Sizing and surface treatment: The keys to carbon fiber's future?

摘要

As carbon reinforcements find new applications, unfamiliar processes and resin systems make sizing and treatment surprisingly hot topics. After developing a new how-temperature-cure carbon/epoxy prepreg for a customer recently, Lewcott Corp. (Millbury, Mass., U.S.A.) produced small runs of the prepreg for testing, using 3K and 12K fabric. The customer reported that the cured 12K prepreg performed as expected, but the 3K product would not cure at the desired temperature, says Nick DiMeo, Lewcott director of sales and marketing. A subsequent investigation turned up the culprit: the only difference between the fibers in the two fabrics was the sizing, which in the case of the 3K fabric apparently interfered with the matrix resin's crosslinking. Not surprisingly, Lewcott's weaver could not tell DiMeo exactly how the sizings differed. Surface treatment and sizing, the final two steps in the carbon fiber manufacturing process, are the subject of notable trade secrecy. "These are the subtleties that make one fiber different than another fiber," explains Chris Levan, technical service manager for Cytec Carbon Fibers LLC (Piedmont, S.C., U.S.A.). In fact, sizings and surface treatments play vital roles in composite performance: Surface treatment produces additional bonding sites on the fiber surface, while sizing enhances fiber processability with a protective coating on the fiber surface and can provide a coupling agent for the fiber/resin bond. The relationship between surface treatment and sizing is complex, and the effectiveness of each depends on its compatibility with both the fiber and the resin.