Polyacrylonitrile thermal properties

Janowska G, Mikolajczyk T, Bogun M (2007) Effect of the type of nanoaddition on the thermal properties of polyacrylonitrile fibres. J Therm Anal Calorim 89 613-618... 

So far, most polymer nanocomposites contain only one type of nanofiller. Recent studies revealed that combination of clay and Si02 has a more enhanced effect on the polymer matrix. In this chapter, we discuss the structure and properties of clay- and silica-based polymer nanocomposites prepared by in situ emulsion polymerization, especially polyacrylonitrile (PAN)-clay-silica ternary nanocomposites. The chapter consists of three parts (1) synthesis and structure of polymer-clay-silica nanocomposites (2) thermal properties of polymer-clay-silica nanocomposites and (3) mechanical properties of polymer-clay-silica nanocomposites. 

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. 

The ruthenium(II) polypyridyl complexes are also popular but the brightnesses do not exceed 15,000 and thermal quenching is rather significant. This property can be utilized to design temperature-sensitive probes providing that the dyes are effectively shielded from oxygen (e.g., in polyacrylonitrile beads). Despite often very high emission quantum yields the visible absorption of cyclometallated complexes of iridium(III) and platinum(II) is usually poor (e < 10,000 M-1cm-1), thus,... 

The details of so-called Black Orion production have been given in many papers. Also, the properties of carbonized polyacrylonitrile are well known because of which it is in demand especially as a component of composites, mainly because of its strength and high thermal resistance. 

Thermal treatment of polyacrylonitrile at 200-300 °C leads to the appearance of conjugated bonds and electronic semiconductor properties. The main photoconductivity maximum is situated at 420 nm. An increase of the temperature treatment shifts the photosensitivity to the long wavelengths. The estimated mobilities were from 10" 7 to 104m2 V"1 s"1. The main results obtained proved the sufficiency of the conjugated bonds for the appearance of the semiconductive properties. 

Membrane permeation properties are largely governed by the pore sizes and the pore size distributions of UF membranes. Rather, thermal, chemical, mechanical, and biological stability are considered of greater importance. Typical UF membrane materials are polysulfone (PS), poly(ether sulfone), poly(ether ether ketone) (PEEK), cellulose acetate and other cellulose esters, polyacrylonitrile (PAN), poly(vinyKdene fluoride) (PVDF), polyimide (PI), poly(etherimide) (PEI), and aliphatic polyamide (PA). All these polymers have a Tg higher than 145 °C except for celliflose esters. They are also stable chemically and mechanically, and their biodegradabflity is low. The membranes are made by the dry-wet phase inversion technique. 

Composite conductive fibers based on poly(3,4-ethylene-diox)d hiophene]-polystyrene sulfonic acid (PEDOT-PSS) solution blended with polyacrylonitrile (PAN] were obtained via wet spinning. The influence of draw ratio on the morphology, structure, thermal degradation, electrical conductivity, and mechanical properties of the resulting fibers was investigated. The results revealed that the PEDOT-PSS/PAN composite conductive fibers crystallization, electrical conductivity and mechanical properties were improved with the increase of draw ratio. The thermal stability of the fibers was almost independent of draw ratio, and only decreased slightty with draw ratio. Besides, when the draw ratio was 6, the conductivity of the PEDOT-PSS/PAN fibers was 5.0 S cm, ten times the conductivity when the draw ratio was 2 (Fig 5.10]. ... 

Polyacrylonitrile is most commonly used in fiber form. Since it softens only slightly below its thermal degradation temperature, it must be processed by wet or dry spinning rather than melt spinning. Some typical properties are Glass Transition Temperature, Tg = 85 C Melting Temperature, Tm = 317 C Amorphous density at 25 C = 1.184 g/cc Molecular weight of repeat unit = 53.06 g/mole. 

Carbon fibers are made from many different feedstocks. The most important commercial fiber is made from polyacrylonitrile (PAN). It is four times stronger than steel, the same modulus or higher, and does not fail in creep or fatigue. These properties made the fiber attractive for aerospace applications initially, and later for sporting and industrial applications. Another important feedstock is pitch from refinery or steel-making operations, which leads to fibers with very high modulus and thermal and electrical conductivities. Properties of the fibers, and critical steps in their manufacture are described, together with structural characteristics and failure mechanisms. 

The majority of commercial carbon fibers are produced from polyacrylonitrile (PAN) fibers. In fact, HTA-12K PAN-based carbon fibers are the most commonly used commercial carbon fiber (15). PAN-based fibers are the strongest commercially available carbon fibers and dominate structural applications. Mesophase pitch-based carbon fibers represent a smaller but significant market niche. These fibers develop exceptional moduli and excel in lattice-based properties, including stiffness and thermal conductivity (1). Rayon-based fibers are used in heat shielding and in missile nosecones (16). Carbon fibers made from high performance pol5oners (17-19) or from chemical vapor deposition of hydrocarbons, such as benzene or methane, display imique properties that make them potentially attractive futime alternatives (20-22). 

DWI s manufacturing process relies on standard wet-laid processing. The materials are blended uniformly, and then fed into a headbox at very high dilution. The water is removed, and the web is dried. The materials are polymers selected for the application. In Titanium, the combination is chosen for alkaline resistance as well as high porosity. In Silver, polyacrylonitrile nanohbers are blended with cellulose to achieve maximum cycle life, rate capability, and minimum pore size, which also achieve advanced flame-resistant properties. In Gold, the backbone is para-aramid Twaron, which gives superior thermal stability. 

Although elimination reactions are clearly degradation, leading to color and char formation, they can have advantages. Conjugated sequences and ladder structures confer thermal stability on the polymers, forming stable chars. This is the basis of the preparation of carbon fibers by pyrolysis of polyacrylonitrile. It is also one reason for the use of plasticized PVC in electrical insulation in a fire, the char acts as a protective coating and maintains the electrical insulation properties of the cable. 

For a wide range of apphcations, composites reinforced with continuous fibers are the most efficient structural materials at low to moderate temperatures. Consequently, we focus on them. Table 5.3 presents room-temperature mechanical properties of unidirectional polymer matrix composites reinforced with key fibers E-glass, aramid, boron, standard modulus (SM) PAN (polyacrylonitrile) carbon, intermediate modulus (IM) PAN carbon, ultrahigh modulus (UHM) PAN carbon, ultrahigh modulus (UHM) pitch carbon, and ul-trahigh thermal conductivity (UHK) pitch carbon. The fiber volume fraction is 60 percent, a typical value. 

Fiber reinforcement is an established means of improving the mechanical properties of a variety of matrices. Sarvaranta, et al., l studied by TG/DSC the thermal behavior of polypropylene and two types of polyacrylonitrile fibers. A DSC examination revealed that the... 

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