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

Abstract

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.

Biodegradation of blend films PVA/PVC, PVA/PCL in soil and soil with landfill leachate

“…The calorimeter was properly calibrated using the indium standard (Tf = 159.11°C; ∆H = 30.66 J/g). The degree of crystallinity of the blends was calculated based on ∆H values of 136 J/g (Kesel et al, 1999) for 100% crystalline PCL and 152 J/g (Martins-Franchetti et al, 2008) for 100% crystalline PVA, using the follow equation (Quental et al, 2005).…”

Avaliação das propriedades físico-químicas de nanocompósitos de polietileno linear de baixa densidade e montmorilonita organofílica obtidos por extrusão

“…A entalpia de fusão ΔH m correspondente à área do pico, a qual foi utilizada no cálculo do grau de cristalinidade (α c ) através da razão de ΔH m / ΔH m° multiplicado por 100, onde ΔH m é a entalpia de fusão do PELBD obtidas por DSC, e ΔH m° é a entalpia de fusão para o PEAD 100 % cristalino, cujo valor é igual a 293 J/g [8]. O PELBD puro apresentou αc = 47,71 %, enquanto o aumento percentual de nanoargila aumentou o grau de cristalinidade das amostras, com destaque para a amostra PELBD/OMMT 2,5% que apresentou grau de cristalinidade αc = 52,73 %.…”

The influence of soil and landfill leachate microorganisms in the degradation of PVC/PCL films cast from DMF

“…The melting points and heat of fusion were obtained from the DSC curves, in order to calculate the degree of crystallinity of the films before and after the microbial treatment, using Equation 1 [32] . (Equation 1) peak, but the temperature of melting increased slightly, suggesting better organization of the chains.…”