| Melt blowing is a technology that processes molten polymer into micro-nanofiber nonwovens.Among them,polypropylene（PP）has become the main melt blowing raw material due to its low cost,good comprehensive performance,and environmental friendliness.Flammability is one of its characteristics.During the combustion process,the dripping phenomenon will easily cause the fire to spread,which will endanger the safety of life and property,the obvious disadvantages will greatly limits the application of melt blowing filter materials in the direction of high protection requirements.On the other hand,the filtration efficiency of traditional PP non-woven fabrics is still low,thought high-efficiency filtration can be achieved by means such as electrets.Electrospinning is highly used in high-efficiency filter materials because of its nanometer scale and large specific surface area.Therefore,it is a research direction to combine melt blowing nonwovens and electrospinning fiber membranes to obtain high-efficiency filter materials.Therefore,this topic combines melt-blown and electrospinning non-woven materials,and at the same time,halogen-free flame retardant ammonium polyphosphate（APP）was added into the electrospinning solution to obtain flame retardant air filtration performance.:（1）The process parameters were optimized to obtain PP melt-blown substrates with better filtration properties,mechanical properties and other properties.Through single factor experiment,the influence of flow rate,receiving distance,hot air temperature and hot air pressure of metering pump on the properties of nonwovens was analyzed.The following conclusions were drawn on the premise that other parameters remained unchanged:The flow rate of metering pump has a great influence on the surface density and thickness of melt-blown cloth.As the flow rate increases,the polymer extrusion speed increases,the fiber amount per unit area increases,the surface density and thickness become larger,and the material becomes brittle and poor,and the permeability becomes worse,but the filtration efficiency increases.Receiving distance has little effect on the performance of melt-blown cloth,but when receiving distance increases gradually,the feel of melt-blown cloth becomes softer.When the temperature of hot air rises,the surface density and thickness have little influence,and the filtration efficiency is stable in a certain range.When the hot air pressure increases,the draft air speed increases,the surface density and thickness are small,the bending length is small,and the softness is good.The mechanical properties increase first and then decrease,and the filtration efficiency rises first and then gently.（2）The PAN/APP electrostatic nanofiber membrane was composited on the PP substrate to prepare the micro-nanofiber non-woven flame-retardant filter material,and the flame-retardant filter material was prepared without destroying the micro-nanofiber structure.After a series of tests,it was found that filtration of the composite material for 0.3μm aerosol particles can reach more than 98%.Due to the existence of APP,the micro-nanofiber composite material burns slowly after ignition,and there is no droplet dripping during burning.The afterburning time is0s.The carbon content of the surface layer of the flame retardant filter material increases significantly;TG results show that the thermal performance of PP/PAN@APP is better than that of PP/PAN material,and the residual carbon content is more than 7 times that of the latter.（3）Using the synergistic flame retardant effect between P-N-Si,nano-Si O2 is used as silicon source,APP is used as P and N source,and nano-Si O2 is used to migrate to the polymer surface during the combustion process to form a dense and uniform silicon-containing carbon layer,The advantages of blocking the entry of external oxygen and preventing the escape of combustion volatiles and smoke can further increase the flame retardant properties of PP/PAN@APP nonwovens.It is found that when the nano-Si O2 concentration is 4%,the burning surface of the material is covered with a black carbon layer,which is non-combustible and drip-free in case of open fire,and has a high-efficiency flame-retardant effect;The efficiency of the samples is greater than 92%.At the same time,because nano-Si O2 is hydrophilic,the contact angle of the surface of the nanofiber material is 67.33°,while the PP melt blowing contact angle of the substrate of the composite material is 125°,indicating that the material has both hydrophilic and hydrophobic functions. |
