Surface modification of low‐density polyethylene films by UV‐induced graft copolymerization with a fluorescent monomer

Surface modification of argon plasma–pretreated low‐density polyethylene (LDPE) film via UV‐induced graft copolymerization with a fluorescent monomer, (pyrenyl)methyl methacrylate (Py)MMA, was carried out. The chemical composition and morphology of the (Py)MMA‐graft‐copolymerized LDPE [(Py)MMA‐g‐LDPE] surfaces were characterized, respectively, by X‐ray photoelectron spectroscopy (XPS) and by atomic force microscopy (AFM). The concentration of the surface‐grafted (Py)MMA polymer increased with Ar plasma pretreatment time and UV graft copolymerization time. The photophysical properties of the (Py)MMA‐g‐LDPE surfaces were measured by fluorescence spectroscopy. After graft copolymerization with the fluorescent monomer, the surface of the LDPE film was found to have incorporated new and unique functionalities. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1526–1534, 2001     

Calendar of events

The growth of Cu and Al films thermally evaporated onto polyethylene (PE) and polyethyleneterephthalate (PET) surfaces is followed in situ by XPS (X-ray Photoelectron Spectroscopy) and XAES (X-ray Auger Electron Spectroscopy) from the early submonolayer stages up to the completion of a metallic film. PE and PET surfaces were metallized first without any preliminary treatment. A second series of metallization experiments were run on the polymer surfaces but pretreated by a remote O₂ microwave plasma (2.45 GHz). These metal films have also been investigated by AFM (Atomic Force Microscopy) in air. Both metals are shown not to undergo chemical interaction with low surface energy polyolefin such as PE. While an abrupt interface is seen with A1, a diffusion of Cu into the bulk of the polymer is demonstrated. Large size clusters are evidenced by AFM in the initial steps of deposition. Cu and A1 are both shown to react with PET, but not in the same way. In the case of A1, the chemical interaction across the metal/polymer interface proceeds through an electron transfer from the metal toward the ester group O=C-O. With Cu, the chemical interaction is not so clearly evidenced and the Cu is found to diffuse into the PET. Oxygenated functionalities grafted by O₂ plasma on PE and PET are C-O, C=O, O-C-O, O-C=O, and O₂C=O. The roughness of the PE and PET surfaces is observed by AFM to increase with the plasma treatment. A metal-CO type complex is clearly observed with Al/treated PE and Cu/treated PET. No chemical interaction was observed at the Cu/treated PE interface.     

Morphology monitoring of PE/PBT blends by reactive processing

Polyethylene (PE)/poly(butylene terephthalate) (PBT) blends were in situ compatibilized during a processing operation by the addition of a partially hydroxylated ethylene vinyl acetate copolymer (EVAh). This copolymer, obtained from ethylene vinyl acetate (EVA), was as compatible with PE as EVA was before modification. In the presence of EVAh, the dispersion of PBT in the PE matrix was finer, and the interfacial adhesion was improved. These results are relevant for the compatibilization of PE/PBT blends. Moreover, such blends present good toluene barrier properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3568–3577, 2001     

Surface functionalization and biomolecule immobilization using plasma-generated free radicals on polypropylene

In this study are presented evidences for the functionalization of polypropylene surfaces accomplished in a sequential process: argon- or oxygen-plasma enhanced generation of free radical sites on polypropylene surfaces was followed by “in situ” gas phase derivatization in the absence of plasma using ethylene diamine, or propylene diamine; and an “in situ”, gas phase derivatization using oxallyl chloride or “ex situ” derivatization in the presence of glutaraldehyde. The free radicals’ presence on the plasma-exposed polypropylene surfaces was confirmed using “in situ” sulfur dioxide or nitric oxide labeling techniques. It was shown that the free radical sites readily react under “in situ” conditions with the stable chain-precursor components and generate the desired spacer-chain molecules revealed by ESCA analysis. Functionalized polypropylene substrates were used for immobilization of α-chymotrypsin in the presence of spacer-chain molecules. The activity of the immobilized α-chymotrypsin was found to be comparable to the activity of the free enzyme when the spacer molecules have been used.     

