Thermoplastic precursor

FIGURE 2.18 Preparation process of activated carbon from thermosetting and thermoplastic precursors. 

The synthesis of boron nitride (BN) fiber has been attempted. The thermoplastic precursor for BN fiber was obtained by the reaction between B-tris(methy-lamino)borazine and lauric amine [28,29],... 

PVA, another thermoplastic precursor, allows the preparation of CNFs through thermal treatment processes [132], Unlike thermoplastic precursors, electrospun thermosetting nanofibers can directly undergo carbonization for preparing CNFs without the need of the costly stabilization process. Therefore, they have gained increasing attention in recent years. For example, electrospun Pl-based CNFs were prepared by Kim et al. The electrical conductivity of the CNFs carbonized at 1000 °C was measured to be 2.5 S cm, higherthan that (1.96 S cm ) of PAN-based CNFs treated at the same carbonization temperature [90]. PBI and PXTC are other precursors for CNF preparation [41]. 

Morishita, T., R. Suzuki, T. Nishikawa, T. Tsumura, and M. Inagaki, Preparation of porons carbons by carbonization of the mixture of thermoplastic precursors with MgO. TANSO 2005 [No. 219] (2005) 226-231 [in Japanese]. 

STABILIZATION TREATMENT OF THERMOPLASTIC PRECURSOR FIBERS FOR CARBON FIBERS... 

The stabilization treatment of thermoplastic precursor fibers for carbon fibers is usually a heat treatment process performed in an oxidizing atmosphere above 470K. For stabilization treatment of PAN fibers, 600K is the highest temperature up to which cyclizjation, dehydrogenation and oxidation processes prevail. 

Elastomeric or rubber materials result from the wide-mesh crosslinking of amorphous, thermoplastic precursors (natural rubber). These weak chemical bonds between polymer chains result in typical rubbery, highly elastic behavior above the glass transition temperature [2]. 

Morishita T, Soneda Y, Tsumura T, Inagaki M (2006) Preparation of porous carbons from thermoplastic precursors and their performance for electric double layer capacitors. Carbon... 

Glass fibres dominate this field either as long continuous fibres (several centimetres long), which are hand-laid with the thermoset precursors, e.g., phenolics, epoxy, polyester, styrenics, and finally cured (often called fibre glass reinforcement plastic or polymer (FRP)). With thermoplastic polymers, e.g., PP, short fibres (less than 1 mm) are used. During processing with an extruder, these short fibres orient in the extrusion/draw direction giving anisotropic behaviour (properties perpendicular to the fibre direction are weaker). 

If a large number of branches exist that connect all of the backbone molecules into a three-dimensional network, the material will not flow when heated, and it is considered a thermoset resin. Vulcanized rubber is an example where the sulfur linkages create a three-dimensional network, converting the precursor rubber into a solid thermoset material. Crosslinked backbone chains are shown in Fig. 2.8(e). When extruding many thermoplastics, the polymer can undergo chemical reactions to form small amounts of crosslinked material. Partial crosslinking is a problem with some PE resins that contain residual double bonds that are made using... 

Alkenes and carbon monoxide are currently copolymerised in the presence of homogeneous Pd catalysts to give thermoplastic materials vith a perfectly alternating structure (Scheme 7.1a) [1, 2]. The non-perfect alternation of monomers (Scheme 7.1b) has been uniquely observed for ethene/CO copolymerisation reactions catalysed by Pd precursors vith anionic P-O ligands [3]. H NMR... 

Recently, a new concept in the preparation of TPVs has been introduced, based on the reaction-induced phase separation (RIPS) of miscible blends of a semicrystalline thermoplastic in combination with an elastomer, with the potential for obtaining submicrometer rubber dispersions. This RIPS can be applied to a variety of miscible blends, in which the elastomer precursor phase was selectively crosslinked to induce phase separation. Plausible schematic representation of the morphological evolution of dynamic vulcanization of immiscible and miscible blends is shown in Fig. 9. For immiscible blends, dynamic vulcanization leads to a decrease in the size... 

To ensure sufficient contact between the fibers and the matrix, it is desirable to use a liquid precursor with a low viscosity. Reactive liquids are usually preferred over thermoplastics due to the low viscosity of liquids relative to polymer melts. The reactive liquid is typically a multi-component mixture. The reactive liquid may contain a monomer and an activator, which will cause the monomer to polymerize into a solid polymer matrix. 

Thermoset precursors are frequently formulated by adding other components than monomers these components, which are generically called modifiers, include small molecules, oils, low- or high-molar mass rubbers or thermoplastics, etc. Depending on the required applications and desired properties, the amount of modifier may vary in a broad range, from about 2 to 50 wt% of the total mixture with monomers. 

The precursors of thermosetting polymers are usually one of the ingredients of complex formulations. They may be present in very small amounts, as in the manufacture of abrasive disks where the thermoset acts as an aggluti-nant in medium amounts, as in the case of filler-reinforced thermosets or as the only components, in formulations used for encapsulation purposes. Apart from fillers, fibers, pigments, etc., some formulations contain rubber or thermoplastic modifiers that phase-separate upon the polymerization reaction (cure). 

The interesting molecular mass range for technical applications lies between a Mr value of 200,000 to 400,000 for the thermoplastic polyvinyl plastics and between 15,000 and 25,000 for the polyamides. For polyesters which are used as precursors for hardened crosslinked plastics, the optimum molecular mass lies around 2000 to 4000. 

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