High-density Polyethylene Surface Research Articles

Effect of plasma treatment on the degree of AAm grafting for high-density polyethylene

The aim of this article was to determine a suitable method and optimal conditions for grafting of acrylamide (AAm) monomer onto the surface of high-density polyethylene (HDPE). We studied argon plasma treatment of HDPE (PHDPE) and AAm graft copolymerization (AAm-g–PHDPE) using thermal induction with or without adding an initiator, benzoyl peroxide (BPO) [AAm-g (BPO)–PHDPE]. The 1,1-diphenyl-2-picrvlhydrazyl (DPPH) method was adopted to estimate the concentration of peroxide, and consequently the appropriate plasma treatment conditions were determined according to its optimal concentration. ATR-FTIR spectroscopy and ESCA analysis were used to evaluate the degree of grafting copolymerization. The maximum degree of grafting was 0.55 and 2.41 as evaluated by total-reflectance Fourier-transform IR (ATR-FTIR) spectroscopy and electron spectroscopy for chemical analysis (ESCA), respectively. The degree of grafting shows similar trends by ATR-FTIR and ESCA analysis and the optimal grafting time is 4 h. The result also shows that the degree of grafting is also affected by the plasma treatment time. DPPH measurements showed that the maximum peroxide introduced onto HDPE sheets by plasma treatment at 40 W for 3 min and air exposure for 1 h is 5.2×10 −8 mol cm −2. In this investigation, the best graft copolymerization conditions for HDPE are plasma treatment at 40 W for 3 min and thermally induced grafting for 4 h with an initiator (2×10 −3 M).

A closer look into the behavior of oxygen plasma-treated high-density polyethylene

X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure investigation have been used to characterize the surfaces of two oxygen plasma-treated high-density polyethylene (HDPE) samples having different crystalline fractions. Both the observations indicate that a higher degree of crystallinity restricts the mobility of the polar functional groups on the HDPE surface. An increased crystalline order lowers the amount of oxidation and the aging of polar functional groups on the substrate surface. The results are supported by contact angle measurements and field emission scanning electron microscopic observations.

Transient current generation during wear of high-density polyethylene by a stainless-steel stylus

Contact electrification between metals and insulators lead to dramatic transient charge transfer phenomena during sliding contact. We report simultaneous transient current and lateral force measurements as a stainless-steel stylus is drawn across a high-density polyethylene surface in vacuum. Stylus motion in this system is marked by unstable transitions between high and low velocity modes, similar to stickslip. The high velocity events coincide with falling lateral forces and high current signals. Scanning electron microscope images of the resulting wear tracks show slip-related features at intervals consistent with the lateral force and current fluctuations. Although average charge densities along the wear track ranged from 0.4−1 mC/m2, measurements at low normal forces are consistent with higher charge densities (up to 3 mC/m2) at isolated asperity contacts. Current transients as short as 60 μs were observed with total charges consistent with the detachment of 40×40 μm2 contact areas.

Use of cationic surfactant to remove solvent-based ink from rigid high density polyethylene surfaces

Increasing space limitations for disposal of solid waste and shortages of raw materials for plastic have increased the need for recycling. However, printed plastic surfaces cannot be effectively recycled unless the inks are removed. The use of surfactants for deinking rather than organic solvents or chlorine bleaches is environmentally attractive. In this study, the effect of cationic surfactant concentration, pH, process temperature, pre-soaking time, shaking time and abrasion were investigated for blue solvent-based ink on rigid high density polyethylene surfaces. The cationic surfactant (n-hexadecyl trimethyl ammonium bromide) was effective only at concentrations above the critical micelle concentration (CMC) and at high pH levels (11.75 and above). Both below and above the CMC, ink removal was promoted by increasing temperature, pre-soaking time and shaking time. The presence of an abrasive also helped to detach the loosened ink from the plastic surface. Solubilization appears to be an important mechanism aiding deinking.

