Hydrothermal mass production of MgBO2(OH) nanowhiskers and subsequent thermal conversion to Mg2B2O5 nanorods for biaxially oriented polypropylene resins reinforcement

Mass production of one-dimensional (1D) nanomaterials has emerged as one of the most significant challenges in powder technology. In this contribution, MgBO2(OH) nanowhiskers were hydrothermally produced at a kilogram scale in a 150 L stainless steel autoclave at 200 °C for 12.0 h by using MgCl2·6H2O, H3BO3 and NaOH as the raw materials. The subsequent thermal conversion of the MgBO2(OH) nanowhiskers at 700 °C for 6 h led to 3.75 kg of high crystallinity monoclinic Mg2B2O5 nanorods, with a length of 0.47–1.3 µm, a diameter of 55–160 nm, and an aspect ratio of 3–15. After the nanorods have been surface modified with the silane coupling agent KH-550, the reinforcing and toughening effects of the Mg2B2O5 nanorods on the biaxially oriented polypropylene resins (BOPP-D1) were evaluated. The filling of the Mg2B2O5 nanorods into the resins resulted in the increase in the tensile strength, the impact strength, and the melt flow index of the BOPP-D1 composites. The appropriate ratio of coupling agent to fillers (Mg2B2O5 nanorods) and the ratio of fillers to resins were determined within the range of 0.6–1.2 wt.% and 8–15 wt.%, respectively. The optimal ratio of fillers to resins was ca. 10 wt.%. The present mass production of MgBO2(OH) nanowhiskers and Mg2B2O5 nanorods is believed to be helpful for enlarging and propelling the applications of the 1D magnesium borate nanostructures in the near future.