Papers by Author: Robert Kwok Yiu Li

Abstract: Results on the effect of water absorption on the mechanical and dielectric properties of nano-size spherical alumina (Al2O3) filled epoxy are presented in this paper. The results from tensile tests indicate that incorporation of the Al2O3 nanoparticles into the epoxy can improve the stiffness of the matrix. DMA results show that the stiffness improvement is more pronounced at the rubbery region of the matrix. The alumina nanoparticles can increase the dielectric constant of the epoxy resin due to the increase in the total interfacial area. Upon water absorption, the mechanical properties of the alumina/epoxy nanocomposites decrease evidently, because of the damages induced by water on the epoxy resin. However, the ductility of epoxy can be improved by the water absorption process. In addition, the dielectric constant of the alumina/epoxy nanocomposites increased greatly after water absorption treatment.

Abstract: Isotactic polypropylene (PP)/carbon nanotube (CNT) composites compatibilized by maleic anhydride grafted styrene-ethylene/butylenes-styrene copolymer (MA-SEBS) were prepared by melt compunding and compression moulding. The melt compouding torque, thermal properties, dynamical mechanical behavior, mechanical and anti-static properties of the PP/CNT composites were systematically invertigated. The results indicated that MA-SEBS is an effective compatilizer for the PP/CNT composites. The melting and crsytallization temperatures (Tm and Tc), crystallinity degree (Xc) of the PP phase in PP/CNT composites increase remarkably with the CNT content. Compared with PP/CNT composites, the incorporation of MA-SEBS increases Tm, but decreases Tc, crystallization rate and Xc of PP phases in PP/MA-SEBS/CNT composites. Owing to MA-SEBS as a compatibilizer to enhance formation of a perfect percolation network, the thermal, mechanical and anti-static properties of PP/CNT are improved.

Abstract: Through-thickness stitching is one of the most effective techniques to improve the delamination resistance of composite laminates. The effects of two different stitching patterns on the mode-I interlaminar fracture toughness of unidirectional carbon fiber reinforced plastics (CFRP) are examined experimentally in the present paper by using the double cantilever beam (DCB) test method. It is found that the zigzag stitching pattern results in a better toughening effect than the straight line pattern, and that the stitching density also has a considerable influence on the mode-I fracture toughness.