| As one of the five general plastics, polypropylene (PP) has been widely used in daily life. However, PP is highly flammable and aplenty of smoke is generated during burning. Intumescent flame retardant (IFR) is often used in PP composite because of their environmental-friendly. Synergist, such as montmorillonite, kaolinite, and zeolite, is widely added to the IFR system to enhance the efficiency of flame retardancy.In this work, zeolite in association with a conventional IFR system containing ammonium polyphosphate and pentaerythritol was introduced to enhance the flame retardancy of PP. Different positive ions were introduced into zeolite by ion exchange method to improve the catalytic performance of zeolite. The effect and mechanism of modified zeolite on the synergism of flame retardant with IFR were also investigated.1. Zeolite contained Lewis acid sites (4A-L) was prepared by ion-exchange and calcination. The crystallinity characterization using X-ray diffraction (XRD) and chemical structure characterization by Fourier transform infrared (FTIR) spectroscopy showed that Lewis acid sites were presented in modified zeolite. The fire properties of PP composites were evaluated by thermo-gravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 vertical burning and cone calorimeter. The results indicated that the LOI value could reach 31.1 and the heat release rate (HRR) of PP/IFR composite decreased to 244.2 (kW/m2) for the PP composite sample containing IFR (18 wt.%) and 4A-L zeolite (2 wt.%). The morphology of the char was investigated by digital photos and scanning electron microscope (SEM). The result demonstrated that the presence of 4A-L could cause the formation of compact and thick char layers. The mechanical property test results indicated that the presence of 4A-L had minimal negative effect on tensile strength of PP composite compared with other samples. It was suggested that IFR/4A-L combination could retard the degradation of PP through the formation of compact char layer, which protects the matrix effectively from heat penetrating inside and further degradation, resulting in lower weight loss rate and better fire performance.2. Zeolite contained lanthanum (4A-La) and holmium (4A-Ho) respectively was prepared by ion-exchange. X-ray fluorescence (XRF) spectrum analysis showed that La or Ho was sucessfully introduced into zeolite, respectively. The difference of the zeolite skeleton structure before and after ion exchange was negligible based on the XRD curves, but the interplanar spacing and the degree of crystallinity was decreased. The result of TGA indicated that 4A-La can absorb more water than 4A-Ho. LOI and UL-94 tests showed that 4A-La has excellent flame retardant synergism with IFR, leading to reduce the amount of smoke. PP/IFR containing 4A-La showed the best burning behavior (LOI:32.7%, UL-94:V-1)3. Six kinds of metallic ions were introduced into zeolite by ion exchange and calcination to obtain 4A-Me. PP/IFR/4A-Cu showed the best flame retardant property in terms of LOI, UL-94 and cone test results. The PP/IFR/Cu possessed the LOI vaule 31.3%, and the V-1 grade in UL-94 test. It is suggested that 4A-Cu can promote the formation of char in the preliminary stage of burning, leaving more C and N in char residual (EDS). This compact char layer can segregate matrix and prevents oxygen and fuel from feeding the flames. |
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