Coating of Carbon Fiber with Polyhedral Oligomeric Silsesquioxane (POSS) to Enhance Mechanical Properties and Durability of Carbon/Vinyl Ester Composites

Abstract

Our continuing quest to improve the performance of polymer composites under moist and saltwater environments has gained momentum in recent years with the reinforcement of inorganic nanoparticles into the polymer. The key to mitigate degradation of composites under such environments is to maintain the integrity of the fiber/matrix (F/M) interface. In this study, the F/M interface of carbon/vinyl ester composites has been modified by coating the carbon fiber with polyhedral oligomeric silsesquioxane (POSS). POSS is a nanostructured inorganic-organic hybrid particle with a cubic structure having silicon atoms at the core and linked to oxygen atoms. The advantage of using POSS is that the silicon atoms can be linked to a substituent that can be almost any chemical group known in organic chemistry. Cubic silica cores are ‘hard particles’ and are about 0.53 nm in diameter. The peripheral organic unit is a sphere of about 1–3 nm in diameter. Further, cubic structure of POSS remains intact during the polymerization process and therefore with appropriate functional groups, if installed on the fiber surface, would provide a stable and strong F/M interface. Two POSS systems with two different functional groups; namely, octaisobutyl and trisilanolphenyl have been investigated. A set of chemical and mechanical procedures has been developed to coat carbon fibers with POSS, and to fabricate layered composites with vinyl ester resin. Interlaminar shear and low velocity impact tests have indicated around 17–38% improvement in mechanical properties with respect to control samples made without the POSS coating. Saltwater and hygrothermal tests at various environmental conditions have revealed that coating with POSS reduces water absorption by 20–30% and retains the composite properties.

Synthesis of an Open‐Cage Structure POSS Containing Various Functional Groups and Their Effect on the Formation and Properties of Langmuir Monolayers

“…The extrapolated cross‐sectional area obtained from the π – A isotherm (limiting area A o ) indicates that closely packed PEG‐POSS molecules occupy about 230 Å 2 of the interface. Taking into account that the cubic structure of the POSS cage is about 5 Å in size, it seems that the value of A o suggests such an orientation of the PEG‐POSS molecules in which the hydrophilic moieties (i.e., the PEG groups) lie on the water surface, whereas the silica cage is located above, without direct contact with the subphase. Thus, the limiting area of the PEG‐POSS molecules is determined by the dimensions of the hydrophilic PEG moieties.…”

“…Ta king into account that the cubic structure of the POSS cage is about 5 in size, [31] it seems that the value of A o suggests such an orientation of the PEG-POSS molecules in which the hydrophilic moieties( i.e.,t he PEG groups)l ie on the water surface, whereas the silica cage is located above, withoutd irect contact with the subphase. Ta king into account that the cubic structure of the POSS cage is about 5 in size, [31] it seems that the value of A o suggests such an orientation of the PEG-POSS molecules in which the hydrophilic moieties( i.e.,t he PEG groups)l ie on the water surface, whereas the silica cage is located above, withoutd irect contact with the subphase.…”

Effects of functional groups on the solubilities of polyhedral oligomeric silsesquioxanes (POSS) in supercritical carbon dioxide

“…Other applications include surface modification and coating [49,50] and formation of polymeric films [51]. Methacryl POSS/PMMA exhibited the most effective behaviour in both Tg and relaxation enthalpy (ΔHRelax) because of the physical aging [47].…”

Flame retardant and mechanism of vinyl ester resin modified by octaphenyl polyhedral oligomeric silsesquioxane

“…Over the past two decades, polyhedral oligomeric silsesquioxane (POSS) additives, which belong to organic‐inorganic hybrid material and contain basic polyhedral siliconeoxygen nanostructured skeleton or cage, have been incorporated into many polymers by means of copolymers, grafts, or melt blends . The organic structure of POSS is diverse, and it is possible to attach different functional organic groups to the corner Si atoms to enhance interactions with a matrix material, and it might potentially lead to significant improvements in polymer properties, including upper use temperature, oxidative resistance, heat endurance, and surface hardening . Therefore, polymeric composites modified by POSS, such as octaphenyl polyhedral oligomeric silsesquioxane (OPS), will be, prospectively, widely and intensively employed in engineering applications due to their excellent heat resistance, mechanical properties, and non‐pollution.…”