As a promising alternative to traditional prepreg, carbon fiber/poly(ether ether ketone) (CF/PEEK) hybrid composites have attracted wide public interest for their flexibility and conformability. However, modification methods focused on the hybrid premix have not been previously studied. In the present work, the interfacial strength of the hybrid composite was improved by treating the carbon and PEEK fibers together in a radiofrequency (RF) plasma containing one of the following gases to achieve surface activation: air, Ar, or Ar–air. After plasma treatment, the increased roughness of CF and the grafted chemical groups of CFs and PEEK fibers were propitious to the mechanical interlocking and interfacial strength. Significant interfacial shear strength (IFSS) enhancement was achieved after Ar 1 min, air 1 min plasma treatment. This study offers an alternative method for improving the interfacial properties of CF/PEEK composites by focusing on the boundary layer and modifying and controlling the fiber–matrix interface.

The design and development of thermal insulation materials is very important for the treatment of offshore oil pipelines. Understanding thermal energy transport in thermal insulation materials and predicting their thermal conductivities have important theoretical and practical value for the design of thermal insulation materials. In this work, lightweight and thermally insulated (LWTI) composites with the desired mechanical strength for offshore oil pipelines applications were prepared using epoxy resin (EP) as the matrix and hollow glass microspheres (HGMs) as the filler. The morphology, density, and mechanical properties of HGM/EP LWTI composites were studied first. The flexural strength and the flexural modulus of HGM/EP LWTI composites could still be as high as 22.34 ± 2.75 Mpa and 1.34 ± 0.03 GPa, respectively, while the density was only 0.591 g/cm³. The relationship between the effective thermal conductivity of HGM/EP LWTI composites and material parameters (sizes and contents together) has been studied systematically. A three-phase prediction model was built using the self-consistent approximation method to predict the effective thermal conductivity of HGM/EP LWTI composites, and the resin matrix, the wall thickness, the HGM particle size, and other parameters (such as air) were fully considered during the derivation of this three-phase thermal conductivity model. Finally, the insulation mechanism of HGM/EP LWTI composites was systematically analyzed. The thermal conductivities of HGM/EP LWTI composites with different diameters and HGM contents calculated by the three-phase prediction model agreed well with the experimental test results, with a minimum error of only 0.69%. Thus, this three-phase thermal conductivity model can be used to theoretically simulate the thermal conductivity of epoxy resin-based LWTI composites and can be the theoretical basis for the design and prediction of the thermal conductivity of other similar hollow spheres filled materials.

In this study, the curing kinetics of the phenolic amine/epoxy resin system were investigated by nonisothermal differential scanning calorimetry (DSC). The model-free isoconversional method of Ozawa–Flynn–Wall reveals a dependence of E_α (activation energy) on conversion (α), which interprets the autocatalytic curing reaction mechanism of the phenolic amine/epoxy resin system. Studies on the effects of nano-SiO₂ particles on the tensile properties and tensile fracture face morphology of nanocomposites show that the uniform dispersion of SiO₂ nanoparticles plays an important role in promoting the tensile performance of nanocomposites. Additionally, increases of 184.1% and 217.2% were achieved by adding 1.5% weight parts of nano-SiO₂ in composites for the tensile strength and tensile modulus, respectively.