Plasma-treated Polyethylene Research Articles

Inhibition of aging in plasma-treated high-density polyethylene

The effects of cross-linking and crystallinity on the aging of plasma-treated high-density polyethylene (HDPE) have been investigated. In the case of mixed argon and oxygen, aging has been found to be reduced with an increased amount of argon in the mixture owing to an increased degree of cross-linking. A similar decrease in hydrophobic recovery has been achieved by increasing the crystallinity of HDPE. Diffusion of polar functional groups from the surface into the bulk has been observed to be lowered by both increasing the degree of cross-linking and crystallinity. The samples were analyzed by angle-resolved XPS, contact angle measurements and SEM investigations.

The aging effects of repeated oxygen plasma treatment on the surface rearrangement and adhesion of LDPE to aluminum

The effects of aging temperature and time on the adhesion properties of oxygen plasmatreated low-density polyethylene (LDPE) were investigated. As the aging temperature and time increased, surface rearrangement and the migration of molecules containing polar functional groups into the bulk were accelerated to the surface to form a hydrophobic surface. The adhesion strength of oxygen plasma-treated LDPE/aluminum joints was measured using a 90° peel test by varying the plasma treatment time and aging temperature. The adhesion strength was constant, regardless of the plasma treatment time. As the aging temperature increased, the adhesion strength of the LDPE/aluminum joints decreased and the locus of failure changed from cohesive to interfacial failure. It was also found that the polar functional groups buried in the bulk could be reoriented to the surface in a polar environment. This study also investigated whether repeated oxygen plasma treatment would increase the concentration of polar functional groups at the surface and reduce the surface rearrangement and the migration of molecules containing polar functional groups during aging. Contact angle measurements and X-ray photoelectron spectroscopy (XPS) showed that repeated oxygen plasma treatments increased the concentration of polar functional groups at the surface. However, the aging time between plasma treatments had a negligible effect on the concentration of polar functional groups at the surface.

Immobilization of Heparin and Highly-Sulphated Hyaluronic Acid onto Plasma-Treated Polyethylene

Heparin and highly-sulphated hyaluronic acid have been successfully immobilized onto plasma-processed polyethylene via a diamine polyethyleneglycol (PEG) spacer molecule. Two different plasma-processes have been utilized, i.e. a treatment and a deposition process, for providing polyethylene surface with the COOH groups necessary for the immobilization reactions. XPS integrated with derivatization procedures, ATR-FTIR and Water Contact Angle measurements have been carried out for characterizing each modification step: 1) the plasma-process, 2) the immobilization of the spacer molecule and 3) the immobilization of the biomolecules. The thrombin time of the modified surfaces has been measured, and their platelet activation characteristics evaluated. The results indicate a certain nonthrombogenic character of the biomolecule-immobilized polyethylene samples.

Crack bridging and fibre pull-out in polyethylene fibre reinforced epoxy resins

An investigation has been undertaken of the stress distributions in high-performance polyethylene fibres bridging cracks in model epoxy composites. The axial fibre stress has been determined from stress-induced Raman band shifts and the effect of fibre surface treatment has been followed using untreated and plasma-treated polyethylene fibres. It is found that when the specimen is cracked, the fibres do not break and stress is transmitted from the matrix to the fibre across the fibre/matrix interface. A debond propagates along the fibre/matrix interface accompanied by friction along the debonded interface. The axial stress distributions in the fibres can be analysed using a partial-debonding model based upon shear-lag theory and it is found that the maximum interfacial shear stress at the bond/debond transition is a function of the debond length. The debonding process has been modelled successfully in terms of the interfacial fracture energy-based criterion developed by Hsueh for the propagation of a debond along a fibre/matrix interface accompanied by constant friction along the interface.

Fracture strengths of provisional restorations reinforced with plasma-treated woven polyethylene fiber

Statement of problem. Fracture strength of interim fixed partial prosthesis is of great concern, especially in long-span restorations or areas of heavy occlusal stress.Purpose. Effects of a plasma-treated woven polyethylene fiber (Ribbond) on the fracture strength of polymethyl methacrylate (Coldpac) and a resin-based two-phase curing provisional restorative material (Provipont DC) were evaluated.Material and methods. A polyvinyl siloxane template was used to fabricate three-unit posterior provisional prostheses on a stainless steel die with two abutments 22 mm apart. The reinforced groups were fabricated by affixing 3 mm wide pieces of fiber treated with methyl methacrylate monomer or polyisocyanate (activator part of Provipont DC) on the occlusal surfaces of abutments. The interim materials were mixed, according to the manufacturers' specifications, and placed in the template. The template was pressed on the die and held secure until complete setting of the material occurred by light curing (Provipont DC) or autopolymerization (PMMA). The specimens were divided into 4 groups of 10 each (A, reinforced Provipont DC; B, unreinforced Provipont DC; C, reinforced PMMA; and D, unreinforced PMMA). A central compressive load force was exerted on the specimen to determine the fracture load of the restorations.Results. The data revealed mean fracture loads of A, 65.59 ± 11.27 kg; B, 46.59 ± 14.84 kg; C, 53.46 ± 7.76 kg; and D, 49.86 ± 14.44 kg.Conclusion. Plasma-treated polyethylene reinforced PMMA restorations showed no significant increase in fracture loads when compared with unreinforced restorations ( p > 0.10), whereas reinforced resin-based restorations revealed significantly higher fracture loads ( p < 0.01) than the unreinforced resin-based and PMMA provisional restorations. (J Prosthet Dent 1997;78:447-50.)

