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No description available.

The crystallization and melting behaviors of an ethylene/1-hexene copolymer and series of narrow molecular weight linear polyethylene and poly(ethylene oxide) fractions were studied using a combination of ultra-fast and conventional differential scanning calorimetry, optical microscopy, small angle X-ray scattering, and wide angle X-ray diffraction. In the case of linear polyethylene and poly(ethylene oxide), the zero-entropy production melting temperatures of initial lamellae of isothermally crystallized fractions were analyzed in the context of the non-linear Hoffman-Weeks method. Using the Huggins equation, limiting equilibrium melting temperatures of 141.4 ± 0.8oC and 81.4 ± 1.0oC were estimated for linear polyethylene and poly(ethylene oxide), respectively. The former and the latter are about 4oC lower and 12.5oC higher than these predicted by Flory/Vrij and Buckley/Kovacs, respectively. Accuracy of the non-linear Hoffman-Weeks method was also examined using initial lamellar thickness literature data for a linear polyethylene fraction at different crystallization temperatures. The equilibrium melting temperature obtained by the Gibbs-Thomson approach and the C2 value extracted from the initial lamellar thickness vs. reciprocal of undercooling plot were similar within the limits of experimental error to those obtained here through the non-linear Hoffman-Weeks method. In the next step, the Lauritzen-Hoffman (LH) secondary nucleation theory was modified to account for the effect of stem length fluctuations, tilt angle of the crystallized stems, and temperature dependence of the lateral surface free energy. Analysis of spherulite growth rate and wide angle X-ray diffraction data for 26 linear polyethylene and 5 poly(ethylene oxide) fractions revealed that the undercooling at the regime I/II transition, the equilibrium fold surface free energy, the strength of the stem length fluctuations and the substrate length at the regime I/II transition are independent of chain length. The value of the equilibrium fold surface free energy derived from crystal growth rate data using the modified Lauritzen-Hoffman theory matches that calculated from lamellar thickness and melting data through the Gibbs-Thomson equation for both linear polyethylene and poly(ethylene oxide). Larger spherulitic growth rates for linear polyethylene than for poly(ethylene oxide) at low undercooling is explained by the higher secondary nucleation constant of poly(ethylene oxide). While the apparent friction coefficient of a crystallizing linear polyethylene chain is 2 to 8 times higher than that of a chain undergoing reptation in the melt state, the apparent friction coefficient of a crystallizing poly(ethylene oxide) chain is about two orders of magnitude lower. This observation suggests that segmental mobility on the crystal phase plays a significant role in the crystal growth process. In case of the statistical ethylene/1-hexene copolymer, the fold surface free energies of the copolymer lamellae at the time of crystallization and melting increase with increasing undercooling, approaching the same magnitude at high undercooling. As a result of this temperature dependence, the experimental melting vs. crystallization temperature plot is parallel to the Tm = Tc line and the corresponding Gibbs-Thomson plot is non-linear. This behavior is attributed to the fact that longer ethylene sequences form a chain-folded structure with lower concentration of branch points on the lamellar surface at lower undercooling, while shorter ethylene sequences form lamellar structures at higher undercooling exhibiting a higher concentration of branch points on the lamellar surface. Branch points limit the ability of lamellar structures to relax their kinetic stem-length fluctuations during heating prior to melting. / Ph. D. / Morphology of semi-crystalline polymers is strongly affected by their crystallization conditions. Thermodynamic and kinetic models allow us to understand the crystallization mechanism of a semi-crystalline polymer and relate its crystallization conditions to the final morphology. In this research, we studied the molar mass dependence of the crystallization and melting behaviors of narrow molecular weight distribution linear polyethylene (LPE) and poly(ethylene oxide) (PEO) fractions using a modified Lauritzen-Hoffman (LH) secondary nucleation theory. We have shown that the equilibrium melting temperature of LPE and PEO fractions found from the non-linear Hoffman-Weeks method are within the experimental uncertainty identical with these measured directly for extended chain crystals or derived from a Gibbs-Thomson analysis. The value of the equilibrium fold surface free energy derived from crystal growth rate data using the modified LH theory matches that calculated from lamellar thickness and melting data through the Gibbs-Thomson equation for both LPE and PEO. We reported that the higher segmental mobility of PEO in the crystalline phase leads to significantly lower apparent chain friction coefficients during crystal growth compared to LPE. We also studied the role of short-chain branching in the crystal growth kinetics of ethylene/1-hexene copolymers. We observed that the fold surface free energies during crystallization and during melting are both function of the undercooling while the ratio of the former to the latter decreases with increasing undercooling. We proposed that this behavior may be related to the concentration of short-chain branches at the surface of the lamellae, where higher concentration leads to lower relaxation.

