Interfacial Interactions and Flammability of Flame-Retarded and Short Fiber-Reinforced Polyamides

Abstract

Interfacial properties, crystallinity and flammability of short fiber reinforced and flame retarded polyamide 6 and polyamide 66 compounds are investigated, emphasizing the influence of flame retardant fillers on the resistance of fiber/matrix interface to shear. Interfacial shear strengths are derived through a micromechanical approach by determining the tensile properties and residual fiber length distributions. Validated by fracture morphologies, interfacial strengths are found to be governed by filler – induced apparent crystallinities and fractional occurrence of polyamide polymorphs, obtained via peak deconvolution of X-Ray diffraction patterns. Although flame retardant additives based on Br/Sb synergism are found to impart excellent flammability reductions regarding oxygen index and UL94 classifications (V-0 rating), degree of crystallinity; thus, interfacial properties are deteriorated due to lowered thermal expansion and increased cooling rates. Red phosphorus as a flame retardant also induces a UL94 V-0 and significant reduction in flammability together with the facts that crystallinity is not altered and a strong fiber/matrix interface is maintained. Use of melamine cyanurate in an unreinforced polyamide improves the limiting oxygen index considerably; however, the UL94 rating remains unchanged as V-2 as a consequence of increased level of melt dripping. Melamine cyanurate additionally increases the degree of crystallinity through promotion of heterogeneous nucleation.

Keywords:

• Crystallinity
• Flame retardancy
• Interfacial strength
• Mechanical properties
• Polyamide
• Short glass fiber

ACKNOWLEDGEMENT

Partial financial support of this research as part of the Project 107M347 by TUBITAK, the Scientific and Technological Research Council of Turkey, is gratefully acknowledged.

Authors also wish to acknowledge EUROTEC Engineering Thermoplastics Inc. (Turkey) for providing the equipments of twin-screw extruder and UL94 flammability meter.

Notes

^a PA66 has no γ-form^{[ 33 ]}.