γ‐Irradiated poly(tetrafluoroethylene) particle‐filled low‐density polyethylene. I. Effect of silane coupling agents on mechanical,thermal, and morphological properties

Poly(tetrafluoroethylene) (PTFE) scraps were recovered as a filler material for low‐density polyethylene (LDPE) after they were degraded by Co‐60 γ‐rays under atmospheric conditions to make small‐size powder. The powder PTFE, which was called secondary PTFE (2°‐PTFE), was melt mixed with LDPE and then extruded to obtain 200 µm films. The mechanical and thermal properties and also the morphology of the fractured surface of these 2°‐PTFE–filled LDPE were studied. It was found that the addition of 2°‐PTFE resulted in thermofilm property of LDPE but it slightly decreased the thermal oxidative temperature of LDPE. The tensile strength and ultimate elongation of LDPE were found to decrease with the addition of 2°‐PTFE. However, when it is compared to the addition of virgin PTFE into LDPE, 2°‐PTFE shows better mechanical properties due to the presence of oxy groups which are capable of interacting with the main matrix. A further improvement in mechanical properties was achieved by silane coupling agent treatment of 2°‐PTFE. Silane coupling agents were found to enhance the interfacial adhesion between 2°‐PTFE and LDPE. The study on the fractured surfaces by scanning electron microscope revealed this adhesion between these two polymers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 866–876, 1999     

Plasma‐induced solid‐state polymerization modified poly(tetrafluoroethylene) membrane for pervaporation separation of aqueous alcohol mixtures

Acrylamide (AAm) solid state polymerization was induced using argon plasma to improve the pervaporation performance of poly(tetrafluoroethylene) (PTFE) membranes (PTFE‐g‐PAAm) in aqueous alcohol mixtures. The surface morphology, chemical composition, and hydrophilicity changes in the PTFE and PTFE‐g‐PAAm membranes were investigated using ATR‐FTIR, SEM, AFM, X‐ray photoelectron spectroscopy, and water contact angle measurements. The surface hydrophilicity rapidly increased with increasing Ar exposure time, but decreased after longer Ar exposure time because of the degradation in the PTFE‐g‐PAAm membrane grafted layer. Compared with the hydrophilicity of the pristine PTFE membrane (water contact angle = 120°), the argon plasma induced acrylamide (AAm) solid‐state polymerization onto the PTFE surface (water contact angle = 43.3°) and effectively improved the hydrophilicity of the PTFE membrane. This value increases slowly with increasing aging time and then reaches a plateau value of about 50° after 10 days of storage under air. The pervaporation separation performances of the PTFE‐g‐PAAm membranes were higher than that of the pristine PTFE membrane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:909–919, 2006     

Improved adhesion of poly(tetrafluoroethylene) by NH3-plasma treatment

—Surface modification of poly(tetrafluor oethylene) (PTFE) by NH₃-plasma treatment was investigated by means of contact angle measurement, XPS, and ATR FT/IR spectroscopy. The modified surfaces were adhesively bonded to nitril rubber. The NH₃-plasma irradiation made PTFE surfaces hydrophilic. The contact angle of water on the modified PTFE surface was 16 deg, and the surface energy was 62-63 mJ/m². The NH₃-plasma irradiation improved adhesion between PTFE and nitril rubber using a phenol-type adhesive. The peel strength of the joints reached 8.1 × 10³ N/m. Carbonyl and amido groups were created on PTFE surfaces by the NH₃-plasma irradiation. The mechanism of the improvement of adhesion by the NH₃-plasma irradiation is discussed.     

Part II. Properties of the grafted and sulfonated membranes

The physical and chemical properties of polystyrene grafted and sulfonated polytetrafluoroethylene (PTFE‐graft‐PSSA) membranes prepared by radiation‐induced grafting of styrene onto commercial PTFE films using simultaneous irradiation technique followed by a sulfonation reaction are evaluated. The investigated properties include water uptake, ion exchange capacity, hydration number and ionic conductivity. All properties are correlated with the amount of grafted polystyrene (degree of grafting). The thermal stability of the membrane evaluated by thermal gravimetric analysis (TGA) is compared with that of original and grafted PTFE films. The membrane surface structural properties are analysed by electron spectroscopy for chemical analysis (ESCA). Membranes having degrees of grafting of 18 % and above show a good combination of physical and chemical properties that allow them to be proposed for use as proton conducting membranes, provided that they have sufficient chemical and mechanical stability. © 2000 Society of Chemical Industry     

Radiation‐initiated graft polymerization of methylmethacrylate onto poly(tetrafluoroethylene): Characterization by 1H‐NMR

