| Polypropylene has been widely used in automotive industry,packaging and electronic industry due to its low price,light weight,non-toxic and other advantages.Unfortunately,polypropylene is extremely easy to burn and difficult to flame retardancy attributed to it containing only carbon and hydrogen element and C-C,which results in the poor char forming of polypropylene.Besides,plenty of smoke and toxic gases are generated during the combustion of polypropylene,posing a great threat to the safety of human life and properties.Therefore,the enhancement of flame retardancy for polyolefin is always a hot but challenging research field on polymer composites.Magnesium hydroxide has attracted much atention due to its non-toxic,inexpensive and ability to improve the flame retardance and smoke suppression performance of polypropylene at the same time.However,the carbonization performance of polypropylene/magnesium hydroxide system is poor,and the magnesium oxide layer formed in the combustion process owns low strength,which results in the generation of cracks in the magnesium oxide layer,deteriorating the flame retardancy and smoke suppression performance of polypropylene/magnesium hydroxide system.To solve above problems,a series of core-shell magnesium hydroxide-based flame retardant composites with high catalytic carbonization effect on polypropylene were designed and synthesized in this paper.Then,the foamed intumescent structure,porous ceramic structure or porous intumescent structure were introduced into polypropylene/magnesium hydroxide-based flame retardant composites for improving the carbonization property of polypropylene and constructing the carbon layer with enhanced flame retardance and smoke suppression performance.Furthermore,the relationship between the structure of the carbon layer and the flame retardance and smoke suppression performance was discussed.The results are as follows:1.The carbonization performance of polypropylene system was improved by the in-situ generated multi-walled carbon nanotubes.The nickel hydroxide@magnesium hydroxide composite flame retardant was synthesized by precipitation method.The flame retardancy and smoke suppression properties and carbonization of polypropylene/nickel hydroxide@magnesium hydroxide were investigated.The results showed that nickel hydroxide@magnesium hydroxide in-situ catalyzed the dehydrocarbonization of PP into multiwall carbon nanotubes,which improved the carbonization of the system.The total heat release,total smoke production and total carbon monoxide production of polypropylene/nickel hydroxide@magnesium hydroxide with 60 wt%addition amount were decreased by 81.5%,94.6%and 81.8%,respectively,compared with pure polypropylene.2.The intumescence of the char layer was improved by orientated multi-wall carbon nanotubes in-situ generated in polypropylene system.The nickel-molybdenum@magnesium hydroxide flame-retardant composite was prepared by co-precipitation method.The flame retardancy and smoke suppression properties of polypropylene/nickelmolybdenum@magnesium hydroxide were investigated.And the carbonization mechanism and char layer structure of the polypropylene/nickel-molybdenum@magnesium hydroxide were explored.The results showed that nickel-molybdenum@magnesium hydroxide catalytic carbonized polypropylene,resulting in the orientated growth of multi-wall carbon nanotube array on the surface of flame retardant particles,which improved the intumescence of the carbon layer,and enhanced the barrier effect of the char layer.3.The intumescence of char layers for polypropylene system was improved by the rapid intumescence of foamed carbon layers at the early stage of burning.The foamed intumescent carbon layer structure was introduced into the polypropylene/nickel catalyst@magnesium hydroxide system by the rapid carbonization of ester generated from the synergism of the intumescent flame retardant(ammonium polyphosphate+pentaerythritol)and nickel catalyst@magnesium hydroxide for improving the flame retardancy of polypropylene which was dragged by the hysteresis of the catalytic carbonization of polypropylene at the early stage of burnig.The structure-function relationship between the flame retardance and smoke suppression performance and the structure of char layers in polypropylene/intumescent flame retardant/nickel catalyst@magnesium hydroxide system was investigated.The results showed that nickel-molybdenum@magnesium hydroxide promoted the esterification between ammonium polyphosphate and pentaerythritol into char,forming foamed intumescent carbon layers rapidly,which improved the intumescence and barrier effect of carbon layers at the initial stage of combustion.The peak heat release rate of polypropylene/intumescent flame retardant/nickel-molybdenum@magnesium hydroxide was decreased by 39.8%in comparison to polypropylene/nickel-molybdenum@magnesium hydroxide with 60 wt%addition amount of flame retardant.4.Porous ceramic char layers were constructed to improve the smoke absorption capacity of the char layer in polypropylene system.The porous ceramic char layers were constructed with the addition of the porous ceramic flame retardant(aluminum phosphate@aluminum hydroxide+zinc borate)and nickel catalyst@magnesium hydroxide into polypropylene for overcoming the increase of smoke production in foamed intumescent carbon layer system.The structure-function relationship between the smoke absorption capacity of the char layer and its structure in polypropylene/porous ceramic flame retardant/nickel catalyst@magnesium hydroxide system was investigated.The results showed that the smoke absorption capacity of the porous ceramic char layer was improved owing to its porous structure in comparison with the foamed intumescent carbon layers.And the total smoke production of polypropylene/porous ceramic flame retardant/nickel-molybdenum@magnesium hydroxide was decreased by 87.4%compared to polypropylene/intumescent flame retardant/nickel-molybdenum@magnesium hydroxide with 60 wt%addition amount of flame retardant.Unfortunately,the reduce of intumescence for the porous ceramic char layer resulted the decline of the barrier effect.5.Porous intumescent char layers were constructed to improve the flame retardant and smoke suppression performance of polypropylene system.Expanded graphite was introduced into polypropylene/nickel catalyst@magnesium hydroxide system to construct porous intumescent carbon layer.The structure-function relationship between the flame retardance and smoke suppression performance and the structure of char layers in polypropylene/expanded graphite/nickel catalyst@magnesium hydroxide system was investigated.The results showed that the porous intumescent carbon layer constructed by expanded graphite and nickel hydroxide@magnesium hydroxide improved the intumescence and smoke absorption capacity of char layers and enhanced the carbonization of polypropylene system.The total heat release,total smoke production and total carbon monoxide production of polypropylene/expanded graphite/nickel hydroxide@magnesium hydroxide with 60%addition amount(55%nickel hydroxide@magnesium hydroxide+5%expanded graphite)were decreased by 83.8%,97.3%and 83.9%,respectively,compared with polypropylene. |
PDF Full Text Request