No abstract

The poor thermal conductivity of polymer composites has long been a deterrent to their increased use in high-end aerospace or defence applications. This study describes a new approach for the incorporation of graphene in an epoxy resin, through the addition of graphene as free-standing film in the polymeric matrix. The electrical and thermal conductivity of composites embedding two different freestanding graphene films was compared to composites with embedded carbon nanotube buckypapers (CNT-BP). Considerably higher thermal conductivity values than those achieved with conventional dispersing methods of graphene or CNTs in epoxy resins were obtained. The characterisation was complemented with a study of the structure at the microscale by cross-sectional scanning electron microscopy (SEM) images and a thermogravimetric analysis (TGA). The films are preconditioned in order to incorporate them into the composites, and the complete manufacturing process proposed allows the production and processing of these materials in large batches. The high thermal conductivity obtained for the composites opens the way for their use in demanding thermal management applications, such as electronic enclosures or platforms facing critical temperature loads.

Spectroscopic (Raman) and gravimetric (acid titration, TGA) techniques were compared to determine the functionalization degree of multiwalled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) with poly(L-lactic acid) (PLLA), following a two-step oxidation/esterification process. After oxidation with HNO 3 , carbon nanotubes (CNTs) were activated with thionyl chloride to the corresponding acid chlorides and then grafted with PLLA. FTIR spectroscopy confirmed the formation of very similarly grafted CNT-PLLA materials for both SWNT and MWNT. But, according to chemical titration and TGA results, oxidized and esterified SWNT showed a significantly higher degree of functionalization than their MWNT counterparts. Contrary to these observations, the increase of the Raman I D /I G ratio was higher for MWNT-derived materials than for the SWNT counterparts. Therefore, it was concluded that this spectroscopic technique is unsuitable for the quantitative determination of the degree of functionalization when MWNT and SWNT are compared.

Lithium metal can be used to reduce single-walled carbon nanotubes (SWNT) to carbide-like species under the catalytic effect of di-tert-butyl-biphenyl (DTBP). The resulting nanotube polycarbanions show a significantly increased dispersability in THF and react "in situ" with trimethylchlorosilane, methyl methacrylate, and methyl N-acetamidoacrylate to afford covalently functionalized silyl nanotubes and polymer-wrapped SWNT. The density and average length of the polymer chains attached to the nanotube wall can be widely modified by varying the amount of monomer, lithium, and catalyst.