correlação entre propriedades reológicas e ópticas de filmes tubulares de polietileno linear de baixa densidade com diferentes distribuições de ramificações curtas correlation between rheological and optical properties of lldpe blown films with different distributions of short chain branching
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ID: 233630
2006
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Abstract
Devido a suas excelentes propriedades mecânicas o polietileno linear de baixa densidade, PELBD, tem ganhado cada vez mais importância na indústria de embalagens. Essas propriedades são resultado de sua estrutura molecular, da existência de ramificações curtas, SCB, e da distribuição dessas ramificações, DSCB. Junto com o peso molecular, PM, e sua distribuição, DPM, as ramificações curtas também afetam o processo de sopro de filmes influenciando na solidificação do filme até a linha de neve, já que a cinética de cristalização é dependente da distribuição destas ramificações. Assim, este trabalho teve como objetivo verificar a influência da DSCB do PELBD nas propriedades reológicas e óticas de filmes tubulares. Para isso, três PELBD foram escolhidos; dois sintetizados com catalisador Ziegler-Natta e um com catalisador metaloceno, de peso molecular ponderal médio, Mw, similar e DSCB diferentes. Observou-se que a DSCB exerce influência nas propriedades reológicas que refletem a elasticidade do material como a primeira diferença de tensões normais N1, o módulo de armazenamento G'(w), e a deformação recuperável gamar; entretanto na viscosidade em função da taxa de cisalhamento eta(gama), e no módulo de perda G"(ômega), a diferença nessa distribuição não foi percebida. Observou-se também que quanto maior a deformação recuperável dos PELBD, menores foram as estruturas cristalinas formadas o que diminuiu a opacidade dos filmes. Porém essa proporcionalidade manteve-se até uma determinada gamar mínima, acima da qual a fratura do fundido se sobrepôs à recuperação da deformação e a opacidade voltou a aumentar.
Linear low-density polyethylene, LLDPE, has increased its market share in the packaging industry due to its excellent mechanical properties. These properties are the result of its molecular structure due to its short chain branching, SCB, and their distribution, DSCB. Together with the molecular weight and the distribution of molecular weights, the SCB affects the blown film process because it interferes in the film solidification and crystallization kinetics up to the freezing line. The objective of this work was to verify the influence of the DSCB of LLDPE in the rheological and optical properties of blown films. Three LLDPE, synthesized with Ziegler-Natta and metallocene catalysts, were studied, all with similar weight average molecular weight, Mw, but with different DSCB. It was observed that the DSCB influenced the rheological properties that reflect the material elasticity, such as the first normal tension difference, N1(g), the storage modulus G'(w) and the recoverable strain gammar; however, the rheological properties that reflect the viscosity, such as the shear viscosity eta(gamma) and the loss modulus G"(w), were not affected. In addition, the higher the gammar of the LLDPE, the lower the crystalline structures of the films, which decreased their opacity. However this proportionality was kept up to a given value of gammar above which the melt fracture dominated the recoverable strain and the opacity increased again.
Linear low-density polyethylene, LLDPE, has increased its market share in the packaging industry due to its excellent mechanical properties. These properties are the result of its molecular structure due to its short chain branching, SCB, and their distribution, DSCB. Together with the molecular weight and the distribution of molecular weights, the SCB affects the blown film process because it interferes in the film solidification and crystallization kinetics up to the freezing line. The objective of this work was to verify the influence of the DSCB of LLDPE in the rheological and optical properties of blown films. Three LLDPE, synthesized with Ziegler-Natta and metallocene catalysts, were studied, all with similar weight average molecular weight, Mw, but with different DSCB. It was observed that the DSCB influenced the rheological properties that reflect the material elasticity, such as the first normal tension difference, N1(g), the storage modulus G'(w) and the recoverable strain gammar; however, the rheological properties that reflect the viscosity, such as the shear viscosity eta(gamma) and the loss modulus G"(w), were not affected. In addition, the higher the gammar of the LLDPE, the lower the crystalline structures of the films, which decreased their opacity. However this proportionality was kept up to a given value of gammar above which the melt fracture dominated the recoverable strain and the opacity increased again.
| Reference Key |
basso2006polmeroscorrelao
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|---|---|
| Authors | ;Glayton M. Basso;Pedro I. Paulin-Filho;Rosario E. S. Bretas;Alessandro Bernardi |
| Journal | journal of the chemical society, perkin transactions 1 |
| Year | 2006 |
| DOI |
10.1590/S0104-14282006000200016
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| URL | |
| Keywords | Keywords not found |
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