Thermosets
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Thermostes
Explanation of terms
Thermosetting materials, also known as thermosets, duromers, or resins, are a subgroup of plastics that exhibit a high degree of three-dimensional cross-linking of the main chemical valence bonds. Due to this macromolecular structure, they are classified as glass-like and hard plastics. In terms of recyclability, a key feature is that, just like elastomers, they cannot be deformed or melted under the influence of heat after curing or cross-linking and are decomposed or combusted by pyrolysis above their decomposition temperature.
Macroscopic properties
The macroscopic energy-elastic properties are characterized, for example, by high tensile strengths and moduli of elasticity, very low elongation at break (see: tensile strength), and low impact strengths (see also: toughness). The term “brittle materials” is often used for classification purposes, although the term “plastics with low ductility” would be more accurate. Classification is often based on elongation at break, which is less than 10 % for these materials, and in most cases significantly below this limit. These plastics often react to mechanical or mechanical-thermal stresses with crack initiation and brittle failure (see: fracture types), in some cases also exhibiting a high tendency to shrinkage (see also: shrinkage test). Due to the partially exothermic curing process, high internal stresses (see: tensile test residual stresses orientations) or discoloration may occur in some areas as a result of thermal stress.
Fibre-reinforced plastics with thermosetting matrix
Due to these properties, these plastics are either extended with inorganic fillers or reinforced with various fibers (glass fibers, carbon fibers, mineral fibers, aramid or natural fibers) for economic and design reasons (see: fiber-reinforced plastics), which significantly changes their strength, impact toughness, and elongation at break. Filling or reinforcement levels of up to 70 m.-% can be achieved (globtops in microelectronics, car body and aircraft construction). The specific strengths or moduli can reach higher values than those of metallic materials. At the same time, this reduces the formation of residual stress), although the anisotropy of the properties can increase significantly, particularly in the case of reinforcement (glass or carbon fleece, glass fabric, GF or CF mats, and rovings).
The most important thermosetting plastics used in technical applications are epoxy and polyester resins, amino and phenolic resins, melamine resins, polyurethanes, and cross-linked polyacrylates, although some biopolymers can also be classified in this material group alongside silicones.
Thermosetting plastics are usually produced using a polycondensation process, in which the polymer chains are cross-linked by heat, irradiation, or chemical additives (hardeners). With the aid of catalysts or thermal activation, linear macromolecules are first formed, which then form a mechanically and thermally stable superstructure through three-dimensional cross-linking.
Today, the manufacturing processes for plastic components range from hand lay-up to pressing and injection molding to the prepreg process and injection molding.
See also
References
| [1] | Altstädt, V.: Testing of Composite Materials. In: Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 515–567 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see AMK-Library under A 22) |
| [2] | Elsner, P., Eyerer, P., https://de.wikipedia.org/wiki/Peter_Eyerer Hirth, T. (Eds.): Domininghaus – Kunststoffe, Eigenschaften und Anwendungen. Springer, Berlin (2012) 8th new revised and expanded Edition, (ISBN 978-3-642-16172-8; see AMK-Library under G 4)) |
| [3] | Schürmann, H.: Konstruieren mit Faser-Kunststoff-Verbunden. Springer, Berlin (2007) 2nd Edition (ISBN 978-3-540-72190-1) |
| [4] | Neitzel, M., Mitschang, P., Breuer, U.: Handbuch Verbundwerkstoffe: Werkstoffe, Verarbeitung, Anwendung. Carl Hanser, Munich (2014), (ISBN 3-446-22041-0; see AMK-Library under G 12) |
| [5] | Ehrenstein, G. W.: Faserverbund-Kunststoffe. Carl Hanser, Munich (2006) 2nd Edition, (ISBN 978-3-446-22716-3; see AMK-Library under G 6-2) |
| [6] | Erhard, G.: Konstruieren mit Kunststoffen. Carl Hanser, Munich (2008) 4th Edition (ISBN 978-3-446-41646-8; see AMK-Library under G 59) |
| [7] | Ehrenstein, G. W.: Mit Kunststoffen konstruieren. 3rd Edition, Carl Hanser, Munich (2007), (ISBN 978-3-446-41322-1; see AMK-Library under G 42) |
| [8] | Ehrenstein, G. W.: Polymerwerkstoffe – Struktur – Eigenschaften – Anwendung. Carl Hanser, Munich (2011) 3rd Edition (ISBN 978-3-446-42283-4; see AMK-Library under G 91) |