Orientador: Rondinelli Donizetti Herculano / Resumo: Em um cenário, onde ulceras dérmicas correspondem a um grave problema de saúde pública, surgiu há mais de duas décadas, o látex da seringueira. A membrana de látex, cerne desse estudo, foi composta por dois elementos advindos da flora nativa brasileira: a) o látex da seringueira, Hevea brasiliensis, com grande capacidade de promover o aumento da vascularização, epitelização, neoformação de glândulas submucosas e fibras musculares; b) o extrato do barbatimão, do gênero Stryphnodendron barbatimam Mart.com alto teor de taninos capazes de promover a contração da ferida e aumentar a formação de vasos e fibroblastos. Assim, esta pesquisa se desenvolveu com o objetivo de comparar o potencial cicatrizante da membrana de látex natural porosa, reforçada com extrato de barbatimão em comparação a outros cinco tipos de coberturas, dentre os quais, três diferentes formas de membrana de látex natural, pomada de barbatimão e carvão ativado com prata. Tratou-se de um estudo experimental não randomizado, com controle na composição dos grupos. Essa amostra foi distribuída em grupos que foram constituídos com participantes de diferentes idades, entre 20 e 90 anos. Os grupos foram compostos como segue: Grupo - G1 (Membrana de látex natural porosa incorporada com extrato de barbatimão); Grupo - G2 (Membrana de látex natural incorporada com extrato de barbatimão); Grupo - G3 (Membrana de látex natural); Grupo - G4 (Membrana de látex natural porosa); Grupo - G5; (pomada de barbatimão); Grupo - G6; (... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In a scenario that dermic ulcer correspond to a public health severe problem, a long time ago has surged the rubber tree latex. The latex membrane, that is this study´s core, consisted of two Brazilian native flora elements: a) the rubber tree latex, Hevea brasiliensis, with a great capability of vascularization, epitheliarization, submucosal glands´ neoformation and muscle fibers; b) the Barbatimão extract, from the Stryphnodendron barbatimam Mart. genus, with a high percentage of tannins able to promote the wound contraction increase the vessels and fibroblasts formation. Therefore, this research was developed with the purpose to compare the healing potential from the porous natural latex membrane, reinforced with Barbatimão extract in comparison with another five kinds of covering, among them, three different of natural latex membrane, barbatimão ointment and silver activated charcoal. It was an nonrandomized and experimental study with control in this groups composition. This sample was distributed in groups that were constituted with different ages participants, between 20 and 90 years old. The groups were composed as follows: Group – G1 ( Porous natural latex membrane incorporated with barbatimão extrac); Group – G2 (natural latex membrane with barbatimão extract); Group – G3 (Natural Latex Membrane); Group – G4 (Porous natural latex membrane); Group – G5 (barbatimão ointment); Group – G6 (Silver activated charcoal plate). All groups were submitted to the elaborated ins... (Complete abstract click electronic access below) / Doutor

Orientador: Rondinelli Donizetti Herculano / Resumo: O látex de natural, extraído da seringueira Hevea brasiliensis, pode estimular a regeneração tecidual, isso ocorre pela formação de capilares sanguíneos que aumentam a vascularização no local de sua aplicação. No entanto, a aplicação do látex natural encontra desafios como o aumento do exsudato quando aplicado em feridas diabéticas, a necessidade de remoção cirúrgica quando utilizado como implante, entre outros. Portanto, é necessário o desenvolvimento de matrizes que apresentem a característica do látex natural de estímulo da regeneração tecidual, aliada à outras propriedades, tais como a absorção de fluídos em aplicações no tratamento de lesões exsudativas, aumento da degradabilidade do material em tratamentos onde o implante é necessário, e o fornecimento de nutrientes que auxiliem na regeneração dos tecidos. O presente trabalho apresenta os resultados do desenvolvimento e caracterização membranas composta por látex natural, alginato e colágeno. Por meio de técnicas padrões de caracterização de biomateriais, foi observado que, devido às suas propriedades mecânicas, químicas e biológicas, membrans híbridas compostos por bNRL, alginato e colágeno mostram uma grande promessa para o tratamento de feridas dérmicas como úlceras diabéticas. A biocompatibilidade das membrans e a capacidade de criar um ambiente favorável ao redor do leito da ferida são características-chave que contribuem para o seu valor em facilitar e acelerar a regeneração de tecidos. / Abstract: Natural latex from the rubber tree Hevea brasiliensis can stimulate tissue regeneration, this occurs by the formation of blood capillaries that increase vascularization at the site of its application. However, the application of natural latex faces challenges such as increased