2019/05/22

AIMPLAS hosts the IV edition of the Fire-Retardant Plastics Conference

The fourth Fire Retardant Plastics Conference, organised by AIMPLAS with pinfa support in Valencia, Spain, 4th April, brought together seventy flame retardant producers, compounders, flame retardant users and retailers. Luis Roca of AIMPLAS (the Spanish Plastics Technology Centre) and Adrian Beard, pinfa President, opened the conference which presented both research and company product innovations in PIN flame retardants, with the theme “Recyclability, sustainability and future trends”.

Research towards tomorrow’s PIN fire safety

Rodolphe Sonnier, C2MA Mines d’Alès, France, outlined different possible routes for developing bio-based PIN flame retardants. Bio-based molecules can have a high oxygen/carbon ratio (so low energy release in fire), functional groups enabling grafting of flame retardant molecules, and an inherent capacity to generate char (carbon content). Examples cited include lignin or phenols, which can be functionalised with phosphorus, but a challenge is stability in processing. Studies have shown effectiveness of ground olive pomace (olive stone pressing waste) to replace pentaerythritol in intumescents, but black coloration is an obstacle. Phytic acid, naturally found in seeds and which has high phosphorus content, offers potential because it can be combined with different metal salts. The economics of bio-based FRs can be improved if they also have another function in the polymer, e.g. as a plasticiser.

See also the book “Towards bio-based flame retardant polymers” (Springer, 2018) https://www.springer.com/us/book/9783319670829

Begoña Galindo, AIMPLAS, indicated that the bio-plastics are expected to grow from 2% of the world market in 2015 to 40% in 2030. She presented the example of fish processing waste: 2 million tonnes/year is generated annually in Europe. Testing in the DAFIA project  (see pinfa Newsletter n°86) has shown that DNA recovered from fishery wastes can be an effective flame retardant in polyamide (UL94-V0, 1.6 mm, at 20% loading). Challenges include higher smoke production than with commercial phosphorus flame retardant, black color, deterioration of mechanical properties.

Belén Redondo, AIMPLAS, presented the example of bio-based FRs derived from poultry production by-products (feathers, of which 3 million tonnes are generated annually in Europe). In the KaRMA project (Horizon 2020), functionalised keratins are being tested for FR coating of synthetic fibres, wood and concrete; and the feathers themselves to bring both structure and fire resistance in composites with bio-derived polymers (humins from cellulose).

Fouad Laoutid, Materia Nova, Belgium, outlined a number of research areas looking at PIN flame retardant solutions for bio-based polylactide polymers, including metal phytate salts, phosphorus functionalised lignin, insertion of DOPO based molecules (phosphorus containing) and DABP (4,4’-diaminobenzophenone) into the PLA polymer chain and plasma enhanced chemical vapour deposition (PECVD) of phosphorus compounds onto PLA fibres. The reaction of these phosphorus groups into the PLA chain showed to improve fire resistance.

Gerard Lligadas, University Rovira i Virgili, Spain, also showed a number of different research directions based on functionalisation of undecylenic acid, derived from natural plant oils. These were tested to react DOPO into epoxies or polyesters, or silicon into polyurethanes. He further discussed the action of boron-functionalised bio-based FRs, which act to neutralise radicals in the gas phase during fire.

Laura Martí and Miguel Angel Valera, AIMPLAS, presented a diversity of research routes towards integrating PIN flame retardancy into polymers, including reactive and polymeric / oligomeric PIN FRs, and resulting in intrinsically FR polymers. Approaches include integration of phosphorus or phosphorus-nitrogen groups or monomers into polymer chains, or grafting of phosphorus groups (e.g. DOPO based) onto polymers. Work presented covered polyethylene, polypropylene, polyamide, PET, ABS (project with ELIX Polymers and GIDAI group of UNICAN) . Cross-linking of polymers can also improve fire performance (e.g. polyurethanes) but modifies mechanical properties. Aimplas is testing “reactive extrusion” (REX), where PIN FR functional molecules are reacted with polymers during extrusion, using a specifically designed research and testing extruder and control software.

Ehsan Kalali, IMDEA Madrid, summarised research into use of different nano-forms of minerals as synergists for PIN flame retardants, including ferrocene (nano iron oxide F2O3), layered double hydroxides (LDH) with nano nickel hydroxide, nano cobalt hydroxide, zinc cobalt. These inorganic nano compounds, at doses of up to 5%, have been shown to be highly effective in reducing smoke emissions (in some cases, nearly 60% less smoke) and in improving fire performance (e.g. reduction in peak heat release rate pHRR). It is hypothesised that these nano particles act in the gas phase by rapidly converting to char the flammable volatile compounds released by polymers in fire (by condensation or catalysis), thus preventing these gases burning.

