At present, flame-retardant plastic parts past their service lifetime are predominantly used energetically. The further development of the circular economy makes it necessary to rethink materials recycling. However, this issue becomes increasingly complex wherever such additives as flame retardants, fibers, or fillers are used. 

Recycling Halogen-Free Flame-Retardant Plastics. Example: Polyamide 

Polyamide

Additive

Flammschutzmittel

Wiederaufbereitung

Kunststoff-Recycling

Secondary Raw Materials of the Future  

Red phosphorus is an established flame-retardant additive for polyamide 66 (PA66). Even small amounts of it are enough to provide thermoplastics with good fire-resistant characteristics with scarcely any impact on the mechanical properties. However, such compounds have recently undergone significant price increases, as both polyamide 66 base resin and red phosphorus have become more expensive. Consequently, Lanxess AG, Cologne, Germany, is noticing growing demand for high-performance alternative materials based on polyamide 6 and 66 that feature flame-retardant characteristics in other ways, particularly in the electrical/electronic and IT industries. 

PA6 and PA66 with Halogen-Free Flame-Retardant Packages 

Alternatives to PA66 Compounds Containing Red Phosphorus 

Optics play an increasingly important role in plastic components. Glossy and even surfaces are decisive for an attractive appearance. With glass fiber-reinforced polyamides (PA), these requirements can usually only be achieved with an additional coating. A PA specially developed for surface design offers an alternative approach.

For visible components, an even, glossy surface is often desired, which is often difficult to achieve with glass fiber-reinforced PA. PA Grivory G7V from EMS now solves this problem

Aliphatic High-Performance Polyamide for Plastic Surfaces

Spritzgießen

Kunststoffverarbeitung: Verfahren

Kunststoff Werkstoffe

Thermoplaste

Oberflächentechnik

Kunststoff

Bauwesen

Baustoffe

Faserverbundwerkstoffe

Andere Werkstoffe

Kunststofffasern

Verstärkungsstoffe

Glossy Components without Painting

TER HELL PLASTIC GMBH, one of the leading distribution and compounding companies for plastics raw materials in Germany, Europe and China. It is an important partner of well-known, global plastics manufacturers such as Azoty Tarnow, Chevron Phillips, Clariant, DSM, Evonik, Franplast, Momentive, Lucobit, Polimeri, Sabic, Samsung, Teknor Apex and Total Petrochemicals.

Ter Hell Plastic GmbH  

https://www.terhell.de

Antistatika

Compound

Kunststoffhandel

Handel

Dienstleistungen

Polypropylen

Polystyrol

Styrol-Copolymerisate

Treibmittel

Verarbeitungshilfmittel

Weichmacher

Kunststoff-Aufbereitung

For efficient lightweight construction fiber-reinforced plastics with a thermoplastic matrix are increasingly being used. How can these so-called organo sheets be optimised?

Verbundwerkstoffe / Werkstoffverbunde

Gewebe, technisch

Halbzeuge und Zwischenprodukte

Kunststoff-Halbzeuge

Organobleche (gewebeverstärkte Thermoplast-Halbzeuge)

Short fiber modification of matrix-rich zones of fabric-reinforced thermoplastic composites by in-situ melt impregnation – influence on quasi-static properties

Vehicle weight reduction requirements today pose great challenges not only to automotive manufacturers and suppliers but also to material producers. The materials used must cut weight while at the same time withstanding the mechanical and chemical stresses encountered in service. This can be achieved, for example, with blends of polyamide and polypropylene. These blends also offer other useful advantages.

Fig. 4. Test bars after contact with a calcium chloride solution. The grey points indicate degradation. The bars made from the PA+PP blends show basically no degradation, unlike those made from PA.

16:9

Blends of PP and PA Reduce Weight and Improve Chemical Resistance

Blend

Kfz-Elektronik

Elektronik

Lighter Together

The influence of different coupling mechanisms on the structure-properties-relationships of highly filled, flame-retardant EVA/LLDPE based cable compounds.

Polyethylen

Kabel

Automatisierungstechnik

Signalübertragung

Halogen-free flame-retardant cable compounds based on highly filled EVA/LLDPE blend systems – Influence of the coupling mechanisms

Like lightweight design, customized products continue to remain on trend. These require materials which must fulfill a growing number of functions simultaneously and which in turn can usually only be implemented with additives and compounds. Sustainability is increasingly coming into the spotlight. 

