Novel DOPO-based flame retardants in high-performance carbon fibre epoxy composites for aviation

Abstract Two novel, halogen-free, phosphorus-based oligomeric flame retardants are investigated in the commercial epoxy resin RTM6 and ∼70 wt.% carbon fibre RTM6 composites (RTM6-CF) with respect to pyrolysis and fire behaviour. The flame retardants are based on 9,10-dihydro-9-oxy-10-phosphaphenanthrene-10-oxide (DOPO) units linked to the star-shaped aliphatic ground body tetra-[(acryloyloxy)ethyl] pentarythrit (DOPP), or heterocyclic tris-[(acryloyloxy)ethyl] isocyanurate (DOPI), respectively. The glass transition temperature is reduced by adding DOPP and DOPI, but the mechanical properties of the composites (e.g. interlaminar shear strength (ILSS) and Gc in mode I and II) remain unchanged. Decomposition models are proposed based on mass loss, evolved gas analysis (TG–FTIR) and condensed product analysis (hot stage cell within FTIR). The fire behaviour is investigated comprehensively (UL 94, limiting oxygen index (LOI) and cone calorimeter). Both flame retardants act in the gas phase through flame inhibition and in the condensed phase through charring. The UL 94 of RTM6 is improved from HB to V-1 and V-0; the LOI from 25% to 34–38%. Peak heat release rate (PHRR) and total heat evolved (THE) are lowered by 31-49% and 40–44%, respectively. Adding CF increases the residue, reduces the THE, but suppresses the charring due to RTM6 and flame retardants. Thus the THE of RTM6-CF is reduced by about 25% when DOPI and DOPP are added. However, UL 94: V-0 and LOI of 45% and 48% are achieved with ∼0.6 wt.% phosphorus.

[1]  C. Lin,et al.  Properties and curing kinetic of diglycidyl ether of bisphenol A cured with a phosphorus‐containing diamine , 1999 .

[2]  A. I. Balabanovich,et al.  Effective halogen-free flame retardancy for a monocomponent polyfunctional epoxy using an oligomeric organophosphorus compound , 2006 .

[3]  L. Lee.  Mechanisms of thermal degradation of phenolic condensation polymers. II. Thermal stability and degradation schemes of epoxy resins , 1965 .

[4]  Bryan Ellis,et al.  Chemistry and technology of epoxy resins , 1992 .

[5]  Henry Lee,et al.  Handbook of Epoxy Resins , 1967 .

[6]  M. Döring,et al.  Effect of DOP-based compounds on fire retardancy, thermal stability, and mechanical properties of DGEBA cured with 4,4′-DDS , 2006 .

[7]  Joseph G. Smith,et al.  Flame retardant aircraft epoxy resins containing phosphorus , 2005 .

[8]  G. Camino,et al.  Mechanistic study of thermal behavior and combustion performance of epoxy resins: I homopolymerized TGDDM , 1995 .

[9]  A. I. Balabanovich,et al.  Pyrolysis of epoxy resins and fire behavior of epoxy resin composites flame‐retarded with 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide additives , 2007 .

[10]  S. Levchik,et al.  A Review of Recent Progress in Phosphorus-based Flame Retardants , 2006 .

[11]  D. A. Smith,et al.  Combined pyrolysis and radiochemical gas chromatography for studying the thermal degradation of epoxy resins and polyimides. I. The degradation of epoxy resins in nitrogen between 400°C and 700°C , 1970 .

[12]  Ying‐Ling Liu.  Epoxy resins from novel monomers with a bis‐(9,10‐dihydro‐9‐oxa‐10‐oxide‐10‐phosphaphenanthrene‐10‐yl‐) substituent , 2002 .

[13]  M. Döring,et al.  A Novel DOPO‐Based Diamine as Hardener and Flame Retardant for Epoxy Resin Systems , 2008 .

[14]  S. Levchik,et al.  Thermal decomposition, combustion and flame‐retardancy of epoxy resins—a review of the recent literature , 2004 .

[15]  L. Lee.  Mechanisms of thermal degradation of phenolic condensation polymers. III. Cleavage of phenolic segments during the thermal degradation of uncured epoxy resins , 1965 .

[16]  E. Barbero.  Introduction to Composite Materials Design , 1998 .

[17]  C. Lin,et al.  Flame‐retardant epoxy resins with high glass‐transition temperatures. II. Using a novel hexafunctional curing agent: 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐yl‐tris(4‐aminophenyl) methane , 2005 .

[18]  Kathryn M. Butler,et al.  Thermal and flammability properties of polypropylene/carbon nanotube nanocomposites , 2004 .

[19]  M. Döring,et al.  A New Halogen‐Free Flame Retardant Based on 9,10‐Dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide for Epoxy Resins and their Carbon Fiber Composites for the Automotive and Aviation Industries , 2011 .

[20]  A. I. Balabanovich,et al.  Influence of the oxidation state of phosphorus on the decomposition and fire behaviour of flame-retarded epoxy resin composites , 2006 .

[21]  G. Camino,et al.  Mechanistic study of thermal behaviour and combustion performance of carbon fibre-epoxy resin composites fire retarded with a phosphorus-based curing system , 1996 .

[22]  A. M. Stephen,et al.  The thermal degradation of model compounds of amine-cured epoxide resins. II. The thermal degradation of 1,3-diphenoxypropan-2-ol and 1,3-diphenoxypropene , 1973 .

[23]  M. Döring,et al.  Novel efficient DOPO-based flame-retardants for PWB relevant epoxy resins with high glass transition temperatures† , 2008 .

[24]  G. Nelson.  Fire and Polymers: Hazards Identification and Prevention , 1990 .

[25]  M. Döring,et al.  Effective halogen-free flame retardants for carbon fibre-reinforced epoxy composites , 2006 .

[26]  Edward D. Weil,et al.  A Review of Current Flame Retardant Systems for Epoxy Resins , 2004 .

[27]  A. Mouritz,et al.  Fire Properties of Polymer Composite Materials , 2006 .

[28]  Charles A. Harper,et al.  Handbook of Building Materials for Fire Protection , 2003 .

[29]  A. I. Balabanovich,et al.  Pyrolysis and fire behaviour of epoxy systems containing a novel 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-(DOPO)-based diamino hardener , 2008 .

[30]  Hans Zweifel,et al.  Plastics Additives Handbook , 2009 .