Effect Of Intercalated LDHs On Flame Retardancy And Mechanical Properties Of Polypropylene

Polypropylene(PP),as an important commodity plastic,has been widely used in various fields.However due to its flammability and dripping behaviors,which greatly limits its application,so it is necessary to enhance the flame-retar-dant performances.Layered double hydroxides(LDHs),a class of very important anionic layered clays,which have been shown to offer good flame retardancy and smoke suppression due to their unique chemical composition and layered structure.In the last two decades there has been considerable interest in polymer/LDHs nanocomposites due to their remarkably enhanced mechanical,thermal,electrical and fire retardant properties.In this paper,LDHs intercalated with some organic ions containing the flame retardant elements was synersized and then used in PP composites,the effects of these modified LDHs on thermal stability and fire behaviors of PP were explored.The main work is as follows:1.Firstly,AB-LDHs was prepared by an anion exchange method.Infrared spectroscopy(FTIR),X-ray diffraction(XRD)andThermogravimetric analysis(TGA)results confirmed the AB anions were intercalated into LDHs,the interlayer spacing was enlarged from 0.76 nm by 1.52 nm.The LOI,UL-94 and TGA results show that LDHs and AB-LDHs will improve flame retardant performance by enhancing the residual carbon content and prolonging the dripping time.XRD and SEM results confirmed that LDHs/AB-LDHs were partially exfoliated in the PP matrix.The composites acquired the best tensile strength at 2phr LDHs/AB-LDHs loading.2.Secondly,AB-LDHs were introduced into PP/40IFR system by melt blending method.The LOI,UL-94 and CONE results showed that PP/38IFR/2AB-LDHs had the best flame retardancy,its LOI was 36.5%,and passed the UL-94 V-0 rating and the peak heat release rate(PHRR)of decreased to 363 kW.m-2,an approximately 75.4%reduction compared to pure PP.SEM and XRD results confirmed that AB-LDHs achieved better dispersion in the matrix.The results of SEM,FTIR and EDS of residual chars showed that AB-LDHs led to a compact and continuous residue duringcombustion,which served as an effective thermal insulationlayer to retard flammable volatiles escaping from the interior and also shield the underlying matrix from exterior heat irradiation.3.Finally,Mo-Mg-Al-LDHs(B-LDHs)and Mo-Zn-Mg-Al-LDHs(T-LDHs)were prepared by ion exchange method,then they were introduced into PP/PP-g-MA/IFR system respectively.FTIR,XRD,TGA and EDS results indicated that Mo7O246-had been successfully intercalated to the Mg-Al-LDHs and Zn-Mg-Al-LDHs,and the basal spacing was increased from 0.87 and 0.76 nm to 1.12 and 1.09 nm,respectively.LOI,UL-94 and Cone results of PP composties showed that the flame retardancy of PP/PP-g-MA/37IFR/3t-LDHs acquired the best performance,the LOI was 35.3%,passed the V-0 rating and PHRR was 338 kW.m-2,which was 77.1%lower than pure PP.SEM and EDS of residual char and FTIR of PP/PP-g-MA/IFR composites results showed that B-LDHs and T-LDHs can make more P elements remained in the residual carbon,forming a more dense and complete carbon layer,isolate combustible gases to better protect the polymer.