Latex polymers serve as binders in a wide range of architectural paints and coatings. A latex is an aqueous colloidal dispersion of polymer particles that when dried above the polymer’s film formation temperature coalesces into a dry polymer film (Dragnevski, Routh, Murray, & Donald, 2010). The other main components of paint include associative thickeners, surfactants, pigments and fillers with the thickener being the primary area of focus for this study. The relatively simple system of latex, associative thickener and surfactant has been studied extensively. These studies have shown the mechanism of thickening for the associative thickener, and surfactant effects on both latex and thickener; however, there are few studies conducted for a fully-formulated system. The introduction of pigments, fillers, coalescing aids, functional amines, and other additives greatly increases the difficulty of research in this area. The addition of many additives ultimately affects the stability and physical properties of the end-product. Phase separation of the paints, also called syneresis, is a major concern of paint formulators because paints need to be as stable when left sitting in a paint-can for an extended period of time. The goal of this project is to essentially probe the areas of phase separation for some hydrophobically modified ethoxylated urethane (HEUR) thickened paint systems that are very similar to commercially used paint formulations. The probing of these phase separated regions includes the careful preparation of each paint sample, physical property testing, as well as new experimental development in the area of syneresis, rheology, followed by statistical analysis of data. Dispersion phase diagrams (DPDs) were first reported by Kostansek (2003) in a simple system of HEUR thickener, surfactant, and latex. They are a plot of the three possible dispersion states for an associative thickened system. These states include bridging flocculation which occurs at low levels of HEUR in which 50% or less of the latex particle surface is covered by the associative thickener. The second state is a good dispersion, which does not show any signs of flocculation. The third state is a mode of flocculation called depletion flocculation that occurs when the particle surfaces of the system are covered mostly with surfactant. The free associative polymer in the system is excluded from the free space in between particles, and the latex particles form aggregates (Otsubo, 1995). The three dispersion phases are then plotted with wt% HEUR on the continuous phase versus wt% surfactant on the continuous phase. The ideal end product for this project would be to use various combinations of latex, surfactant, and associative thickeners (ATs) to create multiple DPDs, which then could be used to troubleshoot formulations and samples in which flocculation is present. Each formulation was made using a thickening package of two non-ionic HEURs: a low-shear and high-shear thickener. Surfactant additions were made after the HEUR in small incremental amounts. Each DPD would consist of one surfactant, the previously stated combination of HEURs, and an all-acrylic latex. Three different surfactants were used in the study: two non-ionic surfactants, and an anionic surfactant. The first non-ionic surfactant was not studied in full as the other two surfactants due to time constraints. Two different all-acrylic latexes were used which varied in the particle size. The first latex studied, Acrylic-A, has an average particle size of 105 nm, and the second latex was Acrylic-B with 150 nm particle size. The TiO2 used in each DPD was surface treated and used in powder form. By the end of the project, 4 full-scale DPDs were made with the following combinations: Acrylic-A and a non-ionic surfactant, Acrylic-A and an anionic surfactant, Acrylic-B and a non-ionic surfactant, and Acrylic-B and an anionic surfactant. From these DPDs the mechanistic interactions of various components of the system could be made. The DPDs could also be used to troubleshoot problematic paints and even hypothesize new formulations.

This dissertation presents the results of a study performed to investigate methods for increasing the damping capacity of concrete. A variety of additives, both particle and latex based, were added to standard concrete mixtures by replacing up to 20% of the fine aggregate to measure their effects on strength, stiffness, damping, and air content. The additives included rubber particles from recycled tires, calcium carbonate particles, styrene butadiene rubber (SBR) latex, and a commercially available product named ConcreDamp which contains vegetable gum suspended in styrene butadiene latex. An initial investigation resulted in the observation that all of the additives with the exception of the SBR latex would both increase air content and decrease compressive strength. As a result, combinations of additives were investigated to see if both the mechanical and dynamic properties could be improved. The addition of steel fibers to mixtures with ground rubber were found to significantly increase air content which offset any gains in compressive strength. The combination of ground rubber and latex was shown to improve both increase compressive strength and reduce air content. The study advanced to investigate the effects of rubber size on air content, strength, and damping. It was found that for the same volume of rubber, a larger rubber particle would decrease air content, decrease compressive strength, and improve damping. The results of this study show that the best performing additive was the vegetable gum latex which improved the concrete damping by a factor of 2 when added as 15% of the fine aggregate. Additionally, an equation is presented for calculating a strength reduction factor for concrete containing rubber particles of different sizes. Finally, two full scale footbridge laboratory specimens were tested to investigate the effect of increased material damping at the structural level. One footbridge was constructed using a base concrete mixture without damping admixtures. The second was constructed with a concrete mixture that contained a replacement of 15% of the fine aggregate with ground rubber. The results were used to create a finite element model in SAP2000 that was used to predict the effects that high damping concretes would have on the footbridge specimen. / Ph. D.