exudate when applied to diabetic wounds, the need for surgical removal when used as an implant, among others. Therefore, it is necessary to develop matrices that have the characteristic of natural latex to stimulate tissue regeneration, combined with other properties, such as fluid absorption in applications in the treatment of exudative lesions, increased material degradability in treatments where the implant it is necessary, and the supply of nutrients that assist in tissue regeneration. The present work presents the results of the development and characterization of membranes composed of natural latex, alginate, and collagen. Through standard techniques for characterizing biomaterials, it was observed that, due to their mechanical, chemical, and biological properties, membranes composed of bNRL, alginate, and collagen show great promise for the treatment of dermal wounds such as diabetic ulcers. The biocompatibility of the membranes and the ability to create a favorable environment around the wound bed are key characteristics that contribute to its value in facilitating and accelerating tissue regeneration. / Doutor

This research aims to add to the current knowledge available for miniemulsion polymerization reactions and to use this knowledge to synthesize multifunctional nanosized latex particles that have the potential to be used in catalysis. The physical properties of the latex can be adjusted to suit various environments due to the multiple functional groups present. For this research, styrene, pentafluorostyrene, azidomethyl styrene, pentafluorostyrene with azidomethyl styrene and pentafluorostyrene with styrene latexes were produced, and analyzed by dynamic light scattering. The latexes were synthesized using a miniemulsion polymerization technique found through this research. Potassium oleate and potassium 1,1,2,2,3,3,4,4-nonafluorobutane-1-sulfonate were used as surfactants during the miniemulsion polymerization reaction to synthesize pentafluorostyrene with azidomethyl styrene latex. Transmission electron microscopy data and dynamic light scattering data have been collected to analyze the structure of this latex, and it has been synthesized using a number of conditions, differing in reaction time, surfactant amount and sonication methods. We have also improved the solubility of the latex through a copper(I) catalyzed 1,3-dipolar azide-alkyne reaction, by clicking (polyethylene glycol)5000 onto the azide functional groups.

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Water-borne latex coatings represent a safer, more user-friendly, and environmentally responsible alternative to solvent-borne coatings, and are growing in popularity each year. However, these coatings often exhibit unfavorable performance when exposed to water for extended periods of time. This prolonged exposure often results in water uptake, which may give rise to other detrimental effects such as a decrease in modulus, blushing or water-whitening, reduced serviceable life, and softening of the film. In this study, various polymer composition latex design spaces are studied to develop an understanding of how water uptake can be modulated and minimized using common synthetic approaches. Factors including monomer selection, particle size, polymer molecular weight, crosslinking density, surfactant choice and particle stabilization, processing variables and Tg are considered. In addition, some formulation modifications including PVC, film thickness, and choice of coalescent package are explored to gain a more comprehensive understanding of final product performance. In quantifying the total water uptake of the films, gravimetric analysis tends to be the preferred method employed in the coatings industry. However, other analytical approaches can be used to better understand the effect that water has on the properties of the film. These methods may include differential scanning calorimetry, electrochemical impedance spectroscopy, immersion testing using dynamic mechanical analysis, and others. In the work, it has been shown that interparticle crosslinking, surfactant, and monomer selection can have an extreme influence on the water uptake of free films. Film samples exhibit a range of water uptake values from nearly 200% to less than 5% over a one-week soak in deionized water. It is thought that the surfactant may provide hydrophilic channels that allow water to v penetrate the film and form heterogeneous domains within the coating. These domains then grow and scatter light, leading to water-whitening and an increase in mass when compared to the dry film. Utilizing monomers with differing relative solubilities in water, such as methyl methacrylate and styrene, further allow control of this effect. Interparticle crosslinking via keto-hydrazide crosslinking, which is achieved during the film formation process, can also prevent the formation and growth of these large water domains, thus resulting in better performing films.

