SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Acrylonitrile butadiene styrene

27

The technology used in the manufacturing of televisions and monitors has been changing in recent years. Monitors with liquid crystal displays (LCD) emerged in the market with the aim of replacing cathode ray tube monitors. As a result, the disposal of this type of product, which is already very high, will increase. Thus, without accurate knowledge of the components and materials present in an LCD monitor, the recycling of materials, such as mercury, thermoplastic polymers, glasses, metals and precious metals amongst others, is not only performed, but allows contamination of soil, water and air with the liberation of toxic compounds present in this type of waste when disposed of improperly. Therefore, the objective of this study was to disassemble and characterize the materials in this type of waste, identify the composition, amount and form to enable, in further work, the development of recycling routes. After various tests and analyses, it was observed that an LCD display can be recycled, provided that precautions are taken. Levels of lead, fluoride and copper are above those permitted by the Brazilian law, characterizing this residue as having a high pollution potential. The materials present in printed circuit boards (base and precious metals)-thermoplastics, such as polyethylene terephthalate, acrylic, acrylonitrile butadiene styrene and polycarbonate and metals, such as steel and aluminum, and a layer of indium (in the internal face of the glass)-are components that make a point in terms of their potential for recycling.

Concepts: Liquid crystal display, Recycling, Liquid crystal, Thermoplastic, Acrylonitrile butadiene styrene, Polyethylene terephthalate, Printed circuit board, Cathode ray tube

27

Well-controlled assembly of proteins on supramolecular templates of block copolymers can be extremely useful for high-throughput biodetection. We report the adsorption and assembly characteristics of a model antibody protein to various polystyrene-block-poly(4-vinylpyridine) templates whose distinctive nanoscale structures are obtained through time-regulated exposure to chloroform vapor. The strong adsorption preference of the protein to the polystyrene segment in the diblock copolymer templates leads to an easily predictable, controllable, rich set of nanoscale protein morphologies through self-assembly. We also demonstrate that the chemical identities of various subareas within individual nanostructures can be readily elucidated by investigating the corresponding protein adsorption behavior on each chemically distinct area of the template. In our approach, a rich set of intricate nanoscale morphologies of protein arrays that cannot be easily attained through other means can be generated straightforwardly via self-assembly of proteins on chemically treated diblock copolymer surfaces, without the use of clean-room-based fabrication tools. Our approach provides much-needed flexibility and versatility for the use of block copolymer-based protein arrays in biodetection. The ease of fabrication in producing well-defined and self-assembled templates can contribute to a high degree of versatility and simplicity in acquiring an intricate nanoscale geometry and spatial distribution of proteins in arrays. These advantages can be extremely beneficial both for fundamental research and biomedical detection, especially in the areas of solid-state-based, high-throughput protein sensing.

Concepts: Polymer, Copolymer, Polymer chemistry, Acrylonitrile butadiene styrene

12

Most desktop 3D printers designed for the consumer market utilize a plastic filament extrusion and deposition process to fabricate solid objects. Previous research has shown that the operation of extrusion-based desktop 3D printers can emit large numbers of ultrafine particles (UFPs: particles less than 100 nm) and some hazardous volatile organic compounds (VOCs), although very few filament and printer combinations have been tested to date. Here we quantify emissions of UFPs and speciated VOCs from five commercially available desktop 3D printers utilizing up to nine different filaments using controlled experiments in a test chamber. Median estimates of time-varying UFP emission rates ranged from ~108 to ~1011 #/min across all tested combinations, varying primarily by filament material and, to a lesser extent, bed temperature. The individual VOCs emitted in the largest quantities included caprolactam from nylon-based and imitation wood and brick filaments (ranging from ~2 to ~180 μg/min), styrene from acrylonitrile butadiene styrene (ABS) and high-impact polystyrene (HIPS) filaments (~10 to ~110 μg/min), and lactide from polylactic acid (PLA) filaments (~4 to ~5 μg/min). Results from a screening analysis of the potential exposures to these products in a typical small office environment suggest caution should be used when operating many of the printer and filament combinations in enclosed or poorly ventilated spaces or without the aid of a combined gas and particle filtration system.

