Eräiden paperinvalmistuksessa käytettävien vahadispersioiden stabiilisuuden hallinta

Diplomityön tavoitteena oli selvittää millainen laaduntarkastus AKD-dispersioille tulisi suorittaa kuormien vastaanotossa ja tulisiko dispersioiden laatu tarkastaa uudelleen ennen annostelua. Tätä varten seurattiin toimituserien laadun tasaisuutta ja tarkasteltiin varastointiolosuhteiden vaikutusta dispersioiden säilyvyyteen. Lisäksi kartoitettiin dispersioiden käsittelyssä ja kartonginvalmistusprosessissa esiintyvien riskitekijöiden vaikutuksia kaupallisten dispersioiden stabiilisuuteen. Kirjallisuusosassa perehdyttiin kolloidisiin dispersioihin sekä niiden stabiilisuuteen vaikuttaviin tekijöihin. AKD-dispersiot valmistetaan emulgointitekniikoiden avulla, joten dispergointimenetelmien ohella käsiteltiin myös emulsioiden valmistamista. Lisäksi luotiin katsaus dispersioteknologian tärkeimpiin analyysimenetelmiin. Alkyyliketeenidimeerin osalta käsiteltiin emulgoinnin lisäksi vahan ja muiden lisäaineiden vaikutuksia dispersioiden stabiilisuuteen ja myös niiden merkitystä dispersioiden formuloinnissa. AKD-liimauksen osalta esiin tuotiin AKD:n tärkeimmät reaktiomekanismit, sillä ne liittyvät osittain myös dispersioiden stabiilisuuteen. Lopuksi luotiin lyhyt katsaus AKD-dispersioiden stabiilisuutta käsittelevään tutkimukseen, jota on toistaiseksi julkaistu varsin niukasti. Kokeellisessaosassa tarkastelun kohteeksi valittiin neljä kaupallista alkyyliketeenidimeerinvesidispersiota, joiden koostumus ja ominaisuudet selvitettiin perusteellisesti. Tarkoituksena oli auttaa ymmärtämään dispersioiden stabiilisuudessa mahdollisesti esiintyviä eroja. Laajamittainen dispersioiden karakterisointi näyttää olevan tarpeen ainakin otettaessa uutta AKD-laatua käyttöön, sillä dispersioiden koostumus ja ominaisuudet voivat vaihdella merkittävästi. AKD-dispersioiden laadussa esiintyi vaihtelua eri toimituserien välillä. Suurimmat vaihtelut havaittiin dispersioiden varaustiloissa ja partikkelikokojakaumissa. Laadun epätasaisuuden vuoksi vastaanottotarkastuksen merkitys korostuu. Vastaanottotarkastuksessa syytä olisi kiinnittää dispersion kuiva-ainepitoisuuden ohella sen viskositeettiin, varaustilaan, tehoainepitoisuuteen sekä rakenteeseen. Rakenteen tarkastelussa optinen mikroskooppi voi rutiininomaisessa seurannassa korvata partikkelikokojakauman määrittämisen. Varastointilämpötilan vaikutus dispersioidenlaatuun on merkittävä. Dispersiot säilyvät parhaiten viileässä, joten jos varastosäiliöissä ei ole jäähdytystä, on dispersioiden laadun tarkastus tarpeen myös ennen annostelua. Jotta dispersion kunnosta saadaan luotettava arvio, on viskositeetin määrittämiseen yhdistettävä vähintään rakenteen tarkastelu optisella mikroskoopilla. Mekaaninen rasitus voi dominoivasta stabilointimekanismistariippuen aiheuttaa dispersiossa hienoaineen muodostumista tai partikkelien flokkaantumista. Stabilointimekanismi vaikuttaa niin ikään partikkelien käyttäytymiseen korkeissa lämpötiloissa. Dispersioiden stabiilisuuden todettiin heikkenevän pH:n kohotessa emäksiselle alueelle. Elektrolyyttikonsentraatio vaikuttaa partikkelien mikroelektroforeettiseen ioniliikkuvuuteen merkittävästi. Kartonkikoneen märkäosan kemikaaleista anionisen retentioaineen (BMA) todettiin vuorovaikuttavan kationisten AKD-partikkelien kanssa selvimmin. Mikroelektroforeettisen ioniliikkuvuuden mittaaminen kiertovedessä todettiin tärkeäksi, sillä se kuvaa dispersion käyttäytymistä sen käyttöympäristössä.

