Ökningen av världspopulationen har orsakat en ökad avfallsgenerering. Avfallet kan innehålla betydelsefulla ämnen, vilka kan användas som råvaror i många olika material och för olika ändamål. Därför har omfattande forskning genomförts för att ta till vara på avfall som orsakar miljöföroreningar och ur dessa utveckla mer hållbara och biologiskt nedbrytbara material. Exempel på detta är fibrer och textilier framställda av polysackaridmaterial, särskilt från kitin och kitosan, som finns tillgängliga som biprodukt från såväl skaldjur som insekter och cellväggar från svampar. Kitin är efter cellulosa den vanligaste aminopolysackarid-polymeren som har en liknande struktur, medan kitosan är den deacetylerade formen av kitin som är den mest välkända och det viktigaste derivatet av kitin. Kitosan kan framställas från kitin genom antingen kemisk deacetylering eller enzymatiska beredningar, men för kommersiell skala idag, är produktion av kitosan med kemisk metod som deacetylering av kitin med en alkali såsom NaOH, mer lämplig och att föredra. Både kitin och kitosan är biobaserade material som har speciella egenskaper såsom hög specifik styvhet och hållfasthet, samtidigt som biologisk nedbrytbarhet är möjlig. Dessutom förekommer materialen rikligt i naturen, vilket gör dem till passande och konkurrenskraftiga ersättare till traditionella fibrer. Textilier är en stor källa till koldioxidutsläpp på grund av massiv global produktion och att även icke-nedbrytbara fibrer i vissa fall används i produktionen. Fibrer är den elementära enheten i textilier förutom bomull, som traditionellt används för textilproduktion. Det finns olika typer av fibrer som vanligtvis delas in i syntet- och biobaserade fibrer härrörande från förnybara resurser. Dessa förnybara fibrer har skapat ett stort intresse från världens textiltillverkare för att ställa om sin produktion och exempelvis producera gasbindor med återvinningsbara och biologiskt nedbrytbara material. Användningen av kitin och kitosan i textilindustrin är mycket intressant och viktig, dels på grund av deras mångsidighet och stora överflöd i naturen, dels då materialen annars anses vara spill eller restprodukter utan signifikant betydelse. Syftet med denna avhandling var att göra en litteraturöversikt om metoder för produktion av fibrer och textilier från kitin och kitosan, samt att undersöka hur de kan användas och dess miljövänliga aspekter. I denna avhandling har olika metoder baserade på många undersökningar och experiment introducerats, för att förstå och utvärdera möjliga processer för bildning av kitin- och kitosanfibrer. Dessutom har egenskaperna hos de framtagna fibrerna såsom draghållfasthet och töjning undersökts. För kitinproduktion har fem olika metoder studerats med användning av olika lösningsmedel av joniska vätskor såsom 1-etyl-3-metylimidazoliumacetat [C2mim] OAc, 1-butyl-3-metylimidazoliumklorid [C4mim] Cl och 1-etyl-3-metylimidazoliumklorid [C2mim] Cl, triklorättiksyra (TCA) och metylenklorid, en kombination av TCA, klorhydrat och metylenklorid, en blandning av myrsyra (FA), diklorättiksyra (DCA) och isopropyleter (iPE), liksom en direkt upplösning i NaOH/tiourea/urea. Produktion av nanofibrer från krabbskal, räkskal, kommersiella kitinpulver och svamp har undersökts, samt sårförband som en icke-vävd textil, genom att undersöka två olika produktionsmetoder. Många studier på kitosanproduktion har listats med fokus på typen av spinnteknik såsom våtspinning med användning av en cellulosa/kitosan-kompositlösning samt fibrer bildade av myrsyramodifierad kitosan. Dessutom listas olika typer av tekniker för torrspinning, torrstråle-våtspinning och elektrospinning. Slutligen har sårförbandsprocessen med användning av icke-vävda textilier av chitosan/hyaluronan också inkluderats. Sammanfattningsvis är produktion av textilfibrer med kitin och kitosan möjlig och kan göras på olika sätt. På grund av deras egenskaper och antimikrobiella effekter blir de intressanta alternativ till medicinska tillämpningar såsom suturer, sårförband, vävnadsteknik och antimikrobiellt medel. I likhet med andra material har kitin och kitosan fördelar, men även vissa nackdelar såsom svag och låg draghållfasthet hos de framtagna fibrerna och att de är delvis lösliga i substanser med pH under 5,5. Produktion av fibrer och textilier baserade på kitin och kitosan är fortfarande en utmaning på grund av de många modifieringssteg som krävs. Bland annat måste man ta hänsyn till lösningsmedlet som används för upplösning, välja rätt spinnteknik samt att använda ett lämpligt koagulationsbad följt av en flerstegs tvätt- och torkningsprocess. Dessa metoder hjälper till för att uppnå önskade fibrer med en mycket god kvalitet. För att uppnå en kostnadseffektiv, miljövänlig, konkurrenskraftig och storskalig textilproduktion - särskilt inom klädindustrin - krävs därför framtida arbete för att förfina och utveckla tekniken. / The growing of the world population caused an increase in waste generation which may contain high-value substances that can be used as raw materials in many applications. Therefore, tremendous research has