Para-aramid fibre

L G P Dalmolen, J Willing, A Goksoyr and P Osen, Para-aramid fibre-reinforced composite bellmouths for a floating production platform . Conference on Structural Materials in Marine Environments, London, loM/MTD/IMechE/ IMarE, 11-12 May 1994, pp 109-118. 

A copolymeric derivative of the para-aramid fibres was introduced by Teijin in 1985 under the tradename Technora . This fibre is based on the copolymeric structure copoly-(paraphenylene/3,4 -oxydiphenylene terephthalamide) and is claimed to have a much higher chemical resistance than PPTA as well as increased abrasion and steam resistance, which are useful properties in many protective applications. Technora has a decomposition temperature of about 500 °C, and other properties are comparable with PPTA although its LOI value is slightly lower at 25 vol%. 

Kevlar 29 is included as the typical para-aramid fibre used in tyres. ... 

An early view of fracture of para-aramid fibres was given by Yang (1993, p. 97), who refers to three basic forms. The caption to his fig. 3.28 describes fracture morphology of Kevlar aramid fibre in tensile breaks as Type (a), pointed break type (b) fibrillated break type (c) kink-band break. The kink-band breaks, which extend over a length approximately equal to a fibre diameter can be attributed to fibres that have been weakened by axial compression and will be discussed in a later section. 

Research has been reported on Kevlar para-aramid fibres, which possess three times the tracking resistance of glass reinforced plastic flame retardant compounds [49]. 

Para-Aramid Fibres (provide low lammability, low GTE, low de, insulation) ... 

Although the uses of ceramic fibres in composite structures lie mainly in ceramic-matrix and metal-matrix composites, where their outstanding chemical and thermal resistance are important, there are a few applications in organic polymers. Their relevant properties are low thermal expansion, low electrical conductivity, low dielectric constant, high stiffness, good compressive strength, and in most cases complete resistance to combustion. On the other hand they are very brittle, hard to process, and mostly considerably more expensive than carbon and para-aramid fibres. They have, for example, been used in hybrid structures with carbon and para-aramid and in electronic circuit boards. The fibres available or potentially available include alumina, combinations of alumina with... 

There are two types of aramid (fully aromatic polyamide) fibre those with high thermal stability and flame resistant properties but mechanical properties similar to those of standard textile fibres such as polyester, sometimes referred to as meta-aramid fibres because the main commercial products are of this chemical structure the others with additionally exceptionally high tensile strength and modulus, sometimes referred to as para-aramid fibres on similar grounds. The former type is not widely used in composite structures, but some of the most important uses of the latter lie in this area. 

Para-aramid fibres inherently have relatively poor surface adhesion properties unless pre-treated, but are available from the producers with enhanced adhesive properties. A particularly important feature of their mechanical behaviour is that beyond a certain flexural couple they undergo failure by fibrillation on the strained outer side and by a crushing mechanism, involving formation of kink bands in the structure, on the compressed inner side. This behaviour does not result in rupture, as observed with a brittle fibre, and therefore permits retention of some mechanical strength in the reinforcing material. 

We have developed different nonwoven stmctures with para-aramid fibres, and produced thick 3D stmctures by associating several nonwoven monolayers with a consolidation treatment. Porous composites were afterwards manufactured by impregnating the fibrous stmctures with an epoxy resin. Both dry and impregnated materials were characterized in terms of stmcture (density, fibre volume fraction), and compression tests were used to evaluate mechanical properties. Equivalent pore size and distance between fibre contacts were determined using theoretical models. They help to provide some insight on the mechanical behaviour of the different stmctures. 

In comparison with the simple case of para-aramid fibres, formulation of the structure-modulus relationships for semicrystalline fibres is much more complex. This is due to the segregation of crystalline and noncrystalline regions and to chain folding. The usual approach is based on recasting the structural models into mechanical models proposed by Takayanagi et as shown in... 

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