Preparation And Characterization Of Intumescent Flame Retardant And Silane-crosslinked PP And Its EPDM Composites

Polypropylene(PP) and PP/ethylene propylene diene rubber(EPDM) have been widely used in many fields due to its outstanding comprehensive properties.However, their applications are restricted because of their flammable properties and less thermally stability.Intumescent flame retardant(IFR) and silane-grafted-crosslinking (SGC) technologies have played an important role in improving the flame retardancy and thermal stability of polyolefin and plastic/rubber materials.On the basis of summarizing the applications of IFR and SGC technologies in PP and PP/EPDM,in this dissertation,we designed a new IFR system and studied its use in PP and PP/EPDM.Moreover,we also studied the flame retardant,char formation and synergy mechanism of the IFR system.In addition,we applied SGC technology into PP/EPDM and discussed the grafting mechanism.At last,the synergy effect between IFR and SGC was also studied in this dissertation.This dissertation is composed of four parts.1.Pentaerythritol phosphate(PEPA) synthesized by the reaction between pentaerythritol(PER) and POCl₃ combined with melamine phosphate(MP) was used to prepare flame retarded PP and PP/EPDM composites.It was found that the combination of MP and PEPA show more effective flame retardation than the individual component.All composites containing both MP and PEPA had a high LOI value and reached the UL-94 V-O rating.Cone calorimeter results demonstrated that MP in combination with PEPA can help to reduce the HRR and smoke emission.TG studies proved that the MP/PEPA flame retarded PP and PP/EPDM composites were more thermal stable than the untreated PP and PP/EPDM.It was observed from the RTFTIR study that many complicated reactions would take place during the thermal degradation process of the PP/EPDM/PEPA/MP composites.FTIR,XPS,SEM,XRD and Raman experiments testify that the char formed after cone calorimeter testing could be divided into three parts,i.e.outer,middle and inner char layer,according to their different components and structures.In terms of the testing results,the outer and middle char mainly consists of pyrophosphate and polyphosphate,whereas the inner char is mostly composed of the undegraded PP/MP/PEPA composite.During the combustion process of the PP/MP/PEPA,the formation of a good intumesent char could protect the underlying materials form the heat and flame and thus enhance the flame retardancy of the material.2.Ni²⁺-Fe³⁺ LDH,Fe-OMT,OZrP and POSS,as synergist,were added into MP/PEPA IFR system to prepare the synergistic intumescent flame retardant PP composites.The flame retardancy,thermal stability,char formation mechanism and crystallization behavior of the composites were studied compared with the PP/MP/PEPA composite without synergist.According to the study,it had been found that Ni²⁺-Fe³⁺ LDH was the most effective synergist among the four kinds of synergists.The Ni²⁺-Fe³⁺ LDH synergistic composite increased the LOI value from 32 to 35 and decreased the PHRR value from 207 to 164 kW/m3,respectively.It also had been found that a kind of "microtube" existed in the outer char layer of Ni²⁺-Fe³⁺ LDH,OZrP and POSS synergistic composites after CONE testing.3.The melt grafting of vinyltrimethoxysilane(VTMS) onto PP/EPDM blends was studied.The effect of VTMS,EPDM and initiator concentrations on mechanical properties,melt flow index(MFI) and gel content of the modified PP/EPDM samples were investigated.The influence of coagents,i.e.styrene and trimethyloipropane trimethacrylate was also studied.Scanning electron microscopy(SEM) was used to observe the fractured surface of PP/EPDM and the modified PP/EPDM blends.The VTMS grafting reaction was in situ monitored using differential scanning calorimetry (DSC).Moreover,the thermal and crystallization behavior of VTMS-crosslinked PP/EPDM blends were studied by thermogravimetric analysis(TG) and DSC, respectively.It had been found that the thermal stability of VTMS-crosslinked PP/EPDM was improved.DSC measurements showed that the grafting reaction occurs from 170 to 220℃and the crystallization temperatures increased compared with those of the untreated PP/EPDM.4.The influence of SGC technologies on IFR system was studied.First,It was found that the incorporation of vinyl trimethoxysilane(VTMS) into the PP/EPDM composites containing MP and DPER as intumescent flame retardants leaded to an increase in LOI.However,after the silane crosslinking,the flame retardancy of the PP/EPDM composites decreased,which may be caused by the leakage of some flame retardants during the immersion of the composites in the hot water.Both the tensile strength and the elongation at break of the PP/EPDM composites containing VTMS (without silane crossinking) increased in comparison with the composite without the silane,whereas the silane crosslinking resulted in an increase in the tensile strength and a decreased in the elongation at break of the PP/EPDM composite.Moreover,the thermal behavior of the PP/EPDM composites was affected by the crosslinking.Both XPS and real time FTIR results revealed that the residue left from the PP/EPDM composites decomposed at higher temperatures are mainly composed of phosphorus and oxygen-containing compounds.Second,APP is microencapsulated with PU resin by in situ polymerization method. TG results show that the initial decomposition temperature of PUMAPP is advanced, while it possesses a relatively higher thermal stability when temperature is up to 618℃.According to LOI values,UL-94 test and cone calorimeter results,it has been found that the PP/EPDM/PUMAPP/DPER composites possesses a better flame retardancy compared with the PP/EPDM/APP/DPER composite at the same loading. The testing results of mechanical properties show that the microencapsulation of APP is beneficial to improve the compatibility of APP in the polymer resin.The interest of the use of VTMS as synergistic agent in the formulations is also investigated.The addition of a small quantity of VTMS results in an improvement of the fire retardant effect It has also been demonstrated that,under hydrolytic conditions,the crosslinking of VTMS allows reducing the migration of flame retardants and keeping good fire retardant properties.