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Interesting facts about plastics and rubber

We come across plastics and rubber everywhere in our daily lives. Discover fascinating stories, surprising facts and interesting background information – from historical developments and well-known products to key figures and innovations in the industry.

Results (423)

  • Light shines on chemical production method

    The picture illustrates the redox potential controlled selective oxidation of styrenes for regio- and stereoselective crossed intermolecular [2 + 2] cycloaddition via organophotoredox catalysis. Image: Yujiro Hoshino, Yokohama National University A team of researchers from Japan has demonstrated a light-based reaction that yields high numbers of the base chemical component required to produce bioactive compounds used in common industry products. They published their results on June 11 in Organic Letters. "We developed a redox potential-controlled and cost-effective method to synthesize multisubstituted cyclobutanes, which are present in the core structure of various products and bioactive components," said paper author Yujiro Hoshino, a research associate at Yokohama National University. Cycloaddition reactions allow to prepare carbocyclic and heterocyclic organic compounds with atom-efficiency. For a long time, researchers carried out photocycloadditions of olefins such as styrenes, a chemical used in the production of plastics and rubber, by treating them with high-energy ultraviolet light or transition metal catalysts, which are known to be toxic and expensive chemical reagents. The reaction mainly provides homo-dimer, not hetero-dimer. In addition, the powerful light damages the bonds holding the chemical together, allowing it to break apart and reform in a new configuration, known as a cyclobutene ring. Redox potential refers to how easily a chemical loses or gains electrons. Hoshino and co-workers take advantage of this characteristic and applied a green, visible light to styrenes situated in a two-by-two arrangement, allowing the chemical components and bonds to selectively reorganize as the light freed electrons from the styrenes. The newly organized chemical components were multisubstituted cyclobutanes. "By focusing on the different redox potential between various styrenes and optimizing our light catalysts, we developed a mild and clean method to synthesize multisubstituted cyclobutanes," Kenta Tanaka, paper first author and an assistant professor at Tokyo University of Science, said. "Emphasis will be placed on the strategy which shows the potential to synthesize multisubstituted cyclobutanes via radical cation species without any transition metal catalysts," said another corresponding author Kiyoshi Honda, a professor at Yokohama National University. Next, the researchers plan to expand the use of various visible-light catalysis methods. "We hope our reaction system provides an efficient and new method for green-light-driven organic chemical reactions, and that we continue to contribute to the field," Hoshino said. Reference Tanak et al., Redox Potential Controlled Selective Oxidation of Styrenes for Regio- and Stereoselective Crossed Intermolecular [2 + 2] Cycloaddition via Organophotoredox Catalysis, Organic Letters 22 (2020) 5207-5211, https://doi.org/10.1021/acs.orglett.0c01852

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  • Analyzing pros and cons of two composite manufacturing methods

    Comparing bulk and frontal polymerization. Image: P. H. Geubelle, Grainger Engineering Airplane wings, wind turbine blades, and other large parts are typically created using bulk polymerization in composite manufacturing facilities. They are heated and cured in enormous autoclaves and heated molds as big as the finished part. Frontal polymerization is a new out-of-autoclave method for composite manufacturing that doesn't require a large facility investment. Researchers at the University of Illinois Urbana-Champaign conducted a study pitting one process against the other to discover the pros and cons of each. "Frontal polymerization doesn't use an autoclave at all, so it doesn't require that huge upfront investment," said Bliss Professor Philippe Geubelle in the Department of Aerospace Engineering at the U of I. "It's a chemical reaction sustained by the release of heat as the front propagates. It can save a lot of energy and it generates much less carbon dioxide, so that's an environmental benefit." Geubelle said they began comparing the two methods by looking at the thermo-chemical equations in order to model the two polymerization processes. In that way, they could compare the methods for a variety of composite materials, and particularly, the time duration each method takes to manufacture the same part. "The key contribution from the theoretical point of view is that we've rewritten the reaction-diffusion equations to extract the two most important nondimensional parameters," Geubelle said. "Using just these two parameters allowed us to look at a wide range of chemical parameters, such as the activation energy and the heat of reaction, and at the impact of the initial temperature of the resin." Geubelle said this method helped to compare the composite manufacturing processes based on bulk and frontal polymerization in terms of the time it takes to manufacture a part. The study found that there were instances when one or the other was faster. "Imagine you want to make something that is one meter long. Frontal polymerization will be able to do complete the task before bulk polymerization starts to kick in," Geubelle said. "On the other hand, if you want to make something that is 10 meters long, then bulk polymerization may actually take place before the front reaches the other end of the part. It's the competition between these two processes that we analyzed in this study." He went on to say there are several ways to speed up the process for frontal polymerization: start the front at both ends so it goes twice as fast, or heat it from the bottom by using a heated panel beneath it. "That process is so fast, we refer to it as flash curing," Geubelle said, "but it does use more energy than for a single front." Manufacturing composite parts using frontal polymerization instead of bulk polymerization has a lot of advantages. "With frontal polymerization, you don't need the large capital investment of the autoclave, making it a very attractive option," Geubelle said. "The time it takes to cure a composite part is also much shorter and the environmental impact is substantially reduced." Reference Vyas et al., Frontal vs. bulk polymerization of fiber-reinforced polymer-matrix composites, Composites Science and Technology 198 (2020), https://doi.org/10.1016/j.compscitech.2020.108303

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  • Sweat science: Engineers detect health markers in thread-based, wearable sweat sensors

