Synthesis and characterization of novel phenolic resins containing aryl-boron backbone and their utilization in polymeric composites with improved thermal and mechanical properties

Polyurethane Acrylate Oligomer (PUA) Microspheres Prepared Using the Pickering Method for Reinforcing the Mechanical and Thermal Properties of 3D Printing Resin

Some photosensitive resins have poor mechanical properties after 3D printing. To overcome these limitations, a polyurethane acrylate oligomer (PUA) microsphere was prepared using the Pickering emulsion template method and ultraviolet (UV) curing technology in this paper. The prepared PUA microspheres were added to PUA-1,6-hexanediol diacrylate (HDDA) photosensitive resin system for digital light processing (DLP) 3D printing technology. The preparation process of PUA microspheres was discussed based on micromorphology, and it was found that the oil-water ratio of the Pickering emulsion and the emulsification speed had a certain effect on the microsphere size. As the oil-water ratio and the emulsification speed increased, the microsphere particle size decreased to a certain extent. Adding a suitable proportion of PUA microspheres to the photosensitive resin can improve the mechanical properties and thermal stability. When the modified photosensitive resin microsphere content was 0.5%, the tensile strength, elongation at break, bending strength, and initial thermal decomposition temperature were increased by 79.14%, 47.26%, 26.69%, and 10.65%, respectively, compared with the unmodified photosensitive resin. This study provides a new way to improve the mechanical properties of photosensitive resin 3D printing. The resin materials studied in this work have potential application value in the fields of ceramic 3D printing and dental temporary replacement materials.

Research Progress in Boron-Modified Phenolic Resin and Its Composites

As one of the most successful modified phenolic resins, boron-modified phenolic resin (BPF) has excellent heat resistance and ablative resistance, good mechanical and wear resistance, and flame retardancy. BPF and its composites can be widely used in areas such as aerospace, weapons and equipment, automobile brakes, and fire retardants. In this review, the current state of development of BPF and its composites is presented and discussed. After introducing various methods to synthesize BPF, functionalization of BPF is briefly summarized. Particular emphasis is placed on general methods used to fabricate BPF-based composites and the heat resistance, ablative resistance, mechanical property, wear resistance, flame retardancy, and water resistance of BPF-based composites. Finally, the challenges of this research area are summarized and its future outlook is prospected.

Strong Effect of Process Parameters on the Properties of Boron-Containing Phenolic Resins with High Char Yield

This work is focused on the optimization of critical process parameters for preparation of boron-containing phenolic resin (B-containing PR), including the molar ratios of formaldehyde/phenol and potassium borate/phenol, reaction time; and measurement of surface tension of B-containing PR solution and wettability between B-containing PR solution and carbon fibers. The effects of the formaldehyde/phenol and potassium borate/phenol molar ratios on the char yield of the B-containing PR was studied. The highest char yield of B-containing PR could be as high as 71% under optimal conditions (molar ratios of formaldehyde/phenol = 1.8 and potassium borate/phenol = 0.2, and reaction time = 13 h). The effect of concentration and tested temperature on the surface tension of B-containing PR solution was investigated, and the wettability between B-containing PR solution and carbon fibers was evaluated for the first time, providing useful theory and experimental data for the preparation of B-containing PR-based composites.

Fabrication of high B-doped ordered mesoporous carbon with 4-hydroxyphenylborate phenolic resin for supercapacitor electrode materials

The high B-doped ordered mesoporous carbon (HPB-OMC) was prepared by using 4-hydroxyphenylboronic acid-modified phenolic resin (HPBPF) as a boron and carbon precursor via the evaporation-induced self-assembly (EISA) approach. The chemical composite, mesoporous structure, and electrochemical properties of the as-prepared HPB-OMC are investigated. The results show that both highly boron-doped and well-ordered mesoporous structure are achieved for HPB-OMCs, owing to the improvement of solubility of the resins in ethanol, and the enhancement of thermal stability of pore channels during carbonization. Moreover, the HPB-OMCs exhibit an ideal electric double-layer capacitor performance. With the increase of the B-doped content, the specific capacitance of the HPB-OMC electrode rises gradually, then drops off a little. The HPB-OMC with a high B content (3.96 wt%) shows a much high specific capacitance of 183 F g⁻¹ at a current density of 1 A g⁻¹, suggesting its promising application in the field of supercapacitors.