A broad‐line ¹H‐NMR study was carried out to examine the local structure of poly(methylmethacrylate) (PMMA) grafted onto Poly(tetrafluoroethylene) (PTFE). The NMR spectra were observed for three different samples with 1.0, 5.4, and 7.0 wt % PMMA over the temperature range from 150 to 380 K. With the help of selectively deuterated PMMA (PMMA‐d₅ and PMMA‐d₈)‐grafted samples, the NMR spectra were analyzed in terms of two components—a Gaussian (G) component, and a Lorentzian (L) component. Based on the second moments (〈ΔH²〉) analysis, the L and G components were attributed to the ¹H–¹H dipolar interactions within one CH₃ group and the interactions of CH₃ groups that are closely located in aggregated PMMA chains. Combining the results with the temperature dependence of 〈ΔH²〉 and the angular resolved XPS, the location and rotational motion of PMMA grafted onto PTFE are discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1386–1394, 1999     

Surface photografting polymerization of vinyl acetate (VAc), maleic anhydride (MAH), and their charge transfer complex (CTC). III. VAc(3)

Vinyl acetate (VAc) was grafted onto low‐density polyethylene (LDPE) substrates by UV irradiation with benzophenone (BP) as the photoinitiator. BP preabsorbed film samples and BP precoated film samples were prepared in advance and applied as the substrates onto which VAc was photografted, together with the method in which BP was dissolved in VAc directly. In addition, the efficiency of the polymerizations applying the preirradiation technology was examined. The conversion percent, grafting percent, and grafting efficiency were determined by a gravimetric method. The contact angles of the grafted films against water were also measured. The results show that BP preabsorbing and precoating were favorable to grafting polymerization, especially the BP precoating method, which was due to its simple operation and the ease of controlling the amount of BP. The diffusion of BP and VAc through the substrates proved to be an important factor for grafting polymerization. Through UV irradiation, dormant groups can be introduced onto LDPE film, which may be activated again by UV irradiation or by heating, leading to the formation of free radicals. Grafting polymerization can be initiated during the activation process in the presence of monomer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1426–1433, 2001     

Proton exchange membranes prepared by simultaneous radiation grafting of styrene onto poly(tetrafluoroethylene‐co‐hexafluoropropylene) films. I. Effect of grafting conditions

The simultaneous radiation grafting of styrene onto poly(tetrafluoroethylene‐co‐hexafluoropropylene) (FEP) films was studied at room temperature. The effects of grafting conditions (type of solvent, irradiation dose, dose rate, and monomer concentration) were investigated. The degree of grafting was found to be dependent on the investigated grafting conditions. The dependence of the initial rate of grafting on the dose rate and the monomer concentration was found to be of 0.5 and 1.3 orders, respectively. The results suggest that grafting proceeds by the so‐called front mechanism in which the grafting front starts at the surface of the film and moves internally toward the middle of the film by successive diffusion of styrene through the grafted layers. Some selected properties of the grafted films were evaluated in correlation with the degree of grafting. We found that the grafted FEP films possess good mechanical stability, which encourages their use for the preparation of proton exchange membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 220–227, 2000     

Synthesis of poly(tetrafluoroethylene)/poly(butadiene) core-shell particles and their graft copolymerization

This article describes how to convert the unreactive surface of poly(tetrafluoroethylene) (PTFE) into poly(styrene-co-acrylonitrile) (SAN). Composite particles with a crosslinked poly(butadiene) (PB) shell covered over a PTFE core were prepared by an emulsifier-free seeded emulsion polymerization of butadiene in the presence of PTFE latex. It was found that the increase in the PB crosslink density resulted in depressing the formation of PB secondary particles. Then, styrene and acrylonitrile were able to graft onto PB shell in high efficiency of 70%. SAN-modified PTFE/PB core-shell particles could eventually be dispersed homogeneously in a SAN matrix. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:185–190, 1998     

Argon plasma treatment-induced grafting of acrylic acid onto expanded poly(tetrafluoroethylene) membranes

Expanded poly(tetrafluoroethylene) (ePTFE) is used in facial reconstruction surgery. For some specific applications ePTFE is required to interface with the underlying bone. However, ePTFE is classified as bioinert thus limiting integration at the bone-tissue interface. The incorporation of functional groups onto the ePTFE surface was carried out in the current study using argon plasma treatment-induced grafting of acrylic acid (AA) to improve integration. High surface coverage (grafting extent from XPS of up to 90%) was achieved and resulted in high hydrophilicity and high water uptake (up to 470% of the grafted PAA mass). The contribution of species present in the plasma to the incorporation of functional groups onto the ePTFE surface was evaluated with charged species observed to play an equally important role to neutral species in this study. The effects of sample position in the plasma chamber as well as the effect of grafting parameters (plasma power, monomer concentration, and reaction time) on the grafting outcome were evaluated. The mechanical properties of the AA grafted membranes under tensile, compression and nanoindentation were evaluated.     

