Ultrafiltration membranes are widely used for separation processes of aqueous solutions in various industries such as food, dairy, beverage, pharmaceutical, textile, electronics, and chemical industries. They are mostly applied for water treatment such as the production of pure water to remove microorganisms, bacteria, virus, colloidal substances, and suspended micro particles from the water [1, 2]. Other application of ultrafiltration membranes is for the concentration of protein or enzyme [3, 4]. Ultrafiltration membranes have usually a porous asymmetric structure with a macroporous cross section and a smooth active layer that is able to reject high molecular weight solutes such as protein, virus, bacteria, etc., whereas water or low molecular weight solutes can permeate through the membrane. The separation using the ultrafiltration membrane is a pressure-driven separation process, which can be simply operated using a pump without the use of heat. Therefore, the use of the ultrafiltration membrane for separation processes has many advantages due to the lower energy consumption and the high selectivity.
Commercial ultrafiltration membranes available in the market are usually made from cellulose acetate, polysulfone, polyethersulfone or polyvinylidene fluoride. Many studies to develop ultrafiltration membranes using other polymer materials such as polyetherimide, polyvinyl chloride, chitosan, and other materials have been reported [5, 6, 7]. Studies on the modification of the membranes to improve the permeate flux and the rejection have also been reported [1, 8, 9]. Recently, our previous study on the use of polyethylene terephthalate (PET) bottles to prepare PET ultrafiltration membranes have been reported . PET packaging is widely used by the food and beverage industries because of its excellent mechanical strength, good chemical resistance, good transparency, and excellent gas-barrier resistance. PET films are also suitable for many other applications due to their excellent mechanical properties [11, 12], and good chemical resistance against acids and low concentration of alkalies . The outstanding mechanical and chemical properties of PET open the opportunity to fabricate ultrafiltration membranes from PET. The source of the polymer material even can be found in used PET bottles or other used PET packaging that are usually considered as waste. In our previous study on the development of ultrafiltration membranes using PET bottle waste, it was observed that the permeate fluxes increased by decreasing the polarity of the non-solvent, by increasing the molecular weight of the additive, or by increasing the additive concentration . However, it was observed that the permeate flux enhancement was followed by a decline of the rejection rate, because of the enlargement of the membrane pore size. The same phenomenon has been also reported in other studies [5, 14]. Ultrafiltration membranes with high permeate fluxes are desired since the ultrafiltration membranes have been known to have a drawback, namely fouling problem, that is the permeate flux decline with the operating time because of the concentration polarization on the surface of the membranes. In order to eliminate fouling, many studies have been done to develop membranes with improved permeate fluxes [1, 7, 8, 9]. However, the increase in the permeate flux is usually followed with the decrease in the rejection of the membranes. Thus, it is very crucial to develop ultrafiltration membranes with improved permeate flux without any decrease in the rejection.
The objective of this work is to develop PET ultrafiltration membranes which exhibit improved permeate fluxes with high rejection values. The membranes were developed using PET bottle waste as the polymer material using polyethylene glycol with molecular weight of 400 Da (PEG 400) as the additive. The aim of the utilization of PET bottle waste is also to give a contribution in the plastic recycling to reduce plastic waste. Since PET bottles are originally produced from PET resin, PET resin was also used in this work as the polymer material to prepare the membranes with the aim to compare the characteristics of the membrane developed from PET bottles and that from PET resin. The effect of the PEG 400 concentration on the microstructure, the hydrophilicity and the porosity of the membranes was studied by using Scanning Electron Microscopy (SEM), water contact angle measurement, and gravimetric method, respectively. The membranes were characterized using Fourier Transform Infrared (FTIR) spectroscopy to study the chemical properties. Furthermore, the membranes were characterized for their ultrafiltration performances through ultrafiltration experiments using pure water and a feed solution containing Bovine Serum Albumin (BSA) molecules (MW: 66,000 Da) as a feed model.