O consumidor está cada vez mais consciente da relação entre dieta e doença, que tem impulsionado as pesquisas sobre alimentos funcionais e seus efeitos sobre o corpo. O papel dos óleos e gorduras na nutrição humana tem sido intensamente estudado e discutido por décadas. Tem sido enfatizada a importância da ingestão de ômega-3, ômega-6 e ômega-9 ácidos graxos redução de ácidos graxos saturados e, mais recentemente, controle da ingestão de ácidos graxos trans. Através da mistura e interesterificação química e enzimática de óleos e gorduras, gorduras trans-livre pode ser produzido. Mistura de gordura, foram formuladas por misturas ternárias de estearina de palma, uma gordura láurica (óleo de coco ou óleo de palmiste) e um óleo poliinsaturado (óleo de canola ou azeite de oliva) em diferentes proporções que foram interesterificadas. Neste trabalho, foram produzidos lipídios estruturados por interesterificação química e enzimática. A interesterificação química foi realizada nas seguintes condições: a 88 °C, 60 minutos de reação, 0,4% de catalisador metóxido de sódio, sob agitação e vácuo. A interesterificação enzimática, sendo realizada com duas lipases comerciais Thermomyces lanuginosa e Rhizomucor miehei, com seletividade sn-1,3. A interesterificação enzimática por batelada foi realizado seguindo um planejamento matriz central compósito rotativo em função da temperatura e da composição do meio, estearina de palma, óleo de palmiste e azeite de oliva e catalisado pelas lipases comerciais. O decréscimo do conteúdo de gordura sólida foi observado a 10 e 35 °C após a interesterificação. O biorreator contínuo foi operado nas seguintes condições: mistura de estearina de palma, óleo de palmiste, azeite de oliva (45:30:25), 10 gr de biocatalisador, 65 °C, com tempo de residência de 7 min e por 226 h para Thermomyces lanuginosa e 188 h para Rhizomucor miehei. A atividade do biocatalisador foi avaliada em termos da diminuição do conteúdo de gordura sólida a 35 °C, o qual é um parâmetro chave na produção de margarinas. O perfil de inativação do biocatalisador pode ser bem descrita pelo modelo de desativação de primeira ordem: meia-vida de 88 e 60 h foram estimados quando Thermomyces lanuginosa e Rhizomucor miehei, respectivamente, foram utilizados. Os óleos puros, as misturas originais e interesterificadas foram avaliados quanto à composição de ácidos graxos e triacilgliceróis, distribuição regioespecífica dos ácidos graxos nos triacilgliceróis, ponto de fusão e amolecimento, consistência, conteúdo de gordura sólida, comportamento de fusão e cristalização, estabilidade oxidativa, estrutura cristalina e polimorfismo. A interesterificação química e enzimática promoveram diminuição de triacilgliceróis trissaturados e triinsaturados e aumento dos monossaturados-diinsaturados e dissaturados-monoinsaturados, o que resultou no respectivo decréscimo dos pontos de fusão e amolecimento, consistência e conteúdo de gordura sólida, aumentando a plasticidade das gorduras. As curvas de fusão e cristalização das misturas foram modificadas pela alteração da composição dos triacilgliceróis pela interesterificação química e enzimática. Estabilidade térmica e a temperatura de oxidação da estearina de palma, óleo de coco e óleo de canola e suas misturas foram dependente da composição de ácidos graxos e independente da interesterificação química. Os resultados mostram que a interesterificação química e enzimática oferecem uma ferramenta útil para a concepção de gorduras com sintonizáveis propriedades físico-químicas, melhorando em relação a esse das gorduras de partida. / The consumer is becoming more aware of the relationship between diet and disease, which has driven the research on functional foods and their effects on the body. The role of fats and oils in human nutrition has been intensively studied and discussed for decades. It has been emphasized the importance of intake of omega-3, omega-6 and omega-9 fatty acids, reduction of saturated fatty acids and, more recently, control of intake of trans fatty acids. Through the blend and interesterification of oils and fats, trans-free fats can be produced. Fat blends, formulated by ternary blends of palm stearin, lauric fat (coconut oil and palm kernel oil) and polyunsaturated oils (canola oil and olive oil) were done in different ratios. In this work, were produced by chemical and enzymatic interesterification. Chemical interesterification was performed under the following conditions: at 88°C, 60 minutes reaction times, 0.4% sodium methoxide, under agitation and