Direct observation of the fracture behavior of the polyether ketone ketone (PEKK) spherulites

This article reports the direct observation of the fracture of individual poly‐ether‐ketone‐ketone (PEKK) spherulites. A single layer of PEKK spherulites was obtained by bonding a PEKK film in‐between two sandblasted Ti alloy plates using an autoclave. The crack of an individual PEKK spherulite was achieved by opening the Ti/PEKK/Ti sandwich using a double cantilever beam test. The fracture morphology of the PEKK spherulite was characterized using scanning electron microscopy and atomic force microscopy. It was found that under tensile stress the crack of the individual spherulite propagates along the middle plane and crosses the nucleation core. This is due to the symmetric radial structure of the spherulite. Moreover, it was found that the fracture surface morphology at the core of the spherulite is strongly influenced by the local crystalline structure, which is anisotropic and determined by the initial nucleation growth direction. As a result, the area fraction experiencing plastic deformation during the fracture of PEKK spherulites at different orientations may vary by an order of 10. Our results show the important role of the initial nucleation growth direction on the mechanical properties of the polymer crystals and may provide a new approach to the design of high‐performance polymer materials with tailored crystalline structures

Synergistically enhancing the performance of cardanol-rich epoxy anticorrosive coatings using cardanol-based reactive diluent and its functionalized graphene oxide

In this paper, a new anti-corrosion composite coating with high-volume fraction of cardanol-based components was prepared using epoxy, cardanol-based reactive diluent (602A), and 602A functionalized graphene oxide nanosheets (A-GO). A one-step, low-cost method was adopted to synthesize the A-GO. By synergistically enhancing the matrix compactness, filler dispersibility, and matrix hydrophobicity, the cardanol-rich epoxy composite coating (A-GO/602A/epoxy) shows high anti-corrosion performance in the long term. The morphology and structure analyses show that the A-GO/602A/epoxy composite coating has i. enhanced matrix compactness, ii. optimized filler dispersibility and filler/matrix bonding strength, and iii. improved matrix hydrophobicity. The electrochemical impedance spectroscopy (EIS) test was used to determine the anti-corrosion performance of the A-GO/602A/epoxy composite coating. After immersing in diluent NaCl solution (3.5 wt%) for 90 days, the increase of the impedance modulus of the A-GO/602A/epoxy composite coating maintains three orders of magnitude at low frequencies (0.01 Hz) compared to the pure petroleum-based epoxy coating, indicating that the corrosion properties of the composite coating can be significantly enhanced by synergistically optimization of the three factors. Our results show the high potential of cardanol-rich epoxy coatings in the field of anti-corrosion epoxy coatings, and may give a guide to the design of high-performance anti-corrosion epoxy coatings

Microbubble on fiber method to determine the contact angle between steel substrates and highly viscous molten PEKK and PA 6

Determining the contact angle between a molten thermoplastic and a solid is important for the processing of thermoplastics and their composites. The well-known sessile drop method can be used to determine the contact angle of thermoplastics. However, complex instrumental systems are needed due to the high viscosity and high melting point of thermoplastics. Inspired by the captive bubble method, a simple method based on the system of an air bubble on a substrate in the molten thermoplastic was proposed. This system is prepared by melting fibers and thermoplastic powder materials mixtures in between two glass plates using a hot stage. The contact angle of a microbubble in contact with fiber in molten thermoplastic is measured using an optical microscope. The system of a microbubble in molten thermoplastic can easily reach the equilibrium state. Two types of highly viscous thermoplastics in contact with stainless steel fibers are studied and the contact angle is sensitive to both the physicochemical properties of the fiber surface and the type of polymer matrix materials, which demonstrates the applicability of this method. Our proposed method is promising to be further developed into a general method to determine the contact angle between thermoplastics and solid surfaces.</p

Microbubble on fiber method to determine the contact angle between steel substrates and highly viscous molten PEKK and PA 6

Determining the contact angle between a molten thermoplastic and a solid is important for the processing of thermoplastics and their composites. The well-known sessile drop method can be used to determine the contact angle of thermoplastics. However, complex instrumental systems are needed due to the high viscosity and high melting point of thermoplastics. Inspired by the captive bubble method, a simple method based on the system of an air bubble on a substrate in the molten thermoplastic was proposed. This system is prepared by melting fibers and thermoplastic powder materials mixtures in between two glass plates using a hot stage. The contact angle of a microbubble in contact with fiber in molten thermoplastic is measured using an optical microscope. The system of a microbubble in molten thermoplastic can easily reach the equilibrium state. Two types of highly viscous thermoplastics in contact with stainless steel fibers are studied and the contact angle is sensitive to both the physicochemical properties of the fiber surface and the type of polymer matrix materials, which demonstrates the applicability of this method. Our proposed method is promising to be further developed into a general method to determine the contact angle between thermoplastics and solid surfaces