Effect of Varying Stiffness and Functionalization on the Interfacial Failure Behavior of Isotactic Polypropylene on Hydroxylated γ-Al2O3 by MD Simulation

This study focuses on polymer-metal joints consisting of isotactic polypropylene (iPP) or iPP grafted with maleic anhydride (iPP-g-MA) and hydroxylated γ-Al₂O₃, which is a model for an oxidized aluminum surface, and investigates the contributions of the Young's moduli of iPP and iPP-g-MA and chemical functionality (MA groups) in iPP-g-MA to the interfacial failure behaviors using the molecular dynamics (MD) simulation method. First, our calculations demonstrated that the tensile strength observed in interfacial failures of the joints increases as Young's modulus of the polymer in the joints increases. This is because a higher stiffness makes it harder for a void to form within the polymer matrix under the applied tensile strain and to reach the interface. Second, in iPP-g-MA-γ-Al₂O₃ joints, MA groups work more effectively to improve the interfacial strength as the Young's modulus of the polymer in the joints increases. For iPP-g-MA with a lower Young's modulus, the polymer molecules are pulled off the surface in a peel mode with increasing normal strain due to their greater flexibility. This results in a gradual removal of the MA groups and thus reduces their contribution. Meanwhile, for a higher Young's modulus, iPP-g-MA molecules at the interface are removed in a tensile mode because of their increased stiffness. This leads to more MA groups required to be detached from the surface at the same time to cause interfacial failure, thus increasing the contributions of the MA groups.

4-Dialkylaminopyridine modified magnetic nanoparticles: as an efficient nano-organocatalyst for one-pot synthesis of 2-amino-4H-chromene-3-carbonitrile derivatives in water

A new DMAP-based magnetic nano-organocatalyst was developed for efficient one-pot synthesis of 2-amino-4H-chromene-3-carbonitrile derivatives in water as a green solvent.

Optimization of Dispersion of Nanosilica Particles in a PP Matrix and Their Effect on Foaming

Nanocomposites based on isotactic polypropylene (PP) and nanosilica (SiO2) were prepared using a co-rotating twin-screw extruder (TSE). The effect of operating variables, such as screw speed and screw configuration on the dispersion of nanosilica in the polymer matrix has been studied, using TEM imaging. High shear stress, sufficient residence time, and high fill ratio in the melting section of the screw were the most important factors in achieving good nanosilica dispersion. Furthermore, the effects of filler loading and amount of a maleated polypropylene (PP-g-MA) compatibilizer on the degree of SiO2 dispersion were investigated. The foaming performance of the composites was evaluated using a batch foaming simulation system, and an extrusion foaming setup that employed respectively N2 and CO2 blowing agents. Well-dispersed surface-modified hydrophobic SiO2 particles acted as effective nucleating agents for foaming, when used at loadings below 1 phr.

One-step synthesis of highly monodisperse hybrid silica spheres in aqueous solution

An effective and reproducible method of preparing highly monodisperse organic-inorganic hybrid silica spheres was studied. One process, one precursor (organosilane) and one solvent (water) were used in our experiments. The size of hybrid silica spheres could be adjusted from 360 to 770 nm with relative standard deviation below 2% by controlling the concentration of the organosilane precursor and the ammonia catalyst. The increasing of the precursor concentration increases the particle size while the catalyst concentration has a reverse effect on the particle size. The concept of homogeneous nucleation and growth processes are introduced to explain the formation mechanism and the effect of reaction conditions. The scanning electron microscopy (SEM) images illustrate the copiousness in quantity and the uniformity in size/shape of the particles that could be routinely accomplished in this synthesis. Fourier transform infrared (FT-IR) and (29)Si nuclear magnetic resonance (NMR) spectra confirm the structure of vinyl hybrid silica spheres, where the vinyl group (-CH=CH(2)) exists and connects to the silicon atom. This method has also been extended to design and prepare other organic-inorganic hybrid materials especially in monodisperse surface-modified silica spheres.