Kevlar® Surfaces

Keller, T.S., Hoffmann. A.S., Ratner, B.D., McElroy, B.J. (1981). Chemical modification of Kevlar surfaces for improved adhesion to epoxy resin matrices I. Surface characterization. In Proc. Intern. Symp. Polymer Surfaces. Voi. 2 (K.L. Mittal ed ). Plenum Press, New York, pp. 861-879. 

McElroy, "Chemical Modification of Kevlar Surfaces for Improved Adhesion to Epoxy Resin Matrices I. Surface Characterization," p. 861 in Ref. 16. 

Modifications to Kevlar surfaces produced by plasmas were studied by electron spin resonance, and infrared spectroscopy in the FMIR-mode. The former involved a JEOL-JES-ME X-band spectrometer, the latter a Perkin-Elmer 467 spectrometer equipped with a KRS-5 crystal. A Cambridge stereoscan electron microscope was used for surface analyses, and water uptake properties of Kevlar cloth were measured on a Cahn RG electrobalance. Infrared and water uptake data are discussed here the additional analyses have been discussed in an earlier publication (8). 

We conclude therefore that the major effects of Type IV plasmas on laminate bond strength reported in Table I, are strongly correlated with the formation of plasma-pol3nners at the Kevlar surface. A more or less effective coupling effect is due to these polymers, presumably depending on their chemical composition and on their interaction with the wetting resin. 

Fig. 11. Chemical treatment of Kevlar to increase hydrophilictty and bondability to epoxy resin matrices. Treatment with either strong base or strong acid causes chain scission at the surface. From ref. [57].

Fluoroelastomers Novikova et al. [32] reported unproved physico-mechanical properties of fluoro mbbers by reinforcement with chopped polyamide fibers. Other fiber reinforcements are covered by Grinblat et al. [33]. Watson and Francis [34] described the use of aramid (Kevlar) as short fiber reinforcement for vulcanized fluoroelastomer along with polychloroprene mbber and a co-polyester TPE in terms of improvement in the wear properties of the composites. Rubber diaphragms, made up of fluorosilicone mbbers, can be reinforced using aramid fiber in order to impart better mechanical properties to the composite, though surface modification of the fiber is needed to improve the adhesion between fluorosUicone mbber and the fiber [35]. Bhattacharya et al. [36] studied the crack growth resistance of fluoroelastomer vulcanizates filled with Kevlar fiber. 

The photodegradation of para-aramid in an 0 atmosphere allows the differentiation between the accelerated experimental photooxidative conditions from its usual daylight exposure effects. This study illustrated an estimation of the rates of photooxidation of a commercial para-aramid product (i.e., DuPont s Kevlar-29 woven fabric) based on the oxygen-18-labelled carbon dioxide ( CC and CC ) decarboxylated from the sample. The oxygen-18-labelled atoms, which are inserted in the macromolecules, were analyzed for the photodegradation processes. This technique also allows the radial l O-distribution measurement from the fiber surface toward the fiber center. 

Fabric Cleaning. The Kevlar-29 woven fabric was obtained through the courtesy of Naval Weapons Center. A special pair of serrated shears was purchased from Technology Associates for cutting the fabric. The fabric (2.5 cm x 18 cm) was placed in a Soxhlet thimble and extracted by 100 ml of chloroform for 24 hours to remove its surface lubricants (about 3% by weight). The fabric was then removed from the thimble and agitated in a 20 ml of hot distilled DMAc for 15 minutes, before it was placed back into the thimble and extracted for another 8 hours using fresh chloroform solvent. The solvent-cleaned fabric was dried in a vacuo at room temperature. 

This new and novel method to study the photochemical degradation of Kevlar-29 fabric in air divides into four steps (1) fabric cleaning, (2) photolysis at specified temperature and time in 0.2 atm - 02, (3) preparation of the degraded (DMAc-soluble) sample surface for decarboxylation at 25° and 196°C in the concentrated sulfuric acid, and (4) the total carbon dioxide analyses by gas chromatography and the isotopic carbon dioxide ( °C02 and 48co2) ratios by GC-mass spectrometer. 

This new analytical method determines the rate constant and activation energy of Kevlar s photooxidative processes. The 0.2 atm of oxygen-18-labelled environment in a solar chamber simulates the air-exposure under sunlight conditions. The technique also allows the radial 0-distribution measurement from the fiber surface toward the fiber center. The data from the accelerated experimental conditions in the solar chamber in an 02-atmosphere are differentiated from the usual daylight exposure effects. 

Data are deduced from pseudo first order decarboxylations at 196°C for 20 m1n from the top surface layer of the photolyzed Kevlar ... 

Penn, L.S., Tesoro, G.C. and Zhou, H.X. (1988). Some effects of surface-controlled reaction of Kevlar 29 on the interface in epoxy composites. Polym. Composites 9, 184-191. 

Inagaki, N., Tasaka, S. and Kawai, H. (1992). Surface modification of Kevlar 49 fiber by a combination of plasma treatment and coupling agent treatment for silicon rubber composite. J. Adhesion Sci. Technol. 6, 279-291. 

Wang, Q., Kaliaguine, S. and Ait-kadi, A. (1992b). Polyethylene-plasma treated Kevlar fiber composites analysis of the fiber surface, J. Appl. Polym. Sci. 48, 121-136. 

Penn L.S., Bystry F A. and Marchionni H.3. (1983). Relation of interfacial adhesion in Kevlar/epoxy systems to surface characterisation and composite performance. Polym. Composites 4, 26. 

Recently, Caster et al. described the surface modification of multifilament fibers such as nylon or Kevlar [70]. Coating techniques using preformed ROMP-based polymers and process contact metathesis polymerization (CMP), initially described by Grubbs et al. [71], were both used. The latter involves a procedure where the initiator is physisorbed onto the surface of a substrate and fed with a ROMP-active monomer that finally encapsulates the substrate. These modified fibers showed improved adhesion to natural rubber elastomers. 

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