Cross-linked PAN

Scheme 2.—Formation of Cross-linked PAN Gels Containing Immobilized Enzymes.

PERVAP 2200 Sulzer Chemtech PVA cross-linked/PAN support Hydrophilic... 

PERVAP 2201 Sulzer Chemtech PVA highly cross-linked/PAN Hydrophilic... 

PERVAP 1060 Sulzer Chemtech" PDMS cross-linked/PAN support Hydrophobic... 

Preparation of cross-linked PAN supports has been reported in the literature by Peinemann et al. (2001), when an epoxidized PAN copolymer was subjected to ammono-lysis providing highly solvent stable [including stability in dimethylformamide (DMF)] supports. A highly solvent-resistant UF membrane based on poly(acrylonitrile-co-glycidyl methacrylate) (PANGMA) was reported (Hicke et al., 2002). This membrane was prepared by phase inversion followed by ammonolysis and was also stable in DMF, thus being a very attractive support for preparation of OSN-TFC membranes. 

Further improvements in the properties of PAN-based carbon fibers are likely to emerge through improved stabilization, that is, by creating the ideally cross-linked fiber. On the other hand, as purer pitch precursors become available, further improvements in mesophase pitch-based carbon fibers are likely to arise from optimized spinnerette designs and enhanced understanding of the relationship between pitch chemistry and its flow/orientation behavior. Of course, the development of new precursors offers the potential to form carbon fibers with a balance of properties ideal for a given application. 

PBDEs are used in different resins, polymers, and substrates at levels ranging from 5 to 30% by weight (EU 2001). Plastic materials that utilize PBDEs as flame retardants include ABS polyacrylonitrile (PAN) polyamide(PA) polybutylene terephthalate (PBT) polyethylene (PE) cross-linked polyethylene (XPE) polyethylene terephthalate (PET) polypropylene (PP) polystyrene (PS) high-impact polystyrene (HIPS) polyvinyl chloride (PVC) polyurethane (PUR) and unsaturated polyester (UPE). These polymers and examples of their final products are summarized inTable 5-2 (Hardy 2002 WHO 1994a). 

ABS = Acrylonitrile Butadene Styrene PA = Polyamide PAN = Polyacrylonitrile PBT = Polybbutylene Terephthalate PE= Polyethylene PET = Polyethylene Terephthalate PP = Polypropylene PUR = Polyirethane PVC = Polyvinyl chloride UPE = Un saturated polyester XPE = Cross-linked polyethylene ... 

Among the various materials are crosslinked PAN, polyphosphazenes, polyphe-nylenesulfide, polyetheretherketone, and various polymer blends [28-31]. Particularly interesting is the use of zeolites as filler in organic polymers, which aims at improving the performance of (silicone-based) membranes for separations in nonpolar solvents, by adding more cross-links to the membrane material [32, 33]. 

Polyacrylonitrile (PAN) is the most common precursor used to make carbon fibers. A flow diagram showing the steps involved in making PAN-based carbon fiber is shown in Fig. 8.3. The PAN precursor has a flexible polymer chain structure like any other polymer, but it has an all carbon backbone chain that contains polar nitrile groups, as shown in Fig. 8.4. During the stabilization treatment, the PAN precursor fiber is heated to 200-220 C, under tension. When this is done oxygen is absorbed, and it serves to cross-link the chains the fibers turn black, and a stable ladder structure is formed. A ladder polymer is a rigid... 

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