Proliferation rate of fibroblast cells on polyethylene surfaces with wettability gradient

Surface wettability on anchorage‐dependent cells has an important role in cell growth rate. In our previous studies, we prepared a wettability gradient on polyethylene (PE) surfaces using corona discharge treatment from a knife‐type electrode whose power increased gradually along the sample length. The PE surfaces were oxidized gradually with increasing power and characterized by Fourier transform infrared spectroscopy, contact angle goniometry, and electron spectroscopy for chemical analysis. The purpose of this study is to determine the rate of proliferation on polymer surfaces with different wettability. The behavior of cell growth for NIH/3T3 fibroblast cells attached on the polymer surfaces with different hydrophilicity was investigated using wettability gradient PE surfaces prepared by corona discharge treatment. They were investigated for the number of grown cells from 24 to 60 h in terms of surface wettability. From the slope of cell number on PE gradient surface versus culture time, the proliferation rates (number of cell/cm² · h) were calculated. It was observed that the proliferation rate was increased more on positions with moderate hydrophilicity of the wettability gradient surface than on the more hydrophobic or hydrophilic positions, i.e., 1111 (number of cell/cm² · h) of 57° of water contact angle at the 2.5‐cm position (P < 0.05). This result seems closely related to the serum protein adsorption on the surface: the serum proteins were also adsorbed more on the moderately hydrophilic surface. In conclusion, surface wettability plays an important role in cell adhesion, spreading, and proliferation on the polymer surfaces. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 599–606, 2004     

Morphology of the transparent IPN‐like system PE: (BMA‐co‐S)

In the study of interpenetrating polymer networks (IPN)‐like systems consisting of polyethylene (PE) and butyl methacrylate (BMA)–styrene (S) copolymer PE/(BMA‐co‐S), the effect of the crosslinker on the morphology of IPN by using electron microscopy and atomic force microscopy (AFM) was investigated. The IPN‐like system PE/(BMA‐co‐S) represents a two‐phase system with finely dispersed domains of crosslinked PE matrix. The interphase between dispersed domains and PE matrix is inhomogeneous and is considered the most interpenetrated part of this IPN‐like system. The size of the domains decreases with the content of crosslinker used. The AFM micrographs allowed the observation of PE lamellae with lengths of about 25 nm. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2615–2620, 2001     

Introduction of functional groups on polyethylene surfaces by a carbon dioxide plasma treatment

Poly(ethylene) (PE) films were treated with a carbon dioxide (CO₂) plasma to study the formation of oxygen-containing functional groups at the surface. Modified and nonmodified films were characterized by X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. During the CO₂ plasma treatment, the PE surface is etched and oxidized, yielding films with a very hydrophilic surface. The oxygen incorporation at the surface is fast and can be described by a combination of a zero-order incoraporation and a first-order etching process. Several oxygen functionalities such as carboxylic acid (approximately 14% of the oxygen persent), ketone/aldehyde (25%), and hydroxyl/epoxide (5–9%) groups were introduced at the surface by the plasma treatment. This was shown by using derivatization reactions for specific functional groups followed by XPS analysis. The wettability of the plasma-treated surface decreased when the films were stroed for prolonged periods of time in air. This aging process could not be completely reversed by immersion of the films in water. © 1995 John Wiley & Sons, Inc.     

Surface tailoring of biomedical polymers: An FTIR study

A multistep, surface-tailoring process of polymeric materials was developed with two consecutive plasma treatments and followed by derivatization reactions. In the first step, tetrafluoroethylene was plasma-polymerized, generating a highly crosslinked perfluoric surface layer. The next step introduced amine groups into the plasma polymer through exposure of the surface to plasma of ammonia. The reactive amine moieties were then used as anchoring sites for further derivatization. Finally, poly(ethylene glycol) chains were grafted onto the surface via a hexamethylene diisocyanate spacer. This method, aimed at the chemical modification of polymers for biomedical applications, was first demonstrated with poly(ethylene terephthalate) (PET) as a substrate in a previously published study (Cohn, D.; Stern, T. Macromolecules 2000, 33, 137). The aim of this study was to demonstrate the applicability of the method described previously to different polymers: poly(lactic acid), poly(ethylene) (PE), polystyrene (PST), poly(methyl methacrylate), a polybutadiene-based polyurethane (PEUOXAB-20), and Lycra. Fourier transform infrared (FTIR) spectroscopy was used to characterize the surface-modified substrates and the various control treatments. The results obtained were consistent with the derivatization scheme and in full agreement with the FTIR and ESCA results previously obtained for PET. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2203–2209, 2001     

Graft polymerization of acrylonitrile onto starch‐coated polyethylene film surfaces

