Adhesion of polymers

https://biblio.ugent.be/publication/792032/file/8599453.pdf

Nonthermal Plasma Technology as a Versatile Strategy for Polymeric Biomaterials Surface Modification: A Review

In this paper, polyester (PET) and polypropylene (PP) films are modified by a dielectric barrier discharge in air, helium and argon at medium pressure (5.0 kPa). The plasma-modified surfaces are characterized by contact angle measurements and X-ray photoelectron spectroscopy (XPS) as a function of energy density. The polymer films, modified in air, helium and argon, show a remarkable increase in hydrophilicity due to the implantation of oxygen-containing groups, such as C–O, O–C O and C O. Atomic oxygen, OH radicals, UV photons and ions, present in the discharge, create radicals at the polymer surfaces, which are able to react with oxygen species, resulting in the formation of oxygen-containing functionalities on the polymer surfaces. It is shown that an air plasma is more efficient in implanting oxygen functionalities than an argon plasma, which is more efficient than a helium plasma. In an air plasma, most of the created radicals at the polymer surface will quickly react with an oxygen particle, resulting in an efficient implantation of oxygen functionalities. However, in an argon and helium plasma, the created radicals can react with an oxygen particle, but can also recombine with each other resulting in the formation of an oxidized cross-linked structure. This cross-linking process will inhibit the implantation of oxygen, resulting in a lower efficiency. In argon plasma, more ions are present to create radicals, therefore, more radicals are able to react with oxygen species. This can explain the higher efficiency of an argon plasma compared to a helium plasma.

Treatment of polymer films with a dielectric barrier discharge in air, helium and argon at medium pressure

A new cold plasma jet has been developed for surface modification of materials at atmospheric pressure. This new cold plasma jet generator is composed of two concentric cylindrical all-metal tube electrodes. The argon is fed into the inner-grounded electrode, the outer electrode is connected to the high-voltage power supply and covered with a layer of dielectric, and then a stable cold plasma jet is formed and blown out into air. The plasma gas temperature is only 25–30 °C. Preliminary results are presented on the modification of polypropylene (PP) and polyethylene terephthalate (PET) fibres by this cold plasma jet. The water contact angle of these materials is found to decrease after plasma treatment and it will recover a little in two months. The chemical changes on the surface of polymers are studied by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) is used to study the changes in surface feature of polymers due to plasma treatment. The hydrophilicity and surface structure of these materials after plasma treatment are discussed. The results show that such a plasma jet is effective.

Surface modification of polymer fibre by the new atmospheric pressure cold plasma jet

Adhesive properties of polypropylene (PP) and polyethylene terephthalate (PET) film surfaces treated by DC glow discharge plasma

We introduced carboxylic groups on the surface of polyurethane (PU) with the aid of oxygen plasma treatment and the post-grafting of acrylic acid (AAc) in an aqueous solution. After plasma treatment, PU was exposed to the air to generate peroxides. Peroxides were confirmed by the 1,1-diphenyl-2-picrylhydrazyl method. We chose different parameters of plasma treatment to get the optimum condition for introducing maximum peroxides on the surface. Peroxides are known to be the species responsible for initiating the graft co-polymerization when PU reacts with AAc to produce AAc grafted PU. The AAc grafted on the surfaces was characterized by water contact angle measurement, Fourier transform infrared by attenuated total reflectance and electron spectroscopy for chemical analysis and optical microscopy. After confirming a successful grafting of AAc, we studied the effect of reaction temperature, reaction time, monomer concentration and Mohr's salt on the grafting degree of AAc.

Plasma-induced graft co-polymerization of acrylic acid onto the polyurethane surface

After the atmospheric pressure plasma treatment of polypropylene (PP) film surface, we measured the contact angle of the surface by using polar solvent (water) and nonpolar solvent (diiodomethane). We also calculated the surface free energy of PP film by using the measured values of contact angles. And then we analyzed the change of the contact angle and surface free energy with respect to the conditions of atmospheric pressure plasma treatment. Upon each condition of atmospheric pressure plasma treatment, the contact angle and surface free energy showed optimum value or leveled off. Through AFM analysis, we also observed the change of surface morphology and roughness before and after plasma treatment. The surface roughness of PP film showed the highest value when the plasma treatment time was 90 s. Finally, we analyzed the change of chemical compositions on the PP film surface through XPS. As the result of analysis, we observed that polar functional groups, such as –CO, –C=O, and –COO were introduced on the PP film surface after atmospheric pressure plasma treatment.

Surface characteristics of polypropylene film treated by an atmospheric pressure plasma

In an attempt to modify the hydrophobic surface properties of polypropylene (PP) films, this study examined the optimum process parameters of atmospheric pressure plasma (APP) using Ar gas. Under optimized conditions, the effects of a mixed gas (Ar/O2) plasma treatment on the surface-free energy of a PP film were investigated as a function of the O2 content. The polar contribution of the surface-free energy of the PP film increased with increasing O2 content in the gas mixture. However, slightly more oxygen-containing polar functional groups such as CO, CO, and COO were introduced on the PP film surface by the Ar gas only rather than by the Ar/O2 gas mixture. In addition, AFM analysis showed that the Ar plasma treatment of the PP film produced the smoothest surface as a result of the relatively homogeneous etching process.

Comparison of the surface characteristics of polypropylene films treated by Ar and mixed gas (Ar/O2) atmospheric pressure plasma.

The adhesion between AISI 316 L stainless steel plates was studied using a poly(pyromellitic dianhydride-co-4,4′-oxydianiline), amic acid as adhesive. The surfaces of two 316 L stainless steel plates were pre-treated using an atmospheric pressure plasma to improve the surface properties before adhesion tests. The surface free energies of the stainless steel plates were improved with plasma treatment and the optimum plasma treatment conditions such as plasma treatment time, plasma treatment power, gas flow rate, gap distance between power source and substrates and aging time after plasma treatment were investigated. When the mixed gas (Ar and O2) plasma was used, the surface free energy of the stainless steel was more enhanced. The surface compositions of the stainless steel were examined by X-ray Photoelectron Spectroscopy (XPS) after plasma treatment and it was proved that new oxygen-containing groups were generated after plasma treatment. Finally, tensile tests confirmed that new oxygen-containing groups formed through plasma treatment improved the adhesion strength between two stainless steel plates.

Sung-Woon Myung

Papers

Plasma-induced graft co-polymerization of acrylic acid onto the polyurethane surface

Surface characteristics of polypropylene film treated by an atmospheric pressure plasma

Comparison of the surface characteristics of polypropylene films treated by Ar and mixed gas (Ar/O2) atmospheric pressure plasma.

Enhancement of adhesion strength between two AISI 316 L stainless steel plates through atmospheric pressure plasma treatment

Effect of washing on surface free energy of polystyrene plate treated by RF atmospheric pressure plasma