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The influence of molecular architecture on interfacial self-adhesion above polyethylene film melt temperature was examined in this study. The investigated molecular structures include molecular weight (Mw), molecular weight distribution, long chain branch amount and distribution and short chain branch among and along polyethylene chains. The long chain branches concentration was quantified using gel permeation chromatography and short branches concentration using nuclear magnetic resonance techniques. The adhesion strength was measured immediately after melt bonding using a T-Peel test. The results showed that increasing Mw resulted in higher adhesion strength in linear metallocene ethylene α-olefins. Low long chain branch concentrations hinder reptation motion and diffusion, and result in lower adhesion strength. Low density polyethylene with highly branched chains yielded very low self-adhesion. A drastic difference in adhesion strength between metallocene and conventional linear low density polyethylene is attributed to homogeneity versus heterogeneity of composition distribution. The low interfacial self-adhesion in conventional polyethylene was concluded to be due to enrichment of highly branched low molecular weight chains at the film surface. These segregated chains at the interface diffuse before the high molecular weight chains located in the bulk.

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Seal strength behavior of low density polyethylene and ethylene vinyl acetate copolymer (PE/EVA) blends as well as that of blends of as eal 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 ad ecrease in seal initiation temperature and broadness of sealability plateau. This was interpreted as due to the formation of finer crystals, adecrease 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 ellipsoidald omains. This type of morphology affected the mechanical and seal properties of the blends. As aresult 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 %d ispersed content compared advantageously to commercially available polyolefin based sealant resins. The seal and hottack initiation temperatures were shifted to lower temperatures by as much as 30 8 C, which can allow faster and more energy efficient sealing process. 1I ntroductionHeat sealing is an important operation in packaging. Modern vertical and horizontal form fill seal (VFFS and HFFS) machines have aneed for operating at higher speeds. This requirement and the fact that the final package integrity is ultimately dependent on the results of the sealing process requires that the polymers used for the seal layer have superior hot-tack strength, low seal initiation temperature and wider sealing temperatures range. Although resin suppliers provide awide range of resins for the seal layer, with avariety of performances and physical properties, materials optimization is still achallenge. This challenge is even greater when the production line aims to use biodegradable materials which still cannot provide as superior properties as commercially available resins. Achieving sufficient adhesion upon sealing two semicrystalline polymer films in the fully or partially molten state is mainly ascribed to chain interdiffusion across the interface, amorphous fraction of material, and polymer chain functional groups.Coextrusion of low density polyethylene (LDPE) and ethylene vinyl acetate copolymer(EVA) has been used in industry to tailor as ealant layer. However, studies on correlation of physical properties ...

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