In this thesis, copolymer latexes comprised of various fractions of methyl methacrylate (MMA) and butyl acrylate (BA) were synthesized through surfactant-free emulsion polymerization. A carbon dioxide responsive comonomer, 2-(diethyl)aminoethyl methacrylate (DEAEMA) was also used with an equimolar amount of hydrochloric acid (HCl) to promote its partitioning into the water phase. Changing the MMA/BA fraction gave control over the resulting glass transition temperature of the particles. Following polymerization, the particles from the resulting latexes could be effectively coagulated be adding a small amount of caustic soda, and could be easily separated from water. After washing the particles with deionized water, CO2-redispersibility of the latex particles was evaluated as a function of their respective glass transition temperature. It was determined that coagulated particles higher in MMA content could be easily redispersed into carbonated water with the aid of ultrasonication, preparing stable latexes of the same solids content. For latex particles with a glass transition temperature below ambient conditions, coagulation led to the fusion of individual particles, which inhibited their ability to be redispersed. By conducting the coagulation and redispersion cycles at temperatures cold enough for the BA-rich particles to be below their glass transition temperature, these same latex particles could be effectively redispersed. The relationship between the glass transition temperature of the latexes and their CO2-redispersibility provides guidance from a practical sense for the applicability of CO2-sensitive amine-functionalized molecules in developing industrially useful CO2-redispersible latex products. / Thesis / Master of Applied Science (MASc) / This work examines special type of coagulatable and redispersible latex paint that could potentially reduce the costs in storing and transporting latex paint products. After synthesizing the latex, the nanoscopic polymer particles that make up the latex could be easily coagulated by adding a small amount of sodium hydroxide. Following this, water could be removed and a condensed form of the paint was obtained. The ability to redisperse the particles back into carbonated water was subsequently examined based on the softness of the polymer particles by synthesizing a series of latexes with different fractions of methyl methacrylate (MMA) and butyl acrylate (BA). After synthesis, the latexes that contained higher fractions of MMA were comprised of particles that were less soft than the BA-rich latexes, which made the redispersibility of these particles much easier. Upon coagulation, BA-rich particles fused together upon contact and could not be separated, hence inhibiting their redispersibility. When these same BA-rich latex particles were coagulated at colder temperatures, fusion was inhibited and the redispersibility of particles was greatly improved. Overall, the particles were found to be redispersible if the glass transition temperature of polymer chains within the particles was lower than ambient temperature. Since softer polymer particles are often used for latex paint-based applications, this work provides important and relevant insight in the development of industrially useful CO2-redispersible products.

