**2.2. Preparation and characterization of sugarcane bagasse microfibers**

Sugarcane as received was cleaned with distilled water in order to take off soil and residues from the lignocellulosic material. Clean bagasse was later dried at 60°C for 6 h until constant weight. Around 500 g of bagasse was then grounded using a Kinematica™ Polymix™ PX-MFC 90 D Lab mill drive and a sieve size of 200 μm. The sample was divided in three groups: one used as it was obtained after milling with no further treatment. A second group was treated with an aqueous solution of 8% NaOH using a 1:1 bagasse/solution ratio during 2 h, in order to remove lignin from the bagasse's surface. A third group of fibers were silanized after lignin removal. For silanization, a solution of 2 × 10−<sup>3</sup> M of octadecyltrimethoxysilane in an 8:2 ethanol/water ratio as solvent was prepared. The pH of solution was kept at 3 using acetic acid. A time of 10 minutes was allowed for hydrolysis after addition of silane and before the solution was sprayed over bagasse fibers using a plastic spray bottle. Wet fibers were allowed to dry at 90°C for 24 h in a forced air oven. After drying, fibers were kept in plastic bags until used in the composition process with polypropylene.

Each group of fibers was characterized by thermal gravimetric analysis (TGA) using a nonreactive atmosphere (N2 at 50 mL/min) from 25 to 650°C at a heating rate of 10°C/min using a TGA/DSC 2 STAR system, from Mettler Toledo. Surface structure of fibers was characterized by scanning electron microscopy (SEM), and chemical maps are also obtained by electron dispersed spectroscopy (EDS) using an ultra-high-resolution analytical FE-SEM SU-70 from Hitachi. All samples were sputtered with gold before analysis. Silicon content on fibers was quantified by flame atomic absorption spectrometry (FAAS). Around 0.5 g of fibers was calcinated at 550°C for 4 h in porcelain crucibles. After calcination each sample was treated with 2 mL of HF (48–50%) and 98 mL of H<sup>2</sup> SO4 0.08 M. Samples were kept for 24 h in polypropylene containers for 24 h and then filtered. Quantification using Analist 800 from Perkin Elmer was performed using a nitrous oxide/acetylene flame.
