Seyed H. Tabatabaei

Structure-orientation-properties relationships for polypropylene nanoclay composite films

In this study, the morphology, orientation, as well as the mechanical and barrier properties of monolayer and multilayer nanoclay filled polypropylene (PP) obtained from the film blowing process were investigated. A significant alignment of nanoclay along the flow direction was observed from scanning electron microscopy images of the cross-section of the etched monolayer and trilayer films. The orientations of PP crystallites and clay platelets as well as the extent of intercalation and exfoliation were analyzed using a wide angle X-ray diffraction. The crystalline structure formed in PP alone was such that the b-axis oriented in the normal and transverse directions (ND and TD, respectively) and the c-axis aligned in the machine direction (MD). The addition of clay changed the orientation of the b-axis to ND, enhanced the a-axis orientation in MD, and also improved the c-axis alignment along MD. Moreover, the 001 plane (normal to platelets plane) of the nanoclays lay into ND drastically. With the incorporation of the clay tactoid, the Young’s modulus was enhanced by 25—40%, the tensile strength remained almost unchanged, and the elongation at break along TD decreased by more than 70% for all the films. The permeability to oxygen and tear resistance along MD and TD were slightly reduced with the presence of nanoparticles and percentage of nanofiller studied. The haze of the nanocomposite films increased upon the presence of clay particles, except in the case of low clay contents of 1.5 and 2.5 wt%.

Effect of initial crystalline morphology on properties of polypropylene cast films

Three polypropylene cast films of different initial morphologies (only spherulitic structure, coexisting rows of lamellae and spherulites, and lamellar structure) were prepared by extrusion followed by stretching using a chill roll. The effects of the original morphology on the orientation, mechanical responses, tear resistance, and oxygen permeability were investigated. The crystallinity and crystal size distribution of the films were studied using differential scanning calorimetry (DSC). The orientation of crystalline and amorphous phases were measured using wide angle X-ray diffraction and Fourier transform—infrared. The precursor film with the lamellar morphology showed much larger crystallinity, crystalline alignment, Young’s modulus, tensile strength, and tensile toughness along the machine direction, but smaller barrier to oxygen compared to the precursors with the only spherulitic structure and coexisting rows of lamellae and spherulites. The obtained results were discussed in terms of the miocrostructure of the precursor films.

Effect of Machine Direction Orientation Conditions On Properties of Hdpe Films

In this study, the effects of machine direction orientation (MDO) conditions on crystalline orientation, morphology, and mechanical performance of a high-density polyethylene film were investigated. The MDO variables studied were feed speed, stretching temperature, draw ratio (DR) as well as annealing temperature. The type of crystals (spherulites or fibrils) and crystallinity of the films were considered using differential scanning calorimetry. The MDO process increased the film crystallinity by 18% and melting temperature (Tm ) by 5°C. The crystalline phase orientation was measured using Fourier transform infrared and wide angle X-ray diffraction. Stretching noticeably increased the crystalline alignment. The Young’s modulus decreased with increasing extrusion temperature and feed speed and enhanced with rising annealing temperature. However, up to DR = 6, the Young’s modulus decreased with draw ratio whereas it increased beyond DR = 6. Upon drawing, the tear resistance along the machine direction decreased significantly, but the puncture resistance along the normal direction increased drastically. Finally, drawing lowered haze for the films dramatically, hence, improved the clarity significantly.

Properties of co-extruded nanoclay-filled aliphatic nylon (PA6)/linear low-density polyethylene and aromatic nylon (MXD6)/ linear low-density polyethylene multilayer films

In this study, coextruded multilayer films with aliphatic (polyamide 6) and aromatic (poly (m-xylene adipamide)) nylons as well as their in-situ polymerized nanocomposites with 4 wt% nanoclay, as an oxygen barrier layer (core), and a linear low-density polyethylene, as a moisture barrier layer (skin), were produced and characterized. Five-layer films were prepared by cast coextrusion and rapidly cooled using an air knife. Dynamic rheological measurements showed that the selected materials can be coextruded with a minimum interfacial instability between the melt flows in the feed block. Type of crystals, crystallinity and thermal transitions of layers were investigated using differential scanning calorimetry and modulated differential scanning calorimetry. The mechanical, optical, oxygen and water vapor barrier properties of the coextruded multilayer films were measured and discussed. Although the crystallinity of the poly (m-xylene adipamide) layer in the multilayer films was lower compared to the polyamide 6 layer, the impermeability to oxygen and water vapor was much better for the former multilayer films. In addition, substituting the neat polyamide 6 and poly (m-xylene adipamide) by their nanocomposites improved the oxygen barrier of the multilayer films by more than 50%. The series resistance model was not able to predict the barrier properties of the multilayer films due to the difference in polymer behavior for the single layer and multilayer, and boundary adjacent layer effects. The coextruded polyamide linear low-density polyethylene multilayer films showed higher toughness, tear and flex crack resistance compared to the poly (m-xylene adipamide)/linear low-density polyethylene samples. The pristine poly (m-xylene adipamide)-based multilayer film showed a lower haze compared to the polyamide 6 films due to very little crystallinity in the former.

Peel/seal properties of poly(ethylene methyl acrylate)/polybutene-1 blend films

Nowadays, the possibility to easy open a food package is of great interest both from the consumer and food producers’ perspective. In this study, the peel/seal properties of poly (ethylene methyl acrylate) (EMA)/polybutene-1 (PB-1) blend films were investigated. Three blends of EMA/PB-1 with different methyl acrylate (MA) content were prepared using cast extrusion process. Differential Scanning Calorimetry (DSC) was used to investigate the thermal behavior as well as the crystalinity of the blends. The effect of polymer matrix on the crystalline structure of PB-1 was studied using Wide Angle X-ray Diffraction (WAXD) and DSC. T-peel tests were carried out on the heat sealed films at various seal temperatures. The effect of MA content and heat seal temperature on peel/seal properties (i.e. peel initiation temperature, temperature window of sealability and peel strength) of the films were studied.

Applications of biaxial stretched films

Abstract: More recently, as increasing pressure is directed to increase the shelf-life of foods and to reduce the rejection and defect rate in metallized high barrier films, attention is focusing on the orientation of nanocomposite and multilayer films. In this chapter, structural deformation of biaxial oriented nanocomposite and multilayer films are presented. In addition, various processes for making biaxial oriented structures are discussed.