Hydrogels of cellulose acetate crosslinked with pyromellitic dianhydride: part I: synthesis and swelling kinetics

This work describes the synthesis of hydrogels of cellulose acetate (AC) crosslinked with 1,2,4,5-benzenotetracarboxylic dianhydride (PMDA). The crosslinking reaction was monitored by FTIR. Analysis of aromatic fragments from the alkaline hydrolysis of the gels by UV spectroscopy indicated that an increase in the stoichiometric ratio of dianhydride resulted in higher degrees of crosslinking. The non-porous nature of the gels was confirmed by analysis of nitrogen adsorption. Water absorption isotherms showed that as the temperature and degree of crosslinking increased, the percentage of water absorbed at equilibrium (%Seq) also increased. The hydrogels presented second order swelling kinetics.

ISOLATION AND CHARACTERIZATION OF NANOFIBRILLATED CELLULOSE FROM OAT HULLS

The objectives of this work were to investigate the microstructure, crystallinity and thermal stability of nanofibrillated cellulose obtained from oat hulls using bleaching and acid hydrolysis at a mild temperature (45 ºC) followed by ultrasonication. The oat hulls were bleached with peracetic acid, and after bleaching, the compact structure around the cellulosic fibers was removed, and the bundles became individualized. The extraction time (30 or 60 min) did not affect the properties of the nanofibrillated cellulose, which presented a higher crystallinity index and thermal stability than the raw material (oat hulls). The nanocellulose formed interconnected webs of tiny fibers with diameters of 70-100 nm and lengths of several micrometers, producing nanofibers with a relatively high aspect ratio, thus indicating that these materials are suitable for polymer reinforcement.

HYDROLYTIC DEGRADATION BEHAVIOR OF PLLA NANOCOMPOSITES REINFORCED WITH MODIFIED CELLULOSE NANOCRYSTALS

Bionanocomposites derived from poly(L-Lactide) (PLLA) were reinforced with chemically modified cellulose nanocrystals (m-CNCs). The effects of these modified cellulose nanoparticles on the mechanical and hydrolytic degradation behavior of polylactide were studied. The m-CNCs were prepared by a method in which hydrolysis of cellulose chains is performed simultaneously with the esterification of hydroxyl groups to produce modified nanocrystals with ester groups. FTIR, elemental analysis, TEM, XRD and contact angle measurements were used to confirm and characterize the chemical modifications of the m-CNCs. These bionanocomposites gave considerably better mechanical properties than neat PLLA based on an approximately 100% increase in tensile strength. Due to the hydrophobic properties of the esterified nanocrystals incorporated into a polymer matrix, it was also demonstrated that a small amount of m-CNCs could lead to a remarkable decrease in the hydrolytic degradation rate of the biopolymer. In addition, the m-CNCs considerably delay the degradation of the nanocomposite by providing a physical barrier that prevents the permeation of water, which thus hinders the overall absorption of water into the matrix. The results obtained in this study show the nanocrystals can be used to reinforce polylactides and fine-tune their degradation rates in moist or physiological environments.

A NOVEL POLYACRYLAMIDE-BASED HYDROGEL CROSSLINKED WITH CELLULOSE ACETATE AND PREPARED BY PRECIPITATION POLYMERIZATION

The synthesis of polyacrylamide-cellulose acetate hydrogels by precipitation polymerization in acetone solution is reported herein. These hydrogels exhibit smaller swelling ratios and larger compression moduli than homo polyacrylamide hydrogels. For cellulose acetate concentrations above 20 wt.%, hydrogels with N,N'-methylenebisacrylamide as a crosslinker exhibit swelling ratios and compression moduli similar to those of the hydrogels without the crosslinker. A possible explanation for this behavior is that cellulose acetate crosslinks polyacrylamide via free-radical reaction. The hydrogels obtained without the N,N'-methylenebisacrylamide crosslinker exhibit compression moduli up to 1.7 MPa, making them suitable for tissue engineering applications such as cartilage replacement.