Industrial applications: recycling, 3D printing and XEV

Arthur Schwesig, MGG Polymers, Austria, presented the company’s activity “urban mining” materials from end-of-life plastics. He presented examples of consumer products today produced using recycled plastics, recovered and re-compounded by MGG from waste polymers. The performance of sorting of the waste plastic stream is essential, and is a key part of MGG’s know-how: whilst a 10% error rate in recycling is adequate for downcycling, recycling for polymer use in technical applications requires at least 98% accuracy in sorting. This is a real challenge: for example, end-of-life automotive plastics must be separated into over 200 distinct streams. MGG now offers a PC-ABS polymers based on post-consumer recovered plastics: UL94-V0, a range of colours, bromine-free and recyclable, with the Fraunhofer “Circularity Approved” label. Mr Schwesig underlined the difficult problem of dealing with post-consumer plastics containing brominated flame retardants, for which no recycling routes are available in Europe.

Adrian Beard, Clariant, explained that the company decided voluntarily to move out of halogenated flame retardants in the 2000’s, considering them to be non-sustainable. Indeed, the products in question are today banned or on REACH evaluation lists. Clariant is also looking for routes to phosphorus flame retardants which avoid PCl4: the companies DEPAL products (di aluminium phosphite) can instead be produced from P4 via sodium hypo-phosphite. Clariant has also developed a PIN smoke represent, effective in synergy with phosphorus FRs, to substitute for zinc borate, because of concerns resulting from the classification of other boron compounds (see pinfa Newsletter n°91). Clariant’s product policy is driven by the company’s internal portfolio sustainability assessment system “Ecotain” (pinfa Newsletter n°79) based on independent external evaluations, such as ENFIRO and GreenScreen (pinfa Newsletters 36 and 100).

Antonio Nerone, Dupont, summarised the need for PIN fire safety solutions for electric vehicles (XEV) and the considerable new performance requirement challenges posed by this market. It is estimated that a third of the world car market will be electric or hybrid by 2030. The high voltage and currents required for electrical motorisation, combined with increasing use of polymers in vehicles for design performance and weight gain, imply both considerably increased fire risk (more electrics with risks of arcing, overheating, specific fire risks of batteries …) and more demanding materials requirements. Materials requirements are multiple and daunting: electrical (CTI, dialectric), mechanical, heat and chemical resistance and durability, thermal stability (CLT) and warpage, processing (thin parts), density, aesthetic and visual (e.g. the orange colour, essential to enable identification of high-voltage cables in case of maintenance or accident). PIN FRs (with non-halogenated pigments) enable “low halogen” solutions, important to avoid halide emissions leading to voltaic corrosion. The need for tither fire safety is recognised, but clarification is needed on standard specifications: UL94-V0, EN 62368 “communications” systems (increasingly required by car manufacturers).

Sebastian Hörold, Clariant, discussed flame retardants for 3D-printing. The market today for 3D-printing polymers is around 1.2 billion US$, with an expected growth of +75% per year. There are three main technologies today: powder bed laser fusion (currently limited to polyamides PA12 and PA11), laser photopolymerisation (certain photopolymers) and filament or pellet extrusion (which functions rather like an ink-jet printer). Clariant has developed PIN FR solutions for filament extrusion, able to achieve UL94-V0 (0.4 mm) after printing and low-smoke with limited mechanical performance loss compared to neat polymer. Clariant has also developed a PIN FR EOS solution with a dry blend of polymers (uniform 20 µm powder) able to achieve UL94-V0 (2 mm) for aircraft applications.

Brigit Fassbender, Budenheim, presented developments in nitrogen and phosphorus inorganic (PIN) flame retardants for different polymers. These PIN FRs function by generating an intumescent char layer on the polymer surface, which isolates the polymer from fire and also reduces smoke release. Widely used PIN FRs such as melamine cyanurate, melamine polyphosphate or ammonium polyphosphate offer good ecotoxicity properties and high thermal stability, but pose challenges in thin applications, polymer content is insufficient to generate protective char (difficult to achieve UL94-V0 below 0.8 mm). Difficulties of compatibility between such inorganics and polymers can lead to migration of the FR to the polymer surface (blooming). These challenges are addressed by adapting FR formulations, including with specific coatings, for different polymers. These formulations can deliver intumescent fire performance, whilst conserving or even improving polymer materials properties such as elasticity or elongation at break.