Starch‐coated polyethylene (PE) films were prepared by immersing PE in a hot, jet cooked solution of starch. They were allowed to react with acrylonitrile (AN) in the presence of ceric ammonium nitrate initiator, and the graft polymerization that occurred produced starch‐g‐polyacrylonitrile (PAN) coatings that contained about 25 wt % grafted PAN. The starch‐g‐PAN coatings tightly adhered to the PE film surfaces. When grafted starch coatings were wetted with water and the surfaces vigorously rubbed, less than 20% of the coating was removed. The fact that PAN‐grafted coatings were not removed with boiling water provided further evidence for their strong adherence. When starch was removed from the coating by acid hydrolysis, the residual grafted PAN still remained adsorbed on the PE surface. Because the grafted coating was completely removed by treatment with refluxing 0.7N sodium hydroxide, there is apparently no chemical bonding between starch‐g‐PAN and PE. The dimensional changes associated with the evaporation of water from these PAN‐grafted coatings caused the films to curl during drying. Because the final shape of these coated films depends upon the presence or absence of water in the surrounding environment, these films may be considered to be a type of stimulus‐responsive polymer. Attempts to graft polymerize methyl methacrylate and methyl acrylate onto starch‐coated PE surfaces, under conditions similar to those used with AN, were unsuccessful. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3323–3328, 2003     

Effect of polyethylene‐graft‐maleic anhydride as a compatibilizer on the mechanical and tribological behaviors of ultrahigh‐molecular‐weight polyethylene/copper composites

Ultrahigh‐molecular‐weight polyethylene/copper (UHMWPE/Cu) composites compatibilized with polyethylene‐graft‐maleic anhydride (PE‐g‐MAH) were prepared by compression molding. The effects of the compatibilizer on the mechanical, thermal, and tribological properties of the UHMWPE/Cu composites were investigated. These properties of the composites were evaluated at various compositions, and worn steel surfaces and composite surfaces were examined with scanning electron microscopy and X‐ray photoelectron spectroscopy. The incorporation of PE‐g‐MAH reduced the melting points of the composites and increased their crystallinity to some extent. Moreover, the inclusion of the PE‐g‐MAH compatibilizer greatly increased the tensile rupture strength and tensile modulus of the composites, and this improved the wear resistance of the composites. These improvements in the mechanical and tribological behavior of the ultrahigh‐molecular‐weight‐polyethylene‐matrix composites with the PE‐g‐MAH compatibilizer could be closely related to the enhanced crosslinking function of the composites in the presence of the compatibilizer. Moreover, the compatibilizer had an effect on the transfer and oxidation behavior of the filler Cu particulates, which could be critical to the application of metallic‐particulate‐filled polymer composites in engineering. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 948–955, 2004     

Polyethylene grafted maleic anhydride to improve wettability of liquid on polyethylene films

Blends of linear low density polyethylene (LLDPE) and LLDPE grafted maleic anhydride (LLDPE‐g‐MA) were prepared by melt mixing. The surface of cast films with different contents and types of maleated PE were characterized through contact angle and wetting tension measurements, as well as attenuated total reflection IR spectroscopy. The tensile properties and light transmission of extruded films, as well as the performance of these films compared with commercial “antifog” films, for greenhouses were determined. The carbonyl polar groups on the surface of LLDPE/LLDPE‐g‐MA blends increased, and the equilibrium contact angles of water and dimethylformamide decreased when the content of maleated PE increased. Films made with these blends showed a noticeable reduction in water drop formation as the MA content was increased and when using LLDPE‐g‐MA of lower molecular weight. The light transmission through these films under condensation was improved when using increased contents of MA, which promotes better wetting of the water on the surface. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1802–1808, 2001     

Morphologies of polyethylene–ethylene/propylene/diene monomer particles in polypropylene‐rich polyolefin blends: Flake structure

Morphologies of polyethylene–ethylene/propylene/diene monomer (PE/EPDM) particles in 93/7 polypropylene (PP)/PE blends were investigated. SEM micrographs of KMnO₄‐etched cut surfaces and fracture surfaces of the blends revealed the existence of the “flake” structure. In the particles, crystalline PE formations with flake shape, which remain after etching, are called flakes. In addition to the PE‐crystalline flakes, amorphous PE, located between PE crystalline lamellae and EPDM rubber, complement the flake structure. The flakes are usually linked with the PP matrix, as seen in the heptane‐treated cut surfaces. These links, although observed with compatibilized samples, originate from the crystalline nature of PE particles, if no compatibilizer is added. Separately, the morphology of Royalene (consisting of high‐density PE and EPDM rubber, used as a PP/PE compatibilizer) was investigated by low‐voltage scanning TEM. The interaction of the components in the PE/EPDM blends can explain the formation of the flakes and toughening of the PP/PE blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3087–3092, 2003     

Toughening of polyamide 11 via addition of crystallizable polyethylene derivatives

