Flammability thermoset composites

Thermoset composite systems of phenol and formaldehyde, some of which can he substituted for a number of structural applications can also be considered as engineering plastics and they have been in use for a very long time. In recent applications, improved urea - melamine resins have been used as matrices more and more for composite systems, because of their non-melting, high thermal and chemical resistances, hardnesses, mechanical-dimensional stabilities and low flammabilities. 

Reinforced thermoset composites of UP are used extensively because of their non-melting, high thermal and chemical resistances, hardness, mechanical properties, dimensional stabilities and low flammabilities. 

The use of nanocomposites to reinforce traditional composites has also been increasing and will continue to be a near-term trend. The emphasis for these applications, however, has been on additional mechanical reinforcement rather than flammability reduction.Since more traditional fiber-filled composites are exposed to fire risk scenarios, it makes sense to use a nanocomposite with the traditional composite to improve both mechanical and flammability performance. Of course, this does create an additional level of complexity, especially in handling the large increases in viscosity seen with nanocomposites used with thermoset composites. At this time, most nanocomposite-fiberglass/carbon fiber composites are used for military and aerospace applications, but the benefit of lightweight materials may also move these materials into automotive and mass transportation (e.g., bus, rail), where flammability performance is strongly needed. 

It is of note that the respective amounts of char and flammable volatiles produced by the thermal decomposition of the composite are highly dependent on the chemical nature of the organic phases, i.e., the polymer matrix and synthetic fibres, if present (Levchnick and Wilkie, 2000 Mouritz, 2007). As regards the main thermosetting polymers used in construction (i.e., polyesters, vinylesters and epoxies), pyrolysis yields a large amount of volatiles but retains a small amount of char (10-20% of the initial mass). FRP composites based on these thermoset matrices are thus highly flammable materials. 

To prepare the FRP composite, the respective fiber is embedded in a polymer matrix mostly thermoset or thermoplastic resins. The role of the matrix is (i) to bind the fibers together, (ii) to transfer stresses between fibers, and (iii) to protect them against environmental attack and damage due to mechanical abrasion. The matrix also controls the processability, the maximum service temperatures, as well as the flammability and corrosion resistance of FRP. Most FRPs are made in order to improve mechanical performances such as elastic properties (modulus of elasticity) and ultimate properties (strength, toughness). To some extent and based on the choice of constituents, preparation of composites makes it also possible to tailor other physical properties, such as electrical conductivity, mass transport properties, heat conduction, etc. [49]. 

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