Development of a polyamide12/Carbon nanotube nanocomposite for laser sintering

This thesis presents a comprehensive study on the preparation, processing and characterisation of a polymer nanocomposite for laser sintering. Well-dispersed nanocomposite powder with near-spherical morphology and suitable particle size for processing by laser sintering was successfully produced by a novel method of coating individual polyamide 12 (PA12) powder particles with carbon nanotubes (CNTs). Mechanical specimens produced by laser sintering the PA12-CNT powder showed good definition and no distortion. Compared to the laser sintered PA12 parts, PA12-CNT nanocomposite parts showed enhanced flexural, impact and tensile properties without sacrificing elongation at break. This enhancement may be attributed to the well-dispersed CNTs in the PA12 matrix and corresponding denser laser sintered parts. By adding the CNTs into the PA12 powder, the thermal conductivity was increased. This could increase the fusion of the powder and flow of melted PA12, resulting in denser and stronger parts. Parallel oscillatory rheology tests were completed in co-operation with Toyota Technological Institute (TTI), Japan. Results demonstrated that CNTs have a significant effect on the melt rheological properties of the PA12-CNT nanocomposites, as the storage modulus G’, loss modulus G’’ and viscosity [eta] of the PA12-CNT nanocomposites increased compared to neat PA12. To evaluate the dispersion of CNTs in the laser sintered PA12-CNT nanocomposite parts, three dimensional transmission electron microscopy (3D-TEM) was carried out at National Institute for Materials Science (NIMS), Japan. Results revealed that the CNTs were dispersed well in the laser sintered PA12-CNT parts without agglomerates, which is very important for the mechanical enhancement by nanofillers. The method used in this work III appears to be a cost-efficient and effective way to produce polymer nanocomposite powders for laser sintering, while maintaining the optimum powder morphology for the laser sintering process and enhancing the mechanical properties of the laser sintered parts

Influence of carbon nanotubes on the rheology and dynamic mechanical properties of polyamide-12 for laser sintering

The rheological behaviour of polymer nanocomposites is very important for polymer processing and understanding the structure-properties relationship. In this paper, the rheological properties of a polyamide 12 (PA12) - carbon nanotube (CNT) nanocomposite for laser sintering were studied. Compared to neat PA12, the presence of CNTs resulted in higher storage modulus (G′), loss modulus (G″) and viscosity (η). With an increase in temperature, viscosity showed an unusual increase for both PA12 and the PA12-CNT nanocomposites, which is likely to result from incomplete melting of powder particles. Dynamic mechanical analysis was carried out to examine the effect the CNTs were having on the laser sintered parts. The laser sintered PA12-CNT nanocomposite had an increased elastic modulus compared to that of neat PA12. The CNT and polymer matrix interaction hindered the chain motions, which resulted in higher loss modulus and decreased the thermal expansion coefficient