Novel Methods for Producing Cellulose Nanocrystals from Lignocellulosic Materials and Cellulose Nanocrystals Reinforced Polymer Nanocomposites

Cellulose nanocrystals (nanofibers) represent a new emerging biological source of reinforcing biofillers. In this dissertation, we report the results of a study to produce cellulose nanocrystals from recycled pulp, hardwood and pine dissolving pulps using maleic acid, ultrasonic-assisted (sono-chemical treatment) and enzyme-mediated hydrolysis followed by fragmentation of cellulose crystallites using ultrasonic treatment. Additionally, the effect of two modes of heating: conventional and microwave, on enzyme-mediated and maleic acid hydrolysis were investigated. Cellulose nanocrystals yields from maleic acid hydrolysis of lignocellulosic materials were lower than that obtained from endoglucanase mediated hydrolysis of lignocellulosic materials. Sonochemical treatment of lignocellulosic materials produced both spherical and cylindrical cellulose nanocrystals. Yields of cellulose nanocrystals obtained from some enzyme-mediated hydrolysis treatments of lignocellulosic materials were circa 50% based on the initial weight of lignocellulosic materials. Analysis of hydroyzates enzyme-mediated hydrolysis of pulps using high-performance liquid chromatography coupled to evaporative light scattering detection analysis showed significant amount of glucose and cellobiose. Cellulose nanocrystals were characterized by a number of physical methods including light scattering, polarizing and electron microscopy and X-ray diffraction. Cellulose nanocrystals produced were incorporated into polyimide to form nanocomposites at 0, 5, 10 and 20 wt % loadings of cellulose nanocrystals. Modulus of elasticity and tensile strength of cellulose nanocrystals reinforced polyimide nanocomposites decreased with increasing loadings of cellulose nanocrystals. Thermal analyses of the nanocomposites were further carried out. Fourier transform-infrared coupled to attenuated total reflectance disc spectra of the nanocomposites revealed interaction between hydroxyl groups in cellulose nanocrystals and carbonyl groups in polyimide

Functionalization of Cellulose Nanocrystals in Choline Lactate Ionic Liquid

Cellulose nanocrystals (CNCs) are valuable nanomaterials obtained from renewable resources. Their properties make them suitable for a wide range of applications, including polymer reinforcement. However, due to their highly hydrophilic character, it is necessary to modify their surface with non-polar functional groups before their incorporation into a hydrophobic polymer matrix. In this work, cellulose nanocrystals were modified using a silane coupling agent and choline lactate, an ionic liquid derived from renewable resources, as a reaction medium. Modified cellulose nanocrystals were characterized by infrared spectroscopy, showing new peaks associated to the modification performed. X-ray diffraction was used to analyze the crystalline structure of functionalized cellulose nanocrystals and to optimize the amount of silane for functionalization. Poly(lactic acid) (PLA) nanocomposites containing 1 wt % of functionalized cellulose nanocrystals were prepared. They were characterized by field-emission scanning electron microscopy (FE-SEM) and mechanical tests. The use of choline lactate as reaction media has been shown to be an alternative method for the dispersion and silanization of the cellulose nanocrystals without the addition of an external catalyst.Financial support from the European Commission (FP7 Program, ECLIPSE project FP7-NMP-280786) is gratefully acknowledged

Cellulose nanocrystals coating – A novel paper coating for use in the graphic industry

The rising concern about the impact of printing material on the environment is pushing the graphic industry to turn towards the use of materials derived from abundant, renewable resources. The end-result of this process would be a replacement of conventional printing materials that are often derived from unsustainable resources. The aim of this study was the application of cellulose nanocrystals (CNC) coating as a novel type of sustainable coating that might eliminate use of synthetic coatings. The selected coating was prepared from cellulose nanocrystals suspension that was derived from cellulose fibrils on the laboratory scale. The coating formulation examined in this paper was not yet used on the industrial scale. Experimental research was carried out in the form of preliminary laboratory tests for offset printing application using IGT test methods of ink transfer and set-off. Paper coated with cellulose nanocrystals was used as a printing substrate, while vegetable oil-based ink was used as a printing ink in order to stay in line with environmentally preferred choice of printing materials. The results indicated an increase in surface gloss on paper coated with cellulose nanocrystals, as well as in print gloss on printed paper coated with cellulose nanocrystals. The downside of cellulose nanocrystals coating was the prolonged drying time of ink. Further research should be dedicated to improving cellulose nanocrystals coating as the formulation used in this study caused undesirable cockling and waviness on selected paper grade

Nanocellulose Fragmentation Mechanisms and Inversion of Chirality from the Single Particle to the Cholesteric Phase

Understanding how nanostructure and nanomechanics influence physical material properties on the micro- and macroscale is an essential goal in soft condensed matter research. Mechanisms governing fragmentation and chirality inversion of filamentous colloids are of specific interest because of their critical role in load-bearing and self-organizing functionalities of soft nanomaterials. Here we provide a fundamental insight into the self-organization across several length scales of nanocellulose, an important bio-colloid system with wide-ranging applications as structural, insulating and functional material. Through a combined microscopic and statistical analysis of nanocellulose fibrils at the single particle level, we show how mechanically and chemically induced fragmentation proceed in this system. Moreover, by studying the bottom-up self-assembly of fragmented carboxylated cellulose nanofibrils into cholesteric liquid crystals, we show via direct microscopic observations, that the chirality is inverted from right-handed at the nanofibril level to left-handed at the level of the liquid crystal phase. These results improve our fundamental understanding of nanocellulose and provide an important rationale for their application in colloidal systems, liquid crystals and nanomaterials

