Search

In this work, octamercapto polyhedral oligomeric silsesquioxane (POSS-8SH) and octaphenol polyhedral oligomeric silsesquioxane (POSS-8Phenol) were successfully synthetized. POSS-8Phenol was added into the synthesis process of liquid thermoset phenolic resin (PR) to obtain POSS-modified phenolic resin (POSS-PR). Chemical structures of POSS-8SH, POSS-8Phenol, and POSS-PR were confirmed by FTIR and 1H-NMR. TG and DTG analysis under different atmosphere showed that char yield of POSS-PR at 1,000°C increased from 58.6% to 65.2% in N2, which in air increased from 2.3% to 26.9% at 700°C. The maximum pyrolysis temperature in air increased from 543°C to 680°C, which meant better anti-oxidation properties. XRD results confirmed both POSS-8Phenol and POSS-PR-generated crystalline SiO2 in air, which could explain the improvement of anti-oxidation properties. SEM showed that the POSS-PR had phase separation during curing process. Finally, carbon fiber fabric-reinforced POSS-PR (C-POSS-PR) was prepared to verify the anti-oxidation properties of POSS-PR.

In this study, bentonite/epoxy sheet molding compound composites (BS/ESMC) were prepared with different bentonite contents (0.5, 1, 1.5, 2, 2.5, 5, and 10 wt%) by hot compression molding. The effects of BS content on the mechanical properties, thermal stability, and fire-retardant properties of samples were investigated. When the BS addition amount is 1.5%, the tensile strength, flexural strength, and impact strength reach the maximum, increasing by 24.15%, 26.56%, and 51.33%, respectively. The measurement of mechanical properties showed that the fracture toughness of BS/ESMC composite has been greatly improved from 71.41 to 108.07 MPa. As the content of the bentonite increases, the heat resistance of the sample increases, and the residual carbon content of the system increases by 61.54% when the amount of the bentonite added is 10%. In addition, the value of LOI increased from 25.6 to 27.9 with the addition of the bentonite.

In our research described here, a strong acid oxidizing agent was selected to modify the surface of carbon black (CB) to obtain oxidized carbon black (OCB) particles. These OCB particles were then subjected to an ionic bonding reaction with alkaline amine groups present on the surface of octadecylamine polyoxyethylene ether (AC1830) in the form of a paste, resulting in the production of polyether amine-modified oxidized carbon black particles (A-CB). FTIR confirmed the successful production of the A-CB particles. The PVA composite films were prepared using the casting method with varying amounts of A-CB as filler and PVA as the matrix. The films were then analyzed using tensile, scanning electron microscopy, dynamic thermo-mechanical analysis, DSC, and water absorption testing. The results showed that the tensile strength was highest at 3% A-CB, reaching 154.85 MPa. A-CB was well dispersed in PVA at low contents (1% and 3%). The loss modulus, energy storage modulus, crystallinity, and crystallization rate of the A-CB/PVA films improved compared to PVA films. Additionally, the issue of excessive water absorption in A-CB/PVA has been improved. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced epoxy resin composite (CF/EP) is widely used in aerospace applications, automotive industry, construction engineering and many other important sectors, for it has excellent mechanical properties and corrosion resistance. However, the three-dimensional cross-linked structure of the cured epoxy resin determines its insolubility and non-melting characteristics, which makes it challenging to efficiently degrade CF/EP waste and recycle the high-value carbon fibers. In this study we propose a strategy that degrades the CF/EP waste via a facile and efficient solvothermal degradation route. The results showed that the degradation ratio of the resin increased significantly with the rise in reaction temperature. When the reaction temperature reached 180 °C there were no obvious resin residues on the surface of the recycled carbon fibers. It was found that the recycled carbon fibers were not obviously damaged during the solvothermal degradation process, as shown by the scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman analyses. [ABSTRACT FROM AUTHOR]

In recent years, with the advancement of laser equipment and technology, several papers have documented the utilization of laser technology in the domain of plate edge sealing. However, there is currently a lack of research on suitable materials for laser edge sealing. Therefore, in our research described in this paper we mainly explored the use of a functional layer of a kind of edge sealing material used in laser edge sealing technology, namely a laser hot melt adhesive material. In this study we used polypropylene (PP) and ethylene-vinyl acetate (EVA) as matrix materials to prepare laser hot melt adhesive materials which can be activated by a 1065 nm near-infrared laser. Compared with the traditional edge sealing technology, our operation process is simpler, the beauty of the product is better and all its performances meet the relevant standards. The thermogravimetric analysis (TGA) and other thermal analysis methods demonstrated that the laser adhesive can undergo melting upon laser activation, provided an appropriate amount of inorganic laser-sensitive agent is added, without undergoing any thermal decomposition. The influence of the elastomeric EVA resin on the crystallinity of the PP was investigated using X-ray diffraction (XRD) and differential scanning calorimetry (DSC), demonstrating a significant impact on the resulting blend properties. X-ray photoelectron spectroscopy (XPS) shows a partial reduction of Cu2+ to Cu+ within the laser sensitizer after activation of the adhesive by the laser. The optimal mass ratio of PP and EVA in the laser adhesive was investigated through experimental analysis. The morphological changes of the laser adhesive before and after laser activation were observed using scanning electron microscopy (SEM). We believe the research conducted by our team has significantly advanced the progress of laser edge banding technology and expedited its application in the field of furniture manufacturing. [ABSTRACT FROM AUTHOR]

