New polymer expands composite options in demanding environments
One of the first applications where the ATSP polymer was considered was a NASA-funded project involving roll-up or collapsible composites for deployable structures. In order to participate, late last year, ATSP Innovations sent a polymer in film form to a prepreg that successfully impregnated a thin-ply plain weave carbon fiber fabric. Photo credit, all images: ATSP Innovations Inc.
One hundred and sixty years after Alexander Parkes introduced the first man-made plastic at the London International Exhibition, and 115 years after Leo Bakeland created the first commercially successful fully synthetic polymer, the development of new plastic systems resin – as opposed to new blends and alloys of existing polymer families – are no longer commonplace. Therefore, when an organization introduces a new polymer – especially a polymer with a unique combination of properties allowing the material to be used in a variety of applications and supplied in many form factors – it is worth to pay attention to it. Such is the case with an industry-new resin system that was invented 12 years ago by Dr. James Economy, a longtime professor and former head of the Department of Materials Science and Engineering at the University of Illinois at Urbana-Champaign. . Economy died at the age of 92 in the fall of 2021leaving a body of work consisting of 250 research papers, 47 book chapters, more than 100 U.S. patents, including the invention of at least 20 polymer technologies, and countless contributions to the science and engineering of materials.
Called aromatic thermoset copolyester (ATSP), the new resin technology is owned by ATSP Innovations Inc. (Houston, Texas, USA). The material was showcased during a technical presentation at the 2021 Society of Plastics Engineers (SPE, Danbury, Conn., US) Automotive Composites Conference & Exhibition (ACCE) last November. We caught up with presenter, Dr. Jacob Meyer, co-founder and vice president of technology of ATSP Innovations, and alumnus of Economics, to discuss the unique properties of the polymer and some potential applications currently being explored. .
Thermosetting and thermoplastic properties
ATSP is an uncatalyzed condensation polymerizable polymer system combining continuous liquid crystal and amorphous segments. As such it offers an interesting hybrid of properties commonly found among thermosets and thermoplastics. For example, like thermosets, once cured and cross-linked, it offers high thermal and chemical resistance as well as tight control of dimensional stability. Its glass transition temperature (Tg) is above 250°C and does not thermally degrade at temperatures below 500°C, meaning it is ideal for use in really demanding environments where most polymers have long since melted or disintegrated.
However, like thermoplastics, it offers good processability, post-mold “weldability” and melt reprocessability, allowing recycling of scrap and end-of-life (EOL) parts. It softens between 170 and 180°C, is an unhardened liquid between 230 and 240°C, begins to harden at 270°C and is fully hardened at 340°C. Depending on the form factor and the rate at which one wishes to heat and cure the polymer, heat sources such as infrared, microwave and induction can be used. Even its mechanical properties combine the best of thermosets (tensile modulus of 4.2 GPa) and thermoplastics (8 to 10% strain at break).
The scanning electron micrograph (SEM) image at top shows that a fracture has occurred entirely within the matrix at 90° to the carbon fiber cable, as no broken fibers are observable. This indicates that the failure was matrix dominated and that the material exhibited high fiber/matrix interfacial shear strength. The SEM image at the bottom shows the resin still tightly bonded to the fibers at the fracture surface.
Since it is aromatic – i.e. it starts with a cyclic structure – and an oligomer, the application of heat from 270 to 340°C before polymerization results in a rapid drop in viscosity (this varies depending on formulation, but is in the range of 4,000 to 10,000 centipoise), allowing ATSP to wet a wide variety of fibers including carbon, glass, basalt, and natural fibers. In fact, Meyers claims that ATSP has produced carbon fiber reinforced composites with up to 70% fiber volume fraction (FVF). He says the material also offers excellent binding to a variety of nanoparticles, including graphene.
In neat form, ATSP has a specific gravity of 1.32. It is said to be low outgassing, free of volatile organic compounds (VOCs) and to pose no environmental, health or safety concerns. Equally interesting, it has a long shelf life without the need to refrigerate or freeze it. In fact, Meyer remembers finding a batch of ATSP powder that had sat on the shelf for three years and successfully producing a cast film with it.
A good electrical insulator, pure ATSP has a dielectric constant of 5.0 at 25°C and 10 kilohertz and a dielectric breakdown strength of 384.4 volts/micrometer. The material also offers high oxidation stability, easy machinability with little dust (useful when machining shapes) and a very low moisture absorption rate of 0.2-0.3%.
