The recent implementation of new environmental legislations led to a change in the manufacturing of composites that has repercussions on printed wiring boards (PWB). This in turn led to alternate processing methods (e.g., lead-free soldering), which affected the required physical and chemical properties of the additives used to impart flame retardancy. This review will discuss the latest advancements in phosphorus containing flame retardants for electrical and electronic (EE) applications and compare them with commercially available ones. The mechanism of degradation and flame retardancy of phosphorus flame retardants in epoxy resins will also be discussed.

https://www.mdpi.com/1996-1944/3/8/4300/pdf

Recent Developments in Halogen Free Flame Retardants for Epoxy Resins for Electrical and Electronic Applications.

The ubiquity of polymeric materials in daily life comes with an increased fire risk, and sustained research into efficient flame retardants is key to ensuring the safety of the populace and material goods from accidental fires. Phosphorus, a versatile and effective element for use in flame retardants, has the potential to supersede the halogenated variants that are still widely used today: current formulations employ a variety of modes of action and methods of implementation, as additives or as reactants, to solve the task of developing flame-retarding polymeric materials. Phosphorus-based flame retardants can act in both the gas and condensed phase during a fire. This Review investigates how current phosphorus chemistry helps in reducing the flammability of polymers, and addresses the future of sustainable, efficient, and safe phosphorus-based flame-retardants from renewable sources.

/pdf/molecular-firefighting-how-modern-phosphorus-chemistry-can-1eit1frfy2.pdf

Molecular Firefighting—How Modern Phosphorus Chemistry Can Help Solve the Challenge of Flame Retardancy

Phosphorus-containing flame retardant epoxy thermosets: Recent advances and future perspectives

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

Polymer/polyhedral oligomeric silsesquioxane (POSS) nanocomposites: An overview of fire retardance

The pyrolysis and fire behavior of halogen-free flame-retarded DGEBA/DMC, RTM6 and their corresponding 60 vol.-% carbon fibers (CF) composites were investigated. A novel phosphorous compound (DOPI) was used. Its action is dependent on the epoxy matrix. DGEBA/DMC and DOPI decompose independently of each other. Only flame inhibition occurs in the gas phase. RTM6 shows flame inhibition and a condensed phase interaction increasing charring. Both mechanisms decrease with increasing irradiance, whereas in RTM6-CF charring is suppressed at low ones. RTM6 + DOPI shows a higher LOI (34.2%) than DGEBA/ DMC + DOPI and a V-0 classification in UL 94. Adding CF only enhances the LOI, DOPI + CF leads to a superposition in LOI for DGEBA/DMC-CF + DOPI (31.8%, V-0) and a synergism for RTM6-CF + DOPI (47.7%, V-0).

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

The present article will highlight two different approaches to obtaining phosphorus-modified epoxy materials which are expected to be qualified for high performance printed wiring boards (PWB). The first method involves the incorporation of novel non-reactive derivatives of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) in an epoxy novolac (DEN 438) and subsequent curing with dicyandiamide (DICY) and fenuron. An alternative process for the manufacture of phosphorus-modified epoxy materials is the reactive introduction (preformulation) of aldehyde adducts of DOPO and 2,8-dimethyl-phenoxaphosphine-10-oxide (DPPO) into the backbone of the DEN 438 novolac, followed by curing with 4,4'-diaminodiphenylmethane (DDM). The epoxy materials obtained in this way reached the UL 94 V-0 rating at low phosphorus concentrations (0.6-1.4% P) and high Tg values (180-190 °C). Comparison of the results obtained by both methods, however, revealed a slight superiority of the application of non-reactive additives in the epoxy system used. Whereas all formulations containing aldehyde adducts of DOPO and DPPO exhibited an insignificant drop of T g , this parameter was maintained at the high level of the unmodified material when DOPO-based additives bearing bridging and nitrogen-containing substructures were applied. These novel DOPO derivatives are the first non-reactive additives that do not influence the Tg of an epoxy material. DEN 438 samples containing commercially available and various other already known organo-phosphorus compounds were manufactured in an analogous manner. All of them showed lower Tg values and poorer flame retardant efficiencies than the novel phosphorus-modified materials. To explain the superior flame inhibition activity of phosphacyclic compounds, the decomposition behaviors of DOPO and DPPO, including their sulfur derivatives, were investigated by means of thermal desorption mass spectroscopy (TDMS) and high-resolution mass spectroscopy (HRMS). PO radicals as well as PS radicals were identified as gas-phase active species. However, such fragments could not be detected when investigating samples containing open-chained phosphorus compounds.

Jan Diederichs

Papers

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

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

Advanced Flame-Retardant Epoxy Resins for Composite Materials