The HPB-OMCs, with 3.96 wt% boron-doped and well-ordered structure, show a much high specific capacitance of 183 F g⁻¹ at the current density of 1 A g⁻¹ and ideal electrochemical performances.

Boric Acid as a Coupling Agent for Preparation of Phenolic Resin Containing Boron and Silicon with Enhanced Char Yield

In this study, an innovative, facile, and low-cost method is developed to prepare phenolic resin (PR) containing boron and silicon (BSiPR). BSiPR is synthesized by a solvent-free, one-pot method using boric acid as the coupling agent instead of silane, and methyltriethoxysilane as the silicon source. The results show that boron and silicon elements are introduced into PR via BOC and BOSi structures. The char yield of the resulting resin at 800 °C is improved to 76%. The reasons for higher char yield are investigated. The formation of BOC can reduce the content of phenolic hydroxyl, which helps to decrease the weight loss. B₂ O₃ is also formed at 400 °C, and it can prevent the release of carbon oxides. Moreover, thermally stable BOSi and SiO structures remain stable during the pyrolysis. In addition, the mechanical and ablative properties of fiber-reinforced composites are also enhanced.

Switching Brake Materials To Extremely Wear-Resistant Self-Lubrication Materials via Tuning Interface Nanostructures

Tribological performance of motion components is one of the key aspects that must be considered in a wide range of applications such as vehicles, aircrafts, and manufacturing equipment. This work demonstrates that further addition of only low-loading hard nanoparticles into a formulated nonasbestos organic brake material directly switches its functionality to a self-lubrication material. More importantly, the newly developed nanocomposites exhibit an extremely low wear rate. Comprehensive investigations on the friction interface reveal that the great friction and wear reduction are due to the formation of a nanostructured lubricious tribofilm. Tribofilm formation is continuously fed by complex molecular species released from the bulk nanocomposites, for which nanoparticles digested within the tribofilm greatly enhance its robustness and lubricity. This work gains insight into the crucial role of the interface nanostructure and paves a route for developing extremely wear-resistant self-lubrication composites for numerous applications.

The Effect of Introducing B and N on Pyrolysis Process of High Ortho Novolac Resin

In this contribution, high ortho novolac resins modified with phenylboronic acid were synthesized. The thermal stability of novolac resins cured with hexamethylenetetramine (HMTA) and chemical states of B and N via a pyrolysis process were studied. For the cured o-novolac modified with phenylboronic acid, the temperature with maximum decomposition rate increased by 43.5 °C, and the char yield increased by 5.3% at 800 °C compared with cured o-novolac. Density functional theory (DFT) calculations show the existence of hydrogen bonding between N of HMTA and H of phenol in modified resin. Thus, N could still be found at high temperature and C=N structure could be formed via a pyrolysis process. B₂O₃ was obtained at 400 °C by the cleavage of B–O–C and B–C bonds and it reduces the oxygen loss which may take part in the formation of carbon oxides in the system. The melting B₂O₃ on the surface of the resin will prevent small molecules and carbon oxides from releasing. Moreover, introducing B into the system helps to decrease the interlayer distance and improve graphite structures via a pyrolysis process.

Effects of tetrahedral molybdenum oxide species and MoOx domains on the selective oxidation of dimethyl ether under mild conditions

A new preparation method for MoO₃–SnO₂ catalysts precipitated by HNO₃ was developed to selectively synthesize industrially useful chemicals formaldehyde and methyl formate via oxidation of dimethyl ether.

Synthesis and properties of graphene oxide–boron-modified phenolic resin composites

Boron–modified phenolic resin (BPR) has a good thermal property, but it has deficiencies in mechanical performance. To obtain PR materials with good thermal property, graphene oxide (GO) was added along with BPR to form a GO–boron-modified PR (GO-BPR). In this study, BPR and GO-BPR were prepared and their thermal resistance and mechanical properties were investigated. In addition, the effects of GO content on the thermal resistance of GO-BPR were studied. Results demonstrate that the optimal GO content was 0.5%. The thermal properties of GO-BPR with 0.5% GO improved 1.06 times when compared with that of BPR, and the peak degradation temperature of GO-BPR increased by approximately 10°C. When compared with BPR composite, the bending, tensile, and impact strengths of the GO-BPR composite materials with 0.5% GO-BPR increased by 46, 38, and 53%, respectively.