Sealability and Seal Characteristics of PE/EVA and PLA/PCL Blends

Abstract

Abstract Seal strength behavior of low density polyethylene and ethylene vinyl acetate copolymer (PE/EVA) blends as well as that of blends of a seal grade PLA with aliphatic polyester (PCL) was studied. Polyethylene is commonly used for seal application in packaging multilayer structures and amorphous PLA is considered to be its counterpart for compostable and/or biodegradables ones. Incorporation of EVA in polyethylene improves its sealability in terms of a decrease in seal initiation temperature and broadness of sealability plateau. This was interpreted as due to the formation of finer crystals, a decrease in the melting point and presence of vinyl acetate polar group. These were supported by results obtained from differential scanning calorimetry (DSC) and Scanning electron microscopy (SEM). For the PLA/PCL system, the dispersed phase was stretched into elongated ellipsoidal domains. This type of morphology affected the mechanical and seal properties of the blends. As a result of blending, both hot-tack initiation temperature and strength as well as seal initiation temperature were enhanced. The enhancement in these seal properties was significant when the concentration of the dispersed phase exceeded 20 wt% in the blend. Hot-tack strength of up to twice of pure PLA was achieved through blending. This was attributed to the lower glass transition temperature of PCL, resulting in enhanced mobility of PLA chains and also the high aspect ratio of the dispersed phase. The maximum obtained hot-tack strength (1 200 g/25 mm) at 40 % dispersed content compared advantageously to commercially available polyolefin based sealant resins. The seal and hot-tack initiation temperatures were shifted to lower temperatures by as much as 30 °C, which can allow faster and more energy efficient sealing process.