Granulation tissue formation -The effect of hydroxyapatite coating of cellulose on cellular differentiation

Haavan jyväiskudoksen muodostuminen – Hydroksiapatiittipinnoi-tetun selluloosasienen vaikutus solujen erilaistumiseen paranemisprosessin aikana Etsittäessä uusia luun bioyhteensopivia täytemateriaaleja selluloosasieni päällystettiin luun koostumusta muistuttavalla runsaasti piitä sisältävällä hydroksiapatiittikerroksella. Vastoin odotuksia hydroksiapatiittipinnoitettu selluloosa ei parantanut luun kasvua, vaan päinvastoin ylläpiti tulehdusta ja sidekudossolujen hakeutumista vamma-alueelle. Ihon alle implantoituna sama sienimateriaali edisti merkittävästi haavan verekkään jyväiskudoksen kasvua. Tämän löydöksen perusteella hydroksiapatiittipinnoitetun selluloosasienen vaikutusta haavan soluihin paranemisprosessin aikana tutkittiin tarkemmin ja havaittiin, että tulehdussolujen lisäksi sieniin kertyi tavallista enemmän sekä hematopoieettisia että mesenkymaalisia kantasoluja. Hematopoieettiset kantasolut sijaitsevat luuytimessä lähellä luun sisäpintaa. Luun hydroksiapatiitista vapautuu kalsiumioneja luun jatkuvan fysiologisen uudismuodostuksen ja hajottamisen yhteydessä. Kantasolut etsiytyvät luuytimeen kalsiumia aistivien reseptorien välityksellä. Koska luun pintakerrosta muistuttavasta hydroksiapatiittipinnoitteesta vapautuu kalsiumia, tämän ajateltiin toimivan selityksenä sille, että hematopoieettiset kantasolut hakeutuvat runsaslukuisesti juuri hydroksiapatiittipinnoitettuihin selluloosasieniin. Tämän hypoteesin mukaisesti hydroksiapatiittipinnoitettujen selluloosapalkkien läheisyydestä löydettiin suuria määriä kalsiumreseptoreja sisältäviä soluja. Jatkotutkimuksissa todettiin lisäksi, että hematopoieettiset kantasolut pystyivät sienissä erilaistumaan hemoglobiinia tuottaviksi soluiksi. Havaittujen punasolulinjan merkkiaineiden perusteella näyttäisikin siltä, että haavan paranemiskudoksessa tapahtuu paranemisen aikana ekstramedullaarista erytropoieesia. Nämä soluja ohjaavat vaikutukset saattavat olla hyödyllisiä vaikeasti paranevien haavojen hoidossa.

Adsorption of hydrogen sulfide by modified cellulose nano/microcrystals

Hydrogen sulfide is toxic and hazardous pollutant. It has been under great interest for past few years because of all the time tighten environmental regulations and increased interest of mining. Hydrogen sulfide gas originates from mining and wastewater treatment systems have caused death in two cases. It also causes acid rains and corrosion for wastewater pipelines. The aim of this master thesis was to study if chemically modified cellulose nanocrystals could be used as adsorbents to purify hydrogen sulfide out from water and what are the adsorption capacities of these adsorbents. The effects of pH and backgrounds on adsorption capacities of different adsorbents are tested. In theoretical section hydrogen sulfide, its properties and different purification methods are presented. Also analytical detection methods for hydrogen sulfide are presented. Cellulose nano/microcrystals, properties, application and different modification methods are discussed and finally theory of adsorption and modeling of adsorption is shortly discussed. In experimental section different cellulose nanocrystals based adsorbents are prepared and tested at different hydrogen sulfide concentrations and in different conditions. Result of experimental section was that the highest adsorption capacity at one component adsorption had wet MFC/CaCO3. At different pH the adsorption capacities of adsorbents changed quite dramatically. Also change of hydrogen sulfide solution background did have effect on adsorption capacities. Although, when tested adsorbents’ adsorption capacities are compared to those find in literatures, it seems that more development of MFC based adsorbents is needed.

