Ultra high modulus fibers

Ultra-high modulus fibers such as aramid and carbon fibers have been currently utilized for composite material fabrication. Ultra-high modulus polyethylene (UHMPE) fiber is also applicable for composite fabrication because of the light weight in addition to its high modulus, vibration damping, and resistance to chemicals. However, this fiber has drawbacks such as poor interfacial adhesion with the polymer matrix of the composite because of highly hydrophobic nature of the fiber surface. 

Society of Plastics Engineers (1975), Polym. Eng. Sci. 15(3), based on the United States-Italy Symposium on Advanced Polymer Mechanics-Composite Materials and Ultra-High-Modulus Fibers, Santa Margharita Ligure, May 27-31, 1974. 

If L > Lo, the polymer may be considered as a rigid rod. Rigid polymers are of importance for the manufacture of ultra-high modulus fibers and therefore have attracted a great deal of attention in recent years. 

Miscibility or compatibility provided by the compatibilizer or TLCP itself can affect the dimensional stability of in situ composites. The feature of ultra-high modulus and low viscosity melt of a nematic liquid crystalline polymer is suitable to induce greater dimensional stability in the composites. For drawn amorphous polymers, if the formed articles are exposed to sufficiently high temperatures, the extended chains are retracted by the entropic driving force of the stretched backbone, similar to the contraction of the stretched rubber network [61,62]. The presence of filler in the extruded articles significantly reduces the total extent of recoil. This can be attributed to the orientation of the fibers in the direction of drawing, which may act as a constraint for a certain amount of polymeric material surrounding them. 

Biro. D.A.. Plcizeicr, G. and Deslandes, Y. (1993a). Application of the microbond technique. HI. Efl ecls of plasma treatment on the ultra-high modulus polyethylene fiber-epoxy interface, J. Mater. Sci. Lett. II, 698-710. 

Amoco has developed a family of ultra high modulus continuous graphite fibers and preforms with axial thermal conductivity to llOOW/mK. The extremely high thermal conductivity is a direct result of an extremely high degree of crystallinity during carbonization of the mesophase pitch precursor fiber. Table... 

Similar reactions to those used in interfacial polymerizations are sometimes carried out in solution and are employed to prepare some polymers which yield ultra-high-strength high modulus fibers. Tliese species typically contain para-linked aromatic rings and amide or ester linkages in the polymer backbone. 

The polyaromatic mesophase (PA-MP) is a nematic, discotic, chemotropic liquid crystal. Owing to its high density (about 1.5 gcm ), its high carbon yield of about 90 %, and its thermoplasticity, it is unique as a precursor of structure carbons. An important application is the manufacture of high modulus (HM) and ultra-high modulus (UHM) carbon fibers [1]. By alloying with silicon, physical and chemical properties of the materials, such as strength, hardness and oxidation resistance, can be improved. These modified carbons were available by chemical vapor deposition (CVD) processes only up to now. The preparation by liquid phase pyrolysis is novel, economic, and thus opens a completely new field of applications. 

With proper resolution of the technical problems, molecular composites should offer significant commercial promise. This will require adapting the technology to the existing commodity or engineering polymers. Polyamides appear to be the best opportunity based on the literature references. However, even commodity polymers such as polyethylene should not be ruled out. An example of this can be found in work reported by Teishev et al. [1993] where ultra high modulus polyethylene fibers were dispersed in a HOPE matrix. 

Other applications of PBI are in drogue parachutes and lines for military aircraft as well as ablative heat shields. The PBI fibers have also shown promise as reverse osmosis membranes and in graphitization to high-strength, high-modulus fibers for use in composites. The development of ultra-fine PBI fibers for use in battery separator and fuel cell applications has been undertaken by Celanese. 

AJ. Pennings and K.E. Meihuizen, Polyethylene fibers with ultra-high modulus and strength... 

Table VI. Ultra-high modulus Si-Al-O-N glass fibers...

CARBON FIBERS TYPE UHM (ULTRA HIGH MODULUS) designates a class of CARBON FIBERS having very high values of Young s modulus, greater than 600 GPa. 

Fukunaga A, Komami T, Ueda S and Nagumo M (1999) Plasma treatment of pitch-based ultra high modulus carbon fibers. Carbon 37 1087-1091. 

Carbon fibers type UHM (ultra-high modulus) have moduli of elasticity in excess of 600 GPa, surpassing 50 of the theoretical C// number. Such high values of Young s modulus can be achieved most readily in MPP-based carbon fibers. 

In most cases, a 1 MPa pull out strength associated with a cohesive failure in the honeycomb or in the composite skins is often considered as acceptable for satellite sandwich parts (see O Fig. 45.20). With such a result, a value of 300-MPa compressive strength associated to a Young s modulus of 150 GPa delivered by the implementation of ultra high modulus carbon fiber is displayed by satellite composite sandwich structural parts designed and experimented. 

As a result, ultra high modulus carbon fibers are preferred to others for their high stiffness/ density ratio for a low CTE compared with titanium or aluminum. Since composites are preferred to metal parts, bonding becomes the mandatory technology for fastening parts, because drilling and the bolt/nut/rivet principle require holes which affect the mechanical properties of the joint due to concentrations of loads around sectioned fibers. 

As moitioned b ie, composites can be prepared electrochemically, typically by polymerizing the monomer on an electrode that had been pretreat with a pol)rmer. This process has beat performed with pyrrole using (with a variety of modifications as well) poly(vinyl alcohol), pol)Kvinyl diloride), polyurethane, and as a graft onto polystyrene functionalized with benzyl chloride side- ains. Pyrrole has been mixed with Kevlar (an ultra high modulus polymer) and chemically polymerized to form a very strong "alloy" fiber of polypyrrole and Kevlar. s... 

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