Preparation Of Bio-based Flame Retardants And Their Applications In Polypropylene

Polypropylene(PP)is one of the most widely used polymer materials in modern life due to its excellent physical and chemical properties.Nevertheless,the flammability of PP limits its application in multiple fields.In recent years,environmental protection and safety of materials have attracted people's attentions.Therefore developing environmental friendly flame-retarded PP has been a hot research for several decades.Developing flame retardants based on biological sources is a good candidate to meet the requirements of sustainable strategy for safety and environmental protection,and related research has been widely concerned.However,the thermal stability of most bio-based materials is poor which limits them to be used in many materials that need to be process at high temperature.Moreover,the flame retardant efficiency for lots of bio-based flame retardants is poor which hinders their use as excellent flame retardants.Modifying bio-based materials by using physical or chemical methods may give them the characteristics that can be used as perfect fl ame retardants.This is necessary for the development of bio-based flame retardant technologies.In this article,bio-based materials phytic acid and cytosine(Cy)were used as raw materials to prepare metal phytate,piperazine phytate(PA-Pi)and triazine carbon-forming agent CC-Cy.These products were used as components of flame retardants and combined with commercial intumescent flame retardants(IFR)with different formulations.These IFR system were used to prepare flame-retarded PP composites.The detailed research includes the following three parts:1.Zinc phytate(PA-Zn),nickel phytate(PA-Ni),cobalt phytate(PA-Co)were prepared by using zinc(Zn2+),nickel(Ni2+)and cobalt(Co2+)as catalytic component and phytate as flame retardant component,respectively.These metallic phytates were used as synergists with commercial IFR to form an IFR system.They were used to prepare PP composites by melt blending.The results showed PP/17IFR/2PA-Zn which contains 17 wt% IFR and 2 wt% PA-Zn obtains a LOI value of 29.2 vol%,which is 5.1 vol% higher than that of PP composites containing 19 wt% IFR alone.1 wt% PA-Ni and 17 wt% IFR make the PP composites achieve a LOI of 29.5 vol%,and substituting PA-Co for PA-Ni a LOI 28.6 vol% is obtained for the PP composites.The results showed that the catalytic effects of PA-Ni and PA-Co are similar,and the flame-retardant efficiency is better than that of PA-Zn.These metallic phytates modify the quality of char residues which resulting in good flame retardancy for PP composites.The flame retardant mechanism was analyzed by using thermogravimetric analysis(TGA),scanning electron microscopy(SEM)and Raman spectroscopy etc.The results TGA showed that metallic phytates help to improve the crosslinking degree and thermal stability of IFR at high temperature,and thus improve the quantity of char residues.Moreover metallic phytates modify the quality of char and result in intumescent char with lots folds and cellular structure which is good for preventing heat and gas from combustion.In addition,the structure of char residues does not changed,so these synergists improve the flame retardant efficiency by accelerating or delaying the char formation.2.PA-Pi was prepared by using phytic acid and piperazine.It was used as acid source and compounded with dispentaerythritol(DPER)to form an IFR system.The PP/PA-Pi/DPER composites were prepared by melt blending.The flame retardancy of PP/PA-Pi/DPER composites with different formulations were studied.It was found that LOI of PP composites is 28.1 vol% when IFR(PA-Pi: DPER = 3:1)is 25 wt%,and passes the test of UL-94 V-0 rating.The flame retardant mechanism was analyzed by TGA,SEM and Raman spectroscopy etc.The results of TGA showed that the reactions between PA-Pi and DPER are complex.Both catalytic and cross-linking effects exist.The for mer occurs at early degradation and the later occurs at the later stage of degradation.SEM and Raman spectroscopy showed that the surface of char layer is more compact and complete with the content of IFR increasing,the defects decrease and the quality o f the char layer is improved,thus a higher flame retardant efficiency is obtained.3.A triazine derivation CC-Cy was synthesized by the reaction of cytosine and cyanuric chloride.CC-Cy as a charring agent,APP and BDP form an IFR system which was used to improve the flame retardant properties of PP.The results showed the PP sample containing 20 wt% APP and 5 wt% CC-Cy achieves the UL-94 V-2 rating.While the PP sample with 18 wt% IFR(APP/CC-Cy=4:1)and 3 wt% BDP obtains the UL-94 V-0 rating indicating the improved flame retardant efficiency and a synergistic effect among them.The flame retardant mechanism was analyzed by using TGA,SEM and Raman spectra.The results showed that the reactions between APP and CC-Cy promote the formation of char residues,and the addition of BDP further enhances the char formation.Infrared thermal imaging found that BDP can reduce the surface temperature of PP samples.Furthermore,BDP may not only work in the gas phase,but also promote the charring reactions in the solid phase.The synergistic effects among APP,CC-Cy and BDP promote the formation of effective and cellular char layer and improve the flame retardant efficiency.