Concepts: Polystyrene, Volatile organic compound, Thermoplastic, Polylactic acid, Acrylonitrile butadiene styrene, Volatile, Styrene, Ozone

2

Mechanical metamaterials that are engineered with sub-unit structures present unusual mechanical properties depending on the loading direction. Although they show promise, their practical utility has so far been somewhat limited because, to the best of our knowledge, no study about the potential of mechanical metamaterials made from sophisticatedly tailored sub-unit structures has been made. Here, we present a mechanical metamaterial whose mechanical properties can be systematically designed without changing its chemical composition or weight. We study the mechanical properties of triply periodic bicontinuous structures whose detailed sub-unit structure can be precisely fabricated using various sub-micron fabrication methods. Simulation results show that the effective wave velocity of the structures along with different directions can be designed to introduce the anisotropy of stiffness by changing a volume fraction and aspect ratio. The ratio of Young’s modulus to shear modulus can be increased by up to at least 100, which is a 3500% increase over that of isotropic material (2.8, acrylonitrile butadiene styrene). Furthermore, Poisson’s ratio of the constituent material changes the ratio while Young’s modulus does not influence it. This study presents the promising potential of mechanical metamaterials for versatile industrial and biomedical applications.

Concepts: Ratio, Materials science, Anisotropy, Young's modulus, Elastic modulus, Hooke's law, Acrylonitrile butadiene styrene, Impulse excitation technique

1

Micelles formed by the self-assembly of block copolymers in selective solvents have attracted widespread attention and have uses in a wide variety of fields, whereas applications based on their electronic properties are virtually unexplored. Herein we describe studies of solution-processable, low-dispersity, electroactive fibre-like micelles of controlled length from π-conjugated diblock copolymers containing a crystalline regioregular poly(3-hexylthiophene) core and a solubilizing, amorphous regiosymmetric poly(3-hexylthiophene) or polystyrene corona. Tunnelling atomic force microscopy measurements demonstrate that the individual fibres exhibit appreciable conductivity. The fibres were subsequently incorporated as the active layer in field-effect transistors. The resulting charge carrier mobility strongly depends on both the degree of polymerization of the core-forming block and the fibre length, and is independent of corona composition. The use of uniform, colloidally stable electroactive fibre-like micelles based on common π-conjugated block copolymers highlights their significant potential to provide fundamental insight into charge carrier processes in devices, and to enable future electronic applications.

Concepts: Atom, Polymer, Copolymer, Polymer chemistry, Transistor, Solid, Electronics, Acrylonitrile butadiene styrene

1

Printing devices are known to emit chemicals into the indoor atmosphere. Understanding factors that influence release of chemical contaminants from printers is necessary to develop effective exposure assessment and control strategies. In this study, a desktop fused deposition modeling (FDM) 3-D printer using acrylonitrile butadiene styrene (ABS) or polylactic acid (PLA) filaments and two monochrome laser printers were evaluated in a 0.5 m(3) chamber. During printing, chamber air was monitored for vapors using a real-time photoionization detector (results expressed as isobutylene equivalents) to measure total volatile organic compound (TVOC) concentrations, evacuated canisters to identify specific VOCs by off-line gas chromatography-mass spectrometry (GC-MS) analysis, and liquid bubblers to identify carbonyl compounds by GC-MS. Airborne particles were collected on filters for off-line analysis using scanning electron microscopy with an energy dispersive x-ray detector to identify elemental constituents. For 3-D printing, TVOC emission rates were influenced by a printer malfunction, filament type, and to a lesser extent, by filament color; however, rates were not influenced by the number of printer nozzles used or the manufacturer’s provided cover. TVOC emission rates were significantly lower for the 3-D printer (49 to 3552 µg h(-1)) compared to the laser printers (5782 to 7735 µg h(-1)). A total of 14 VOCs were identified during 3-D printing that were not present during laser printing. 3-D printed objects continued to off-gas styrene, indicating potential for continued exposure after the print job is completed. Carbonyl reaction products were likely formed from emissions of the 3-D printer, including 4-oxopentanal. Ultrafine particles generated by the 3-D printer using ABS and a laser printer contained chromium. Consideration of the factors that influenced the release of chemical contaminants (including known and suspected asthmagens such as styrene and 4-oxopentanal) from a FDM 3-D printer should be made when designing exposure assessment and control strategies.

