Abstract
Interfacial adhesion between polymer matrix and reinforcing silica nanoparticles plays an important role in strengthening polypropylene (PP) composite. To improve the adhesion strength, the surface of silica nanoparticles can be modified by grafted functional molecules. Using atomistic simulations, we examined the effect of functionalization of silica nanoparticles by hexamethyldisilazane (HMDS) and octyltriethoxysilane (OTES) molecules on the deformation and failure of silica-reinforced PP composite. We found that the ultimate tensile strength (UTS) of PP composite functionalized by OTES (28 MPa) is higher than that of HMDS (25 MPa), which is in turn higher than that passivated only by hydrogen (22 MPa). To understand the underlying mechanistic origin, we calculated the adhesive energy and interfacial strength of the interphase region, and found that both the adhesive energy and interfacial strength are the highest for the silica nanoparticles functionalized by OTES molecules, while both are the lowest by hydrogen. The ultimate failure of the polymer composite is initiated by the cavitation in the interphase region with the lowest mass density, and this cavitation failure mode is common for all the examined PP composites, but the cavitation position is dependent on the tail length of the functional molecules. The present work provides interesting insights into the deformation and cavitation failure mechanisms of the silica-reinforced PP composites, and the findings can be used as useful guidelines in selecting chemical agents for surface treatment of silica nanoparticles.
Highlights
Interfacial adhesion between polymer matrix and reinforcing silica nanoparticles plays an important role in strengthening polypropylene (PP) composite
Our objective is to study the effect of surface functionalization of silica nanoparticles by HMDS and OTES molecules on the structure and properties of the interphase region, as well as on the deformation and cavitation failure mechanisms of PP composites subjected to uniaxial tensile load
The obtained stress–strain curves for the PP composites containing SiO2 passivated by hydrogen and in addition functionalized with HMDS or OTES molecules are plotted in Fig. 5a, while the stress–strain curve for the pure PP matrix is added for comparison
Summary
Interfacial adhesion between polymer matrix and reinforcing silica nanoparticles plays an important role in strengthening polypropylene (PP) composite. The study of large-scale phenomena, such as interfaces in polymer composites which involve the polymer matrix, reinforcer and molecular linker, from a bottom-up route requires efficient atomistic modelling techniques, such as molecular dynamics approach Such simulations will allow us to gain the understanding of structure–property relations, and to select and optimize basic components at the interfaces to improve their properties and to maximize their performance. Thermoplastic polymers, such as polypropylene, polyethylene and polystyrene et al, have been widely used in the field of packaging, electric and automobile industries due to their low density, high chemical resistance and remarkable thermal s tability[1,2]. The mobility in the interphase region is often significantly reduced due to the polymer crowding and o rdering[11,12,13,14]
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