There is a strong motivation in society to recycle polymers to achieve sustainable development. Most polymers are either landfilled or burned, which creates ecological and environmental issues. Recycling strategies such as thermomechanical and chemical processes are being investigated to recycle the polymers however commercial applications are limited. The presence of flame retardant additives or monomers creates further complicacies in the recycling process. This presentation will focus on different state of art strategies to recycle flame retardant polymers. In addition, our current work on recycling thermoplastics (PET) and thermoset will be presented.
Dr. Gaan received his PhD in chemistry from UC Davis in 2007. He has been working at Empa since 2007 and is currently head of the Additives and Chemistry group in the Advanced Fibers department. His group specializes in the development of additives for bulk polymers, coatings on metals and polymers, and recycling of polymers. His group has developed several phosphorus flame retardants that are in various stages of commercialization. He has published more than 100 scientific articles and 8 patents. Dr. Gaan's Group was awarded the Empa Innovation Prize in 2016 for the successful transfer of technology to industry. The innovation was the synthesis of a new, halogen-free flame retardant EDA-DOPO and its use in polyurethane foams.
Radical generators as flame retardant synergists have been known and used for many years mainly in polystyrene formulations. Later on the need to find efficient halogen free flame retardants resulted inter alia in the discovery and commercialization of alkoxyamines (NOR-HALS). NOR-HALS provide flame retardancy of polypropylene and polyolefin fibers, non-wovens and films. Through formation of radicals a fast degradation of the polymer chain is induced and flame retardancy is achieved by removing the substrate from the flame. Moreover alkoxy amines can act as synergists with brominated flame retardants. However, due to the chemical structure alkoxy amines show only limited thermal stability during usual processing steps and the often requested UL 94 V-0 classification is difficult to achieve despite several structural advancements. The performance gap to provide advanced halogen free flame retardants and flame retardant synergists for polyolefins has been closed through the discovery of a new class of nitrogen based radical generators with oxyimide structure. Thermal stability and degradation of the novel oxyimides into radicals is correlated to the molecular structure and can be adjusted in line with the degradation of the polymer and the synergist. In combination with selected phosphorus derivatives, e.g. aliphatic phosphonates, flame retarded polypropylene with UL 94 V-0 classification is accessible at loadings as low as 6 %. Similar synergistic combinations offer UL 94 V-0 classification for the polyethylene family. Meanwhile the application field of oxyimides has been extended to engineering plastics by introducing oxyimide ethers and to further polymers such as polylactic acid and thermoplastic polyurethanes.
Rudolf Pfaendner studied chemistry at the University of Bayreuth in Germany and received his PhD in 1985 with a thesis on electrically conductive polymers.
During 25 years he held different positions in R&D at the specialty chemicals company “Ciba” inter alia as Global Head of Research for the business segment “Plastic Additives” and as Senior Research Fellow.
Rudolf is now Division Director Plastics of the Fraunhofer Institute for Structural Durability and System Reliability LBF and Honorary Professor at the Technical University of Darmstadt, Germany.
He has over thirty years of experience in polymer synthesis, plastics and coatings additives, stabilizers, recycling, reactive extrusion, nanocomposites, flame retardants and innovation management including numerous patents and publications.