    Backdrop: readout of lactate in sweat during exercise. Image: Sameer Sonkusale, Nano Lab, Tufts University Engineers at Tufts University have created a first-of-its-kind flexible electronic sensing patch that can be sewn into clothing to analyze your sweat for multiple markers. The patch could be used to to diagnose and monitor acute and chronic health conditions or to monitor health during athletic or workplace performance. The device, described today in the journal NPJ Flexible Electronics, consists of special sensing threads, electronic components and wireless connectivity for real time data acquisition, storage and processing. Typical consumer health monitors can track heart rate, temperature, glucose, walking distance and other gross measurements. But a more detailed understanding of the health, stress and performance of an individual is required for medical data collection or high performance athletic or military applications. In particular, metabolic markers such as electrolytes and other biological molecules provide a more direct indicator of human health for accurate assessment of athletic performance, workplace safety, clinical diagnosis, and managing chronic health conditions. The patch device created by the Tufts engineers performs real-time measurements of important biomarkers present in sweat including sodium and ammonium ions (electrolytes), lactate (a metabolite) and acidity (pH). The device platform is also versatile enough to incorporate a wide range of sensors cabable of tracking nearly every marker present in sweat. The measurements taken can have useful diagnostic applications. For example, sodium from sweat can indicate the hydration status and electrolyte imbalance in a body; lactate concentration can be an indicator of muscle fatigue; chloride ion levels can be used to diagnosis and monitor cystic fibrosis; and cortisol, a stress hormone, can be used to assess emotional stress as well as metabolic and immune functions. Athletes could monitor a wide range of markers during physical exertion to aid in predicting performance peaks or declines during competition. The ability to integrate the sensors into clothing is made possible by flexible threads coated with conductive inks. Different coatings alter the functionality of the threads; for example, lactate can be detected by coating a thread with an enzymatic sensing material incorporating the enzyme lactate oxidase. A pH sensing thread is coated with polyaniline that responds to acidity, and so on. The array of thread sensors is integrated into clothing or a patch and connected to a miniature circuit module and microprocessor, with wireless capability to communicate with a smartphone. "Sweat is a useful fluid for heath monitoring since it is easily accessible and can be collected non-invasively," said Trupti Terse-Thakoor, formerly a post-doctoral scholar at Tufts University School of Engineering and first author of the study. "The markers we can pick up in sweat also correlate well with blood plasma levels which makes it an excellent surrogate diagnostic fluid." Researchers tested the device on human subjects, monitoring their electrolyte and metabolite response during a maximum exertion exercise on stationary bikes. The sensors were able to detect variation in analyte levels as they moved up and down, within 5 to 30 second intervals - sufficient for most real-time tracking needs. The subjects included men and women with a range of physical conditioning, from physically active on a performance-tailored diet, to individuals who were not physically active and had no specific dietary restrictions. While the current study was not meant to determine a correlation between analyte readings and performance and conditioning, it did establish that the sensor was able to detect consistent patterns of analyte expression that could be used for future studies identifying these correlations. "The sensor patch that we developed is part of a larger strategy to make completely flexible thread-based electronic devices," said Sameer Sonkusale, professor of electrical and computer engineering at Tufts' School of Engineering and corresponding author of the study. "Flexible devices woven into fabric and acting directly on the skin means that we can track health and performance not only non-invasively, but completely unobtrusively - the wearer may not even feel it or notice it." Reference Terse-Thakoor et al., Thread-based multiplexed sensor patch for real-time sweat monitoring, npj Flexible Electronics 4 (2020), http://dx.doi.org/10.1038/s41528-020-00081-w

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  • Mapping crystal shapes could fast-track 2D materials

    Materials scientists at Rice University and the University of Pennsylvania are calling for a collective, global effort to fast-track the mass production of 2D materials like graphene and molybdenum disulfide. In a perspective article published online in Materials Today, journal editor-in-chief Jun Lou and colleagues make a case for a focused, collective effort to address the research challenges that could clear the way for large-scale mass production of 2D materials. Lou and fellow Rice materials scientists Ming Tang, Jing Zhang and Fan Wang joined Penn's Vivek Shenoy in describing the potential transformation in 2D materials technology that could result from a systematic, communitywide effort to map the shapes of the 2D crystals that are being grown in labs worldwide via a process known as chemical vapor deposition (CVD). "Like snowflakes in nature, 2D crystals exhibit a rich variety of morphologies under different growth conditions," they wrote. Mapping these unique crystal patterns and compiling the maps in a global database, alongside the recipes for creating each pattern, could unlock a wealth of information "for understanding, diagnosing and controlling the CVD process and environment for 2D material growth," the researchers wrote. CVD is a commonly used process for creating thin films, including commercially important materials in the semiconductor industry. In a typical CVD reaction, a flat sheet of material called a substrate is placed in a reaction chamber and gases are flowed through the chamber in such a way that they react and form a solid film atop the substrate. One goal of the field is developing computer software that can accurately predict the properties of a thin film that will result from the mixing of specific reactant gases under specific conditions. Creating such models is complicated by both an incomplete understanding of the physical and chemical processes that take place during CVD and by the existence of dozens of CVD reactor formats. Inspired by the work of Japanese snowflake researcher Ukichiro Nakaya, materials scientists from Rice University the University of Pennsylvania created a Nakaya-like diagram of 2D crystal shapes of molybdenum disulfide produced via chemical vapor deposition (left) and a complete morphology diagram of molybdenum sulfide (right). Image: MSNE/Rice University An array of crystal shapes of 2D transition metal dichalcogenides as imaged with a scanning electron microscope. Image: MSNE/Rice University Cataloging the shape of crystals produced by CVD experiments could provide materials scientists with important information about their synthesis, in much the same way that mineralogists retrieve valuable clues about the history of Earth based on examination of naturally occurring crystal structures, Lou and colleagues suggested. "Take the beautiful snowflakes as an example," the authors wrote. "A perhaps surprising fact to many is that snow crystals can exhibit many different categories of shapes, which depend on the temperature and water supersaturation of the atmosphere in which they are formed." The Japanese scientist Ukichiro Nakaya, through extensive observations of snowflakes in both nature and the laboratory, developed a figure known as the Nakaya diagram to help decipher the information in snowflakes. By examining the shapes in a snowflake, and seeing where those shapes lie on Nakaya's diagram, scientists can determine the exact atmospheric conditions that produced the snowflake, which Nakaya poetically referred to as "a letter from the sky." Inspired by Nakaya's work, Lou and colleagues created a Nakaya-like diagram of 2D crystal patterns that have been produced via CVD and demonstrated how it and other morphology diagrams could be used to infer clues about process variables like gas flow rates and heating temperatures that produced each pattern. Thanks to advances in real-time imaging and in automated systems that can produce large datasets of crystal structures, the authors said there is "real potential for morphology diagram development to become a common practice and serve as a cornerstone of crystal growth." Reference Zhang et al., Towards controlled synthesis of 2D crystals by chemical vapor deposition (CVD), Materialstoday (2020), https://doi.org/10.1016/j.mattod.2020.06.012

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  • Smallest 3D printed miniature endoscope in the world