Lamination of conductive polypyrrole films to poly(tetrafluoroethylene) films via interfacial graft copolymerization

A simple technique for the lamination of a conductive polymer film to an inert dielectric polymer film was demonstrated. The electrochemically synthesized and p‐toluenesulfonic acid‐doped polypyrrole (PPY) film was laminated simultaneously to the argon plasma‐pretreated PTFE film during the thermally induced graft copolymerization of the PTFE surface with a functional monomer. The graft copolymerization was carried out using glycidyl methacrylate (GMA) monomer containing 20% v/v hexamethyldiamine (HMDA) and in the absence of any polymerization initiator. Thermally induced graft copolymerization of the GMA monomer on the PPY surface was minimal. The lap shear and T‐peel adhesion strengths of the laminates were found to be dependent on the GMA graft concentration on the PTFE surface, which, in turn, was affected by the plasma pretreatment time of the film. To increase the GMA graft concentration for the enhancement of adhesion strength, the plasma‐pretreated PTFE surfaces were premodified via UV‐induced graft copolymerization with GMA prior to the simultaneous thermal graft copolymerization and lamination process. The modified surfaces and interfaces were characterized by X‐ray photoelectron spectroscopy (XPS). Through XPS measurements of the delaminated surfaces, it was found that the PPY/PTFE laminates failed predominantly by cohesive failure inside the PTFE substrate. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 716–727, 2001     

Surface modification of poly(tetrafluoroethylene) film by plasma graft polymerization of sodium vinylsulfonate

Poly(tetrafluoroethylene) (PTFE) surface was modified by the graft polymerization of sodium vinylsulfonate, and the chemical composition of the graft-polymerized PTFE surface was analyzed by X-ray photoelectron spectroscopy. Peroxides were formed on the PTFE surface by a combination procedure of argon plasma irradiation and air exposure, and the graft polymerization of sodium vinylsulfonate was initiated by the peroxide groups at 65–80°C. The peroxide concentration is 3 × 10⁺¹³ to 5 × 10⁺¹³ numbers/cm². The average degree of polymerization of the graft polymers was 3.4 × 10³. The graft polymer is distributed over the PTFE surface, but part of the PTFE surface remains uncovered. The coverage with the graft polymer is 43%. The PTFE surface graft polymerized with sodium vinylsulfonate was somewhat hydrophilic, but the hydrophilicity was lower than that of the PTFE surface modified by plasma treatment. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 77–84, 1997     

Emulsion grafting of vinyl acetate onto preirradiated poly(3‐hydroxybutyrate) film

Vinyl acetate (VAc) was grafted onto poly(3‐hydroxybutyrate) film by a preirradiation method. Grafting reactions were carried out in VAc/water/surfactant emulsion, VAc/water, and VAc/methanol systems. For emulsion grafting, Nonion L‐4 was ascertained to be the optimum surfactant with respect to the stability of a single emulsion layer. The emulsion with a 10 : 1 (w/w) ratio of VAc to surfactant yielded the highest degree of grafting: 23%. The grafting efficiency in the emulsion and the water and methanol solvents were evaluated. The results indicated that the grafting efficiency of the emulsion was 100 times that of VAc/methanol when the same 2 wt % VAc was used in the grafting reaction. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Processing and characterization of multilayer films of poly(ethylene terephthalate) and surface-modified poly(tetrafluoroethylene)

Multilayer films were prepared from poly(tetrafluoroethylene) (PTFE) and poly(ethylene terephthalate) (PET) films together with using an adhesion promoting layer (tie-layer) consisting of ethylene-methyl acrylate-glycidyl methacrylate (E-MA-GMA) terpolymer and low density polyethylene (LDPE) blend. Na/naphthalene treatment and subsequent acrylic acid grafting were applied on the surfaces of PTFE for chemical modification. FT-IR spectroscopy, XPS analysis and surface energy measurements were performed to characterize the modified PTFE films. The analyses showed defluorination and oxidation of PTFE surface, and supported the acrylic acid grafting. The surface energy of modified surfaces enhanced with respect to unmodified one, which promoted adhesion. The multilayers were subjected to T-peel tests to measure the adhesion strength between PET and modified PTFE. Peel strength between the films increased with increasing E-MA-GMA amount in the tie-layer. A proportional dependence of peel strength on Na/naphthalene treatment time was observed for multilayers containing acrylic acid grafted or ungrafted PTFE. From SEM analysis, it was observed that the texture of the PTFE surface after modifications became rougher when compared to untreated PTFE. The peeled surfaces were also analyzed by SEM. The micrographs evidence that the energy absorbing mechanism is the plastic deformation of the tie-layer, which is responsible for obtaining high peel strengths.     

