By Jon Evans
Several advanced medical polymers were showcased in the technical sessions at ANTEC 2017. Suneel Bandi from EVONIK gave an overview of the company’s range of high-performance polyamides. These include flexible polyamides, bio-based polyamides and transparent polyamides for use in catheters, balloons, surgical instrumentation and drug delivery devices. Tony Walder from Lubrizol introduced its new class of non-softening thermoplastic polyurethanes (TPUs). These possess all the benefits of conventional TPUs, including low temperature flexibility, excellent abrasion resistance, high tensile strength and good processing characteristics, but don’t soften in the body.
Cheryl Weckle from Trinseo unveiled several new polycarbonate grades that can tolerate multiple cleanings using aggressive disinfectants, which are required for preventing hospital-acquired infections (HAIs). According to Weckle, these grades boast a superior combination of toughness, easy processing, color stability and durability. Foster Corporation is taking a different approach to tackling HAIs, by developing silver-based antimicrobial additives that can be incorporated into polymer melts. Lawrence Acquarulo, founder and CEO of the company, spoke about the effectiveness and efficiency of this additive when added to polycarbonate, TPU and acrylonitrile butadiene styrene (ABS).
Many plastic medical devices are very small or possess very small features that require special fabrication processes, such as micro molding and 3D printing. Alex Maroon from MTD Micro Molding spoke about the challenges of micro molding bioadsorbable polymers, which require a much more extensive and specialized approach than conventional thermoplastics. Roger Narayan, professor in the joint department of biomedical engineering at the University of North Carolina and North Carolina State University, described using a 3D printing process called two photon polymerization to fabricate features less than 1µm in size, which could be useful for medical devices.
Also known as additive manufacturing, 3D printing has proved to be an ideal process for producing complex parts from plastic. This is especially the case for a form of 3D printing known as fused filament fabrication (FFF), in which plastic is printed as a thin, molten filament. But 3D printing is not without its difficulties, because the process can have over 100 unique variables and settings, all of which can affect the properties of the printed component.
Several of the presentations at ANTEC 2017 described efforts to understand the effects of these variables and settings. Steven Kreuzer from Exponent presented an empirical method utilizing a statistical design of experimental technique and standardized mechanical testing that can expose the trends and variable interactions in 3D printing. Omar Ahmed Mohammed from Swinburne University of Technology in Australia described his study into the effect of operating conditions on the mechanical properties of parts printed by FFF from polycarbonate/ABS, especially on their creep deformation behavior. This allowed him to determine the best process parameters to use for practical purposes.
Other speakers presented their work on novel plastic materials for 3D printing. Joamin Gonzalez-Gutierrez from Montanuniversität Leoben in Austria spoke about developing a magnetic plastic material for 3D printing, based on incorporating strontium ferrite powder into the plastic filament, and the effect that different concentrations of the powder had on the plastic’s mechanical and printing properties. Martin Spoerk, also from Montanuniversität Leoben, spoke about incorporating glass spheres into polypropylene, which led to a reduction in shrinkage and an increase in the crystallization temperature.
One of the most popular current plastics for 3D printing is the bioplastic polylactic acid (PLA), which was the subject of numerous presentations at ANTEC 2017. Several speakers described their efforts to modify PLA’s physical properties by creating blends with other plastic materials or incorporating additives. Svenja Göttermann at the Institut für Kunststofftechnik in Germany gave a presentation on her work looking at the effect of adding various different chemical modifiers to PLA, in order to induce crosslinking, chain extension or grafting by means of reactive extrusion on a twin-screw extruder. She achieved the best results with organic peroxide, which improved the melt strength and crystallization rate and led to foams with a closed-cell structure and low density. Margaret Sobkowicz at the University of Massachusetts, Lowell, described developing a blend of PLA and polyamide for use with a novel, high-speed twin-screw extrusion process.
David Grewell from Iowa State University spoke about his work on welding PLA, using ultrasonic welding for rigid PLA samples and impulse welding for PLA films. For ultrasonic welding, weld distance and velocity had the greatest effect on weld strength, while for impulse welding heating time and temperature had the greatest effect.
Another biomaterial that received much attention at ANTEC 2017 was cellulose. Kim Nelson from American Process, which offers five different varieties of nanocellulose products, revealed how this natural nanomaterial can increase the strength of various materials, including conventional and biodegradable plastics, polyurethane foams and cement. This can help in the development of lighter plastic components, as required by industries such as aerospace and automotive.
Ways to lighten the materials used in vehicles was the subject of many other presentations at ANTEC 2017. Omar Faruk from the University of Toronto in Canada reported the development of an automotive oil pan made from a material comprising 20% recycled carbon fiber and 80% recycled polyamide, which was 15% lighter than a conventional oil pan. Matthew Thompson from Advanced Composites spoke about evaluating the effect of several other options for reducing the weight of injected-molded parts, including composite density reduction, wall thickness reduction and foaming.
Lightweighting can also be achieved by simply replacing metal components with plastic versions, and Luigi Alzati from IMERYS Graphite & Carbon spoke about using graphite-containing plastics as potential replacements for metal heat sinks in vehicles. The company has tested several commercially-available graphite grades in polyolefin plastics and found that that crystallinity, average particle size and aspect ratio are the three main factors that promote thermal conductivity.
Still, plastic parts cannot replace all the metal components in vehicles, and so plastic and metal parts will need to be bonded together for the foreseeable future. The junction between plastic and metal parts is a site of high potential risk, however, providing a potential pathway for the ingress of water, air, and other materials that may adversely affect the plastic-to-metal bond. Andy Stecher from Plasmatreat provided details on its new, cost-efficient plasma sealing technology for obtaining a tight seal between metal and plastic components that is resistant to outside elements.