Preparation and property improvement of three layered shrink film based on recycled low density polyethylene

Abstract

Three layered shrink films based on recycled low density polyethylene re-LDPE) were prepared by blown film co-extrusion. The outer layers contained only virgin LDPE while the middle layer composed of the blends between LDPE and re-LDPE at weight ratios of 100:0, 85:15, 70:30, 55:45, 40:60 and 0:100. From mechanical tests and thermal analysis, it was found that all films prepared from polymer blends and from re-LDPE 100 wt% (LDPE/re-LDPE/LDPE film) exhibited better mechanical properties and thermal behaviors than the film containing only LDPE. The mechanical properties including tensile properties, seal strength and shrink ability of LDPE/re-LDPE/LDPE film were improved by blending the middle layer with medium density polyethylene (MDPE) and the outer layer with linear low density polyethylene (LLDPE). It was found that using 30 wt% of MDPE and 30 wt% of LLDPE gave the film that had highest seal strength and better tensile properties than the film containing only LDPE and re-LDPE. In addition, this film also exhibited the shrink ability within the commercial standard for shrink film applications. On the other hand, adding calcium carbonate (CaCO3) into re-LDPE middle layer also improved mechanical properties of LDPE/re-LDPE/LDPE film. SEM analysis revealed the good dispersion of CaCO3 in re-LDPE matrix resulting in better tensile properties. However, adding too much CaCO3 decreased the optical property and seal strength but increased shrink ability. The suitable amount of CaCO3 to be added was 7.5 wt%.