Synthesis Of Novel Flame Retardants Based On Schiff Bases And Their Applications In EVA Copolymer

Many halogen-free flame retardant cables are used for the consideration of security. Ethylene-vinyl acetate (EVA) copolymers were widely used in wire and cable industry as insulating materials due to its good mechanical and physical properties, easy processing as well as good resistance to chemicals. However, EVA copolymers burn very rapidly, without leaving any char residue, so how to improve the flammability of EVA is very important. In this thesis, based on the molecular design, three series of intumescent flame retardants (IFRs) containing phosphorus and nitrogen were synthesized from Schiff bases in the use of their variable substrate structures. The flame retardant effect and mechanism in EVA with different organic functional groups and oligomers’ structures were studied. On the above basis, nano-flame retarded EVA systems and synergism between nano-flame retardants and IFRs were also studied.First, two novel oligomeric intumescent flame retardants containing both phosphorous and nitrogen, poly(amino phosphonate ester)s (PAPEs), were synthesized by reacting diethyl phosphite with two different polyschiff bases obtained from the reaction of diamines with dialdehyde. The chemical structures of PAPEs were characterized by NMR and Fourier Transform infrared (FTIR). The results of thermogravimetric analysis (TGA) showed that PAPEs had excellent charring ability in nitrogen. Thermal stability and flammability properties of EVA blends with various PAPE contents were investigated. The results showed that PAPEs could effectively improve the flame retardancy of EVA. EVA/30%PAPE-e blend has a LOI value of28and a reduction of36%in the PHRR value.Secondly, polyphosphate esters (designated as PDP, PEP, and PPP), were synthesized by reacting phenyl dichlorophosphate with three bis-hydroxy azomethine monomers through interfacial polycondensation. The polyphosphate esters were characterized by NMR, FTIR, and gel permeation chromatography (GPC). Thermal stability and flammability properties of EVA/30%IFRs blends were investigated by TGA, limited oxygen index (LOI), and MCC. The EVA/IFRs blends exhibited high thermal stabilities and char yields at600℃were11-19%in nitrogen. The results from MCC indicated that the addition of PPP to EVA reduced the PHRR by about33%, while the LOI values increased from19to22.Thirdly, based on the above results, we used raw materials of p-hydroxybenzaldehyde, diamine, diethyl phosphite and benzenephosphonic dichloride to synthesize three intumescent flame retardants (PAB, PEB, and PPB). The results from UL-94showed that EVA/IFRs blends all could reach V-2rating. The addition of PAB into EVA reduced the PHRR value by31%, and the LOI value increased from19to24.Fourthly, synergistic effect was studied between organo-montmorillonite (OMT) and PAB in EVA nanocomposites. The results of transmission electron microscopy (TEM) showed that OMT preferentially located in PAB. The results showed that synergistic effect of flame retardancy exsited between PAB and OMT in EVA resins. The value of PHRR was reduced and the LOI value was increased. Silicoaluminophosphate structure was formed by reactions between phosphoric acid generated by PAB with SiO2and Al2O3.SiO2from OMT. Moreover, the decomposition of the organic intercalation agent could form protonic acid which may further favor the oxidative dehydrogenation crosslinking charring process.Subsequently, PAPE-e was covalently grafted onto the surface of carboxyl multi-walled carbon nanotube (MWNT-COOH) to obtain MWNT-PAPE. The product was characterized by FTIR. Through the results of TGA it could predict that the grafting ration of MWNT-PAPE is about15%. MWNT-PAPE was soluble and stable in polar solvent, such as DMF. The addition of MWNT-PAPE into EVA resin could improve the flame retardancy of the nanocomposites.