Adhesion enhancement of evaporated copper on HDPE surface modified by plasma polymerization of glycidyl methacrylate

AbstractSurface modification of high‐density polyethylene (HDPE) surfaces by plasma polymerization of glycidyl methacrylate (GMA) (the pp‐GMA‐HDPE surfaces), in the absence and presence of Ar plasma pre‐activation of the HDPE substrates, was carried out to enhance the adhesion of the polymer with evaporated copper. THe FTIR and X‐ray photoelectron spectroscopy (XPS) results suggested that the epoxide functional groups on the pp‐GMA‐HDPE surfaces had been preserved to various extents, depending on the RF power used during plasma polymerization. Ar plasma pre‐activation of the HDPE surface led to the strong interaction of the pp‐GMA layer with the HDPE substrate. GMA plasma polymerization at low RF powers and in the presence of Ar plasma pre‐activation was shown to be an effective method for enhancing the adhesion of HDPE with the evaporated Cu. An optimum adhesion strength of about 16 N/cm was achieved between the evaporated Cu and the pp‐GMA‐HDPE surface prepared by plasma polymerization of GMA at 5 W, 100 Pa, 20 sccm for 5 s on the HDPE surface pre‐activated by Ar plasma at 35 W, 100 Pa 20 sccm for 20 s. The adhesion enhancement of the Cu/pp‐GMA‐HDPE assemblies in the presence of Ar plasma pre‐activation of the HDPE substrate was attributed to the covalent bonding of the plasma‐polymerized GMA (pp‐GMA) layer with the HDPE surface, the preservation of the epoxide functional groups in the pp‐GMA layer, and the spatial interactions of pp‐GMA chains with the evaporated Cu matrix.

Surface modification of high density polyethylene tubes by coating chitosan, chitosan hydrogel and heparin

Chitosan and chitosan hydrogel were immobilized on both the inside and outside surfaces of high density polyethylene (HDPE) tubes with 2.5x4 mm diameters. First, acrylic acid was grafted on the surfaces of HDPE by electron beam (2.5 Mrad) preirradiation method. Then chitosan/HCl and chitosan/lactic acid solutions were coated on the modified hydrophilic HDPE surfaces, the latter could form a pH-sensitive hydrogel layer on the surfaces. The tube surfaces were further modified with heparin by surface interpenetrating method to improve blood compatibility. ATR-FTIR and ESCA methods were used to characterize the coated surfaces. The morphology changes were monitored by Scanning Electron Microscope (SEM).

HDPE Surface Functionalization by Low-Energy Ion-Beam Irradiation under a Reactive O2 Environment and Its Effect on the HDPE/Nylon 66 Blend

A low energy Ar+ ion-beam was used to modify the surface of a high-density polyethylene (HDPE) dry powder. The modification reaction was promoted by the oxygen gas injected during the irradiation. This simple modification route is characterized as a heterogeneous, solvent-free, environmentally favorable process. The surface functional groups of the modified HDPE were confirmed with X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy as being various oxygen-containing functional groups. The concentration of the functional groups varied rapidly with the irradiation time, reached a maximum value and then slowly decreased. Because of the low-energy characteristics of the ion beam, the changes in the molecular weight, the melting temperature, and the crystallinity of the modified HDPE were not significant, as evidenced by gel-permeation chromatography and differential scanning calorimetry. The rheological behavior of an HDPE/nylon 66 (Ny66) blend, which depends on the blend composition, was complicated due to immiscibility whereas the ion-beam-irradiated HDPE/Ny66 blend showed a more systematic behavior. Also, the compatibility effect of ion-beam-treated HDPE was investigated in the blend of HDPE/ Ny66. In the ion-beam-irradiated HDPE/blends, a significant decrease in the domain size of the dispersed phase was observed. Theoretical models were used to estimate the interfacial tension of HDPE/Ny66 blends. The calculated interfacial tension of an ion-beam-treated HDPE/Ny66 blend was less than that of a nontreated HDPE/Ny66 blend, indicating a greater interaction between the ion-beam-treated HDPE and the Ny66 phases. In addition, the mechanical properties of the ion-beam-treated HDPE/Ny66 blend showed a positive deviation from the rule of mixture. Finally, an explanation of the compatibilizing effect of ion-beam-treated HDPE is presented.

Surface modification of plasma-pretreated high density polyethylene films by graft copolymerization for adhesion improvement with evaporated copper

Surface modification of Ar plasma-pretreated high density polyethylene (HDPE) film via UV-induced graft copolymerization with glycidyl methacrylate (GMA) and 2-hydroxyethylacrylate (HEA) was carried out to improve the adhesion with evaporated copper. The surface compositions of the modified HDPE surfaces were characterized by X-ray photoelectron spectroscopy (XPS). The adhesion strengths of evaporated copper with the graft-copolymerized HDPE films were affected by the Ar plasma pretreatment time, the monomer concentration used for graft copolymerization, and the graft concentration. Post-treatments, such as plasma post-treatments after graft copolymerization and thermal treatment (curing) after metallization, further enhanced the adhesion strength of the Cu/HDPE laminates. The T-type peel strengths of the laminates involving the graft-modified and plasma post-treated HDPE films were greater than 15 N/cm. The enhanced adhesion strength resulted from the strong affinity of the graft chains for Cu and the fact that the graft chains were covalently tethered on the HDPE surface. XPS characterization of the delaminated surfaces of the Cu/HDPE laminates revealed that the failure mode of the laminates with T-peel adhesion strengths greater than 5 N/cm was cohesive in nature.