    3D printed miniature endoscope optics inside a blood vessel. Photo: Florian Sterl, Sterltech Optics Researchers of the Universities of Stuttgart and Adelaide in cooperation with medical research centers in Australia developed a special microoptical tool with a thickness of only 125 microns. This enables endoscopic examimations within blood vessels whose diameter is smaller than 0.5 mm and helps detecting plaques or thrombs to reduce the danger of a stroke or a heart attack. Endoscopy allows to examine the body with tubular instruments. Examples include colonoscopy of the intestines or gastroscopy of the stomach. However, such endoscopes are often still as thick as a finger. They are not suited to enter small blood vessels. Glass fiber technology is a promising technique to inspect to such fine veins, because the fibers are just 125 µm in diameter. The main technological issue is the extremely small optics on the tip of the fiber: it should look sideways to deflect a laser beam from inside the fiber to the inside vessel wall, detect its shape and depth composition, and send its reflection back into the fiber. This way a doctor can get an image from inside the body. The examination uses a technology called optical coherence tomography (OCT), which one might know from eye and retina examinations. It uses a laser beam whose spectrum of colors is relatively broad that penetrates the tissue. The analysis of the reflected light allows for exact depth mapping of the tissue, similarly to ultrasound, but with much higher spatial resolution. The 3D-printed endoscope, consisting of a transparent glass fibre, a guiding tube for fiber rotation (black) and a transparent sheath for protection, has an overall diameter of less than 0.5 mm. Photo: Universität Stuttgart/ PI 4 Dr. Simon Thiele from the group of Prof. Alois Herkommer at the Institute of Technical Optics at University of Stuttgart teamed up with 3D printing experts of the group of Prof. Harald Giessen in Stuttgart and developed together with fiber OCT experts Dr. Jiawen Li and Prof. Robert McLaughlin from University of Adelaide the smallest endoscope of the world, with an outer diameter including the sheath of less than 0.5 mm. Together with colleagues from Royal Adelaide Hospital, SAHMRI Institute in Adelaide and Monash Cardiovascular Research Center in Melbourne, they used the 3D printed microoptical OCT endoscope to examine the inside of blood vessels of mice and humans. The doctors obtained highly accurate 3-dimensional images of the veins, which were later compared with histological stained images. Plaques and cholesterol crystals can be detected early Left: Endoscopic OCT imaging in a severely diseased human carotid artery. Cross-sectional endoscopic OCT image. Right: Masson’s trichrome staining of adjacent sections; blue arrows indicate thrombus that appears to contain fibrin, platelets, and cellular debris. Photo: University of Stuttgart/ PI 4 The 3D printed microoptics focused to laser beam from the fiber to a fine spot, correcting also for the aberrations in the cylindrical plastic sheath. The OCT system was able to detect plaques as well as cholesterol crystals in human carotid arteries as well as in aortas of obese mice. These causes for vascular deseases could be well detected by the fiber endoscope, which rotated like a spiral inside the blood vessels. Comparisons with stained microscope images of the sliced tissue confirmed the early detection by OCT. Dr. Simon Thiele, who designed the miniature optics, believes that the new system could add significantly to the already 400 000 performed OCT endoscopic examinations. Millions more could be performed inside blood veins and detect early plaques and cholesterol crystals. He believes that one might be able to dissolve such plaques in the future with a suited laser beam using such a miniature endoscope, which can easily enter such small vessels. From technology demonstration to market Simon Thiele is about to spin out the 3D printed micro-optical technology into a commercial enterprise called “Printoptics GmbH”. The company Nanoscribe GmbH from Karlsruhe, which was spun off from KIT about 11 years ago and who employs now over 70 people, supplied the ultraprecise 3D laser printer. Carl Zeiss AG from Oberkochen in Germany, who is a key player in the world market of medical technology, took already a stake in Nanoscribe. Support for this research in Germany came from the Ministry of Research, the Baden-Württemberg-Foundation, and from DAAD. Reference J. Li, S. Thiele, B. Quirk, R. Kirk, J. Verjans, E. Akers, C. Bursill, S. Nicholls, A. Herkommer, H. Giessen and R. McLaughlin,Ultrathin monolithic 3D printed optical coherence tomography endoscope for preclinical and clinical use, Nature Light Science and Applications 9 (2020), https://www.nature.com/articles/s41377-020-00365-w

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  • 3D hand-sensing wristband signals future of wearable tech

    In a potential breakthrough in wearable sensing technology, researchers from Cornell University and the University of Wisconsin, Madison, have designed a wrist-mounted device that continuously tracks the entire human hand in 3D. The bracelet, called FingerTrak, can sense and translate into 3D the many positions of the human hand, including 20 finger joint positions, using three or four miniature, low-resolution thermal cameras that read contours on the wrist. The device could be used in sign language translation, virtual reality, mobile health, human-robot interaction and other areas, the researchers said. "This was a major discovery by our team - that by looking at your wrist contours, the technology could reconstruct in 3D, with keen accuracy, where your fingers are," said Cheng Zhang, assistant professor of information science and director of Cornell's new SciFi Lab, where FingerTrak was developed. "It's the first system to reconstruct your full hand posture based on the contours of the wrist." Past wrist-mounted cameras have been considered too bulky and obtrusive for everyday use, and most could reconstruct only a few discrete hand gestures. FingerTrak's breakthrough is a lightweight bracelet, allowing for free movement. Instead of using cameras to directly capture the position of the fingers, the focus of most prior research, FingerTrak uses a combination of thermal imaging and machine learning to virtually reconstruct the hand. The bracelet's four miniature, thermal cameras - each about the size of a pea - snap multiple "silhouette" images to form an outline of the hand. A deep neural network then stitches these silhouette images together and reconstructs the virtual hand in 3D. Through this method, Zhang and his fellow researchers were able to capture the entire hand pose, even when the hand is holding an object. While the technology has a wide range of possible uses, Zhang said the most promising is its potential application in sign language translation. "Current sign language translation technology requires the user to either wear a glove or have a camera in the environment, both of which are cumbersome," he said. "This could really push the current technology into new areas." FingerTrak could also have an impact on health care applications, specifically in monitoring disorders that affect fine-motor skills, said Yin Li, assistant professor of biostatistics and medical informatics at the University of Wisconsin, Madison School of Medicine and Public Health, who contributed to the software behind FingerTrak. "How we move our hands and fingers often tells about our health condition," Li said. "A device like this might be used to better understand how the elderly use their hands in daily life, helping to detect early signs of diseases like Parkinson's and Alzheimer's." "FingerTrak: Continuous 3D Hand Pose Tracking by Deep Learning Hand Silhouettes Captured by Miniature Thermal Cameras on Wrist," was published in the Proceedings of the Association for Computing Machinery on Interactive, Mobile, Wearable and Ubiquitous Technologies. It also will be presented at the 2020 ACM International Joint Conference on Pervasive and Ubiquitous Computing, taking place virtually Sept. 12-16. Reference Hu et al.,FingerTrak: Continuous 3D Hand Pose Tracking by Deep Learning Hand Silhouettes Captured by Miniature Thermal Cameras on Wrist, Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies (2020), http://dx.doi.org/10.1145/3397306

