Stephen J. Eichhorn

Isolation and characterization of microcrystalline cellulose from oil palm biomass residue

In this work, we successfully isolated microcrystalline cellulose (MCC) from oil palm empty fruit bunch (OPEFB) fiber-total chlorine free (TCF) pulp using acid hydrolysis method. TCF pulp bleaching carried out using an oxygen-ozone-hydrogen peroxide bleaching sequence. Fourier transform infrared (FT-IR) spectroscopy indicates that acid hydrolysis does not affect the chemical structure of the cellulosic fragments. The morphology of the hydrolyzed MCC was investigated using scanning electron microscopy (SEM), showing a compact structure and a rough surface. Furthermore, atomic force microscopy (AFM) image of the surface indicates the presence of spherical features. X-ray diffraction (XRD) shows that the MCC produced is a cellulose-I polymorph, with 87% crystallinity. The MCC obtained from OPEFB-pulp is shown to have a good thermal stability. The potential for a range of applications such as green nano biocomposites reinforced with this form of MCC and pharmaceutical tableting material is discussed.

Oriented surfaces of adsorbed cellulose nanowhiskers promote skeletal muscle myogenesis.

Cellulose nanowhiskers (CNWs) are high-aspect-ratio rod-like nanoparticles prepared via partial hydrolysis of cellulose. For the first time, CNWs have been extracted from the marine invertebrate Ascidiella aspersa, yielding animal-derived CNWs with particularly small diameters of only a few nanometres. Oriented surfaces of adsorbed CNWs were prepared using a flexible and facile spin-coating method, allowing the modulation of CNW adsorption and relative orientation. Due to the shape and nanoscale dimensions of the CNWs, C2C12 myoblasts adopted increasingly oriented morphologies in response to more densely adsorbed and oriented CNW surfaces. In addition, the degree of myoblast fusion was greatest on the highly oriented CNW surfaces, and even low-orientation CNW surfaces promoted more extensive fusion than flat control surfaces. Highly oriented multinuclear myotubes formed on the oriented CNW surfaces and fibrillar fibronectin deposited on the surfaces was also modelled in a highly oriented arrangement after only 4 days in culture. With a mean feature height of only 5-6 nm, the CNW surfaces present the smallest features ever reported to induce contact guidance in skeletal muscle myoblasts, highlighting the potential for nanoscale materials for engineering oriented tissues such as skeletal muscle.

Biomimetic phantom for the validation of diffusion magnetic resonance imaging

A range of advanced diffusion MRI (dMRI) techniques are currently in development which characterize the orientation of white matter fibers using diffusion tensor imaging (DTI). There is a need for a physical phantom with microstructural features of the brains white matter to help validate these methods.

Enhanced ductility and tensile properties of hybrid montmorillonite/cellulose nanowhiskers reinforced polylactic acid nanocomposites

Montmorillonite (MMT)/cellulose nanowhiskers (CNW) reinforced polylactic acid (PLA) hybrid nanocomposites were prepared by solution casting. CNW were isolated from microcrystalline cellulose using a chemical swelling method. An initial study showed that the optimum MMT content, for mechanical properties, in a PLA/MMT nanocomposite is five parts per hundred parts of polymer (phr). Various amounts of CNW were added to the optimum formulation of PLA/MMT to produce PLA/MMT/CNW hybrid nanocomposites. FT-IR analysis indicated the formation of some polar interactions, resulting in enhanced tensile properties of the hybrid nanocomposites. The highest tensile strength for the hybrid nanocomposites was obtained for a 1 phr CNW content. Young’s modulus was also found to increase with an increasing CNW content. Interestingly, the strain to failure (or ductility) of the hybrid nanocomposites increased significantly from ~10 to ~90xa0% with the addition of 1 phr CNW. This increase in ductility was proposed to be due to the nucleation of crazes and the formation of shear bands in the PLA.

Orientation of cellulose nanocrystals in electrospun polymer fibres

Polystyrene and poly(vinyl alcohol) nanofibres containing cellulose nanocrystals (CNCs) were successfully produced by electrospinning. Knowledge of the local orientation of CNCs in electrospun fibres is critical to understand and exploit their mechanical properties. The orientation of CNCs in these electrospun fibres was investigated using transmission electron microscopy (TEM) and Raman spectroscopy. A Raman band located at ~1095xa0cm−1, associated with the C–O ring stretching of the cellulose backbone, was used to quantify the orientation of the CNCs within the fibres. Raman spectra were fitted using a theoretical model to characterize the extent of orientation. From these data, it is observed that the CNCs have little orientation along the direction parallel to the axis of the fibres. Evidences for both oriented and non-oriented regions of CNCs in the fibres are presented from TEM images of nanofibres. These results contradict previously published work in this area and micromechanical modelling calculations suggest a uniform orientation of CNCs in electrospun polymer fibres. It is demonstrated that this explains why the mechanical properties of electrospun fibre mats containing CNCs are not always the same as that would be expected for a fully oriented system.