Additives and Compounds Are Combining More and More Properties Songwon 

Farbstoffe

Stabilisatoren

Pigmente

Masterbatches

Fasern

Compoundeure

Versatility Wanted Glass Fiber-Reinforced Polypropylene with  Long-Term Thermal Stability  

Good fire resistance is important in technically demanding applications. However, the use of suitable additives reduces the mechanical properties of a material, e. g. impact resistance and tensile strength. It can now be shown that this effect can be counteracted by means of regenerated cellulose fibers. 

PBT Compounds Modified with Natural Fiber Reinforcement as Flame Retardant 

Gehäuse aus Kunststoff

HV-Anwendungen / Hybridisierung / Elektrifizierung

Celluloseester, -ether

Naturally Non-Flammable 

A function carrier connects in the instrument panel area the driver-side displays and functional elements with the center console. As a result, this component must be dimensionally stable and meet tight tolerances. Long glass fiber-reinforced ABS has proven to meet all part performance requirements at considerably lower weight in comparison the currently used cast magnesium.  

Long Glass Fiber-Reinforced ABS Replaces Magnesium in a Semi-Structural Component 

Glasfasern / -matten

Working within the Framework 

Lightweight design with fiber-reinforced plastics saves energy resources in the use phase of automobiles and aircraft. However, the savings are often offset by higher consumption in production. Therefore, the focus is increasingly shifting to sustainability in manufacturing. The Research Institute Neue Materialien Bayreuth has conducted a corresponding sustainability analysis for the processing of thermoplastic UD tapes into functionally integrated components.

Fig. 4. The demonstrator component “2D-MultiMat” was manufactured with laminates of woven fabric organosheets and UD tapes (CF or GF/CF hybrid) based on PP and injection-molded functional integration (PP-GF) with the FORCE process chain.

Evaluate the Environmental Impact of the Production of FRP Components

Faserverarbeitung

Kunststoffverarbeitung: Maschinen und Komponenten

UD-Tapes

Nachhaltigkeit

Umweltmanagement

Schnüre, Bänder, Tapes

How Sustainable Is  Lightweight Design Really?

The FiberXpert fiber feeder is an example of how Kubota Brabender Technologie has developed new, pioneering processes and feeders from innovative ideas.

FiberXpert FX225 is ideal for feeding long, irregular fibers. 

Messe K-Kunststoffmesse

kunststoffe-international.com

kunststoffe.de

Materialhandling

Feeding of Long, Recycled Fibers

Looper Textile Co.intends to collect, sort and sell used and unwanted garments and textiles and thereby extend the highest use of these valuable resources.

The waste management company Remondis and the Swedish fashion retailer H&M are pulling together to recycle clothes.

Recycling

H&M and Remondis Create Joint Venture

Electric vehicles can be charged not only at charging stations, but also wirelessly. Here, the energy exchange takes place between an induction coil positioned in the ground and a receiver coil mounted in the e-car.

Wireless charging could increase the range, and therefore the acceptance of electromobility.

Flame Retardant Polyamide for Inductive Charging Systems

Elektromobilität

Mobilität

Technische Kunststoffe

No Cable thanks to Suitable Compounds

At K, Radici will present the Renycle product family. These engineering compounds have a variable proportion of mechanically recycled PA obtained from PIR and PCR.

Reducing weight and ensuring safety are the aims of compounds developed by Radici specifically for electromobility.

More Comprehensive  Life Cycle Analysis

Polyamide fibers need to be sufficiently flame-retardant for the use in textile applications. Flame-retardants containing halogens and coating fibers with those is a common practice, although it has some severe disadvantages. Inherently flame-retardant polymers, which are processed along with polyamide to form blends and subsequently spun into fibers, provide an attractive alternative.

With an annual production volume of approximately 5.4 million t and a share of 5 % of the global fiber market, polyamide (PA) fibers form the second largest group of synthetic fibers [1]. Polyamide fibers’ applications range from home textiles and toothbrushes to airbags. A significant disadvantage of polyamide its low flame-retardant property. This disadvantage does not allow the use of polyamides in many applications without additional flame-retardants (FRs) [2].

