Spinnable dope

An important application of polydimethylsilane is as a source of silicon carbide (SiC) fibres, which are manufactured under the trade-name Nicalon by Nippon Carbon in Japan. Heating in an autoclave under pressure converts polydimethylsilane to spinnable polycarbosilane (-Me2Si-CH2-) with elimination of methane. The spun fibres are then subjected to temperatures of 1200-1400 °C to produce silicon carbide fibres with very high tensile strengths and elastic moduli." As a result of their conductivity, polysilanes have also been used as hole transport layers in electroluminescent devices. In addition, the photoconductivity of polymethylphenylsilane doped with Cgo has been found to be particularly impressive. ... 

As Rosenau et al. [49] indicated that paper grade pulp, unbleached chemical pulp, cotton and rayon fiber wastes, or even paper wastes can be used as raw materials for Lyocell fiber production, even though problems with spinnability may be encountered in some cases. In preparation for spinning dope, a 50-60% aqueous NMMO is used with the addition of 0.01 0.10% antioxidant to prevent cellulose degradation. A typical antioxidant is PG [50]. In a typical Lyocell industrial process, the slurry is produced from cellulose pulp and an aqueous NMMO solution. Typical compositions are 50-60% NMMO, 20 30% water, and 10-15% pulp [48]. Subsequently excess water is efficiently evaporated at temperatures lower than 150°C and... 

It is very important to mention that at ambient temperature carbamate groups tend to hydrolyze under alkaline conditions more easily. Therefore, solutions of cellulose carbamate must be chilled off [3]. Struszczyk [82,83] demonstrated that such solutions are stable below 0°C. All commercial processes, namely dissolution of cellulose carbamate and solution storage must be handled at low temperatures to avoid changes in viscosity. Some additives also can be used to control the solution s viscosity and to reduce gelation. The addition of 1-3% zinc oxide to a spinning dope tends to increase the viscosities of these solutions and improves the spinnability [3]. This additive also extends the solution s storage life. 

Blending with a spinnable polymer is a common way to compensate poor spinnability. However, the presence of an insulating carrier polymer introduces a conductivity percolation threshold by limiting their usage in the applications where high conductivities are required. The polymerization of a conductive monomer on the surface of a fiber, made with a common polymer and a catalyser/ doping agent is also another approach. ° ° ... 

The precursor of a similar fiber was prepared by polycondensation of an organoaluminum compound, such as monoisopropoxydiethyl aluminum, dissolved in ethylether [60]. Some isopropoxy groups were presumably replaced by a phenoxy group, such as ethyl 0-hydroxybenzoate, in order to improve the spinnability of the final dope. The polyaluminoxane was dissolved in benzene, the ether was distilled off and ethyl silicate was added. After concentration, the dope was dry spun and the green fibers were aged in a humid atmosphere and calcined. The fibers (Table II) had a glassy appearance and were composed of a nanocrystalline Al-Si spinel phase (or r /y-transition alumina) in an amorphous silica based matrix [33] [53]. After mullitization that starts at 1150 C and is complete after 2 min at 1400 C, the fibers were composed of mullite and corundum [33]. 

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