Mechanical properties and flame retarding properties of nylon composites -: Relationship between molecular structures of reactive flame retardants and effects of γ-ray crosslinking

In the present study were synthesized several reactive flame retardants (RFRs) carrying phosphorus- and nitrogen-containing formulae with allyl functionalities, and the corresponding RFR-nylon66 composites were prepared by extrusion with inorganic fillers. The test pieces post-crosslinked by the gamma-ray irradiation showed improved mechanical strength being dependent on the numbers of allyl groups of RFR used, and they showed storage modulus as high as 0.1 similar to 0.3 GPa at 250 degrees C, where non-crosslinked nylon66 fused. Although the higher phosphorus content in the RFR molecule gave better flame retardation effect because of the carbonaceous skin layer (char) formation by the incomplete combustion, the higher allyl group content was revealed to decrease the flame retardation effect not only due to the interference of phosphorus-containing fragment formation but also the evolution of combustive gases originating to the non-crosslinked allyl groups. In total, the nylon composites both with the improved mechanical strength at the elevated temperature and the flame retardation grade of UL94/V-l were realized.