been done towards the conversion of those wastes, that cause environmental pollution, in more sustainable and biodegradable materials. Part of these materials are fibers and textiles produced from polysaccharide materials especially from chitin and chitosan. Both chitin and chitosan are available as a by-product of seafood as well as in insects and cell walls of fungi, and can be used in many different applications. Chitin is the most abundant amino polysaccharide polymer after cellulose which has a very similar structure to cellulose, while chitosan is the deacylated form of chitin and it is the well-known and the most important derivative of chitin. Chitosan can be produced from chitin by either chemical deacetylation or enzymatic preparations. However, at commercial scale nowadays, the production of chitosan by chemical method like deacetylation of chitin with an alkali such as NaOH, is more suitable and preferable. Both chitin and chitosan are bio-based materials that have special properties such as high specific stiffness and strength, they are biodegradable and plentifully available in the nature, which make them an active competitive to the production of the synthetic fibers. Textiles are a big source for carbon emissions because of their large volume production and origin, in some cases, from non-biodegradable fibers. Fibers are the elementary units of textiles besides cotton that is traditionally used for textile production. There are different types of fibers that are usually divided into synthetic- and bio-based fibers derived from renewable resources which are getting a lot of interest in order to produce more biodegradable materials. Therefore, using chitin and chitosan in the textile industry is very important due to their versatility and large abundancy in nature. Additionally, they are biodegradable, biocompatible, non-toxic, and they are essentially able to form fibers and textiles. The purpose of this thesis was to make a literature review about the methods for the production of fibers and textiles from chitin and chitosan, including their applications and their environmentally friendly aspects. Different methods have been introduced in this thesis based on many researches and experiments in order to understand and evaluate which are the possible processes for chitin and chitosan fiber formation as well as the properties of the resulted fibers such as tensile strength and elongation. For fiber production from chitin has been studied by using different solvents including ionic liquids such as 1-ethyl-3-methylimidazolium acetate [C2mim]OAc, 1-butyl-3-methylimidazolium chloride [C4mim]Cl and 1-ethyl-3-methylimidazolium chloride [C2mim]Cl, trichloroacetic acid (TCA) and methylene chloride, a combination of TCA, chloral hydrate and methylene chloride, a mixture of formic acid (FA), dichloroacetic acid (DCA) and isopropyl ether (iPE), as well as a direct dissolution in NaOH/ thiourea/ urea. Additionally, nanofibers production from crab shells, prawn shells, shrimp shells, commercial chitin powders and mushrooms has been studied. Finally, wound dressing which is one of the nonwoven fabrics applications is introduced by referring to two methods of production. For fiber production from chitosan, many studies have been listed focusing on the type of the spinning technique such as wet spinning by using a cellulose/chitosan composite solution as well as fibers formed from formic acid modified chitosan. In addition, dry spinning, dry-jet wet spinning and electrospinning techniques have been studied. The wound dressing process by using chitosan/hyaluronan nonwoven fabrics has also been introduced. In conclusion, the production of textile fibers made of chitin and chitosan is possible and can be made in different ways. And because of their properties as biocompatibility, nontoxicity as well as their antimicrobial effects, they become interesting candidates for medical applications such as in sutures, wound dressing, tissue engineering and as antimicrobial agent. Similar to other manufactural industries, the production of fibers and textiles from chitin and chitosan have many advantages such as good values for dry tensile strength and elongation at break, antimicrobial activity and many more. At the same time, this production has some disadvantages such as the weak and low tensile strength of the resulted fibers and that they are partially soluble at pH below 5.5. Producing fibers and textiles based on chitin and chitosan is still a challenge because of the many modification steps that are needed. The modifications include the solvent used for dissolution, choosing the proper spinning technique as well as using an appropriate coagulation bath followed by the conditions of washing and drying steps. Thus, the desired fibers with a very good quality mentioned before would be achieved. Therefore, a lot of future work is needed in this manner because the intention is to achieve a cost-effective, environmentally friendly and a competitive technology for the large scale textile production especially in clothing industries.

