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Properties and applications of engineering materials
Published in Alan Darbyshire, Charles Gibson, Mechanical Engineering, 2023
Alan Darbyshire, Charles Gibson
Plastics can be subdivided into thermoplastics, thermosetting plastics and rubbers. Thermoplastics can be softened and remoulded by heating whereas thermosetting plastics cannot. Rubbers are polymer materials known as elastomers which have the property of being able to return to their original shape after large amounts of deformation.
Emergence, Chemical Nature, Classification, Environmental Impact, and Analytical Challenges of Various Plastics
Published in Hyunjung Kim, Microplastics, 2023
Thermoplastics consist of macromolecular chains with no crosslinks between the chains. The macromolecular chains can have statistically oriented side chains or build statistically distributed crystalline phases. The chemistry and structure of thermoplastic resins influence the chemical resistance and resistance against environmental effects like UV radiation. Thermoplastic resins can vary from optically transparent to opaque, depending on the type and structure of the material. Thermoplastic resins can be reversibly melted by heating and resolidified by cooling without significantly changing mechanical and optical properties. The melt’s viscosity depends on the inner structure, like average molecular weight and spreading of the molecular weight around the average value (Skrovanek et al., 1986). The macromolecular structure of thermoplastics can be given by the chemical structure of the monomer units, the order of the monomer units in the molecule chain, and the existing side chains. Therefore, thermoplastic resins can be amorphous and semicrystalline types (Klein, 2011; Batzer, 1985; Frank and Biederbick, 1984). Figure 1.5 indicates amorphous and semicrystalline thermoplastics with typical material properties and temperature behavior.
Influence of Hybridization on the Free Vibration and Damping Characteristics of Bast Fiber-Based Polymer Composites
Published in Senthil Muthu Kumar Thiagamani, Md Enamul Hoque, Senthilkumar Krishnasamy, Chandrasekar Muthukumar, Suchart Siengchin, Vibration and Damping Behavior of Biocomposites, 2022
The polymer matrices for FRP composites can be either thermoplastic or thermoset, which have different processing conditions and preparation methods. The selection of polymer matrix affects the composite performance as well, and hence the polymer matrix should be appropriately selected in accordance with the area of applications. The main difference between thermoset and thermoplastic polymers is that the thermoset polymer is not recyclable. Thermoset polymers cannot be remolded or reshaped upon curing. The formation of three-dimensional cross-link networks held by strong covalent bonds after the curing of thermoset limits its recyclability (Post et al. 2020). In contrast, thermoplastic polymers can be remolded and reshaped easily by applying heat up to their melting temperature. Moreover, thermoplastic polymers have better ductility, inferring that they can be formed into any complex three-dimensional shape. Even though thermoset polymers have difficulty in recycling, the mechanical properties, thermal stability, chemical resistance, and durability of thermoset outperform thermoplastic polymers (Yan, Chouw, and Jayaraman 2014).
Mechanism of bonding during laser transmission welding using EIP absorber
Published in Materials and Manufacturing Processes, 2023
Lightweight and high-strength thermoplastics provide excellent replacements for metallic materials in industrial applications and are most widely used in the food packaging, biomedical, aerospace, and automotive industries.[1–3] Several components made of thermoplastics are required in industries to connect together to form large and complex shapes.[4,5] Apart from conventional methods like screwing, bolting, and adhesive joining, several alternative methods are used to join the plastics, such as ultrasonic welding, friction stir welding, induction welding, hot plate welding, and laser transmission welding.[6,7] Among these techniques, laser transmission welding has more capability to use in broad applications owing to the distinct properties of laser, such as low heat affected zone, high flexibility, lower residual stresses, and fast processing time.[8–12]
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).
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.