Valkaisemattomien koivusulfaattimassojen käyttö nanofibrilloidun selluloosan valmistuksessa

The purpose of this thesis was to investigate if unbleached or only partially bleached kraft birch pulp is a suitable raw material for nanofibrillated cellulose (NFC) preparation. The pulps used in the experiments were taken from three parts of the pulp mill: after cooking, after oxygen delignification and after bleaching. These pulps were later Masuko refined without using any chemical or enzymatic pre-treatment. The main methods in this thesis were UV Raman spectroscopy that was used for determining the lignin and hexA contents of the pulps before and after refining, X-ray photoelectron spectroscopy (XPS/ESCA) with which surface lignin and carbohydrates were measured before and after Masuko treatment, and electron paramagnetic resonance spectroscopy (EPRIESR) that provided information on the mechanoradical formation. Furthermore, fibrillation progress was monitored with dynamic drainage analysis and Kajaani Fiberlab measurements, and charge densities were determined by conductometry. It was found that mechanical refining causes free radical formation, which can result in polymerization reactions in cellulose chains and even hexenuronic acids. Lignin is a known antioxidant that is capable of inhibiting such reactions. This results in more effective fibrillation of lignin containing pulps. NFCs that were made of different pulps were very similar in their dimensions and surface compositions. However, there was a significant difference in charge density: the bleached pulp had a charge density that was only about half of that of the unbleached and oxygen delignified pulps. This suggests that hemicellulose removal during bleaching decreases fiber swelling and thus lowers its level of fibrillation in refining. Also, it is probable that the more charged NFC will form a more stable suspension. Thus, unbleached or only partially bleached birch pulps can be used as a raw material for NFC preparation. Their usage would decrease energy consumption in refining, increase the portion of wood material that is put in use and decrease bleaching chemical consumption. However, the light brown colour of the unbleached NFC might cause limitations in some applications.Tämän työn tarkoituksena oli selvittää valkaisemattomien tai vain osittain valkaistujen koivusulfaattimassojen soveltuvuutta nanofibrilloidun selluloosan (NFC) raaka-aineeksi. Tutkittavat koivumassat otettiin kolmesta kohtaa valmistusprosessia: keiton jälkeen, happidelignifioinnin jälkeen sekä valkaisusekvenssin jälkeen. Näistä valmistettiin näytteet Masuko-jauhamalla ilman kemiallisia tai entsymaattisia esikäsittelyjä. Tärkeimmät työssä käytetyt tutkimusmenetelmät olivat UV-Raman-spektroskopia, jolla selvitettiin massan ligniini- ja heksenuronihappopitoisuus ennen ja jälkeen jauhatuksen, röntgensädefotoelektronispektroskopia (XPS/ESCA), jolla tutkittiin pintaligniinin ja -hiilihydraattien määrää ennen ja jälkeen jauhatuksen, sekä elektroniparamagneettinen resonanssi (EPR/ESR) -spektroskopia, jolla mitattiin jauhatuksessa syntyviä mekanoradikaaleja. Lisäksi tutkittiin jauhatuksen edistymistä dynamic drainage analysis (DDA)- ja Kajaani Fiberlab -mittauksin ja selvitettiin massojen varaustiheyserot konduktometrisella titrauksella. Työssä havaittiin, että mekaaninen jauhatus saa aikaan vapaiden radikaalien muodostumista, mikä voi aiheuttaa polymeroitumisreaktioita paitsi selluloosaketjujen. myös heksenuronihappojen välille. Ligniinin tiedetään toimivan antioksidanttina, joten ligniiniä sisältävissä massoissa tällainen polymeroituminen jäi vähäisemmäksi. Tämä puolestaan näkyy tehostuneena fibrilloitumisena NFC:n valmistuksessa. Eri lähtömassasta jauhettujen NFC:iden dimensioissa ja pintakoostumuksissa ei ollut suuria eroja - merkittävä ero oli kuitenkin varaustiheydessä, joka oli valkaistussa massassa noin puolet valkaisemattoman tai happidelignifioidun massan varaustiheydestä. Hemiselluloosien poistuminen valkaisussa vähentää kuidun turpoamista ja vaikeuttaa sen jauhautumista. Lisäksi on todennäköistä, että enemmän varautunut NFC muodostaa stabiilimman suspension. Näin ollen vaikuttaa silti, että valkaisemattomat tai vain osin valkaistut massat soveltuvat käytettäviksi NFC:n raaka-aineena. Niiden käytön myötä olisi mahdollista säästää jauhatusenergiaa. hyödyntää suurempi osa puuraaka-aineesta sekä vähentää valkaisukemikaalien käyttöä. Osassa sovelluskohteita rajoituksia saattaa aiheuttaa valkaisemattoman NFC:n vaaleanruskea väri

