Modification Of Fly Ash And Its Study On Flame Retardancy And Mechanical Properties Of Polypropylene

Fly ash(FA)is a coal-fired waste with an increase in emissions as our demand for energy increases year by year.Currently,In China some FA have been used in construction,agriculture and industrial production,but the majority of FA is still in the open-air which not only occupies a lot of land,but also caused great pollution on the lake and the environment.Therefore,it is urgent to find a way to solve this problem.Zeolite is a kind of silicate with large specific surface area and then exhibit good adsorption.The synthesis of zeolite from FA is a major route of FA reusage for high value-added.Polypropylene(PP)is a kind of generally used plastic,but for safety consideration,its use is limited in more scope recently for its flammability.Most generally flame retardant used in PP involved intumescent flame retardant(IFR),however the flame retardant efficiency is strongly dependent on IFR loading,Some study found a small amount of silicate can be used as synergist in PP/IFR.For the composition of FA is mainly Si/Al/O,in this study,FA was used as synergist firstly and furthermore 4A/4A-Zn zeolite synthesized from FA was instead of FA as synergists.The main work is as follows:Firstly,FA was added into PP/IFR system to substitute some IFR.The combustion behavior of PP composites was analyzed by limited oxygen index(LOI),vertical combustion(UL-94)and cone calorimetric test(Cone).The results show that FA exhibited a little synerigism with IFR in PP.Through thermogravimetic analysis(TGA)and scanning electron microscopy(SEM)found that FA can promote the formation of residual char.However,some mechanical performance including tensile strength,elongation at break and impact strength of PP composites became worsening.4A zeolite(4A)were synthesized by alkali-melting-hydrothermal treatment,and its structure is characterized by FTIR,X-ray diffraction(XRD)and SEM.The results showed that 2.5%4A lifted the LOI of the PP/IFR system to 33.9%,and reached UL-94 V-0 grade.In CONE peak heat release rate(PHRR)decreased from 436 KW/m2 to 188 KW/m2,Total heat release(THR)reduced from 123 MJ/m2 to 55 MJ/m2.Different from the addition of FA,4A brought little mechanical properties worsen to PP/IFR.Finally,zinc(Zn)were introduced into 4A during its synthesis process and the product is 4A-Zn.Its structure and Zn loading was characterized by FTIR,XRD,SEM,XPS and EDS.and the results showed the Al atoms in 4A were replaced by Zn in 4A-Zn.The addition of 2wt%4A-Zn in PP/IFR enhanced LOI of PP/IFR further to 37.2%and obtained UL-94 V-0 grade.PHRR value reduced to 136 KW/m2,and THR reduced to 40 MJ/m2.By mechanism analysis,it was documented that Zn in 4A-Zn can form Lewis acid sites and improve the flame retardancy by catalyzing the formation of char.Similar as the addition of 4A,a small amount of 4A-Zn also brought limited deteriotation on mechanical performance to PP/IFR.