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  • Better wastewater treatment? It's a wrap

    A shield of graphene helps particles destroy antibiotic-resistant bacteria and free-floating antibiotic resistance genes in wastewater treatment plants. Think of the new strategy developed at Rice University as "wrap, trap and zap." The labs of Rice environmental scientist Pedro Alvarez and Yalei Zhang, a professor of environmental engineering at Tongji University, Shanghai, introduced microspheres wrapped in graphene oxide in the Elsevier journal Water Research. Alvarez and his partners in the Rice-based Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment (NEWT) have worked toward quenching antibiotic-resistant "superbugs" since first finding them in wastewater treatment plants in 2013. "Superbugs are known to breed in wastewater treatment plants and release extracellular antibiotic resistance genes (ARGs) when they are killed as the effluent is disinfected," Alvarez said. "These ARGs are then discharged and may transform indigenous bacteria in the receiving environment, which become resistome reservoirs. "Our innovation would minimize the discharge of extracellular ARGs, and thus mitigate dissemination of antibiotic resistance from wastewater treatment plants," he said. The Rice lab showed its spheres -- cores of bismuth, oxygen and carbon wrapped with nitrogen-doped graphene oxide -- inactivated multidrug-resistant Escherichia coli bacteria and degraded plasmid-encoded antibiotic-resistant genes in secondary wastewater effluent. The graphene-wrapped spheres kill nasties in effluent by producing three times the amount of reactive oxygen species (ROS) as compared to the spheres alone. Image: Improved bacterial affinity and reactive oxygen species generation enhances antibacterial inactivation in wastewater by graphene oxide-wrapped nanospheres developed by scientists at Rice University and Tongji University, Shanghai. Antibiotic resistance genes (eARG) released by inactivated antibiotic resistant bacteria (ARB) in the vicinity of photocatalytic sites on the spheres facilitates their degradation. Source: Alvarez Research Group/Rice University The spheres themselves are photocatalysts that produce ROS when exposed to light. Lab tests showed that wrapping the spheres minimized the ability of ROS scavengers to curtail their ability to disinfect the solution. The researchers said nitrogen-doping the shells increases their ability to capture bacteria, giving the catalytic spheres more time to kill them. The enhanced particles then immediately capture and degrade the resistant genes released by the dead bacteria before they contaminate the effluent. "Wrapping improved bacterial affinity for the microspheres through enhanced hydrophobic interaction between the bacterial surface and the shell," said co-lead author Pingfeng Yu, a postdoctoral research associate at Rice's Brown School of Engineering. "This mitigated ROS dilution and scavenging by background constituents and facilitated immediate capture and degradation of the released ARGs." Because the wrapped spheres are large enough to be filtered out of the disinfected effluent, they can be reused, Yu said. Tests showed the photocatalytic activity of the spheres was relatively stable, with no significant decrease in activity after 10 cycles. That was significantly better than the cycle lifetime of the same spheres minus the wrap. Reference Li et al., Hierarchical Bi2O2CO3 wrapped with modified graphene oxide for adsorption-enhanced photocatalytic inactivation of antibiotic resistant bacteria and resistance genes, Water Research 184 (2020), https://doi.org/10.1016/j.watres.2020.116157

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  • Powerful human-like hands create safer human-robotics interactions

    The novel humanoid hand design is a soft-hard hybrid flexible gripper that can generate larger grasping force than a traditional pure soft hand. Image: Changyong Cao Need a robot with a soft touch? A team of Michigan State University engineers has designed and developed a novel humanoid hand that may be able to help. In industrial settings, robots often are used for tasks that require repetitive grasping and manipulation of objects. The end of a robot where a human hand would be found is known as an end effector or gripper. "The novel humanoid hand design is a soft-hard hybrid flexible gripper. It can generate larger grasping force than a traditional pure soft hand, and simultaneously be more stable for accurate manipulation than other counterparts used for heavier objects," said lead author Changyong Cao, director of the Laboratory for Soft Machines and Electronics at MSU and assistant professor in Packaging, Mechanical Engineering, and Electrical and Computer Engineering. This new research, "Soft Humanoid Hands with Large Grasping Force Enabled by Flexible Hybrid Pneumatic Actuators," is published in Soft Robotics. Generally, soft-hand grippers -- which are used primarily in settings where an object may be fragile, light and irregularly shaped -- present several disadvantages: sharp surfaces, poor stability in grasping unbalanced loads and relatively weak grasping force for handling heavy loads. When designing the new model, Cao and his team took into consideration a number of human-environment interactions, from fruit picking to sensitive medical care. They identified that some processes require a safe but firm interaction with fragile objects; most existing gripping systems are not suitable for these purposes. The team explained that the design novelty resulted in a prototype demonstrating the merits of a responsive, fast, lightweight gripper capable of handling a multitude of tasks that traditionally required different types of gripping systems. Each finger of the soft humanoid hand is constructed from a flexible hybrid pneumatic actuator -- or FHPA -- driven to bend by pressurized air, creating a modular framework for movement in which each digit moves independently of the others. "Traditional rigid grippers for industrial applications are generally made of simple but re- liable rigid structures that help in generating large forces, high accuracy and repeatability," Cao said. "The proposed soft humanoid hand has demonstrated excellent adaptability and compatibility in grasping complex-shaped and fragile objects while simultaneously maintaining a high level of stiffness for exerting strong clamping forces to lift heavy loads." In essence, the best of both worlds, Cao explained. The FHPA is composed of both hard and soft components, built around a unique structural combination of actuated air bladders and a bone-like spring core. "They combine the advantages of the deformability, adaptability and compliance of soft grippers while maintaining the large output force originated from the rigidity of the actuator," Cao said. He believes the prototype can be useful in industries such as fruit picking, automated packaging, medical care, rehabilitation and surgical robotics. With ample room for future research and development, the team hopes to combine its advances with Cao's recent work on so-called 'smart' grippers, integrating printed sensors in the gripping material. And by combining the hybrid gripper with 'soft arms' models, the researchers aim to more accurately mimic precise human actions. Reference Liu et al., Soft Humanoid Hands with Large Grasping Force Enabled by Flexible Hybrid Pneumatic Actuators, Soft Robotics (2020), http://dx.doi.org/10.1089/soro.2020.0001

