Synthesis Of Zirconium Organophosphonate And Study On Properties And Mechanisms Of Flame Retarded And Toughened Epoxy Composites

Epoxy resin(EP)has good mechanical strength,electrical insulation,chemical stability,corrosion resistance,and excellent bonding properties,presenting huge potential in various fields.However,similar to other polymer materials,EP composed of C,H,and O elements is extremely flammable and easy to cause fires.The release of a large amount of smoke and toxic gases brings great difficulties to rescuers.Moreover,the crosslinking density of EP after being cured is very high,resulting in high rigidity,high brittleness,and easy brittle fracture.Therefore,the flammability and brittleness of EP limit its scope of application.Aiming at the improvement of flammability and brittleness of EP mentioned above,this paper uses zirconium organophosphonate with excellent thermal stability and acid-catalyzed carbon-forming ability as the flame retardant,smoke suppressant,strengthening,and toughening agent of EP.The organic zirconium phosphonate nanoparticles have weak Bronsted acid sites and strong Lewis acid sites derived from P-OH and Zr4+,which have an acid catalysis effect and can promote the carbon formation reaction of EP.The dense carbon layer formed can act as a physical barrier,cutting off the heat and mass exchange.Zirconium organophosphonate has good interface compatibility with EP and can be uniformly dispersed in the EP matrix,thus presenting a strengthening and toughening effect.The synthesis of different zirconium organophosphonates through molecular design shows that these zirconium organophosphonates have good flame retardant and smoke suppression as well as toughening effects on EP composites.1.The layered compound zirconium phenylphosphonate(ZrPP)was prepared by using a monophosphonic acid phenylphosphonic acid as a raw material.XRD results showed that the interlayer space of ZrPP was 1.474 nm which was larger than α-ZrP(0.743 nm).This is because a lot of phenyl groups are bonded to the layer of ZrPP,which is larger than the hydroxyl group on α-ZrP,thus enlarging the interlamellar spacing.The lamellar structure characteristics of ZrPP were observed by scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The electron microscopy results showed that ZrPP exhibited a similar lamellar structure toα-ZrP,and the lamellar size was basically within 1 μm.The size distribution was relatively scattered.Thermogravimetric analysis(TGA)results showed that ZrPP had good thermal stability,and the pyrolysis mass loss was mainly due to the phenyl group.The combustion of pure EP produced a large amount of flue gas and heat.Compared with pure EP,the peak of heat release rate(PHRR),total heat release(THR),total smoke release(TSR)and peak of CO production rate of 3wt%ZrPP-EP composite material were reduced by 7.6%,11.2%,17.5%,and 16.7%,respectively.It can be seen that ZrPP had a certain flame-retardant and smoke-suppressing effect on EP.The tensile strength of pure EP was 35.10 MPa,and the elongation at break was 3.31%.Compared with pure EP,the tensile strength of the 2wt%ZrPP-EP composite was increased to 49.49 MPa,showing an increase of 41.0%.Meanwhile,the elongation at break was increased by 49.8%.With the increase of ZrPP addition,the tensile strength and elongation at break of ZrPP-EP composites gradually increased,indicating that ZrPP had the dual strengthening and toughening effect.The impact strength test results further confirmed the toughening effect of ZrPP on EP.2.A kind of bisphosphonate N,N-bis(phosphonate methyl)glycine(GDMP)was prepared by Mannich reaction and complexed with zirconium oxychloride to form layered Zirconium N,N-bis(phosphonate methyl)glycine(ZrGDMP).Compared with pure EP,the tensile strength of 3wt%ZrGDMP-EP was increased to 57.65 MPa,presenting an increase of 73.2%.The elongation at break was 5.67%,increased by 56.6%.The impact strength of 3wt%ZrGDMP-EP reached 24.8 kJ/m2,which was an increase of 55%compared with pure EP.It can be seen that ZrGDMP had a strengthening and toughening effect on EP composites.Compared with the ZrPP prepared in chapter 2,ZrGDMP had a better flame retardancy and smoke suppression effect on epoxy resin.It may be attributed that the bisphosphonic acid structure of GDMP makes ZrGDMP has higher flame retardant efficiency.The elemental composition also proved this point(the P content of ZrPP was 10.49 at.%,without N element,while the N content of ZrGDMP was 6.93 at.%,and the P content was 14.21 at.