HOT-MELT ADHESIVE MODEL - INTERFACIAL ADHESION AND POLYMER TACKIFIER/WAX INTERACTIONS/

This work continues our study of the hot melt adhesive (BMA) model pub lished earlier [1]. This HMA model was developed based on the pressure sensitive adhesive (PSA) tack model established previously [2]: P = P 0BD (1) where P is the adhesive bond strength, P-0 is the interfacial (intrinsic) adhesion term, B is the bonding term and D is the debondin g term. The previous paper [I] describes the B and D terms in detail. However, only a brief discussion of the P-0 term was given. The presen t paper will provide a more in-depth but still rather qualitative stud y of the P-0 term within the framework of the adhesion model described in Eq. (1). HMAs studied are ethylene/vinyl acetate copolymer (EVA)/t ackifier/wax blends. Substrates studied are untreated and corona-disch arge-treated polyolefins such as polypropylene (PP) and polyethylene ( PE). First, it has been found that the tackifier surface tension could be roughly correlated with one of its thermodynamic parameters: the s olubility parameter dispersion component. Secondly, except for EVA/tac kifier binary blends, the compatibility of any two of these three comp onents, the EVA polymer, the tackifier and the wax, in a HMA can be es timated from surface tension and X-ray photoelectron spectroscopy (XPS ) measurements. Thirdly, based on the study of the EVA/mixed aliphatic -aromatic tackifier/wax model HMA system, it has been observed that th e HMA/polyolefin substrate interfacial composition depends on the wax/ substrate compatibility. The cause of an inferior peel strength of a H MA containing a high wax content to a polyolefin substrate is possibly due to the formation of a weak boundary layer (WBL) of wax at the int erface and/or low dissipative properties of the HMA. Also, the relatio nship between EVA/tackifier/wax interactions and HMA peel strength wil l be discussed. A correlation between the EVA/tackifier compatibility measured by cloud point and viscoelastic experiments to the debonding term, D, in Eq. (1) has been found.