Khaled Mezghani

Miscibility of hexene-LLDPE and LDPE blends: influence of branch content and composition distribution

Abstract The influences of branch content (BC) and composition distribution (CD) of hexene linear low-density polyethylene (LLDPE) on its miscibility with low-density polyethylene (LDPE) were investigated. Ziegler–Natta (ZN) and metallocene-LLDPE (m-LLDPE) were used to study the melt miscibility using rheological tools. Dynamic, steady shear and transient measurements were carried out in an ARES rheometer at 190 °C. The miscibility was revealed by the dependence of their ηo, η′(ω), G′, and N 1 ( γ ) on blend composition. The CD of LLDPE has influenced its miscibility with LDPE. The ZN–LLDPE blend with LDPE was found to be more miscible than an m-LLDPE of the same Mw and similar BC. On the other hand, a high-BC m-LLDPE (32.2 CH3/1000 C) was found to be more miscible with LDPE than a low-BC m-LLDPE (14.4 CH3/1000 C) of the same Mw and MWD. The high-BC m-LLDPE blends with LDPE were partially miscible and immiscibility is likely to develop in LDPE-rich blends. Agreement was observed between the measured rheology and theoretical predictions of Einstein, Scholz et al., Palierne, and Bousmina emulsion models.

Crystallization Kinetics of Polymers

There are several methods for studying crystallization kinetics of polymers, which fall into two general categories: bulk or volumetric analysis, and crystal growth analysis. The simplest experimental study is the bulk growth, but it is the most difficult to analyze in detail. However, it can be analyzed partially using the Avrami equation [1,2]. The Avrami equation was derived from prior work by Poisson based on expanding waves created by raindrops on a pond and results in the general equation:

Effect of –COOH Functionalized Carbon Nanotubes on Mechanical, Dynamic Mechanical and Thermal Properties of Polypropylene Nanocomposites

Multi-walled carbon nanotubes (CNTs) were functionalized on treatment with nitric acid and the surface-modified CNT was characterized using Fourier transform infrared spectroscopy (FTIR). Isotactic polypropylene (iPP)/CNT composites at different CNT loadings (i.e., 0.1, 0.25, 1.00, and 5.00 wt%) were prepared by melt blending in a mini blender. The differential scanning calorimetric (DSC) studies showed the nucleating effect of CNTs on the crystallization behavior of iPP. Results of X-ray diffraction studies are in conformity with the results of DSC studies. Results of stress–strain measurements reveal that Youngs modulus increases, while elongation at break decreases with increase in CNT loading and the ductility of the composites is adversely affected at high loading of CNTs (>1.0 wt%). Functionalization of CNTs causes an improvement in Youngs modulus, at all loadings studied, but elongation at break increases only up to 0.25%. At higher loading, the elongation at break drops down. Storage modulus increases with increase in CNT loading and the effect is greater in the case of functionalized CNTs. Tan δ shows a decrease with increase in CNT loading, but the effect is less pronounced at high CNT loading (>0.1 wt%).

Effect of High Shear Mixing Parameters and Degassing Temperature on the Morphology of Epoxy-Clay Nanocomposites

Epoxy-clay nanocomposites were prepared by high shear mixing method using Nanomer I.30E nanoclay as nano-reinforcement in diglycidyl ether of bisphenol A (DGEBA). The effect of mixing speed and time on the nature and degree of clay dispersion were investigated by varying the mixing speed in the range of 500-8000 RPM and mixing time in the range of 15-90 minutes. The effect of degassing temperature on the morphology of the resultant nanocomposites was also studied. Scanning and transmission microscopy (SEM & TEM) along with x-ray diffraction (XRD) have been used to characterize the effect of shear mixing speed, mixing time and degassing temperature on the structure of the resultant nanocomposites. The SEM, TEM and XRD examinations demonstrated that the degree of clay dispersion was improved with increasing the high shear mixing speed and mixing time. The results showed that the optimum high shear mixing speed and mixing time were 6000 rpm and 60 min, respectively. It was observed that the structure of the nanocomposites that have been degassed at 65oC was dominated by ordered intercalated morphology while disordered intercalated with some exfoliated morphology was found for the sample degassed at 100oC for the first 2 hours of the degassing process.

Analysis of dart impact resistance of low-density polyethylene and linear low-density polyethylene blown films via an improved instrumented impact test method:

An improved instrumented impact test method is used to correlate the impact resistance of low-density polyethylene and linear low-density polyethylene blown films to their solid-state deformation process during impact test. The two materials, low-density polyethylene and linear low-density polyethylene, showed different deformation behaviors under the same impact testing conditions. The region before the peak force in the load versus deformation plot for low-density polyethylene was linear, whereas for linear low-density polyethylene two different slopes were observed. The average peak force values of linear low-density polyethylene film is about 14% greater than that of low-density polyethylene film. Furthermore, the measured deflection at the peak force is about 50% higher in the case of linear low-density polyethylene film. In addition, the energy to peak force of linear low-density polyethylene is more than twice higher than that of low-density polyethylene. In the region after the peak point, the low-density polyethylene exhibited another peak before failing and no such peak was observed for linear low-density polyethylene. Tensile test results with low strain rate of deformation have also been compared. The tensile stress–strain in machine direction (MD) and transverse direction (TD) direction play an important role during the biaxial deformation during the impact test. The crystallographic deformations were explained using the scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) techniques for lamellar structure and orientation. The low-density polyethylene film has developed columnar clusters of lamellae, which are aligned parallel to the TD direction. On the other hand, the linear low-density polyethylene film structure shows more randomly orientated and thicker lamellae than that of the low-density polyethylene film. The result of this structure is a more balanced toughness in both MD and TD directions.

Effect of Blend Ratio of h-LLDPE and LDPE on Tear Properties of Blown Films

Abstract In the present study, blown films of h-LLDPE, LDPE, and their blends were produced using a twin screw extruder. The tear properties of all films were determined in the machine direction (MD) and the transverse direction (TD). On one hand, similar values of the MD tear-resistance for the two virgin polymers, h-LLDPE and LDPE, were measured to be 100 and 120 kN/m, respectively. On the other hand, the TD tear-resistance value of h-LLDPE was 180 kN/m, four times higher than that of LDPE, 45 kN/m. It was observed that small additions of LDPE (5 to 20 wt.%) to h-LLDPE produced blends with better TD tear-resistance films, 400 kN/m. The main reason for this large increase in tear-resistance was attributed to the morphological changes induced by the addition of the LDPE polymer, as shown by SEM, FTIR, and birefringence techniques.