Gas transport properties of cellular hollow fiber membranes based on LLDPE/LDPE blends

Abstract

The production of foamed hollow fiber membranes (HFMs) is presented based on polymer blends using various concentrations of linear low-density polyethylene (LLDPE) and low-density polyethylene (LPDE) combined with azodicarbonamide (chemical blowing agent) to prepare samples via twin-screw extrusion. In particular, the blowing agent concentration as well as the stretching speed were found to be the most important parameters to achieve a good cellular structure for membrane application. From the samples obtained, a complete set of morphological, thermal, and gas transport characterization was performed. The results show that LLDPE/LDPE blends compared to neat LLDPE lead to higher cell density at high stretching speed, which is appropriate for membranes having higher gas permeability and selectivity due to lower cell wall thickness. The results also show that the developed cellular structure has high potential for the continuous production of HFMs for different gas separation, especially for hydrogen recovery.

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

“…This work is also a second step to improving upon the results obtained from the authors’ previous studies [6,7,13]. In fact, the idea was to propose a sustainable alternative production method for hollow fiber mixed matrix membranes.…”

“…The use of leachable particles such as salts was shown to produce an open-cell structure based on polystyrene [9], polypropylene [10], and polyethylene [11]. Other solvent-free methods are stretching with or without particles [12] and direct foaming of semi-crystalline thermoplastics such as high-density polyethylene (HDPE) and polypropylene (PP) [7,13]. For stretching methods, the porosity is created by delamination between the matrix and local stress concentration points such as solid particles or crystalline zones, but thermal post-treatment is needed to stabilize the newly created microporous and crystalline structure to avoid shrinkage and warpage, which are the main drawbacks of such methods.…”

“…The authors’ previous works showed how the morphological properties, such as cell size uniformity as well as cell density, can control the physical, mechanical and gas transport properties of hollow fiber polymer membranes [5,6,7,13]. Since these properties are tunable, this led to membrane performance enhancement via simultaneous improvement of both the surface area as well as gas transport properties [7,22].…”

“…), and post-processing (stretching) conditions were the main parameters to control the porous membrane structure. Direct foaming is interesting because it is solvent free, continuous, and fast to produce a porous structure in hollow fibers [5,7,13]. This configuration is the most interesting because of its higher active surface area per unit volume compared with flat membranes.…”

“…To improve membrane properties, different particles have been used. The focus for this study was the zeolite nanoparticle [7,13]. However, the main issues in matrix membrane production are particle spatial distribution (agglomeration) [6], as well as possible interfacial rigidification and pore blockage [37].…”