Carbon nanotube-reinforced composites effective dispersions

Multi-walled carbon nanotubes can be functionalized with PBI via a Friedel-Crafts acylation reaction in a phosphorus pentoxide/methanesulfonic acid medium [23]. The composites have been used as reinforced fillers in 100% acidified poly(hydroxyamino-ether) to prepare mixed composites. The acid-base interaction between the PBI chains attached on multi-walled carbon nanotubes plays a crucial role with regard to good dispersion and effective reinforcement. 

More recently nanoscale fillers such as clay platelets, silica, nano-calcium carbonate, titanium dioxide, and carbon nanotube nanoparticles have been used extensively to achieve reinforcement, improve barrier properties, flame retardancy and thermal stability, as well as synthesize electrically conductive composites. In contrast to micron-size fillers, the desired effects can be usually achieved through addihon of very small amounts (a few weight percent) of nanofillers [4]. For example, it has been reported that the addition of 5 wt% of nanoclays to a thermoplastic matrix provides the same degree of reinforcement as 20 wt% of talc [5]. The dispersion and/or exfoliahon of nanofillers have been identified as a critical factor in order to reach optimum performance. Techniques such as filler modification and matrix functionalization have been employed to facilitate the breakup of filler agglomerates and to improve their interactions with the polymeric matrix. 

Thermal characteristics are also important in numerous industrial processes, and thus the development of composites with high thermal conductivity and a low coefficient of thermal expansion is important to achieve effective heat conduction (Kim et al., 2007). The use of some reinforcements such as carbon nanotubes, carbon fibers, nano silica powders, metal particles, boron nitrite and glass fibers can improve the thermal conductivity of phenolic composites (Kim et al., 2007 Simitzis et al., 2011 Srikanth et al., 2010). Kim et al. (2007) demonstrated that the homogeneous dispersion of 7 wt% carbon nanotubes in a phenolic resin acted as an effective thermal bridge between adjacent carbon fibers and enhanced the thermal conductivity (393 W m-i K-i). 

Carbon nanotubes generally tend to exist as bundles or even networks of aggregates because of strong nonbonded interactions. To exploit their full potential as fillers, however, techniques that achieve near-complete dispersion of nanofibers and improve tbeir compatibility with the polymers, need to be developed. Data on single-fiber measurements that illustrate the reinforcing effect of CNTs in fibers are sparse in the literature (Pomes et al. 2006 Moore et al. 2004). Recent studies on melt-spun conventional composite fibers of polypropylene illustrates reinforcement by CNTs (Moore et al. 2004). 

Wide angle X-ray diffraction (WAXD) of multi walled carbon nanotube (MWCNTs). Reinforced polyethylene composites showed that the MWCNTs are very well distributed and dispersed in the PE matrix [61], There is a broadening and reduction in intensity of the 110 and 200 PE rejections with increasing MWCNT concentration, indicative of altered amorphous and crystalline phases. XRD results of calcium carbonate and PE composites were studied and the results showed that the adoption of calcium carbonate in polyethylene has two primary effects the reinforcement and the nucleating effect. The reinforcement effect increases the bulk crystallinity and modulus, while the nucleating effect decreases the spher-ulite size. 

---