Polyethylene wettability

Khang, G., Jeon, J.H., and Lee, H.B., 1998b. Fibroblast cell migration on polyethylene wettability chemogradient surfaces, to appear. 

UV irradiation on a polymer surface produces chemical modification as well as wettability and bondability improvement. It causes chain scission and oxidation on polymer surfaces. -iven in the presence of an inert gas [45]. Carbonyls are found to be introduced onto polyethylenes on UV irradiation. Sivram et al. [46] have used photochemical treatments for surface modification of polymers. They have generated surfaces of vaying surface energies by simple organic reactions. 

Thermal aging is another simple pretreatment process that can effectively improve adhesion properties of polymers. Polyethylene becomes wettable and bondable by exposing to a blast of hot ( 500°C) air [47]. Melt-extruded polyethylene gets oxidized and as a result, carbonyl, carboxyl, and hydroperoxide groups are introduced onto the surface [48]. 

The modification of the chemical composition of polymer surfaces, and thus their wettability with chemical substances, can be realized in different ways electric discharges more commonly called Corona effect, oxidation by a flame, plasma treatment, UV irradiation and also UV irradiation under ozone atmosphere. Numerous studies have been devoted to the effects of these different treatments. More recently, Strobel et al. [204] compared the effects of these treatments on polypropylene and polyethylene terephthalate using analytical methods such as E.S.C.A., F.T.I.R., and contact angle measurements. They demonstrated that a flame oxidizes polymers only superficially (2-3 nm) whereas treatment realized by plasma effect or Corona effect permits one to work deeply in the polymer (10 nm). The combination of UV irradiation with ozone flux modifies the chemical composition of the polymers to a depth much greater than 10 nm, introducing oxygenated functions into the core of the polymer. 

One of the simplest methods of assessing such treatment of a polyethylene moulding is to immerse it in clean, cold water, withdraw it and then to observe the behaviour of the water on the surface over a given period of time. If the moulding was treated adequately, so that the surface was fully wettable, the aqueous surface film will be unbroken. Comparisons may be made by recording the times taken for the films of water to break up on bottles having different levels of treatment. 

Thermal History. The polyethylene was molded at 175°C. for varying lengths of time, then cooled by circulating cold water through the press platens. The rate of cooling had no apparent effect on either the mechanical strength of the surface region or the wettability. 

Although a large number of substrates have been used to nucleate and crystallize polyethylene (14), only the wettabilities of polyethylenes... 

Strong joints with epoxy adhesives can be made to polyethylene surfaces which have been oxidized by a variety of techniques (4, 5). The general belief has been that the presence of polar groups on the polymer surface creates an affinity for the polar epoxy adhesive which improves wettability and results in a strong adhesive joint. 

Table II. Surface Density and Crystallinity of Polyethylene Films as Determined by Wettability at 20°C.

Figure 6. A Fowkes-Young plot of the wettability data for a variety of polyethylene surfaces...

Wettability. A comparison of contact angles for methylene iodide and pure water on natural films with the contact angles of the same liquids on known materials is shown in Table I. By the contact angle criterion, the natural films obviously resemble the two polar (but nonionic) polyamide materials much more closely than the high energy platinum or the non-polar polyethylene. There is a particularly close... 

Polyolefins. Low density polyethylene and polypropylene have been developed as sheet and hollow fiber mlcroporous membranes, respectively, for use In plasmapheresis. Polyethylene Is made porous by stretching the annealed film ( ), while polypropylene la made porous by coextruding hollow fibers with a leachable plasticizer. Neither membrane has been prepared with small pore dimensions suitable for protein rejection. These polyolefin membranes are characterized by good chemical stability, but require special surfactant treatments to make them wettable. Their low deformation temperature precludes the use of steam sterilization. Because they are extruded without the usual antl-oxldants and stabilizers, their stability la lower than Injection molding formulations of the same polymer. 

Abstract. In this work, nitrogen was grafted on the surface of polyethylene powders in a fluidized bed coupled to a nitrogen microwave post-discharge, under low pressure (lOTorr) and low temperature (<90°C). The influences of treatment-duration (1 to 9 h) and nitrogen flow-rate on the XPS (X-ray Photoelectron Spectroscopy) N/C atomic ratio and on the powder wettability have been studied. 

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