<p> Nonaqueous poly(methyl methacrylate) latices were prepared by nonaqueous dispersion polymerization of poly(methyl methacrylate) in heptane in the presence of either trimethylsilyl terminated or vinyl terminated polydimethylsiloxane stabilizer. Poly(methyl methacrylate) particles stabilized by vinyl terminated polydimethylsiloxane showed smaller particle sizes than did those stabilized by trimethylsilyl terminated polydimethylsiloxane. Diameters of the various latex preparations ranged from 1.4 to 0.8 μm and silicone content was around 2 mole percent in each case. Differences between the two types of latex were explained in terms of the nucleation mechanism operating during the preparation of the latices and in terms of the type of attachment of the stabilizer chain to the poly(methyl methacrylate) core.</p> <p> The effect of the silicone concentration present during particle formation was investigated. Vinyl terminated polydimethylsiloxane stabilized latex gave better stabilized particles than did methyl terminated polydimethylsiloxane stabilized latex. The results of varying the concentration and type of initiator were consistent with the conclusions about differences in nucleation and grafting mechanisms.</p> <p> The stability of polydimethylsiloxane stabilized poly(methyl methacrylate) particles was investigated in n-heptane. Acidified montmorillonite clay was determined as the optimum catalyst for this latex system. Flocculation set in at 70% of the original silicone content when the siloxane on the particle surface was degraded with montmorillonite clay in a good solvent. Flocculation was irreversible and occurred abruptly. The point of flocculation was reproducible and the rate of flocculation was identical for two different types of silicone stabilized poly(methyl methacrylate) latex.</p> / Thesis / Master of Science (MSc)

Thesis (PhD)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Healthcare workers (HCWs) wear latex gloves to protect themselves and their patients against the transmission of microbial, viral and bloodborne diseases. These individuals are primarily exposed to latex via cutaneous (direct contact) and mucocutaneous (inhalation of airborne allergens on glove powder) routes. Repeated exposure leads to the formation of circulating latex-specific IgE and subsequent sensitisation with varying clinical expression. The airconditioning system of the Tygerberg Hospital (TBH) complex was investigated for the presence of aerosolised cornstarch glove powder and proteins. Dust samples were collected from 14 areas with different levels of latex glove usage. Dust samples were spectrophotometrically compared to a calibration graph of pure glove powder. The detection of starch and proteins in all the dust samples confirmed the presence of glove powder and possibly airborne latex allergens in the airconditioning ducts. As expected, the high exposure areas showed the highest concentrations of both starch and proteins. It is possible that other proteins than latex were involved, but the confirmed high level of protein contamination should be a cause for concern. Correlation between starch and protein levels was highly significant (p<0.01) in all instances. A total of 500 questionnaires were circulated for completion by HCWs from TBH. The response rate was 69.8%. After considering specific inclusion criteria, a study group of 152 individuals was compiled (28 males, 124 females). All subjects had current latex exposure and suffered from at least three pre-defined symptoms. Serum was collected from all subjects and dermal fluid from 31 subjects. Total IgE and latex specific IgE analysis were done on all serum and dermal fluid samples. Latex-specific IgE was positive (>0.35 IU/ℓ) in 23 serum and six dermal fluid samples. Skin prick tests (SPTs)for latex were done on 59 subjects with negative serum latex-specific IgE and 34 had positive results. Twelve subjects with negative latex-specific IgE and latex SPTs underwent patch tests with the European Standard Series, a piece of latex glove and glove powder in petrolatum. Three subjects had positive results