Caracterização de polietilenos lineares de baixa densidade I.: determinação do teor de ramificação por métodos espectroscópicos

Linear low-density polyethylenes (LLDPE) are a class of polyethylenes with linear chains containing only short chain branches due to the insertion of α-olefin units during the copolymerization with ethene. The α-olefins commonly used are 1-butene, 1-hexene and 1-octene. Depending on the α-olefin and the catalyst used for the polymerization, LLDPE presents different microstructures which determine the thermal and mechanical properties. One simple and efficient method to evaluate the microstructure of LLDPE is the fractionation by Multiple-Step Isothermal Crystallization from Melting State conducted by DSC. This method is based on several steps of isothermal crystallization of the polymer on decreasing the temperature from the melt. This process favors the separation of the crystalline material into groups having different lamellae thickness depending on the amount and distribution of the α-olefin units in the macromolecular chains and on the molar mass. The melting endotherm of a fractionated sample is made up of the same number of peaks as the isothermal crystallization steps, which inform the relative comonomers distributions between different LLDPE chains. In this work, this methodology was applied to determine the relative comonomers distribution of different LLDPE. The isothermal temperature, temperature range and the time influence the efficiency of the fractionation and these parameters must be chosen according to the LLDPE microstructure.

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Caracterização de polietilenos lineares de baixa densidade I.: determinação do teor de ramificação por métodos espectroscópicos

Cited by 2 publications

References 8 publications

Mechanical, Thermal and Morphological Characterization of High-Density Polyethylene and Vermiculate Composites

Mechanical, Thermal and Morphological Characterization of High-Density Polyethylene and Vermiculate Composites

Caracterização de polietilenos lineares de baixa densidade II: fracionamento por cristalização isotérmica a partir do estado fundido

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