The microstructure, hardness, impact toughness and ring block wear properties of a novel bainitic steel were investigated by means of scanning electron microscopy (SEM), transmission electron ...microscopy (TEM), laser confocal microscopy (LCM), X-ray diffraction (XRD), Rockwell hardness tester, impact tester and MM-200 wear tester (Jinan Sida Testing Technology Co., LTD, China). The above steel was austenitized at 900 °C, and was isothermally quenched at 250, 280, 310, 340, 370, 400 and 430 °C respectively. The results showed that the microstructure of the bainitic steel was mainly composed of bainitic ferrite (BF), retained austenite (RA), and martensite/austenite (M/A). A part of the RA underwent a phase transition and transformed into martensite during the wear process, resulting in the increase of the hardness. The wear morphology of bainitic steel was dominated by straight furrows. The wear mechanisms were mainly abrasive wear and oxidative wear. With the increase of the austempering temperature, the microstructure coarsened, the amount of the blocky RA content increased, the hardness of the high silicon bainitic steel increased slightly first and then decreased, the impact toughness improved significantly first and then reduced, and the wear resistance increased first and then decreased. Under the same test conditions, the high silicon bainitic steel after austempering at 340 °C had better combination of hardness and toughness, stable and low friction coefficient, and excellent wear resistance.
The purpose of this study was to clarify the effect of boron content on the microstructure evolution, mechanical properties, and three-body abrasive wear property of as-cast Fe–Si–Mn–Cr–B alloys, and ...to reveal the wear mechanism of Fe–Si–Mn–Cr–B alloys. The results indicated that the microstructure of the Fe–Si–Mn–Cr–B alloy was mainly composed of bainite, retained austenite (RA), M3B2, and M2B (M stands for the metal atom, in this case, it refers to Fe, Cr, and Mn). With the increase of boron content, the volume fraction of the boride phase increased, the morphology of the boride phase was dominated by fishbone, the microhardness of the boride phase and the macrohardness of the alloy increased, and the wear resistance of the alloy was significantly enhanced. Compared with the 0.5wt.% B alloy, the macrohardness of the 2.0wt.% B alloy was increased by 19.5%, the maximum microhardness of the boride phase reached 1440 HV0.2, the Charpy impact toughness was reduced by 45%, and the wear resistance was increased by 268%. The morphology, content and distribution of the boride phase play a key role in improving the hardness and wear resistance of the alloy. The synergy between the high-hardness boride phase and the softer metal matrix phase, which was composed of bainite and RA, gave the alloy excellent wear resistance. The main wear mechanisms of the alloy were abrasive wear and fretting wear.
A novel biobased epoxy monomer with conjugated double bonds, glycidyl ester of eleostearic acid (GEEA) was synthesized from tung oil fatty acids and characterized by (1)H and (13)C NMR. Differential ...scanning calorimeter analysis (DSC) and Fourier transform infrared spectroscopy (FT-IR) were utilized to investigate the curing process of GEEA with dienophiles and anhydrides. DSC indicated that GEEA could cross-link with both dienophiles and anhydrides through Diels-Alder reaction and epoxy/anhydride ring-opening reaction. Furthermore, Diels-Alder cross-link was much more active than the ring-opening of epoxy and anhydride in the curing process. FT-IR also revealed that GEEA successively reacted with dienophiles and anhydrides in both cross-linking methods. Dynamic mechanical analysis and mechanical tensile testing were used to study the thermal and mechanical properties of GEEA cured by maleic anhydride, nadic methyl anhydride and 1,1'-(methylenedi-4,1-phenylene)bismaleimide. Due to the independence between the curing agents, dienophile and anhydride, a series of thermosetting polymers with various properties could be obtained by adjusting the composition of these two curing agents.
Polyols with different number of hydroxyl groups were synthesized from ricinoleic acid and oleic acid. These plant oil derived polyols can be used as plasticizers and combined with ethyl cellulose ...(EC) through supramolecular system to prepare ethyl cellulose composite films. The morphology, thermal stability and mechanical properties of the prepared ethyl cellulose films were studied in detail to indicate the plasticizing efficiency of these polyols and the effect of the number of hydroxyl groups in polyols on EC composite film’s properties. With the addition of polyols, the tensile strength of EC composite films decreased, while the elongation at break increased. The elongation at break of EC composite films can be improved by 11–12 times when the polyols contain 1–3 hydroxyl groups. Thus, the plant oil derived polyols with 1–3 hydroxyl groups can be used as plasticizers for EC films. In addition, molecular dynamic simulations were performed to further probe the effects of the number of hydroxyl groups in polyols on EC composite film’s properties.
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Novel functional dynamic covalent-bonded polymer networks (DCPN) containing dynamic disulfide bonds were prepared from castor oil via a simple process. Firstly, UV-curable castor-oil-based ...polyurethane acrylate (COPUA) containing disulfide bonds and unsaturated double bonds was synthesized, then added with glycidyl methacrylate (GMA) to reduce viscosity (named COPUA-GMA) and mixed with different proportions of glycidyl esters containing unsaturated double bonds to form a series of UV-cured polymers named COPUA-GMA-EP. FTIR and NMR demonstrated the target pre-polymers and DCPNs were successfully synthesized. The DCPNs possessed controllable mechanical properties. Tensile tests showed the polymers had a range of tunable stiffness and flexibility. The COPUA-GMA-EP-2 copolymerized system containing 50 wt% COPUA-GMA had relatively excellent tensile strength of 11.8 MPa and elongation at break of 72.3%. Thermal analysis showed that DCPNs had excellent thermal stability, and COPUA-GMA-EP-2 had higher crosslinking density. Importantly, COPUA-GMA-EP-2 displayed excellent shape memory properties with Rf of 98.9% and Rr of 79.0%. Meanwhile, this DCPN exhibited certain self-healing properties. The DCPNs will be widely applied with good prospects owing to their excellent UV-curable, eco-friendly and shape memory properties.
