RESUM Les reïnes epoxi constitueixen un dels polímers més emprats en el món de la industria, si bé presenten una sèrie d’inconvenients, els més importants dels quals són: la seva inherent fragilitat, la seva excessiva resistència tèrmica que en dificulta l’eliminació d’un substrat un cop finalitzada la seva vida útil i l’encongiment que experimenten durant el procés de curat. Per tal de reduir o eliminar aquests problemes aquesta tesi proposa l’ús de polímers hiperramificats així com polímers estrella i copolímers lineal-hiperramificat de bloc com a modificants químics de reïnes comercials. Amb aquesta estratègia s’han aconseguit millorar la tenacitat degut a efectes flexibilitzants o a separacions de fase del modificant en la matriu epoxídica, així com reduir l’encongiment en el curat o la degradabilitat de les reïnes, sense afectar altres propietats de la reïna com la seva Tg o la seva duresa. / ABSTRACT Epoxy resins are one of the most used polymers in the field of technological applications. However, they present some drawbacks being the most important the following: they are inherently brittle materials; they present excessive thermal resistance that limits their reworkability; and the shrinkage they experiment during curing. To overcome these problems this thesis proposes the use of hyperbranched polymers, as well as star polymers and lineal-hyperbranched block copolymers as chemical modifiers of commercially available epoxy resins. With this strategy tougher materials have been obtained due to either a flexibilizing effect or a phase separation of the modifier within the epoxy matrix. Moreover, the shrinkage on curing and the degradability of the thermosets have been improved without compromising other properties of the resin such as its Tg or its hardness.

Some Gulf of Mexico (GOM) wells destroyed by hurricanes have become environment and safety hazard and cannot be abandoned by conventional methods since pumping and circulating cement into the casing is impossible when the platforms have been completely destroyed and toppled. This project tested the curing properties of several epoxy resin systems in different environments. A bisphenol-F/epichlorohydrin (BPF) resin cured by curing agent MBOEA system was successfully tested in the laboratory as a potential plugging material to abandon wells destroyed in the GOM. The BPF/MBOEA resin system had the most suitable curing time in a synthetic seawater environment. The system could be successfully weighted by barite up to 16.8 ppg and cured properly. Weighting allows the resin system fall more efficiently through the casing annulus. This laboratory verification of properties will lead to field test in the test wells.

Extraction of mangrove bark with 4.0% aqueous sodium sulfite and 0.4% aqueous sodium carbonate at 100° and 2 hours gives 24-26% yields compared with extraction by water at 70° for 2 hours which gives 21%. The hot water extracts are more acidic (pH 3.6) than is the sulfite extract (pH 5.6); both are reasonably reactive toward formaldehyde (Stiasny number 70.6 using water and 85.4 using aqueous sulfite-carbonate). The ¹³C NMR spectra of <I>R. mucronata </I>shows this tannin to have phloroglucinolic A-rings with hydroxy groups at C-5 and C-7 and pyrogallolic B-rings with hydroxy groups at C-3', C-4', and C-5'. The interflavanoid linkages are C-4→C-8 and C-4→C-6. The ¹³C NMR spectra also indicate the presence of a considerable amount of carbohydrate which is shown to be mainly rhamnose, glucose, arabinose, and uronic acids. Sulfitation of <I>R. mucronata </I>bark reduces the total carbohydrate and the rhamnose extracted but increases the amount of arabinose and uronic acids. The bark storage period has significant effects on the pH and the reactivity of the aqueous tannin solution. Barks stored for <4 weeks produce higher extraction yields than those stored for > 6 weeks and contain significantly larger amount of reactive tannin and have shorter gel times. The reactivity of bark extracts towards formaldehyde can be controlled either by limiting the duration of bark storage to 4 weeks or by maintaining the aqueous tannin solution at pH <10.0. The aqueous tannin solution from <I>R. mucronata </I>exhibited properties such as viscosity, solubility and tackiness which were superior to those from the <I>R. apiculata </I>extract while the mixed <I>R. mucronata-R. apiculata </I>aqueous tannin solution had properties in between these. These barks could be used singly or together as a source of tannin without the bond strength of the resulting glued joints being significantly affected. The "honeymoon" bonding technique improved the bond strengths of joints made using sulfited tannin but is suitable only for tannin solutions containing > 4% aqueous sodium hydroxide. The viscosity of sulfited tannin adhesives is influenced by (a) the amount of aqueous sodium hydroxide added to the aqueous tannin solution, and (b) the lapse time, i.e. the period between the addition of sodium hydroxide to the aqueous tannin solution and the addition of phenol-resorcinol-formaldehyde (PRF) resin, hardener, and paraformaldehyde. The present study shows that with the addition of 5% w/w sodium hydroxide and at a curing temperature of 40° the sulfited tannin extracts from the bark of mangrove trees can replace about 50% w/w of the PRF resin in cold-setting wood adhesives with the production of bond strengths comparable to those produced by 100% PRF resin.

Low phosphate fertilizer efficiency in high pH soils is primarily due to the retardation of P movement in the soil-P fertilizer reaction zone. The objective of this study was to obtain fundamental information on the influence of multi-ionic interactions on the solubility and diffusion of P in columns containing a model soil system and two soil types. The study also aimed to identify the salt combinations and factors that have the potential to enhance the solubility and movement of P in calcareous soil condition. The results showed that the interaction of NH4+ and SO42- was consistent at enhancing the water solubility and movement of P under a high soil pH condition. This effect was attributed to the combination of various mechanistic factors associated with (NH4)2SO4 compound including significant pH reduction, cation exchange reaction of NH4+ with the exchangeable Ca2+, and anionic competition of SO42- with P for precipitation with Ca2+.

No description available.

No description available.

No description available.

Low phosphate fertilizer efficiency in high pH soils is primarily due to the retardation of P movement in the soil-P fertilizer reaction zone. The objective of this study was to obtain fundamental information on the influence of multi-ionic interactions on the solubility and diffusion of P in columns containing a model soil system and two soil types. The study also aimed to identify the salt combinations and factors that have the potential to enhance the solubility and movement of P in calcareous soil condition. The results showed that the interaction of NH4+ and SO42- was consistent at enhancing the water solubility and movement of P under a high soil pH condition. This effect was attributed to the combination of various mechanistic factors associated with (NH4)2SO4 compound including significant pH reduction, cation exchange reaction of NH4+ with the exchangeable Ca2+, and anionic competition of SO42- with P for precipitation with Ca2+.

Thesis (M. Sc.)--University of Toronto, 1998. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M. Sc.)--University of Toronto, 1998. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.