Abstract
Three metal salts of dicyclohexyl hypophosphite, namely dicyclohexyl aluminum hypophosphite (ADCP), dicyclohexyl magnesium hypophosphite (MDCP), and dicyclohexyl zinc hypophosphite (ZDCP), were synthesized. These flame retardants were subjected to thermogravimetric analysis, and the results showed that ADCP and ZDCP had higher thermal stabilities than MDCP. They were then separately mixed with polyamide 66 (PA66)to prepare composite materials, of which the combustion properties were determined by the limiting oxygen index method and horizontal/vertical burning experiments. The mechanical properties of the materials were further evaluated using an electronic universal testing machine. The results showed that all the three flame retardants exerted a flame-retardant effect on PA66, but the flame-retardant effect of MDCP was inferior to those of ADCP and ZDCP. All the composites also showed similar mechanical properties. Among the three flame retardants, ADCP had the best overall performance for raw materials, showing good flame-retardant properties while maintaining the mechanical properties of the raw materials. The optimal dosage of ADCP was 15 wt %, at which a V-0 rating in the vertical burning test (UL 94 test) can be obtained.
Highlights
Flame retardants have developed rapidly with extensive applications of polymer materials.Phosphorus-based flame retardants are an important class of nonhalogen flame retardants
MDCP cannot meet the required processing temperature of polymer materials due to the common heat instability and the decomposition reaction occurring below 350 ◦ C. These findings show that this flame retardant cannot be applied to polyamide 66 (PA66)
Adding the single-component flame retardants, namely ADCP, MDCP, and ZDCP, to PA66 reduced the tensile properties of the composite but increased its flexural strength
Summary
Flame retardants have developed rapidly with extensive applications of polymer materials. For polymers that do not contain oxygen in their molecular structures, such as styrene and polyolefins, phosphorus-based flame retardants have a poor char-forming effect. With addition of APBu to ABS, the flame retardancy of the material was greatly improved, the LOI value was as high as 29.8%, and a UL 94 V-0 rating was obtained. The composite material had an LOI of 34.1% and a combustion rating of UL 94 V-0 They further explored the pyrolysis kinetics of the ADCP flame-retardant polyamide and the synergistic flame-retardant effect with nanosilica, and they found that the ADCP flame-retardant addition can improve the decomposition activation energy of polyamides, rendering the material difficult to burn. The suitability of the three flame retardants to the materials was evaluated
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