Gotowa bibliografia na temat „Polybutene-1”

There are two main goals of this thesis: to investigate the flow-induced crystallization behaviour of Polybutene-1 (PB-1 samples, and to study the effects of molecular parameters on the crystallization behaviour While flow-induced crystallization is not a new area in polymer research, well-defined experimental methods that allow access to high flow rate range comparable to that encountered in real processing are still lacking. Two types of flow are considered: shear and uniaxial elongational. Regarding the second aim, several molecular parameters considered are: molecular weight, molecular weight distribution, isotacticity, presence of nucleating agents, and copolymer content. For this purpose an array of PB-1 samples were used. It is found that each of these parameters can have significant effect on the crystallization behaviour. Mainly rheological methods were utilized to conduct the flow-induced crystallization experiments. Crystallization onset time is define d from the change in viscosity or other related parameters. The experiments begin with low shear rate range, to ensure that the results are comparable with literature data. In this range we encounter the quasi-quiescent onset time at very small. shear rates, which draws an interesting comparison with another physical parameter, the gel time. Beyond a critical flow rate a decrease in the onset time is seen, and a plateau-and-slope trend is evident for a curve of onset time vs. shear rate. Using a combination of three experimental methods, shear rates ranging from Q0001 - 500 s-1 are successfully achieved, and a good agreement between these methods is observed. Furthermore, a normalization procedure is introduced, which yields temperature-invariant curves for the mentioned range of shear rate. For the uniaxial elongation flow, the Elongational Viscosity Fixture (EVF) is employed, with the strain rate ranging from 0.0001 - 10 s'. A greater reduction in onset time as compared to shear (at the same shear/strain r ate) is observed, and the difference in the onset times for shear and elongation already reaches more than one decade for a flow rate of 10 5. This quantitative comparison is particularly important; since not so many data on elongation-induced crystallization are available in the literature. Finally, the thesis compares several flow induced crystallization models that can be useful as prediction tools and selects one of these models to be compared with the experimental data. A qualitative agreement is found, however, for better quantitative prediction the model still needs to be.

Le polymorphisme cristallin du poly(butene-1) isotactique (pbu) est etudie, essentiellement par microscopie electronique et diffraction des electrons. Les trois structures connues du pbu different par la conformation de la chaine (helices de symetrie: 3#1, 11#3, et 4#1) et par la geometrie et les parametres des mailles cristallines. Ces trois formes cristallines ont ete obtenues par cristallisation epitaxique sur des substrats, qui sont en general des acides ou des sels de molecules organiques aromatiques, eventuellement substitues. Les relations epitaxiques et les concordances structurales sont etablies. Les epitaxies permettent d'obtenir des echantillons monocristallins et de definir, dans un cas au moins, le sens droit ou gauche des helices en interaction avec le substrat. La transformation spontanee de la forme ii en forme i est etudiee sur des monocristaux. Les resultats infirment un modele classique mettant en jeu les orientations des plis et la sectorisation des monocristaux. Un desordre structural dans la forme i est suggere par des stries caracteristiques du cliche de diffraction. Il est correctement modelise par le remplacement statistique d'helices dont le sens structural est oppose. La structure cristalline de la forme iii est determinee par cristallographie electronique en exploitant l'ensemble des taches de diffraction accessibles grace aux monocristaux et aux films epitaxies. Cette structure est comparable a une structure determinee par rayons x. La methode ainsi etablie est generalement applicable aux formes instables des polymeres

Le polymorphisme cristallin du polybutene 1 isotactique a ete etudie par les techniques de resonance magnetique nucleaire (rmn) #1h large bande et #1#3c haute resolution en phase solide. L'analyse des signaux aborde a la fois ce polymere sous un aspect structural et sous l'angle de la dynamique moleculaire. Le polymorphisme se manifeste par une variation des angles de torsion des chaines en conformation helicoidale allant de pair avec differents empaquetages d'helices. Les formes i et i' se caracterisent par une faible densite spectrale des mouvements du squelette dans la phase cristalline. L'analyse en temperature du spectre #1#3c nous a conduit a proposer pour cette forme un mecanisme precis de sauts entre conformations du groupement lateral. Le spectre #1#3c s'avere egalement utile pour l'identification de la symetrie r#3#c- parmi les differents groupes d'espace jusqu'ici proposes dans la litterature. La forme iii presente certaines similitudes avec la forme i par son caractere heterogene tant sur le plan structural que dynamique. Elle se distingue neanmoins de cette derniere par un processus de relaxation dans la phase cristalline dont les mouvements ne detruisent pas la periodicite de l'helice. Contrairement aux deux autres formes, la phase cristalline de la forme ii presente moins de contrastes avec la phase amorphe. Le maintien de la structure periodique dans le plan transversal associee au desordre dynamique le long de l'helice nous a amene a comparer cette forme a un cristal condis (conformational disorder)