to one or more of these allergens. Western blot analysis for latex was done on all positive sera and dermal fluid collected from these subjects. Western blot analysis for latex proved to be more sensitive than the capRAST, because it was able to identify specific bands in samples with negative capRAST results. All subjects showed a band for Hev b 1, which has been confirmed as a powder-bound airborne allergen. Hev b 6.01 is associated with HCWs with cutaneous symptoms and this band was recognised by 81% of the subjects. These findings confirmed that airborne and cutaneous routes are the major routes of exposure in HCWs. According to their laboratory results, subjects were divided into the following subgroups and compared statistically: Group A (serum positive, n=23), Group B (SPT positive, n=34) and Group C (negative, n=25). Group D (withdrawn, n=70) could not be used for statistical comparisons, due to incomplete results. An overall latex allergy prevalence of 38% was found. Group A differed significantly from Group B and Group C for most clinical and special investigations. Group A and B were also combined to represent all subjects with positive results (Cohort AB). The Allergy Score and Class were highly significant when Cohort AB was compared to Group C. The selection of clinical symptoms was confirmed to be relevant and work-related deterioration on any of the symptoms should bear a high index of suspicion in the evaluation of latex allergy. Numerical indices and specific symptoms showed high positive predictive values and the Allergy Score produced statistical significance in the positive subgroups when compared to the negative subgroup. Paired statistical significance was confirmed between the Allergy Score and occupational exposure (number of years, hours and pairs per week). The areas with the highest occupational latex exposure in HCWs are the face and hands. Different occupations also have different levels of exposure and two subgroups of HCWs (16 laboratory technologists and 13 theatre staff) were investigated for sebum content on different facial areas and the palms and dorsal areas of both hands. Baseline measurements were done before putting on gloves. In 21 subjects follow up measurements were done following three to four hours of occupational exposure, but before washing their hands. Baseline and follow up values were compared for all the different anatomical regions. Levels on the forehead and cheeks increased over time, while the level on the nose decreased. All hand regions decreased significantly during occupational exposure, suggesting that glove powder contributes to dryness of the skin. In conclusion, the problem posed by latex allergy will not be solved overnight and will probably remain a major occupational hazard for years to come. It is currently not possible to avoid exposure to latex, but it is imperative to institute safety measures to prevent further sensitisation in predisposed individuals and manage those already affected. / AFRIKAANSE OPSOMMING: Gesondheidswerkers dra lateks handskoene om hulleself en hulle pasiënte te beskerm teen die oordrag van mikrobiale, virale en bloed-gedraagde siektes. Die lateks blootstelling vind hier hoofsaaklik plaas via kutane (direkte velkontak) en mukokutane (inaseming van lug-gedraagde allergene op hanskoen poeier) roetes. Herhaalde blootstelling veroorsaak sirkulerende lateksspesifieke IgE en sensitisasie met variërende kliniese beelde. Die lugreëlingstelsel van die Tygerberg hospitaalkompleks is ondersoek vir die teenwoordigheid van handskoenpoeier (stysel) en lateks proteïene. Stofmonsters is versamel in 14 areas wat verskillende blootstellingsvlakke verteenwoordig het. Die stofmonsters is spektrofotometries vergelyk met "n kalibrasiekurwe van suiwer hanskoenpoeier. Stysel en proteïene kon in al die stofmonsters aangetoon word en het die teenwoordigheid van handskoenpoeier en moontlike luggedraagde lateks proteïene in die lugreëlingstelsel bevestig. Soos verwag kon word, het die hoogste stysel en proteïen waardes in hoë blootstellingsareas voorgekom. Hoogs beduidende statistiese korrelasies (p<0.01) tussen die stysel en proteïenvlakke kon aangedui word in alle monsters. "n Totaal van 500 vraelyste is gesirkuleer vir voltooiing deur TBH gesondheidswerkers, waarvan 69.8% voltooide vraelyste terugontvang is. Na evaluering van insluitingskriteria, is "n studiegroep van 152 individue saamgestel (28 mans, 124 vrouens). Almal het huidige lateks blootstelling en ten minste drie het vooraf gedefinieerde simptome gerapporteer. Serum is van die hele groep versamel en dermale vog van 31 proefpersone. Totale IgE en lateks-spesifieke IgE vlakke is op alle serum en dermale vog bepaal. Positiewe resultate (>0.35 IU/ℓ) is verkry in 23 serum en ses dermaIe vog monsters. Velpriktoets vir lateks is op 59 proefpersone uitgevoer en 34 daarvan het positiewe resultate opgelewer. Twaalf proefpersone met negatiewe lateks-spesifieke IgE en velpriktoets resultate het kutane plaktoetse ondergaan met die Europese Standaard Reeks, "n stukkie lateks handskoen en handskoenpoeier in petrolatum. Drie proefpersone het positiewe resultate teen een of meer van die allergene gehad. Westerse kladanalise vir lateks is op alle positiewe serum gedoen, asook die dermale vogte van hierdie proefpersone. Westerse kladanalise vir lateks blyk baie meer sensitief te wees as die capRAST, aangesien dit spesifieke bande kon identifiseer in monsters capRAST resultate. Alle monsters het "n band getoon vir Hev b 1, "n poeier-gebinde, luggedraade allergeen. Hev b 6.01 is geassosieer met gesondheidswerkers met velsimptome en hierdie band is gevind in 81% van die monsters. Hierdie resultate bevestig dat die belangrikste blootstelling aan lateks in gesondheidswerkers deur die vel en inaseming plaasvind. Proefpersone is in die volgende drie groepe verdeel volgens laboratorium resultate en statisties vergelyk: Groep A (positiewe serum, n=23), Groep B (positiewe velpriktoetse, n=34) en Groep C (negatief, n=25). Groep D (onttrek, n=70) kon nie vir betekenisvolle statistiese vergelykings aangewend word nie, as gevolg van onvolledige resultate. 'n Finale lateks allergie prevalensie van 38% is gevind. Groep A het hoogs beduidend verskil van Groep B en C vir die meeste van die kliniese en spesiale laboratoriumondersoeke. Groep A en B is gekombineer om alle proefpersone in te sluit met positiewe resultate (Kohort AB). Die Allergie Telling en Klas van Kohort AB was hoogs beduidend in vergelyking met Groep C. Die gekose simptome is bevestig as relevant en enige werksverwante verergering van simptome moet met 'n hoë mate van agterdog bejeën word in lateks allergie. Numeriese indekse en spesifieke simptome het hoë positiewe voorspellingswaardes gelewer en die Allergie Telling was hoogs beduidend in die positiewe subgroep in vergelyking met die negatiewe subgroep. Gepaarde statistiese beduidenheid is ook gevind tussen die Allergie Telling en beroepsblootstelling (jare van blootstelling, uur en paar handskoene per week). Die meeste beroepsblootstelling aan lateks in gesondheidswerkers vind plaas op die hande en gesig. Verskillende beroepe het ook verskillende blootstellingsvlakke en two subgroepe gesondheidswerkers (16 laboratorium tegnoloë en 13 teater personeel) is ondersoek vir die sebumgehalte op veskillende areas van die gesig en hande. Basislynvlakke is gemeet voordat handskoene aangetrek is en in 21 gevalle is opvolgvlakke gemeet na drie tot vier uur beroepsblootstelling, maar voor die hande gewas is. Basislyn en opvolgvlakke is met mekaar vergelyk vir al die anatomiese areas. Die voorkop en wange het 'n toename in sebumgehalte getoon, terwyl dié van die neus afgeneem het. AI die areas op die hande toon 'n hoogs beduidende afname tydens beroepsblootstelling, wat impliseer dat hanskoenpoeier moontlik bydra tot droogheid van die vel. In samevatting, die lateks allergie probleem sal nie oornag opgelos word nie en sal waarskynlik 'n belangrike beroepsrisiko bly vir die aansienlike toekoms. Totale vermyding van lateks is tans onmoontlik en daarom is dit van uiterste belang om voorsorgmaatreëls in plek te stel om verdere sensitisasie in blootgestelde individue te verhoed en die wat reeds geaffekteer is, effektief te hanteer.

