Composites conductive reinforcements

Keywords poly(vinyl) alcohol, carbon nanotubes, composite, processing, reinforcement, conductivity. 

Conductive reinforcements in thermoplastics are a new application of composites [2891. High temperature resistant thermoplastics, such as PPS, PEI, PPO and liquid crystal polyesters, have been combined with conductive fibers, generally chopped graphite and nickel coated graphite. Fiber distribution, orientation and fracture morphology were determined by optical and SEM techniques. Poor bonding in the nickel coated graphite composite, as observed in SEM tensile fractures, resulted in lowered tensile and impact properties. 

N/inm. Composites reinforced with lyocell 6.7 and lyocell 15.0 multilayer webs reached values of 36 N/mm and 28 N/mm respectively. For the needle felt reinforced composites clear reinforcement effects were determined (lyocell 1.3-PLA = 63 N/ mm, lyocell 6.7-PLA = 61 N/mm and lyocell 15.0-PLA = 57 N/mm ). These results lead to the assumption that the kind of the semi-finished product has a clear influence on the mechanical characteristics of the composites produced by the compression molding technique CP-1. This effect could be attributed to a more homogeneous fiber distribution in the PLA matrix due to the additional needling process and the lower thickness of the needle felts compared to the multilayer webs. It is assumed that the lower thickness lead already in the pre-heating phase to a better heat conductivity and drying in the press. 

Tekce H. Serkan, Kumlutas Dilek, and Tavman Ismail Hakki. Effect of particle shape on thermal conductivity of copper reinforced polymer composites. J. Reinforced Plast. Compos. 26 no. 1 (2007) 113—121. 

The reinforcement of polymers with particles of higher radius leads to a decrease in constriction resistance. If the protrusions that form the contacts are assumed to be larger in radius with increasing particle size, larger filler particles should result in a higher composite conductivity (McLeod et al. 1984 Ruschau et al. 1992). 

The experimental values indicate a significant shift towards more positive values of potential in those primers with decreasing amoimts of conducting reinforcement fibers in their composition (2.0,1.5 and 1.0% w/w ratio, in that order). 

In the case of primers, which have got incorporated conductive reinforcing fibers, results allow concluding that it is possible to reduce appreciably the PVC without affecting significantly the efficiency in service. In addition, it is important to mention that the quoted diminution of zinc content in the film is direct proportional to decrease the primer cost since it is the most expensive component of the composition. 

In aerospace appHcations, low density coupled with other desirable features, such as tailored thermal expansion and conductivity, high stiffness and strength, etc, ate the main drivers. Performance rather than cost is an important item. Inasmuch as continuous fiber-reinforced MMCs deUver superior performance to particle-reinforced composites, the former are ftequendy used in aerospace appHcations. In nonaerospace appHcations, cost and performance are important, ie, an optimum combination of these items is requited. It is thus understandable that particle-reinforced MMCs are increa singly finding appHcations in nonaerospace appHcations. 

Cross-linked polyester composites have a relatively low coefficient of thermal conductivity that can provide beneficial property retention in thick laminates at high temperatures as well as remove the need for secondary insulation. The coefficient of thermal expansion of glass-reinforced composites is similar to aluminum but higher than most common metals. 

Carbon Blacks. The high electrical conductivity of carbon black is utili2ed where its color is not objectionable and its reinforcing action is used (see Fillers Composites). Carbon black increases the electrical conductance of the polymer to which it is added, and therefore its effectiveness does not depend on moisture absorption (see Carbon, carbon black). 

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. 

Applied Sciences, Inc. has, in the past few years, used the fixed catalyst fiber to fabricate and analyze VGCF-reinforced composites which could be candidate materials for thermal management substrates in high density, high power electronic devices and space power system radiator fins and high performance applications such as plasma facing components in experimental nuclear fusion reactors. These composites include carbon/carbon (CC) composites, polymer matrix composites, and metal matrix composites (MMC). Measurements have been made of thermal conductivity, coefficient of thermal expansion (CTE), tensile strength, and tensile modulus. Representative results are described below. 

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