Modification of xylan via an oxidation-reduction reaction

Xylan is a biopolymer readily available from forest resources. Various modification methods, including oxidation with sodium periodate, have been shown to facilitate the engineering applications of xylan. However, modification procedures are often optimized for semicrystalline high molecular weight polysaccharide cellulose rather than for lower molecular weight and amorphous polysaccharide xylan. This paper elucidates the procedure for the periodate oxidation of xylan into dialdehyde xylan and its further reduction into a dialcohol form and is focused on the modification work up. The oxidation–reduction reaction decreased the molecular weight of xylan while increased the dispersity more than 50%. Unlike the unmodified xylan, all the modified grades could be solubilized in water, which we see essential for facilitating the future engineering applications of xylan. The selection of quenching and purification procedures and pH-adjustment of the reduction step had no significant effect on the degree of oxidation, molecular weight and only a minor effect on the hydrodynamic radius in water. Hence, it is possible to choose the simplest oxidation-reduction route without time consuming purification steps within the sequence.Peer reviewe

Dynamic and Static Assembly of Sulfated Cellulose Nanocrystals with Alkali Metal Counter Cations

Sulfate groups on cellulose particles such as cellulose nanocrystals (CNCs) provide colloidal stability credit to electrostatic repulsion between the like-charged particles. The introduction of sodium counter cations on the sulfate groups enables drying of the CNC suspensions without irreversible aggregation. Less is known about the effect of other counter cations than sodium on extending the properties of the CNC particles. Here, we introduce the alkali metal counter cations, Li+, Na+, K+, Rb+, and Cs+, on sulfated CNCs without an ion exchange resin, which, so far, has been a common practice. We demonstrate that the facile ion exchange is an efficient method to exchange to any alkali metal cation of sulfate half esters, with exchange rates between 76 and 89%. The ability to form liquid crystalline order in rest was observed by the presence of birefringence patterns and followed the Hofmeister series prediction of a decreasing ability to form anisotropy with an increasing element number. However, we observed the K-CNC rheology and birefringence as a stand-out case within the series of alkali metal modifications, with dynamic moduli and loss tangent indicating a network disruptive effect compared to the other counter cations, whereas observation of the development of birefringence patterns in flow showed the absence of self- or dynamically-assembled liquid crystalline order

Unmodified multi-wall carbon nanotubes in polylactic acid for electrically conductive injection-moulded composites

Tailoring the properties of natural polymers such as electrical conductivity is vital to widen the range of future applications. In this article, the potential of electrically conducting multi-wall carbon nanotube (MWCNT)/polylactic acid (PLA) composites produced by industrially viable melt mixing is assessed simultaneously to MWCNT influence on the composite’s mechanical strength and polymer crystallinity. Atomic force microscopy observations showed that melt mixing achieved an effective distribution and individualization of unmodified nanotubes within the polymer matrix. However, as a trade-off of the poor tube/matrix adhesion, the tensile strength was lowered. With 10 wt% MWCNT loading, the tensile strength was 26% lower than for neat PLA. Differential scanning calorimetric measurements indicated that polymer crystallization after injection moulding was nearly unaffected by the presence of nanotubes and remained at 15%. The resulting composites became conductive below 5 wt% loading and reached conductivities of 51 S m−1 at 10 wt%, which is comparable with conductivities reported for similar nanocomposites obtained at lab scale. </jats:p

Potential of Wood Hemicelluloses and Their Derivates as Food Ingredients

A holistic utilization of all lignocellulosic wood biomass, instead of the current approach of using only the cellulose fraction, is crucial for the efficient, ecological, and economical use of the forest resources. Use of wood constituents in the food and feed sector is a potential way of promoting the global economy. However, industrially established food products utilizing such components are still scarce, with the exception of cellulose derivatives. Hemicelluloses that include xylans and mannans are major constituents of wood. The wood hemicelluloses are structurally similar to hemicelluloses from crops, which are included in our diet, for example, as a part of dietary fibers. Hence, structurally similar wood hemicelluloses have the potential for similar uses. We review the current status and future potential of wood hemicelluloses as food ingredients. We include an inventory of the extraction routes of wood hemicelluloses, their physicochemical properties, and some of their gastrointestinal characteristics, and we also consider the regulatory route that research findings need to follow to be approved for food solutions, as well as the current status of the wood hemicellulose applications on that route.Peer reviewe

Design of Friction, Morphology, Wetting, and Protein Affinity by Cellulose Blend Thin Film Composition

Cellulose derivate phase separation in thin films was applied to generate patterned films with distinct surface morphology. Patterned polymer thin films are utilized in electronics, optics, and biotechnology but films based on bio-polymers are scarce. Film formation, roughness, wetting, and patterning are often investigated when it comes to characterization of the films. Frictional properties, on the other hand, have not been studied extensively. We extend the fundamental understanding of spin coated complex cellulose blend films via revealing their surface friction using Friction Force Microscopy (FFM). Two cellulose derivatives were transformed into two-phase blend films with one phase comprising trimethyl silyl cellulose (TMSC) regenerated to cellulose with hydroxyl groups exposed to the film surface. Adjusting the volume fraction of the spin coating solution resulted in variation of the surface fraction with the other, hydroxypropylcellulose stearate (HPCE) phase. The film morphology confirmed lateral and vertical separation and was translated into effective surface fraction. Phase separation as well as regeneration contributed to the surface morphology resulting in roughness variation of the blend films from 1.1 to 19.8 nm depending on the film composition. Friction analysis was successfully established, and then revealed that the friction coefficient of the films could be tuned and the blend films exhibited lowered friction force coefficient compared to the single-component films. Protein affinity of the films was investigated with bovine serum albumin (BSA) and depended mainly on the surface free energy (SFE) while no direct correlation with roughness or friction was found. BSA adsorption on film formed with 1:1 spinning solution volume ratio was an outlier and exhibited unexpected minimum in adsorption