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  • Plastic in art, film, music and literature

    Topic of the Month Part 2: Plastic design By Guido Deussing Art and design often go hand in hand. Both live from the design, and also from materials that are used and used to express art and design. Plastics play a central role in both design areas. Objects made of plastic are constant features of our everyday lives; we are literally surrounded by them. Synthetic materials (polymers) really have proved to be all-round solutions for products from files to toothbrushes and are in the meantime essential elements of our working, living and leisure environments. Their variety is concealed a little by use of the general term “plastic”, whereas what is in actual fact involved when a closer look is taken ranges from a washing basket made of polypropylene, a milk container made of melamine resin or a chair made of acrylic styrene acrylonitrile. And then there is the paradox that plastics are hardly noticed as such any more since we encounter them everywhere – they have become second nature to us. We would only really notice that they exist if they did not exist any longer: we would have to do without many useful things if plastics were not available. The aesthetically inclined will be right to point out here that there are also plastic objects of which we are aware when they exist rather than if and when they do not exist. However, this is due primarily to their design rather than to the material: design objects made from plastic, furniture in particular, have even found their way into museums, where they can be admired as avant-garde classics. Product designers discovered plastics for their work almost as soon as industrial manufacturing of them began. The product environment started to be revolutionised at the latest in 1907 with the invention by the Belgian chemist Leo Hendrik Baekeland (1863 – 1944) of Bakelite, a compound made from phenol and formaldehyde that was the first thermoformable polymer – the foundation was laid for the development of plastic into the material of the 20th century. Until then, plastics had only replaced natural materials that were expensive because they were rare. Celluloid, for example, a biopolymer obtained from wood (nitrocellulose) and camphor, that was patented in the USA in 1868, imitated expensive ivory and was initially used to make billiard balls. Plastic design began with Bakelite The history of plastic design began with Bakelite too, because product designers accepted the challenge of creating new objects with the innovative new material for which there were no historical models, particularly cameras, radios and telephones. The history of plastic design began with Bakelite too, because product designers accepted the challenge of creating new objects with the innovative new material for which there were no historical models, particularly cameras, telephones (see picture gallery) and radios. Art nouveau and art deco costume jewellery was also made from bakelite, however. By modern-day standards, the variety of different designs at this early stage was strictly limited by the restrictions of technical and economic efficiency. “This did not change until the streamlined form from the USA defined a distinctive formal language for the Bakelite material – and thus for plastic in general – for the first time from 1930 onwards”, as Andrej Kupetz ), the executive director of the German Design Council in Frankfurt am Main, explains in an essay about the “Evolution of design in the course of time”.Although it at first glance seems to be pointless to give a cupboard or an ashtray a streamlined shape, this development proved to be an incredible success in the consumer goods field. Following the economic crisis in 1929, it stood for the start of a new era, full of optimism and with a strong belief in the future.” A real breakthrough was not made in Germany until after 1945. At a time when the country was reluctant to focus on the past, streamlined shaping stood for a new beginning – looking forward rather than back. The “kidney table” became the most well-known design object of this period. The Bakelite heyday did not last very long. The gloomy colour of the plastic was considered to be a disadvantage and restricted the range of possible uses. Melamine resin, on the other hand, could be given many different colours – even almost pure white – which made it the plastic of choice for tableware, for example. Since then , plastics have become a symbol of practically unlimited choice where both colour and, above all, shape are concerned. Product styling is sometimes “sober” and sometimes “bizarre”, while the irreconcilable opposites of minimalistic understatement and brash exuberance are encountered depending on the zeitgeist and design concept (see ”Current exhibitions: plastics in museums”). The dominant trend at the moment is reduction – as a design tool, but also where weight and costs are concerned. Plastic remains a lightweight material even where large volumes are involved; the objects can be reproduced as often as is required, particularly by the injection moulding process, while the unit price gets lower and lower the larger the production run. Attractive features that make demand for plastics so strong – something that is not a recent development but was already a convincing argument when industrial mass production was just starting to establish itself – and became the driving force behind this movement. The “all-purpose” material outshines wood, glass and metal in many respects, albeit at the expense of an appearance that takes some getting used to occasionally at the aesthetic level. Quite apart from the fact that some plastics suffer from the effects of oxygen (oxidation), humidity, UV radiation and microorganisms: they are deformed or discoloured, become brittle or tacky, lose their gloss and start to look shabby. In extreme cases, they even disintegrate into their basic components sooner or later, i.e. the polymers (huge molecules) become monomers again. Plastics - “you can do whatever you want with the material – and that is xactly the problem designers – or I at least – face”, Konstantin Grcic admitted in an interview in 1988. Nine years later, at “K 2007” in Düsseldorf, Grcic’s chair “Myto” premiered. Problems are encountered primarily with objects made from celluloid, complain the curators of the plastic museum “Plart” in Naples. Seating made from foamed polyurethane can literally disintegrate in the course of time too, however. Fortunately, this is now a thing of the past to a large extent: plastic designers no longer need to worry about the durability of their material. Stabilisers and additives have made plastics much more durable, weather-resistant and scratch-resistant. There has been progress at the aesthetic level too: polypropylene, for example, used to be a milky substance, but polymer research has in the meantime succeeded in producing translucent polypropylene that looks almost like glass, which is processed into objects with a grainy, slightly rough surface. From the mid-90s onwards, style was defined here by the bathroom and kitchen accessories developed by the German company “Authentics”, established by Hansjerg Maier-Aichen, Professor for Product Design at the Design University (HfG) in Karlsruhe. The services of Konstantic Grcic (born in 1965) from Munich, the superstar of the German design community, as a designer were obtained. To enable the characteristic surface structure to be achieved, the metal mould was processed in an etching bath. Grcic: “The method produces not just a new look but also a new feel, the object makes a warmer and, at the same time, higher-quality impression.” What is known as “author design” has a tradition in the plastic field, attracting not only Grcic, who the magazine “art” has called the “greatest living designer”, but also such illustrious names as Eero Aarnio (born in Finland in 1932) with his “Bubble Chair” (1968), Luigi (Lutz) Colani (born in Germany in 1968) with his “Zocker Seat” (1971), Vico Magistretti (1920-2006) from Italy with his standard lamp “Mezzachimera” (1969), Jasper Morrison (born in England in 1959) with his “Basel Chair” (2008), Ettore Sottsass (1917-2007), Italo-Austrian, with his portable typewriter “Valentine” (1968), Philippe Starck (born in France in 1949) with his “Mr. Impossible Chair” (2007) and Wilhelm Wagenfeld (1900-1990) from Germany with aircraft tableware for Lufthansa (1955). Plastics can be put to more varied uses than ever before nowadays. So it is no surprise that designers are faithful to them and regularly discover new sides to them. The unlimited possibilities have a downside as well, however: they make it difficult to commit oneself. “You can do whatever you want with the material – and that is exactly the problem designers – or I at least – face”, Konstantin Grcic admitted in an interview in 1988. Nine years later, at “K 2007” in Düsseldorf, Grcic’s chair “Myto” “Myto” premiered. A monoblock cantilever chair made from polybutylene terephthalate (“Ultradur High Speed”), developed by BASF; the Italian furniture manufacturer Plank is responsible for producing and selling the chair. On this occasion, the properties of the material determined the scope available for design creativity. In a manner of speaking, the design serves to highlight the potential of the new plastic Ultradur, aiming to exploit its excellent flow properties to the full and to demonstrate them in a complex object that is styled comprehensively, right down to the smallest detail. In the final analysis, this is also what justified presentation of Myto first of all at the Düsseldorf plastics trade fair rather than at the obvious choice of the International Furniture Fair in Milan, where Myto was showcased a year later. Andrej Kupetz identifies a new trend in the development of the material, the properties of which specify the design principle – something that could set a precedent for plastic design in the 21st century. It cannot, however, be expected that designers will submit to this trend in the long term. They are likely to experience problems with their own conception of themselves if they are labelled as mere assistants to industry. Incidentally: since 2006, industrial designers have had the opportunity to obtain advice about plastics at the BASF “design factory” in Ludwigshafen, although no-one expects or demands that product designers turn into polymer experts. “It goes without saying that we have to know about the material, but we do not need to be specialists”, is how Grcic puts it too. “We benefit from our naivety, because an open-minded spirit is able to take advantage of the material in a completely different way. In his initial designs for Kartell, Philippe Starck was completely inexperienced in dealing with plastic. He was able to take a fresh look and come up with entirely new inventions. As a result of this, a seam that was a technical necessity became an ornament, a distinctive feature.” Myto is not the first cantilever chair and is not the first one made of plastic either. The prototype was created in 1960 by the Danish designer Verner Panton (1926-1998) with his “Panton Chair”, a chair that is moulded completely in one piece. Myto is not, of course, the first cantilever chair and is not the first one made of plastic either. The prototype was created in 1960 by the Danish designer Verner Panton (1926-1998) with his “Panton Chair”, a chair that is moulded completely in one piece and that fills space like a single curved line. The material, styrene acrylonitrile copolymers (Luran S) modified with acrylic rubber to provide impact resistance, also comes from the BASF laboratories. Its aesthetic shape made it a sensation at the time and it is now an icon of plastic design, although it is far less well-known and is in far less widespread use than the monoblock that graced or – as we think nowadays - disfigured terraces and gardens by the million until recently. What we are talking about here is the first stackable chair made of plastic (polyethylene, polypropylene), which is or was extremely popular, because it is practical and not at all expensive while being recyclable too. The monoblock has more critics than friends in the meantime. In Freiburg im Breisgau, it has been banned completely from outdoor catering outlets – in an attempt to reduce visual pollution of the environment. “The main advantages of the monoblock were its low price and its functional efficiency. At the aesthetic level, it reflected mass taste, not dissimilar to Gelsenkirchen baroque”, says the industrial designer Jörg Gätjens (see also Interview) from Cologne. “To be honest, most designers always considered the chair to be terrible, but it was a successful product for a long time anyway. Once they have been taken out of service, you come across the chairs again in Africa and Asia”. For Gätjens, the abandonment of the monoblock in Germany is an excellent example of how fragile an image plastic has even in the design field: “Visual fatigue is generally high, because perception is determined by fashion trends, which are changing faster and faster. This is particularly true of plastic objects, because the material itself is associated with a short life, in contrast to wood. I fear that Myto will prove to be no exception here either, even if I as a designer can only admire this chair.” There is no doubt that more than the design quality of the material used is expressed in objects of everyday culture. First and foremost, the objects are reflections of our needs and desires (or of what we as consumers are supposed to consider they are). In view of this, plastic design has, historically, gone through a process of ups and downs, which is determined by political, social, economic and environmental influences. During the ‘economic miracle’ in the 50s, when the focus was on consumption, an atmosphere developed that encouraged plastics. Avant-garde designers spearheaded the functionalism movement (“less design is more design”). The stronghold of industrial design was the Design University in Ulm, the concepts of which were implemented by the Braun company with its head designer Dieter Rams (born in 1932). The record player “SK4”, better known as “Snow White’s coffin”, had a lid made from Plexiglas (polymethyl methacrylate) – something that had never been seen before – and received a triumphant reception at the Internationale Funkaustellung in 1955. The wild 60s broke with functionalism, but plastic boomed even more than before. The material was considered to be progressive and encouraged designers to experiment off the mainstream track. Using plastic stood for a lifestyle that combined social protest with a belief in progress, an obsession with freedom and enthusiasm for technology. Designers wanted to push the envelope: the Italian Cesare “Joe” Colombo (1930-1971) designed entire kitchens and bathrooms from plastic, while Verner Panton presented his synthetic living environment “Visiona 2“ at the Cologne Furniture Fair in 1970, staged by Bayer AG. The plastics trend stopped suddenly when the oil crisis hit in 1973. The obvious waste of raw materials in modern-day consumer society, growing volumes of rubbish and increasing environmental pollution led to a slump in the popularity of plastics. Plastics were then marginalised to a very large extent in the 80s as the environmental movement gained momentum. Stable economic growth, social hedonism and the start of the digital era helped plastic design to achieve a tremendous comeback in the 90s. Designers upgraded the material, the Authentics products mentioned above being one example of this. The “iMac” from Apple caused a sensation in 1998 as the aesthetic symbol of digitisation – with its all-in-one housing made from semi-translucent polycarbonate in the colour “Bondi Blue”. Plastics designers have recently started to reflect on the historical origins of their profession in the 19th century, the biopolymer era, again. At the Milan Furniture Fair 2011, the German designer Werner Aisslinger (born in 1964) presented his “Hemp Chair”, a structure made from an environmentally sound composite material (the natural fibres hemp and kenaf plus Acrodur as the bonding agent) that is both elastic and tough. It seems to be the case that design and society are at a crossroads again. But plastics have shown that this kind of material has the potencial to be the one in the 21st century.

