The present study attempts to investigate the influence of multiwalled carbon nanotubes (MWCNTs) and graphite nanoplatelets (GNPs) on thermal conductivity (TC) of nanoreinforced polymers and nanomodified carbon fiber epoxy composites (CFRPs). Loading levels from 1 to 3% wt. of MWCNTs and from 1 to 15% wt. of GNPs were used. The results indicate that TC of nanofilled epoxy composites increased with the increase of GNP content. Quantitatively, 176% and 48% increase of TC were achieved in nanoreinforced polymers and nanomodified CFRPs, respectively, with the addition of 15% wt. GNPs into the epoxy matrix. Finally, micromechanical models were applied in order to predict analytically the TC of polymers and CFRPs. Lewis-Nielsen model with optimized parameters provides results very close to the experimental ones in the case of polymers. As far as the composites are concerned, the Hashin and Clayton models proved to be sufficiently accurate for the prediction at lower filler contents.

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The preparation procedure of epoxy and benzoxazine multi-walled carbon nanotube buckypaper composites is described. The morphology of the buckypaper is characterized by scanning electron microscopy and porosimetry, revealing a non-uniform porous structure. The wetting behavior of epoxy and benzoxazine resins in the buckypaper surface is studied by contact angle measurements. Scanning electron microscopy photographs of the composites obtained by infiltration of the buckypaper with epoxy and benzoxazine resins and subsequent curing reveal that a good impregnation is achieved. Thermal conductivity results reveal higher values for pristine buckypaper than for the composites, which is explained by the extremely small thermal conductance of the nanotube–polymer interface. The thicker resin layer surrounding the nanotubes observed in the buckypaper/epoxy composite justifies its lower conductivity, as compared with the buckypaper/benzoxazine composite.

In this work, the aging of two different carbon fiber reinforced cyanate ester polymer matrices (CFRP-A and CFRP-B) was investigated after their exposure to aggressive thermo-oxidative conditions. The materials' degradation at 230 C under 1 atm for 30 days in oxidative atmosphere was evaluated with regard to changes in mass (mass loss), glass transition temperature T g , interlaminar shear strength, as well as physical characteristics that were examined under scanning electron microscopy. For both the systems, the aging study showed significant mass loss that reached $4% in the case of CFRP-B. The mass loss is accompanied with a considerable decrease in interlaminar shear strength and T g properties. The study of the scanning electron microscopic images clearly shows the surface deterioration due to the oxidation process, accompanied with formation of matrix microcracking and development of matrix-fiber interfacial debonding. The contribution of the chains scission to the materials degradation was also detected by performing in situ aging through isothermal thermo-gravimetric analysis measurements at 230 C under oxidative and inert atmosphere. However, the thermo-gravimetric analysis results showed minor chain scission proving thus, that the oxidation was the main degradation mechanism for both materials.

A study dealing with the effect of the carbon nanotubes (CNTs), at various weight fractions, on the effective thermal conductivity of a CNT‐reinforced polymer by associating it with the Kapitza resistance (RKap) phenomena is presented. The finite element method was utilized as a tool for the models' solution by using the principles of the representative volume element. An intermediate continuum layer between polymer matrix and CNTs was considered for the representation of the RKap phenomena. The influence of the intensity of RKap phenomena at various CNT contents was investigated through the parametric study of the RKap value and the thickness of the intermediate layer. The predicted results were compared against experimental measurements derived from an equivalent CNT–epoxy resin system. The discrepancy between calculated and measured values is diminished when the RKap phenomena are taken into account, thus confirming the existence of thermal resistance between the CNTs and the polymer matrix. The RKap rise as the % CNT weight content is increased. This behavior is correlated to the higher CNT agglomeration at higher CNT contents, which is proven by the scanning electron microscopy and thus providing a first indication of the effect of the CNT agglomeration on the effective thermal conductivity at various CNT contents. POLYM. COMPOS., 35:1997–2009, 2014. © 2014 Society of Plastics Engineers