O látex de borracha natural foi formulado, radiovulcanizado e, em seguida, estabilizado radioliticamente (GAMATEX), para ser empregado na fabricação de artefatos de borracha utilizados na área médica. A eficiência de reticulação do látex, quando radiovulcanizado com raios gama, correlacionou-se matematicamente com a razão de concentração do sistema de radiosensibilizador (x1 = [An-B] / [KOH]) e com a dose de vulcanização (x2), apresentando alto grau de interação, segundo o seguinte modelo matemático: , onde representa a resistência à tração na ruptura. O processo RVNRL foi otimizado para baixas doses de vulcanização e altas concentrações de An-B. A resistência radioxidativa da borracha, obtida a partir do GAMATEX, foi atingida adicionando-se uma mistura de antioxidantes (45% BANOX S + 55% TNPP). Esta mistura apresentou um efeito sinérgico. O látex apresentou comportamento pseudoplástico com a ocorrência de tensão de escoamento. A taxa de desestabilização irreversível do látex foi diretamente proporcional à [An-B] e inversamente proporcional à [KOH]. O efeito pós-irradiação do látex ou a desestabilização reversível, ocorreu devido à presença de uma concentração residual de An-B que não reagiu. A irradiação melhorou a estabilidade coloidal do GAMATEX, devido ao aumento da tixotropia e da tendência newtoniana além da correlação entre o grau de consistência (k) e o índice pseudoplástico (n), de acordo com o modelo matemático . Este fato permite um tempo maior de estocagem do GAMATEX. A viscosidade relativa do látex correlaciona-se com a temperatura e com o teor da borracha seca conforme o modelo matemático: , onde rw é a razão (BS/100-BS). O látex radiovulcanizado coagulou à temperatura de –10ºC no sistema de refrigeração projetado. / The natural rubber latex was formulated, irradiation vulcanized and stabilized (GAMATEX) to make rubber goods for medical purpose. When the latex was vulcanized by gamma rays the effectiveness crosslinking of GAMATEX relationship between the concentration ratio of sensitizer system (x1=[n-BA]/[KOH]) and the vulcanization dose (x2), showing high interaction grade according to the following the mathematical equation: , where is the tensile strength. The RVNRL process was optimized for low vulcanization doses and high concentrations of n-BA. The resistance to radiolitic oxidation of rubber obtained from GAMATEX was attained when one antioxidants mixture (45% BANOX S + 55% TNPP) was added. This mixture exhibited synergetic effect. The latex showed pseudoplastic rheological behavior and the yield stress occurrence. The irreversible destabilization rate of latex was direct proportional to [n-BA] and indirect proportional to [KOH]. The post-irradiation effects or reversible destabilization of latex occurred because there is a residual concentration of [n-BA] that it was not reacted. The colloidal stability of GAMATEX improved with irradiation, showing showing the increase of thixotropic behavior and the tendency to newtonian behavior flow besides the relationship between the viscosity index (k) and the pseudoplastic index (n) according to the mathematical model: . This fact allows the higher storage time of GAMATEX. The relative viscosity of latex was relationship between the temperature and the total dry rubber content according to the mathematical model: , where rw is the ratio (BS/100-BS). The radiation vulcanized latex coagulated at –10ºC into the projected freezing system.

Os revestimentos cerâmicos aderidos têm grandes vantagens estéticas e funcionais e seu emprego no mercado nacional vem sendo crescente, sobretudo com o uso de placas de porcelanato. Essas vantagens somente se concretizam com uma adequada durabilidade e vida útil, o que não vem ocorrendo com esses revestimentos aplicados em bases sujeitas a deformações e ou movimentações, como o caso de fachadas. Como camada de ligação entre o substrato e a placa cerâmica, as argamassas colantes apresentam papel fundamental para o revestimento cerâmico, tais como: suportar deformações e ou movimentações diferenciais, apresentar resistência mecânica duradoura e ter capacidade de aderir com segurança em qualquer substrato e placa cerâmica. O objetivo desse trabalho foi de estudar o comportamento de argamassas colantes com a aditivação de látex acrílico. Foi realizado um estudo experimental comparativo entre argamassas colantes monocomponentes e argamassas colantes aditivadas com látex acrílico. Para verificar o comportamento que essa aditivação proporciona, foram realizados ensaios de resistência de aderência, flexibilidade, resistência à compressão, resistência à tração na flexão com determinação de módulo de deformação e tempo em aberto com placas de porcelanato. Os resultados mostraram de uma forma geral que a aditivação de argamassas colantes proporcionam aumento significativo na flexibilidade. Ocorre melhora na resistência de aderência, resistência à compressão e resistência à tração na flexão e também na capacidade de absorver deformações com o aumento do teor de polímero/argamassa. A aderência em placas de baixa porosidade como o porcelanato é melhorada e o tempo em aberto de laboratório também é estendido para as argamassas modificadas com látex. / The directed adhere ceramic tiles has aesthetic and functional advantages, and its use in the national market is increasing specially with the use along with porcelain tile. These advantages can only be seen though, if the system has adequate durability and service live, which doesn\'t happen once it is applied on irreversible or cyclic movement basis as building façades. As the clingy layer between the ceramic tile and the substrate, the tile adhesives have fundamental importance for the directed adhered ceramic tile, working on deformation and movements support capability, long-term durability mechanic resistance and safety and reliability to adhere on all type of substrates and ceramic tile. The purpose of this work was to study the behavior of dry set mortar modified with acrylic latex. An experimental study has been done, comparing dry set mortar to acrylic latex Portland cement mortar. To verify the behavior that the latex provides, the following tests were realized: tensile bond adhesion, deformability, compressive strength and tensile strength with deformation modulus and open time with porcelain tile. The results showed in general, that the latex improved the flexibility of dry set mortar and the improvement of the tensile adhesion, compressive and tensile strength and deformability capacity by increasing the polymer/mortar content. The adhesion and open time in porcelain tile has been improved with latex Portland cement mortar.

