Mechanistic studies of adhesion promotion by γ‐aminopropyl triethoxy silane in α‐Al₂O₃/polyethylene joint

Abstract

Abstract In order to understand the mechanism of adhesion promotion by organo silane in joints where its chemical reaction with a polymer matrix may be negligible, we studied the role of γ‐aminopropyl triethoxy silane (γ‐APS) in α‐Al 2 O 3 / polyethylene joints. When adsorbed or deposited on α‐A1 2 O 3 / and moderately dried, γ‐APS forms a multimolecular film that is not fully cured. Drying at elevated temperatures for an extended time leads to further curing, resulting in a glassy silane film with a T g around 108°C, while prolonged dry may cause some degradation. Joint strength is markedly improved by the application of a γ‐APS film with a maximum peel strength of 2.3 kg/cm when the silane is applied from a 2 percent aqueous solution. Drying the silane at an elevated temperature prior to joint formation reduces joint strength and also changes the failure mode from cohesive failure through the polyethylene to a mixed mode. Evidence of interdiffusion between γ‐APS film and polyethylene at a temperature (149°C) that is above the melting point of polyethylene and the T g of the silane film was obtained by measuring the Si concentration profile across the interface of the laminate of polyethylene/γ‐APS/polyethylene. Diffusion constants in the order of 10 −12 cm 2 /s were obtained, with a teridency toward reduced diffusion as a consequence of extensive drying. DSC results indicate at least partial miscibility of the silane polymer in the amorphous region of polyethylene. It is proposed that the interdiffusion between γ‐APS silane film and polyethylene is an important mechanism for adhesion promotion of the joints investigated in this study.