Fibre/resin compatibility in glass/phenolic laminating systems

Compatibility between fibre and resin in a composite is said to exist when 'wetting-out' is easy, when matrix curing proceeds to completion in a reasonable time, and when a sound laminate with good properties is produced. For the relatively new cold-cure phenolic resins, until specially formulated glass finishes become available, there is a need for information on their compatibility with existing products. The factors controlling compatibility in its various aspects must be identified, so that improved finishes may be developed. In the work described here, eight different commercial reinforcement mats were assessed for their compatibility with a single cold-cure phenolic resin, BP Cellobond J2027L. Assessments were made at three stages of manufacture. Contact-angle measurements against liquid resin determined compatibility at the layup stage. The influence of glass and finish upon the degree of resin cure achieved was found by differential scanning calorimetry, thus indicating compatibility at the curing stage. The overriding criterion of compatibility, the integrity of the resulting laminate, was assessed by measurement of inter-laminar shear strength on boards produced by resin transfer moulding (RTM). Despite appreciable disparity between these individual indicators, it has been shown that they could be combined to give an overall assessment. Of the eight reinforcements tested, all of which were formulated for use with polyester or epoxy resins, two were outstandingly successful with the chosen phenolic resin, three gave laminates of acceptable quality, and three were clearly incompatible.