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  • New model connects respiratory droplet physics with spread of Covid-19

    A droplet suspended in an acoustic levitator. Image: Abhishek Saha, UC San Diego Respiratory droplets from a cough or sneeze travel farther and last longer in humid, cold climates than in hot, dry ones, according to a study on droplet physics by an international team of engineers. The researchers incorporated this understanding of the impact of environmental factors on droplet spread into a mathematical model that can be used to predict the early spread of respiratory viruses including COVID-19, and the role of respiratory droplets in that spread. The team developed this new model to better understand the role that droplet clouds play in the spread of respiratory viruses. Their model is the first to be based on a fundamental approach taken to study chemical reactions called collision rate theory, which looks at the interaction and collision rates of a droplet cloud exhaled by an infected person with healthy people. Their work connects population-scale human interaction with their micro-scale droplet physics results on how far and fast droplets spread, and how long they last. Their results were published June 30 in the journal Physics of Fluids. "The basic fundamental form of a chemical reaction is two molecules are colliding. How frequently they're colliding will give you how fast the reaction progresses," said Abhishek Saha, a professor of mechanical engineering at the University of California San Diego, and one of the authors of the paper. "It's exactly the same here; how frequently healthy people are coming in contact with an infected droplet cloud can be a measure of how fast the disease can spread." Experimental setup showing the acoustic levitation of a droplet illuminated by a cold LED source. A diffuser plate is used for uniform imaging of the droplet. A CCD camera fitted with the zoom lens assembly is used for illumination. The schematic is not to scale. Image: Chaudhuri et al. They found that, depending on weather conditions, some respiratory droplets travel between 8 feet and 13 feet away from their source before evaporating, without even accounting for wind. This means that without masks, six feet of social distance may not be enough to keep one person's exhalated particles from reaching someone else. "Droplet physics are significantly dependent on weather," said Saha. "If you're in a colder, humid climate, droplets from a sneeze or cough are going to last longer and spread farther than if you're in a hot dry climate, where they'll get evaporated faster. We incorporated these parameters into our model of infection spread; they aren't included in existing models as far as we can tell." The researchers hope that their more detailed model for rate of infection spread and droplet spread will help inform public health policies at a more local level, and can be used in the future to better understand the role of environmental factors in virus spread. They found that at 35C (95F) and 40 percent relative humidity, a droplet can travel about 8 feet. However, at 5C (41F) and 80 percent humidity, a droplet can travel up to 12 feet. The team also found that droplets in the range of 14-48 microns possess higher risk as they take longer to evaporate and travel greater distances. Smaller droplets, on the other hand, evaporate within a fraction of a second, while droplets larger than 100 microns quickly settle to the ground due to weight. A flow-diagram outlining the interconnections of the model. Image: Swetaprovo Chaudhuri, Saptarshi Basu, Prasenjit Kabi, Vishnu R. Unni, and Abhishek Saha This is further evidence of the importance of wearing masks, which would trap particles in this critical range. The team of engineers from the UC San Diego Jacobs School of Engineering, University of Toronto and Indian Institute of Science are all experts in the aerodynamics and physics of droplets for applications including propulsion systems, combustion or thermal sprays. They turned their attention and expertise to droplets released when people sneeze, cough or talk when it became clear that COVID-19 is spread through these respiratory droplets. They applied existing models for chemical reactions and physics principles to droplets of a salt water solution--saliva is high in sodium chloride--which they studied in an ultrasonic levitator to determine the size, spread, and lifespan of these particles in various environmental conditions. Many current pandemic models use fitting parameters to be able to apply the data to an entire population. The new model aims to change that. "Our model is completely based on "first principles" by connecting physical laws that are well understood, so there is next to no fitting involved," said Swetaprovo Chaudhuri, professor at University of Toronto and a co-author. "Of course, we make idealized assumptions, and there are variabilities in some parameters, but as we improve each of the submodels with specific experiments and including the present best practices in epidemiology, maybe a first principles pandemic model with high predictive capability could be possible." There are limitations to this new model, but the team is already working to increase the model's versatility. "Our next step is to relax a few simplifications and to generalize the model by including different modes of transmission," said Saptarshi Basu, professor at the Indian Institute of Science and a co-author. "A set of experiments are also underway to investigate the respiratory droplets that settle on commonly touched surfaces." Reference Chauduri et al., Modeling the role of respiratory droplets in Covid-19 type pandemics, Physics of Fluids (2020), https://doi.org/10.1063/5.0015984

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  • Molecularly thin interface between polymers - for efficient CO2 capture membrane

