Unique blend of properties

Because of their unique blend of properties, composites reinforced with high performance carbon fibers find use in many structural applications. However, it is possible to produce carbon fibers with very different properties, depending on the precursor used and processing conditions employed. Commercially, continuous high performance carbon fibers currently are formed from two precursor fibers, polyacrylonitrile (PAN) and mesophase pitch. The PAN-based carbon fiber dominates the ultra-high strength, high temperature fiber market (and represents about 90% of the total carbon fiber production), while the mesophase pitch fibers can achieve stiffnesses and thermal conductivities unsurpassed by any other continuous fiber. This chapter compares the processes, structures, and properties of these two classes of fibers. 

During the last two decades the sol-gel approach has been fiuther developed by material chemists to insert POMs within various inorganic matrices. Many sol-gel/POM composites have been reported [66,67,150-152] however, the number of their applications as liquid-phase oxidation catalysts is still not as large as one might have anticipated based on the advantages that POMs offer in the ease of incorporation into sol-gel matrixes and on then-unique blend of properties. One of possible reasons is the lack of information on the stability of the composite materials with respect to POM leaching in polar media. 

In the thermoplastics area, precipitated calcium carbonate is principally used in PVC applications, a market with which it has been associated since the early days of the polymer. Despite some erosion by coated natural products, the combination of small particle size and fatty acid coating continues to give a unique blend of properties in both unplasticised and plasticised PVC formulations. The advantages include easier processing, better surface finish, good low temperature properties and resistance to crease whitening and to scratching. 

Due to the nature of metallic bonds, it is relatively easy to introduce other elements into the metallic crystal, forming an alloy. An alloy is a mixture of elements that has metallic properties. Because of their unique blend of properties, alloys have a wide range of commercial applications. Stainless steel, brass, and cast iron are a few of the many useful alloys. 

Polyanisidine (PANIS) is a new and novel electrically conductive polymer (1) that is generating much interest due to it s combination of air stability, electrical conductivity, and solubility in organic solvents. This unique blend of properties has been heretofore unavailable in synthetic conductors. PANIS is synthesized by either chemical or electrochemical means. The polymer may exist in four unique states, each a function of the level of oxidation and protonation. Each state is characterized by a unique set of electrical and optical properties, solubility and air stability. The states are easily convertible by simple chemical and electrical means. The most conductive and stable form of PANIS is the oxidized acid form shown in Figure 1. 

Acrylic Resins. The first synthetic polymer denture material, used throughout much of the 20th century, was based on the discovery of vulcanised mbber in 1839. Other polymers explored for denture and other dental uses have included ceUuloid, phenolformaldehyde resins, and vinyl chloride copolymers. Polystyrene, polycarbonates, polyurethanes, and acryHc resins have also been used for dental polymers. Because of the unique combination of properties, eg, aesthetics and ease of fabrication, acryHc resins based on methyl methacrylate and its polymer and/or copolymers have received the most attention since their introduction in 1937. However, deficiencies include excessive polymerization shrinkage and poor abrasion resistance. Polymers used in dental appHcation should have minimal dimensional changes during and subsequent to polymerization exceUent chemical, physical, and color stabiHty processabiHty and biocompatibiHty and the abiHty to blend with contiguous tissues. 

TPEs from thermoplastics-mbber blends are materials having the characteristics of thermoplastics at processing temperature and that of elastomers at service temperature. This unique combination of properties of vulcanized mbber and the easy processability of thermoplastics bridges the gap between conventional elastomers and thermoplastics. Cross-linking of the mbber phase by dynamic vulcanization improves the properties of the TPE. The key factor that controls the properties of TPE is the blend morphology. It is essential that in a continuous plastic phase, the mbber phase should be dispersed uniformly, and the finer the dispersed phase the better are the properties. A number of TPEs from dynamically vulcanized mbber-plastic blends have been developed by Bhowmick and coworkers [98-102]. 

It is most unlikely that a conducting polymer will ever be used as a substitute for copper as an electrical conductor unless its conductivity and mechanical properties can be appropriately increased. However, the unique combination of properties which can be displayed by a conducting polymer or its blends with conventional polymers appear to show great promise for a variety of uses. A remarkable feature of several conducting polymers... 

Improved properties of commingled plastics via blend modification by reactive functionalization and compatibilization have been reported by several workers (58,65). This work is confined to a two-phase PE-PP morphology. In the two-phase immiscible PE-PP system, poor interfacial adhesion results in poor blend mechanical properties. The lack of stability in the morphology causes gross separation or stratification during later processing or use. Block and graft copolymers of the form A-B have been used as compatibilizers to improve interfacial adhesion and reduce interfacial tension between A-rich and B-rich phases to provide A-B alloys with improved and unique balances of properties. 

As seen from the application examples, polyamide-imides possess a unique blend of high-performance properties. An overview of polyamide-imide properties for compounded materials is shown in Table 12.1. 

In comparison to the other commercially available absorbable materials, PCL is one of the most flexible and easy to process. However, PCL has one of the slowest degradation rates of all such materials. This unique blend of characteristics fills a gap in the property spectrum unmatched by any other absorbable material. 

Thermotropic main-chain LCPs have unique combination of properties from both LC and conventional thermoplastic states these include melt processibil-ity, high mechanical properties, low moisture take-up, and excellent thermal and chemical resistance. With the successful development of these LCPs and recognition of their imique properties, comprehensive research and development have been carried out by both academia and industry (3,5,9,11,14,16-26). Among various R D directions, the synthesis of new LCPs (3,14,16,17,19-22,24,26), their rheology behavior (27-31), morphology, compatibility and processing of LCPs and blends (32-34) have received most attention. 

When blended with glass fibres and other fillers, PPS has a unique combination of properties including ... 

Shim et al. recently studied [488] the PL and EL properties of unique blends of poly(2-methoxy-5-(2-ethylhexyloxy)-l, 4-phenylene vinylene] (MEH-PPV) with aklystyryl carbazole group containing poly (methacrylate) (CZ-PMA). These blends showed two isolated PL emissions at 440 and 560 nm corresponding to their component polymers, but only one EL peak, at ca. 580 nm, identical to that of MEH-PPV alone, but with very significantly enhanced intensity. Fig. 12-10 shows some of their data. 

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