Multi-scale effects on deformation mechanisms of polymer nanocomposites: Experimental characterisation and numerical study.

摘要

In order to make much stiffer, light weight and high performance material products, polymer nanocomposites play an emerging role in the material innovation. Unlike other thermoplastics, polymer nanocomposites are fabricated by introducing a small amount of solid nano-scale fillers (normally less than 5 wt%) such as nanoclay, carbon nanotubes or nanofibres into a plastic resin to dramatically enhance its stiffness, strength and thermal properties. The difference between nanocomposites and conventional fibre composites is that the added fillers are extremely small, only one-millionth of a millimetre thick, and provide a much larger interface area per unit volume for greatly improving the interfacial bonding effect between nanofillers and the polymer matrix.;More importantly, polypropylene (PP)/clay nanocomposites have quite a high potential to form such innovative materials and replace the conventional plastics in many automotive and packaging applications. Nevertheless, the growth of PP/clay nanocomposites faces an obstacle of hydrophobic polymer's low interactions with hydrophilic clay. Maleic anhydride (MA) grafted PP (MAPP), commonly used as a compatibiliser, has been proven to facilitate a good clay dispersion within the PP matrix through its functionalised MA groups. But despite the great attention from the manufacturers and researchers in recent years, commercial PP/clay nanocomposites with reliable material properties are still limited in availability. The major problem stems from the complex influences of the material selection and processing methods.;The present work developed a comprehensive approach from the material formulation and processing, experimental characterisation to the numerical modelling of PP/clay nanocomposites based on the finite element analysis (FEA) of micro/nanostructures. Initially, effects of the material selection including the clay type and content, MAPP content and PP matrix viscosity were investigated for the mechanical property enhancement of PP/clay nanocomposites. These nanocomposites were prepared using twin screw extrusion and injection moulding processes with a well-known Taguchi design of experiments (DoE) method in order to statistically detect the significant factors for influencing their mechanical properties. The preferred material formulations were then determined by Pareto analysis of variance (ANOVA) with the technical and economic considerations. The fundamental material characterisation was also conducted on those formulated nanocomposites using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). Overall mechanical properties of neat PP and corresponding nanocomposites were determined by the general tensile, flexural and impact tests. Finally, computational models were established by implementing both the representative volume element (RVE) technique and innovative object-oriented finite element (OOF) analysis to predict the tensile moduli of PP/clay nanocomposites in comparison to the experimental data and available composites theoretical models.