Abstract:

As a common flame retardant, ammonium polyphosphate (APP) can considerably improve the flame retardancy of rubber, but the molecular structure of APP shows that it contains a large number of ammonium phosphate groups, rendering it highly hygroscopic. To address this hygroscopic issue of APP, microencapsulated APP (MF201) was obtained by coating APP microcapsules with melamine resin. Although MF201 can solve the hygroscopic issue of APP, the presence of microencapsulated shells may affect the properties of rubber. To study the difference between the two flame retardants, APP and MF201 were introduced into a natural rubber/butadiene rubber (NR/BR) composite to investigate their impacts on the hardness, flame retardancy, wear resistance, and other physical and mechanical properties of NR/BR composites. The results show that the addition of APP and MF201 can improve the flame retardancy, hardness, mechanical properties, and wear resistance of NR/BR composites. Due to the plasticizing effect of the melamine resin shell, the hardness of NR/BR composites decreases slightly when MF201 is added. Furthermore, APP and MF201 improve the flame retardancy of NR/BR composites to the same extend. For example, 45 phr APP and MF201 increase the limiting oxygen index of NR/BR composites to 25.5% and their UL-94 combustion rating to HB. In addition, the effects of APP and MF201 on wear resistance are basically the same. The NR/BR composites with MF201 added have lower hardness and higher elongation at break. Therefore, the microencapsulated shell did not change the flame retardant and wear resistance of APP to NR/BR composites, but increased the elongation at break and reduced the hardness.

Key words: phosphorous flame retardant, flame retardancy, wear, natural rubber, butadiene rubber