The use of branched ketenedimers in solving the deposit problems related to the internal sizing of uncoated fine paper

Alkyl ketene dimers (AKD) are effective and highly hydrophobic sizing agents for the internal sizing of alkaline papers, but in some cases they may form deposits on paper machines and copiers. In addition, alkenyl succinic anhydrides (ASA)- based sizing agents are highly reactive, producing on-machine sizing, but under uncontrolled wet end conditions the hydrolysis of ASA may cause problems. This thesis aims at developing an improved ketene dimer based sizing agent that would have a lower deposit formation tendency on paper machines and copiers than a traditional type of AKD. The aim is also to improve the ink jet printability of a AKD sized paper. The sizing characteristics ofketene dimers have been compared to those of ASA. A lower tendency of ketene dimer deposit formation was shown in paper machine trials and in printability tests when branched fatty acids were used in the manufacture of a ketene dimer basedsizing agent. Fitting the melting and solidification temperature of a ketene dimer size to the process temperature of a paper machine or a copier contributes to machine cleanliness. A lower hydrophobicity of the paper sized with branched ketene dimer compared to the paper sized with traditional AKD was discovered. However, the ink jet print quality could be improved by the use of a branched ketene dimer. The branched ketene dimer helps in balancing the paper hydrophobicity for both black and color printing. The use of a high amount of protective colloidin the emulsification was considered to be useful for the sizing performance ofthe liquid type of sizing agents. Similar findings were indicated for both the branched ketene dimer and ASA.

Pitkäketjuisten keteenien valmistusreaktiot ja kinetiikka.

Tämän diplomityön tarkoituksena oli tutkia pitkäketjuisten rasvahappokloridien ja alkyyliketeenidimeerien (AKD) valmistusreaktioiden kinetiikkaa. Työn tavoitteena oli saada mittaustuloksia, joiden perusteella voitaisiin kehittää reaktioille kineettinen kineettinen malli ja suorittaa valmistusprosessien alustava optimointi. Teoreettisessa osassa on selvitetty rasvahappokloridien ja alkyyliketeenidimeerien (AKD) eri valmistustapoja. Lisäksi on perehdytty tarkemmin rasvahappokloridien dehydrohalogenointireaktioiden reaktiomekanismeihin ja valmistusprosessin problematiikkaan. Kokeellisessa osassa tutkittiin rasvahappokloridien valmistusta klooraamalla öljyhappoa 30 mol-% fosforitrikloridiylimäärällä lämpötiloissa 45, 50 ja 55OC. Alkyyliketeenidimeerien valmistusta tutkittiin dehydrohalogenoimalla palmitiini- ja öljyhappokloridia 0-30 mol-% trietyyliamiiniylimäärällä inertissä liuottimessa, lämpötiloissa 45 ja 50OC. Reaktiot toteutettiin puolipanosreaktiona, joissa reaktioastiassa olevaan reagenssin ja liuottimen seokseen lisättiin lähtöaine tasaisena massavirtana. Reaktioiden etenemistä seurattiin FT-IR- ja GC-analyysien avulla. Kalorimetrisilla kokeilla tutkittiin öljyhappokloridin dimeroitumisreaktion reaktiolämmön muodostumista ja UV-VIS-analyyseillä seurattiin öljyhappokloridin vanhenemista. Öljyhappokloridin valmistusreaktiolle saatiin hyvä kineettinen malli. Kineettisen mallin puutteena voidaan pitää sitä, ettei kokeissa saatu tietoa mahdollisten sivutuotteiden muodostumisesta. Sovitusohjelmalla saatiin sovitettua estimaatit reaktionopeusvakioille lämpötiloissa 45, 50 ja 55OC. Happokloridien dimeroitumisreaktioiden kineettisen mallin sopivuudelle saatiin suhteellisen hyvä kuva Kuten öljyhappokloridin tapauksessa, myöskään AKD:n valmistusreaktioissa syntynyt sivutuotteita, joten niiden osuutta oletettuun kineettiseen malliin ei tunneta. Sovitusohjelmalla saatiin sovitettua estimaatit reaktionopeusvakioille lämpötiloissa 45 ja 50OC.

