Surface modification and degradation of poly(lactic acid) films by Ar-plasma

Surface modification of poly(lactic acid) (PLA) film surface by Ar-plasma was investigated by contact angle measurements and XPS in order to answer the following two questions. (1) Could the Ar-plasma modify the PLA film surfaces? (2) What chemical reactions occurred on the film surfaces during the Ar-plasma treatment? The Ar-plasma treatment did not lead to hydrophilic modification of the PLA film surface, but to degradation reactions of the PLA film. Poor modification may be due to instability of the carbon radicals formed from C—O bond scission in the PLA chains by the Ar-plasma.     

Oxygen plasma modification of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) film surfaces for tissue engineering purposes

Plasma glow‐discharge application is known as a technique to coat or modify the surfaces of various materials. In this study, the influence of oxygen rf‐plasma treatment on surface and bulk properties of a biological polyester, poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), were studied by determining water content and water contact angle, and by using X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The plasma‐treated films absorbed more water than the untreated film, and the absorbance increased with the total power applied. The water contact angles decreased and O/C atomic ratio increased on treatment, indicating that the material became more hydrophilic due to increases in the oxygen‐containing functional groups on the surface of the polymer. A direct relation could be observed when the O/C ratio was plotted against the total power applied (treatment duration × treatment power). SEM revealed a visual record of surface modification, the extent of which increased with increased total power. It was thus possible to alter the surface chemistry and relevant properties of the polymer film using oxygen plasma as a tool. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1285–1289, 2003     

Surface modification of PET films by pulsed argon plasma

The rf power was modulated (discharge on‐time of 10 μs and discharge off‐time of 50–500 μs), for pulsed argon (Ar) and oxygen (O₂) plasmas used to irradiate PET film surfaces to modify the film surfaces. From data regarding the contact angle for the modified PET film surfaces and chemical analyses with XPS, effects of the rf power modulation on the surface modification are discussed. The pulsed Ar and O₂ plasmas are effective in modification of the PET film surface. There is no difference in the contact angle between the pulsed plasma and the continuous plasma. Furthermore, the pulsed Ar plasma is advantageous in formation of hydroxyl groups on the PET film surfaces. The rf power modulation has a possibility to modify into peculiar surfaces. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2845–2852, 2002     

Poly(vinyl alcohol) hydrogel fixation on poly(ethylene terephthalate) surface for biomedical application

A surface modification technique was developed for the covalent immobilization of poly(vinyl alcohol) (PVA) hydrogel onto poly(ethylene terephthalate) (PET) to improve the biocompatibility of the film. The PET film was first graft copolymerized with poly(ethylene glycol) monomethacrylate (PEGMA) in the presence of ethylene glycol dimethacrylate (EGDMA) as crosslinker, and then oxidized with a mixture of acetic anhydride (Ac₂O) and dimethyl sulfoxide (DMSO) to produce aldehyde groups on the PET surface. Finally, the prepared PVA solution was cast onto the film and covalently immobilized on the film through the reaction between the aldehyde groups on the PET film and the hydroxyl groups of PVA. The good attachment of the PVA layer to the PET film was confirmed by observing the cross-section of the PET-PVA film using scanning electron microscopy (SEM). Heparin was immobilized on the PVA layered PET using two different methods, physical entrapment and covalent bonding, to further improve the biocompatibility of the film. Attenuated total reflectance (ATR) FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize the chemical composition of the surface modified films. The biocompatibility of the various surface modified PET films was evaluated using plasma recalcification time (PRT) and platelet adhesion.     

Grafting polymer from poly(ethylene terephthalate) films by surface‐initiated ATRP

Surface‐initiated atom transfer radical polymerization (ATRP) from poly(ethylene terephthalate) (PET) film was studied. Poly(methyl methacrylate) (PMMA), poly (acrylamide) (PAAM), and their diblock copolymer (PMMA/PAAM) on the surface of PET film were successfully prepared by surface‐initiated ATRP. The structures and properties of the modified PET film were characterized by FT‐IR/ATR, X‐ray photoelectron spectroscopy (XPS), measurements of contact angles, and scanning electronic microscopy (SEM). The results indicate that the surface properties of PET film were greatly improved by grafted polymer. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A new approach for selective surface modification of fluoropolymers by remote plasmas

