Mary Jane Walzak

A comparison of gas-phase methods of modifying polymer surfaces

Oxidation is the most common surface modification of polymers. This paper presents a comparison of five gas-phase surface oxidation processes: corona discharge, flame, remote air plasma, ozone, and combined UV/ozone treatments. Well-characterized biaxially oriented films of polypropylene and poly(ethylene terephthalate) were treated by each of the five techniques. The surface-treated films were then analyzed by X-ray photoelectron spectroscopy (XPS or ESCA), contact-angle measurements, and Fourier-transform IR (FTIR) spectroscopy. Corona, flame, and remote-plasma processes rapidly oxidize polymer surfaces, attaining XPS O/C atomic ratios on polypropylene of greater than 0.10 in less than 0.5 s. In contrast, the various UV/ozone treatments require orders of magnitude greater exposure time to reach the same levels of surface oxidation. While corona treatment and flame treatment are well known as efficient means of oxidizing polymer surfaces, the ability of plasma treatments to rapidly oxidize polymers is no...

UV and ozone treatment of polypropylene and poly(ethylene terephthalate)

The effects of exposure to ultraviolet (UV) light and ozone, separately and in combination, were investigated with respect to polypropylene (PP) and poly(ethylene terephthalate) (PET) surfaces. Three combinations of UV light and ozone were studied: ozone only, UV light in air (producing ozone), and UV light in air (producing ozone) supplemented by additional ozone in the incoming air. The effect of the exposure time of the PP and PET to each treatment was studied. The samples were analyzed by X-ray photoelectron spectroscopy (XPS) to determine the surface composition, and by dynamic contact angle to determine the water wettability. The results showed that the effect of the treament was dependent on the properties of the exposed polymer, with PET being more sensitive to the UV light and PP being more sensitive to the reactive species in the gas. The exposure times studied ranged from 1 to 90 min. By monitoring the oxygen uptake levels, we were able to determine that surface modification occurred within min...

Atomic force microscopy study of polypropylene surfaces treated by UV and ozone exposure: modification of morphology and adhesion force

Exposing polypropylene (PP) to ozone in the presence of UV light is a simple and effective way of modifying its surface to improve its wettability and adhesion. Atomic force microscopy (AFM) showed a dramatic change in the morphology and a clear increase in the adhesion force resulting from the modification of a PP film by UV/ozone exposure. A relationship has been demonstrated between a change in surface energy (measured by wetting contact angle) and the adhesion force (measured by AFM).

Hidden plastics of Lake Ontario, Canada and their potential preservation in the sediment record

Microplastics are a source of environmental pollution resulting from degradation of plastic products and spillage of resin pellets. We report the amounts of microplastics from various sites of Lake Ontario and evaluate their potential for preservation in the sediment record. A total of 4635 pellets were sampled from the Humber Bay shoreline on three sampling dates. Pellet colours were similar to those from the Humber River bank, suggesting that the river is a pathway for plastics transport into Lake Ontario. Once in the lake, high density microplastics, including mineral-polyethylene and mineral-polypropylene mixtures, sink to the bottom. The minerals may be fillers that were combined with plastics during production, or may have adsorbed to the surfaces of the polymers in the water column or on the lake bottom. Based on sediment depths and accumulation rates, microplastics have accumulated in the offshore region for less than 38 years. Their burial increases the chance of microplastics preservation. Shoreline pellets may not be preserved because they are mingled with organic debris that is reworked during storm events.

Plasma surface modification of polyethylene: short-term vs. long-term plasma treatment

A remote plasma reactor, with air as the plasma gas, has been used for in-line surface modification of linear low-density polyethylene tape (LLDPE) passing 10 cm below the main plasma zone. Line speeds of up to 0.70 m/s were tested, allowing the study of 0.014 s exposure times to the plasma. Oxygen to carbon (O/C) ratios averaging 0.11 were observed on a reproducible basis. The reactor was also used for static plasma treatment under similar experiment onditions. This allowed a comparative study of short-term (milliseconds) vs. long-term (several seconds) plasma treatment. High-resolution X-ray photoelectron spectroscopy (XPS) analysis of the treated polymer surface suggested the formation of hydroxyl (C-OH), carbonyl (C=O) and carboxyl (O-C=O) groups, even after short plasma treatment. The intensities of these components were seen to increase in approximately equal quantities with increasing O/C ratio. Water washing of polyethylene surfaces with high O/C ratios showed a loss of oxygen, apparent as a decre...

