Investigation On The Preparation Of Hydrophobic Ammonium Polyphosphate And The Properties Of IFR-PP Composites

Ammonium polyphosphate (APP) is a common flame retardant for polymers. However, some defects containing strong hygroscopicity, easily hydrolytic tendency, different polarity and poor compatibility with polymers limit its wider application. Therefore, APP was surfacially mofided with low surface energy silicon resin. Then the modified APP was mixed with triazine char-foaming agent (CFA) with to prepare intumescent flame retardant (IFR) which was incorporated into PP to obtain IFR-PP composites. The properties of modified APP and IFR-PP composites were also investigated.Ammonium polyphosphate (APP) was firstly surface modified with (3-Aminopropyl)triethoxysilane (KH550), then microencapsulated by silicone through situ polymerization of tetraethyl orthosilicate (TEOS), finally surface-modified with (Heptadecafluoro-1,1,2,2-tetradecyl) trimethoxysilane to prepare the modified APP (MAPP-1). The wettability of MAPP-1 was well characterized by water contact angle (WCA) and test. The CA of the MAPP-1 reached 134°, which demonstrate the modified APP possessed obviously hydrophobic property. The flame retardancy and thermal degradation behavior of PP/MAPP-1/CFA and PP/APP/CFA were evaluated by limiting oxygen index (LOI), vertical burning, cone calorimeter measurement (CONE) and thermal gravimetric analysis (TGA) tests. The water resistant property of PP/MAPP-1/CFA and PP/APP/CFA were evaluated by water resistant test, and the mechanical properties were measured by the tensile, flexural and impact strength test, the compatibility between the flame retardant and polymer was investigated by scanning electron microscopy (SEM). The results indicated that PP/MAPP-1/CFA composite with the thickness of 1.6mm reached V-0 flammability rating in vertical burning test when the loading amount of IFR was 23wt%, PP/MAPP-1/CFA after water resistance test still successfully passed V-0 rating and the mass loss ratio was only 0.92%. Under the same experimental conditions, the PP/APP/CFA composite after water resistance test was no rating in vertical burning test and its mass loss ratio was 2.45%. It can be deduced that hydrophobic MAPP-1 can greatly improve the water resistance of PP/MAPP-1/CFA. The CONE and TGA results showed that the modification of APP had little effects on the thermal degradation behavior of IFR-PP composite, but decreased the HRR and THR of IFR-PP composite. The results of SEM and mechanical test revealed that the modification of APP improved the compatibility between the flame retardant and PP matrix, which resulting in the increase of the mechanical properties of the PP/MAPP-1/CFA composites.However, the above modified process needed to introduce a small amount of water, resulting in partiall hydrolysis of APP. To further improve the hydrophobicity of APP, APP was firstly surface modified with KH550 to reduce the surface energy of APP, and then microencapsulated with silicon resin to prepare MAPP-2. The properties of MAPP-2 and the IFR-PP composites were also evaluated. The contact angle (CA) of MAPP-2 and IFR consisting of MAPP-2 and CFA was as high as 148°and 144°, respectively, which demonstrated they possessed more excellent hydrophobic property. The properties of IFR-PP composites were investigated. The results demonstrated that PP/MAPP-2/CFA composite with the thickness of 1.6mm reached V-0 flammability rating in vertical burning test when the loading amount of IFR was 22wt%, PP/MAPP-2/CFA after water resistance test still successfully passed V-0 rating and the mass loss ratio was only 0.85%. It can be concluded that MAPP-2 dramatically improved the water resistance of PP/MAPP-2/CFA composite. The CONE and TGA results showed that the modification of APP not only greatly decreased the HRR and THR, but also enhanced the thermal stability of PP/MAPP-2/CFA composites. The results of the morphologies of the surface and fracture and mechanical properties of flame retardant PP composites indicated that MAPP-2 enhanced the comparability between IFR and PP matrix, which led to the enhancement of mechanical properties and water resistance of PP/MAPP-2/CFA composites.