Ethylene‐co‐tetrafluoroethylene (ETFE) and poly (vinylidene fluoride) (PVDF) films were exposed to the remote Ar, H₂, and O₂ plasmas. The modified polymer surfaces were characterized by X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact angle measurement. The plasma exposure led to weight loss and changes in the chemical composition on the polymer surface. Selective surface modification of fluoropolymers introduces various functional groups without altering the bulk properties. The results may be summarized as follows: the remote hydrogen plasma was the most effective in alternation from C? F to C? H (abstraction of fluorine). On the other hand, the remote oxygen plasma was unfavorable to abstract fluorine atoms, but effective in dehydrogenation (abstraction of hydrogen). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1012–1020, 2004     

Modification of poly(octadecene‐alt‐maleic anhydride) films by reaction with functional amines

Thin films of poly(octadecene‐alt‐maleic anhydride) on top of Si wafers and glass plates were modified by reactions with different functional amines to be used in future studies on the relevance of certain molecular surface properties for the covalent immobilization of proteins. For that aim, a strategy was developed and applied to convert the anhydride moieties of the copolymer by functional amines into side chains bearing hydrophilic groups of acidic (carboxylic acid, sulfonic acid), basic (amines), or neutral (poly(ethylene oxide) (PEO), glucose) character. The modification of the copolymer films was achieved through the two‐step formation of a cyclic imide, which was very stable in aqueous solution. Depending on the reactivity of the applied amine, the adjustment of the reaction time was suitable for the preparation of partially converted surfaces of the polymer film. Degrees of modification between 5 and 30% (according to X‐ray photoelectron spectroscopy data) were obtained. Annealing the modified polymer films induced efficient back‐formation of the anhydride groups. By reaction of the layered polyanhydrides with highly crosslinked diamines, amine‐functionalized polymer films were produced that were capable of binding secondary polyanhydride layers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1255–1266, 2003     

Comparative studies on surface modification of poly(ethylene terephthalate) by remote and direct argon plasmas

Surface modification of poly(ethylene terephthalate) (PET) film by an argon (Ar) plasma was investigated as a function of the distance from the Ar plasma zone. Changes in distance between the PET film and the Ar plasma zone had a strong influence on the surface modification of the film. The direct Ar plasma treatment (distance between the PET film and Ar plasma zone = 0 cm) was effective in hydrophilic surface modification, but heavy etching reactions occurred during the modification. On the other hand, the remote Ar plasma treatment (distance between the PET film and Ar plasma zone = 80 cm) modified the PET film surfaces to be hydrophilic without heavy etching reactions, although the hydrophilicity of the PET was lower than that by the direct Ar plasma. The remote Ar plasma treatment was distinguished from the direct Ar plasma treatment from the viewpoint of degradation reactions. The remote Ar plasma treatment rather than the direct Ar plasma treatment was an adequate procedure for surface modification and caused less polymer degradation on the film surface. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 808–815, 2001     

Grafting sulfobetaine monomer onto silicone surface to improve haemocompatibility

Silicone rubber has been used as a biomaterial for more than two decades and displays good mechanical and optical properties, but its chemical nature, poor antithrombogenicity, as well as its hydrophobicity, prevents its use in many demanding biomedical applications. In order to provide modified silicone with enhanced haemocompatibility, surface modification techniques were used. Ozonization was used to introduce active peroxide groups onto the silicone film surface and, subsequently, graft polymerization of N,N′‐dimethyl‐N‐methacryloyloxyethyl‐N‐(3‐sulfopropyl) ammonium (DMMSA), a zwitterionic sulfobetaine structure, onto the ozone activated silicone surface was conducted. Surface analysis was accomplished by means of attenuated total reflectance‐Fourier‐transform infrared (ATR‐FTIR), and X‐ray photoelectron spectra (XPS), and scanning electron microscopy (SEM) and contact angle measurement. ATR‐FTIR and XPS investigation confirmed the graft polymerization. The grafted film possessed a relatively hydrophilic surface as indicated by contact angle measurement. The blood compatibility of the grafted films was evaluated by platelet adhesion in platelet‐rich plasma (PRP) and protein adsorption in bovine fibrinogen using silicone film as the reference. No platelet adhesion was observed for the grafted films incubated in PRP for 120 min. The protein adsorption was reduced on the grafted films after incubated in bovine fibrinogen for 120 min. These results confirmed that the improved blood compatibility was obtained by grafting this new zwitterronic sulfobetaine structure onto silicone film. Copyright © 2003 Society of Chemical Industry     

