POLYETHYLENE

Author: MARTÍN RAUSEO SANDRA.
Year: 2004.
University: COMPLUTENSE DE MADRID [www.ucm.es].
Place of defense: FACULTAD DE CIENCIAS QUÍMICAS.
Place of preparation: INSTITUTO DE ESTRUCTURA DE LA MATERIA, CSIC.

Summary: The Polymer Science has been taken as a reference system polyethylene because of the simplicity of its chemical structure. However, lack of materials homogeneous structure has prevented until a very few years ago a systematic study for achieving direct links between the properties of these materials and their molecular structure. With the advance in the process of synthesis of polyolefins has emerged a new generation of materials controlled chemical structure. Using new generation of polyethylenes obtained through catalysis metalocénica in memory of this thesis aims to explore some of the fundamental aspects of the relationship between structure and properties, such as the effect of the content of short chain ramifications on the process crystallization, the glass transition and the mechanical and rheological properties, as well as the potential impact of cocristalización in mixtures of these materials. For this purpose were used two families of copolymers structure controlled etileno/1-hexeno with different contents of ramifications. This study concludes that these materials are partially miscible and immiscible in the solid state, and no evidence of cocristalaizaicón between any of the components of mixtures. The mechanical properties module Young and the creep strain of mixtures are ADDITIVE. The behavior of these mechanical properties can be described by the models of coupling between phases Tsai-Halpin and Takayanagi to make a correction in the design of the module amorphous laid on both models. As for the crystallization process can be concluded that there is a dependency of the process of crystallization kinetics with the contents of ramifications, as well as evidence of schemes I and II of crystallization. There is also a strong dependence of the phenomenon of a glass transition with the content ramifications. Finally, we see a clear influence of comonómero in rheological behavior.

Author: SAENZ DE JUANO ARBONA VICTOR.
Year: 2006.
University: POLITÉCNICA DE VALENCIA [www.upv.es].
Place of defense: Dep. Termodinamica Aplicada.
Place of preparation: Universidad Politécnica de Valencia.

Summary: The objective of this thesis is to study Doctoral the degradation of polyethylene films for agricultural applications subjected to periods of 12, 16, 20, 24 and 31 months of environmental degradation or "weathering." The films were prepared by extrusion with linear low density polyethylene (LLDPE), low density polyethylene graft (LDPE) and mixtures with different proportions of the two polyethylenes LLDPE / LDPE (15/85, 32/68, 50/50, 68 / 32 and 85/15). All of them were stabilized with HALS (amines estéricamente disabled) CHIMASORB 119. Contrary to what was published in other works, this thesis raises analyze the physical properties of a macroscopic polymeric materials used by Thermal Analysis and relate these properties with the process of environmental degradation. The basic experimental techniques that have been considered in this work are: The Termogravimetría (TGA) combined with mass spectroscopy (MS), Differential Scanning Calorimetry (DSC) and the Analysis Termo-Mecánico-Dinámico (DMTA). Based on the termogramas termogravimétricos has studied the kinetics of termodegradación each film by both methods as integral differential. The termogramas calorimétricos to analyze the impact of environmental degradation on the morphology of polymer. We have calculated the melting temperature, the rate of crystallinity and distribution of thicknesses lamelares. Trials termo-mecánicos-dinámicos allow study the mechanical properties of polymers degraded from its full spectrum of relajaciones mechanical. These were isolated by deconvolution method proposed by Charlesworth. Each of the relajaciones identified has been characterized by the model Fuoss-Kirkwood and has calculated its activation energy. It has also proposed a molecular origin for each relaxation.