Synthesis and Characterization of Cellulose fiber-silica nanocomposites

Cellulose fiber-silica nanocomposites with novel mechanical, chemical and thermal properties have potential to be widely applied in different area. Monodispered silica nanoparticles play an important role in enhancing hybrids properties of hardness, strength, thermal stability etc. On the other hand, cellulose is one of the world’s most abundant and renewable polymers and possesses several unique properties required in many areas and biomedicine. The aim of this master thesis is to study if silica particles from reaction of sodium silicate and sulphuric acid can be adsorbed onto cellulose fiber surfaces via in situ growth. First, nanosilica particles were synthesized. Effect of pH and silica contents were tested. In theoretical part, introduction of silica, methods of preparation of nanosilica from sodium silicate, effect factors and additives were discussed. Then, cellulose fiber-silica nanocomposites were synthesis via route from sodium silicate and route silicic acid. In the experiment of route from sodium silicate, the effects of types of sodium silicate, pH and target ratio of silica to fiber were investigated. From another aspect, the effects of types of sodium silicate, fiber concentration in mixture solution and target ratio of silica to fiber were tested in the experiment of route from silicic acid. Samples were investigated via zeta potential measurement, particle size distribution, ash content measurement and Scanning Electron Microscopy (SEM). The Results of the experiment of preparing silica sol were that the particle size of silica sol was smaller prepared in pH 11.7 than that prepared in pH 9.3. Then in the experiment of synthesis of cellulose fiber-silica nanocomposites, it was concluded that the zeta potential of all the samples were around -16 mV and the highest ash content of all the samples was only 1.4%. The results of SEM images showed only a few of silica particles could be observed on the fiber surface, which corresponded to the value of ash content measurement.

Dietary cellulose has no effect on the regeneration of hemoglobin in growing rats with iron deficiency anemia

The objective of the present study was to determine the effect of cellulose on intestinal iron absorption in rats during recovery from iron deficiency anemia. Twenty-one-day-old male Wistar-EPM rats were fed an iron-free ration for two weeks to induce anemia. At 5 weeks of age, the rats were divided into two groups (both groups receiving 35 mg of elemental iron per kg diet): cellulose group (N = 12), receiving a diet containing 100 g of cellulose/kg and control (N = 12), receiving a diet containing no cellulose. The fresh weight of the feces collected over a 3-day period between the 15th and 18th day of dietary treatment was 10.7 ± 3.5 g in the group receiving cellulose and 1.9 ± 1.2 g in the control group (P<0.001). Total food intake was higher in the cellulose group (343.4 ± 22.0 g) than in the control (322.1 ± 13.1 g, P = 0.009) during the 3 weeks of dietary treatment. No significant difference was observed in weight gain (cellulose group = 132.8 ± 19.2, control = 128.0 ± 16.3 g), hemoglobin increment (cellulose group = 8.0 ± 0.8, control = 8.0 ± 1.0 g/dl), hemoglobin level (cellulose group = 12.3 ± 1.2, control = 12.1 ± 1.3 g/dl) or in hepatic iron levels (cellulose group = 333.6 ± 112.4, control = 398.4 ± 168.0 µg/g dry tissue). We conclude that cellulose does not adversely affect the regeneration of hemoglobin, hepatic iron level or the growth of rats during recovery from iron deficiency anemia.