BACKGROUND: Conventional rubber‐like toughening modifiers are soft and amorphous, and when used to toughen polyamide 11 (PA11) they commonly induce a decrease in the tensile strength and modulus. In this study, crystallizable polyethylene (PE) derivatives, i.e. linear low‐density polyethylene (LLDPE) and maleic anhydride‐grafted polyethylene (PE‐g‐MA), were adopted to toughen PA11. RESULTS: Compared to pure PA11, a highest improvement by a factor of eight in the impact toughness was achieved; also, the tensile strength and modulus could be maintained at a relatively high level. PE‐g‐MA acted as a compatibilizer for PA11 and LLDPE, bringing strong interfacial adherence, and especially a domain‐in‐domain morphology observed in PA11/PE‐g‐MA/LLDPE (70/10/20 by weight) blends. The observation that PA11 was toughened by the crystallizable PE derivatives is discussed in depth, based on the combined effect of surface crystallization of LLDPE on pre‐formed PA11 crystallites and interfacial compatiblization between PA11 and PE‐g‐MA. CONCLUSION: The crystallizable PE derivatives LLDPE and PE‐g‐MA were shown to be effective toughening modifiers for the proportions PA11/PE‐g‐MA/LLDPE 70/10/20 (by weight), which is considered to be an optimum composition: special domain‐in‐domain morphology was observed indicating a good dispersion of PE in the PA11 matrix and strong interfacial adherence between PE phase and PA11 phase. The reason why strength and modulus were maintained at a high level in the as‐prepared blends was attributed to the existence of rigid crystalline domains in PE. Copyright © 2009 Society of Chemical Industry     

Development of a new thermoplastic laminate system

In this investigation an all-olefin thermoplastic laminate was developed and characterized. Commingled glass-fiber polypropylene (PP) composite was used as skin and HDPE (PE) foam with closed cells as core. Infra-red heating was used for melting the surfaces of the substrates for surface fusion bonding with a cold press. Two tie-layer films, viz., ethylene-propylene copolymer (EPC) and HDPE/elastomer blend were used as hot-melt adhesives for bonding the substrates. Singlelap shear joints were prepared from PP composite and PE foam adherends with a bonding area of 25.4 mm × 25.4 mm to determine the bond strength. EPC tie-layer adhesive provided higher bond strength (2.68 × 10⁶ N/m²) to the all-olefin laminate than that based on HDPE/elastomer blend (1.93 × 106 N/m²). For EPC tie-layer-based laminates, a mixed mode of failure was observed in the failed lap shear samples: about 40% was cohesive failure through the tie-layer, and the rest of failure was interfacial, either at PP composite or PE foam surfaces. Environmental scanning electron micrographs (ESEM) revealed that in the process of surface fusion bonding, PE foam cells in the vicinity of interphase (800-μm-thick) were coalesced with high temperature and pressure. No macro-level penetration of the tie-layer melt front into the foam cells was observed. As the surface morphology of foam was altered due to IR surface heating and the PP composite bonding side had a resin-rich layer, the bonding situation was closer to that between two polymer film surfaces.     

Processing and characterization of LDPE/starch products

Low‐density polyethylene/plastisized starch blends varying in starch content were processed by conventional extrusion, injection‐molding, and film‐blowing techniques. Polyethylene‐g‐maleic anhydride (PE‐g‐MA) was used as a compatibilizer. X‐ray diffraction was used to investigate starch destructurization during extrusion and on subsequent processing. The effect of starch content on the blends was evaluated by mechanical property measurement and scanning electron microscopy. Starch, except for being a biodegradable material, can also act as a reinforcing agent. The reinforcing effect of starch was only realized in injection‐molded materials. Processing–structure–property relationships could explain this behavior. The present study also brought out the effect that the degree of molecular orientation existing in a polymeric matrix may have on the coupling performance of an adhesion promoter. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2548–2557, 2001     

Introduction of amino functionalities on ethylene-co-tetrafluoroethylene film surfaces by NH3 plasmas

In order to form active sites for grafting amino groups, a predominant elimination of fluorine atoms from fluoropolymers such as poly(tetrafluoroethylene), ethylene-co-tetrafluoroethylene co-polymer (ETFE) and poly(vinylidene fluoride) was carried out using the plasma irradiation technique, and the possibility that amino functional groups could be formed on the fluoropolymer surfaces was investigated. The NH₃ plasma irradiation led to considerable elimination of fluorine atoms from the fluoropolymers, as well as grafting of nitrogen functionalities. The formation of nitrogen-containing groups was strongly influenced by the magnitude of the W/FM parameter, and the NH₃ plasma operated at a low W/FM parameter of 79 MJ/kg was found to be preferable for the surface modification process. XPS spectra for the NH₃ plasma-modified surfaces showed that the NH₃ plasma attacked predominantly CF₂—CF₂ sequences rather than CH₂—CH₂ sequences in the ETFE polymer. The primary amino groups formed on the ETFE film surfaces were determined by fluorescence measurements. The concentration of the amino groups formed on the surfaces was not constant but varied according to the W/FM parameter. NH₃ plasma operated at a low W/FM parameter of 79 MJ/kg was found to be preferable in grafting amino groups on the ETFE film surfaces.     

