Hollow Fiber Porous Nanocomposite Membranes Produced via Continuous Extrusion: Morphology and Gas Transport Properties.

Zahir Razzaz,Denis Rodrigue

doi:10.3390/ma11112311

Abstract

In this work, hollow fiber porous nanocomposite membranes were successfully prepared by the incorporation of a porous nanoparticle (zeolite 5A) into a blend of linear low-density polyethylene (LLDPE)/low-density polyethylene (LDPE) combined with azodicarbonamide as a chemical blowing agent (CBA). Processing was performed via continuous extrusion using a twin-screw extruder coupled with a calendaring system. The process was firstly optimized in terms of extrusion and post-extrusion conditions, as well as formulation to obtain a good cellular structure (uniform cell size distribution and high cell density). Scanning electron microscopy (SEM) was used to determine the cellular structure as well as nanoparticle dispersion. Then, the samples were characterized in terms of mechanical and thermal stability via tensile tests and thermogravimetric analysis (TGA), as well as differential scanning calorimetry (DSC). The results showed that the zeolite nanoparticles were able to act as effective nucleating agents during the foaming process. However, the optimum nanoparticle content was strongly related to the foaming conditions. Finally, the membrane separation performances were investigated for different gases (CO2, CH4, N2, O2, and H2) showing that the incorporation of porous zeolite significantly improved the gas transport properties of semi-crystalline polyolefin membranes due to lower cell wall thickness (controlling permeability) and improved separation properties (controlling selectivity). These results show that mixed matrix membranes (MMMs) can be cost-effective, easy to process, and efficient in terms of processing rate, especially for the petroleum industry where H2/CH4 and H2/N2 separation/purification are important for hydrogen recovery.

Highlights

Microporous polymer membranes are currently considered as commercially attractive due to their low operating temperature and manufacturing costs, as well as good processability
The results show that the permeance significantly increases with zeolite addition compared to hollow fibers based on foamed and unfoamed MMFM0 membranes for all the gases studied
Zeolite addition to the unfoamed hollow fiber (L-15) membrane led to a negligible variation in separation performance compared to the unfilled and unfoamed hollow fiber (L-0) samples (Figure 13)

Summary

Introduction

Microporous polymer membranes are currently considered as commercially attractive due to their low operating temperature and manufacturing costs, as well as good processability. Due to limited polymer thermal stability and the plasticization effect, their applications have been restricted to separation processes where severe conditions are not encountered [1,2]. One effective approach to improve the performance of polymer membranes is to incorporate inorganic nanoparticles such as zeolites and carbon-based molecular sieves since they have higher thermal resistance and chemical stability, combined with molecular sieving property This led to the concept of mixed matrix membranes (MMMs) which were shown to have increased selectivity and permeability compared to neat polymer membranes [3,4]. The addition of these inorganic particles makes the membranes more fragile.

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