Nanoparticles are very interesting components. Due to their very large specific surface area they possess properties in between molecules and macroscopic materials. In addition, a material built up of hierarchically assembled nanoparticles could obtain unique properties, not possessed by the nanoparticles themself. A very interesting group of nanoparticles is the cellulose nanofibrils. The fibrils are found in various renewable resources such as wood, bacteria and tunicates. In this work fibrils extracted from wood is studied. In wood the fibrils are the smallest fibrous component with the approximate dimensions; 4 nm in width and length in the micrometer range, providing a high aspect ratio. In addition, they have a crystallinity above 60% and, hence, a high stiffness. These fibrils are hierarchically ordered in the wood fiber to give it its unique combination of flexibility and strength. The properties of the fibrils make them very suitable to be used as reinforcement elements in composites and, due to their ability to closely pack, to make films with excellent gas barrier properties. The key aspect to design materials, efficiently utilizing the properties of the individual fibrils, is to control the arrangement of the fibrils in the final material. In order to do so, the interactions between fibrils have to be well characterized and controlled. In this thesis the interaction between fibrils in aqueous dispersions is studied, where the main interactions are attractive van der Waals forces and repulsive electrostatic forces. The electrostatic forces arise from carboxyl groups at the fibrils surface, which either are due to hemicelluloses at the fibrils surfaces or chemically introduced to the cellulose chain. This force is sensitive to the chemical environment. It decreases if the pH is reduced or if the salt concentration is increased. If it is strongly reduced the system aggregates. In dilute dispersions aggregation causes formation of multiple clusters, whereas in semi-dilute dispersions (above the overlap concentration) a volume filling network, i.e. a gel, is formed. The tendency of aggregation, i.e. the colloidal stability, can be predicted by using the DLVO theory. In this thesis DLVO predictions are compared to aggregation measurements conducted with dynamic light scattering. Good agreement between experiments and the designed theoretical model was found by including specific interactions between added counter-ions and the carboxyl groups of the fibrils in the model. Thus, the surface charge is both reduced by protonation and by specific interactions. This emphasizes a much larger effect of the counter-ions on the stability then generally thought. Hence, this work significantly improves the understanding of the interfibril interactions in aqueous media. As mentioned above, the fibrils can be physically cross-linked to form a gel. The gelation is an instant process, occurring at pH or salt levels causing the interfibril repulsion to decrease close to zero. If a well dispersed stationary dispersion is gelled, the homogenous and random distribution of the fibrils is preserved in the gel. These gels can be used as templates to produce composites by allowing monomers or polymers to enter the network by diffusion. In an effort to mimic processes occurring in the tree, producing materials with fibrils aligned in a preferred direction, the ability to form gels with controlled fibril orientation were studied. Such networks were successfully produced by applying strain to the system prior or past gelation. Orientation prior gelation was obtained by subjecting the dispersion to elongational flow and freezing the orientation by “turning off” the electrostatic repulsion. Orienting the fibrils after gelation was achieved by applying shear strain. Due to the physical nature of the crosslinks, rotation in the fibril-fibril joints can occur, enabling the fibrils to align in the shear direction. This alignment significantly increased the stiffness of the gels in the shear direction. / QC 20111205

Electrospinning is a useful technique that can generate micro- and nano-meter sized fibers from polymer materials. Modification of the electrospinning parameters and apparatus can generate nanofibers for use in diverse applications ranging from tissue engineering to nanocomposite fabrication; however, electrospun fibers are typically collected in a random orientation and over large areas limiting their applications.  Here we present several methods to control the deposition of electrospun nanofibers, such as the use of a single auxiliary electrode ring and a negatively charged collector substrate to control the deposition area and the construction of a parallel electrode collector known as the triple electrode setup to control the uniaxial alignment of nanofibers. The numerous constructed setups were advanced by the use of electric field computations to assess the distribution of the electric field and its effect on the deposition behavior and morphology of the electrospun nanofibers. The electrostatic force imposed by the auxiliary electrodes provides converged electric fields that direct the nanofibers to their desired deposition targets. Here it is shown that the use of the auxiliary electrode ring dramatically decreased the deposition area of nanofibers, the negatively charged substrate yielded more uniform nanofibers and the triple electrode setup is a viable method to achieve uniaxially aligned nanofiber mats.    