conduct electricity. able to impart) such as tensile strength, impact This property makes them suitable for such items as resistance electrical utility poles and circuit boards in electronics. – Provides a better finish to the final product. If electrical conductivity is needed, it is possible to make – Supports the overall structure. some composites conductive. – Wear resistance Reinforcing elements may be in the form of particles, – Fatigue life flakes, or whiskers. According to that, the following are the – Acoustic insulation classifications of reinforcements: – Attractiveness – Fiber reinforced: in which, length to diameter ratio is – Damping properties: composite materials can be remarkably high (of the order 1000). Continuous fibers engineered to get the desired damping properties. are essentially characterized by one exceptionally long – Temperature resistance. axis with the other two axes either often circular or near-circular. A composite with fiber reinforcement is And composites have many more advantages. Composites called a fibrous composite. can be made to fulfill the requirements of properties that – Particle reinforced: in which particles are used as rein- only one single material cannot fulfill. Current application forcement. These particles do not have any long areas of engineered composites are shown in Table 2. dimensions. Generally, particles have neither preferred orientation nor shape. A composite with particles as Table : Natural and engineered composites. reinforcement is called a particulate composite. – Flake reinforced: flakes are small in length direction Natural composites Manmade/engineered composites compare to continuous fibers. Wood (fibrous composite) Concrete (particulate composite) – Whisker reinforced: whiskers are nearly perfect single Bone (fibrous composite) Plywood (fibrous composite) crystal fiber. Whiskers are short, discontinuous, and fi Granite (particulate composite) Fiberglass (short brous composite) have a polygonal cross-section. K.S. Randhawa and A.D. Patel: Tribo-mechanical properties of nylon composites 341 Table : Application areas of engineered composites. Automotive sector Aerospace sector Sports Transportation Infrastructure Biomedical industry Car body Nose Tennis rackets Railway coaches Dams Artificial legs Brake pads Aircraft, rocket, and missile body Hockey sticks (glass fiber Ships Bridges Dentistry Driveshafts Doors composite) Trucks Artificial joints Fuel tank Struts Bikes Hoods/bonnet Trunnion Boats Spoilers Fuel tanks Golf Satellite frames and other structural parts Antenna (smart materials) Table : Matrix materials. purposes of heat resistance or conduction, corrosion resis- tance, and provide rigidity. Reinforcement can be made to Thermoplastics Thermosets Metals Ceramics perform all or one of these functions as per the requirements. Polypropylene Polyesters Aluminum Carbon Areinforcementthatembellishes the matrix strength must be Polyvinyl chloride (PVC) Epoxies Titanium Silicon stronger and stiffer than the matrix and capable of changing carbide the failure mechanism to the advantage of the composite. Nylon Polyimides Copper Silicon nitride Polyurethane Tin Briefly, it must Poly-ether-ether ketone – Contribute desired properties (PEEK) – Be load-carrying Polyphenylene sulfide (PPS) – Transfer the strength to the matrix. Table : General properties of matrix materials. Figure 1 shows the classification according to the orienta- tion of fibers/particles and the layers. Thermoplastics/ Metals Ceramics thermosets Operating Higher use operating Extremely 1.1 Classifications of particulate fillers temperature range temperature range high-temperature < °C (> °Cupto °C range > °C Various metals and metal compounds are used as the filler and more) (most cases) Lighter Heavier Heavier materials for enhancing the tribo-mechanical