1. Flame retardant properties

When compounded with 2 wt% AMC and 24 wt% IFR, the LOI of the PP composite can reach 31.2% and pass the V-0 test of UL-94. At this time, the best addition mass ratio of IFR to AMC is 12. :1. From the macroscopic morphology of carbon formation, the thermal stability of the carbon layer of the PP sample is the best, and there is no obvious shrinkage phenomenon. optimal. And it was found that the residues of AMC showed a gradient distribution in the carbon layer, and the content of the inner surface was higher than that of the outer surface. From the perspective of physical structure, this had a better effect on stabilizing the carbon layer. From a chemical point of view, the addition of AMC promotes the dehydration and cross-linking reaction, and at the same time promotes the transformation of amorphous carbon to an ordered carbon layer, which makes the carbon layer more heat-resistant and has better mechanical properties.

(a) EDS of the carbon layer on the outer surface,

(b) EDS of the carbon layer on the inner surface, 

(c) Point scan EDS of the enlarged area of the inner surface

2. Thermal stability

After compounding AMC, the T5%, T50% and Tmax of the composites all increased, and reached the maximum value when 2 wt% AMC and 24 wt% IFR were added, and the final carbon residue also reached a maximum value. value. When MCA is added alone, the thermal stability of the composite material decreases in a higher temperature range, and the final carbon formation also decreases, indicating that α-ZrP can enhance the carbon layer and improve the thermal stability of the carbon layer. , and at the same time can improve the final amount of carbon. The thermal degradation kinetics study showed that the apparent activation energy (Ea) of thermal degradation of the composite was improved after compounding 25 wt% IFR, and the Ea of the composite was further improved when AMC was added, which indicated that the Higher temperature is converted into thermal energy to drive molecular chain degradation, that is, higher conversion energy levels are required. It can be seen that there are consistent results between thermal stability and thermal degradation kinetics, indicating that the addition of AMC does help to improve the overall thermal stability of the composite.

3. Mechanical properties

When AMC was not added, the mechanical tensile strength of the composite was 25.8 MPa, and the impact strength was 2.3 kJ/m2. When 2wt% AMC was added, the tensile strength of the composite increased to 30.3 MPa, and the elongation at break increased from 21.3%. It increased to 30.5%, and the impact strength increased to 3.2 kJ/m 2 . The microscopic morphology of the brittle fracture section showed that the pores were significantly reduced, and the IFR and AMC particles were more uniformly dispersed, and the particle size of the IFR became smaller, indicating that the Adding it can not only improve the dispersibility of the flame retardant, but also improve the compatibility of the flame retardant with the matrix, and finally improve the mechanical properties of the composite material.

4. Synergistic flame retardant mechanism of IFR compounded with AMC

In the early stage of PP degradation, MPP is degraded into polyphosphoric acid and melamine, the former acts as an acid source for dehydration and carbonization, and the latter acts as a gas source to dilute the concentration of flammable gas; after that, melamine-cyanuric acid on the surface of AMC is degraded to generate incombustible gas, which acts as a part of gas source, and part of the nitrogen-oxygen radicals capture macromolecular chain fragments in the condensed phase, delaying the further degradation of PP; with the degradation of the AMC shell, the inner α-ZrP core is gradually exposed, and the Lewis acid site on the surface plays a catalytic reaction, It can promote the esterification reaction between PER and polyphosphoric acid and convert it into an effective carbon layer; at higher temperatures, the AMC product ZrP2O7 can strengthen the carbon layer and resist the heat flow and airflow during the combustion process, so that it can effectively It exerts a barrier effect; and, with the promotion of pyrophosphate, the carbon layer can be converted from amorphous carbon to crystalline carbon, the carbon layer is more ordered, and the thermal stability and mechanical properties of the carbon layer are improved. In addition, the non-combustible gas is enclosed in the middle of the carbon layer, which can play the role of expanding the carbon layer, effectively avoid the contact between the combustible material and the fire source, and improve the flame retardant performance.

Classification standard of polypropylene (PP) flame retardant grades

Flammability UL94 rating is the most widely used standard for the flammability performance of plastic materials. It is used to evaluate the ability of a material to extinguish after being ignited. There are many ways to judge according to the burning speed, burning time, anti-drip ability and whether the drip bead burns.

The flame retardant grade increases step by step from HB, V-2, V-1, to V-0.

HB: The lowest flame retardant grade in the UL94 standard. Requires a burning rate of less than 40 mm per minute for samples 3 to 13 mm thick; less than 70 mm per minute for samples less than 3 mm thick; or extinguishes before the 100 mm mark;

V-2: After the sample is subjected to two 10-second combustion tests, the flame is extinguished within 60 seconds, and no burning objects can fall;

V-1: After the sample is subjected to two 10-second combustion tests, the flame is extinguished within 60 seconds, and no burning objects can fall;

V-0: After the sample is subjected to two 10-second burning tests, the flame is extinguished within 30 seconds, and no burning objects can fall.