Preparation and characterization of grafting polyacrylamide from PET films by SI‐ATRP via water‐borne system

The grafted homopolymer and comb‐shaped copolymer of polyacrylamide were prepared by combining the self‐assembly of initiator and water‐borne surface‐initiated atom transfer radical polymerization (SI‐ATRP). The structures, composition, properties, and surface morphology of the modified PET films were characterized by FTIR/ATR, X‐ray photoelectron spectroscopy (XPS), contact angle measurement, and scanning electronic microscopy (SEM). The results show that the surface of PET films was covered by equable grafting polymer layer after grafted polyacrylamide (PAM). The amount of grafting polymer increased linearly with the polymerization time added. The GPC date show that the polymerization in the water‐borne medium at lower temperature (50°C) shows better “living” and control. After modified by comb‐shaped copolymer brushes, the modified PET film was completely covered with the second polymer layer (PAM) and water contact angle decreased to 13.6°. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Surface modification of ethylene copolymers moulded against different mould surfaces-1. Surface enrichment by functional groups

A polymer surface chemical composition can be changed by the influence of different environments. Results presented from this study show that the surface of the mould influences the outermost polymer surface by enriching it with specific functional groups. This was done by moulding random copolymers against polymer films with low and high surface energies. The values presented are interpreted in terms of differences in surface energy between the mould surface and the copolymer. The random copolymers used were poly(ethylene-co-vinylacetate) (EVA) and poly(ethylene-co-acrylic acid) (EAA), both with a different comonomer content. The copolymers were moulded in contact with mould surfaces made of polymer films which were perfluorinated ethylene propylene copolymer (FEP), poly(tetrafluoroethylene) (PTFE), and poly(ethylene terephthalate) (PET). The resultant surfaces were characterized by X-ray photoelectron spectroscopy (XPS or ESCA) and contact angle measurements The surface content of acrylic acid functional groups increased in the case of EAA copolymer moulded against PET, and decreased when moulded against FEP as compared to the bulk concentration. EVA copolymers were found to be enriched in acetate groups when moulded against FEP and deficient when moulded against PET. The contact angle measurements together with the XPS measurements showed significant differences between materials moulded in contact with low and high energy surfaces. A low molecular weight additive (an internal release agent), in an EVA copolymer, was found to be enriched at the moulded polymer surface when a PET film was used as mould surface. A material transfer was also found to occur from the solid polymer films to the moulded polymer surface.     

Superficial modification in recycled PET by plasma etching for food packaging

An oxygen plasma treatment has been used to improve the adhesion of amorphous hydrogenated carbon (a‐C:H) films onto surfaces of recycled poly(ethylene terephthalate) (PET). Modifications produced by the oxygen plasma on the PET surface in chemical bonds and morphology were investigated by X‐ray photoelectron spectroscopy and atomic force microscopy, respectively. Contact angle measurements were used to study the changes in the surface wettability. Adhesion of the a‐C:H film onto the PET surface was investigated by the tape test method. It was observed that the improvement in film adhesion is in good correlation with the increase in surface roughness, due to plasma etching, and with the appearance of oxygen‐related functional groups at the surface. The results of this study indicate that a‐C:H‐coated recycled PET can be used in food packaging. The a‐C:H film could be used as a functional barrier to reduce or prevent migration of contaminants from the polymer to the package content. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Reactive modification and compatibilization of poly(lactide) and poly(butylene adipate‐co‐terephthalate) blends with epoxy functionalized‐poly(lactide) for blown film applications

