Effect of Low Molecular Weight Oxidized Materials and Nitrogen Groups on Adhesive Joints of Polypropylene Treated by a Cold Atmospheric Plasma Jet.

Kateřina Polášková,Miloš Klíma,Lucie Blahová,Zdeňka Jeníková,Lenka Zajíčková

doi:10.3390/polym13244396

Abstract

Polypropylene is a typical representative of synthetic polymers that, for many applications including adhesive joints, requires an increase in wettability and chemical surface reactivity. Plasma processing offers efficient methods for such surface modifications. A particular disadvantage of the plasma jets can be the small plasma area. Here, we present a cold atmospheric plasma radio-frequency slit jet developed with a width of 150 mm applied to polypropylene plasma treatment in Ar, Ar/O and Ar/N We identified two main parameters influencing the tensile strength of adhesive joints mediated by epoxy adhesive DP 190, nitrogen content, and the amount of low molecular weight oxidized materials (LMWOMs). Nitrogen functional groups promoted adhesion between epoxy adhesive DP 190 and the PP by taking part in the curing process. LMWOMs formed a weak boundary layer, inhibiting adhesion by inducing a cohesive failure of the joint. A trade off between these two parameters determined the optimized conditions at which the strength of the adhesive joint increased 4.5 times. Higher adhesion strength was previously observed when using a translational plasma gliding arc plasma jet with higher plasma gas temperatures, resulting in better cross linking of polymer chains caused by local PP melting.

Highlights

Plasma treatment of polymers is a well-established technique used to increase wettability and, subsequently, the adhesion of a polymer surface [1,2,3]
As the topic of plasma treatment is quite broad, we will focus only on the results previously achieved for the synthetic polymer utilized in this study: polypropylene
We present a radio-frequency plasma slit jet (PSJ), a cold atmospheric plasma (CAP) developed in the width of 150 mm and demonstrate its performance on the polypropylene plasma treatment in Ar, Ar/O2, and Ar/N2

Summary

Introduction

Plasma treatment of polymers is a well-established technique used to increase wettability and, subsequently, the adhesion of a polymer surface [1,2,3]. A wide variety of plasma source types, each one with different advantages and drawbacks, has been applied to the modification of various synthetic polymers (e.g., polypropylene, polyethylene, and polytetrafluoroethylene). Polypropylene (PP) is a cheap, versatile, and fully recyclable thermoplastic polymer with many beneficial properties such as low density, resistance to corrosion, or high thermal and chemical stability [4,5]. It is the most widely used thermoplastic, with applications ranging from food packaging to fabrics and plastic tools manufacturing to automotive industry [6]. Out of the possible environmentally friendly and automated alternatives, such as flame treatment [9,10] and UV irradiation [11], plasma treatment appears to be the most promising one [12]

Methods

Results

Conclusion