Additive manufacturing (AM) fabricates complex geometries inaccessible through other manufacturing techniques. However, each AM platform imposes unique process-induced constraints which are not addressed by traditional polymeric materials. Vat photopolymerization (VP) represents a leading AM platform which yields high geometric resolution, surface finish, and isotropic mechanical properties. However, this process requires low viscosity (<20 Pa·s) photocurable liquids, which generally restricts the molecular weight of suitable VP precursors. This obstacle, in concert with the inability to polymerize high molecular weight polymers in the printer vat, effectively limits the molecular weight of linear network strands between crosslink points (Mc) and diminishes the mechanical and elastic performance of VP printed objects. Polymer colloids (latex) effectively decouple the relationship between viscosity and molecular weight by sequestering large polymer chains within discrete, non-continuous particles dispersed in water, thereby mitigating long-range entanglements throughout the colloid. Incorporation of photocrosslinking chemistry into the continuous, aqueous phase of latex combined photocurability with the rheological advantages of latex and yielded a high molecular weight precursor suitable for VP. Continuous-phase photocrosslinking generated a hydrogel scaffold network which surrounded the particles and yielded a solid "green body" structure. Photorheology elucidated rapid photocuring behavior and tunable green body storage moduli based on scaffold composition. Subsequent water removal and annealing promoted particle coalescence by penetration through the scaffold, demonstrating a novel approach to semiinterpenetrating network (sIPN) formation. The sIPN's retained the geometric shape of the photocured green body yet exhibited mechanical properties dominated by the high molecular weight latex polymer. Dynamic mechanical analysis (DMA) revealed shifting of the latex polymer and photocrosslinked scaffold T_g's to a common value, a well-established phenomenon due phasemixing in (s)IPN's. Tensile analysis confirmed elastic behavior and ultimate strains above 500% for printed styrene-butadiene rubber (SBR) latexes which confirmed the efficacy of this approach to print high performance elastomers. Further investigations probed the versatility of this approach to other polymer compositions and a broader range of latex thermal properties. Semibatch emulsion polymerization generated a systematic series of random copolymer latexes with varied compositional ratios of hexyl methacrylate (HMA) and methyl methacrylate (MMA), and thus established a platform for investigating the effect of latex particle thermal properties on this newly discovered latex photoprocessing approach. Incorporation of scaffold monomer, N-vinyl pyrrolidone (NVP), and crosslinker, N,N'-methylene bisacrylamide (MBAm), into the continuous, aqueous phase of each latex afforded tunable photocurability. Photorheology revealed higher storage moduli for green bodies embedded with glassy latex particles, suggesting a reinforcing effect. Post-cure processing elucidated the necessity to anneal the green bodies above the T_g of the polymer particles to promote flow and particle coalescence, which was evidenced by an optical transition from opaque to transparent upon loss of the light-scattering particle domains. Differential scanning calorimetry (DSC) provided a comparison of the thermal properties of each neat latex polymer with the corresponding sIPN. Another direction investigated the modularity of this approach to 3D print mixtures of dissimilar particles (hybrid colloids). Polymer-inorganic hybrid colloids containing SBR and silica nanoparticles provided a highly tunable route to printing elastomeric nanocomposite sIPN's. The bimodal particle size distribution introduced by the mixture of SBR (150 nm) and silica (12 nm) nanoparticles enabled tuning of colloid behavior to introduce yield-stress behavior at high particle concentrations. High-silica hybrid colloids therefore exhibited both a shear-induced reversible liquid-solid transition (indicated by a modulus crossover) and irreversible photocrosslinking, which established a unique processing window for UV-assisted direct ink write (UV-DIW) AM. Concentric cylinder rheology probed the yield-stress behavior of hybrid colloids at high particle concentrations which facilitated both the extrusion of these materials through the UV-DIW nozzle and the retention of their as-deposited shaped during printing. Photorheology confirmed rapid photocuring of all hybrid colloids to yield increased moduli capable of supporting subsequent layers. Scanning electron microscopy (SEM) confirmed well-dispersed silica aggregates in the nanocomposite sIPN's. DMA and tensile confirmed significant reinforcement of (thermo)mechanical properties as a result of silica incorporation. sIPN's with relative weight ratio of 30:70 silica:SBR achieved maximum strains above 300% and maximum strengths over 10 MPa. In a different approach to enhancing VP part mechanical properties, thiol-ene chemistry provided simultaneous linear chain extension and crosslinking in oligomeric diacrylate systems, providing