Lignoselluloosamateriaalien mekanokemialliset reaktiot

In this work, industrially relevant mechanochemical processes of lignocellulosic materials were investigated. To this day, mechanochemistry remains unknown even to most chemists, and reports on its effects in the forest products industry are scarce. As many processes of the pulp and paper sector include mechanical treatments, the effect of such treatments on the chemical properties of the materials should be known.  The treatments that were studied herein were: preparation of nanofibrillated cellulose (NFC) by Masuko refining, thermomechanical pulping at high temperatures (HT-TMP) and ball milling in the presence of a reactive vinyl monomer, namely, styrene. The HT-TMP was also studied as a potential reinforcing agent in biocomposites. Material properties were characterized with techniques such as electron paramagnetic resonance (EPR) and ultraviolet resonance Raman (UVRR) spectroscopies, optical analysis of fiber dimensions, tensile testing, and scanning electron microscopy (SEM).  The main hypothesis of the work was that mechanoradicals are formed upon various mechanical treatments. This was confirmed for kraft pulp homogenization into NFC and reactive ball milling of cotton. With mechanical pulping, the situation is more complex: thermal and mechanical effects are simultaneous and therefore difficult to distinguish. The same holds true for composite preparation by extrusion, where both heating and shear forces are present.  Mechanoradicals were shown to be able to act as starting points for cellulose copolymerization but the efficacy of these reactions was greatly affected by the presence of oxygen and water. HT-TMP fibers were shown to have potential in industrial composite reinforcement due to their hydrophobicity, ease of dispersion in the PLA matrix, and low specific energy consumption.  In conclusion, acknowledging the formation of mechanoradicals in industrial processes is crucial. These radicals may participate in unwanted side reactions, such as oxidation or polymer degradation. On the other hand, mechanical processing may yield new avenues for fiber modification.Tässä työssä tarkasteltiin teollisia prosesseja, joissa lignoselluloosamateriaalit altistuvat mekaaniselle rasitukselle. Mekanokemia on vielä varsin huonosti tunnettu tieteenala, joka tutkii mekaanisesti aiheutettuja kemiallisia muutoksia. Koska monet puunjalostustekniikan prosessit sisältävät mekaanisia käsittelyitä, niiden vaikutukset materiaaliominaisuuksiin olisi tärkeää tuntea.  Työssä tutkitut käsittelyt olivat: nanofibrilloidun selluloosan (NFC) valmistaminen Masuko-jauhatuksen avulla, hierteenvalmistus korkeassa lämpötilassa (HT-TMP) ja kuulamyllyjauhatus reaktiivisen monomeerin läsnä ollessa. Myös HT-TMP:n potentiaalia biokomposiittilujitteena selvitettiin. Työn keskeisiä analyysimenetelmiä olivat muun muassa elektroniparamagneettinen resonanssi (EPR) ja ultraviolettiresonanssiraman (UVRR) -spektroskopiat, kuitudimensioiden optinen analyysi, vetokokeet sekä pyyhkäisyelektronimikroskopia (SEM).  Keskeisenä työhypoteesina oli vapaiden radikaalien muodostuminen erityyppisten mekaanisten käsittelyjen seurauksena. Näiden mekanoradikaalien muodostuminen vahvistettiinkin koivusulfaattimassan Masuko-jauhatuksen sekä puuvillakuitujen reaktiivisen kuulamyllyjauhatuksen tapauksessa. Hierteenvalmistuksen tapauksessa tapahtuu sekä mekaanista että termistä hajoamista, mikä hankaloittaa mekanoradikaalien osuuden todentamista. Sama pätee komposiittien valmistukseen ekstruusion eli suulakepuristuksen avulla – myös sen aikana materiaali altistuu sekä kuumuudelle että mekaaniselle rasitukselle.  Mekanoradikaalien todettiin pystyvän aloittamaan kopolymeroitumisreaktioita, mutta reaktioiden eteneminen riippui pitkälti olosuhteista, kuten veden ja hapen läsnäolosta.  HT-TMP-kuitujen havaittiin soveltuvan komposiittien lujitekäyttöön, koska ne ovat hydrofobisia, ne on helppo sekoittaa tasaisesti PLA-matriisiin ja niiden valmistuksen ominaisenergiankulutus on alhainen.  Yhteenvetona voidaan todeta, että mekanoradikaalien muodostuminen teollisissa prosesseissa tulisi ottaa nykyistä paremmin huomioon. Radikaalit voivat aiheuttaa ei-toivottuja sivureaktioita, mutta niitä voidaan myös hyödyntää kuitujen muokkauksessa