Surface characterization of chemically modified fiber, wood and paper

Inorganic-organic sol-gel hybrid coatings can be used for improving and modifying properties of wood-based materials. By selecting a proper precursor, wood can be made water repellent, decay-, moisture- or UV-resistant. However, to control the barrier properties of sol-gel coatings on wood substrates against moisture uptake and weathering, an understanding of the surface morphology and chemistry of the deposited sol-gel coatings on wood substrates is needed. Mechanical pulp is used in production of wood-containing printing papers. The physical and chemical fiber surface characteristics, as created in the chosen mechanical pulp manufacturing process, play a key role in controlling the properties of the end-use product. A detailed understanding of how process parameters influence fiber surfaces can help improving cost-effectiveness of pulp and paper production. The current work focuses on physico-chemical characterization of modified wood-based materials with surface sensitive analytical tools. The overall objectives were, through advanced microscopy and chemical analysis techniques, (i) to collect versatile information about the surface structures of Norway spruce thermomechanical pulp fiber walls and understand how they are influenced by the selected chemical treatments, and (ii) to clarify the effect of various sol-gel coatings on surface structural and chemical properties of wood-based substrates. A special emphasis was on understanding the effect of sol-gel coatings on the water repellency of modified wood and paper surfaces. In the first part of the work, effects of chemical treatment on micro- and nano-scale surface structure of 1st stage TMP latewood fibers from Norway spruce were investigated. The chemicals applied were buffered sodium oxalate and hydrochloric acid. The outer and the inner fiber wall layers of the untreated and chemically treated fibers were separately analyzed by light microscopy, atomic force microscopy and field-emission scanning electron microscopy. The selected characterization methods enabled the demonstration of the effect of different treatments on the fiber surface structure, both visually and quantitatively. The outer fiber wall areas appeared as intact bands surrounding the fiber and they were clearly rougher than areas of exposed inner fiber wall. The roughness of the outer fiber wall areas increased most in the sodium oxalate treatment. The results indicated formation of more surface pores on the exposed inner fiber wall areas than on the corresponding outer fiber wall areas as a result of the chemical treatments. The hydrochloric acid treatment seemed to increase the surface porosity of the inner wall areas. In the second part of the work, three silane-based sol-gel hybrid coatings were selected in order to improve moisture resistance of wood and paper substrates. The coatings differed from each other in terms of having different alkyl (CH3–, CH3-(CH2)7–) and fluorocarbon (CF3–) chains attached to the trialkoxysilane sol-gel precursor. The sol-gel coatings were deposited by a wet coating method, i.e. spraying or spreading by brush. The effect of solgel coatings on surface structural and chemical properties of wood-based substrates was studied by using advanced surface analyzing tools: atomic force microscopy, X-ray photoelectron spectroscopy and time-of-flight secondary ion spectroscopy. The results show that the applied sol-gel coatings, deposited as thin films or particulate coatings, have different effects on surface characteristics of wood and wood-based materials. The coating which has a long hydrocarbon chain (CH3-(CH2)7–) attached to the silane backbone (octyltriethoxysilane) produced the highest hydrophobicity for wood and wood-based materials.

Methyl and ethyl chloride synthesis in microreactors

Methyl chloride is an important chemical intermediate with a variety of applications. It is produced today in large units and shipped to the endusers. Most of the derived products are harmless, as silicones, butyl rubber and methyl cellulose. However, methyl chloride is highly toxic and flammable. On-site production in the required quantities is desirable to reduce the risks involved in transportation and storage. Ethyl chloride is a smaller-scale chemical intermediate that is mainly used in the production of cellulose derivatives. Thus, the combination of onsite production of methyl and ethyl chloride is attractive for the cellulose processing industry, e.g. current and future biorefineries. Both alkyl chlorides can be produced by hydrochlorination of the corresponding alcohol, ethanol or methanol. Microreactors are attractive for the on-site production as the reactions are very fast and involve toxic chemicals. In microreactors, the diffusion limitations can be suppressed and the process safety can be improved. The modular setup of microreactors is flexible to adjust the production capacity as needed. Although methyl and ethyl chloride are important chemical intermediates, the literature available on potential catalysts and reaction kinetics is limited. Thus the thesis includes an extensive catalyst screening and characterization, along with kinetic studies and engineering the hydrochlorination process in microreactors. A range of zeolite and alumina based catalysts, neat and impregnated with ZnCl2, were screened for the methanol hydrochlorination. The influence of zinc loading, support, zinc precursor and pH was investigated. The catalysts were characterized with FTIR, TEM, XPS, nitrogen physisorption, XRD and EDX to identify the relationship between the catalyst characteristics and the activity and selectivity in the methyl chloride synthesis. The acidic properties of the catalyst were strongly influenced upon the ZnCl2 modification. In both cases, alumina and zeolite supports, zinc reacted to a certain amount with specific surface sites, which resulted in a decrease of strong and medium Brønsted and Lewis acid sites and the formation of zinc-based weak Lewis acid sites. The latter are highly active and selective in methanol hydrochlorination. Along with the molecular zinc sites, bulk zinc species are present on the support material. Zinc modified zeolite catalysts exhibited the highest activity also at low temperatures (ca 200 °C), however, showing deactivation with time-onstream. Zn/H-ZSM-5 zeolite catalysts had a higher stability than ZnCl2 modified H-Beta and they could be regenerated by burning the coke in air at 400 °C. Neat alumina and zinc modified alumina catalysts were active and selective at 300 °C and higher temperatures. However, zeolite catalysts can be suitable for methyl chloride synthesis at lower temperatures, i.e. 200 °C. Neat γ-alumina was found to be the most stable catalyst when coated in a microreactor channel and it was thus used as the catalyst for systematic kinetic studies in the microreactor. A binder-free and reproducible catalyst coating technique was developed. The uniformity, thickness and stability of the coatings were extensively characterized by SEM, confocal microscopy and EDX analysis. A stable coating could be obtained by thermally pretreating the microreactor platelets and ball milling the alumina to obtain a small particle size. Slurry aging and slow drying improved the coating uniformity. Methyl chloride synthesis from methanol and hydrochloric acid was performed in an alumina-coated microreactor. Conversions from 4% to 83% were achieved in the investigated temperature range of 280-340 °C. This demonstrated that the reaction is fast enough to be successfully performed in a microreactor system. The performance of the microreactor was compared with a tubular fixed bed reactor. The results obtained with both reactors were comparable, but the microreactor allows a rapid catalytic screening with low consumption of chemicals. As a complete conversion of methanol could not be reached in a single microreactor, a second microreactor was coupled in series. A maximum conversion of 97.6 % and a selectivity of 98.8 % were reached at 340°C, which is close to the calculated values at a thermodynamic equilibrium. A kinetic model based on kinetic experiments and thermodynamic calculations was developed. The model was based on a Langmuir Hinshelwood-type mechanism and a plug flow model for the microreactor. The influence of the reactant adsorption on the catalyst surface was investigated by performing transient experiments and comparing different kinetic models. The obtained activation energy for methyl chloride was ca. two fold higher than the previously published, indicating diffusion limitations in the previous studies. A detailed modeling of the diffusion in the porous catalyst layer revealed that severe diffusion limitations occur starting from catalyst coating thicknesses of 50 μm. At a catalyst coating thickness of ca 15 μm as in the microreactor, the conditions of intrinsic kinetics prevail. Ethanol hydrochlorination was performed successfully in the microreactor system. The reaction temperature was 240-340°C. An almost complete conversion of ethanol was achieved at 340°C. The product distribution was broader than for methanol hydrochlorination. Ethylene, diethyl ether and acetaldehyde were detected as by-products, ethylene being the most dominant by-product. A kinetic model including a thorough thermodynamic analysis was developed and the influence of adsorbed HCl on the reaction rate of ethanol dehydration reactions was demonstrated. The separation of methyl chloride using condensers was investigated. The proposed microreactor-condenser concept enables the production of methyl chloride with a high purity of 99%.

New families of highly efficient, halogen-free flame retardants for polypropylene (PP)

The driving forces for current research of flame retardants are increased fire safety in combination with flame retardant formulations that fulfill the criteria of sustainable production and products. In recent years, important questions about the environmental safety of antimony, and in particular, brominated flame retardants have been raised. As a consequence of this, the current doctoral thesis work describes efforts to develop new halogen-free flame retardants that are based on various radical generators and phosphorous compounds. The investigation was first focused on compounds that are capable of generating alkyl radicals in order to study their role on flame retardancy of polypropylene. The family of azoalkanes was selected as the cleanest and most convenient source of free alkyl radicals. Therefore, a number of symmetrical and unsymmetrical azoalkanes of the general formula R-N=N-R’ were prepared. The experimental results show that in the series of different sized azocycloalkanes the flame retardant efficacy decreased in the following order: R = R´= cyclohexyl > cyclopentyl > cyclobutyl > cyclooctanyl > cyclododecanyl. However, in the series of aliphatic azoalkanes compounds, the efficacy decreased as followed: R = R´= n-alkyl > tert-butyl > tert-octyl. The most striking difference in flame retardant efficacy was observed in thick polypropylene plaques of 1 mm, e.g. azocyclohexane (AZO) had a much better flame retardant performance than did the commercial reference FR (Flamestab® NOR116) in thick PP sections. In addition, some of the prepared azoalkane flame retardants e.g. 4’4- bis(cyclohexylazocyclohexyl) methane (BISAZO) exhibited non-burning dripping behavior. Extrusion coating experiments of flame retarded low density polyethylene (LDPE) onto a standard machine finished Kraft paper were carried out in order to investigate the potential of azoalkanes in multilayer facings. The results show that azocyclohexane (AZO) and 4’4-bis (cyclohexylazocyclohexyl) methane (BISAZO) can significantly improve the flame retardant properties of low density polyethylene coated paper already at 0.5 wt.% loadings, provided that the maximum extrusion temperature of 260 oC is not exceeded and coating weight is kept low at 13 g/m2. In addition, various triazene-based flame retardants (RN1=N2-N3R’R’’) were prepared. For example, polypropylene samples containing a very low concentration of only 0.5 wt.% of bis- 4’4’-(3’3’-dimethyltriazene) diphenyl ether and other triazenes passed the DIN 4102-1 test with B2 classification. It is noteworthy that no burning dripping could be detected and the average burning times were very short with exceptionally low weight losses. Therefore, triazene compounds constitute a new and interesting family of radical generators for flame retarding of polymeric materials. The high flame retardant potential of triazenes can be attributed to their ability to generate various types of radicals during their thermal decomposition. According to thermogravimetric analysis/Fourier transform infrared spectroscopy/MS analysis, triazene units are homolytically cleaved into various aminyl, resonance-stabilized aryl radicals, and different CH fragments with simultaneous evolution of elemental nitrogen. Furthermore, the potential of thirteen aliphatic, aromatic, thiuram and heterocyclic substituted organic disulfide derivatives of the general formula R-S-S-R’ as a new group of halogen-free flame retardants for polypropylene films have been investigated. According to the DIN 4102- 1 standard ignitibility test, for the first time it has been demonstrated that many of the disulfides alone can effectively provide flame retardancy and self-extinguishing properties to polypropylene films at already very low concentrations of 0.5 wt.%. For the disulfide family, the highest FR activity was recorded for 5’5’-dithiobis (2-nitrobenzoic acid). Very low values for burning length (53 mm) and burning time (10 s) reflect significantly increased fire retardant performance of this disulfide compared to other compounds in this series as well as to Flamestab® NOR116. Finally, two new, phosphorus-based flame retardants were synthesized: P’P-diphenyl phosphinic hydrazide (PAH) and melamine phenyl phosphonate (MPhP). The DIN 4102-1 test and the more stringent UL94 vertical burning test (UL94 V) were used to assess the formulations ability to extinguish a flame once ignited. A very strong synergistic effect with azoalkanes was found, i.e. in combination with these radical generators even UL94 V0 rate could be obtained.