The electrospinning of copolymers appears as an attractive option for enhancing the overall properties of nanofibers as it offers possibility of an intrinsic control of the polymeric material itself. The poly(methyl methacrylate)-graft-poly(dimethylsiloxane) graft copolymer  (PMMA-g-PDMS) is considered to be an organic-inorganic hybrid material with much potential in its use in nanocomposites, and in this work has been successfully synthesized and electrospun via the various constructed electrospinning setups.   In the final elements of this work, the triple electrode setup is used in combination with a dynamic rotating collector to yield a novel collector and has been successfully used to produce PMMA-g-PDMS nanofiber sheets that were further incorporated in a PDMS matrix to yield nanocomposite sheets. A variant of the triple electrode setup with partially insulated electrodes is devised in combination with a methodology to remove the nanofibers from the collector. The nanofibers once removed and dried were incorporated in a PDMS matrix to yield nanocomposites. The preferential dissolution of the fibers from the matrix rendered the fibers to templates and a final porous material with uniaxial nanochannels could be obtained.   This work is believed to be able to lead to a better understanding of the mechanisms of nanofiber deposition and alignment, and should be of help to the design of more practical collecting structures, hence promoting the applications of the electrospinning technique.

Biological organisms, organs and tissues have evolved through natural selection diverse functional and structural traits to accomplish complex tasks. For example, small insects with tiny thermal capacitance have developed tailored spectral properties and behavioral tactics to mitigate rapid changes of body temperatures caused by environmental electromagnetic radiations; neural networks in the brain, through changing the efficacy of synapses, can recognize hidden patterns and correlations in raw data, cluster and classify them, and continuously learn and improve over time. These biological systems are a rich source of bio-inspiration for developing solutions to address engineering challenges. My thesis work focuses on the intersection between photonics and biology and explores three unique biological systems and their technological implications. Beginning with the investigation of butterfly wings, we observed that the wings contain a matrix of living structures, including mechanical and thermal sensory neural cells, hemocytes, pheromone producing organs, , and even “wing hearts”, and that these living structures carry out their specific functions over the entire life span of butterflies but are vulnerable to sustained high temperatures. We discovered that butterflies have evolved heterogeneously thickened wing cuticles and special nanostructured wing scales to locally enhance thermal emissivity so that the regions of the wings containing living structures can better dissipate heat through thermal radiation. Furthermore, we discovered that butterfly wings almost always possess enhanced reflectivity in the near-infrared, which can significantly reduce heating caused by solar radiation. This enhanced near-infrared reflectivity is found to originate from optical scattering at the porous wing scales, especially pale-colored scales underneath the surface layer of colorful ones. Besides these structural adaptations, our bioassays showed that butterflies utilize a number of behavioral strategies to avoid overheating or overcooling of their wings. We found that butterflies can use their wings as a fast and sensitive temperature monitor to detect the direction and strength of sunlight or artificial light applied onto the wings; as such, they can adapt the most suitable postures to minimize overheating of the wings if the illumination is too strong and to warm up the wings when ambident temperatures are insufficient for taking flight. Drawing inspiration from the multi-layered wing scales, which impart coloration to the wings while maintaining their high near-infrared reflectivity, we developed a double-layered, radiative-cooling coating that is able to minimize solar heating while still stay colorful. The second part of my thesis work explored nanostructured fibers and textiles as a novel solution for radiative cooling. The work was motivated by our discovery that the silk fibers produced by the caterpillars of the Madagascan moon moth (Argema mittrei) contain a high density of filamentary air voids, which enable individual fibers of the moth to strongly reflect light over the solar spectrum. This, in combination with natural polymers’ intrinsic high mid-infrared emissivity, provides the cocoons of the moth with remarkable passive radiative-cooling properties. We developed fabrication platforms to produce synthetic fibers with filamentary air voids by modifying both