Orientation and deformation of wet-stretched all-cellulose nanocomposites

Cellulose nanowhiskers (CNWs) are used to reinforce an all-cellulose composite. This composite comprises a matrix formed by dissolution of plant cellulose using a lithium chloride/N,N-dimethylacetamide solvent system into which high stiffness CNWs are dispersed. It is shown that the Young’s modulus and strength of the composites decrease dramatically when the material is wetted. Raman spectroscopy is used to show how the two bands located at 1095 and 895xa0cm−1 can be used to follow both the molecular deformation and orientation of the CNWs and the matrix phases, respectively, both in the wet and dry states. The disruption of the stress transfer process is observable via the lack of shift in the position of both Raman peaks upon deformation in the wet state. This shift is restored when the samples are dried, and some recovery is noted in the materials. The orientation of both the matrix and CNWs phases is monitored during stretching, both in wet and dry states. Little orientation of the CNWs is observed at low strains. Significant orientation of the CNWs occurs at high strain, for samples deformed both in the wet and dry states. The most significant orientation is observed for cellulose molecular chains present in the matrix phase. It is thought that this component of the orientation contributes significantly to the mechanical properties of the nanocomposites. The use of these approaches opens up opportunities to use wet processing to induce orientation of cellulose nanofibers, and to monitor the development of mechanical properties using Raman spectroscopy in a wet environment.

Production and cross-sectional characterization of aligned co-electrospun hollow microfibrous bulk assemblies

The development of co-electrospun (co-ES) hollow microfibrous assemblies of an appreciable thickness is critical for many practical applications, including filtration membranes and tissue-mimicking scaffolds. In this study, thick uniaxially aligned hollow microfibrous assemblies forming fiber bundles and strips were prepared by co-ES of polycaprolactone (PCL) and polyethylene oxide (PEO) as shell and core materials, respectively. Hollow microfiber bundles were deposited on a fixed rotating disc, which resulted in non-controllable cross-sectional shapes on a macroscopic scale. In comparison, fiber strips were produced with tuneable thickness and width by additionally employing an x–y translation stage in co-ES. Scanning electron microscopy (SEM) images of cross-sections of fiber assemblies were analyzed to investigate the effects of production time (from 0.5 h to 12 h), core flow rate (from 0.8 mL/h to 2.0 mL/h) and/or translation speed (from 0.2 mm/s to 5 mm/s) on the pores and porosity. We observed significant changes in pore size and shape with core flow rate but the influence of production time varied; five strips produced under the same conditions had reasonably good size and porosity reproducibility; pore sizes didnt vary significantly from strip bottom to surface, although the porosity gradually decreased and then returned to the initial level.

Stress Transfer Quantification in Gelatin-Matrix Natural Composites with Tunable Optical Properties

This work reports on the preparation and characterization of natural composite materials prepared from bacterial cellulose (BC) incorporated into a gelatin matrix. Composite morphology was studied using scanning electron microscopy and 2D Raman imaging revealing an inhomogeneous dispersion of BC within the gelatin matrix. The composite materials showed controllable degrees of transparency to visible light and opacity to UV light depending on BC weight fraction. By adding a 10 wt % fraction of BC in gelatin, visible (λ = 550 nm) and UV (λ = 350 nm) transmittances were found to decrease by ∼35 and 40%, respectively. Additionally, stress transfer occurring between the gelatin and BC fibrils was quantified using Raman spectroscopy. This is the first report for a gelatin-matrix composite containing cellulose. As a function of strain, two distinct domains, both showing linear relationships, were observed for which an average initial shift rate with respect to strain of -0.63 ± 0.2 cm(-1)%(-1) was observed, followed by an average shift rate of -0.25 ± 0.03 cm(-1)%(-1). The average initial Raman band shift rate value corresponds to an average effective Youngs modulus of 39 ± 13 GPa and 73 ± 25 GPa, respectively, for either a 2D and 3D network of BC fibrils embedded in the gelatin matrix. As a function of stress, a linear relationship was observed with a Raman band shift rate of -27 ± 3 cm(-1)GPa(-1). The potential use of these composite materials as a UV blocking food coating is discussed.

Preparation and characterization of polycaprolactone microspheres by electrospraying

ABSTRACT The ability to reproducibly produce and effectively collect electrosprayed polymeric microspheres with controlled morphology and size in bulk form is challenging. In this study, microparticles were produced by electrospraying polycaprolactone (PCL) of various molecular weights and solution concentrations in chloroform, and by collecting materials on different substrates. The resultant PCL microparticles were characterized by optical and electron microscopy to investigate the effect of molecular weight, solution concentration, applied voltage, working distance, and flow rate on their morphology and size. The work demonstrates the key role of a moderate molecular weight and/or solution concentration in the formation of spherical PCL particles via an electrospraying process. Increasing the applied voltage was found to produce smaller and more uniform PCL microparticles. There was a relatively low increase in the particle average size with an increase in the working distance and flow rate. Four types of substrates were adopted to collect electrosprayed PCL particles: a glass slide, aluminium foil, liquid bath, and copper wire. Unlike 2D bulk structures collected on the other substrates, a 3D tubular structure of microspheres was formed on the copper wire which could find application in the construction of 3D tumor mimics.

Bio-inspired iridescent layer-by-layer assembled cellulose nanocrystal Bragg stacks

Layer-by-layer (LbL) assembly was used to fabricate a synthetic analogue of the color producing multilayered structure commonly found in many biological systems, particularly Coleoptera. The resulting iridescent films comprise multiple LbL-deposited layers designed to control color appearance through the materials refractive indices and individual multilayer layer thicknesses. The fabricated systems, referred to as Bragg stacks, exhibited very similar optical behavior to the model and the beetle, selectively reflecting the desired color in a narrow band of visible wavelengths and displaying iridescent behavior.