Yousoo Han

Drying cellulose nanofibrils: in search of a suitable method

Increasing research activity on cellulose nanofibril-based materials provides great opportunities for novel, scalable manufacturing approaches. Cellulose nanofibrils (CNFs) are typically processed as aqueous suspensions because of their hydrophilic nature. One of the major manufacturing challenges is to obtain dry CNFs while maintaining their nano-scale dimensions. Four methods were examined to dry cellulose nanocrystal and nanofibrillated cellulose suspensions: (1) oven drying, (2) freeze drying (FD), (3) supercritical drying (SCD), and (4) spray-drying (SD). The particle size and morphology of the CNFs were determined via dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and morphological analysis. SCD preserved the nano-scale dimensions of the cellulose nanofibrils. FD formed ribbon-like structures of the CNFs with nano-scale thicknesses. Width and length were observed in tens to hundreds of microns. SD formed particles with a size distribution ranging from nanometer to several microns. Spray-drying is proposed as a technically suitable manufacturing process to dry CNF suspensions.

Influence of drying method on the surface energy of cellulose nanofibrils determined by inverse gas chromatography

Research and development of the renewable nanomaterial cellulose nanofibrils (CNFs) has received considerable attention. The effect of drying on the surface energy of CNFs was investigated. Samples of nanofibrillated cellulose (NFC) and cellulose nanocrystals (CNC) were each subjected to four separate drying methods: air-drying, freeze-drying, spray-drying, and supercritical-drying. The surface morphology of the dried CNFs was examined using a scanning electron microscope. The surface energy of the dried CNFs was determined using inverse gas chromatography at infinite dilution and column temperatures: 30, 40, 50, 55, and 60 °C. Surface energy measurements of supercritical-dried NFCs were performed also at column temperatures: 70, 75, and 80 °C. Different drying methods produced CNFs with different morphologies which in turn significantly influenced their surface energy. Supercritical-drying resulted in NFCs having a dispersion component of surface energy of 98.3±5.8 mJ/m(2) at 30 °C. The dispersion component of surface energy of freeze-dried NFCs (44.3±0.4 mJ/m(2) at 30 °C) and CNCs (46.5±0.9 mJ/m(2) at 30 °C) were the lowest among all the CNFs. The pre-freezing treatment during the freeze-drying process is hypothesized to have a major impact on the dispersion component of surface energy of the CNFs. The acid and base parameters of all the dried CNFs were amphoteric (acidic and basic) although predominantly basic in nature.

Method to reinforce polylactic acid with cellulose nanofibers via a polyhydroxybutyrate carrier system.

The elastic moduli of PLA reinforced with 5 and 10wt.% CNF with the carrier, at a frequency (ω) of 0.07, were 67% and 415% higher, respectively, than that of neat PLA. The shear viscosity at a shear rate of 0.01 (η0.01) for PLA+10wt.% CNF was 32% higher than that of the neat PLA matrix. The η0.01 of PLA reinforced with 5wt.% CNF and the PHB carrier was similar to neat PLA. The tensile and flexural moduli of elasticity of the nanocomposites continuously increased with increased CNF loading. The results of the mechanical property measurements are in accordance with the rheological data. The CNF appeared to be better dispersed (less-aggregated nanofibers) in the PLA reinforced with 5wt.% CNF and the PHB carrier. Possible applications for the composites studied in this research are packaging materials, construction materials, and auto parts for interior applications.

Thermal Analysis of Micro- and Nano-Lignocellulosic Reinforced Styrene Maleic Anhydride Composite Foams

The aim of this study was to measure the thermal properties of foamed nano/macro filler–reinforced styrene maleic anhydride (SMA) composites. SMA (66%) as a polymer matrix (10% maleic anhydride content) and various fillers including wood flour, starch, α-cellulose, microcrystalline cellulose and cellulose nanofibrils as reinforcing agents (30%) and lubricant (4%) were used to manufacture the composites in a twin-screw extruder. According to the thermogravimetric analysis (TGA) results, thermal degradation of all the foamed composites was found to be lower than that of SMA composites. The storage modulus values were negatively affected with a second time foaming (reprocessing [recycling] the initially processed composites a second time), as were loss modulus and Tg. As a result, second-time-foamed composite modulus values were lower than those of the foamed composites. According to the melt flow index (MFI) results, viscosity of the SMA was found to increase with the addition of fillers.

