| Polypropylene(PP)is widely used in construction,housewares,manufacturing,and other fields due to its advantages of being lightweight,corrosion-resistant,and easy to process.However,PP is extremely combustible,and its melting point is much lower than its degradation temperature.The high temperature generated by combustion makes the melt easily flow and form melting drops,further enlarging the combustion hazard.The anti-dropping property of PP is mainly achieved by adding flame retardant to the substrate,which form high-quality protective char layers during combustion and reduce the fluidity of high-temperature melt.However,it is difficult to obtain excellent anti-dropping property only by forming protective char layers.Moreover,due to the poor char formation and low melting point of PP,the addition of flame retardant is generally large,significantly reducing its mechanical properties.Based on forming protective char layers,inhibiting the flow of high-temperature melt of PP can be achieved by transforming the linear molecular chains into crosslinked structures.Irradiation treatment of PP containing a crosslinking agent effectively produces crosslinked structures in its matrix.In addition,the most widely used flame retardant in PP is intumescent flame retardant(IFR),which has the flaws of low flame retardant efficiency and large additive amount.To preserve its mechanical properties as far as possible to ensure the antidropping property of flame retardant PP after irradiation,the flame retardant efficiency of the traditional IFR should be further improved to reduce the total amount of additives in the matrix.Based on this,to improve the anti-dropping property of PP,we prepared the crosslinked PP by γ-irradiation while studying the effect of radiation dose and additives of crosslinking agent on its irradiation effect.At the same time,the flame-retardant efficiency of IFR was improved by the synthesis of a char-forming agent and synergistic flame-retardant,which was applied to improve the flame retardancy of PP.Finally,the anti-dropping property of PP was improved by irradiation with the combination of flame retardant PP and irradiation crosslinking strategy.The main contents of this paper are as follows:Improving the irradiation crosslinking strategy to enhance the crosslinking degree of polypropylene: In order to prepare highly crosslinked polypropylene,polypropylene samples containing the crosslinking agent trimethylpropane triacrylate(TMPTA)and polybutadiene(PB)were subjected to different doses(0,20,40,60,80,and 100 k Gy)of γ-irradiation treatment.It was proven that both the increase of crosslinking agent and radiation dose enhanced the crosslinking degree of PP.However,high radiation doses would enhance the irradiation degradation effect,impairing the mechanical property of PP.To restrict the irradiation degradation and improve the crosslinked effect of irradiation,the γ-irradiation effect of Cu(Ⅱ)on PP was further investigated.It was found that Cu(Ⅱ)could promote the formation of crosslinked structures,which was particularly significant at low radiation doses.The crosslinked structure inhibited the melting and crystallization of PP and improved its thermal stability and mechanical properties.The mechanism analysis showed that Cu(Ⅱ)could promote the reaction between crosslinking agent and PP free radicals to enhance the crosslinking degree.It also improved the stability of PP free radicals to weaken the irradiation degradation.Hence,the crosslinking degree of PP could be enhanced.With the increase of radiation dose,Cu(Ⅱ)gradually transformed into Cu(Ⅰ)and lost its promoting effect.Therefore,Cu(Ⅱ)’s promoting effect on PP radiation crosslinking was most apparent at low radiation doses.Improving the formulation of intumescent flame retardant to enhance the flame retardancy of polypropylene: The traditional flame retardants have insufficient flame retardant efficiency,and their high addition level reduces the mechanical properties of polypropylene.Triazine-based charring agent ETDPCs were synthesized by a one-pot method.It was mixed with flame retardant(flame retardant(FR): 2/1 mass ratio of ammonium polyphosphate(APP)and melamine pyrophosphate(MPP))as IFR to improve the flame retardancy of PP.An outstanding LOI value of 30.4% and UL-94 of V-0 rating for PP were achieved with the optimal mass ratio of FR/ETDPCs(3/1)at 20 wt% total loadings.The char layer during the burning of PP exhibited an excellent inhibition effect on the release process and total amount of heat and smoke.The flame retardant mechanism of ETDPCs was further revealed: the benzene ring and triazine group of ETDPCs could participate in forming residual char to improve its quality,which enhanced the insulation effect of heat flow and inflammable gas to improve its flame retardancy.Adding synergistic flame retardants to improve the flame retardancy of polypropylene:Synergistic flame retardants can improve the quality of the char layer during the combustion process of polypropylene,thereby enhancing its flame retardancy.Zirconium phosphate was used as a synergistic flame retardant with IFR to further improve the flame retardant efficiency and mechanical properties of PP.The c Zr P was prepared by intercalation modification of zirconium phosphate,and the effect of c Zr P as a synergistic flame retardant with IFR on the flame retardant efficiency of PP was further studied.When the total amount was 18 wt%,and the mass ratio of c Zr P/IFR was 1/8,PP exhibited the best flame retardancy with a LOI of 31.6%,passing the V-0rating of 3.2 mm UL-94.Moreover,the addition of c Zr P also promoted the improvement of mechanical properties of modified PP.The synergistic flame retardant mechanism of c Zr P exhibited that the catalytic char-forming effect and the barrier effect of the lamellar Zr P enhanced the quality of residual char to improve the flame retardancy of PP.Combining of irradiation flame retardant strategies to improve the droplet resistance of polypropylene: The irradiated PP containing flame retardant was prepared by combining flame retardant PP with irradiation crosslinking strategies.Lower radiation doses(0,5,10,15,20,and 25 k Gy)were executed to reduce the irradiation degradation effect of PP.The flame retardancy and irradiation effect of PP showed good synergism.The addition of flame retardants would not affect the radiation crosslinking effect of PP basically,and the crosslinking structure generated by γ-irradiation would slightly enhance the flame retardancy of PP.It was revealed that γ-irradiation not only improved the anti-dropping properties of PP but also enhanced its mechanical properties and thermal stability.The investigation of the anti-dropping mechanism by irradiation revealed that the crosslinked molecule structures of irradiated PP containing flame retardant produced by γ-irradiation exhibited extremely poor fluidity at high temperature,which was conducive to the formation of high-strength dense char layers maintaining the original shape.Therefore,the fluidity of high-temperature melt was effectively reduced and the flame retardancy of PP was enhanced,which promoted the achievement of the flame retardancy and anti-dropping property of PP. |
PDF Full Text Request