Intumescent Flame Retardation And Nano-Flame Retardation For ABS Resin

Acrylonitrile-butadiene-styrene(ABS)is a widely used thermoplastic material due to its banlanced mechanical properties,chemical resistance and processing advantages. In many application cases,it is necessary to construct a flame retarded composition for ABS resin.Compared with other flame retarded polymer systems including PE,PP, EVA,PA,much work should be done for non-halogenated flame retarded ABS system due to the pressure of environment issues.Considering the specialty of ABS resin,three aspects for the flame retarded ABS resin were studied including ABS/intumescent flame retardant(IFR),nano-flame retarded ABS systems and synergism between nano-flame retardants and IFRs.A novel phosphorous-nitrogen containing intumescent flame retardant,poly (4,4-diaminodiphenyl methane spirocyclic pentaerythritol bisphosphonate)(PDSPB) based on phosphorus oxychloride(POCl₃),pentaerythritol(PER)and 4, 4'-diaminodiphenyl methane(DDM)was synthesized and characterized by FTIR,¹H NMR and TGA.The results showed that PDSPB had excellent thermal stability and charring ability.The addition of PDSPB enhanced the thermal stability and flame retardancy of ABS significantly.The weight of residues improved greatly with the addition of PDSPB.It is worth noting that crosslinking of ABS by PDSPB can further enhance the thermal stability and flame retardancy of materials.The grafting of MAH onto ABS can improve the ability of catalytic carbonization.ABS-g-MAH with different grafting degree were prepared using dicumyl peroxide as the initiator and styrene as the comonomer and mixed with OMT via melt blending. FTIR spectra results indicate that MAH was successfully grafted onto butadiene chains of the ABS backbone in the molten state and the relative grafting degree increased with increasing loading of MAH.TEM images show the size of the dispersed rubber domains of ABS-g-MAH increased and the dispersion is more uniform than that of neat ABS resin.XRD and TEM results show that intercalated/exfoliated structure formed in ABS-g-MAH/OMT nanocomposites and the rubber phase intercalated into OMT layers distributed in both SAN phase and rubber phase.TGA results reveal the intercalated/exfoliated structure of ABS-g-MAH/OMT nanocomposites has better barrier properties and thermal stability than intercalated ones of ABS/OMT nanocomposites.OMT network structure was found to be formed in ABS-g-MAH/OMT nanocomposites,which strongly affected the flammability properties of the nanocomposites.The OMT network improves the melt viscosity and results in restraint on the mobility of the polymer chains during combustion,which leads to significant improvement of flame retardancy,thermal stability and T_g for the nanocomposites.ABS/MWNTs nanocomposites were prepared by melt blending.TGA results showed that the addition of MWNTs accelerated the degradation of ABS especially in air atmosphere.Carbon nanotubes form a network in the composite at the percolation threshold,and the thermal stability,viscoelasticity,electrical conductivity and flammability properties of ABS/MWNTs nanocomposites are strongly affected by the network structure.The rheological percolation threshold,0.60 wt%,was determined on the basis of a power law relation.The effect of network structure of MWNTs on the flammability properties was complicated and time to ignition as well as average mass loss rate were affected most by the network structure.Synergistic effects between MWNTs and OMT during combustion for improving the flame retardaney of ABS resin were studied.The dispersion of OMT was enhanced by the addition of MWNTs and intercalated/exfoliated structure was formed in ABS/OMT/MWNT nanocomposites.Flammability properties measured by cone calorimeter revealed that synergistic effect exists between OMT and MWNTs.The combination of OMT and MWNT can enhance the thermal stability under nitrogen but does not have any improvement with the participation of oxygen.Linear viscoelastic properties of the ABS nanocomposites show that the co-existence of OMT and MWNTs can enhance the network structure that can hinder the movement of polymer chains and improve flame retardancy.The existence of OMT enhances the graphitization degree of MWNTs during combustion and improves the anti-oxidative ability and flame retardancy of materials. Synergistic effect was studied between OMT and PDSPB in ABS nanocomposites. The OMT dispersion was characterized by X-ray diffraction(XRD)and transmission electron microscopy(TEM).OMT preferentially located in PDSPB and exfoliated structure was formed instead the intercalated structure in ABS resin.Significant synergistic effect exists between OMT and PDSPB.Incorporating PDSPB with OMT can enhance both thermal stability and flame retardancy of ABS resin. Silicoaluminophosphate(SAPO)structure was formed by reactions between the phosphoric acid generated on heating from PDSPB and SiO₂ and Al₂O₃·SiO₂ of OMT after decomposition.Moreover,the decomposition of the amine silicate modifier leaves a strong acid catalytic site that may further favor the oxidative dehydrogenation crosslinking charring process and increase the char yield.PDSPB was covalently grafted onto the surfaces of MWNTs to obtain MWNT-PDSPB and according nanocomposites were prepared via melt blending.The grafting reaction was characterized by FTIR,¹H NMR.After high density PDSPB(65 wt%)were attached to the MWNTs,core-shell nanostructures with MWNTs as the hard core and PDSPB as the soft shell were formed.The resultant MWNT-PDSPB was soluble and stable in polar solvents,such as DMF.MWNT-PDSPB has excellent thermal stability and charring ability.The optical microscopy and TEM results showed that the functionalized MWNTs could achieve better dispersion in ABS matrix.The addition of 0.2%MWNT-PDSPB can achieve same flame retarded efficiency as 1.0% MWNT in ABS nanocomposites.The linear viscoelastic behavior indicated that MWNT-PDSPB could form network structure at very low nanotube loading(0.2%)than un-functionalized MWNTs.The grafting of intumescent flame retardant of PDSPB can improve both the dispersion of nanotubes in polymer matrix and flame retardancy of the nanocomposites.