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•Novel castor oil based functional dynamic covalent-bonded polymer networks (DCPNs) were prepared via a simple UV cured process.•The fabricated DCPNs contained reactive dynamic disulfide bonds.•The obtained DCPNs possessed controllable mechanical properties with a range of tunable stiffness and flexibility.•The designed DCPNs had excellent shape memory properties and certain scratch self-healing properties.•The prepared DCPNs were of potential application value owing to their excellent eco-friendly and shape memory properties.
The exploration of novel bio-based functional polymers has high application value and confirms to sustainable development strategies following the increasing shortage of fossil resources. In this ...research, several different recyclable bio-based dynamic covalent polymer networks (DCPNs) containing dynamic Diels-Alder bonds from vegetable oil and furan were designed and fabricated via a simple preparation process. The reprocessability, shape memory, molecular structures, thermal properties and mechanical properties of the DCPNs were all investigated. 1H nuclear magnetic resonance (1H-NMR) and Fourier transform infrared spectroscopy (FTIR) analysises demonstrated the target reactive products were all successfully synthesized. Variable-temperature FTIR and differential scanning calorimetry revealed the changing rule of dynamic Diels-Alder bond molecular structures with temperature. The DCPNs possess controllable tensile properties including superior ductility and certain rigidity via adjusting fatty chain component, which is in accordance with the result of dynamic mechanical analysis. Thermal gravimetric analysis demonstrated the DCPNs had excellent thermostability, and the main peak decomposition temperatures were all above 460 °C. The nature of the dynamic Diels-Alder bonds could make shattered DCPNs be reprocessed multiple times under relatively mild conditions. The DCPNs displayed certain shape memory properties, and the shape fixation and recovery ratio at the last two cycles were kept above 95.53% and 84.58%, respectively. This work will help with the development on this kind of bio-based polymers containing dynamic Diels-Alder covalent bonds.
•Novel functional dynamic covalent-bonded polymer networks (DCPNs) were designed and fabricated.•The prepared DCPNs contain reversible Diels-Alder adducts of vegetable oils and furfural.•The resulting bio-based DCPNs possess controllable tensile properties, reprocessability, and superior shape memory properties.
Selective and sensitive water content measurement in organic solvents is extremely significant for both industrial use and laboratory preparation. Carbon nanodots are promising carbon nanomaterials ...with unique and novel properties and thus have drawn growing attention. However, the hydrothermal approach for the preparation of carbon dots always uses water as solvent, and consequently, the development of carbon dots from biomass materials for fluorescence detection of water content remains unexplored. Here, carbon dots were prepared from gallic acid via a cheap and facile one-step method. The as-prepared carbon dots present excellent sensitivity and selectivity toward water content and exhibits good linear relationships with water content in range of 0–10%. The carbon dots demonstrated a strong antioxidation capacity and colour-reaction of Fe
3+
like gallic acid. The carbon dots also showed solid-state lighting.
Biobased lipoic acid (LA) can be used as a plasticizer and combine with ethyl cellulose (EC) to form ethyl cellulose supramolecular composite films. The morphology, hydrophilic performance, thermal ...stability and mechanical properties of the composite films were investigated. The introduction of LA can significantly improve the flexibility and processability of ethyl cellulose films because LA can weaken both hydrogen bonding and hydrophobic interaction in EC chains. The elongation at break of EC composite films can be increased by 5.5~11.1 times when the LA content is 20~50%. In addition, comparative experiments and molecular dynamic simulations were performed to explain the superiority of LA as a plasticizer for EC films.
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Biomass eugenol derived polyols with two or three functionalities were synthesized and used for the preparation of self-healing polyurethanes PU-2SH and PU-3SH, respectively. The structure of PU-2SH ...and PU-3SH were characterized by Fourier transition infrared spectroscopy (FTIR). Variable temperature FTIR and swelling test were carried out to analysis the self-healing behavior and determine the self-healing temperature of PU-2SH and PU-3SH. The thermal stability, dynamic mechanical properties, swelling performance and self-healing performance of the prepared PU-2SH and PU-3SH were studied in detail. Compared with PU-2SH, PU-3SH showed higher stability, Tg and storage modulus, and weaker self-healing abilities.
•Thiols were used to obtain eugenol derived polyphenols through thio-ene reactions at room temperature.•Eugenol derived bio-based polyurethanes were prepared.•The polyurethanes are equipped with self-healing ability without introducing additional reversible covalent bonds.
A tung-oil-based polyphenol (ATOM), containing the phenolic hydroxyl group, was synthesized from tung oil and 4-maleimidophenol by the Diels–Alder addition reaction. Then self-healing thermosetting ...polyurethanes were prepared from ATOM and the polyurethane prepolymer. The chemical structure and cross-link network were confirmed by Fourier transform infrared spectroscopy (FTIR) and swelling tests. The products partially dissolved in trichlorobenzene when the temperature rose to 110 °C. Temperature-variable FTIR confirmed that the phenolic urethane starts to partially dissolve at 100 °C, which can be explained by the experimental phenomenon in swelling tests. Tensile property analysis showed that the broken and healed thermosets maintained about 46–64% of their original tensile strengths and 81–88% of their original elongations at break, respectively.
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