Surface modification of poly(ethylene-co-vinyl alcohol) (EVA). Part I. Introduction of carboxyl groups and immobilization of collagen.

To enhance the surface biocompatibility of poly(ethylene-co-vinyl alcohol) (EVA) and high-density polyethylene (HDPE), carboxyl groups were introduced by ozone exposure. Type I collagen was immobilized onto the surface through polyion complexing. The carboxyl groups on the EVA were characterized by electron spectroscopy for chemical analysis and neutralization. The amounts of the carboxylic group and collagen increased with increases in time and temperature of exposure. Water-soluble fragments were produced by ozone exposure to EVA, and they acted as collagen crosslinkers. The differences in charge distribution of carboxyl groups affected the amount of collagen immobilization. Graft polymerization of acrylic acid was also carried out onto EVA and HDPE surfaces. The amount of collagen immobilized by graft polymerization was much higher than that by ozone exposure despite the introduction of almost the same amounts of carboxylic groups. It was suggested that the negative charge distribution influences the amount of collagen immobilized onto films.

Low-energy ion scattering (LEIS) study of the ageing of oxygen-plasma-treated high-density polyethylene (HDPE) surfaces

Static low-energy ion scattering (LEIS or ISS) and x-ray photoelectron spectroscopy (XPS) are used to study the surface of high-density polyethylene (HDPE) that has been modified by exposing it to a 'cold' oxygen plasma. The HDPE surface composition is monitored by both techniques as a function of time after the plasma treatment. With LEIS, large differences in ageing are observed between a sample that is exposed to air after the plasma treatment and a sample that is not exposed to air, but rather kept under vacuum. The hydrophobic recovery of the sample exposed to air is very large, whereas no recovery is observed on the other sample. The XPS measurements also show a decrease in oxygen concentration as a function of time for the sample that was exposed to air, but not as steep as in the LEIS measurements. The differences between the air- and vacuum-exposed samples are explained in terms of differences in composition and cross-linking in the surface region. Static LEIS seems to be a promising method to study the ageing of plasma-treated polymers.

The role of surface physicochemical properties in determining the distribution of the autochthonous microflora in mineral water bottles.

Investigation of the distribution of the viable autochthonous microflora in three brands of 1-2-month-old bottled mineral water showed that 1.8 x 10(4) (S.E.M. 8.9 x 10(3), n = 5) to 1.2 x 10(5) (S.E.M. 1.3 x 10(4), n = 5) cfu ml-1 were planktonic cells while 11 (S.E.M. 4, n = 5)-632 (S.E.M. 176, n = 5) cfu cm-2 were found in the biofilm. The biofilm represented between 0.03 and 1.79% of the total viable microbial population in the 1.5 litre bottles studied. Scanning electron microscopy studies showed that the cells adhering to the polyethylene terephthalate (PET) bottles were predominantly rod-shaped, sparsely distributed over the surface. In contrast, the cells adhering to the high density polyethylene (HDPE) caps were found to be mainly clumps of coccoid cells, suggesting that the bottle may provide different microhabitats for different microfloras. Large-scale roughness, such as that observed as lettering inside the cap (average height (z) = 93 microns) was associated with a 46-fold increase in cell numbers. Increased small-scale roughness, as measured by atomic force microscopy on PET and HDPE surfaces (average roughness (Ra) = 5-551 (nm), showed no correlation with adhesion. Investigations of surface hydrophobicity by the sessile drop technique showed that contact angles (theta) were greater on the HDPE caps (theta = 89-96 degrees) than on the PET surfaces (theta = 69-80 degrees). However, no correlation was found between contact angle and attached cell numbers. Measurements of surface electrostatic charge by streaming potential showed that the PET carried an overall negative charge, measuring -15.9 to -16.6 mV in mineral water. No significant change in charge occurred when the monomer composition of the PET was altered. It was concluded that surface roughness, in particular the scale of surface topographical features, is the most important physicochemical surface characteristic determining the distribution of the autochthonous microflora in mineral water bottles.