tunable increases to Mc of the photocured networks. Hydrogenated polybutadiene diacrylate (HPBDA) oligomers provided the first example of hydrocarbon elastomer photopolymers for VP. 1,6-hexanedithiol provided a miscible dithiol chain extender which introduced linear thiol-ene chain extension to compete with acrylate crosslinking. DMA and tensile confirmed a decrease in T_g and increased strain-at-break with decreased crosslink density. Other work investigated the synthesis and characterization of first-ever phosphonium polyzwitterions. Free radical polymerization synthesized air-stable triarylphosphine-containing polymers and random copolymers from the monomer 4-(diphenylphosphino) styrene (DPPS). ³¹P NMR spectroscopy confirmed quantitative post-polymerization alkylation of pendant triarylphosphines to yield phosphonium ionomers and polyzwitterions. Systematic comparison of neutral, ionomer, and polyzwitterions elucidated significant (thermo)mechanical reinforcement by interactions between large phosphonium sulfobetaine dipoles. Broadband dielectric spectroscopy (BDS) confirmed the presence of these dipoles through significant increases in static dielectric content. Small-angle X-ray scattering (SAX) illustrated ionic domain formation for all charged polymers. / Doctor of Philosophy / Additive manufacturing (AM) revolutionizes the fabrication of complex geometries, however the utility of these 3D objects for real world applications remains hindered by characteristically poor mechanical properties. As a primary example, many AM process restrict the maximum viscosity of suitable materials which limits their molecular weight and mechanical properties. This dissertation encompasses the design of new photopolymers to circumvent this restriction and enhance the mechanical performance of printed materials, with an emphasis on elastomers. Primarily, my work investigated the use of latex polymer colloids, polymer particles dispersed in water, as a novel route to provide high molecular weight polymers necessary for elastic properties in a low viscosity, liquid form. The addition of photoreactive molecules into the aqueous phase of latex introduces the necessary photocurability for vat photopolymerization (VP) AM. Photocuring in the printer fabricates a three-dimensional object which comprises a hydrogel embedded with polymer particles. Upon drying, these particles coalesce by penetrating through the hydrogel scaffold without disrupting the printed shape and provide mechanical properties comparable with the high molecular weight latex polymer. As a result, this work introduces high molecular weight, high performance polymers to VP and reimagines latex applications beyond 2D coatings. Further investigations demonstrate the versatility of this approach beyond elastomers with successful implementations with glassy polymers and inorganic (silica) particles which yield nanocomposites.

Granplantor behandlades på plantskola med ett latexbaserat barriärskydd mot snytbagge. Dessa plantor frystes sedan ned innan latexbehandlingen hunnit torka. Syftet med studien var att undersöka om plantor som frysts ned direkt efter behandling med latex går att tina upp, för att sedan låta behandlingen torka färdigt i kartongerna de är förpackade i. Metoderna för studien innefattade litteraturstudier och ett experiment. I de försök som genomfördes på plantorna påvisades fläckar utan latex, främst då en större andel av latexbeläggningen var fuktig. Dessa fläckar verkade ha ett samband med skyddets fuktnivå, då det blev fler fläckar ju fuktigare behandlingen var. Gemensamt för de 3 grupper där latex torkat mest är att de var placerade i miljöer där temperaturen låg på 20 ⁰C eller högre.

The objective of this thesis is to incorporate cellulose nanocrystals (CNCs) into polymer latexes prepared using various emulsion polymerization methods. CNCs are a promising new class of renewable materials with unique properties including nanoscale dimensions, a high aspect ratio, low density, and high strength. They show significant promise to enhance the properties of existing materials, but challenges often arise due to incompatibility and processing difficulties. This work investigates novel surface modification routes to improve the compatibility of CNCs with emulsion polymerization components, and aims to control the location and function of CNCs in latex systems in order to modify latex properties. Three approaches to incorporate CNCs into polymer latexes are presented: (1) exploiting CNC-surfactant interactions in order to promote CNCs as Pickering stabilizers or as “passive” additives in the water phase, (2) enhancing the surface activity of CNCs by adsorbing the surface active biopolymer methyl cellulose (MC) to act as Pickering co-stabilizers, or (3) hydrophobic modification of CNCs through polymer grafting in order to provide improved compatibility between CNCs and the monomer/polymer phase to incorporate CNCs into the latex core. First, the interactions between CNCs and surfactants were studied in suspension and at surfaces and the CNC-surfactant combinations were used to stabilize miniemulsion polymerization of methyl methacrylate (MMA), a model system used in this work. Oppositely charged CNCs and surfactants