Concepts: Laser, Inkjet printer, Xerography, Acrylonitrile butadiene styrene, Ozone, Selective laser sintering, Fused deposition modeling, Laser printer

1

The fast development of low-cost desktop three-dimensional (3D) printers has made those devices widely accessible for goods manufacturing at home. However, is it safe? Users may belittle the effects or influences of pollutants (organic compounds and ultrafine particles) generated by the devices in question. Within the scope of this study, the authors attempt to investigate thermal decomposition of the following commonly used, commercially available thermoplastic filaments: acrylonitrile-butadiene-styrene (ABS), polylactic acid (PLA), polyethylene terephthalate (PET), and nylon. Thermogravimetric analysis has shown the detailed thermal patterns of their behavior upon increasing temperature in neutral atmosphere, while GC analysis of organic vapors emitted during the process of heating thermoplastics have made it possible to obtain crucial pieces of information about the toxicity of 3D printing process. The conducted study has shown that ABS is significantly more toxic than PLA. The emission of volatile organic compounds (VOC) has been in the range of 0.50 μmol/h. Styrene has accounted for more than 30% of total VOC emitted from ABS, while for PLA, methyl methacrylate has been detected as the predominant compound (44% of total VOCs emission). Moreover, the authors have summarized available or applicable methods that can eliminate formed pollutants and protect the users of 3D printers. This paper summarizes theoretical knowledge on thermal degradation of polymers used for 3D printers and shows results of authors' investigation, as well as presents forward-looking solutions that may increase the safety of utilization of 3D printers.

Concepts: Polymer, Plastic, Volatile organic compound, Thermoplastic, Polylactic acid, Acrylonitrile butadiene styrene, Polyethylene terephthalate, Thermoplastics

1

Desktop three-dimensional (3D) printers are becoming commonplace in business offices, public libraries, university labs and classrooms, and even private homes; however, these settings are generally not designed for exposure control. Prior experience with a variety of office equipment devices such as laser printers that emit ultrafine particles (UFP) suggests the need to characterize 3D printer emissions to enable reliable risk assessment. The aim of this study was to examine factors that influence particulate emissions from 3D printers and characterize their physical properties to inform risk assessment. Emissions were evaluated in a 0.5-m(3) chamber and in a small room (32.7 m(3)) using real-time instrumentation to measure particle number, size distribution, mass, and surface area. Factors evaluated included filament composition and color, as well as the manufacturer-provided printer emissions control technologies while printing an object. Filament type significantly influenced emissions, with acrylonitrile butadiene styrene (ABS) emitting larger particles than polylactic acid (PLA), which may have been the result of agglomeration. Geometric mean particle sizes and total particle (TP) number and mass emissions differed significantly among colors of a given filament type. Use of a cover on the printer reduced TP emissions by a factor of 2. Lung deposition calculations indicated a threefold higher PLA particle deposition in alveoli compared to ABS. Desktop 3D printers emit high levels of UFP, which are released into indoor environments where adequate ventilation may not be present to control emissions. Emissions in nonindustrial settings need to be reduced through the use of a hierarchy of controls, beginning with device design, followed by engineering controls (ventilation) and administrative controls such as choice of filament composition and color.

Concepts: Particulate, Air pollution, Acrylonitrile butadiene styrene, Diesel particulate matter

0

Novel styryl-substituted thioureas and squaramides were obtained in three steps from commercially available 4-hydroxy-3,5-dichloroaniline. These organocatalysts promote cascade reactions in high yields and excellent stereoselection. By using only 5 mol% loading of catalyst it is possible to obtain 2,3,4-trisubtituted benzopyrans by reaction of α-amidosulfones derived from salicyladehydes and nitrostyrenes, or 2,3,4-trisubstituted 4H-chromenes by reaction of the same α-amidosulfones with phenylsulfonylacetonitrile in excellent diastereo- and enantioselectivities. Two polymeric thiourea and squaramide were prepared by copolymerization of the best monomeric catalysts with styrene and divinylbenzene and used for the same transformations. These polymers behave also as excellent stereoselective catalysts that can be recovered and reused for five cycles.

Concepts: Amino acid, Chemical reaction, Polymer, Copolymer, Polymer chemistry, Acrylonitrile butadiene styrene, Synthetic rubber, Structural unit

0

The electrostatic combination of anionic block copolymers with cationic gold(i) complexes leads to the formation of spherical micelles, where gold(i)-containing ionic cores were formed with anionic blocks and further stabilized by neutral blocks of polystyrene or poly(ethylene oxide). This self-assembled strategy induces remarkable phosphorescence enhancement of the gold(i) complexes in solution. The emissive intensity increases unexpectedly with increasing molecular weight of the anionic block that is not coordinated onto the gold(i) complexes. The intensely phosphorescent micelles formed in water can be utilized as a luminescence bioimaging probe in living cells.

Concepts: Polymer, Copolymer, Acrylonitrile butadiene styrene