Preparation and characteristics of thin film with wear-resistant behavior on HDPE surface polymerized by C2H2-H2-SiH4 plasma

Plasma-polymerized deposition of an acetylene–hydrogen–silane mixture (C2H2–H2–SiH4) to obtain thin film with good wear behavior on a high-density polyethylene (HDPE) surface was present in this work. It was found that the bond between thin film and HDPE substrate was excellent and H2 gas in system led the deposited thin film to better adhesive properties, but slower thin film deposition rate. Surface wear-resistant properties of modified HDPE were improved with the input of SiH4. Infrared and X-ray photoelectron spectroscopy spectra suggested that there be large quantities of >CO, OH, CSi, and SiO groups in thin film and that the ratio of C to Si was increased due to the addition of SiH4 and H2, which inferred that the thin film structure and components lie between organic and inorganic materials. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1561–1566, 1998

Hydrogen Bonding and Wettability of Surface-Grafted Organophosphate Polymer

Thin layers of grafted polymer chains were produced by ultraviolet light-induced graft polymerization of a hydrophilic monomer, methacryloxyethyl phosphate, onto the Ar plasma-pretreated film surface of high-density polyethylene. The hydrogen-bonding interactions in the grafted polymer and the wettability of the grafted layers were studied by Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy and water contact angle measurements, respectively. The grafted layers exhibited a distinct wetting transition with an increase in the graft density, which closely correlated with a clearly observable change in the hydrogen-bonding extent of the grafted chains.

Optical emission from tetrafluoromethane plasma and its relationship to surface modification of hexatriacontane

The optical emission from tetrafluoromethane plasma (2% argon included) has been studied by emission spectroscopy. The evolution ofCF*,CF2*, andF emissions has been followed during the treatment of an organic surface. An-alkane, hexatriacontane, has been used as a model for high density polyethylene surface and treated in different plasma conditions. We found that the evolution of fluorinated species emissions in the plasma gas phase is not only a measurement of the reactive species concentrations, but also an indication of the surface modifications. The surface properties, such as surface energy and surface roughness are correlated to the emission intensity of reactives species in the plasma gas phase. A mild exposure to the plasma can result in a great decrease of surface energy corresponding to the fluorination. The surface roughness only changes under drastic plasma conditions.

The effect of surface fluorination on the wettability of high density polyethylene

High-density polyethylene (HDPE) samples have been fluorinated and oxyfluorinated for different times. Dynamic contact angle analysis was used to determine the effect of fluorine gas mixtures on the surface of HDPE. The total surface tension of HDPE increased drastically with the length of oxyfluorination treatment, but levelled off after longer treatments. Fluorination resulted in a marked decrease in the total surface tension of HDPE. During fluorination, the dispersive component of the surface tension decreased progressively with fluorination time, while the polar component increased initially but decreased again with longer fluorination treatments. This indicates that short fluorination times lead to increased wettability by polar liquids, while longer fluorination times have the opposite effect. Fluorinated and oxyfluorinated surfaces were exposed to elevated temperatures. Whereas it was found that fluorinated surfaces changed measurably, oxyfluorinated surfaces changed dramatically upon heating at 100 °C. Photoacoustic FT-IR spectroscopy indicated that this was probably due to migration of surface polar groups into the bulk of the polymer, rather than chemical change.

Changing of HDPE film due to surface effects during fabrication

Abstract High density polyethylene (HDPE) films have been fabricated using a presse-sheet system. The results of thermally stimulated discharge current (TSDC) analysis on these films are presented. The relationship between TSDC results and film manufacturing parameters are also presented. The following are the parameters investigated; cooling rate, film forming pressure and surface roughness. The surface roughness is shown to be dependent on the “forming plate” material. These materials investigated are Teflon TM , stainless steel and aluminum. Using Teflon TM as the forming plate causes the HDPE film to display a large TSDC homocurrent peak at 120°C. However, using stainless steel as the forming plate causes the HDPE film to display no TSDC peaks. Results of the characterization of HDPE surfaces immediately following the peeling of the forming plate materials are presented. Results of the characterization of plasma treated surfaces are presented before and after a second treatment using a low pressure glow discharge.

