ABSTRACT:In the present work, attempts have been made to prepare nanocomposite type of hydrogels (NC gels) by crosslinking the polyacrylamide/montmorillonite (Na-MMT) clay aqueous solutions with chromium (III). The Xray diffraction patterns of the NC gels exhibited a significant increase in d 001 spacing between the clay layers, indicating the formation of intercalated as well as exfoliated type of morphology. Exfoliation of the clay layers through out the gel network was found to be predominated, which evidences the high interaction between the polyacrylamide segments and montmorillonite layers. Gelation time as well as variation of viscoelastic parameters such as storage modulus (GЈ) of the gel network during gelation process at 75°C was studied and followed by rheomechanical spectroscopy (RMS). The NC gels prepared with lower crosslinker concentration showed higher strength and elastic modulus compared with the similar but unfilled polyacrylamide gel. This distinct characteristic of the NC gels yields a gel network structure with high resistance towards syneresis at high temperature in the presence of the oil reservoir formation water. The effects of the composition, such as clay content, crosslinker concentration, and also water salinity upon the gelation rate, gel strength as well as rate of syneresis have been investigated. To optimize the injectivity of the intercalated polyacrylamide solution before the onset of gelation with the gel strength of the final developed gel, sodium lactate was employed as retarder. This was found to be effective to balance these two characteristics of the NC gels, which are aimed to be used for water shut-off and as profile modifier in enhanced oil recovery (EOR) process during water flooding process. The nanocomposite gels showed much more elasticity and extensibility at low crosslinker concentration compared with the similar but unfilled gel, which makes the NC gels suitable as an in-depth profile modifier, and also as an oil displacing agent in the heterogeneous oil reservoir in chemical EOR. Effects of the clay content on the thermal stability of the gel network have also been investigated by thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) has been performed upon the NC-gel samples.

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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 ...

In this study, we address heat-seal properties of poly (lactic acid) (PLA), blended with Poly (butylene adipate-co-terephthalate) (PBAT). The objective is to correlate blends crystalline structure and morphology to corresponding heat-seal of blends films. The SEM micrographs show a two-phase elongated morphology where stretched ellipsoids developed through elongational flow during the cast film process. To distinguish the effect of crystallization, we also prepared amorphous and crystalline PBAT films and then compared them to blends with PLA. Heat-sealed areas were created by putting film surfaces in intimate contact for 1 s at the pressure of 0.5 N/mm2 or Pa and in the temperature range of 70 to 140 °C. Thermal analysis shows that the crystalline structure of PBAT has a significant effect on shifting its heat-seal initiation temperature (Tsi) up to 20 °C. Regarding the blends, incorporation of PBAT as a dispersed phase lowers Tsi of blend samples. Here, gradual decrease in PBAT crystallinity caused by the hindering effect of PLA rigid molecules correlates with the shift in heat-seal initiation temperature. As mentioned above, elongated disperse morphology with higher aspect ratio of the dispersed phase compared to spherical dispersed domain, is formed through film cast process. This enhances the adhesion process by providing higher contact area. The blends also show higher toughness and better puncture resistance, which is an asset for flexible packaging applications and would enhance the mechanical performance of the seal layer.

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