Functional cellulose microspheres for pharmaceutical applications

Dissolving cellulose is the first main step in preparing novel cellulosicmaterials. Since cellulosic fibres cannot be easily dissolved in water-based solvents, fibres were pretreated with ethanol-acid solution prior to the dissolution. Solubility and changes on the surface of the fibres were studied with microscopy and capillary viscometry. After the treatment, the cellulose fibres were soluble in alkaline urea-water solvent. The nature of this viscous solution was studied rheologically. Cellulose microspheres were prepared by extruding the alkaline cellulose solution through the needle into an acidic medium. By altering the temperature and acidity of the mediumit was possible to adjust the specific surface area and pore sizes of themicrospheres. A typical skin-core structure was found in all samples. Microspheres were oxidised in order to introduce anionic carboxylic acid groups (AGs). Anionic microspheres are more hydrophilic; their water-uptake increased 25 times after oxidation and they could swell almost to their original state (88%) after drying and shrinking. Swelling was studied in simulated physiological environments, corresponding to stomach acid and intestines (pH 1.2-7.4). Oxidised microspheres were used as a drug carriers. They demonstrated a highmass uniformity, which would enable their use for personalised dosing among different patients, including children. The drug was solidified in microspheres in amorphous form. This enhanced solubility and could be used for more challenging drugs with poor solubility. The pores of themicrospheres also remained open after the drug was loaded and they were dried. Regardless of the swelling, the drug was released at a constant rate in all environments.

Stability and properties of cellulose-sodium hydroxide solution systems

Since cellulose is a linear macromolecule it can be used as a material for regenerated cellulose fiber products e.g. in textile fibers or film manufacturing. Cellulose is not thermoformable, thus the manufacturing of these regenerated fibers is mainly possible through dissolution processes preceding the regeneration process. However, the dissolution of cellulose in common solvents is hindered due to inter- and intra-molecular hydrogen bonds in the cellulose chains, and relatively high crystallinity. Interestingly at subzero temperatures relatively dilute sodium hydroxide solutions can be used to dissolve cellulose to a certain extent. The objective of this work was to investigate the possible factors that govern the solubility of cellulose in aqueous NaOH and the solution stability. Cellulose-NaOH solutions have the tendency to form a gel over time and at elevated temperature, which creates challenges for further processing. The main target of this work was to achieve high solubility of cellulose in aqueous NaOH without excessively compromising the solution stability. In the literature survey an overview of the cellulose dissolution is given and possible factors contributing to the solubility and solution properties of cellulose in aqueous NaOH are reviewed. Furthermore, the concept of solution rheology is discussed. In the experimental part the focus was on the characterization of the used materials and properties of the prepared solutions mainly concentrating on cellulose solubility and solution stability.

Dexamethasone and sodium carboxymethyl cellulose prevent postoperative intraperitoneal adhesions in rats

We aimed to evaluate the effects of the barrier agent sodium carboxymethyl cellulose (SCMC) with and without dexamethasone for the prevention of postoperative adhesion formation in a rat model of postoperative peritoneal adhesion. A total of 160 three-month old male and female Wistar rats underwent a laparotomy, and adhesions were induced by ileocecal abrasion. Rats were randomly assigned to 4 groups (n=40 each): group A, untreated; group B, treated with SCMC only; group C1, treated with SCMC + 3 mg dexamethasone, and group C2, treated with SCMC + 8 mg dexamethasone. After 12 days, adhesion formation and histopathological changes were compared. In groups A, B, C1, and C2, the mortality rates were 10, 5, 5, and 5%, respectively. In groups C1 and C2, the adhesions were filmy and easy to dissect and were milder compared with those in groups A and B. The total adhesion score in group C1 (3.38±0.49) was significantly lower than that of group B (6.01±0.57; P<0.01) or group A (8.01±0.67; P<0.05). There was no significant difference in adhesion formation between groups C1 and C2. Compared with groups A and B, groups C1 and C2 exhibited milder histopathological changes. SCMC in combination with dexamethasone can prevent adhesion formation and is a better barrier agent than SCMC alone. The safety and feasibility of SCMC in combination with dexamethasone to prevent adhesion formation after abdominal surgery warrants further clinical study.

Ultrafiltration performance of PVDF, PES, and cellulose membranes for the treatment of coconut water (Cocos nucifera L.)

