Abstract
This paper proposed a kinetic model that can describe the changes in the adhesion properties of styrene–butadiene (SBS) block copolymer surfaces under the influence of low-temperature plasma treatment. As a measure of these changes, the peel strength of joints formed between the copolymer surface and the polyurethane adhesive was chosen. Five types of low-temperature low-pressure RF plasma, two inert plasmas (Ar and He), and three reactive plasmas (O2, CO2, and CCl4) were tested. It was found that for all these types of plasma, the peel strength with the plasma treatment time first increases rapidly reaching a maximum value, and then there is a visible decrease in peel strength, after which the peel strength increases again. This dependence of the peel strength on the plasma treatment time is very well described by the proposed model, which considers three processes: (1) the generation of radical states followed by the creation of functional groups involved in the adhesive bonding process, (2) the surface cross-linking that decreases the concentration of these functional groups, and (3) the formation of nano-roughness. The model analysis revealed differences between the action of reactive and inert plasmas in the SBS surface cross-linking mechanism and preferential etching process, as well as differences in the generation of radical states between the O2 plasma (electron process) and other plasmas tested (ionic processes).
Highlights
The adhesive bonding of polymers to themselves as well as to other materials presents an important problem, especially in the case of elastomers and rubbers used in the industry.The strength and quality of such adhesive-bonded joints depend, to a great extent, on the chemical structure and morphology of the polymer surface, and can be controlled by various surface treatments
For a more profound understanding of the polymer surface modification created by low-temperature plasma treatments, we analyzed the dependences of the peel strength for adhesive-bonded joints prepared between the SBS surface and PU adhesive on the plasma treatment time and discharge power using various types of plasma
For the description of the peel strength changes as a function of the plasma treatment time, three main processes were considered: (1) the generation of radical states followed by the creation of functional groups involved in the adhesive bonding process, (2) the surface cross‐linking that decreases the concentration of these functional groups, and (3) the formation of nano‐roughness
Summary
The strength and quality of such adhesive-bonded joints depend, to a great extent, on the chemical structure and morphology of the polymer surface, and can be controlled by various surface treatments It is already known for more than 20 years that a useful method in this respect is the low-temperature (non-equilibrium), both low pressure and atmospheric pressure, plasma treatment [1,2,3,4,5,6,7]. Such treatment, which can be performed either in inert plasmas (generated e.g., in Ar or He) or chemically reactive (but non-polymerizable) plasmas (generated e.g., in O2 , CO2 , or H2 O), causes changes in the chemical structure of the polymer surface by two fundamental processes. Functional groups, such as hydroxyl (−OH), carbonyl (>C=O), etc., can be formed directly in the plasma processes (from atoms present in the reactive plasmas) or further after
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