Recent advances in the study of structure and properties of fiber composites with an epoxy matrix

Comparison of Effects of Plasma Surface Modifications of Bamboo and Hemp Fibers on Mechanical Properties of Fiber-Reinforced Epoxy Composites

In this study, we investigated the behaviors of epoxy composites reinforced with bamboo (BF) and hemp (HF) fibers. Both fibers were treated using dielectric barrier discharge (DBD) plasma for various durations (2.5 to 20 min). Epoxy resin (ER) was mixed with BF or HF with and without plasma treatment. The Fourier-transform infrared spectra of the plasma-treated fibers showed an enhanced peak intensity of carboxyl groups. ER/BF treated for 20 min exhibited a high tensile strength (up to 56.5 MPa), while ER/HF treated for 20 min exhibited a more significant increase in elongation at break (6.4%). Flexural tests indicated that the plasma treatment significantly improved the flexural strength of the hemp composites (up to 62.2 MPa) compared to the bamboo composites. The plasma treatment increased the fiber surface roughness and interfacial bonding in both composites. The thermal stability and wettability were improved by the DBD plasma treatment. The DBD plasma treatment enhanced the interfacial adhesion between fibers and ER matrix, which improved the mechanical, thermal, and wettability properties of the composites.

Tailoring TiO2-lignin hybrid materials as a bio-filler for the synthesis of composites based on epoxy resin

In this publication, the functional TiO₂-lignin hybrid materials were designed and characterized. Based on elemental analysis and Fourier transform infrared spectroscopy, the efficiency of the mechanical method used to obtain systems was confirmed. Hybrid materials were also characterized by good electrokinetic stability, in particular in the inert and alkaline environments. The addition of TiO₂ improves thermal stability in the entire analyzed range of temperatures. Similarly, as the content of inorganic component increases, the homogeneity of the system and the occurrence of smaller nanometric particles increase. In addition, a novel synthesis method of cross-linked polymer composites based on a commercial epoxy resin and an amine cross-linker was described as a part of the article, where additionally newly designed hybrids were also used. Subsequently, the obtained composites were subjected to simulated tests of accelerated UV-aging, and then their properties were studied, including changes in wettability (using water, ethylene glycol, and diiodomethane as measurement liquids) and surface free energy by the Owens-Wendt-Eabel-Kealble method. Changes in the chemical structure of the composites were monitored by FTIR spectroscopy due to aging. Microscopic studies of surfaces were also carried out as well as measurements in the field of changes in color parameters in the CIE-Lab system.

Mechanical Performances of Phenolic Modified Epoxy Resins at Room and High Temperatures

Epoxy is an important resin matrix and has been widely applied in laminated composites as a coating or adhesive material. In this article, the phenolic was applied to modify the mechanical properties of epoxy resin. The phenolic modified epoxy resins with various phenolic content were prepared via a polytetrafluoroethylene mould, and the phenolic modified epoxy-based plain woven laminated composites (PWLCs) were manufactured via vacuum assisted resin transfer method for further study of phenolic modified epoxy resins’ mechanical properties. The compression tests were performed perpendicularly to thickness at 2 mm/min to investigate the mechanical performances of phenolic modified epoxy resins and epoxy-based PWLCs. The results showed that the addition of phenolic into epoxy could improve the mechanical performances of epoxy resins and epoxy-based composites at room temperature, and the phenolic influenced epoxy-based PWLC more than epoxy matrix at room temperature. However, at high temperatures, the addition of phenolic decreased the mechanical performances of epoxy resins and epoxy-based composites, and the adverse effect of phenolic became more serious with the increase of phenolic content at high temperature. In addition, the thermogravimetric analyses were also conducted from 30 °C to 800 °C on phenolic modified epoxy resins and the results showed that the phenolic modified epoxy resin had an earlier loss in weight than unmodified epoxy resin. The earlier loss in weight meant that the addition of phenolic into epoxy resin led to the formation of unstable molecules at high temperature.

Controllable fabrication of a hybrid containing dodecyl dihydrogen phosphate modified magnesium borate whisker/hydrated alumina for enhancing the fire safety and mechanical properties of epoxy resin

A composite particle with hydrated alumina deposited on the surface of magnesium borate whisker (MBW@HA) was prepared following a chemical liquid deposition method. Subsequently, dodecyl dihydrogen phosphate (DDP) was grafted onto the surface of the composite particles to synthesize an inorganic-organic hybrid (MBW@HA-DDP). The structure, morphology, and composition of MBW@HA-DDP were well characterized. The results revealed the hybrid of MBW@HA-DDP was successfully synthesized characterized by a hydrophobic surface. Subsequently, the obtained MBW@HA-DDP was incorporated into epoxy resin (EP) to fabricate flame retardant composites. The results revealed that the incorporation of MBW@HA-DDP significantly improved the fire safety of EP, for instance, the total heat release (THR) and peak heat release rate (PHRR) of the EP composite with 10-phr MBW@HA-DDP added were reduced by 28.1% and 32.0%, respectively, accompanied with lower total smoke production (TSP) and smoke production rate (SPR). The improved fire safety was due to the barrier function of MBW and HA, and the dilution effect of water vapor generated from HA. Meanwhile, the phosphorus oxoacids generated from DDP could function as catalysts and increase the degree of graphitization of the char residues, thus protecting the matrix effectively. In relation to mechanical properties, the incorporation of MBW@HA-DDP did not deteriorate the mechanical properties of EP but improved them to some extent. The results presented herein help develop a novel strategy for developing flame retardants characterized by good flame-retardant behavior and improved mechanical properties.