Preparation Of Water-resistant And Highly-efficient Intumescent Flame Retardants And Their Application For Polypropylene

Polypropylene (PP) as one of the five major common plastics has been widely used inmany fields, such as automobiles, housing decorations, electronic and electrical appliances,etc. However, its inherent flammability and burning with dripping have severely restricted itsfurther application. Therefore, it is very important to improve the flame retardancy of PP. Inrecent years, intumescent flame-retardant technique is one of the fastest growingflame-retardant technologies, which provides methods and ideas to prepare high performancehalogen-free flame retardant PP. In this dissertation, lots of research work has been carried outto overcome the deficiencies of the existing intumescent flame retardants (IFR), such as lowefficiency, poor water resistance, thermal instability, and so on. Firstly, melaminepyrophosphate (MPP) was prepared, and used together with pentaerythritol (PER) to form anovel IFR system to flame retard PP. Then, the synergistic effects of polyborosiloxane (pBSil),aryl phosphate and its nanocomposites on PP/IFR composite were studied. Moreover, theeffect of flame retardant masterbatch using thermoplastic polyurethane (TPU) as carrier resinto encapsulate IFR on flame retardant PP was also investigated. Furthermore, a novel charringagent triazine-based macromolecule (TBM) was synthesized, and combined with MPP toflame retard PP. Accordingly, flame retardant PP with highly efficient flame retardancy,outstanding water resistance and good thermostability were prepared, and theirflame-retardant mechanism was intensively studied. The main research contents and resultsare listed as following:First, MPP was synthesized by using melamine and sodium pyrophosphate, and was usedtogether with PER to flame retard PP. The effects of MPP/PER on the mechanical properties,flame retardancy and thermostability of PP were investigated. And the flame-retardantmechanism of MPP/PER was explored by thermogravimetric analysis (TGA), Fouriertransform infrared (FT-IR) and TG-FTIR, etc. The results showed that MPP possessed goodthermostability and outstanding water resistance. PP/MPP/PER composite had good flameretardancy and low smoke release. When the total content of MPP/PER was25wt%, and themass ratio of MPP to PER was3:1, the limiting oxygen index (LOI) value of flame retardantPP was29.0%, and the vertical burning test achieved a UL-94V-1rating. Meanwhile,compared with PP, the peak heat release rate (pHRR), average heat release rate (av-HRR),total heat release (THR), average mass loss rate (av-MLR) and peak specific extinction area(pSEA) of PP/MPP/PER were reduced by67.7%,66.2%,26.6%,52.2%and63.6%,respectively. Furthermore, the possible flame-retardant mechanism of MPP/PER was revealed.When being heated and burned, the IFR generates a swollen multicellular char after undergoing esterification, crosslinking and foaming reaction between MPP and PER, acting asa physical barrier, which slows down heat and mass transfer between gas and condensedphases, thus protecting the underlying material from burning.Second, resorcinol bis(diphenyl) phosphate (RDP) was used together with IFR to flameretard PP, and the effects of RDP on the mechanical properties, rheological properties, flameretardancy and thermostability of PP/IFR composite were studied. It was found that there wasa good synergistic effect between RDP and IFR on flame retardant PP. The addition of RDPimproved the quality and thermostability of the swollen char, forming a more compact anddense char layer. Moreover, RDP could improve the compatibility between IFR and PPsubstrate, thus improving the mechanical properties of the composite. The dynamicmechanical thermal analysis (DMA) result showed that RDP had plasticization andtoughening effects on the PP/IFR composite. With the RDP content increasing, the storagemodulus (E') and glass transition temperature (Tg) gradually decreased. Meanwhile, thedynamic rheological analysis results showed that, the storage modulus (G′), loss modulus(G′′), loss factor (tanδ) and complex viscosity (η*) of the PP/IFR composite were