wet spinning and melt extrusion techniques. The melt extrusion approach, in particular, is implemented in an industry-scale fiber extrusion machine for high-throughput, high-yield production. The fabricated nanostructured fibers reproduce the prominent solar reflectivity of the Madagascan moon moth silk fibers and possess high emissivity due to the variety of chemical bonds in the synthetic polymers used. The melt-extruded fibers were twisted into yarns, which were subsequently woven and knitted into fabrics. The finished fabric samples were demonstrated to perform as effective radiative cooling devices compared to conventional white fabrics. Lastly, inspired by how neural networks in the brain form the basis of learning and motivated by how artificial neural networks are implemented in computers, we develop a novel platform of optical neural computing, a smart glass, for object recognition. Our optical neural network takes advantage of strong light-matter interactions with sub-wavelength resolutions in metasurfaces to emulate the layered computations in a biological or artificial neural network. In the simplest implementation of a single-layer smart glass, a metasurface was trained to provide 2D phase modulations that can transform the complex optical wave scattered from an input object into a characteristic intensity distribution pattern on the output plane corresponding to the identity of the object. We experimentally demonstrated the recognition of handwritten numerical digits and letters with different fonts with high accuracies using the smart glass and explored the capability of a polarization-multiplexing smart glass based on birefringent metasurfaces for performing distinct recognition tasks at orthogonal incident polarizations. This optical neural computing platform represents a new paradigm of computation operating at the speed of light with no power consumption and this physical-wave-based computation guarantees data security beyond digital encryption.

Indiana University-Purdue University Indianapolis (IUPUI) / This study represents a cost-effective method to advance the physical and mechanical properties of carbon fiber-reinforced polymer (CFRP) prepreg composite materials, where electrospun multiwalled carbon nanotubes (CNTs)/epoxy nanofibers fabricated and deposited in between the layers of traditional CFRP prepreg composite. CNT-aligned epoxy nanofibers were uniformly formed by an optimized electrospinning method. Electrospinning is considered one of the most flexible, low-cost, and globally recognized methods for generating continuous filaments from submicron to tens of nanometer diameter. Nanofilaments were incorporated precisely on the layers of prepreg to accomplish increased adhesion and interfacial bonding, leading to increased strength and enhancements in more mechanical properties. As a result, the modulus of the epoxy and CNT/epoxy nanofibers were revealed to be 3.24 GPa and 4.84 GPa, leading to 49% enhancement. Furthermore, interlaminar shear strength (ILSS) and fatigue performance at high-stress regimes improved by 29% and 27%, respectively. Barely visible impact damage (BVID) energy improved considerably by up to 45%. The thermal and electrical conductivities were also increased considerably because of the highly conductive CNT networks present in between the CFRP layers. The newly introduced approach was able to deposit high content uniform CNTs at the ply interface of prepregs to enhance the CFRP properties, that has not been achieved in the past because of the randomly oriented high viscosity CNTs in epoxy resins.

This study represents a cost-effective method to advance the physical and mechanical properties of carbon fiber-reinforced polymer (CFRP) prepreg composite materials, where electrospun multiwalled carbon nanotubes (CNTs)/epoxy nanofibers fabricated and deposited in between the layers of traditional CFRP prepreg composite. CNT-aligned epoxy nanofibers were uniformly formed by an optimized electrospinning method. Electrospinning is considered one of the most flexible, low-cost, and globally recognized methods for generating continuous filaments from submicron to tens of nanometer diameter. Nanofilaments were incorporated precisely on the layers of prepreg to accomplish increased adhesion and interfacial bonding, leading to increased strength and enhancements in more mechanical properties. As a result, the modulus of the epoxy and CNT/epoxy nanofibers were revealed to be 3.24 GPa and 4.84 GPa, leading to 49% enhancement. Furthermore, interlaminar shear strength (ILSS) and fatigue performance at high-stress regimes improved by 29% and 27%, respectively. Barely visible impact damage (BVID) energy improved considerably by up to 45%. The thermal and electrical conductivities were also increased considerably because of the highly conductive CNT networks present in between the CFRP layers. The newly introduced approach was able to deposit high content uniform CNTs at the ply interface of prepregs to enhance the CFRP properties, that has not been achieved in the past because of the randomly oriented high viscosity CNTs in epoxy resins.

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