Modified Ammonium Polyphosphate and Its Application in Polypropylene Resins

Abstract

Herein, a simple and environment-friendly method of coupling agent treatment of APP (ammonium polyphosphate) is provided and an optimum process of modification via coupling agent is identified. The effects of coupling agent type, dosage, modification time, and modification temperature on the modification of ammonium polyphosphate (APP) were investigated using an orthogonal experimental design. The modified ammonium polyphosphate (KAPP) was characterized under optimal process conditions using Fourier Transform Infrared (FT-IR), X-ray Diffraction (XRD), Thermogravimetry (TG), and Scanning Electron Microscope (SEM) analysis. The treatment greatly improved the water solubility, dispersibility, and thermal stability of KAPP; and the application of KAPP in polypropylene (PP) was investigated. The flexural properties, thermal stability, and flame retardancy were studied using mechanical testing, thermogravimetric analysis, oxygen index, and UL-94 vertical combustion. The results show that the KAPP-added polypropylene composites have better bending properties when compared with the APP-added PP composites. SEM analysis suggests that the surface of KAPP became smoother and flat; dispersion was better, compatibility with the PP matrix was improved, and there were no prominent voids and gaps in the cross-section. A different degree of improvement in flame retardancy was also observed as per the LOI and vertical combustion results, wherein the PP composites prepared by adding 20% KAPP achieved the LOI of 27.6% and passed the UL-94 test with V-0 rating.

Application of the PAPP/MCA/APP intumescent flame retardant system in polypropylene

“…Therefore, based on the above investigation results and previous studies, the flame‐retardant mechanism of PAPP/MCA/APP IFRS was proposed (Figure 5). 36,37,46,49–54 In the initial stage of combustion, the dehydration and ionic bond breakage reactions of APP and PAPP started, which led to the generation of the phosphoric acid, metaphosphoric, N‐P compounds, etc. with the releasing of H 2 O vapor 46,54 .…”

“…The thermal and oxidative degradation of PP also happened at this stage, resulting in the formation of O‐containing functional groups such as hydroxyl and carboxyl groups on the carbon chain of PP 50–52 . With the increase of the combustion temperature, metaphosphoric or phosphoric acid can further dehydrate to pyrophosphoric acid and continuously release H 2 O vapor 36 . The phosphoric acid derivatives and N‐P compounds reacted with the O‐containing functional groups on the carbon chain of PP by the dehydration and cross‐linking reactions leading to the formation of the multicomponent residues and the continuous char layer structure 37,46 .…”

“…5). 36,37,46,[49][50][51][52][53][54] In the initial stage of combustion, the dehydration and ionic bond breakage reactions of APP and PAPP started, which led to the generation of the phosphoric acid, metaphosphoric, N-P compounds, etc. with the releasing of H 2 O vapor.…”

“…However, APP, PAPP, and MCA have obvious disadvantages when they were used alone as the flame retardant. APP and PAPP have relatively high phosphorus content, and their decomposition products are mainly phosphoric acid derivatives, which make APP and PAPP play the role of flame retardance mainly in the condensed phase 36,37 . MCA can only exert the flame‐retardant effect in gas phase due to only non‐flammable gases generated during the decomposition of MCA 38,39 .…”

“…APP and PAPP have relatively high phosphorus content, and their decomposition products are mainly phosphoric acid derivatives, which make APP and PAPP play the role of flame retardance mainly in the condensed phase. 36,37 MCA can only exert the flame-retardant effect in gas phase due to only non-flammable gases generated during the decomposition of MCA. 38,39 Thus, it has become a research hotspot to develop IFRS by comprehensively utilizing the advantages of the APP, PAPP, and MCA.…”