decreasedwith the addition of RDP, indicating that the processability of the composite was improved.Third, phosphorus-containing nanosponge (P-NS) and phosphorus-containingmontmorillonite (P-MMT) were prepared by loading RDP onto cyclodextrin nanosponge (NS)and montmorillonite (MMT), respectively. And they were utilized as synergistic agents toimprove the flame retardancy of the PP/IFR composite. It was found that both P-NS andP-MMT had significant synergistic effects with IFR on flame retardant PP, and thethermostability of PP/IFR composite was significantly improved. The X-ray diffraction (XRD)results showed that, after modified by RDP, the interlayer spacing of MMT was increasedfrom1.22nm to2.15nm, indicating that RDP was a good organophilic-modification agent tofunctionalize MMT. In addition, compared with the O-MM modified by octadecyl trimethylammonium chloride (OTAC), P-MMT showed higher thermostability and better synergisticeffect with IFR on flame retardant PP.Fourth, a novel synergistic agent containing boron and silicon, namely polyborosiloxane(pBSil) was prepared via the condensation reaction of boric acid, tetraethoxysilane andoctamethyl cyclotetrasiloxane. The obtained pBSil was then combined with IFR to flameretard PP, and the effects of pBSil on the mechanical properties, flame retardancy andthermostability of the PP/IFR composite were investigated. It was found that pBSil couldimprove the compatibility between IFR and the PP matrix, thereby improving the mechanicalproperties of the composite. Compared with zinc borate, zeolite and nano-silica, pBSilshowed much better flame retardancy and smoke suppression on the PP/IFR composite. When the content of pBSil was3.0wt%, the LOI value of flame retardant PP was increased from29.0%to35.0%, and the UL-94rating was improved from V-1to V-0rating. The TGA, FT-IRand TG-FTIR results showed that, pBSil could enhance the thermostability of IFR, andpromote the char formation. Moreover, the compactness and thermostability of theintumescent char were significantly improved, thus resulting in the improvement of the flameretardancy of the composite.Fifth, a novel flame-retardant masterbatch, namely TPU-e-IFR, using thermoplasticpolyurethane (TPU) as carrier resin to encapsulate IFR, was adopted to flame retard PP. Theeffects of TPU on the mechanical properties, flame retardancy, thermostability andwater-resistance of the flame retardant PP were investigated. The results showed that thedispersion of the IFR and the compatibility between the IFR and PP matrix were improved byTPU, which was responsible for the enhancement of mechanical properties and flameretardancy of the PP/IFR composite. The differential scanning calorimetry (DSC) resultshowed that the initial esterification temperature of IFR was increased from198oC to213oCby incorporation of TPU, thus effectively preventing the esterification reaction between MPPand PER during the processing of the composite. In comparison with IFR, TPU-e-IFR hadbetter thermostability, charring performance, water resistance and flame retardancy.Finally, a novel charring agent triazine-based macromolecule (TBM) was synthesized byusing cyanuric chloride, ethanolamine and diethylenetriamine via nucleophilic reaction, andwas combined with MPP to flame retard PP. The chemical structure of TBM wascharacterized by FT-IR, elementary analysis, and solid-state13C-NMR. And the TGA resultshowed that the initial decomposition temperatures of TBM was298°C, and the residue charof TBM at700°C was as high as38.7wt%. Additionally, TBM exhibited much lower watersolubility than PER. The solubility of TBM was only1/20~1/10of PER at the sametemperature. Moreover, TBM showed an obviously synergistic effect with MPP in flameretardant PP. When the content of MPP was16.7wt%and TBM was8.3wt%, the LOI valueof the PP/MPP/TBM composite was31.0%, and the vertical burning test reached a UL-94V-0rating. Meanwhile, the pHRR, THR and av-MLR of the composite were77.1%,31.4%and58.1%lower than those of the PP matrix, respectively. Furthermore, the composite exhibitedan outstanding water resistance and could still obtain a UL-94V-0rating after being soaked in70oC water for168h.