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Thermoset Polymer Matrix–Based Natural Fiber Composites
Published in Shishir Sinha, G. L. Devnani, Natural Fiber Composites, 2022
Phenolic resin can be considered as the first polymer product produced from simple compounds with lower molecular weight. The phenolic resin was invented by Dr. Leo Baekeland in 1907. These are produced by the reaction of phenols with aldehydes. They are characterized by great properties like higher temperature stability up to 350°C, less toxic, greater friction, higher chemical stability, excellent thermal resistance, and high-performance polymers. The phenolic resins are widely used in a variety of applications like binders, adhesive, matrix, and surface coating. Phenolic resin is utilized for inducting and mass transit (Allen & Ishida, 2001). Phenolic resin is prepared by the condensation reaction of formaldehyde with phenol which gives water as a by-product. Phenolic resins are classified as resoles and novolac. Resoles are formed when the excess of formaldehyde is reacted with phenol in the presence of a base catalyst, the product is a low molecular weight liquid, whereas novolac is formed when the excess of phenol is reacted with formaldehyde in the presence of an acidic catalyst; the product is solid Novolac. Resoles are used for phenolic pre-impregnated material like epoxies. Phenolic resins are one of the better options for producing high thermal resistance composite. The phenolic is pyrolyzed to develop a carbon matrix, but this process develops a porous structure due to the moisture ability of phenolic resin. Some examples of phenolic resins are bakelite, novolac, and catalin.
Terms and Definitions
Published in Rick Houghton, William Bennett, Emergency Characterization of Unknown Materials, 2020
Rick Houghton, William Bennett
Phenol-formaldehyde reactions are commonly used in the production of plastics. The reaction of phenol or a substitute with an aldehyde in the presence of a catalyst is used to prepare phenolic resins. Phenolic resins are used in adhesives, coatings, and other compounds. The type of catalyst used, the ratio of reagents, and heat and pressure determine the properties of the resin. These reactions produce large amounts of heat and are sensitive to physical and chemical conditions. Once the reaction begins, heat generated by the reaction increases the rate of reaction, generating more heat in a continuous feedback. The rate of heat generation will accelerate because the reaction rate is an exponential function of the temperature. A runaway reaction can occur if the large amount of heat produced cannot be dissipated. As the reaction begins to accelerate, the pressure of the system will increase suddenly due to gas production and the induced evaporation of liquid. Excess pressure can exceed the capacity of the container and cause an explosion.
Adhesives in the Wood Industry
Published in A. Pizzi, K. L. Mittal, Handbook of Adhesive Technology, 2017
Due to the equilibrium reactions in all formaldehyde-based resins, some small amounts of residual monomers can always be present. Aminoplastic resins for particleboard and MDF usually contain less than 0.1% free formaldehyde [2]. Monomer concentrations for PF resins are in the range of <0.3% mass for the free formaldehyde and <0.1% mass for free phenol. The content of monomers should always be minimized by the proper production procedure to minimize environmental and health concerns. On the other hand, for aminoplastic resins, the free formaldehyde is necessary to induce the hardening reaction via the reaction with the so-called hardener (mainly ammonium salts); it is an additional cross-linker besides methylol groups. However, it also causes a certain formaldehyde emission during the press cycle and some residual formaldehyde leads to the subsequent formaldehyde emission from the pressed boards. Due to the stringent regulations worldwide concerning subsequent formaldehyde emissions, the molar ratios F:U or F:(NH2)2 were already decreased significantly in the 1980s. No problems occur with phenolic resins due to the strong C–C bonds in the resin (no hydrolysis and, hence, no further liberation of formaldehyde).
Thermogravimetric analysis of flax, jute, and UHMWPE fibers and their composites with melamine and phenol formaldehyde resins
Published in Cogent Engineering, 2023
Srinivas Shenoy Heckadka, Raghuvir Pai Ballambat, Poornima Bhagavath, Manjeshwar Vijaya Kini, Rajeev K Sinha, M.K Sonali, Diya Sen
Now coming to the resin, which is a polymeric material used to bond the fiber reinforcements in polymer composites. Resins such as epoxy, polyester and vinyl ester are extensively utilised with natural/synthetic fibers for manufacturing composites (Rajak et al., 2019). In addition to these resins, the use of formaldehyde resins such as phenol, melamine and urea-formaldehyde is gaining momentum for developing polymer composites. Phenolic resins produced due to the reaction between phenol and formaldehyde under alkaline conditions have excellent mechanical strength, water resistance and chemical and thermal stability. Phenolic resins are used to produce moulded products, including billiard balls, laboratory countertops, hot oil filter applications such as the lube oil filters of automobiles, coatings and adhesives (Kariuki et al., 2019). Melamine formaldehyde resin obtained by condensation of formaldehyde with melamine has improved heat, moisture, scratch, and chemical resistance (Merline et al., 2013). Melamine resins are used to manufacture many products, including kitchenware, laminate flooring, laminate countertops, overlay materials, particleboards, and floor tiles. Melamine and its salts are also used as fire-retardant additives in paints, plastics, and paper (Kumar & Katiyar, 1990; Park & Jeong, 2010; Raval et al., 2006).
Development and characterization of low metallic friction composites filled with brass chips
Published in Tribology - Materials, Surfaces & Interfaces, 2022
Friction composite materials usually consist of a matrix and a large number of different components concentrated around it. Namely, filler, binder, friction modifiers and reinforcing elements are the main components of brake composites [7]. Phenolic resin or phenol-formaldehyde is a very commonly used material as a binder due to its favourable processing properties [8]. Although barite mainly serves to increase economic efficiency as an inert filler in brake pads, it is also known to affect tribo-performance [9]. Metal fillers such as iron, steel, copper and brass are involved in both structural formation and can improve tribological properties. Brass and copper chips are often used in the manufacture of brake pad materials. Metal chips with high thermal conductivity serve to reduce the frictional temperature on the surface. One of the advantages of metal chips is that they increase the frictional force when they expose to the friction surface and participate in the formation of the friction layer during wear [10].