Effects of Boric Acid Ester Modified Magnesium Borate Whisker on the Mechanical Properties and Crystallization Kinetics of Polypropylene Composites

Polypropylene (PP) is notch sensitive and brittle under severe conditions of deformation, limiting wider range of its usage as a structural load-bearing polymer. Hence, in this work the magnesium borate whisker (MBw), with similar mechanical properties to carbon fiber but much less expensive than polycrystalline silicon carbide, was modified by boric acid ester (BAE) and then used to fabricate PP composites. The mechanical properties, morphology, and non-isothermal crystallization property of virgin PP, PP/MBw, and PP/BAE-MBw composites were studied through mechanical testing, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC), respectively. The non-isothermal crystallization data was analyzed via Mo, Kissinger, and Dobreva methods. The results reveal that the incorporation of BAE-MBw into PP matrix results in higher tensile strength and impact strength than those of virgin PP and PP/MBw composite. The activation energies based on Kissinger were 190.20 kJ/mol for virgin PP, 206.59 kJ/mol for PP/MBw, and 218.98 kJ/mol for PP/BAE-MBw. The nucleation activities of whiskers determined by the Dobreva model were 0.86 for PP/MBw and 0.75 for PP/BAE-MBw. As a result, the whiskers, especially the modified whiskers, act as active substrates to facilitate heterogeneous nucleation, which leads to an increase in crystallization rate.

The performances of modified single-walled carbon nanotubes/poly(ether ether ketone) composites prepared by solution blending and melt blending

The modified single-walled carbon nanotubes (m-SWCNTs)/poly(ether ether ketone) (PEEK) composites were prepared by solution blending and melt blending, respectively. The mechanical, dielectric, and frictional performances of the m-SWCNTs/PEEK composites obtained by different processing technic were investigated. The poly(aryl ether ketone)s with pyrene (PAEK-Pys) were synthesized through iridium-catalyzed C−H borylation followed by Suzuki coupling. PAEK-Pys were characterized using ultraviolet–visible spectroscopy, proton nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The polymers were then used for surface modification of pristine SWCNTs. Finally, the m-SWCNTs were used to prepare m-SWCNTs/PEEK composites via co-blending in solution or melt. The mechanical, frictional, and dielectric performance of the m-SWCNTs/PEEK composite by solution blending were better than these in m-SWCNTs/PEEK composite by melt blending. These results suggest that the method of solution blending is more favorable for the dispersion of the SWCNTs in PEEK.

The mechanical and frictional properties of poly(ether ether ketone) composites with modified aluminum borate whiskers

Poly(ether ether ketone)s (PEEKs) are increasingly used in tribological application. Reinforcing materials such as aluminum borate whiskers are often incorporated into polymeric materials to improve mechanical properties. In this work, aluminum borate whiskers were modified by the boron-containing poly(ether ether ketone)s (B-PEEKs). The modified aluminum borate whiskers (g-W)-reinforced PEEK composites were then prepared via melt-blending method. B-PEEKs showed the good coupling effect by the interface micromorphology analysis and performance evaluation of PEEK composites. After grafting treatment with B-PEEKs, aluminum borate whiskers were found to be dispersed evenly in PEEKs matrix without apparent aggregation. Ascribed to the strong interaction between whisker-grafted chains and PEEKs matrix, g-W/PEEK composites show better mechanical properties, lower friction coefficient, and wear ratio than those composites without grafting modification, indicating that the grafted aluminum borate whiskers (g-W)-reinforced PEEK composites may become a wear-resistant material.

Epitaxial growth of aluminum borate whiskers and simultaneous joining of alumina ceramics via a sol–gel method

Aluminum borate whiskers were epitaxially grown on alumina via sol–gel method and successfully used for joining alumina in air.