Mechanical Property Characterization of Fiber-Reinforced Polymer Wood-Polypropylene Composite Panels Manufactured Using a Double Belt Pressing Technology

AbstractA novel manufacturing process for wood-polypropylene composite (WPC) panels reinforced with fiber-reinforced polymer (FRP) sheets was implemented using a double belt pressing technology. FRP sheets were placed on both sides of the WPC agglomerates during fabrication, which resulted in increased productivity and reduced thermal stresses compared with secondary bonding processes. Significant improvements in the mechanical properties of the FRP reinforced sheet panels were found during flexural and tensile tests on the coupon level. Even with addition of only one layer of FRP reinforcement on both sides of a WPC panel, the flexural modulus and strength increased by a factor of 2.6 and 3.8, respectively. Furthermore, the flexural and tensile properties of the WPC material considered in this study were found to be superior compared with the properties of an extruded WPC material. The changes in the flexural modulus of the FRP reinforced WPC panels with respect to the number of FRP layers were predicted...

Influence of Micro- and Nanonatural Fillers on Mechanical and Physical Properties of Foamed SMA Composites

This study is to investigate the reinforcing effects of fillers on mechanical and physical properties of foamed styrene-maleic anhydride (SMA) composites. According to the results, the best foaming was determined for starch reinforced SMA composite. The best result of expansion ratio was found as 22.75% to SMA/starch composites. Stereo light microscopy results demonstrated that the foamed cell distribution is heterogeneous and composed of two sections. The minimum density was found as 0.64 g/cm3 for foamed SMA/starch composites. Mechanical properties of all foamed composites were found to be low as compared to neat SMA composite.

Morphological characterization of foamed natural filler-reinforced styrene maleic anhydride (SMA) composites

The aim of this study is to investigate the foaming of styrene maleic anhydride (SMA) matrix composites with a physical foaming agent, created during the reactive extrusion of natural fillers and SMA. The effect of lubricant on the foaming of SMA composites was also investigated. Whether particle’s crystallinity and hydroxyl number had any effect on cell size and cell density was also studied. The results showed that the greatest cell size and expansion occurred in the starch reinforced SMA composite which also exhibited the highest hydroxyl number and water by-product from reactive extrusion. Whereas microcrystalline cellulose-SMA composite exhibited the least cell number and expansion after extrusion because of the high crystallinity of MCC and the low hydroxyl number. Scanning electron microscopy results revealed that the cell distribution in foamed samples was heterogeneous and cell density increased from the core to skin layer. The results showed that hydroxyl number has an important effect on foaming and cell nucleation of the composites, and cell properties changed with filler’s percentage crystallinity.

Fluorocarbon Barriers on Starch Foam Tray Surfaces Through SF6 Cold Plasma Treatment

Starch foam trays were produced using a laboratory model-baking machine. Surfaces of the trays were treated with SF6 plasma to create fluorine-rich layers on the surfaces. RF power, gas pressure and reaction time were varied to evaluate the effects of each parameter on fluorination of surfaces. The fluorine concentrations of treated sample surfaces ranged from 43.6% to 57.9%. For reaction time dependence, the ratio of oxygen to carbon was decreased since hydroxyl groups might be replaced by fluoro-compounds. Gas pressure and RF power affected fluorination mechanism, which resulted in different shapes of carbon and fluorine ESCA high resolution spectra. Plasma-treated samples have higher contact angles and less uptakes of liquid and vapor water. AFM showed different morphology of untreated and SF6 plasma-treated surfaces.

Southern pine impregnated with silicate solution containing cellulose nanofibrils

Abstract A drying process has been tested to impregnate southern pine (Pinus spp.) samples with sodium silicate solution. The effect of adding cellulose nanofibrils in the treating solution was also studied. The mechanical tests show that the flexural modulus of rupture (MOR) and modulus of elasticity (MOE) increased significantly with increasing concentration of sodium silicate. The highest MOR and MOE of the treated samples were 170±13 MPa and 19±1 GPa, respectively, while the corresponding data of the control sample were 98±8 MPa and 11±1 GPa respectively. Deposition of polymerized silicate in the wood cell lumina was observed. The compression strength was improved by the incorporation of polymerized silicate to increase the measured flexural properties. The presence of cellulose nanofibrils in the sodium silicate solution had no effect.