Gas Plasma Treatment of Kevlar® and Spectra® Fabrics for Advanced Composites - Page 2

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Gas Plasma Equipment

The reactor is a vacuum chamber equipped with vacuum pump, purge plumbing, process gas sources and regulators, a source of electromagnetic energy and a system controller to orchestrate the process.

The equipment operation cycle is carefully monitored and controlled by the electronics package, which operates the valves, pressure/vacuum flow gates and the RF source. In the 4th State system the roll product to be treated (up to 60" width and 19" package diameter) is loaded in the payoff chamber and threaded through the chamber to the take-up reel. The plasma treatment operation is then initiated and entirely controlled by the push of a single button. The process steps are: 1) pump down to predetermined vacuum pressure (base pressure), 2) introduce process gas and allow to stabilize at a desired process pressure, 3) initiation of plasma by providing rf energy, 4) transport product through the system and 5) after treating the desired length, shutting rf power and process gas delivery, 6) pump down to base pressure to eliminate residual process gas(es), 7) vent to atmosphere and 8) remove treated product.

Discussion and Results

Typical composite results for plasma treated and untreated (as received) fabric are presented in Tables I & II. These fibers are as dissimilar as one could ever anticipate in synthetic polymers. Spectra is ostensibly only carbon and hydrogen, an analog of wax but a polymer of extremely high molecular weight and orientation (30:1 draw ratio). Kevlar is a polyaramid with a variety of chemical elements and groups and is primarily aromatic in structure. By the judicious selection of process gas the fiber surface of either fiber is reengineered to make it compatible with and, if desired, reactive to the resin matrix of choice. The improvements in flexural strength and modulus are the result of an increase in interlaminar shear strength which in the case of the Kevlar was measured only for the plasma treated fabric composites.

As is readily seen a plasma treatment provides significant improvements over untreated material, 200 to 300% and more is not uncommon. Since there is a myriad of fabric styles in use, as well as different grades of both Spectra and Kevlar, the above data is presented as representative of typical improvement obtained across a broad matrix of fabric styles and fiber grades. Because the construction of the fabrics are different one should not compare the properties of these different composites, but that similar improvements are realized with all constructions.

Conclusion

The outstanding specific strength and modulus characteristics of advanced fibers can now be more effectively realized in reinforced composites with plasma surface treatment. The plasma treatment process can be readily tailored by the judicious selection of the process gas and process parameters to permit the "reengineering" of the top molecules of the fiber to a specific surface energy, chemical compatibility or reactivity to specific resin matrices. In addition, for fibers such as Kevlar where moisture absorption is known to have deteriorating effects, the plasma process is inherently an effective drying process providing further benefits.

4th State’s plasma system shown has the capability of treating 60" wide products and roll diameters to 19.5". It is available to conduct development trials or toll treatment. Consider your product possibilities by reengineering the reinforcement fiber. 

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Kaplan, S.L., Rose, P.W., Nguyen, H.X. and Chang, H.W., Gas Plasma Treatment of Spectra Fiber, SAMPE Quarterly, Vol. 19, No. 4, July 1988