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Material selections and product prototyping
Published in Fuewen Frank Liou, Rapid Prototyping and Engineering Applications, 2019
Alloy steels (nickel, chromium, manganese) can improve strength, hardness, or resistance to corrosion. In terms of plastics, one can select among composites, polycarbonate, nylon, acetal, and ABS. Composite materials are plastics with additives, fillers, and reinforcing agents, such as glass fibers, carbon, or graphite. Polycarbonate has a very high impact resistance and is easy to produce. It is used for computer parts, peripherals, business machine housings, vacuum cleaner parts, sports helmets, windshields, etc. Nylon (DuPont) is resistant to oils, greases, and most common solvents. It has high strength and high modulus of elasticity, high maximum service temperature, and low friction coefficient. Nylon is commonly used for bearings, bushings, gears, cams, etc. Acetal is strong and stiff, has high resistance to abrasions and chemicals, and has a low coefficient of friction. It is commonly used for brackets, gears, bearings, cams, etc. ABS is good for structural applications, has good thermoformability, has high impact strength, has good fracture resistance, and is inexpensive and available in sheets and rods.
Industrial Polymers
Published in Manas Chanda, Plastics Technology Handbook, 2017
Polyacetal is obtained as a linear polymer (about 80% crystalline) with an average molecular weight of 30,000–50,000. Comparative values for some properties of typical commercial products are given in Table 4.23. The principal features of acetal polymers which render them useful as engineering thermoplastics are high stiffness, mechanical strength over a wide temperature range, high fatigue endurance, resistance to creep, and good appearance. Although similar to nylons in many respects, acetal polymers are superior to them in fatigue resistance, creep resistance, stiffness, and water resistance (24-h water absorption at saturation being 0.22% for acetal copolymer vs. 8.9% for nylon-6,6). The nylons (except under dry conditions) are superior to acetal polymers in impact toughness. Various tests indicate that the acetal polymers are superior to most other plastics and die cast aluminum.
Development of Simulated Moving Bed Reactor Using a Cation Exchange Resin as a Catalyst and Adsorbent for the Synthesis of Acetals
Published in Arup K. SenGupta, Ion Exchange and Solvent Extraction, 2007
Viviana M.T.M. Silva, Ganesh K. Gandi, Alírio E. Rodrigues
The primary process for the preparation of acetals is the reaction of an aldehyde with an alcohol, accordingly 2Alcohol+Aldehyde↔Acetal+Water
Levoglucosenone-derived synthesis of bio-based solvents and polyesters
Published in Green Chemistry Letters and Reviews, 2023
Cicely M. Warne, Sami Fadlallah, Adrian C. Whitwood, James Sherwood, Louis M. M. Mouterde, Florent Allais, Georg M. Guebitz, Con R. McElroy, Alessandro Pellis
When first synthesized in the literature, Cygnet 0.0 (2) formation was acid catalyzed by KSF-200 (25, 28). This catalytic system functioned well but if the heterogeneous catalyst was not freshly prepared, the product would be slightly discolored, presumably from leaching in the system. Discolored (2) gave poorer yields and conversions as compared to that prepared with fresh catalyst. To negate this, phosphoric acid was selected as a weak homogeneous acid to facilitate acetal formation over the ketone (Figure 2a). Due to the high boiling point of the diols (which acted as both solvent and reactant), the reactions were carried out in an open vessel and at elevated temperature to drive off water produced. The excess diol and removal of water helped push the equilibrium towards the right (Figure 2a) and favor the formation of the cygnet acetal. Cygnets (2), (3) and (4) were successfully synthesized using this method (Figures S1–S6). Upon cooling (2) crystallized instantaneously, (3) within minutes and (4) required hours (Figure 2b). The crystal structure of the novel (3) and (4) was also resolved (Figure 2c and Tables S4–S5).
Effects of extracellular enzymes secreted by wild edible fungi mycelia on the surface properties of local soil colloids
Published in Environmental Technology, 2022
Lijuan Cha, Hongjuan Feng, Min Wu, Jing Xing, Jing Li, Quan Chen
The XPS spectra of O1 peak splitting diagrams of soil colloids 2 with or without extracellular enzymes are shown in Figure 6, and the corresponding data are listed in Table 5. As shown in Figure 6 and Table 5, the O-I is allocated to the form of N–C = O, O-II and O-III correspond to the existence form of O–C = O and O–C-O, respectively. These structures could be inferred to be the amide, carboxyl, acetal, or hemiacetal functional groups in the soil colloids [31]. In the soil colloids, the highest proportion of the oxygen-containing functional groups was hydrophilic O–C = O, which was attributed to the carboxyl groups or ester functional groups. After adding extracellular enzymes, the ratios of O–C = O in the soil colloids changed slightly, indicating that this type of hydrophilic functional group did not play the controlling role in the dispersion stability of soil colloids.
Thermal desorption behavior of hemiacetal, acetal, ether, and ester oligomers
Published in Aerosol Science and Technology, 2019
Megan S. Claflin, Paul J. Ziemann
In light of the persistent questions regarding the interpretation of SOA thermal desorption data, the objective of this study was to investigate the thermal desorption properties of selected oligomers with linkages typical of those identified in laboratory studies and expected to be present in atmospheric SOA. By conducting studies on oligomers with known structures, it should then be possible to better predict the thermal desorption behavior of oligomers and identify those that are most likely to behave unpredictably. The classes of oligomers studied were those containing hemiacetal, acetal, ether, and ester linkages. They were either commercially available or synthesized in solution or in an environmental chamber as a component of SOA formed from the reaction of β-pinene with NO3 radicals. We have shown previously (Claflin and Ziemann 2018) that ∼94% of the SOA formed in this reaction consists of a mixture of acetal oligomers, thus providing an opportunity to investigate the thermal desorption properties of authentic SOA that has been carefully characterized and consists almost entirely of a few oligomers. Particles composed of oligomers were studied using a thermal desorption particle beam mass spectrometer (TDPBMS) for both real-time analysis with rapid desorption and slow TPTD. The results provide new information on the thermal desorption behavior of oligomers that are expected to be present in SOA, and should be useful for interpreting measurements made using many of the available thermal desorption methods.