Silicon Hybridization for the Preparation of Room-Temperature Curing and High-Temperature-Resistant Epoxy Resin.

Specialized epoxy resin, capable of achieving room-temperature profound curing and sustaining prolonged exposure to high-temperature environments, stands as a pivotal material in modern high-end manufacturing sectors including aerospace, marine equipment fabrication, machinery production, and the electronics industry. Herein, a silicon-hybridized epoxy resin, amenable to room-temperature curing and designed for high-temperature applications, was synthesized using a sol-gel methodology with silicate esters and silane coupling agents serving as silicon sources. Resin characterization indicates a uniform distribution of silicon elements in the obtained silicon hybrid epoxy resin. In comparison to the non-hybridized epoxy resin, notable improvements are observed in room-temperature curing performance, heat resistance, and mechanical strength.

A pH-responsive, injectable and self-healing chitosan-coumarin hydrogel based on Schiff base and hydrogen bonds.

Smart hydrogels have shown great potential applications in disease treatment due to their controlled and local drug-release ability. Herein, a smart hydrogel with pH-responsive, injectable, and self-healing properties for controlled release of taxifolin (TFL) was prepared by freezing-thawing and photo-crosslinking methods. The crosslinking network of hydrogels (CS-CA hydrogels) was constructed by the hydrogen bonds, Schiff base bonds, and cyclobutane rings using chitosan (CS) and coumarin (CA) as raw materials. The CS-CA hydrogel demonstrated a compressive strength of 1.04 MPa, a self-healing efficiency of 99.9 %, and could maintain structural and functional integrity after injection. In addition, the drug release rate and shape of the CS-CA hydrogels were tunable due to its pH sensitivity. The TFL cumulative release reached 60 % within 12 h at pH = 4, and after equilibration, the cumulative release of TFL at pH = 4 (80 %) was significantly higher than at pH = 9.2 (50 %). The CCK8 experiment showed that the resulting hydrogel had no cytotoxicity. Meanwhile, subcutaneous implantation experiments in mice showed that the CS-CA hydrogels had favorable biodegradability and compatibility.

Two-Way Reversible Shape Memory Behavior of Chitosan/Glycerol Film Triggered by Water.

Reversible shape memory polymers (SRMPs) have been identified as having great potential for biomedical applications due to their ability to switch between different shapes responding to stimuli. In this paper, a chitosan/glycerol (CS/GL) film with a reversible shape memory behavior was prepared, and the reversible shape memory effect (SME) and its mechanism were systematically investigated. The film with 40% glycerin/chitosan mass ratio demonstrated the best performance, with 95.7% shape recovery ratio to temporary shape one and 89.4% shape recovery ratio to temporary shape two. Moreover, it shows the capability to undergo four consecutive shape memory cycles. In addition, a new curvature measurement method was used to accurately calculate the shape recovery ratio. The suction and discharge of free water change the binding form of the hydrogen bonds inside the material, which makes a great reversible shape memory impact on the composite film. The incorporation of glycerol can enhance the precision and repeatability of the reversible shape memory effect and shortens the time used during this process. This paper gives a hypothetical premise to the preparation of two-way reversible shape memory polymers.

Biobased Epoxy Composites Reinforced with Acetylated Corn Straw.

Corn straw/epoxy resin composites (CS/ECs) and maleic anhydride acetylated CS/ECs (MA-CS/ECs) were prepared through dry mixing and high-temperature curing. Corn straw is a kind of abundant, eco-friendly, and low-cost biomass material. Unmodified and modified corn straws were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The interfacial affinity of the composite was testified by the contact angle. The results of XPS and SEM demonstrated that maleic anhydride had been successfully bonded onto the structure of corn straw. Corn straw particle-reinforced epoxy resin composites were prepared using a casting and molding process. Results showed that the MA-CS/EC had better impact and flexural resistance than the unmodified corn straw/epoxy resin composites when the corn straw addition was 15 wt %. The result of the contact angle showed that the interfacial compatibility between composites is also stronger than that of CS/EC.

Self-extracted corn-stalk cellulose/epoxy resin composites.

In order to make full use of crop waste stalk, corn-stalk cellulose (CSC) was extracted by acid-base method and used as modifier of epoxy resin (E51) to prepare the self-extracted corn-stalk cellulose/epoxy resin composites (CSCEC). Differential scanning calorimeter (DSC), thermogravimetry (TG) analysis, dynamic mechanical analysis (DMA), morphology analysis by scanning electron microscope (SEM), the mechanical properties by electronic universal testing machine and impact testing machine were used for characterization and analysis. The experimental results showed that when the CSC content was 20 wt%, the impact strength of the composite was 2.50 kJ/m2, which was 127.2% higher than that of pure epoxy resin. When the CSC content was 20 wt%, the Tg of epoxy resin obtained by DMA was the lowest, 167.4 °C, which decreased by 11.3 °C compared with that of pure epoxy resin. The SEM result showed that the fracture surface of the composite became obviously rough and had of obvious folds, which was a ductile fracture. These results indicated that the addition of CSC could toughen the epoxy resin.

Preparation and Curing Mechanism of Modified Corn Straw by 3-Glycidyl Ether Oxypropyl Trimethoxysilane/Epoxy Resin Composites.

A modified corn straw (CS)/epoxy resin (EP) composite was prepared using bisphenol A EP (i.e., E-51) as matrix, 2-methylimidazole as curing agent, and CS modified by 3-glycidyl ether oxypropyl trimethoxysilane (KHCS) as filler. Its chemical structure was characterized by Fourier transform infrared spectroscopy (FTIR). The dynamic thermodynamic properties, mechanical properties, flame retardant property, and fracture morphology were studied using dynamic mechanical analysis (DMA), a universal testing machine, a micro combustion calorimeter, and a scanning electron microscope (SEM), respectively. The effects of different contents of KHCS on various properties were discussed. The experimental result showed that the CS was bonded toKH560 by a covalent bond. The impact strength, tensile strength, and flexural strength of the composites were all improved compared with those of pure EP. When the content of KHCS was 15 wt%, the maximum impact strength of the composites was 3.31 kJ/m2, which was 1.43 times that of the pure EP. The p HRR and THR of MCSEC-20 were 512.44 W/g and 25.03 kJ/g, respectively, which were 40.71% and 27.76% lower than those of pure EP, when the content of KHCS was 20 wt%. Moreover, the mechanism of the curing composites was investigated.