FRs can protect the polymer with various mechanisms. One mechanism is the inhibition of the formation of reactive radicals that occur in the burning process of plastic. Other FRs forms develop into a protective layer on the polymer’s surface to prevent oxygen from reaching the polymer or cooling the material by evaporating released water [3].

FRs containing halogens such as decabromodiphenyl ether (decaBDE) were predominantly used in the past. Due to their potential environmentally harmful and toxic properties, the use of halogen-based FRs is controversial. Additionally, decaBDE and many other halogen-free FRs are embedded in the polymer matrix as an insoluble filler material. This approach, in turn, negatively impacts the fibers’ mechanical properties and leads to more frequent breakage of the filaments and reduced spinneret operating times during the manufacturing process [2, 4].

One approach to prevent this issue is coating the surfaces of textile structures with FRs [2]. This approach, however, has an economic disadvantage due to the added costs of the additional production step. Furthermore, coatings are often only active for a limited amount of time, and washing the textiles leads to a removal of the coating. The loss of flame-retarding properties is not the only adverse effect, as the halogen-based FRs could enter the environment with wastewater [5].

In recent years there have been several endeavors to develop FRs, that can be molten along with PA6 or PA66 and therefore embedded into polymer matrices. Currently, no products on the market are suited for different polymers, in particular pure PA6 and PA66. The Fraunhofer Institute for Structural Durability and System Reliability (LBF), Darmstadt, Germany, in cooperation with the Institut für Textiltechnik of RWTH Aachen University (ITA), Aachen, Germany, developed two novel phosphorous-based polymers that can be used as FRs and can be embedded into the fiber-matrix. By using these polymers, an additional step of coating textiles would be eliminated, and the production of intrinsically flame-retardant fibers without a loss in mechanical properties is made possible.

These novel polymers are based on phosphorous derivates which exist in thermoplastic polymers as substituents. The FRs’ melt spinning properties can be adjusted purposefully for the used polyamides through a variation of structural parameters such as the molar mass. The LBF-developed FRs were compounded along with PA66 at the ITA using a twin-screw extruder. The resulting polymer blends contained 10 wt.  % of polymeric phosphorous FR. Subsequently, these blends were melt-spun into multifilament yarns and later processed into knitted fabrics on a circular knitting machine.

Particular FRs disrupt the polymer chains’ orientation during the stretching of the fibers. However, the novel FRs developed by the LBF exist in the polyamide fibers as a polymeric blend component. During the stretching process, the polymer chains of the polyamide and the FR are oriented in the stretching-direction, which is pivotal for high mechanical strength [2, 6]. The mechanical properties of the produced fibers made of the blended polymer are comparable with those spun at the same spinning parameters with pure PA66. The high elongation at break of the yarns developed on a pilot scale indicates that a significant increase in strength can be expected from multi-stage post-drawing on an industrial scale melt spinning line. With further process optimization, there is a high probability of these fibers being appropriate for technical applications.

The flame-retardant properties were analyzed with injection molded test rods made of pure PA66 and the compounded polymer based on UL94-V. As expected, the pure PA66 showed a strong tendency to produce flaming droplets, preventing the flames from spreading across the test rod. In turn, this property results in the undesired promotion of fire to the surroundings; therefore, it should be avoided. The compounded material showed a significantly reduced incline to produce droplets, in addition to creating a carbon layer that protected the rod from further ignition.

Flame-Retardance Demonstrated Successfully

However, the results from these tests do not allow precise predictions about the burning behavior of textiles, as their surface area is significantly larger in comparison. For this reason, knitted surfaces made of pure PA66 and the compounded PA66 polymer were also analyzed. Both knits were tested based on UL94-V. The knit made of pure PA66 showed similar drop production to the testing rod. In comparison the entire sample burnt down completely. The knit made of the compound also shows an apparent reduction in droplet production compared to the pure PA66 knit. Furthermore, the knit also developed a carbon surface layer that prevented further ignition (<i>Fig. 1</i>).

Additional tests using a cone calorimeter show a reduced peak heat release rate (pHRR) for the compounded knit compared to the pure polymer (Fig. 2). Based on these results, a flame-retardant effect of the polymeric FR was shown. In particular, the flame-retardant effect was achieved while maintaining the textile properties. The next step will be to investigate the upscaling of the FRs synthesis and process optimization concerning high-strength industrial yarns. With an analysis of the market potential, the industrial realization of intrinsically flame-retardant PA should be made possible. The project is scheduled to start in 2023.

