Polyamide polysulfone blends

Commercial membranes for CO2 removal are polymer based, and the materials of choice are cellulose acetate, polyimides, polyamides, polysulfone, polycarbonates, and polyeth-erimide [12]. The most tested and used material is cellulose acetate, although polyimide has also some potential in certain CO2 removal applications. The properties of polyimides and other polymers can be modified to enhance the performance of the membrane. For instance, polyimide membranes were initially used for hydrogen recovery, but they were then modified for CO2 removal [13]. Cellulose acetate membranes were initially developed for reverse osmosis [14], and now they are the most popular CO2 removal membrane. To overcome state-of-the-art membranes for CO2 separation, new polymers, copolymers, block copolymers, blends and nanocomposites (mixed matrix membranes) have been developed [15-22]. However, many of them have failed during application because of different reasons (expensive materials, weak mechanical and chemical stability, etc.). 

Flat-sheet asymmetric-skinned membranes made from synthetic polymers (also copolymers and blends), track-etched polymer membranes, inorganic membranes with inorganic porous supports and inorganic colloids such as Zr02 or alumina with appropriate binders, and melt-spun thermal inversion membranes (e.g., hollow-fiber membranes) are in current use. The great majority of analytically important UF membranes belong to the first type. They are usually made of polycarbonate, cellulose (esters), polyamide, polysulfone, poly(ethylene terephtha-late), etc. 

Most MF, UF, RO, and NF membranes are synthetic organic polymers. NF membranes are made from cellulose acetate blends, cellulose triacetate (CTA), or polyamide composites such as the RO membranes, or they could be modified forms of UF membranes such as sulfonated polysulfone [27]. On the other hand, poly(vinyl alcohol) (PVA) is a significant polymer for nonaqueous applications. Chemical stmctures of a few of the prominent polymers are shown in Figure 42.4. 

As of 1995, more than 30 different polymer blends were being used in the manufacture of membranes for hemodialysis and hemofiltration (Klinkmann and Vienken, 1995). The various membrane types used for renal replacement therapy can be divided into membranes derived from cellulose (83 percent of 1991 worldwide total) and from synthetic materials (the remaining 17 percent) (Klinkmann and Vienken, 1995). Synthetic membranes have been constructed from such materials as polyacrylonitrile (PAN), polysulfone, polyamide, polymethylmethacrylate, polycarbonate, and ethyl-vinylalchohol copolymer (Klinkmann and Vienken, 1995). In the United States, use of cellulosic materials for membrane construction predominates at around 95 percent of the total number of membranes used (Klinkmann and Vienken, 1995). 

Another polymer that has been investigated in several miscible polymer blends is polysulfone (PSF). Blends made from polyamide 11 (PAll) and sulfonated polysulfone (SPSF) were prepared by solution casting from dimethyl formamide (DMF) (Deimede et al. 2000b). In that work, differential scanning calorimetry (DSC) showed a melting point depression of the equilibrium melting point of the PAll. With lower degrees of sulfonation, less interaction between the two polymers was observed. FT-IR and FT-Raman spectroscopic techniques were used to confirm the nature of the specific interactions involved. 

M. Weber, W. Heckmann, Compatibilization of polysulfone/polyamide-blends by reactive polysulfones-evidence for copolymer formation, Polymer BuUetin 40 (2-3) (1998) 227-234. 

Addition of p-cresol formaldehyde (PCF) into phenolic/NBR blends resulted in rednction in the domain size of the dispersed phase and improvement in mechanical properties [244]. PCF resin has an intermediate polarity compared with NBR and resole and can react faster with NBR. Therefore, PCF molecules are likely to be concentrated at the phenolic/NBR interface and act as an external compatibilising agents [245]. Thus compatibility and chemical bonding between NBR and phenolic resin is improved, leading to the enhancement in properties. The other materials used as toughening agents of phenolic resin include elastomers such as natural rubber and nitrile rubber [246, 247], reactive liquid polymers [248] and thermoplastics such as polysulfone, polyamide, polyethylene oxide [249, 250]. 

The highly intractable chemical stmcture vMch. inq)arts the outstanding mechanical properties also makes the PATs very difficult to process (4, 5). In the ftilly imidized form PAI is not processable hence a poly(amic acid) (PAA) precursor is the usual form in which they are supplied and bricated. The precursors themselves have very hi viscosities in the melt state and hence the flow characteristics tend to be very poor. Semicrystalline and amorphous polyamides (6) and aromatic sulfone polymers such as poly(phenylene sulfide), poly(ether sulfone) and polysulfone (7) have been blended with the precursor to PAI, to obtain better flow characteristics. 

During the last 40 years, ABS blends with most polymers have been patented. For example, wdth PVC in 1951, PC (introduced in 1958) in 1960, polyamide (PA-6) a year later [Grabowski, 1961a], polysulfone (PSF) in 1964, CPE in 1965, PET in 1968, polyarylether sulfone (PAES) and styrene-maleic anhydride (SMA) in 1969 (the blend is one of two resins called high heat ABS — the other being ABS in which at least a part of styrene was replaced with p-methylstyrene), polyethersulfone (PES) in 1970, polyarylates (PAr) in 1971, polyurethane in 1976, polyarylether (PPE or PAE) in 1982, with polyphenylene sulfide (PPS) in 1991, etc. 

Group 1, Polysulfone-family Mmibers Polysulfone (PSu, Fresenius Medical Care, Germany), Polyethersulfone (PES, Membrana, Nipro Medical Corporation, J an), Polyester polymer alloy (PEPA, Nikkiso, Japan), Blends from Polyamide/Polysidfone (PA/PSu, Gambro, Sweden), as well as blends made of PES/PVP. Recent research on membranes with antioxidant features have led to the production of a polysulfone membrane with immobilized Vitamin E (PSuAfit E, ASAHI, Japan). 

HoUow fibers are widely used for filtration, utilizing the semipermeable nature of their capillary walls. In the medical industry, hollow fiber bioreactors are often made from cellulose and synthetic polymers. Cellulose acetate and cuprammonium rayon are the widely used ceUulose-based hollow fibers, while synthetic hollow fibers are often made from polysulfone, polyamide, and polyacrylonitrile. Modifications can be made to these materials to improve their functions by using polymers based on phospholipid, a substance found in the human cell membrane. 2-methaCTyloyloxyethyl phosphoryl-choline (MPC) is a methacrylate monomer with a phospholipid polar group. When MPC-based copolymers are used as additives for polysulfone, protein adsorption and platelet adhesion can be effectively reduced, thereby improving blood compatibility. Cellulose acetate hollow fiber membranes can also be modified with MPC-based copolymers by means of blending or surface coating to obtain improved permeability. 

Ibuki J, Charoensirisomboon P, Chiba T, Ougizawa T, Inouea T, Weberb M, et al. Reactive blending of polysulfone with polyamide a potential for solvent-free preparation of the block copolymer. Polymer 1999 40 647-53. 

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