Study On Preparation, Properties And Mechanism Of The Intumescent Flame Retardant Polypropylene Composites

Polypropylene(PP),as one of the three general plastics,is widely used in many fields,for example,housing,automobiles,electronic and electric industry and so on, due to their good mechanical properties and low density and light weight.However, PP is very combustible and the flame is easy to spread.The new progress about flame retardant PP was reviewed in this paper based on the recent references as well as the relative works in our group,in which intumescent flame retardants(IFRs) have received considerable attention in recent years due to their advantages such as low smoke,low toxicity and no corrosive gas generation.We have prepared intumescent flame retardant(IFR)PP composites by melt-mixing technique.Base on the work of the themal-degradation of IFRs,we prepare the IFR/PP composites. Then the thermal stability and flammablility properties of the composites have been studied.Finally,the application of IFRs in flame retardant PP/ethylene propylene diene rubber(EPDM)has been studied.This dissertation is composed of three parts.In the first part,the experiments are designed to discuss the thermal degradation of the IFRs and to confirm the different types of reactions involved.The results revealed that,when heated,melamine(M) releases some nonflammable gas and dilute the oxygen in the air,while melamine phosphate(MP)not only plays a role as M,but also catalyses the dehydration. Moreover,the IFR system,i.e.pentaerythritol(PER)/MP forms an intumescent carbonaceous protective layer retarding the degradation.The second part of this dissertation tells the application of IFRs in polypropylene(PP)to prepare the IFR PP composite.In order to solve the problem that the IFR system,especially PER,a commonly used carbonization agent,is easily attacked by moisture(or water)and the exudation of the additive leads to a decrease in the properties of the PP composites,not only flame retardancy,but mechanical and electrical insulating properties.Compared with PER,its two derivatives, dipentaerythritol(DPER)and tripentaerythritol(TPER)having much less water solubility are used in the IFR system in the flame retardant PP composite and their mechanism are also investigated.Moreover,polydimethlysiloxane(PDMS)as a substitute for water-soluble polyols is used with melamine phosphate(MP)in the intumescent flame retardant PP composites.It is found that the addition of PDMS into the PP/MP composites increases the water resistance of the PP/MP/PDMS composites,and the thermal degradation of PDMS will form an intumescent protective layer,which can help retard the flammability of the composite.However, only the high content of the IFRs can make the IFR composites with good flame retardant properties.Thus,PP/IFR/metallic-oxide composites are prepared,in which, the metallic oxides,including titanium dioxide(TiO₂),lanthanum trioxide(La₂O₃), zirconium dioxide(ZrO₂),molybdenum trioxide(MoO₃),manganese dioxide(MnO₂) and dichromium trioxide(Cr₂O₃)are selected as synergistic agents.The synergism of the metallic oxides with the IFRs is discussed.It is found that in the case of the IFR composites containing metallic oxides,all of them have higher LOI values than the composites without them,and the composites with 1%zirconium dioxide(ZrO₂) or 1%dichromium trioxide(Cr₂O₃)can achieve the V-0 rating while the PP/IFR(26%)composite achieve no rating at all.Furthermore,Scanning electron microscopy(SEM)reveals that the surface of the intumescent char is strongly modified in the presence of the metallic oxide.The poor compatibility with polymer matrix is another problem associated with the IFR system,and then,EVA,as an efficient interfacial agent,is used in the PP/IFR composite.The effect of EVA on the compatibility between the IFR additives and the polymer matrix and mechanical properties is studied.Moreover,the combustion characteristics of the EVA modified flame retarded composites containing IFRs is also study.It is found that the more the EVA in the composite,the better the compatibility of the IFRs with the matrix.The mechanical properties,especially the elongation at break,increase with increasing EVA content.However,the addition of EVA leads to a decrease in the flame retardancy of the composite.The possible mechanism is proposed.Series of dynamically vulcanized(DV)IFR PP/ethylene propylene diene rubber (EPDM)are made through one step of melt mixing.Three typical vulcanization agents as dicumyl peroxides,sulfur and phenolic resins are selected for the system. The combustion characteristics and the mechanical properties of the DV IFR composites are studied and the work is given as the third part of this dissertation. From the results,it can be seen that dynamically vulcanization not only improves the mechanical properties but also helps the flame retardation of the composites.And above all,the sulfur DV IFR PP/EPDM system performs the best among the three vulcanized systems.