%).ZrGDMP had a higher P content and P-N synergistic flame retardant effect,which effectively reduced the fire hazard of composite materials.3.Zirconium aminotrimethylene phosphonate(ZrATMP)was prepared by a triphosphonic acid amino trimethylene phosphonic acid(ATMP),which exhibited a rod-like structure.Compared with pure EP,the PHRR,THR,TSR,and PCOPR values of EP composites with 3wt%ZrATMP were decreased by 30.4%,39.2%,23.1%,and 47.3%,respectively.The tensile test showed that ZrATMP can significantly increase the tensile strength and elongation at break of EP composites.Compared with pure EP,the tensile strength of 3wt%ZrATMP-EP was increased to 68.03 MPa,presenting an increase of 110.7%.Besides,the elongation at break was 5.55%,an increase of 66.2%.Compared with ZrPP and ZrGDMP prepared in chapters 2 and 3,ZrATMP had better strengthening and toughening effect on epoxy resins,which may be due to the presence of amino and methylene groups on the ZrATMP molecule,which can effectively improve its interface compatibility with the EP matrix.As a result,the ZrATMP molecule can be better dispersed in the EP matrix.When the EP composite material is subjected to an external force,the well-dispersed ZrATMP nanoparticles will produce a stress concentration effect,absorb energy,reduce internal stress,hinder crack propagation,presenting a toughening effect.4.Based on inorganic-organic hybrid technology,a new type of organic zirconium phosphonate(CZrP)was synthesized from biomass cardanol.The interlayer spacing of CZrP increased to d=4.12 nm.This is because the long side chain of cardanol is inserted into the CZrP lamella to increase the interlayer spacing.From TEM pictures of 6wt%ZrP-EP and 6wt%CZrP-EP,it can be seen that the ZrP nanosheets were obviously agglomerated in the EP matrix,while the CZrP nanosheets can be well dispersed in the EP matrix,indicating that the CZrP nanosheets had better interfacial compatibility with EP matrix than the inorganic ZrP nanosheets.Compared with pure EP,the PHRR value of 6wt%CZrP-EP was reduced by 42%.When the same amount of ZrP was added to EP,the PHRR value was only reduced by 16%.Compared with pure EP,the THR value of 6wt%CZrP-EP was reduced by 21%.Compared with pure EP and ZrP-EP composites,all CZrP-EP composites had lower TSP values.The PCOPR values of CZrP-EP composites gradually decreased,which were much lower than those of pure EP and ZrP-EP composites.Compared with pure EP and ZrP-EP composites,all CZrP-EP composites had lower FIGRA values.The FIGRA value was greatly reduced from 13.5 kW/(m2·s)of pure EP to 7.2 kW/(m2·s)of 6wt%CZrP-EP.Compared with pure EP,FIGRA was reduced by 47%,which meaned that CZrP obviously reduced the fire hazard of EP.The tensile strength of 6wt%CZrP-EP was increased to 52.3 MPa,and the elongation at break was increased to 5.4%,which were increased by 28.8%and 170%,respectively,compared with pure EP.The increase in tensile strength of CZrP-EP composites was attributed to the reinforcement of well-dispersed two-dimensional CZrP nanosheets.The increase in elongation at break was attributed to the good toughening effect of the long alkyl chain of cardanol on CZrP.5.From the four zirconium organophosphonates prepared in the first four chapters,the one with the best comprehensive performance was selected to compound the zirconium organophosphonate(ZrGDMP)with intumescent flame retardants(pentaerythritol and ammonium polyphosphate)to study the effect of the compound system on EP flame retardant effect.In addition,in order to solve the problem that inorganic ZrP nanoparticles are easy to agglomerate in the EP matrix,this chapter also prepared organically modified α-zirconium phosphate(OZrP),which was used in combination with the intumescent flame retardant system,in order to develop flame retardant epoxy resin composites with better comprehensive properties.The 2wt%ZrP-EP,2wt%OZrP-EP and 2wt%ZrGDMP-EP samples with thicknesses of 0.8,1.6 and 3.2 mm were selected for the UL-94 vertical burning test.All three samples passed the UL-94 V-0 rating at the three thicknesses,but differed in their burn times.As the thickness decreases,the samples took longer to reach self-extinguishing,as thinner samples are more difficult to achieve UL-94 V-0 rating.Among the three samples,2wt%ZrP-EP took the longest time to reach self-extinguishing,2wt%ZrGDMP-EP took second,and 2wt%OZrP-EP took the shortest time to reach selfextinguishing,indicating the synergistic effect between OZrP and IFR optimal.Compared to the low LOI value of pure EP(25%),the LOI value of EP composites with 20wt%IFR and 3wt%OZrP was increased to 45%.Compared with pure EP,the PHRR,THR,TSR,and PCOPR values of EP composites with 20wt%IFR and 3wt%OZrP were decreased by 79.1%,58.3%,62.8%,and 80.9%,respectively.This was mainly attributed that OZrP had an acid-catalyzed carbon-forming effect,which can catalyze the formation of a protective char layer.The IFR system can quickly form a protective carbon layer on the surface of EP material to inhibit heat and mass exchange.Compared with inorganic ZrP,EP composites with OZrP had higher impact strength,due to the grafted organic molecules of OZrP and the large interlayer spacing.