Adhesion improvement of epoxy resin/polyethylene joints by plasma treatment of polyethylene

Low density polyethylene (LDPE) and high density polyethylene (HDPE) were plasma-treated with N 2 and O 2 plasma. The wettability and polar component of surface free energy of plasma-treated polyethylene were investigated by contact angle measurement. The concentration of functional groups formed by plasma treatment such as hydroxyl and carbonyl groups was measured using attenuated total reflection Fourier transform infrared spectroscopy (ATR FTi.r.). The concentration of polar functional group increased rapidly with 5–10s of plasma treating time and then very slowly after that. The adhesion strength of epoxy resin/plasma-treated polyethylene joints was examined by a 90° peel test. The increase of the adhesion strength was similar to that of concentration of polar functional groups. The higher adhesion strength of epoxy resin/plasma-treated HDPE joints was observed than that of epoxy resin/plasma-treated LDPE joints since HDPE deformed more during the peel tests and had more polar functional groups on the surface.

Effects of solvents on the surface properties of oxygen plasma-treated polyethylene and polypropylene films

The effects of solvents on the surface properties of oxygen plasma-treated polyethylene and polypropylene films have been studied by ESCA, contact angle measurement, and adhesion testing. The results show that oxygen plasma treatment produces some low molecular weight materials (LMWM) on the treated surfaces, which can be removed, to some extent, by solvents. It seems that the LMWM has different solubilities in different solvents. Among the solvents (water, acetone, and 2-propanol) used, acetone has the most significant effect. The removal of LMWM considerably reduces the wettability of the treated materials, but does not impair the adhesion increased by the plasma treatment.

The effect of plasma-treated polyethylene fiber on the fracture strength of polymethyl methacrylate

The effect of a plasma-treated polyethylene fiber on the fracture strength of polymethyl methacrylate was evaluated in this study. Sixteen treated and 16 untreated polymethyl methacrylate bars were tested by use of a three-point compression loading apparatus. Under the conditions of this experiment the treated bars showed a mean fracture strength of 12.56 MPa compared with 9.81 MPa for the untreated samples. In addition to the increased fracture strength, the treated bars also demonstrated resistance to crack propagation. The bars remained in one piece, held together throughout the compression loading by the polyethylene fiber. The clinical implication of these findings is a reduced incidence of fixed provisional restoration failure.

Controlled Interfaces in Low-temperature-cured Phenolic Composites

The surface chemistry and interfacial adhesion of silane-treated E-glass fibers and low-power, oxygen or water plasma-treated ultrahigh-modulus polyethylene (UHMPE) fibers with acid-catalyzed, low-temperature-cured phenolic resins have been measured by X-ray photoelectron spectroscopy, (XPS) and static secondary ion mass spectrometry (SIMS), fiber bundle pullout and flexural and interlaminar shear strength properties of unidirectional composites. The most effective treatment for E-glass involved an epoxy silane rather than an amino silane owing to the protonation by the acid catalyst of the amine as well as the loss of reactive sites by the formation of carbon dioxide adducts stable at the conditions of cure. Scanning electron microscope examination of the cured phenolic resin showed phase-separated water domains; the diameter of these domains decreased towards the fiber surface in a chopped-strand mat composite owing to the lowering of the surface tension produced by the dissolution of the binder by the phenolic resin. Both water and oxygen-plasma treatments of UHMPE increased the fiber bundle pullout force by the same amount and this was attributed to direct chemical bonding to hydroxyl (and possibly epoxy) groups detected by XPS, SSIMS and derivatization. The best composite properties were obtained when oxygen plasma-treated UHMPE was used and this was attributed to the slower restructuring and higher total oxygen content enabling efficient wet-out of the fibers by the resin.