    Composite membranes for CO2 separation contain different functional layers in their structure (e.g. porous mechanical support, selective layer etc.). We found that when selective layer in composite membrane is made ultimately thin - it forms specific interface with supporting gutter polymer, and this structure shows unexpectedly high selectivity towards CO2 over nitrogen. This new finding provides the way to develop better membranes for CO2 capture. Climate breakdown caused by the emissions of carbon dioxide (CO2) into the atmosphere is a major existential problem faced by humanity right now. The most acceptable solution would be complete termination of the use of fossil fuels or at least fast reduction of their use by all countries, in line with the Paris agreement. This will ensure the planetary warming is limited by 2 C. The emissions reductions, however, are slow and most of the countries are unlikely to reach the goals of reduction. Technological solutions for the massive CO2 emissions prevention are therefore critically needed. Some technologies for CO2 capture, for instance, sorption by liquid amine chemicals are already mature to be applied on a scale, however they are costly and come with a burden of toxic chemicals disposal once they lost their CO2 binding property. Alternative technologies are therefore of a great importance. Separation of gases with the help of membranes is emerging as a key technology for the establishment of a sustainable energy society. Wide deployment of membranes can help to capture huge amounts carbon dioxide emitted in the variety of industrial processes. In contrast to conventional CO2 capture, gas separation with membranes provides a promise for cost-efficient solution. However, to achieve economical CO2 capture at mass scale the membranes need several critical features: fast CO2 transport through their structure; high CO2 selectivity (i.e. to be a less permeable barrier for other gases); mechanical strength and chemical resistance. Additionally, membranes should be composed of materials that are inexpensive at mass production, and this is the reason why organic polymers, (conventional plastics and rubbers) are most attractive for industrial applications. Image: Freestanding and mechanically strong nanomembranes composed of two polymeric layers demonstrated superior carbon dioxide separation from nitrogen. As revealed by the study the surface of the composite membrane played a crucial role to achieve the CO2 selectivity. The interface layer composed of the interpenetrated gutter layer (PDMS) and ultrathin selective layer (Pebax-1657) polymers was conveniently controlled by oxygen plasma treatment of PDMS. The discovery provides new insights on the materials performance in the region of nanoscale thicknesses. (Source: Roman Selyanchyn, I2CNER, Kyushu university) Thin-film composite is a specific architecture of the membranes to provide the robust structure for industrial applications. These membranes, that contain multiple functional layers (made of organic polymers) in its structure, offer a good solution for large-scale CO2 capture. However, even benchmark organic polymers with best separation performance (high CO2 permeability and high CO2/N2 selectivity) are struggling to deliver satisfactory separation performance, because of inability to form sufficiently thin, defect free and mechanically stable membranes. In this work we report for the first time how ultimately thin selective layers (thickness of several nanometers) can be used to achieve desired separation properties. We have used well-known polymers for this study: polyether block amide (Pebax-1657) as selective layer and polydimethylsiloxane (PDMS) as gutter layer and examined what happens with the gas separation property when thickness of the selective layer pushed to the extreme of several nanometers. We have discovered that when selective layer of separation membranes becomes very thin it can form specific interface with gutter layer in composite structure. This nanoscale interface delivered unexpectedly high selectivity towards CO2. Gentle and ultra-short plasma treatment of the hydrophobic PDMS layer that is needed to promote adhesion with hydrophilic selective layer revealed itself as a tool to control and tune the "activity" of the molecular interface between two polymers. We found that this interface made a determining impact on the membranes CO2 selectivity. Together with high permeation rates enabled by low thickness, developed membranes fit nicely into the area of the separation properties needed for industrial CO2 capture (e.g. post-combustion capture at fossil fueled power plants). These results open a new unexplored area of the interface-governed gas separation that can be used by engineers to design more efficient membranes for variety of useful applications. Reference Olena Selyanchyn, Roman Selyanchen and Shigenori Fujikawa, Critical Role of the Molecular Interface in Double-Layered Pebax-1657/PDMS Nanomembranes for Highly Efficient CO2/N2 Gas Separation, ACS Applied Materials Interfaces (2020), https://doi.org/10.1021/acsami.0c07344

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  • Researchers create air filter that can kill the coronavirus

    Researchers from the University of Houston, in collaboration with others, have designed a "catch and kill" air filter that can trap the virus responsible for COVID-19, killing it instantly. Zhifeng Ren, director of the Texas Center for Superconductivity at UH, collaborated with Monzer Hourani, CEO of Medistar, a Houston-based medical real estate development firm, and other researchers to design the filter, which is described in a paper published in Materials Today Physics. The researchers reported that virus tests at the Galveston National Laboratory found 99.8% of the novel SARS-CoV-2, the virus that causes COVID-19, was killed in a single pass through a filter made from commercially available nickel foam heated to 200 degrees Centigrade, or about 392 degrees Fahrenheit. It also killed 99.9% of the anthrax spores in testing at the national lab, which is run by the University of Texas Medical Branch. "This filter could be useful in airports and in airplanes, in office buildings, schools and cruise ships to stop the spread of COVID-19," said Ren, MD Anderson Chair Professor of Physics at UH and co-corresponding author for the paper. "Its ability to help control the spread of the virus could be very useful for society." Medistar executives are is also proposing a desk-top model, capable of purifying the air in an office worker's immediate surroundings, he said. Ren said the Texas Center for Superconductivity at the University of Houston (TcSUH) was approached by Medistar on March 31, as the pandemic was spreading throughout the United States, for help in developing the concept of a virus-trapping air filter. Luo Yu of the UH Department of Physics and TcSUH along with Dr. Garrett K. Peel of Medistar and Dr. Faisal Cheema at the UH College of Medicine are co-first authors on the paper. The researchers knew the virus can remain in the air for about three hours, meaning a filter that could remove it quickly was a viable plan. With businesses reopening, controlling the spread in air conditioned spaces was urgent. And Medistar knew the virus can't survive temperatures above 70 degrees Centigrade, about 158 degrees Fahrenheit, so the researchers decided to use a heated filter. By making the filter temperature far hotter - about 200 C - they were able to kill the virus almost instantly. Ren suggested using nickel foam, saying it met several key requirements: It is porous, allowing the flow of air, and electrically conductive, which allowed it to be heated. It is also flexible. But nickel foam has low resistivity, making it difficult to raise the temperature high enough to quickly kill the virus. The researchers solved that problem by folding the foam, connecting multiple compartments with electrical wires to increase the resistance high enough to raise the temperature as high as 250 degrees C. By making the filter electrically heated, rather than heating it from an external source, the researchers said they minimized the amount of heat that escaped from the filter, allowing air conditioning to function with minimal strain. A prototype was built by a local workshop and first tested at Ren's lab for the relationship between voltage/current and temperature; it then went to the Galveston lab to be tested for its ability to kill the virus. Ren said it satisfies the requirements for conventional heating, ventilation and air conditioning (HVAC) systems. "This novel biodefense indoor air protection technology offers the first-in-line prevention against environmentally mediated transmission of airborne SARS-CoV-2 and will be on the forefront of technologies available to combat the current pandemic and any future airborne biothreats in indoor environments," Cheema said. Hourani and Peel have called for a phased roll-out of the device, "beginning with high-priority venues, where essential workers are at elevated risk of exposure (particularly schools, hospitals and health care facilities, as well as public transit environs such as airplanes)." That will both improve safety for frontline workers in essential industries and allow nonessential workers to return to public work spaces, they said. Reference Yu et al., Catching and killing of airborne SARS-CoV-2 to control spread of COVID-19 by a heated air disinfection system, Materials TodayPhysis (2020), https://doi.org/10.1016/j.mtphys.2020.100249

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