[1] TextileExchange. Preferred Fiber & Materials Market Report 2021. <a href="https://textileexchange.org/wp-content/uploads/2021/08/Textile-Exchange_Preferred-Fiber-and-Materials-Market-Report_2021.pdf" target="_blank">https://textileexchange.org/wp-content/uploads/2021/08/Textile-Exchange_Preferred-Fiber-and-Materials-Market-Report_2021.pdf</a>.

[2]   Weil, E. D.; Levchik, S. Current Practice and Recent Commercial Developments in Flame Retardancy of Polyamides. Journal of Fire Sciences 2004, 22 (3), 251–264. DOI: 10.1177/0734904104040546.

[3]   L. Van Wabeeke. Flame Retardant Plastics: A General Review.

[4]   Covaci, A.; Harrad, S.; Abdallah, M. A.-E.; Ali, N.; Law, R. J.; Herzke, D.; Wit, C. A. de. Novel brominated flame retardants: a review of their analysis, environmental fate and behaviour. Environment international 2011, 37 (2), 532–556. DOI: 10.1016/<a href="http://j.envint" target="_blank">j.envint</a>.2010.11.007. Published Online: Dec. 18, 2010.

[5]   Horrocks, A. R.; Kandola, B. K.; Davies, P. J.; Zhang, S.; Padbury, S. A. Developments in flame retardant textiles – a review. Polymer Degradation and Stability 2005, 88 (1), 3–12. DOI: 10.1016/<a href="http://j.polymd" target="_blank">j.polymd</a>egradstab.2003.10.024.

[6]   Fourné, F. Synthetische Fasern: Herstellung, Maschinen und Apparate, Eigenschaften; Handbuch für Anlagenplanung, Maschinenkonstruktion und Betrieb; Hanser, 1995.

Fraunhofer Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF

https://www.lbf.fraunhofer.de

RWTH-Aachen Inst. f. Textiltechnik (ITA) 

https://www.ita.rwth-aachen.de

Ausgabenartikel

Fig. 1. Knitted fabrics made of untreated PA66 before a) and b) after the burning test, as well as a knitted fabric made of intrinsically flame-retardant PA66 before c) and d) after the burning test. 

Fig. 2. Heat release rates of five-layer knitted fabrics made of PA66 and PA66 protected with polymeric FR: the reduced heat release is a reliable indicator of the FR’s flame retardancy.  

KUint9-22_ITA - Hauptartikel

Inherently flame-retardant polymers are processed along with polyamide to form blends and subsequently spun into fibers.

Intrinsically Flame-Retardant Polyamide

Felix Krooss has been working on developing polymer fibers with functional additives at the ITA since February 2020, while evaluating the melt spinning process with simulations and experiments;  <a href="mailto:felix.krooss@ita.rwth-aachen.de">felix.krooss@ita.rwth-aachen.de</a>

Kabelan Thavayogarajah has been researching on the development of polymeric FRs as an additive for polyamide fibers at the LBF since May of 2019.

Martin Pelzer has been researching in melt spinning at the ITA for nearly five years and next to investigating the melt spinning process also examines the post treatment of yarn and the textile processing.

Lais Weber worked on the development of FRs based on phosphorus-nitrogen-compounds in the field of polymer synthesis at the LBF from 2017 to 2021.

Roland Klein has been leading the Group “Grenzflächen und Polymerarchitekturen” (Interfaces and polymer architecture) at the LBF since 2012 and among other topics researches the synthesis of polymer based additives for plastics;  <a href="mailto:roland.klein@lbf.fraunhofer.de">roland.klein@lbf.fraunhofer.de</a>

Prof. Thomas Gries has been head of Institut für Textiltechnik of RWTH Aachen University since 2001.

The research project was carried out in the framework of the industrial collective research program (IGF no. 20575 N). It was supported by the Federal Ministry for Economic Affairs and Energy (BMWi) through the AiF (German Federation of Industrial Research Associations e.V.) based on a decision taken by the German Bundestag.

Read the German version of the  article in our magazine Kunststoffe or at  <a href="https://www.kunststoffe.de/a/fachartikel/intrinsisch-flammgeschuetztes-polyamid-2943159" target="_blank">www.kunststoffe.de</a>