High pressure-assisted magnesium carbonate impregnated natural fiber-reinforced composites

• An external pressure applied to inorganic nanoparticle impregnation (INI) process.
• The INI efficiency was significantly increased by using external pressures.
• The porosity of high-pressure-INI-treated fiber was reduced.
• Mechanical and water-resistant properties of the composites were improved.
• Mechanical properties were comparable with glass-fiber sheet molding compounds.

The kenaf fiber/polyester composites, owning the comparable mechanical properties with commercial glass-fiber sheet molding compounds (SMC) for automotive application, were achieved through the high pressure-assisted magnesium carbonate impregnated fibers and the vacuum-assisted resin transfer molding process. The in situ inorganic nanoparticle impregnation (INI) process was performed by immersing the alkali retted fibers into magnesium chloride solution with various pressures and then treated by sodium carbonate to yield the INI-treated fibers. The magnesium carbonate content was increased by 180.3%, when a 13.79 MPa pressure was applied during the magnesium carbonate immersing process, resulting in lower porosity of fibers. Compared to the un-treated fiber/polyester composite, the mechanical properties of the high pressure-assisted INI-treated fiber/polyester composites were enhanced by 18.6–277.3%, and the 24-h thickness swelling and water absorption were reduced by 64.4% and 62.2%, respectively. The mechanical properties and specific mechanical properties were comparable with or excessed to that of glass-fiber SMC.