Biodegradable blown films comprising of poly(lactide) (PLA) and poly(butylene adipate‐co‐terephthalate) (PBAT) were produced using epoxy functionalized‐poly(lactide) (EF‐PLA) reactive modifiers for rheological enhancement and compatibilization. The epoxy groups on the EF‐PLA modifiers react with PBAT forming an in situ copolymer that localizes at the blend interphase resulting in compatibilization of the polymer blend components. The EF‐PLA modified polymer blends have improved melt strength and the resultant films showed better processability as seen by increased bubbled stability. This allowed for blown films with higher PLA content (70%) compared to the unmodified control films (40%). The static charge build‐up typically experienced with PLA film blowing was decreased with the inclusion of EF‐PLA yielding films with better slip and softness. The compatibilization effect of the EF‐PLA modifiers resulted in significant improvement in mechanical properties. For example, dart test performance was up to four times higher than the control, especially at higher PLA concentrations. Therefore, the rheological enhancement and compatibilization effects of the EF‐PLA reactive modifiers make them ideally suited to create high PLA content films. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43310.     

An XPS investigation of polymer surface dynamics. I. A study of surface modified by CF4 and CF4/CH4 plasmas

For making the surface hydrophobic, poly(ethylene terephthalate) (PET) films were subjected to treatment by CF₄ and CF₄/CH₄ plasmas, and the PET fabrics, to impregnation (padding) with Oleophobol S for comparison. The electronic structure of the modified surface was differenentiated by XPS (ESCA). The surface dynamics upon heating and dipping into water was investigated by the angle-dependent XPS technique. Application of the XPS technique to these topics gave a wealth of information. © 1993 John Wiley & Sons, Inc.     

Surface functionalization of poly(lactic acid) film by UV‐photografting of N‐vinylpyrrolidone

The photoinitiated grafting of N‐vinylpyrrolidone (NVP) onto poly(lactic acid) (PLA) film with the use of benzophenone (BP) as the initiator, modified the natural hydrophobic PLA behavior to an hydrophilic film with desirable wettability. The surface photografting parameters‐percent conversion of monomer to overall photopolymerization (Cp), percent conversion of monomer to the photograft polymerization (Cg), and grafting efficiency (Eg) were calculated. The resulting film surface was analyzed using ATR‐FTIR and UV spectroscopy, derivative spectroscopy and water contact angle. Besides, we demonstrated that the grafted polyvinylpyrrolidone chains could easily react with iodine to form a complex as the homopolymer does with antibacterial activity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Role of carboxyl pendant groups of medium chain length poly(3‐hydroxyalkanoate)s in biomedical temporary applications

The poly(3‐hydroxyoctanoate) (PHO) is a biodegradable polyester containing hydrophobic side chains. One way to obtain more hydrophilic polyester consisted in the introduction of polar groups in the side chains. Carboxyl groups (PHO₇₅COOH₂₅) were introduced by chemical modifications. The role of carboxyl groups was investigated in the first part as potential support for cell seeding by studying the cell adhesion and proliferation, and in the second part as potential drug carrier by comparing the abilities of PHO and PHO₇₅COOH₂₅ to form degradable particles. Measurements of human bladder RT112 cells adhesion were done with or without collagen IV. Adhesive RT112 cells were counted by a colorimetric MTT test. The results showed that the COOH pendant groups of PHO₇₅COOH₂₅ films promoted cell adhesion after 4 h of incubation. The proliferation of cells is not improved after 4 days of incubation because of a reorganization of macromolecular chains and reorientation of COOH groups. This surface restructuration when the film was in contact with water was showed by contact angle measurements. We showed that the presence of COOH groups modified the hydrophobic/hydrophilic balance and enhanced the formation of particles. Stable lyophilisable particles were then obtained with diblock copolymer P(HO₇₅COOH₂₅‐b‐CL); the caprolactone block (CL) was necessary to improve particles stability. The results showed that the release of doxorubicin from the particles is enhanced in presence of hydrophilic and degradable block (PHO₇₅COOH₂₅). It was possible to obtain a degradable functional polyester based on PHO with carboxyl pendant groups to improve degradation rate by simple hydrolysis required for drug delivery systems. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

XPS study of the PET film surface modified by CO2 plasma: effects of the plasma parameters and ageing

