High modulus fibres

The two main processes for making carbon fibres are based on different starting materials, either polyacrylonitrile (PAN carbon fibres) or petroleum and coal tar 

Carbon reinforced cement composites can be produced in a number of ways  

The diameter of the filaments ( 10 /tm) is of the same order of magnitude as the size of a cement particle. For the cement particles to be able to penetrate between the individual filaments, that is, if the spacing between the filaments is about the 

The uniform dispersion of short carbon fibres, particularly at higher fibre volumes, is difficult. The most that can be added using conventional mixing methods and materials is about 1% by volume. The dispersion of the fibres into individual filaments is controlled by the mixing technique. The methods used have included  

Curing of carbon fibre composites can be carried out either by normal room temperature curing or by autoclaving. The fibres are sufficiently stable to endure the high pressure and temperature conditions in the autoclave. 

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The former polymer has been available commercially for some years in the form of high-modulus fibres (Kevlar, Arenka) and current work on the latter points towards its possible use as a material exhibiting even higher mechanical performance. 

Fig. 9. Tensile properties of various high-strength, high-modulus fibres...

Zachariades AE and Porter RS (Eds), "Mechanics of High Modulus Fibres", Marcel Dekker, Inc, New York, 1983. Special references... 

Valenti et al. noted a transition to the mesophase under the effect of the applied external field for those semirigid-chain polymers which do not exhibit the liquid crystalline transition under normal conditions. A moderately concentrated solution of polyterephthalamide of p-aminobenzylhydrazide (X-500) in dimethyl sulphoxide does not exhibit the transition into the liquid crystalline state, which can be explained by a relatively low axial ratio for the macromolecules. The persistence length for this polymer is estimated being equal to 50 A. At the same time, according to the data from the literature, high-modulus fibres have been obtained from the solutions of this polymer, which can be connected only with the appearance of the liquid crystalline state in the process of fibre formation. The authors of believe that this... 

Solution processing also plays a vital role in the manufacture of high value, lyotropic high modulus fibres and also high modulus polyethylene fibres. In all these cases the additional cost and complication of solvent recovery is offset by the high value of the produced product. 

Variations on the diamine-diacid chloride theme have provided oth rigid linear aromatic polyamides which are ultra-high modulus fibre formers, structures Il-V being notable examples and numerous comonomers have been described. Polymer II is said only to give good fibre properties if its structure is deliberately disordered slightly by inclusion of small quantities of co-reactants, the effect being attributed to better solubility and consequent improved spinnability. However, this... 

A particularly interesting copolymer type (VII) which deserves special mention because its structure seems slightly at odds with the usual rule for ultra-high modulus fibre formation is a kind of block copolymer in which rigid segments are hinged together by flexible aliphatic diacid units. 

It is claimed that ultra-high modulus fibres can be made from those compositions which fall within a defined area when plotted on a triangular composition diagram for the three types of repeat unit. These workers have, in effect, mixed together various combinations of the bifunctional... 

One of the ultra-high modulus fibre forming polymers, designated H, contains non-aromatic piperazine rings which in principle could be in either of the two interconvertible conformations known as boat and chair . A further complication is introduced by the possibility of cis and... 

ULTRA-HIGH MODULUS FIBRES AVAILABLE IN DEVELOPMENT OR COMMERCIAL QUANTITIES... 

Woven fabrics (Fig. 2.4) are used in various fields. When compared with knitted fabrics, they show only a low degree of elongation in both directions. High-tech textiles for buildtech are mainly produced in combination with high strength and high modulus fibres. There is a demand for the development of lighter materials with optimised functions. 

Carbon fibre properties depend on the structure of the carbon used and are typically defined as standard, intermediate and high modulus fibres. Several fhousand fibres are twisfed fogether to form a yarn which may be used by itself or woven into a fabric. The yarn or fabric is combined with a resin, usually epoxy, and wound or moulded to shape to form a wide variety of products. 

Hearle, J.W.S. and Wong, B.S. (1977) Flexural fatigue and surface abrasion of Kevlar-29 and other high-modulus fibres. J. Mater. Sci., 12 2447-2455. 

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