Improvement of the chemical adhesion of EPDM rubber to Sheet Moulding Compound (SMC) by the addition of phenolic resin as adhesion promoter

ABSTRACT

The objective of this study is to improve the adhesion between SMC and EPDM Rubber without the application of a solvent-based adhesive. The influence of the addition of different percentages of phenolic resin, as an adhesion promoter, in the SMC, has been studied. The SMC was prepared in a conventional continuous SMC machine. The EPDM rubber was over-injected on the SMC part, and then vulcanized. The chemical bonding between both materials was produced during the rubber vulcanization step. The SMC-EPDM bond quality was characterized in different ways: 1) mechanically, determining the adhesion strength, 2) optically, comparing the surfaces of the SMC and the rubber after separating them, and 3) chemically, analyzing by DSC the heat of reaction of mixtures of rubber with the different resins used. It has been concluded 1) that SMC-EPDM adhesion is achieved with polyester resins but not with vinyl ester resins, 2) that the addition of phenolic resin promotes the chemical adhesion between SMC and EPDM rubber and 3) that the chemical bonding between both materials occurs because of the double bonds of residual maleic units of the polyester, which are more abundant when phenolic resin is added.

KEYWORDS:

• SMC
• EPDM rubber
• adhesion by chemical bonding
• phenolic
• hybrid materials
• peel