Leaf senescence is an essential physiological process related to grain yield potential and nutritional quality. Green leaf duration (GLD) after anthesis directly reflects the leaf senescence process and exhibits large genotypic differences in common wheat; however, the underlying gene regulatory mechanism is still lacking. Here, we identified TaNAM‐A1 as the causal gene of the major loci qGLD‐6A for GLD during grain filling by map‐based cloning. Transgenic assays and TILLING mutant analyses demonstrated that TaNAM‐A1 played a critical role in regulating leaf senescence, and also affected spike length and grain size. Furthermore, the functional divergences among the three haplotypes of TaNAM‐A1 were systematically evaluated. Wheat varieties with TaNAM‐A1d (containing two mutations in the coding DNA sequence of TaNAM‐A1) exhibited a longer GLD and superior yield‐related traits compared to those with the wild type TaNAM‐A1a. All three haplotypes were functional in activating the expression of genes involved in macromolecule degradation and mineral nutrient remobilization, with TaNAM‐A1a showing the strongest activity and TaNAM‐A1d the weakest. TaNAM‐A1 also modulated the expression of the senescence‐related transcription factors TaNAC‐S‐7A and TaNAC016‐3A. TaNAC016‐3A enhanced the transcriptional activation ability of TaNAM‐A1a by protein–protein interaction, thereby promoting the senescence process. Our study offers new insights into the fine‐tuning of the leaf functional period and grain yield formation for wheat breeding under various geographical climatic conditions. [ABSTRACT FROM AUTHOR]

Epoxy sheet molding compound (ESMC) composites have good mechanical properties, insulation performance, and corrosion resistance, and are widely used in the automotive industry. However, the density of a typical ESMC composite is high, which limits its wider application. Lightweight fillers can reduce the density of ESMC composites, but the addition of lightweight fillers can lead to a decrease in the mechanical properties of the composite. In this paper, we describe our research in which hollow glass microspheres (HGM) were utilized to decrease the density of the ESMC composites. In addition, surface modification of the HGM was performed to enhance the compatibility between the HGM and the epoxy resin (EP), thus improving the mechanical properties. Further, montmorillonite (MMT) was introduced to further improve the mechanical properties of the ESMC composites. The results showed that the density of the prepared composite was about 1.5 g/cm3, which was significantly lower than the industry standard sheet molding compound (SMC) density of 1.9 g/cm3. The flexural strength and impact strength of the resulting ESMC composites containing the modified HGM and an appropriate amount of MMT (EP/SiHGM/MMT-1) reached the maximum value of 80.0 MPa and 28.6 kJ/m2, respectively, which were 39.9 and 51.3% higher than that of the ESMC composite containing only HGM (EP/HGM/MMT-0). On the one hand, the modified HGM was well dispersed in the EP for the chemical bonding effect. On the other hand, the fiber/matrix interface was further improved after introducing an appropriate amount of MMT. Thus, the resulting ESMC composite exhibited low density and excellent mechanical properties and showed great potential for applications that require lightweight and high strength. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of refractory metal on the high temperature properties of phenolic resin matrix composites, modified quartz fiber reinforced ceramizable composites were prepared by a molding process with a refractory component, tungsten, as the functional component and boron carbide as the ceramic forming agent. The effects of the tungsten and the boron carbide on the heat resistance of the composite were investigated. The results showed that the introduced refractory metal tungsten and the boron carbide can react to form tungsten borides and tungsten carbides at high temperature, and form a ceramic layer on the surface of the composite, which can fill the defects caused by pyrolysis of matrix and improve the high temperature performance of the composite. When the content of boron carbide was 10 wt% and the content of tungsten powder was 30 wt%, the flexural strength of the composite before and after heat treatment at 1200 °C were increased by 54.6% and 30.2% respectively compared with that without filler. [ABSTRACT FROM AUTHOR]