Organohalogen flame retardants have long been preferred by the polymer industry. In particular, brominated diphenyl ethers have been prominent flame retardants. They can be readily prepared from byproducts of phenol production. As a consequence, they are widely available at modest cost. More importantly, they are effective gas-phase-active flame retardants and may be used at levels below that which would lead to significant changes in the properties of a polymer matrix into which they have been incorporated. However, despite the attractiveness of these materials, it has been increasingly recognized that their use may impose severe negative consequences. At high temperature, as in a fire, these compounds are converted to volatile, very toxic dioxans and furans. They may also migrate from a polymer matrix and enter the environment in which the polymer or fabricated item is used. More importantly, they migrate from items discarded in a landfill and enter the natural environment where they are stable, persist, bioaccumulate and may ultimately enter the human food chain. Human exposure to these materials may lead to a number of disease states, most arising from endocrine disruption. Consequently, the use of these compounds is under increasing societal and regulatory pressure worldwide. Some have been banned from use and others removed from the market voluntarily. Suitable alternatives are being rapidly developed. In the main, these have been organophosphorus compounds. Those derived from readily-available, inexpensive and nontoxic biomaterial precursors are particularly attractive. Effective organophosphorus flame retardants have been prepared using a variety of biobased precursors. Perhaps most notable are those generated from isosorbide, gallic acid or hyperbranched glycerol/adipic acid poly(ester)s, readily available, in a single step, from two nontoxic biomonomers. Using the Martin-Smith statistical approach for the selection of appropriate monomer ratios, hyperbranched poly(ester)s of precise molecular weight, structure, and endgroup functionality may be produced. Because of the hyperbranched structure these materials function as effective plasticizers and may be endcapped with a variety of phosphorus moieties to generate either solid-phase active or gas-phase-active flame retardants compatible with a range of polymer matricies.
Bob A. Howell is professor emeritus of organic chemistry/polymer science at Central Michigan University. He has over thirty years of experience in the area of polymers and polymer additives. Research interests include the use of hyperbranched poly(ester)s for the release of active agents, structural stability of styrene polymers, PVC formulation/stabilization, nitroxylmediated radical polymerization, and thermal methods of analysis/kinetics. A current major focus is the development of nontoxic, biodegradable, environmentally-friendly flame retardants based on renewable biomaterials.
In order to suppress melt dripping and achieve better flame retardant performance, drip suppressants are necessarily important especially in halogen-free, flame-retarded plastics. Polytetrafluoroethylene (PTFE) is a popular choice since 1990s for its viscosity-increasing effect, but potential pollution and health concerns caused by its raw materials and mass production are now getting increased attention, making non-fluorinated alternatives promising choices in the market. This paper summarizes the status of current non-halogenated drip suppressants from the patent and technical literature, and an analysis is directed toward two different anti-dripping mechanisms, i.e., viscosity modifiers and char promoters. Next, some potentially new state-of-the-art materials and technologies in development in academia are discussed. Lastly, the report concludes with a perspective and outlook on the design and production of next-generation drip suppressants.
Yiming Zhang finished his master’s degree in Macromolecular Science and Engineering at Case Western Reserve University in Cleveland, Ohio. Prior to that, he was a graduate of Donghua University, China (2019), where he majored in polymer materials. During his time at Case Western, he studied on polymer gels and learned about flame retardant materials under the guidance of Professor Gary Wnek. He will join the PhD program in Materials Science and Engineering at Georgia Tech in August of 2022.
At Tidal Vision, we are on a mission to create a positive and systemic environmental impact by advancing chitosan chemistry solutions by making them lower cost, more convenient, and better performing than synthetic chemicals. Chitosan is a close derivative of Chitin, and, second only to cellulose, is one of the most abundant biopolymers in the world. Chitin and chitosan occur in crustacean shells, insect exoskeletons, fish scales, and in the cell walls of fungi; Tidal Vision utilizes byproducts from sustainably managed fisheries as the input raw material to manufacture chitosan. There are over 400 established applications for chitosan in industries such as water treatment, textiles, agriculture, food processing, and many more. Currently, the chemical industry is searching for “green” bio-sourced alternatives to traditional halogenated flame retardants and Tidal Vision is working to harness the properties of chitosan to respond to this need. Formulated chitosan chemistry solutions increase thermal stability, char density, and overall fire retardancy in textile and building material applications.
Kari has a passion for understanding and communicating how new products and technologies can solve customers’ problems. She has two degrees, in Marketing and Management, and a minor in international business. She leads Tidal Vision's go-to-market strategies and business development team with Tidal-Tex™ in the textile industry.