Ultrafiltration (UF) inhibits the enzymatic activity which is responsible for color changes of coconut water without the need for heat treatment. In the present study, UF performance in terms of the permeate flux and enzymatic retention of the coconut water was evaluated at laboratory unit (LU) and pilot unit (PU). The membranes studied were polyethersulfone 150 kDa (UP150), polyvinylidene fluoride 150 kDa (UV150) and cellulose 30 kDa (UC030). The UP150 membrane showed the best permeate flux. The UC030 membrane showed the lowest flux, but it resulted in 100% enzymatic retention, while the other membranes showed enzymatic retentions between 71 and 85%. The application of the UC030 in the pilot unit (PU) resulted in a flux value higher than that obtained in the LU due to the tangential velocity effect. The UC030 membrane has proved adequate for industrial applications.

Adsorption capacity of phenolic compounds onto cellulose and xylan

The interaction between three phenolic compounds (catechin, caffeic acid and ferulic acid) onto two dietary fibres (cellulose and xylan) has been evaluated to inquire possible interferences on the biodisponibility of phenolic compounds. The adsorption kinetics were performed using solutions containing 100 mg/L of phenolic compounds during a contact time ranging between 10 and 120 minutes at pH 2.0, 4.5, and 7.0. After the kinetics, isotherms were obtained using phenolic compounds concentration ranging between 10 and 80 mg/L during 60 minutes, at pH 2.0 and 7.0 and temperature of 36 °C. Results indicate that adsorbed quantities mainly changed in function of pH, however the maximum adsorption was only of 0.978 mg of caffeic acid/g of xylan at pH 2 and after 60 min. Redlich-Peterson model were able to predict the adsorption isotherms of all phenolic compounds onto cellulose, except for caffeic acid at pH 7.0. The low adsorption capacities observed suggest that both dietary fibres are unable to compromise the biodisponibility of phenolic compounds, especially in the small intestine, where they are partially absorbed.

Développement de méthodes analytiques de séparation des produits de digestion enzymatique des dérivés de cellulose

La cellulose et ses dérivés sont utilisés dans un vaste nombre d’applications incluant le domaine pharmaceutique pour la fabrication de médicaments en tant qu’excipient. Différents dérivés cellulosiques tels que le carboxyméthylcellulose (CMC) et l’hydroxyéthylcellulose (HEC) sont disponibles sur le commerce. Le degré de polymérisation et de modification diffèrent énormément d’un fournisseur à l’autre tout dépendamment de l’origine de la cellulose et de leur procédé de dérivation, leur conférant ainsi différentes propriétés physico-chimiques qui leurs sont propres, telles que la viscosité et la solubilité. Notre intérêt est de développer une méthode analytique permettant de distinguer la différence entre deux sources d’un produit CMC ou HEC. L’objectif spécifique de cette étude de maitrise était l’obtention d’un profil cartographique de ces biopolymères complexes et ce, par le développement d’une méthode de digestion enzymatique donnant les oligosaccharides de plus petites tailles et par la séparation de ces oligosaccharides par les méthodes chromatographiques simples. La digestion fut étudiée avec différents paramètres, tel que le milieu de l’hydrolyse, le pH, la température, le temps de digestion et le ratio substrat/enzyme. Une cellulase de Trichoderma reesei ATCC 26921 fut utilisée pour la digestion partielle de nos échantillons de cellulose. Les oligosaccharides ne possédant pas de groupements chromophores ou fluorophores, ils ne peuvent donc être détectés ni par absorbance UV-Vis, ni par fluorescence. Il a donc été question d’élaborer une méthode de marquage des oligosaccharides avec différents agents, tels que l’acide 8-aminopyrène-1,3,6-trisulfonique (APTS), le 3-acétylamino-6-aminoacridine (AA-Ac) et la phénylhydrazine (PHN). Enfin, l’utilisation de l’électrophorèse capillaire et la chromatographie liquide à haute performance a permis la séparation des produits de digestion enzymatique des dérivés de cellulose. Pour chacune de ces méthodes analytiques, plusieurs paramètres de séparation ont été étudiés.

Les propriétés mécaniques du réseau cellulose/xyloglucanes dans la croissance apicale du tube pollinique

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal