Evaporation rates from emulsions stabilised by surfactants and nanoparticles

This thesis is concerned with the evaporation rates of emulsions stabilised by either surfactant molecules or nm-size solid particles. Understanding of the mechanisms of the evaporation process plus the control of the rate limiting step of each mechanism involved in such processes is important for a number of practical applications which include cosmetics, paints and agrochemicals.The work of this thesis deals with three main aspects. Firstly the evaporation rates of pure liquids have been determined. Secondly, evaporation rates of surfactant-stabilised creamed, gelled and high internal phase emulsions have been investigated. Lastly, evaporation rates of emulsions stabilised by solid particles will be discussed.The study concerned with the pure liquids was mainly to verify the set-up of the evaporation rig, to compare our results with those obtained by K. J. Beverley (Thesis in preparation, University of Hull) and determine the diffusion coefficients of different liquids in the vapour phase.For creamed emulsions stabilised by surfactants it was found that the evaporation rate of the continuous phase is as that of bulk phase and the evaporation rate of the dispersed phase is slowed down up to 20 times. The retardation in the evaporation rate of the dispersed droplets depends mainly on the solubility of the dispersed phase in the continuous phase. In the case of gelled emulsions, the mass loss of the emulsions gelled by different gelling agents (colloidal particles and water-soluble polymers) show that the evaporation rates depend on the gelling agent. For high internal phase emulsions, evaporation rates of water from emulsions containing involatile oils have been studied. Depending on the geometrical properties of the initial conditions, the mass loss rate is controlled by either diffusion of the liquid in the vapour (large emulsion/sample tube volume ratio) or diffusion of the liquid in the nm-thin films which separate the close-packed oil drops (small emulsion/sample tube volume ratio). The nature of the colloidal forces acting between the dispersed droplets also plays an important role during the evaporation.For emulsions stabilised solely by nm-size silica particles (Pickering emulsions), the evaporation rate is slower compared with that stabilised by surfactants under the same conditions. Moreover, we have found that the solid residues left behind after the total evaporation of the volatile species (oil and water) from Pickering emulsions show macroporous structures. The type of the microstructure is related to that of the parent emulsion and the vapour pressure of the oil. These results may lead to the production of novel macroporous inorganic materials

Fully Biodegradable Biocomposites with High Chicken Feather Content

The aim of this work was to develop new biodegradable polymeric materials with high loadings of chicken feather (CF). In this study, the effect of CF concentration and the type of biodegradable matrix on the physical, mechanical and thermal properties of the biocomposites was investigated. The selected biopolymers were polylactic acid (PLA), polybutyrate adipate terephthalate (PBAT) and a PLA/thermoplastic copolyester blend. The studied biocomposites were manufactured with a torque rheometer having a CF content of 50 and 60 wt %. Due to the low tensile strength of CFs, the resulting materials were penalized in terms of mechanical properties. However, high-loading CF biocomposites resulted in lightweight and thermal-insulating materials when compared with neat bioplastics. Additionally, the adhesion between CFs and the PLA matrix was also investigated and a significant improvement of the wettability of the feathers was obtained with the alkali treatment of the CFs and the addition of a plasticizer like polyethylene glycol (PEG). Considering all the properties, these 100% fully biodegradable biocomposites could be adequate for panel components, flooring or building materials as an alternative to wood–plastic composites, contributing to the valorisation of chicken feather waste as a renewable material.This work was supported by KaRMA2020 project. This project has received funding from the European Union’s Horizon 2020 Research and Innovation program under Grant Agreement n° 723268

Flexible Biocomposites with Enhanced Interfacial Compatibility Based on Keratin Fibers and Sulfur-Containing Poly(urea-urethane)s

Feathers are made of keratin, a fibrous protein with high content of disulfide-crosslinks and hydrogen-bonds. Feathers have been mainly used as reinforcing fiber in the preparation of biocomposites with a wide variety of polymers, also poly(urea-urethane)s. Surface compatibility between the keratin fiber and the matrix is crucial for having homogenous, high quality composites with superior mechanical properties. Poly(urea-urethane) type polymers are convenient for this purpose due to the presence of polar functionalities capable of forming hydrogen-bonds with keratin. Here, we demonstrate that the interfacial compatibility can be further enhanced by incorporating sulfur moieties in the polymer backbone that lead to new fiber-matrix interactions. We comparatively studied two analogous thermoplastic poly(urea-urethane) elastomers prepared starting from the same isocyanate-functionalized polyurethane prepolymer and two aromatic diamine chain extenders, bis(4-aminophenyl) disulfide (TPUU-SS) and the sulfur-free counterpart bis(4-aminophenyl) methane (TPUU). Then, biocomposites with high feather loadings (40, 50, 60 and 75 wt %) were prepared in a torque rheometer and hot-compressed into flexible sheets. Mechanical characterization showed that TPUU-SS based materials underwent higher improvement in mechanical properties than biocomposites made of the reference TPUU (up to 7.5-fold higher tensile strength compared to neat polymer versus 2.3-fold). Field Emission Scanning Electron Microscope (FESEM) images also provided evidence that fibers were completely embedded in the TPUU-SS matrix. Additionally, density, thermal stability, and water absorption of the biocomposites were thoroughly characterized.This work was supported by KaRMA2020 project. This project has received funding from the European Union’s Horizon 2020 Research and Innovation program under Grant Agreement n 723268

Improved Thermal Insulating Properties of Renewable Polyol Based Polyurethane Foams Reinforced with Chicken Feathers

In the present work, sustainable rigid polyurethane foams (RPUF) reinforced with chicken feathers (CF) were prepared and characterized. The bio-based polyol used to formulate the foams was obtained from castor oil. This investigation reports the influence of the chicken feathers fibers as reinforcement of RPUF, on water absorption, thermal, mechanical and morphological properties (field-emission scanning electron microscope—FESEM) and thermal conductivity on water-blown biofoams. It was found that the biofoams improved thermal insulating properties when CF was added. The addition of CF to foams provided lower heat flux density to the biofoams obtaining bio-based materials with better insulation properties. The results obtained in this study proved that the incorporation of CF to RPUF modified the cell structure of the foams affecting their physical and mechanical properties, as well as functional properties such as the heat transmission factor. These biofoams containing up to 45% of bio-based materials have shown the potential to replace fully petroleum-based foams in thermal insulation applications

Nola garbitzen dira arropak garbigailuan?

Gaur egungo etxe gehienek dute garbigailua. Auskalo zenbat aldiz erabiltzen dugun arropak behar bezain garbi edukitzeko. Garbigarrien merkatua kimika arloko handienetariko bat da; baina inoiz pentsatu al dugu ordubete inguru eta hainbat bira eman ondoren nola eta zergatik garbitzen diren arropa zikinak garbigailuan? Historia apur bat Xaboia duela 5.000 urte inguru erabili zen lehen aldiz. Babiloniarrek lortu zuten lehenengo xaboia, hainbat koipe hautsetan egosita, eta, antza, ilea apaintzeko erabiltzen zuten. Geroztik, garai guztietako zibilizazioetan izan dira xaboi-egileak. Egipton, adibidez, orain dela (Argazkia: E. Carton). 3.500 urte, goi-mailako jendea sarri bainatzen zen abere- eta landare-koipez eta gatz alkalinoz egindako xaboiekin. Erromatarrek eta greziarrek ere sarri erabiltzen zituzten xaboiak, garbitzeko eta medikuntzan. Hainbat kondairaren arabera, xaboi hitza erromatarrek eman zioten horren ongi garbitzen zuen produktuari. Badirudi Sapo izeneko mendian sakrifikatutako abereak erre egiten zirela, eta ondoren sortutako errautsak erraz nahasten zirela isuritako abere-koipeekin. Auskalo nola, nahasketa horiek Tiber ibaira isuri eta emakumeek arropak garbitzen zituzten tokira iristen ziren. Emakume horien esanean, arropak errazago garbitzen ziren mendi-tontorrean nahasketa bitxi hori errekara isuri ondoren. Erdi Aroan, xaboi ugari egiten zen oliba-olioa erabiliz Espainian, Frantzian eta Italian. Xaboi-produkzio modernoa 1811. urtean hasi zen, Michel Eugene Chevreul kimikari frantsesak koipeen, gantz-azidoen eta glizerinaren ezaugarriak eta haien arteko kimika ikertu zituenean. Detergentea, ordea, berriagoa da. Merkatuan, 1907. urtean agertu zen lehen aldiz, Persil enpresa alemaniarraren eskutik. Detergente horrek, betiko xaboiak izateaz gain, sodio perboratoa, sodio silikatoa eta sodio karbonatoa zituen (perboratoa + silikatoa = PERSIL). Detergente eta xaboien arteko desberdintasun nabariena jatorria da. Detergenteak sintetikoak dira eta petrolioaren frakzioetatik lortzen dira. Xaboiak, ostera, naturalak dira. Nahiz eta oso garbitzaile onak izan, xaboien errendimendua asko murrizten da ur eta gatz mineralen presentzian. Detergenteena, berriz, handitu egiten da egoera berean. Garbiketa-mekanismoak Detergenteak sintetikoak dira, eta petrolioaren frakzioetatik lortzen dira. (Argazkia. E. Carton). Garbiketa nola gertatzen den ulertzeko, hiru elementuren elkarrekintzari jarri behar zaio arreta: garbitu beharrekoari, ehuna kasu honetan; zikinkeria edo orbanari, hau da, ehunetik garbitu beharrekoari (koipea, orokorrean); eta detergentea disolbaturik dagoen ur-disoluzioari. Hiruren arteko harreman egokian dago garbiketaren gakoa, baina harremanaren xehetasunak jakitea ez da erraza izan. Detergenteen jokabidea azken hamarkadetan egindako ikerkuntzari esker ulertu da, lehen aldiz erabili zirenetik ia ehun urte pasa diren arren. Izan ere, detergenteekin, kosmetiko askorekin gertatzen den bezalaxe, fabrikatzaileek ez dute osagai askoren funtzioa ezagutzen. Jakin badakite, ordea, produktuek balio dutela eta beren eginbeharra ondo betetzen dutela. Garbiketa-prozesua ahalik eta errazen azaltzeko, bi ataletan bana daitezke garbigailuan gertatzen diren pausoak. Lehenengoan, ehunaren garbiketan, ehuna zikintzen duten orban-tantak ehunetik ateratzen dira. Bigarrenean, erronka bikoitza da: tanta horiek detergente disoluzioan sakabanatuta mantentzea eta ehunera ez bueltatzea lortu behar da. Argi dago bigarren atala lehenengoa bezain garrantzitsua dela, bigarrenean gauzak ondo egiten ez badira ehunek zikin egoten jarraituko baitute. Kontuan izan behar da, era berean, garbiketa-mekanismoa ez dela bakarra. Ehun- eta zikinkeria-mota asko dago, eta guztiek ez dute berdin jokatzen; ondorioz, ezinezkoa da garbiketa-prozesua ondo azalduko duen teoria edo mekanismo bakar bat aurkitzea. Orbanaren eta ehunaren arteko elkarrekintza kimikoa bada, lotura kobalentea adibidez, bien arteko lotura gehigarri kimikoen bidez hautsi behar da. Horretarako, entzimak edo lixiba erabiltzen dira. Adibidez, proteasa eta amilasa entzimek txokolate-, esne- edo belar orbanetako almidoi- eta proteina-kateak apurtzen dituzte, eta orbana erabat zatitu eta txikitzen dute. Baina orbana eta ehuna indar elektrostatikoen bidez, edo molekulen arteko erakarpen-indar ahulen bidez badaude itsatsita, garbiketa-mekanismoa guztiz desberdina da. Hori da, adibidez, partikula solidoen zein koipe-tanten kasua. Kasu horietan, surfaktanteak erabiltzen dira orbanei ehunetik ateratzen laguntzeko. Surfaktanteak, molekula tentsioaktibo ere deitzen zaie, detergenteen osagai garrantzitsuenetakoak dira, eta hainbat betebehar dituzte. Ehunaren eta orbanaren gainazal-tentsioa txikitu eta orbana ehunetik ateratzeko egin beharreko lana murrizten dute; gainera, surfaktanteek orbanaren gainazalean ezartzeko joera daukate eta, ondorioz, erraztasun handiz emultsionatzen dituzte uretan. Azkenik, koipe-tantak bata bestetik ondo babesten dituzte, berriz ere elkartu ez daitezen. Orbana likidoa bada, garbiketa-prozesua era sinple batez azal daiteke matematikoki. Jar dezagun olio- edo koipe-tanta bat ehun edo zuntz baten gainean. Tantak ehunarekin angelu bat sortzen du, kontaktu-angelua (q), hain zuzen ere. Angelu horrek ehuna garbitzeko zailtasunaren berri ematen du: txikia bada, orbanaren eta ehunaren arteko ukimen-azalera handia izaten da, eta, beraz, zailagoa da garbitzea. Angelua handia bada, berriz, alderantziz gertatzen da. Logikoa da, lan fisikoa egin behar baita koipe-tantatxoa ehunaren gainazaletik ur-disoluziora eramateko. Lan txikiena ehunaren eta tantatxoaren arteko q angelua 0 denean egin behar da. Orduan, biek puntu batean ukitzen dute elkar, eta garbiketa bat-batekoa da. Zerotik gora, lana handitu besterik ez da egiten. Hala ere, angelua 90º baino txikiagoa bada (B), kontua ez da horren zaila, surfaktanteen laguntza nahikoa izaten baita orbana ehunetik ateratzeko. Angelua 90º eta 180º bitartekoa bada (C), ordea, olio-tantaren zati batek bakarrik alde egiten du ehunetik, eta arropak zikin egoten jarraitzen du garbigailutik ateratzean. Kasu horretan, beste mekanismo bat erabili behar da arropa garbitzeko, olio-tantak disolbatzea, adibidez. (....

Estabilidad de las emulsiones de Pickering utilizadas en la elaboración de productos agroquímicos

The present paper concerns emulsions stabilised by silica nanoparticles with modified surface. Nanoparticles with silanol groups at the surface may stabilise oil-in-water (o/w)) emulsions whereas silica nanoparticles modified with hydrophobic groups stabilise water-in-oil (w/o) emulsions. It has been observed that the nature of the emulsion, o/w or w/o depend on the particle type as well as the oil or water content in the emulsion. The type of the emulsion has been determined by conductivity measurements and drop test.El presente artículo trata sobre emulsiones estabilizadas mediante nanopartículas de sílice cuya naturaleza superficial se puede modificar. Nanopartículas con grupos silanol en la superficie principalmente estabilizan emulsiones de aceite en agua y aquellas nanopartículas modificadas con grupos hidrófobos estabilizan emulsiones de agua en aceite. Se ha observado por lo tanto que la naturaleza de la emulsión, agua en aceite o viceversa depende del tipo de partícula y además de la proporción fase acuosa-fase orgánica. El tipo de emulsión se ha determinado mediante medidas de conductividad y el método de la gota o dispersabilidad

Evaporation rates from emulsions stabilised by surfactants and nanoparticles

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Thermoformable and recyclable CFRP pultruded profile manufactured from an epoxy vitrimer

In the present work a recyclable and reprocessable vitrimer suitable for pultrusion process has been formulated and a pultruded profile reshaped by thermoforming has been manufactured therefrom. A DGEBA epoxy resin with medium range viscosity and a bis(a-aminophenyl disulfide) as dynamic crosslinker were used for the synthesis of the vitrimer. The thermal stability was studied by thermogravimetric analysis (TGA) and curing behaviour and curing kinetics were studied by means of dynamic scanning calorimeter (DSC) and rheology measurements. Mechanical properties of the dynamic resins and its counterpart epoxy resin and of the fabricated carbon fibre reinforced polymers (CFRP) were determined. The dynamic resin showed a fast stress relaxation at temperatures above 150 °C. Finally, as a proof of concept, mechanical recyclability and the thermoforming of the vitrimer-based pultruded profile have been validated