Infrared spectroscopic characterization of plasma-treated polyethylene

Thin polyethylene films cast on copper or gold were treated with low-pressure oxygen plasma. Changes in the chemical structure of these films were investigated by infrared spectroscopy using a reflection method in combination with chemical derivatization (CD) reactions. The potential of the CD is demonstrated for hydroxyl groups and carbonyl groups by the reaction with trifluoroacetic anhydride and hydrazine. The reaction conditions were varied to check for side reactions. The results of the derivatization are discussed in terms of secondary structures. © 1996 John Wiley & Sons, Inc.

Effect of ageing atmospheres on the changes in surface free energies of oxygen plasma-treated polyethylene films

The changes in the surface properties of oxygen plasma-treated polyethylene films during ageing in various atmospheres (water, dry nitrogen gas, and hexane) were studied from the viewpoint of the interaction of the surface functional groups formed on the films and the ageing media. The XPS (x-ray photoelectron spectroscopy) and the SSIMS (static secondary ion mass spectrometry) spectra indicated the formation of polar groups containing oxygen such as C=O on the film surface. The changes in the critical surface tension (γC) of the film with ageing time were largely affected by the ageing atmospheres: the γC value of the film aged in water increased, and those of the films aged in nitrogen gas and hexane decreased with an increase in ageing time. These different tendencies among the ageing media could be understood reasonably with examining the surface free energy ratios (the total energy, γStot, the dispersion force component, γSd/γStot, the polar component, γSp/γStot, the hydrogen bonding component, γSh/γStot) of the films. The ageing in water of which γL is large gave the films with higher γSp/γStot values, suggeting that the overturn and/or the orientation of the polar groups toward the water phase occurred so as to minimize the discrepancy of the surface free energy between the polymer surface and water. On the other hand, the ageing in nitrogen gas and hexane media of which γL are small gave the films with lower γSp/γStot and γSh/γStot values, suggesting the overturn and/or the orientation of the polar groups into the bulk polymer.

Surface properties and platelet adhesion characteristics of acrylic acid and allylamine plasma‐treated polyethylene

AbstractAcidic oxygen‐containing and basic nitrogen‐containing functional groups were incorporated onto thin films formed by plasma polymerization of acrylic acid and allylamine in a lowpressure glow discharge. ESCA, ATR–FTIR spectroscopy, and static contact‐angle measurements confirmed the presence of these functional groups. Surface hydrophilicity of the acrylic acid plasma polymer decreased with time due to the diffusion of hydrophilic oxygencontaining functional groups away from the surface of the plasma‐treated polyethylene. In contrast, the hydrophilicity of the allylamine plasma polymer increased with time because of the extensive post‐plasma‐treatment oxidation with atmospheric oxygen. In assessing the blood compatibility of these two types of plasma polymer surfaces by platelet adhesion and spreading, the acidic acrylic acid plasma polymers showed an improvement in thromboresistance, but the basic allylamine plasma polymers were more thrombogenic than was the untreated low‐density polyethylene base material. © 1993 John Wiley &amp; Sons, Inc.

Chemical reactions on plasma-treated polyethylene surfaces

Oxygen plasma treatment as a surface functionalization technique is discussed. Oxygen-containing functionalities were introduced on the surface of high- (HDPE) and low-density polyethylene (LDPE) by glow discharge. The number of surface hydroxyl groups was increased by a post-discharge wet treatment in a reducing solution. The effects of the substrate nature, the discharge parameters, and the post-discharge wet treatment on the surface functional groups are discussed, and the effectiveness of functionalized surfaces on the yield of coupling reactions is shown.

ＸＰＳの１ｓおよび価電子帯スペクトルによるプラズマ処理ＰＥフィルム表面の検討

Bond-structure of hydrocarbon and density of polar groups at the surface region of argon and oxygen plasma-treated polyethylene (Ar-PE, 02-PE) were investigated by means of the XPS 1 s and valence band spectra. In case of An-PE, branching and cross-linking hydrocarbo n units occur first, then reaction of radical survived with oxygen and/or nitrogen results in polar groups at the film surface. In case of 02-PE, oxidation of the polymer film is prior to branching and cross-linking.

ESCA investigation of low-temperature ammonia plasma-treated polyethylene substrate for immobilization of protein

A low-temperature radiofrequency plasma excited in anhydrous ammonia was used to modify polyethylene substrate surfaces for covalent immobilization of proteins. Electron spectroscopy for chemical application (ESCA) was used for surface characterization of polyethylene to a depth scale of 7 nm. The data revealed that surface modification is extensive and occurs in seconds at low discharge power. Primary amino functionalities were detected on the polyethylene surface and the level is dependent on plasma parameters. 125l-labelled antibodies covalently attached to amino groups via glutaraldehyde allowed the conditions for optimum level of primary amine to be established. Both ESCA data and protein loadings are in excellent agreement.