showed improved stability as Pickering stabilizers and the ability to co-stabilize the monomer/polymer-water interface. When like-charged CNCs and surfactants were used, the poly(methyl methacrylate) (PMMA) polymer particles were stabilized by surfactant only, while the CNCs remained in the water phase. Next, in order to avoid the use of surfactants, CNCs were coated with MC to provide improved surface activity. MC-coated CNCs were effectively used as Pickering stabilizers in the microsuspension polymerization of MMA, where a double morphology of PMMA particles was observed, and the morphology could be tuned based on the ratio of CNC to MC used. Finally, CNCs were modified with hydrophobic polymer via two different “grafting from” methods: free radical polymerization and atom transfer radical polymerization (ATRP). Free radical polymer grafting from CNCs resulted in polymer-grafted CNCs but the method lacked control over polymer graft length and graft density. To overcome this, CNCs were modified via surface initiated ATRP where considerably higher amounts of polymer were grafted from the CNCs in short reaction times and with simple purification steps. Furthermore, polymer-grafted CNCs were added to the monomer phase of the miniemulsion polymerization of MMA and latexes with CNCs inside the hydrophobic polymer particle core were prepared. Given the difficulties in characterizing polymer grafted CNCs, a novel solution state NMR method was used, whereby the modified CNCs were dissolved in ionic liquids and the polymer grafts were cleaved and collected to determine graft length and graft density. Overall, this work provides three approaches for the preparation of nanocomposite latexes with CNCs using PMMA as a model system. The results presented here may expand the use of CNCs in latex products such as adhesives, paints, coatings, and cosmetics. / Thesis / Doctor of Philosophy (PhD) / This research aims to prepare polymer latexes with tailorable properties using renewably-sourced particles and nanotechnology. Latexes are polymer particles dispersed in water, typically on the order of a few hundred to thousand nanometers (where a “nanometer” is one billionth of a meter), and are used in products such as adhesives, paints, and coatings. The field of nanotechnology takes advantage of nanomaterials where unique properties stem from the small size and high surface-area-to-volume ratio. In this work, we use cellulose, the most abundant natural polymer on earth, in the form of cellulose nanocrystals (CNCs). These nanoparticles are extracted from pulp, cotton, and other natural resources to yield nanometer-sized rigid rod-like particles. CNCs have recently gained attention in research and the media because of their new industrial production and “safe nanomaterial” designation in Canada. In this work, CNCs were chemically modified by the attachment of new molecules or by coating them with polymers and were subsequently added during the synthesis of the polymer latex. Incorporating CNCs imparted new properties and the ability to control latex size, shape, and surface topography. CNCs are also expected to improve the overall mechanical strength of the latex, and may enhance the stickiness of adhesive latexes in particular, leading to products that are more environmentally friendly and that show improved performance.

Highway bridge decks are often overlaid to extend service life by reducing the rate of chloride ion ingress and the rate of corrosion of reinforcing steel in the sound chloride-contaminated concrete that is left in-place. Bridge deck overlays in Virginia are usually either latex-modified concrete or microsilica concrete, and both types of overlay are considered equivalent in terms of performance. However, the latex-modified concrete overlays are more expensive to construct than the microsilica concrete overlays. Thus, it is important to determine if these overlays do perform equivalently to ensure that short-term savings do not lead to higher long-term costs. Shrinkage is one of the overlay performance parameters. Shrinkage is a three-dimensional deformation of concrete that results in an overall reduction in volume. Total shrinkage may be measured under either restrained or unrestrained conditions. This research examines the shrinkage performances of Virginia Department of Transportation-approved latex-modified and microsilica concrete overlay mixtures and was conducted on both field-sampled and laboratory-fabricated restrained and unrestrained specimens. Based on crack and delamination surveys of sampled bridge decks and laboratory test results, a shrinkage performance-based specification for the Virginia Department of Transportation was developed. There was no significant difference between the unrestrained shrinkage values of latex-modified and microsilica concrete overlay mixtures for the specified time periods. Restrained microsilica concrete specimens generally cracked earlier and more frequently than restrained latex-modified concrete specimens. However, the bridge deck crack and delamination surveys show that construction conditions and quality and traffic type and frequency may have a greater effect on cracking than the overlay material. / Master of Science