Draw-ratio-dependent morphology of biaxially oriented polypropylene films as determined by atomic force microscopy

Using atomic force microscopy we have examined the surface morphology of sequentially biaxially oriented polypropylene (BOPP) films. The surface was shown to be dominated by a nanometer-scale fiber-like network structure, the configuration of which was found to be determined by the relationship between the draw ratios used in the bi-directional stretching processes [machine draw (MD) and transverse draw (TD)]. For the film fabricated with MD and TD ratios of 5.2:1 and 9:1, respectively, preferential orientation of fine fibers to the TD direction and larger veins to the MD direction were observed. When MD and TD ratios became similar, no predominant TD direction fiber alignment and no larger veins were observed. We have shown that the residual effects of the first stretching of the film surface can provide information on the way in which morphological development of the BOPP occurs.

Effects of aging and washing on UV and ozone-treated poly(ethylene terephthalate) and polypropylene

In this study we investigated the stability of poly(ethylene terephthalate) (PET) and polypropylene (PP) surfaces modified using three combinations of UV light and ozone: ozone only, UV light in air (producing ozone), and UV light in air supplemented by additional ozone in the incoming air. Analysis was done using X-ray photoelectron spectroscopy and dynamic contact angle measurements. Our results showed that PET film is oxidized using these treatment conditions and it changes significantly within the first week of aging and after washing with water. These changes are reflected in the decrease in the Δ(O : C) ratio and the increase in the contact angle. Conversely, PP changes very little on aging or washing. Low-molecular-weight oxidized material (LMWOM), produced on the polymer surfaces treated with UV/air or UV/air + ozone, is easily removed with water washing. On aging PET, a number of the oxidized groups at the surface disappear, seeming to migrate into the bulk. The PP, however, does not favour migra...

Atomic Force Microscopy Study of Biaxially Oriented Polypropylene Films

Atomic force microscopy (AFM) uses a very sharp pointed mechanical probe to collect real-space morphological information of solid surfaces. AFM was used in this study to image the surface morphology of a biaxially oriented polypropylene film. The polymer film is characterized by a nanometer-scale, fiberlike network structure, which reflects the drawing process used during the fabrication of the film. AFM was used to study polymer-surface treatment to improve wettability by exposing the polymer to ozone with or without ultraviolet (UV) irradiation. Surface-morphology changes observed by AFM are the result of the surface oxidation induced by the treatment. Due to the topographic features of the polymer film, the fiberlike structure has been used to check the performance of the AFM tip. An AFM image is a mixture of the surface morphology and the shape of the AFM tip. Therefore, it is important to check the performance of a tip to ensure that the AFM image collected reflects the true surface features of the sample, rather than contamination on the AFM tip.

The use of XPS, FTIR, SEM/EDX, contact angle, and AFM in the characterization of coatings

Coatings are applied to surfaces for a variety of reasons: to enhance their appearance, to protect the substrate, to augment the adhesion to other layers, or to functionalize them for further reactions. To evaluate the efficacy of the coating, it is often necessary to analyze the substrate and the coating to ensure that the needed characteristics are present. To this end, the use of x-ray photoelectron spectroscopy (XPS), contact angle, and atomic force microscopy (AFM) can provide information about the surface composition, its morphology, and its ability to be wetted with various solvents. Scanning electron microscopy with energy dispersive x-ray analysis (SEM/EDX) and Fourier transform infrared spectroscopy (FTIR) can provide a clear picture of the near surface components as well as the continuity of coatings. All of these aspects are valuable in evaluating a coating and essential when problems are encountered. The application of these techniques to the analysis of coatings is discussed.

Use of biaxially oriented polypropylene film for evaluating and cleaning contaminated atomic force microscopy probe tips: An application to blind tip reconstruction

An atomic force microscopy (AFM) image of a surface is basically a convolution of the probe tip geometry and the surface features; it is important to know this tip effect to ensure that an image truly reflects the surface features. We have found that a biaxially oriented polypropylene (BOPP) film is suitable for checking tip performance and for cleaning contaminated tips, thus making it possible to collect images of the same area of a BOPP film surface before and after the tip was cleaned. Therefore, the difference between the two different images is solely due to the contamination of the tip. We took advantage of our ability to collect AFM images of the same area using the same tip, in one instance, contaminated and, in the other, after being cleaned. First we used blind reconstruction on the image collected using the contaminated tip. Blind tip reconstruction allows one to extract the geometry of the tip from a given image. Once we had estimated the geometry of the contaminated tip, we used it to simula...