L'objectif général de cette thèse était d'étudier les mécanismes microbiens intervenant dans l'évolution de la structure et des propriétés du caoutchouc naturel produit à partir du latex d'Hevea brasiliensis lors de la maturation du latex et des coagula de tasse. Pour cela, trois niveaux d'analyses ont été réalisés sur des expériences de maturation en conditions contrôlées : analyse de la structure et des propriétés du caoutchouc sec, analyse des flores microbiennes et analyses biochimiques. Après une phase de mises au point méthodologiques permettant notamment d'optimiser les conditions de maturation en chambre contrôlée et de définir une méthode d'extraction d'ADN adaptée au latex et au sérum de coagulum, des échantillons de caoutchouc sec et de sérum ont été produits à différents temps de maturation et selon différents traitements faisant varier trois paramètres : la présence de microorganismes, la présence d'oxygène, et le mode de coagulation du latex. Les analyses sur caoutchouc sec se sont portées sur la macrostructure (P0, P30 et PRI) et sur la mésostructure (Mw, Mn et gel total). L'analyse des flores microbiennes s'est appuyée sur plusieurs méthodologies complémentaires : comptages sur boîtes, dosage de l'ADN total, clonage/séquençage et pyroséquençage 454. L'objectif était d'évaluer la diversité des flores sur plantation et dans le latex ainsi que de suivre la dynamique de leur évolution au cours de la maturation en milieu contrôlé. Diverses analyses biochimiques ont réalisées sur latex, sérum et caoutchouc sec (taux d'azote, protéines, lipides, sucres, québrachitol, acides organiques). Les résultats obtenus ont ensuite été analysés en vue d'établir des corrélations et de proposer des mécanismes reliant l'évolution des propriétés du caoutchouc sec à celle de la biochimie du latex et des coagula et de leur évolution sous l'action des microorganismes et des enzymes, et de proposer quelques pistes en vue de l'amélioration des itinéraires techniques dans la filière. / The overall objective of this thesis was to study the microbial mechanisms involved in the evolution of the structure and the properties of the natural rubber from Hevea brasiliensis during the maturation of latex and cup-coagula. For this, three levels of analyses were performed on maturation experiments under controlled conditions: dry rubber structure and properties, biochemistry and microbial flora. After a methodology development phase aiming at (i) optimizing maturation conditions in a controlled chamber and (ii) defining suitable DNA extraction methods, samples of serum and dry rubber coagulum were produced at different times and under different maturation treatments varying three parameters: the presence of microorganisms, the presence of oxygen, and the latex coagulation method. Dry rubber analyses concerned macrostructure (P0, P30 and PRI) and mesostructure (Mw, Mn and total gel). The microbial flora was analyzed using several complementary methods: plate-counts, total DNA determination, cloning / sequencing and 454 pyrosequencing. The objective was to assess microbial diversity on field and in latex, and to follow the dynamics of their evolution during maturation in a controlled environment. Various biochemical investigations were performed on latex, serum and dry rubber (nitrogen content, proteins, lipids, sugars, quebrachitol, organic acids). The results were then analyzed for correlations to propose mechanisms linking changes in dry rubber properties, latex and coagula biochemistry, and their evolution under the action of microorganisms and enzymes. Some ideas for improving technical routes in the process are also proposed.

