Thermosetting polyurethane multiwalled carbon nanotube composites

Abstract

Thermosetting polyurethane (PU) multiwalled carbon nanotube (MWCNT) nanocomposites at loadings up to 1 wt % were prepared via an addition polymerization reaction. The morphology of the nanocomposites and degree of dispersion of the MWCNTs was studied using a combination of scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and wide angle X-ray diffraction (WAXD), and revealed the nanotubes to be highly dispersed in the PU matrix. Addition of just 0.1 wt % MWCNTs resulted in significant enhancements in stiffness, strength and toughness. Increases in Young's modulus, % elongation at break and ultimate tensile strength of 561, 302 and 397% were measured for the nanocomposites compared to the unfilled PU. The effect of the MWCNTs on the modulus of the PU was evaluated using the Rule of Mixtures, Krenchel and Halpin-Tsai models. Only the Halpin-Tsai model applied to high aspect ratio nanotubes was in good agreement with the modulus values determined experimentally. Strong interfacial shear stress was found between PU chains and nanotubes, up to 439 MPa, calculated using a modified Kelly-Tyson model. Evidence for strong interfacial interactions was obtained from the Raman spectra of both the precursor materials and nanocomposites. When the MWCNTs were added to the isophorone diisocyanate an up-shift of 14 cm À1 and on average 40 cm À1 was obtained for the position of the carbon-hydrogen (CÀ ÀH) out-of plane bending (766 cm À1) and isocyanate symmetric stretch (1420 cm À1 ) modes respectively. Moreover, an up-shift of 24 cm À1 was recorded for the nanotube tangential mode (G-band) for the 1.0 wt % nanocomposite because of the compressive forces of the PU matrix acting on the MWCNTs. The dynamic mechanical (DMA) properties of the PU thermoset and the nanocomposites were measured as a function of temperature.

Otimização do processo de dispersão de nanotubos de carbono em poliuretano termorrígido

“…Além disso, como destacado por McClory e colaboradores [15] , outro indício dessa interação é que as imagens foram obtidas na superfície de fratura e não foram observadas regiões que indicassem que o MWCNT foi puxado para fora da matriz no momento da fratura. De fato, essa interface MWCNT:matriz é essencial para o reforço mecânico no sistema.…”

“…As imagens das Figura 3c, d exibem MWCNTs curvados e entrelaçados na matriz polimérica, ligando "pontos" da superfície fraturada. Essa morfologia, verificada em outros compósitos nanotubo:PUs (termorrígido ou termoplástico), é essencial para a transferência de tensão entre os CNTs e a matriz quando o material é sujeito a uma solicitação mecânica [15,27] . Como evidência do recobrimento pelo polímero, o diâmetro dos nanotubos de carbono visíveis nas imagens é da ordem de 23 nm a 34,0 nm nos compósitos com MWCNTs não modificados e de 12,0 nm a 36,0 nm nos compósitos com MWCNTs modificados.…”

“…Um diferencial importante para essa rota de processo, que constitui uma maior viabilidade para introdução na indústria, é a utilização de moinho de rolos como equipamento principal de processamento. As referências de PUE/MWCNTs relatam a incorporação da nanocarga por ultrassom ou dispersores de alto cisalhamento [14][15][16] .…”

“…Os poucos trabalhos voltados para o preparo de nanocompósitos CNTs/PUs termorrígidos encontrados na literatura são baseados na síntese do polímero em duas etapas (via pré-polímero) com a dispersão dos nanotubos no isocianato ou no poliol com o auxílio de dispersores de alto cisalhamento ou ultrassom [14][15][16][17] . Foram utilizados nanotubos do tipo SWCNTs (nanotubos de carbono de parede simples) e MWCNTs, purificados, modificados e não modificados quimicamente [15][16][17][18] . Nesses trabalhos, os compósitos foram preparados diretamente na concentração de interesse.…”

Master curves for the sulphur assisted crosslinking reaction of natural rubber in the presence of nano- and nano-structured sp2 carbon allotropes

“…Carbon nanotubes (CNT), both single [1,2] and multi-walled [3,4], graphene (G) [5][6][7][8] or graphitic nanofillers made of a few layers of graphene [9][10][11][12] are used to improve properties such as mechanical reinforcement, electrical and thermal conductivity, thermal and flame resistance, of thermoplastic [13][14][15], elastomeric [14][15][16][17][18] and thermoset [19][20][21] matrices. Such nanosized carbon allotropes can be dispersed as individual particles in the polymer matrix and, thanks to their high surface area, can establish large interaction with the polymer, much larger than the one observed with nanostructured carbon black (CB), whose primary particles are fused together to form aggregates [22].…”