Orientador: Maria do Carmo Gonçalves
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica
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Resumo: Neste trabalho foram estudadas blendas cristalinas de poli(1-buteno) com o copolímero de poli(propileno-co-1-buteno-co-etileno). A influência do tempo de envelhecimento nas características estruturais e nas propriedades térmicas e mecânicas do iPB puro e das blendas de iPB/copolímero foram estudados por difratometria de raios X, termogravimetria (TG), calorimetria diferencial de varredura (DSC) e análise dinâmico-mecânica (DMA). O efeito da adição de copolímero e das condições de cristalização sobre a morfologia dos cristais de iPB foi avaliada por microscopia óptica (MO) e por microscopia de força atômica com modo de força pulsada digital (DPFM). A estabilidade térmica apresentada pelas blendas de iPB/copolímero foi similar à dos polímeros puros. O iPB recém-preparado apresentou cristais de forma II que foram transformados em cristais termodinamicamente estáveis de forma I com o envelhecimento à temperatura ambiente. O grau de cristalinidade obtido para os cristais de forma II e I não foi alterado com a adição de copolímero. Porém, o módulo de armazenamento aumentou com o tempo de envelhecimento e reduziu com o aumento da concentração de copolímero. O iPB apresentou morfologia esferulítica nas diferentes condições de cristalização utilizadas, porém a temperatura de cristalização afetou a densidade de núcleos e a taxa de cristalização. As técnicas microscópicas evidenciaram a segregação do copolímero entre os feixes de lamelas e entre os esferulitos de iPB. Em blendas com concentração superior a 30% de copolímero foram identificados domínios de segregação de fases no estado fundido e que o processo de cristalização ocorreu a partir de nucleação heterogênea. Foi também observado que a transição cristalina do iPB alterou a morfologia das blendas, promovendo a distribuição mais uniforme dos domínios da fase amorfa entre os cristais de iPB. Os parâmetros de Avrami calculados confirmaram a formação de estruturas esferulíticas e a sobreposição de nucleação primária e secundária com o crescimento dos esferulitos. Concluindo, o conjunto de resultados obtidos permite propor que blendas de iPB/poli(propileno-co-1-buteno-co-etileno) apresentaram miscibilidade parcial em concentrações de copolímero inferiores à 20% e imiscibilidade em concentrações mais altas.
Abstract: In this work crystalline blends of isotactic poly(1-butene) and poly(propylene-co-1-butene-co-ethylene) copolymer has been studied. The effect of aging time on the structural and thermal characteristics of these blends has been investigated by X-ray diffraction, thermogravimetry (TG), differencial scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The effect of the addition of copolymer as well as the crystallization conditions on the morphology of iPB crystals was evaluated by polarized light microscopy (OM) and atomic force microscopy in digital pulsed force mode (DPFM). The thermal stability presented by the blends of iPB/copolymer was closed to that one of the pure copolymer. The as-crystallized iPB sample showed crystals of the kinetically favored tetragonal form II, which were transformed to the stable hexagonal crystalline form I with increasing aging time at room temperature. The degree of crystallinity for form II crystals did not change with the addition of the copolymer. However, storage modulus was increased with the increase of the aging time and decreased with the increase of the copolymer concentration. The iPB samples presented spherulitic morphology for different crystallization conditions, however, the crystallization temperature affected the nucleus density and crystallization rate. The microscopic techniques demonstrated that the copolymer segregation occurred between iPB crystalline lamellae and at the interspherulitic regions. In blends containing copolymer concentration higher than 30wt% it were identified phase segregation domains in the melt state and that the crystallization process occurred through heterogeneous nucleation. It was also observed that the iPB crystalline transformation changed the blend morphology, promoting a more uniform distribution of amorphous phase domains in the iPB crystals. The Avrami parameters calculated confirmed the formation of spherulitic structures and the combination of primary and secondary nucleation during the spherulite growing. Based on the obtained results, it is proposed that the iPB/ poly(propylene-co-1-butene-co-ethylene) blends presented partial miscibility at copolymer concentration lower than 20% and immiscibility at higher copolymer concentrations.
Mestrado
Físico-Química
Mestre em Química