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Polyethylenes in blown films: Effect of molecular structure on sealability and crystallization kinetics
Author(s) -
Moreira Ana Cristina Fontes,
Dartora Paula Cristina,
Paulo dos Santos Francisco
Publication year - 2017
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.24384
Subject(s) - branching (polymer chemistry) , materials science , comonomer , crystallization , polymer , extrusion , polyethylene , melting point , dispersity , monomer , composite material , polymer chemistry , kinetics , chemical engineering , physics , quantum mechanics , engineering
Three types of polyethylene (PE), with different molecular structure, were selected and used in the production of films using a semi‐industrial blown film extrusion line. Carbon nuclear magnetic resonance and crystallization analysis fractionation tests were performed on the PE polymers to assess their molecular structure. Sealability properties of the films, as well as crystallization kinetics, were evaluated and the results are discussed according to the molecular structures of the polymers. It was found that distribution of short chain branching (average comonomer sequence nH or nO) on the backbone of the PE chains are the main factor controlling the beginning of sealability. The completely random placement of the comononer on the polymer backbone (monomer dispersity 100%) generated crystals with smaller size and a lower melting temperature. Sealing was controlled by crystal distribution, chain diffusion, and entanglement formation at the interface. PE with lower melting point and linear molecular structure showed greater hot tack strength. PE with long chain branching showed a delay on seal process leading to lower sealing speed. POLYM. ENG. SCI., 57:52–59, 2017. © 2016 Society of Plastics Engineers