vacuum. For enzymatic interesterification being carried out with two commercial lipases Thermomyces lanuginosa e Rhizomucor miehei, with selectivity sn-1,3. Batch enzymatic interesterification were performed, following central composite rotatable designs (CCRDs) as a function temperature and media of palm stearin, palm kernel oil and olive oil formulation and catalyzed by a commercial immobilized lipase. A decrease in all SFC values of the blends at 10 °C and 35°C was observed upon interesterification. The bioreactor operated continuously: mixture of palm stearin, palm kernel oil and olive oil (45:30:25, wt %), at 65 °C, at a residence time of 7 min and for 226 h to Thermomyces lanuginosa and 188 h to Rhizomucor miehei.. Biocatalyst activity was evaluated in terms of the decrease of the solid fat content at 35 °C of the blends, which is a key parameter in margarine manufacture. The inactivation profile of the biocatalyst could be well described by the first-order deactivation model: Half-lives of 88 and 60 h were estimated when Thermomyces lanuginose and Rhizomucor miehei, respectively, were used. Pure oil, the original and interesterified blends were examined for fatty acids and triacylglycerols composition, regiospecific distribution of fatty acids in triacylglycerols, melting and softening points, consistency, solid fat content, thermal behavior, oxidation stability, crystalline microstructure and polymorphism. Chemical and enzymatic interesterification caused reduction of trisaturated and triunsaturated and increase in monosaturated-diunsaturated and disaturated-monounsaturated, lowering the initial melting and softening points, consistency and solid fat content, increasing plasticity of fats. Melting and crystallization curves were significantly modified by changing the composition of triacylglycerols by chemical and enzymatic interesterification. The thermal stability and oxidation temperature of palm stearin, coconut oil and canola oil and their blends were dependent on fatty acid composition and independent on chemical interesterification. The results show that the chemical and enzymatic interesterification provides a useful tool to design fats with tunable physicochemical properties, improved compared to that of the starting fats.

O consumidor está cada vez mais consciente da relação entre dieta e doença, que tem impulsionado as pesquisas sobre alimentos funcionais e seus efeitos sobre o corpo. O papel dos óleos e gorduras na nutrição humana tem sido intensamente estudado e discutido por décadas. Tem sido enfatizada a importância da ingestão de ômega-3, ômega-6 e ômega-9 ácidos graxos redução de ácidos graxos saturados e, mais recentemente, controle da ingestão de ácidos graxos trans. Através da mistura e interesterificação química e enzimática de óleos e gorduras, gorduras trans-livre pode ser produzido. Mistura de gordura, foram formuladas por misturas ternárias de estearina de palma, uma gordura láurica (óleo de coco ou óleo de palmiste) e um óleo poliinsaturado (óleo de canola ou azeite de oliva) em diferentes proporções que foram interesterificadas. Neste trabalho, foram produzidos lipídios estruturados por interesterificação química e enzimática. A interesterificação química foi realizada nas seguintes condições: a 88 °C, 60 minutos de reação, 0,4% de catalisador metóxido de sódio, sob agitação e vácuo. A interesterificação enzimática, sendo realizada com duas lipases comerciais Thermomyces lanuginosa e Rhizomucor miehei, com seletividade sn-1,3. A interesterificação enzimática por batelada foi realizado seguindo um planejamento matriz central compósito rotativo em função da temperatura e da composição do meio, estearina de palma, óleo de palmiste e azeite de oliva e catalisado pelas lipases comerciais. O decréscimo do conteúdo de gordura sólida foi observado a 10 e 35 °C após a interesterificação. O biorreator contínuo foi operado nas seguintes condições: mistura de estearina de palma, óleo de palmiste, azeite de oliva (45:30:25), 10 gr de biocatalisador, 65 °C, com tempo de residência de 7 min e por 226 h para Thermomyces lanuginosa e 188 h para Rhizomucor miehei. A atividade do biocatalisador foi avaliada em termos da diminuição do conteúdo de gordura sólida a 35 °C, o qual é um parâmetro chave na produção de margarinas. O perfil de inativação do biocatalisador pode ser bem descrita pelo modelo de desativação de primeira ordem: meia-vida de 88 e 60 h foram estimados quando Thermomyces lanuginosa e Rhizomucor miehei, respectivamente, foram utilizados. Os