In this work, twill woven hemp fabric reinforced epoxy resin composites were prepared and flame retarded with a dual approach.
On the one hand, the curing agent was replaced by a P-containing amine; on the other hand, the hemp fabrics were treated in order to decrease their flammability.
The modification of the fabrics led to decreased flammability of the reference matrix composites characterized with increased LOI values and by 25% reduced heat release rate.
The flame retardancy of both the matrix and fabrics was necessary to reach the V-0 rating in the UL-94 test.
Regarding the mechanical properties of the composites, unexpected results were found when both the matrix and the fabrics contained phosphorus; despite the poorer mechanical performance of the FR matrix, and the decreased strength of the surface treated fabrics, the measured values for the flame retarded samples reached that of the reference composite in almost all cases.
These surprising results can be explained by the increased fibreematrix adhesion between the treated fabrics and FR matrix, and their easier wetting interaction in the case of the more polar P-containing matrix.