Au cours de ce travail de thèse, nous avons étudié la synthèse de particules de latex par polymérisation en miniémulsion, un procédé de polymérisation en milieu aqueux dispersé. Nous avons synthétisé avec succès et de manière contrôlée des particules de latex de polystyrène de masse molaire élevée (Mn > 30 000 g.mol-1) par polymérisation radicalaire contrôlée par les nitroxydes (NMP) en miniémulsion, en présence et en absence de tensio-actif moléculaire. Des latex stables présentant des diamètres de l’ordre de 150 – 200 nm ont été synthétisés. Une seconde partie de ce travail de thèse est dédié à la transposition de la polymérisation radicalaire contrôlée par les nitroxydes amorcée depuis la surface (« surface-initiated NMP ») d’un procédé en masse vers un procédé en milieu aqueux dispersé (miniémulsion) en vue de synthétiser des nanoparticules cœur@écorce de type silica@polystyrène. La dernière partie du travail de thèse est consacrée à la synthèse de stabilisants polymères et plus précisément à la synthèse de copolymères amphiphiles à base de dextrane ou de poly(acide acrylique) modifiés de manière hydrophobes par des terpènes. L’efficacité de stabilisation de tels copolymères synthétisés à partir de bio-resources a été étudiée au travers leur capacité à stabiliser la polymérisation en miniémulsion du styrène. Tout au long de ce travail, les caractéristiques macromoléculaires des polymères ainsi que la taille et la morphologie des particules ont été caractérisées respectivement par chromatographie d’exclusion stérique, diffusion dynamique de la lumière et microscopie (SEM, TEM, AFM). / During the work of this PhD, we investigated the synthesis of latex particles by miniemulsion, an aqueous dispersed medium process. We managed to synthesize in a controlled manner high molar mass (Mn > 30 000 g.mol-1) polystyrene latex particles via nitroxide mediated radical polymerization (NMP) in miniemulsion in both the presence and absence of molecular surfactant. Stable latex with final diameters within the range of 150-200 nm were synthesized. A second part of the PhD work was devoted to the transposition of surface-initiated NMP from bulk polymerization to polymerization in aqueous dispersed media (miniemulsion) in order to synthesize silica@polystyrene core@shell hybrid nanoparticles. The last part of the PhD work was dedicated to the synthesis of polymeric stabilizers, more precisely to the synthesis of amphiphilic copolymers based on dextran or poly(acrylic acid) polymers hydrophobically modified by terpenes. The stabilization efficiency of such copolymers synthesized from renewable resources to stabilize styrene miniemulsion polymerization was investigated. During this work, we characterized the macromolecular features of polymers along with the size and the morphology of the final particles by respectively size exclusion chromatography (SEC), dynamic light scattering (DLS) and microscopy (SEM, TEM, AFM).

Orientador: Márcia Rita Fernandes Machado / Banca: Antonio Carlos Alessi / Banca: Sheila Canevese Rahal / Resumo: Neste estudo, implantou-se peritônio bovino ou biomembrana de látex natural em defeito (1,5 x 1,5 cm) induzido na parede ventral da bexiga de coelhos, com o intuito de se avaliar o processo de reparação tecidual no que se refere à biocompatibilidade, capacidade de reparação e possíveis complicações. Utilizaram-se 36 coelhos, albinos, raça Nova Zelândia Branco, adultos, machos inteiros, divididos em grupos experimentais: grupo Biomembrana (GB), grupo peritônio bovino (GP) e grupo controle (GC), cada um com 12 animais. Aos sete, 14, 30 e 60 dias de pós-operatório, os animais foram eutanasiados mediante o emprego de uma dose elevada de tiopental sódico para avaliações macroscópica e histopatológica da interface do implante com o tecido nativo. Macroscopicamente, em ambos os grupos (GB, GP e GC), observaramse, em todos os períodos, aderências de estruturas adjacentes ao local do implante, presença de cálculos e ausência de sinais de rejeição. No grupo biomembrana, aos 30 e 60 dias de pós-operatório, constatou-se a presença do biocompósito solto na luz vesical. Sob microscopia de luz, aos sete dias verificaram-se intensa reação inflamatória, neovascularização e presença de fibroblastos proliferados. Aos 14 dias não havia epitélio, porém observaram-se escassos feixes musculares, intensa neovascularização, fibroblastos e infiltrado inflamatório. No grupo GP, aos 30 dias de observação, o implante estava presente, havia fibroblastos, feixes de fibras musculares, moderada população inflamatórias e ausência de epitélio e de lâmina própria. No grupo GB, neste mesmo período, todas as camadas vesicais estavam reconstituídas. Em ambos os grupos, aos 60 dias de pós-operatório, todas as camadas vesicais encontravam-se reparadas e a membrana peritônio bovino não foi observada. No grupo GC, em todos os tempos de avaliação verificou-se integridade... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this study, bovine peritoneum or biomembrane of natural latex were utilized to replace a section of ventral face of the bladder of rabbits, with purpose of evaluation of the tissue repair process in regard of its biocompatility, scar formation ability and possible complications. Thirty-six New Zealand rabbits, adult and entire males were divided in three experimental groups: biomembrane group (GB), bovine peritoneum group (GP) and control group (GC), each one with 12 animals. The animals were euthanized at seven, 14, 30 and 60 days post operative, by use of an elevated dosage of sodium tiopental, followed by macroscopic and histopathological analysis of the implant interface with the native tissue. Macroscopically, in both groups (GB, GP and GC), it was observed, in all time periods, structure adherence to the implant site, presence of calculi and absence of rejection signs. In the GB group, since 30 until 60 days of post operative, it was evidenced the presence of the biomembrane inside the bladder. Under light microscopy, at seven days, there were intense inflammatory reaction, new vessels and proliferated fibroblasts. In 14 days, there was no urotelium, however it saw muscle fibers, intense inflammatory cells, new vessels and fibroblasts. In the GP group, at 30 days the implant was still present, there were fibroblasts, muscle fibers, moderate population of inflammatory cells and absence of urotelium and sheath. In the GB group, in the same time period, all the vesical layers were reconstituted. In both groups, at 60 days of post operative, bladder wall was repaired and the bovine peritoneum membrane was not observed. In the GC group, all the evaluation times, integrity of the vesical wall was verified... (Complete abstract click electronic access below) / Mestre

O látex de borracha natural foi formulado, radiovulcanizado e, em seguida, estabilizado radioliticamente (GAMATEX), para ser empregado na fabricação de artefatos de borracha utilizados na área médica. A eficiência de reticulação do látex, quando radiovulcanizado com raios gama, correlacionou-se matematicamente com a razão de concentração do sistema de radiosensibilizador (x1 = [An-B] / [KOH]) e com a dose de vulcanização (x2), apresentando alto grau de interação, segundo o seguinte modelo matemático: , onde representa a resistência à tração na ruptura. O processo RVNRL foi otimizado para baixas doses de vulcanização e altas concentrações de An-B. A resistência radioxidativa da borracha, obtida a partir do GAMATEX, foi atingida adicionando-se uma mistura de antioxidantes (45% BANOX S + 55% TNPP). Esta mistura apresentou um efeito sinérgico. O látex apresentou comportamento pseudoplástico com a ocorrência de tensão de escoamento. A taxa de desestabilização irreversível do látex foi diretamente proporcional à [An-B] e inversamente proporcional à [KOH]. O efeito pós-irradiação do látex ou a desestabilização reversível, ocorreu devido à presença de uma concentração residual de An-B que não reagiu. A irradiação melhorou a estabilidade coloidal do GAMATEX, devido ao aumento da tixotropia e da tendência newtoniana além da correlação entre o grau de consistência (k) e o índice pseudoplástico (n), de acordo com o modelo matemático . Este fato permite um tempo maior de estocagem do GAMATEX. A viscosidade relativa do látex correlaciona-se com a temperatura e com o teor da borracha seca conforme o modelo matemático: , onde rw é a razão (BS/100-BS). O látex radiovulcanizado coagulou à temperatura de –10ºC no sistema de refrigeração projetado. / The natural rubber latex was formulated, irradiation vulcanized and stabilized (GAMATEX) to make rubber goods for medical purpose. When the latex was vulcanized by gamma rays the effectiveness crosslinking of GAMATEX relationship between the concentration ratio of sensitizer system (x1=[n-BA]/[KOH]) and the vulcanization dose (x2), showing high interaction grade according to the following the mathematical equation: , where is the tensile strength. The RVNRL process was optimized for low vulcanization doses and high concentrations of n-BA. The resistance to radiolitic oxidation of rubber obtained from GAMATEX was attained when one antioxidants mixture (45% BANOX S + 55% TNPP) was added. This mixture exhibited synergetic effect. The latex showed pseudoplastic rheological behavior and the yield stress occurrence. The irreversible destabilization rate of latex was direct proportional to [n-BA] and indirect proportional to [KOH]. The post-irradiation effects or reversible destabilization of latex occurred because there is a residual concentration of [n-BA] that it was not reacted. The colloidal stability of GAMATEX improved with irradiation, showing showing the increase of thixotropic behavior and the tendency to newtonian behavior flow besides the relationship between the viscosity index (k) and the pseudoplastic index (n) according to the mathematical model: . This fact allows the higher storage time of GAMATEX. The relative viscosity of latex was relationship between the temperature and the total dry rubber content according to the mathematical model: , where rw is the ratio (BS/100-BS). The radiation vulcanized latex coagulated at –10ºC into the projected freezing system.