Thermosetting polymer

Thermosets, also called thermosets, are plastics that can not be deformed after curing. Thermosets are hard, glassy polymer materials, which are three-dimensionally cross laid on chemical valency. Crosslinking occurs during the mixing of precursors with branching sites, and is activated either at room temperature by means of catalysts, chemically ( isothermal) or at high temperatures, heat ( exothermic).

Classification

Thermosets form one of three groups, are divided into the polymers. A distinction is made in this case according to the degree of crosslinking between the macromolecular main chains to thermoplastics, elastomers and thermosets. While thermoplastics have no cross-linking sites and are therefore melted, elastomers and thermosets can not be melted due to their networking and disintegrate after exceeding the decomposition temperature ( pyrolysis).

The thermosets include aminoplasts and phenoplasts, are both connected with one another by methylene bridges ( -CH2-) or methylene ether bridges, and also epoxy resins, cross-linked polyacrylates, and other cross-linked polymers. Epoxy resins, acrylates, and polyurethanes can also be made from biopolymers. Biopolymers are polymers based on renewable raw materials (eg vegetable oils) that the petroleum-based resins are similar in their properties so that they can be processed by the known methods. The most common thermosets are melamine resins. These are caused by polycondensation of melamine with formaldehyde.

Production

Thermosets are often prepared by polycondensation. For the preparation of thermoset polymer chains are cross-linked with one another or with monomers. The cross-linking of the modules is initiated by heat, radiation, or chemical additives. In a curing process itself this form linear chain molecules, which are also network with each other three-dimensionally and form a stable structure. After curing, they can not change their shape. On mechanical action they react with cracks or jumps. Through formed during the polycondensation cleavage products thermosets throw often initially bubbles. In addition, some tend to shrink, jumping and crumbling. The latter is due to the reduction of residual stresses arising during manufacture.

History of the material

Thermosets of synthetic resins are among the first industrially manufactured plastic. Originally they were only in Molds from their precursors (eg, phenolic resins from phenolic resins ) are prepared and were therefore referred to as molding compounds, contrary to thermoplastics, which was called the injection molding materials. It was not until the mid-1960s, methods were developed that enabled the production of thermoset injection molding. Nowadays, thermosets are processed in numerous processes. The focus is always at the high thermo-mechanical strength and low specific weight compared to metal.

Areas of application

• Brake Pads
• In fiber composite materials such as CFRP or GFRP as matrix material
• The housing of electronic components
• Household ( iron heat shield, pot handles and stove strips )
• Cable trays
• Body parts
• Power and circuit breaker
• Engine compartment applications ( water pump housing, pulleys, commutators, intake, etc. )
• Reflectors ( car headlights )
• Protective helmets, such as the fireman's helmet

Another application area was formerly the body outer skin of the car Trabant. The compression that took place on thermoset here at a pressure of 400 N / cm ² and a temperature of 170 ° C.

Nowadays, numerous assemblies of metal in automotive engine compartment are replaced by thermoset components. Due to the low density, the relatively high temperature stability and often lower component costs of this trend increases significantly.