Disordered Cellulose-based Nanostructures for Enhanced Light-scattering

Cellulose is the most abundant bio-polymer on earth. Cellulose fibres, such as the one extracted form cotton or woodpulp, have been used by humankind for hundreds of years to make textiles and paper. Here we show how, by engineering light matter-interaction, we can optimise light scattering using exclusively cellulose nanocrystals. The produced material is sustainable, biocompatible and, when compared to ordinary microfibre-based paper, it shows enhanced scattering strength (x4) yielding a transport mean free path as low as 3.5 um in the visible light range. The experimental results are in a good agreement with the theoretical predictions obtained with a diffusive model for light propagation

Ultrasonication of spray- and freeze-dried cellulose nanocrystals in water

The structural and rheological properties of aqueous suspensions of spray-dried cellulose nanocrystals (CNCs) were investigated and compared to those of freeze-dried. The cellulose nanocrystals were obtained from sulfuric acid hydrolysis of wood pulp. Ultrasonication was used to disperse cellulose nanocrystals in Milli-Q water and the power applied during ultrasonication was shown to be the controlling parameter for their dispersion, more than total energy. Dynamic light scattering measurements showed a decrease of the average hydrodynamic diameter down to the same limiting value, i.e. ∼75 nm, for both spray and freeze-dried cellulose nanocrystals. Since the same maximum dispersion state was reached for both CNC types, it indicated that the spray drying process did not limit dispersion, provided that sufficient ultrasonication was provided. Moreover, no desulfation occurred during ultrasonication at ambient temperature. Strong ultrasonication also caused a decrease of intrinsic viscosity, along with an increase in maximum packing concentration. These properties were correlated to agglomerates break-up, which released both ions and water in suspension. The ionic strength increase may lead to a thinner electrostatic double layer surrounding the cellulose nanocrystals, reducing their apparent concentration

Tailoring the chemical structure of cellulose nanocrystals by amine functionalization

The surface functionalization of cellulose nanocrystals is presently considered a useful and straightforward tool for accessing very reliable biocompatible and biodegradable nanostructures with tailored physical and chemical properties. However, to date the fine characterization of the chemical appendages introduced onto cellulose nanocrystals remains a challenge, due to the low sensitivity displayed by the most common techniques towards surface functionalization. In this paper, we demonstrate the easy functionalization of cellulose nanocrystals with aliphatic and aromatic amines, demonstrating the tunability of their properties in dependence on the selected functionality. Then, we apply to colloidal suspensions of modified nanocrystals 1H NMR analysis to elucidate their surface structure. To the best of our knowledge, this is the first report where such investigation was performed on cellulose nanocrystals presenting both surface and reducing end modification. These results involve interesting implications for the fields of cultural heritage and of materials chemistry

A novel enzymatic approach to nanocrystalline cellulose preparation

In this work, conditions for an enzymatic pretreatment prior to NCC isolation from cotton linter were assessed. Different cellulase doses and reaction times were studied within an experimental design and NCC were obtained. At optimal enzymatic conditions (20U, 2 h), a total yield greater than 80% was achieved and the necessary enzymatic treatment time was reduced 90%. Different intensities of enzymatic treatments led to proportional decreases in fiber length and viscosity and also were inversely proportional to the amount of released oligosaccharides. These differences within fibers lead to quantitative differences in NCC: increase in acid hydrolysis yield, reduction of NCC surface charge and crystallinity increase. Benefits produced by enzymatic treatments did not have influence over other NCC characteristics such as their sulfur content (˜1%), size (˜200 nm), zeta potential (˜-50 mV) or degree of polymerization (˜200). Evidence presented in this work would reduce the use of harsh sulfuric acid generating a cleaner stream of profitable oligosaccharidesPostprint (author's final draft

Fat tissue equivalent phantoms for microwave applications by reinforcing gelatin with nanocellulose

Tissue mimicking phantom materials with thermal and dielectric equivalence are vital for the development of microwave diagnostics and treatment. The current phantoms representing fat tissue are challenged by mechanical integrity at relevant temperatures coupled with complex production protocols. We have employed two types of nanocellulose (cellulose nanocrystals and oxidized cellulose nanocrystals) as reinforcement in gelatin stabilized emulsions for mimicking fat tissue. The nanocellulose-gelatin stabilized emulsions were evaluated for their dielectric properties, the moduli-temperature dependence using small deformation rheology, stress-strain behavior using large deformation, and their compliance to quality assurance guidelines for superficial hyperthermia. All emulsions had low permittivity and conductivity within the lower microwave frequency band, accompanied by fat equivalent thermal properties. Small deformation rheology showed reduced temperature dependence of the moduli upon addition of nanocellulose, independent of type. The cellulose nanocrystals gelatin reinforced emulsion complied with the quality assurance guidelines. Hence, we demonstrate that the addition of cellulose nanocrystals to gelatin stabilized emulsions has the potential to be used as fat phantoms for the development of microwave diagnostics and treatment