Water vapor mass transport across nanofibrillated cellulose films: effect of surface hydrophobization

In this paper, porous nanofibrillated cellulose (NFC) films were utilized to produce water-resistant, porous cellulose films. Film porosities of similar to 50% were achieved through solvent exchange from water to acetone, and the resulting films were hydrophobized with an epoxy modifier in non-swelling conditions in acetone, yielding films that were non-wettable by water but permeable to water vapor. The mass transport mechanisms of gaseous and liquid water were studied by water vapor transfer rate (WVTR), water vapor uptake and water contact angle measurements to unfold how these properties were achieved. Surface hydrophobization was found to decrease the moisture uptake but it did not prevent it completely. The WVTR values were in effect similar for the initial and hydrophobized films, even if the water contact angles were higher in the latter. We anticipate that the porous and hydrophobic NFC films presented in this paper may find applications in sportswear, medical, or personal hygiene products

On the potential of lignin-containing cellulose nanofibrils (LCNFs): a review on properties and applications

This review outlines the present state and recent progress in the area of lignin-containing cellulose nanofibrils (LCNFs), an emerging family of green cellulose nanomaterials. Different types of LCNF raw materials are described, with main focus on wood-based raw materials, and the properties of the resulting LCNFs are compared. Common problems faced in industrial utilization of CNFs are discussed in the light of potential improvements from LCNFs, covering areas such as chemical and energy consumption, dewatering and redispersibility. Out of the potential applications, barrier films, emulsions and nanocomposites are considered.Peer reviewe

Fibrillation and characterization of lignin-containing neutral sulphite (NS) pulps rich in hemicelluloses and anionic charge

The potential of neutral sulphite pulps from softwood with different yields (c. 58–84%) and high residual lignin contents (c. 10–25 wt%) was investigated as a raw material for lignin-containing cellulose nanofibrils (LCNFs) by following their fibrillation during grinding. It was found that the lower yield (58–65%) pulps needed two grinding cycles to produce fibrillated fibers with water retention values (WRV) as high as 400 g/g (at the energy consumption level of 1400 kWh/t). In contrast, the high yield (77–84%) pulps fibrillated more slowly, requiring five grinding cycles to reach comparable WRV values. Apparently, higher crosslinking degrees of lignin in the high yield pulps are hampering the fibrillation, although the high hemicellulose contents (21–24 wt%) and the high charge densities (200–350 µmol/g, originating from carboxylic and sulphonic acid groups) of the pulps were expected to enhance the fibrillation. Nevertheless, regardless of the different fibrillation behaviour, most of the pulps formed c. 10–15% of nanosized material below 30 nm and significant amounts of fibrils with size under 100 nm based on the centrifugation method and FE-SEM images. As the pulps were of moderate to high yield and fibrillated easily without any chemical or enzymatic pretreatments, they show promise for cost-efficient production of LCNFs. The nanopapers prepared from the fibrillated pulps showed tensile strengths (73–125 MPa) comparable with the nanopapers from high yield mechanical pulps, whereas the water contact angles (41°–58°) were closer the those of chemical pulps.Peer reviewe