Nanopartikkeleiden pintamodifiointi ja käyttö tasomaisten pintojen muokkaamisessa

Nanoparticle modification and their utilization in the modification of planar substrates were examined. Emphasis was placed on two topics: the control of layer structure during formation and the alteration of the wetting characteristics of modified surfaces. Layer formation was investigated by adsorbing nanoparticles with a distinct shape and charge onto a nanofibrillated cellulose (NFC) substrate. In addition, nanosized silica particles and NFC were adsorbed sequentially with an oppositely charged polyelectrolyte onto an NFC substrate in order to explore the structures achievable using layer-by-layer assembly. Evidently, the utilization of nanoparticles in layer formation demands the control of the nanoparticle dispersion stability and particle affinity to the substrate. When combining nanoparticles with other substances, the properties of the particles define the layer structure; large fibrils were able to form a stratified layer, while silica nanoparticles were able to penetrate the preceding layer and transform the structure into a uniform network of polyelectrolyte and nanoparticles. The effect of nanoparticle surface modification on dispersion properties and on the structure and properties of the layers formed were also of interest. Modification of nanosized silica and precipitated calcium carbonate particles was conducted by treatment with oppositely charged substances. This treatment resulted in stable nanoparticle dispersions able to be further modified with hydrophobic sizing agents. In addition to enhanced stability and functionality, the polyelectrolyte treatment could be used to affect the interaction of the nanoparticles with the other dispersion constituents. Wetting of a smooth and dense substrate was not affected by the nanoscale roughness caused by the nanoparticle coating on the substrate. In order to affect substrate hydrophobicity, chemical hydrophobicity was deemed necessary. The combination of modified nanoparticles and a hydrophobic emulsion resulted in a nanostructure able to change the wetting characteristics of a planar substrate. Treatment of a smooth substrate with a hydrophobic dispersion resulted in slightly enhanced surface hydrophobicity. On paper, the combination of micron and nanoscale roughness with chemical hydrophobicity resulted in a significant increase in hydrophobicity. The coatings consisted of a thin nanoparticle structure with evenly distributed particles. In addition to use as a paper surface treatment, a layer, consisting of inexpensive particles allowing simple surface modification, could be used to functionalize planar substrates and enable the use of paper as a sustainable substrate, even in applications beyond its traditional use.Tässä työssä tutkittiin nanopartikkeleiden käyttöä tasomaisten pintojen muokkauksessa. Erityisesti keskityttiin nanopartikkelikerroksen rakenteeseen sekä muodostuneen rakenteen vaikutukseen tason pintaominaisuuksiin. Nanopartikkelikerroksen muodostumista havainnoitiin muun muassa tutkimalla kahden ominaisuuksiltaan hyvin erilaisen nanopartikkelimateriaalin asettumista selluloosapinnalle. Nanopartikkelidispersion stabiilisuudella, partikkeleiden ja pinnan varauksella sekä liuoksen väliaineen ominaisuuksilla havaittiin olevan välitön vaikutus muodostuneen pinnan rakenteeseen. Nanopartikkeleiden adsorboimisen lisäksi kerroksen rakentumista hallittiin adsorboimalla nanopartikkelidispersio selluloosapinnalle vuorotellen vastakkaisesti varautuneen polyelektrolyyttiliuoksen kanssa. Tämä niin sanottu monikerrosrakenne muodostui eri tavoin riippuen käytettyjen nanopartikkeleiden koosta ja muodosta. Pienet silikananopartikkelit pystyivät tunkeutumaan polyelektrolyyttikerrokseen, ja monikerrosrakenne tasoittui rakenteeksi, jossa nanopartikkelit olivat jakautuneet tasaisesti polyelektrolyyttimatriisiin. Pitkät nanofibrillit taas muodostivat kerroksellisen rakenteen polyelektrolyyttikerroksen kanssa, eikä huomattavaa kerrosten sekoittumista havaittu. Nanopartikkeleiden pintaominaisuuksilla on suuri vaikutus muodostuneeseen rakenteeseen. Niinpä nanopartikkeleita modifioitiin adsorboimalla pintaan vastakkaisesti varautunut polyelektrolyyttikerros, jonka avulla dispersioiden stabiilisuutta sekä partikkeleiden pintavarausta pystyttiin muokkaamaan. Lisäksi modifioinnilla pystyttiin joissakin tapauksissa vaikuttamaan nanopartikkeleiden vuorovaikutukseen muiden dispersion ainesosien kanssa. Nanopartikkeleiden aiheuttama karheus tasolla todettiin hyödyttömäksi nesteiden leviämisominaisuuksien muuttamisessa. Yhdistämällä nanopartikkelit hydrofobisten materiaalien kanssa vesidispersiossa pystyttiin luomaan päällystyskerros, jolla tasaisen pinnan kastumiseen voitiin vaikuttaa. Muodostamalla sama rakenne paperin päälle, siis yhdistämällä mikro- ja nanoluokan karheus kemialliseen hydrofobisuuteen, valmistettiin erittäin vettähylkivä pinta. Vedenkeston lisäksi tällaista hyvin tarkasti määriteltyä nanopartikkelirakennetta, esimerkiksi paperin päällysteenä, voidaan käyttää lisäämään pinnan funktionaalisuutta, ja lisätä niin tämän luonnonmukaisen pohjamateriaalin käyttöä myös muualla kuin perinteisessä tarkoituksessaan