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Molecules 2021, 26, 5276 17 of 22 3. Materials and Methods 3.1. Materials The PLA was obtained from Sigma Aldrich, Pasir Pan-jang Rd, Singapore. The properties of the practical grade PLA 4043D were 53 MPa (tensile strength) and 1.24 (specific gravity). The chitin’s practical grade (90% deacetylated) was purchased from Biobasic, Malaysia. The CNF was prepared from bamboo, and a commercial CNF was obtained from the cellulose lab, Canada, as a standard reference to verify the viability of the isolation technique. 3.2. The Isolation and Characterisation of Cellulose Nanofibrillated Fibre from Bamboo The bamboo CNF was isolated with combined alkaline digestion, chlorine-free pulp- ing, supercritical carbon dioxide defibrillation, acid hydrolysis, and high-pressure ho- mogenisation. The bamboo stalk was cut into small pieces of 20 to 30 mm with a saw and subjected to mild alkaline hydrolysis, using NaOH to obtain the bamboo pulp. The bamboo stalk pieces were heated in 0.2 wt.% of anthraquinone and 25 wt.% alkaline concentration NaOH at 160 ◦C for 4 h (all percentages were based on the bamboo fibre’s weight) [24]. Chlorine-free bleaching was performd using ozone at 30 ◦C and a flow rate of 0.5 L/min to obtain bleached fibre from the bamboo. The bleached fibre was washed in distilled water to remove excess chemicals. The bleached fibre bundle was defibrillated into microsize using supercritical carbon dioxide explosion at a pressure of 50 MPa for 2 h at a temperature of 60 ◦C. This was performed in order to loosen the fibres to enhance the fibre surface area with acid during hydrolysis. After that, the defibrillated fibres were subjected to mild acid hydrolysis using oxalic acid (0.2 M at 40 ◦C) to obtain cellulose microfibrillated fibre. The isolated microfibrillated fibre was homogenised at 56 MPa pressure at 44 homogenisation cycles in order to obtain cellulose nanofibrillated fibre. The transmission electron micro- scope image of the isolated CNF was obtained using a TEM machine from Perkin-Elmer, PC1600, Winter Street Waltham, MA, USA at 40 kV and with a 100 nm scale size. The CNF sample was stained with acetone on a sensitive copper gauze, and the image was taken under the TEM machine. The fibre size was confirmed with a particle suze analyser from Zetasizer Ver. 6.11, Malvern, UK. The CNF FT-IR functional group analysis was performed in order to verify the structural properties. The FT-IR was performed with a FT-IR EFTEM Libra from Carl Zeiss, Selangor, Malaysia, using film produced by mixing the powdered CNF with KBR. The pressed film absorbance band was obtained for both types of CNF. Furthermore, the X-ray diffraction (XRD) analysis of the CNF was obtained using PANalytical X’Pert PRO X-ray Diffraction (Malvern Panalytical, Techlink, Singapore) at 45 volts, with a 40 A tube current, 1.540598 for K-alpha 1 and K-alpha 2, and a wavelength 2θ = 10◦ to 70◦. The zeta potential colloidal stability of the isolated CNF suspension in water was analysed using Zetasizer Ver. 6.11 (Malvern, UK). A similar test was conducted for the commercial CNF. The TGA-DTA was measured using a PerkinElmer TG-IR-GCMS Interface Q500, TA Instruments (PerkinElmer Inc., Akron, OH, USA), for 5 to 10 mg of the CNFs, at 20 ◦C/min and a temperature range of 40 to 800 ◦C 3.3. The Preparation and Characterisation of CNF-Reinforced Bionanocomposite Polylactic acid was blended with chitin at a percentage ratio of 90:10 to form the matrix, using a rheomixer [39]. The blend was then reinforced with 1%, 3%, and 5% cellulose nanofibre [18]. The polymer mix was extruded in a twin-screw extruder Process 11 extruder from Thermo Scientific (Waltham, MA, USA), at a temperature profile of 120 to 180 ◦C and a feeding rate of 100 g/min, to obtain PLA/chitin/CNF biocomposite. The filament was pelletised with a Varicut Pelletizer 11 M (Thermo Fisher Scientific, Waltham, MA, USA). The pellets were spread in a rectangular stainless-steel mould and pressed with a Carver Press (model 3851-0) (Carver, Wabash, IN, USA) into a biocomposite board at 170 ◦C for 15 min. The board was cut into test samples for physical, mechanical, thermal, and wettability analysis.PDF Image | Supercritical Carbon Dioxide Isolation of Cellulose Nanofibre
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