Perfluorattuja yhdisteitä sisältävien jätevesien puhdistus- ja analyysimenetelmät

Perfluoratut alkyyliyhdisteet eli PFAS-yhdisteet ovat synteettisiä orgaanisia yhdisteitä, joissa on fluorattu hiiliketju. Hiilen ja fluorin väliset vahvat sidokset ovat muodostuneet ongelmaksi jätevedenpuhdistamoilla, sillä yhdisteet eivät hajoa puhdistamoilla käytössä olevilla vedenpuhdistusmenetelmillä. Yhdisteitä kertyy luontoon jätevesien mukana. Kandidaatintyössä on vertailtu yhdisteitä sisältävien vesien käsittelymenetelmiä parhaiten soveltuvan menetelmän löytämiseksi. Menetelmien kustannuksia tai soveltuvuutta vedenpuhdistamomittakaavan prosessiksi ei ole arvioitu. Lisäksi työssä on koottu yhdisteitä sisältävien jätevesien analysointiin sopivia analyysimenetelmiä. Soveltuvat puhdistus- ja analyysimenetelmät on esitelty uusien tieteellisten artikkelien pohjalta. Mahdollisia erotusmenetelmiä ovat membraanierotus ja sorptio. Membraaneista soveltuvimpia ovat nanosuodatus- ja käänteisosmoosimembraanit, joilla erottuvat jopa 0,0001 μm:n kokoiset partikkelit. PFAS-yhdisteet voidaan erottaa sorptiolla muun muassa aktiivihiileen. Yhdisteiden rakenne hajoaa nykyaikaisilla hapetusmenetelmillä ja polttamalla lietteen mukana. Hapettaminen permanganaatin avulla ei tuottanut hyvää tulosta, mutta fotokemiallisella hapetuksella ja alhaisen lämpötilan plasmatekniikalla (NTP) yhdisteiden rakenne hajosi lähes kokonaan. Fotokemiallinen hapetus onnistui erityisesti perfluorokarboksyylihapoilla, joiden rakenne hajosi jopa kolmessa tunnissa. Yleisimmin käytetty analyysimenetelmä on nestekromatografin ja massaspektrometrin yhdistelmä (LC-MS/MS) ja matriisivaikutus minimoidaan tyypillisesti kiinteäfaasiuutolla (SPE). Työssä esitellyistä käsittelymenetelmistä parhaiten soveltuva on NTP-menetelmä, koska sillä saatiin tutkimusten mukaan hajotettua yhdisteiden rakenne muita menetelmiä lyhyemmässä ajassa ja se soveltuu parhaiten kaikille PFAS-yhdisteille. NTP-menetelmässä ei tarvita katalyyttiä tai lisäkemikaaleja. Voimakkaana hapettimena toimivat epästabiilit hydroksyyliradikaalit, jotka syntyvät koronapurkauksen kautta. Koronapurkauksessa muodostuu myös otsonia ja lisäksi vapaa happi voi tehostaa hapettumista. Menetelmässä muodostuvien hajoamistuotteiden hallinta vaatii lisätutkimusta. Mahdollinen hallintakeino voisi olla esimerkiksi hapettumisessa vapautuvien fluoridi-ionien saostaminen. Muodostuvien hajoamistuotteiden toksisuutta voitaisiin tarkkailla biosensorilla.