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Curing is a chemical process employed in polymer chemistry and process engineering that produces the toughening or hardening of a polymer material by cross-linking of polymer chains. [1] Even if it is strongly associated with the production of thermosetting polymers , the term "curing" can be used for all the processes where a solid product is ...
In vulcanization, sulfur is the cross-linking agent. Its introduction changes rubber to a more rigid, durable material associated with car and bike tires. This process is often called sulfur curing. In most cases, cross-linking is irreversible, and the resulting thermosetting material will degrade or burn if heated, without melting.
Curing of epoxy resins is an exothermic reaction and in some cases produces sufficient heat to cause thermal degradation if not controlled. [28] Curing does induce residual stress in epoxy systems which have been studied. [29] The induced stresses may be alleviated with flexibilisers.
An exothermic thermite reaction using iron(III) oxide. The sparks flying outwards are globules of molten iron trailing smoke in their wake. Some examples of exothermic processes are: [14] Combustion of fuels such as wood, coal and oil/petroleum; The thermite reaction [15] The reaction of alkali metals and other highly electropositive metals ...
Therefore, by definition, the transition state for tertiary reactions will be at a lower energy than for secondary reactions. However, the BEP principle cannot justify why the energy is lower. Using Hammond's postulate, the lower energy of the tertiary transition state means that its structure is relatively closer to its reactants R(tertiary)-X ...
An energy profile of an exothermic reaction. In an exothermic reaction, by definition, the enthalpy change has a negative value: ΔH = H products - H reactants < 0. where a larger value (the higher energy of the reactants) is subtracted from a smaller value (the lower energy of the products). For example, when hydrogen burns: 2H 2 (g) + O 2 (g ...
Diverse methods are employed to manipulate the initiation, propagation, and termination rates during chain polymerization. A related issue is temperature control, also called heat management, during these reactions, which are often highly exothermic. For example, for the polymerization of ethylene, 93.6 kJ of energy are released per mole of ...
In general, the polymerization is an exothermic process, i.e. negative enthalpy change, since addition of a monomer to the growing polymer chain involves the conversion of π bonds into σ bonds, or a ring–opening reaction that releases the ring tension in a cyclic monomer.