Farhad Sadeghi

Study of polypropylene morphology obtained from blown and cast film processes : Initial morphology requirements for making porous membrane by stretching

Four different polypropylene (PP) resins are extruded using the tubular blown and cast film processes. The resin morphology is observed by SEM and the effect of extrusion processing variables on the morphology is investigated. Melt rheological experiments are also carried out to characterize the polymer melts. It has been found that the molecular weight distribution and the chain structure as well as the processing conditions have important effects on the morphology. Efforts have been focused on developing a row-nucleated morphology from PPs through the control of processing conditions. The possibility of generating a porous membrane from the initial row-nucleated morphology using a stretching technique is evaluated. It has been found that the initial lamellae arrangement of the precursor films and the stretching conditions play a significant role in obtaining a porous structure.

Structure, Mechanical and Barrier Properties of Uniaxially Stretched Multilayer Nylon/Clay Nanocomposite Films

Abstract Multilayer films consisting of a core layer of nylon 6 (PA6) sandwiched between two linear low density polyethylene (LLDPE) layers by using a tie layer were produced using a semi industrial cast film extrusion line. The core layer of the films was produced from neat PA6 and PA6/clay nanocomposite resins. The films were consequently uniaxially stretched in machine direction. The effect of stretching on crystalline structure, orientation as well as mechanical and barrier properties of the samples were investigated. Orientation of the films for both layers: polyethylene and nylon was assessed using FTIR (Fourier Transform Infrared Spectroscopy) and it was found that clay inclusion hindered orientation of the core nylon layer. Interaction of nylon molecules with clay influences the crystalline structure for nylon/clay nanocomposite film during the stretching as it hindered crystal transformation of γ to α phase. The effect of clay interaction on phase structure was also observed in DSC (Dynamic Scanning Calorimetry) results. Stretching improved barrier to oxygen for the samples. Oxygen transmission rate was reduced about 62.5% for the films having a nylon core and 50% for those with nylon/clay core when stretched to a draw ratio of 1.5 and remained nearly constant for higher draw ratios up to 3. Haze of the films was reduced with stretching; however the effect was more effective for the sample with neat nylon in the core layer when compared to the nylon/clay core one. Finally, it was observed that puncture resistance of the samples was improved significantly with stretching.

Effect of molecular structure on seal ability, flex crack and mechanical properties of linear low-density polyethylene films:

In this article, three linear low-density polyethylenes having different molecular structures were selected and films were produced from them using a semi-industrial cast film extrusion line. Rheological and gel permeation chromatography measurements were performed on the resins to assess their molecular structure. Mechanical, physical and sealability properties of the films were evaluated and the results were discussed with regard to the molecular structure of the resins. It was found that molecular weight and distribution of short-chain branching (comonomer) on the backbone of polyethylene chains are the main factors that control sealability, flexural cracking and mechanical properties. Placement of comonomer on medium length chains generated crystals with expanded unit cell that show lower melting peak. Sealing was controlled by crystal size distribution, chain diffusion and entanglement formation at the interface. linear low-density polyethylenes with lower melting point and boarder molecular weight distribution showed lower seal and hot tack initiation temperatures. Polydispersity along with molecular weight contributes to toughness and puncture resistance. Flexural cracking resistance was observed to be related to crystallinity, tie chain density and more importantly to the amorphous phase fraction. The amorphous part could absorb flexing energy and hinders crack initiation and propagation. Seal through contamination (caulkability) was found to be related to flowability and elasticity of the melt.