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Intense Classification of Composite Materials
Published in Subhash Singh, Dinesh Kumar, Fabrication and Machining of Advanced Materials and Composites, 2023
Thermosets, post-curing, possess a well-bonded 3-D molecular structure; hence, only decomposition occurs in thermosets unlike in thermoplastics, where melting/hardening occurs. Altering the resin composition would alter the characteristics or curing conditions of a thermoset polymer. The properties of thermosets could be retained under the conditions of partial curing for longer durations, making thermosets extremely flexible in manufacturing. Therefore, thermosets are ideal for fabricating advanced PMCs of short, premixed fibre reinforcements and epoxy, phenolic polyamides as the matrix materials. If not for thermosets, there wouldn’t have been such a huge research development in the field of structural engineering. Some commonly used thermosets are epoxy, polyester, and phenolic polyamides and the applications of these thermosets are seen in printed circuit boards, automotive and aerospace components, systems of defence, etc. Thermosets are prepared via direct condensation polymerization in which water is the by-product of this reaction [17]. This presence of water results in the formation of composites with voids that would hinder the strength as well as dielectric characteristics of the composite. Epoxy as well as polyester phenolic are the major kinds of thermosetting resins.
Plastics
Published in Arthur Lyons, Materials for Architects and Builders, 2019
Thermosetting plastics have a three-dimensional cross-linked structure, formed by the linkage of adjacent macromolecular chains (Fig. 10.8). Thermosets are not softened by heating, and will only char and degrade if heated to high temperatures. Thermosets are usually produced from a partially polymerised powder or by mixing two components, such as a resin and a hardener. The resin is essentially the macromolecular component and the hardener cross-links the liquid resin into the thermoset plastic. Curing for epoxy resin adhesives and polyesters as in glassfibre-reinforced polyester (GRP) occurs at room temperature, while for phenolic and formaldehyde-based resins a raised temperature and pressure are required. Thermosets, because of their three-dimensional structure, are usually solvent-resistant and harder than thermoplastics.
Monomers, Polymers, and Plastics
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
Thermosets are polymers whose individual chains have been chemically linked by covalent bonds during polymerization or by subsequent chemical or thermal treatment during fabrication. The thermosets usually exist initially as liquids called pre-polymers; they can be shaped into desired forms by the application of heat and pressure. Once formed, these cross-linked networks resist heat softening, creep and solvent attack, and cannot be thermally processed or recycled. Such properties make thermosets suitable materials for composites, coatings, and adhesive applications. Principal examples of thermosets include epoxies, phenol-formaldehyde resins, and unsaturated polyesters. Vulcanized rubber used in the tire industry is also an example of thermosetting polymers. Thermosetting polymers are usually insoluble because the cross-linking causes a tremendous increase in molecular weight. At most, thermosetting polymers only swell in the presence of solvents, as solvent molecules penetrate the network. The designation of a material as thermoplastic reflects the fact that above the glass transition temperature the material may be shaped or pressed into molds, spun or cast from melts, or dissolved in suitable solvents for later fashioning.
Reusing plastic waste in the production of bricks and paving blocks: a review
Published in European Journal of Environmental and Civil Engineering, 2022
Turkeswari Uvarajan, Paran Gani, Ng Chuck Chuan, Nur Hanis Zulkernain
Plastics are a petrochemical substance made from fossil fuel and gas used in large quantities in developed and developing countries (Gilbert, 2016; Palm & Myrin, 2018; Vaverková, 2019). Plastics can be categorised into two main types based on their response when heat is applied: namely thermoplastic and thermosets. Thermoplastics are plastics that can be melted and remolded repeatedly when heat is applied, whereas thermosets on the other hand, undergo irreversible chemical changes when heat is applied, thus cannot be reheated and remolded (Arhant & Davies, 2019; Brouwer et al., 2018; Post et al., 2020). Plastics is a versatile and robust material commonly used in numerous applications such as; packaging, construction material, clothing, household, personals care products, and transportation (d’Ambrières, 2019; Milios et al., 2018; Mrowiec, 2017; Rodrigues et al., 2019).
Insight Into Surface Texture-Induced Dual Effects on Friction of WC-Co Dry Sliding Against Continuous Carbon Fiber-Reinforced Thermoplastic and Thermosetting Composites
Published in Tribology Transactions, 2022
Xin Dong, Chaoyang Dong, Bo Wu
According to the chemical and technological properties of the matrix, polymer composites are divided into three main groups: elastomers, thermosets, and thermoplastics (5, 6, 9). Semicrystalline poly-ether-ether-ketone (PEEK) characterized as an ultra-high-performance polymer and epoxy resin featured as a low-molecular-weight prepolymer are two typical thermoplastics and thermosets, respectively (8–11). Thermoplastic polymer can reversibly become plastic and flow on heating, either by reason of crystal melting or by exceeding glass transition temperature (Tg), whereas manufactured thermosetting polymer is unrecyclable on heating or curing (9, 12). Additional cross-links between carbon chains exist in thermosets, while thermoplastics are linear or branched polymers with only individual chain interactions via van der Waals force (12, 13). This difference in molecular structure indicates that thermosets are inherently brittle and characterized by a lack of toughness compared to thermoplastics (5, 14).
Recycling strategies for vitrimers
Published in International Journal of Smart and Nano Materials, 2022
Haochuan Zhang, Jingjing Cui, Guang Hu, Biao Zhang
In general, plastics can be divided into thermoplastics and thermosets according to their differences in chemical structures [3,4]. Thermoplastics are a class of plastics that are malleable at a certain temperature, and solidify upon cooling, which can repeat this process. The molecular structure is characterized by linear polymer compounds, which generally do not have reactive groups and do not undergo intermolecular cross-linking when subjected to heat [5] (Figure 1). Due to their good fluidity at high temperatures, thermoplastics can be manufactured by a variety of methods, including extrusion, injection molding, thermoforming, and vacuum forming [6]. However, thermoplastics are usually less resistant to organic solvents and less stable than thermosets, limiting their further applications requiring high mechanical performance. Thermosets [7] are a type of polymers where the macromolecular chains covalently bond with each other, forming the chemically cross-linked three-dimensional (3D) networks (Figure 1). Due to the chemically cross-linked property, thermoset materials [8] exhibit excellent mechanical properties, heat resistance, chemical resistance and dimensional stability, which have been used in a wide range of applications, such as aerospace, solar cell sealants, and windmills. However, the insoluble nature of thermosets makes them impossible or difficult to recycle. Therefore, addressing the recycling of thermosets has become an important topic for the sustainable development of society.