Novel recycling of pineapple leaves into cellulose microfibers by two-step grinding of ball milling and high-speed rotor–stator homogenization

Pineapple leaves are one of the most abundant agricultural residues that are wasted either by burning them on-site or utilized for low-value engineering applications such as fabrics, animal feed, and vermicompost. In this work, pineapple leaves with a cellulose content of over 40% are alkaline pre-treated with sodium hydroxide, followed by bleaching with hydrogen peroxide to produce cellulose with a high purity of 79.72% and extraction efficiency of 41.56%. The cellulose microfibers are generated by disintegrating the obtained cellulose-based fibers via a stepwise combination of ball milling and high-speed rotor–stator homogenization. The independent effects of ball milling and homogenization in terms of processing time, and when combining the two grinding methods on final product size, fiber morphology, thermal stability, and chemical structure are investigated comprehensively by Laser Diffraction Spectrometry, Scanning Electron Microscopy, Thermogravimetric Analysis, and Fourier-transform Infrared Spectroscopy. The operating condition when conducting step-by-step ball milling and homogenization with the time of 9 h and 1 h, respectively, results in the smallest fiber size of 8.15 µm. The calculation results show that the size of microfibers fabricated via the developed method in this study has been reduced by 91.24% compared to the previous one, demonstrating the substantial effect when combining ball milling and homogenization.