Chemical modification of the PET surface by carbon dioxide plasma treatment has been studied using X-ray photoelectron spectroscopy (XPS). The plasma process results mainly in the formation of carbonyl, carboxyl, and carbonate groups at the PET surface. Under rather mild treatment conditions (low plasma power combined with a short treatment time), the formation of C-O bonds was found to be dominant, whereas the formation of highly oxidized carbon or double-bonded oxygen-containing groups required a high plasma power or a relatively long treatment time. The treatments performed under excessive conditions frequently led to degradation at the polymer surface. Angle-resolved XPS analyses performed on a freshly modified PET film showed a slight decrease in the O/C atomic ratio when the take-off angle (TOA) increased, indicating a relatively uniform distribution of oxygen within the sampling depth (estimated to be about 8 nm at 80° TOA). The chemical composition of the plasma-modified surface was found to be relatively stable on extended storage in air under ambient conditions. The decrease in oxygen-containing groups at the carbon dioxide-plasma-treated PET surface upon ageing is mainly ascribed to the surface rearrangement of macromolecular segments, the loss of oxygen-containing moieties introduced by the plasma treatment, and the possible migration of non-affected PET chains from the bulk to the surface region.     

Influence of casting substrate on the surface free energy of various polyesters

The surface free energies of various polyester surfaces have been determined from contact angle measurements using several liquid types. The geometric mean, the harmonic mean, and Fowkes' methods for obtaining the components of surface free energy have been compared for poly(L ‐lactic acid) (PLLA), poly(DL ‐lactic acid) (PDLLA), poly(hydroxybutyrate) (PHB), and poly(hydroxybutyrate‐hydroxyvalerate) (PHB–HV) copolymers. Polymer films were obtained by solution casting onto a number of smooth substrates, ranging from high‐energy surfaces (aluminum, mercury, glass, and freshly cleaved mica) to low‐energy surfaces [poly(ethyleneterephthalate) (PET), polytetrafluoroethylene (PTFE), and air]. Results show that the dispersion and polar surface free energy components of polyester surfaces cast against high surface energy (hydrophilic) substrates decrease with aging time toward a stable value. However, when cast against low surface energy substrates, the surface free energy of the resulting polymer/substrate‐contacting surface was independent of aging time. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 997–1008, 2002     

Titania Coatings on Polyethylene Terephthalate: Adhesion and XPS Studies

Titania coatings have been deposited on polyethylene terephtalate (PET) by the r.f. magnetron sputtering method in an oxygen-argon plasma from a titanium target and in a pure argon plasma from a titania target.

The dependence of the structural properties and the composition of the deposited films on the sputtering pressure and the r.f. power have been studied. In order to improve the adhesion strength between the titanium oxide films and their substrate, various cold plasmas are used to treat the polymer surface. These treatments' influence on the adhesion is studied by using the fragmentation test. The best results are obtained with a carbon dioxide plasma. The adhesion of the titania coating on the PET film also depends strongly on the deposition conditions. The highest values are reached when the titanium oxide films are deposited by the reactive sputtering process and when the elaboration parameters combine a total pressure as low as 0.8 Pa and a power density of 2.54 W cm^-2. The titania/PET interface, investigated by XPS, suggests the formation of Ti-O-C bonds in the first stage of the deposition of the titania films obtained by the reactive magnetron sputtering process, while no chemical reaction seems to occur between the PET and the titanium oxide film sputtered under a pure argon plasma.     

Surface modification of polysulfone membranes by low‐temperature plasma–graft poly(ethylene glycol) onto polysulfone membranes

A novel and general method of modifying hydrophobic polysulfone (PSF) to produce highly hydrophilic surfaces was developed. This method is the low‐temperature plasma technique. Graft polymer‐modified surfaces were characterized with the help of Fourier transform infrared attenuated total reflection (FTIR–ATR) and X‐ray photoelectron spectroscopy (XPS). Study results demonstrated that poly(ethylene glycol) (PEG) could be grafted onto the PSF membrane surface by low‐temperature plasma. The hydrophilic character of the modified surfaces was increased in comparison with that of the parent membrane. The contact angle for a modified PSF membrane was reduced apparently. We analyzed the effectiveness of this approach as a function of plasma operating variables including plasma treatment power and treatment time. Hence, plasma‐induced graft polymer modification of membranes can be used to adjust membrane performance by simultaneously controlling the surface hydrophilicity and hemocompatibility. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 979–985, 2000