ATSP also has excellent inherent halogen-free flame retardance with a limiting oxygen index (LOI) of 40% and a UL 94 V-0 listing at 1.5 millimeters. When exposed to an open flame, Meyer says the polymer forms a stable char, which insulates the unburned material below. In addition, it offers high lubricity and low wear, which makes it attractive for tribological applications.
Perhaps its most notable feature is what are called solid-state interchangeable/exchangeable bonds, a function of interchain transesterification reactions (ITRs), which allow previously cross-linked parts to be “welded” together like a thermoplastic after application of heat (in the range of 270-340°C) and pressure (average 1-4 MPa). Want to separate these related parts in a consistent way? Simply turn up the heat and pull them apart.
Many form factors, potential applications
Meyer says the polymer can easily be tailored to produce specific properties, which also allows ATSP Innovations to offer the material in multiple form factors and explore its use in a wide range of potential applications.
For example, it can be supplied as prepolymers (which can be solvated), sheets or pre-cured bulk forms (blocks of pure or reinforced solid polymer used to machine rather than mold parts), or as of structural composite in the form of B-stepped molding compounds with staple fibers or composite laminates with continuous fiber architectures. Moreover, it is also available in powder or film form for coating or impregnating other materials.
In addition to its use as a structural composite, which is of interest to the aerospace and automotive markets, ATSP is currently being evaluated as a high performance melt or solvent spun fiber. It is also being studied as an open cell foam (with foaming produced as a natural by-product of the condensation-hardening reaction). While researchers have only achieved a 0.2 gram/cubic centimeter density reduction to date, the fact that the ATSP foam provides sound dampening as well as excellent thermal insulation (0.10 watts per meter -Kelvin) and a flame retardant make it attractive as a high temperature barrier material. or the core of a sandwich panel composite for building/construction, infrastructure, aerospace and automotive customers where it could potentially compete with polyimide foams.
Additionally, ITR can be used creating a structural adhesive with high shear strength (20 MPa at 80 microns thick) over a wide temperature range. As an adhesive, the material (in powder coat form) is clear, fast bonding, provides excellent adhesion to a wide range of industrial materials including polymer composites, aluminum, steel and glass, and has the similar advantage to thermoplastic of being able to be glued, peeled and re-glued several times without losing its properties. In fact, the non-stick bonding process can be done in the field without the use of gloves or other personal protective equipment (PPE). Reportedly, the adhesive technology was developed in conjunction with NASA (Washington, DC, USA) for potential use in space assembly operations.
On the left is an X-ray computed tomography (CT) image of an interchain transesterification reaction (ITR) bonded carbon fiber reinforced ATSP composite/AI7075 multi-material laminate with a curved geometry. On the right are two SEM images taken from the cross section of the sandwich construct.
Another application area the company is exploring is the production of high performance polymer bearings with an ATSP film/coating that has been formulated for extreme working conditions of high loads, high speeds and high temperatures. And ATSP can even be formulated for 3D printing, opening up additional opportunities.
Aerospace and Oil/Gas customers would be interested in ATSP as a replacement for polyetheretherketone (PEEK), polyetherketoneketone (PEKK) and polyethersulfone (PES). Transport equipment manufacturers would be interested in this one as a replacement for ballistic panels reinforced with para-aramid Nthe eat polymer is said to behave similarly to phenolic, although it is easier to mold.
ASTP Innovations sells its resin powder (for compression molding or spray coating), machinable bulk sheets and compression moldable composite laminates and molding compounds under the Esttherm name. It calls its tribological coatings NOWE and its adhesive products Self-Bond.
“ATSP has such a unique combination of properties that our biggest challenge is not to find one or two good applications, but rather to focus on a few areas – like composites and adhesives – that are likely to be easier to implement and that can help us finally bring this polymer to market,” says Meyer. ATSP Innovations is currently working with Allied Composite Technologies LLC (Rochester Hills, Michigan, USA) on business and application development and l The polymer is also being strategically sampled in the aerospace, automotive, building/construction, infrastructure and oil/gas sectors.The first commercial applications could be seen as early as this In the meantime, Meyer says ATSP Innovations is actively seeking and engaging with potential partners, collaborators and customers to help bring this technology in the market.
When asked where he expects the price to be for ATSP once commercialized, Meyer adds, “It’s largely a matter of scale, but our long-term goal is to be competitive with the nylon (polyamide) and our shorter-term, more conservative prices. should still be viable for pilot-level production.