Influence of molecular architecture and melt rheological characteristic on the optical properties of LDPE blown films

A systematic investigation on the origin of the haze of LDPE blown films was conducted, aiming to correlate the film haze with the molecular architecture and melt rheological properties. First of all, the haze measurement indicated that the surface haze, rather than the bulk haze, is the dominating factor for the total haze of the investigated films. No spherulitic crystals or other superstructures were observed for the LDPE blown films, implying that the crystallites formed in the film-blowing process are too small to be responsible for the optical haze. Rheological study revealed that the surface roughness was originated from the irregular flow of LDPE melt during the extrusion process. NMR, GPC and parallel-plate rheology were applied to study the molecular architecture of the LDPE resins. It was found that the LDPE sample with higher haze value exhibits distinctly larger portion of higher molecular weight component, broader molar mass distribution, significantly higher side chain branch density.