Surface modification of high-density polyethylene by plasma treatment

The extent of the surface crosslinking of high-density polyethylene (HDPE) under various plasma treatment conditions was investigated. The plasma modification efficiency was studied by surface energy and adhesive bond strength measurements. The results show that the surface crosslinking of HDPE takes place as soon as the HDPE is exposed to the plasma and that the crosslinking rate is a function of the plasma conditions. The surface energy and the adhesion of HDPE are greatly increased by the plasma treatment and these improvements are independent of the depth of surface crosslinking. Based on these results and our previous studies on the surface chemical composition and free radical density on the surface of HDPE after plasma treatment, the relationships among various surface changes and the surface modification efficiency are discussed.

Permeation of Selected Organic Compounds Through Untreated and Barrier-Treated High-Density Polyethylene

AbstractThe permeation rates of alkanes, alcohols, and aromatic hydrocarbons through untreated, fluorinated, and sulfonated high-density polyethylene (HDPE) were measured at a variety of temperatures and solvent compositions. The results were then analyzed to separate the individual contributions that solubility and diffusion make to the overall permeation rate. These results are discussed in terms of the chemical characteristics of the permeating constituents, and the barrier treatments on the HDPE surface.

Nucleation of Iow density polyethylene by high density polyethylene

The spherulitic morphology of semicrystalline polymers can be influenced by nucleating agents. With high concentrations of such agents a morphology results which consists of small spherulites. This effect is used, for example, to increase the optical transparency of films or to increase the toughness [1]. A very different nucleating effect occurs in the row nucleation. In this case certain constituents of a polymer, for example, the highest molecular weight fraction or a polymer of higher density added by co-crystallization from xylene are oriented by the special processing conditions and crystallize to produce fibrous crystals which then serve as backbones for the so-called shish-kebab morphology [2]. This morphology exhibits high mechanical moduli. Most nucleating agents are unfortunately nonpolymeric substances with very different chemical and physical properties with respect to the polymer. To overcome this disadvantage work is being carried out to produce nuclefiting agents without these disadvantages by modification of the basic polymer. So electron beam treated polypropylene acts as a suitable nucleant of the unmodified polymer [3]. During our search for a nucleating agent for low density polyethylene (LDPE) we found that high density polyethylene (HDPE) is very succesful for that purpose [4]. This nucleant produced from the same monomeric unit as the polymer to be nucleated is not only interesting for its very similar chemical and physical properties but it can be used to direct the morphology of LDPE regardless of the size of the spherulites. It is also possible to generate a modified shish-kebab structure with a "macroscopic" core of high density polyethylene surrounded by a LDPE matrix or a transcrystalline morphology in LDPE due to the high nucleation density of the HDPE surfaces in contact with LDPE. This letter deals with the principle of the PE-PE nucleation and some basic results. More detailed results will be published elsewhere. The low and high density polyethylenes used are large scale technical products. Both were used as powder, film or as massive pieces (injection moulded test bars) depending on the problem of investigation. The crystallite melting points are in the order of 403 K (HDPE) and 378 K (LDPE). In some cases the HDPE powder was purified by dissolving it in xylene (100 ° C; 0.5 wt %) and vacuum drying the recrystallized polymer after filtration from the cooled (20 ° C) solution. The specimens consisting of combinations of the two polyethylenes as foils or test bars in contact with each other or solid state mixed powders were prepared in special moulds in a oven. The temperature regime was as follows: melting at

Application of attenuated total reflection (ATR) infrared spectroscopy to the study of microstructural changes in high density polyethylene during sliding friction

Attenuated total reflection (ATR) infrared spectroscopy with radiation polarization has been applied to the study of the crystalline orientation, or texture, present at the surface of high density polyethylene (HDPE) which has undergone a dry friction test of long duration. This spectrometric method has been adapted from the work of G. P. Sung et al. (1984). The final superficial crystalline texture has been characterised as a function of the tribological conditions: the nature of the counterface (steel or glass), the applied load and the temperature of the counterface. In the case of steel counterfaces, one type of final texture exists at the surface of HDPE rubbed in the temperature range from 40°C to 80°C; from 80°C, a second type of final texture appears and gradually replaces the first as the temperature rises. The transition near 80°C was also observed in the course of a previous wear study and was attributed to partial melting of the polymer in the contact area. For glass counterfaces, the development of the final superficial texture as a function of temperature is not as simple as in the case of steel counterfaces. The observed phenomena can be explained in terms of poor adhesion of HDPE on glass (in test conditions) which causes irregular transfer and skidding phenomena. This interpretation was also deduced from the wear study mentioned above. The present work allows the study of the orientation of the crystallographic axes in the textured regions to be considered. The resulting information will allow the mechanisms of formation and degradation of the wear debris to be better understood.