óleos puros, as misturas originais e interesterificadas foram avaliados quanto à composição de ácidos graxos e triacilgliceróis, distribuição regioespecífica dos ácidos graxos nos triacilgliceróis, ponto de fusão e amolecimento, consistência, conteúdo de gordura sólida, comportamento de fusão e cristalização, estabilidade oxidativa, estrutura cristalina e polimorfismo. A interesterificação química e enzimática promoveram diminuição de triacilgliceróis trissaturados e triinsaturados e aumento dos monossaturados-diinsaturados e dissaturados-monoinsaturados, o que resultou no respectivo decréscimo dos pontos de fusão e amolecimento, consistência e conteúdo de gordura sólida, aumentando a plasticidade das gorduras. As curvas de fusão e cristalização das misturas foram modificadas pela alteração da composição dos triacilgliceróis pela interesterificação química e enzimática. Estabilidade térmica e a temperatura de oxidação da estearina de palma, óleo de coco e óleo de canola e suas misturas foram dependente da composição de ácidos graxos e independente da interesterificação química. Os resultados mostram que a interesterificação química e enzimática oferecem uma ferramenta útil para a concepção de gorduras com sintonizáveis propriedades físico-químicas, melhorando em relação a esse das gorduras de partida. / The consumer is becoming more aware of the relationship between diet and disease, which has driven the research on functional foods and their effects on the body. The role of fats and oils in human nutrition has been intensively studied and discussed for decades. It has been emphasized the importance of intake of omega-3, omega-6 and omega-9 fatty acids, reduction of saturated fatty acids and, more recently, control of intake of trans fatty acids. Through the blend and interesterification of oils and fats, trans-free fats can be produced. Fat blends, formulated by ternary blends of palm stearin, lauric fat (coconut oil and palm kernel oil) and polyunsaturated oils (canola oil and olive oil) were done in different ratios. In this work, were produced by chemical and enzymatic interesterification. Chemical interesterification was performed under the following conditions: at 88°C, 60 minutes reaction times, 0.4% sodium methoxide, under agitation and vacuum. For enzymatic interesterification being carried out with two commercial lipases Thermomyces lanuginosa e Rhizomucor miehei, with selectivity sn-1,3. Batch enzymatic interesterification were performed, following central composite rotatable designs (CCRDs) as a function temperature and media of palm stearin, palm kernel oil and olive oil formulation and catalyzed by a commercial immobilized lipase. A decrease in all SFC values of the blends at 10 °C and 35°C was observed upon interesterification. The bioreactor operated continuously: mixture of palm stearin, palm kernel oil and olive oil (45:30:25, wt %), at 65 °C, at a residence time of 7 min and for 226 h to Thermomyces lanuginosa and 188 h to Rhizomucor miehei.. Biocatalyst activity was evaluated in terms of the decrease of the solid fat content at 35 °C of the blends, which is a key parameter in margarine manufacture. The inactivation profile of the biocatalyst could be well described by the first-order deactivation model: Half-lives of 88 and 60 h were estimated when Thermomyces lanuginose and Rhizomucor miehei, respectively, were used. Pure oil, the original and interesterified blends were examined for fatty acids and triacylglycerols composition, regiospecific distribution of fatty acids in triacylglycerols, melting and softening points, consistency, solid fat content, thermal behavior, oxidation stability, crystalline microstructure and polymorphism. Chemical and enzymatic interesterification caused reduction of trisaturated and triunsaturated and increase in monosaturated-diunsaturated and disaturated-monounsaturated, lowering the initial melting and softening points, consistency and solid fat content, increasing plasticity of fats. Melting and crystallization curves were significantly modified by changing the composition of triacylglycerols by chemical and enzymatic interesterification. The thermal stability and oxidation temperature of palm stearin, coconut oil and canola oil and their blends were dependent on fatty acid composition and independent on chemical interesterification. The results show that the chemical and enzymatic interesterification provides a useful tool to design fats with tunable physicochemical properties, improved compared to that of the starting fats.