Durability and integrity studies of environmentally conditioned interfaces in fibrous polymeric composites: Critical concepts and comments

Fibre reinforced polymer (FRP) composites are the most promising and elegant material of the present century. Their durability and integrity in various service environments can be altered by the response of its constituent i.e. fibre, polymer matrix, and the existing interface/interphase between the fibre and polymer matrix, in that particular environment. The interphase is generally manifested by chemical bonding, molecular segregation and also by van der Waals bonding. The sizing of fibres generally influences the chemistry and character of the interface/interphase and might generate structural gradient in the polymer matrix. Their susceptibilities to degradation are dependent of the nature of environments and each of the constituents' responds differently and uniquely. Amongst the three constituents, the interface/interphase has a very critical role to play on the performance and reliability of FRP composites. The reduced glass transition temperature of the interphase may induce low modulus area, which subsequently affects fracture toughness and local stresses of the composite. These result in high fracture toughness at ambient temperatures, but significantly reduced performance at high temperatures.     

Effects of plasma treatment of carbon fibers on interfacial properties of BMI resin composites

High performance continuous fiber surface modification by inductively coupled RF plasma (ICP) and dielectric barrier discharge (DBD) low temperature plasma were conducted. X-ray photoelectron spectroscopy (XPS) and other analytical testing methods systematically studied plasma treatment time, discharge power, discharge pressure, etc, on fiber surface state, surface composition, and surface shape changes in the appearance and wetting properties. The results show that after plasma treatment the surface of the fiber is grafted with a large number of polar functional groups such as carboxyl groups and hydroxyl groups. The surface roughness increases, the surface free energy increases, and the fiber wetting property is significantly improved, resulting in improvement in interlaminar shear strength (ILSS) between the fiber and the resin matrix. Finally, the surfaces of the fibers and its relationship with interfacial properties of fiber reinforced bismaleimide composites are also discussed.     

Strong interfacial modified aramid fabric reinforced degradable thermosetting composites: reinforcing and tribological effects

In this work, dense molybdenum disulfide (MoS₂) nanosheets were grown onto polydopamine (PDA) functionalized aramid fabric (AF) surface via a simple hydrothermal method to improve the wettability between AF surface and polyhexahydrotriazine (PHT) resin, thus resulting in stronger AF/resin interfacial bonding. The PDA-assisted surface modification on AF generated a high active interface allowing the nucleation and subsequent growth of MoS₂. Moreover, this nanosheet-coated reinforcement fiber enabled the viscous liquid of resin precursor to spread over and form intimate contact with its surface, which eventually promoted the formation of strong interfacial bonding between AF-MoS₂ and cured resin matrix. In addition, the enhanced interfacial bonding between the reinforcement and matrix generated stable mechanical interlock within the resulting AF-MoS₂/PHT composites, and thus, contributed better thermal stability, higher tensile strength, and tribological properties. Compared with AF/PHT composites, the tensile strength and elongation at break of the AF-MoS₂/PHT composites increased by 32.5% and 50%, and the average friction coefficient and wear rate of AF-MoS₂/PHT composites decreased by 43.9% and 86.3%, respectively. Furthermore, the composites realized the non-destructive recovery of expensive AF at 25 °C. Overall, our study demonstrates a dependable strategy to construct the recyclable AF-MoS₂/PHT composites, which exhibit valuable applications in tribology.     

Influence of an oxidation of the carbon fiber surface by boiling nitric acid on the adhesion strength in carbon fiber‐acrylate composites cured by electron beam

A time‐dependent oxidation of carbon fibers in boiling nitric acid was used to investigate the influence of a modification of the fiber surface properties on the adhesion strength with an acrylate resin cured by electron beam (EB). For each time of treatment, a characterization of the surface topography and the surface chemistry was done (topography at a micrometric and nanometric scale, specific surface area, temperature programmed desorption, X‐ray photoelectron spectroscopy analysis). The oxidation of the fiber surface in boiling nitric acid created a rough surface, which significantly increased the specific surface area, and also generated a high density of hydroxyl groups, carboxylic acids and lactones in comparison to untreated fibers. The adhesion strength with the acrylate resin cured by EB was measured by a pull‐out test. For comparison, an isothermal ultraviolet curing of the matrix was also investigated. The value of the interfacial shear strength, determined by the Greszczuk's model, was increased by the oxidation of the carbon fiber surface for both curing processes, but lower values were systemically obtained with EB curing. Copyright © 2012 John Wiley & Sons, Ltd.     

The thermal stability of highly filled high-density polyethylene quaternary composites: Interactive effects and improved measures

A range of formulations — consisting of high-density polyethylene, surface-coated calcium carbonate, masterbatched carbon black and a stabiliser package — were compared in terms of their thermal stability through the use of several techniques and measures. Notably, calcium carbonate loadings of up to 60 wt% were investigated. The formulations were designed to be I- and D-optimal, based on a quadratic Scheffé polynomial model. Novel and established measures for the thermal stability of the materials were compared, based on data generated using techniques for the determination of oxidative induction time and for studies by time-sweep oscillatory rheometry. For ease of comparison, all tests were performed in air. Fourier-transform infrared spectroscopy was performed on the materials subjected to time-sweep oscillatory rheometry, to ascertain the locality and modes of degradation. Variable effects were found, depending on the technique used. Broadly, strong primary effects were found: positive in the cases of the carbon black and stabiliser pack, negative in the case of calcium carbonate. The latter, however, was offset by the highly synergistic interaction of calcium carbonate with the stabiliser pack. Time-sweep oscillatory rheometry was shown to be a promising method, with it yielding high-quality, comparable results when interpreted using a novel measure.     

The effects of wood-flour on combustion and thermal degradation behaviors of PVC in wood-flour/poly(vinyl chloride) composites

The effects of wood-flour on combustion and thermal degradation behaviors of PVC in wood-flour/poly (vinyl chloride) composites (WF-PVC) were investigated by using cone calorimeter (CONE) and TGA. The results show that thermal degradation behavior of WF-PVC composites has obvious characteristics of that of PVC. Interactions occur between wood-flour and PVC during the combustion and thermal degradation of WF-PVC composites. The thermal degradation of wood-flour can be accelerated by pure PVC. Moreover, the char formation can be raised by adding wood-flour to PVC. Compared with PVC at all flaming stage, when heat flux is kept at 50 kW m⁻², the average heat release rate (av-HRR), the total heat release (THR), the total smoke production (TSP) and the average specific extinction area (av-SEA) of WF-PVC composites are respectively reduced by 44%, 9.2%, 25.8% and 29.9%. In WF-PVC composites, the wood-flour has remarkable effects on the properties of heat release and smoke release of PVC.