Some Surface Chemical Aspects of Glassresin Composites. Part II. The Origin and Removal of Microvoids in Filament-Wound Composites

摘要

Previous work of this program established that a very considerable number of air microvoids are entrained in the glass roving during the winding of glass-resin composites. Air entrapment results from the difficult capillary penetration of resin into spaces between filaments during the impregnation process. The poor resin wettability of commercially finished filaments aggravates the situation. Microscopic examination has shown that the microvoids observed in glass-filament rovings are also present in cured, filament-wound composites, prepreg roving, and glass-resin laminates. The voids are present to the extent of 10 to the 7th power to 10 to the 9th power cu. in., are about 0.4 mil in diameter, and have lengths from 0.4 to 20 mils and even greater. A microscopic examination was made of the process of resin impregnation into a strand of glass filaments under simulated winding conditions with particular attention given to the effect of the operating variables on air entrapment. When the contact angle of the resin against the individual filaments was nonzero the void content was too high to be measurable, even at low resin viscosities and slow strand speeds. On the other hand, reducing the contact angle to zero or causing the tension to oscillate as the strand passed through the resin markedly reduced the number of voids. A combination of good wetting and oscillating strand tension gave better results than either alone. These observations can be explained in terms of the forces that obstruct the release of the air bubbles from between filaments. (Author)