Composites of High-Temperature Thermomechanical Pulps and Polylactic Acid

High-temperature thermomechanical pulps (HT-TMP, defibrated at 150 to 170 degrees C) were compared to a reference TMP (defibrated at 130 degrees C) as a reinforcement for polylactic acid (PLA). Composites were prepared by melt compounding, followed by injection molding, gradually increasing the used fiber content from 0 to 20 wt.%. The injection-molded specimens were characterized by tensile and impact strength tests, scanning electron microscopy, water absorption tests, and differential scanning calorimetry. The TMP fiber damage was also characterized before and after melt compounding by optical analysis. At 20% fiber content, the Young's modulus increased significantly, while the tensile strength remained unchanged and the impact strength decreased slightly. All fibers suffered damage during melt compounding, but the tensile strength remained about the same as in pure PLA. All types of TMP were able to increase the PLA rate of crystallization. The HT-TMP fibers were dispersed more evenly in PLA than the 130degrees C TMP. The 170 degrees C TMP produced composites of lower water absorption than the other two TMP types, probably because of its lower hemicellulose content and its higher surface coverage by lignin.Peer reviewe

Assessment of the Alga Cladophora glomerata as a Source for Cellulose Nanocrystals

Nanocellulose is isolated from cellulosic fibers and exhibits many properties that macroscale cellulose lacks. Cellulose nanocrystals (CNCs) are a subcategory of nanocellulose made of stiff, rodlike, and highly crystalline nanoparticles. Algae of the order Cladophorales are the source of the longest cellulosic nanocrystals, but manufacturing these CNCs is not well-studied. So far, most publications have focused on the applications of this material, with the basic manufacturing parameters and material properties receiving little attention. In this article, we investigate the entirety of the current manufacturing process from raw algal biomass (Cladophora glomerata) to the isolation of algal cellulose nanocrystals. Yields and cellulose purities are investigated for algal cellulose and the relevant process intermediates. Furthermore, the effect of sulfuric acid hydrolysis, which is used to convert cellulose into CNCs and ultimately determines the material properties and some of the sustainability aspects, is examined and compared to literature results on wood cellulose nanocrystals. Long (>4 μm) CNCs form a small fraction of the overall number of CNCs but are still present in measurable amounts. The results define essential material properties for algal CNCs, simplifying their future use in functional cellulosic materials.Peer reviewe

Native Structure of the Plant Cell Wall Utilized for Top-Down Assembly of Aligned Cellulose Nanocrystals into Micrometer-Sized Nanoporous Particles

Despite their sustainable appeal, biomass components are currently undervalued in nanotechnology because means to control the assembly of bio-based nanoparticles are lagging behind the synthetic counterparts. Here, micrometer-sized particles consisting of aligned cellulose nanocrystals (CNCs) are prepared by crosslinking cellulose in cotton linter fibers that are prehydrolyzed with gaseous HCl, resulting in chemical cleavage necessary for CNC formation but retaining the morphology of the native fibers. That way, the intrinsic alignment of cellulose microfibrils within the fiber cell wall can be retained and utilized for top-down CNC alignment. Subsequent crosslinking with citric acid cements the alignment and preserves it, following the dispersion of CNCs trapped end-to-end, connected, and crosslinked within the colloidally stable micrometer-sized particles. Furthermore, thermoporosimetry and cryogenic transmission electron microscopy (Cryo TEM) shows that the particles possess mainly nanoporous (<2 nm) character in water. The approach challenges the current paradigm of predominantly bottom-up methods for nanoparticle assembly.Peer reviewe

Directed Assembly of Cellulose Nanocrystals in Their Native Solid‐State Template of a Processed Fiber Cell Wall

Nanoparticle assembly is intensely surveyed because of the numerous applications within fields such as catalysis, batteries, and biomedicine. Here, directed assembly of rod‐like, biologically derived cellulose nanocrystals (CNCs) within the template of a processed cotton fiber cell wall, that is, the native origin of CNCs, is reported. It is a system where the assembly takes place in solid state simultaneously with the top‐down formation of the CNCs via hydrolysis with HCl vapor. Upon hydrolysis, cellulose microfibrils in the fiber break down to CNCs that then pack together, resulting in reduced pore size distribution of the original fiber. The denser packing is demonstrated by N2 adsorption, water uptake, thermoporometry, and small‐angle X‐ray scattering, and hypothetically assigned to attractive van der Waals interactions between the CNCs.peerReviewe