Nano-silica modified phenolic resin film is prepared using different mass fractions of nano-silica by liquid composites molding (LCM). The effects of nano-silica on the rheology and curing of phenolic resin are studied by rheometer and differential scanning calorimeter (DSC). The results show that the viscosity of nano-silica modified phenolic resin decreases with the increase of temperature, and the viscosity is lowest between 70°C and 90°C. The appropriate resin film infusion (RFI) process is investigated, and the stepped curing process system is established. In addition, the microstructures of modified phenolic film and composites are tested by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Nano-silica can be uniformly dispersed in phenolic resin when the amount of nano-silica added is ≤ 4%. And the mechanical properties of nano-silica modified phenolic composites are tested by universal material testing machine. The optimum nano-silica mass loading for the improvement of mechanical properties is found. This work provides an effective way to prepare the modified phenolic resin film suitable for resin film infusion (RFI) processes, and it maybe become a backbone of thermal protection material in aerospace.

It is urgent to improve the long-term ablation resistance of silicone rubber composites in order to meet the application requirements in the field of aerospace thermal protection. The graphite/ZrO2/silicone rubber (G/ZrO2/SR) composites prepared in this study were for that purpose. Firstly, the thermal stability and ablation properties of the G/ZrO2/SR composites were studied. The results showed that with the increase of graphite content, the initial decomposition temperature of the composites increased from 456.5 °C to 478.6 °C. The linear and mass ablation rates of the G/ZrO2/SR composite with 3 phr graphite were 0.048 mm/s and 0.0,220 g/s, respectively, which were decreased by 14.3% and 9.1%, compared with the ZrO2/SR composite without graphite. Moreover, the phase composition transformation and ceramization mechanism at high temperature of the G/ZrO2/SR composites containing carbon multicomponent system were studied. The results showed that the SR matrix completed the ceramic transformation during the ablation process and -Si-O-C pyrolysis products were formed and served as the skeleton of the ceramic layers. Finally, SiO2 and ZrO2 reacted with the graphite individually and the in-situ SiC and ZrC ceramic products formed enhanced the ceramic layers. [ABSTRACT FROM AUTHOR]

Ceramizable composites have attracted great interest for the thermal protection of hypersonic vehicles. In our research described here the pyrolysis process of almandine/boron phenolic resin ceramizable composites was investigated; we note it can be divided into three stages (room temperature to 300 °C, 300 °C to 700 °C and 700 °C to 1300 °C). In addition, the pyrolysis products were identified by an analytical pyrolyzer coupled with a gas chromatography/mass spectrometry set-up (Py-GC/MS), and they were composed of phenols (69.82%), aromatic hydrocarbons (23.89%), and aromatic ethers and aliphatic esters (6.29%). Furthermore, the possible pyrolysis routes were proposed. Moreover, the pyrolysis kinetic parameters were calculated, and the activation energy, order of the reaction and pre-exponential factor were 54.18 KJ/mol, 0.869 and 2.828 s−1, respectively. In addition, Comsol Multiphysics finite element software was used to simulate the heat transfer and pyrolysis behavior. After the composite (with a thickness of 10 mm) was heated for 200 s at a heat flux of 480 KW/m2, the surface and back surface temperatures were 1200.6 °C and 163.7 °C, respectively. The thicknesses of the carbonized, pyrolysis and original layers were 2.11, 3.67 and 4.22 mm, respectively, which reflects the good thermal insulation behavior of the composite. We suggest the combination of calculation and simulation results can provide a theoretical basis for the design of thermal protection systems for hypersonic vehicles which are able to meet long-term and large-area thermal protection requirements. [ABSTRACT FROM AUTHOR]

As one of the most ideal alternative fuels for internal combustion engines, methanol can achieve near-zero carbon emissions. The main problem of methanol application in compression combustion engines is the phase lag caused by its poor combustion characteristics, but under low load conditions, the fuel activity can be improved by adding the cetane number improver EHN (Isooctyl nitrate), and the dependence on intake heating can be reduced to a certain extent. Based on a three-dimensional CFD simulation, the effects of methanol injection parameters and the addition of EHN on the combustion characteristics of a four-stroke exhaust turbocharged diesel engine were studied in this paper. With or without EHN, the increase in injection pressure and the advance in injection timing lead to an increase in the peak temperature, pressure, and heat release rate, as well as a shortening of the combustion duration. Adding EHN witnesses reduced requirements for methanol ignition, including a decreased peak temperature, pressure, and heat release rate, a significantly shortened ignition delay period, and an extended combustion duration, which thus results in a reduced indicated thermal efficiency. This study innovatively develops a 3D model of a compression combustion engine applicable to in-cylinder direct injection pure methanol fuel and EHN under small load conditions, which provides a reference for future research and development of small-load pure methanol compression combustion engines and has certain guiding significance. [ABSTRACT FROM AUTHOR]