Thiophene Deposition on Paper Surface by Pulsed RF-Plasma

The plasma duty cycle, in addition to power and exposure time, affects the surface atomic composition of thiophene plasma-treated paper. The elemental carbon and sulfur concentration increased from 56.7% to 78.6% and 0% to 13.4%, respectively, while oxygen decreased from 43.3% to 8.0% with the plasma treatment. Relatively large variations in the deposited film-like layer composition could be realized by changing plasma external parameters. The high-resolution (HR) C1s spectra of the thiophene plasma-treated paper clearly exhibit plasma-induced rearrangements and new sulfur functionalities on the paper surface. After a five-hour ex situ doping of thiophene plasma-treated papers with iodine, conductivity ranging from δ = 4.2E-2 to 4.1 S/cm was obtained. The low relative F/C atomic ratio after TFAA derivatization indicates that no hydroxyl groups were present on the paper surface after the thiophene plasma treatment.     

Influence of water addition on the modification of polyethylene surface by nitrogen atmospheric pressure plasma jet

Polyethylene (PE) has many excellent material properties (low density, high flexibility, good chemical resistance, etc.), and is widely used in industrial and medical fields. However, the practical applications of PE are sometimes limited due to its poor wettability. In this article, we employ pure nitrogen atmospheric pressure plasma jet (APPJ) and N₂-H₂O APPJ to hydrophilize PE surfaces. Wettability, time stability, chemical composition, micromorphology, and mechanical properties of the treated surfaces are investigated by contact angle measurement, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and electric digital display push–pull machine. The pure nitrogen APPJ can hydrophilize PE surfaces without inducing obvious microstructure changes, and relatively better wettability (water contact angle = 13°) could thereby be achieved. On the other hand, the N₂-H₂O APPJ creates micro/nanoscale pores on the treated hydrophilic surfaces, contributing to the better time stability and lower tensile strength. The results reported here clearly demonstrate the great potential of nitrogen APPJs with different water mixing ratios in controlling surface wettability and microstructures of polymer surfaces. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47136.     

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

Summary Chitosan and chitosan hydrogel were immobilized on both the inside and outside surfaces of high density polyethylene (HDPE) tubes with 2.5×4 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). Received: 6 December 2000/Revised version: 15 February 2001/Accepted: 16 February 2001     

Studies of sulfonated polyethylene for biliary stent application

Palliative treatment for obstructive jaundice by endoscopic biliary stent insertion is a recent commonly used method. Unfortunately, stent reobstruction may occur within 3 to 6 months as a result of bacterial adhesion and formation of biofilm. Bacterial adhesion was postulated as the initial step of stent clogging and the bacterial enzyme activity of β‐glucuronidase led to the deposition of calcium bilirubinate. In this study, surface sulfonation of the polyethylene lumen was postulated to improve the patency of the biliary stent. Surface modification with sulfonated group formation was carried out with fuming sulfuric acid containing 20 wt % sulfuric trioxide (SO₃). The reaction time varied from 1 to 3 h at room temperature. ATR‐FTIR and ESCA techniques showed that the surface amount of sulfonated functionalities increased with sulfonation time. The contact angle of the sulfonated PE, determined by the sessile drop technique, decreased compared to that of unmodified PE, but cannot be detected by the captive bubble method because of the high surface hydrophilicity. SEM micrographs indicated that the sulfonated PE inner lumen remained relatively smooth after extended sulfonation reaction. Adhesion of Escherichia coli to the sulfonated PE stents after 48‐h bile perfusion was about 10‐ to 20‐fold less than that to the unmodified PE, as observed by SEM and surface spreading method. These results indicated that the surface sulfonated groups could effectively decrease the adhesion of E. coli in human bile, probably attributable to the hydrophilic repellence between the bacterial cell membrane and sulfonated groups. This finding suggested that the sulfonated PE tubing could prolong the patency period of plastic stents and may be of great potential as a biliary stent in a real clinical setting. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2450–2457, 2004