Grafting of poly(3‐hydroxyalkanoate) and linoleic acid onto chitosan

Poly(3‐hydroxy octanoate) (PHO), poly(3‐hydroxy butyrate‐co‐3‐hydroxyvalerate) (PHBV), and linoleic acid were grafted onto chitosan via condensation reactions between carboxylic acids and amine groups. Unreacted PHAs and linoleic acid were eliminated via chloroform extraction and for elimination of unreacted chitosan were used 2 wt % of HOAc solution. The pure chitosan graft copolymers were isolated and then characterized by FTIR, ¹³C‐NMR (in solid state), DSC, and TGA. Microbial polyester percentage grafted onto chitosan backbone was varying from 7 to 52 wt % as a function of molecular weight of PHAs, namely as a function of steric effect. Solubility tests were also performed. Graft copolymers were soluble, partially soluble or insoluble in 2 wt % of HOAc depending on the amount of free primary amine groups on chitosan backbone or degree of grafting percent. Thermal analysis of PHO‐g‐Chitosan graft copolymers indicated that the plastizer effect of PHO by means that they showed melting transitions T_ms at 80, 100, and 113°C or a broad T_ms between 60.5–124.5°C and 75–125°C while pure chitosan showed a sharp T_m at 123°C. In comparison of the solubility and thermal properties of graft copolymers, linoleic acid derivatives of chitosan were used. Thus, the grafting of poly(3‐hydroxyalkanoate) and linoleic acid onto chitosan decrease the thermal stability of chitosan backbone. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:81–89, 2007     

Adsorption and desorption properties of expanded poly(tetrafluoroethylene) films grafted with DMAEMA and their regeneration

An investigation was undertaken on the adsorption and desorption properties of the expanded poly (tetrafluoroethylene) (ePTFE) films grafted with 2‐(dimethylamino)ethyl methacrylate (DMAEMA) to anionic dye anions with one to three sulfonic groups in response to temperature changes. The amount of adsorbed metanil yellow (MY) anions increased with the grafted amount and most of the dimethylamino groups appended to the grafted PDMAEMA chains worked as an adsorption site to MY anions for the DMAEMA‐grafted ePTFE (ePTFE‐g‐PDMAEMA) films with the grafted amounts of higher than 1.1 mmol/g. When the dye‐anion‐adsorbed ePTFE‐g‐PDMAEMA films were alternately immersed in water at two different temperatures, dye anions were desorbed from the ePTFE‐g‐PDMAEMA films at higher temperatures without any chemical agents. The amount of desorbed dye anions increased with an increase in the temperature of water from 40 to 80°C. Desorption of dye anions is caused by either deprotonation of dimethylamino groups appended to the grafted PDMAEMA chains or thermosensitive contraction of the grafted PDMAEMA chains. These results indicate that the ePTFE‐g‐PDMAEMA films can be applied as a regenerative ion‐exchange membrane for adsorption and desorption processes of anionic compounds in response to the temperature change. The thermally regenerative ion‐exchange properties of the ePTFE‐g‐PDMAEMA films was superior to that of the PE‐g‐PDMAEMA films reported in our previous article in the fact that the total degree of desorption was higher for the ePTFE‐g‐PDMAEMA films. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Radiation‐induced grafting of styrene onto poly(tetrafluoroethylene) (PTFE) films. I. Effect of grafting conditions and properties of the grafted films

Radiation‐induced grafting of styrene onto poly(tetrafluoroethylene) (PTFE) films was studied by a simultaneous irradiation technique. Grafting was carried out using γ‐radiation from a ⁶⁰Co source at dose rates of 1.32–15.0 kGy h⁻¹ at room temperature. The effects of type of diluent, dose rate, irradiation dose, and the initial monomer concentration in the grafting solution on the degree of grafting were investigated. The degree of grafting was found to be strongly dependent upon the grafting conditions. The dependence of the initial rate of grafting on the dose rate and the initial monomer concentration in the grafting solution was found to be in the order of 0.6 and 1.7, respectively. The chemical structure and the crystallinity of the grafted PTFE films were studied by means of Fourier‐transform infrared, (FTIR), electron spectroscopy for chemical analysis (ESCA) and X‐ray diffractometry (XRD). © 2000 Society of Chemical Industry     

Surface modification of poly(tetrafluoroethylene) with pulsed hydrogen plasma

Surface modification of polymers by pulsed plasma has been investigated to minimize degradation reactions occurring at the same time as the surface modification reactions. The hydrogen radical, ion, and electron concentrations in the hydrogen plasma were simulated as a function of the elapsed time after turning off the discharge. The contact angle measurement showed that hydrogen plasma treatment, regardless of pulsed or continuous plasma, led to degradation reactions as well as defluorination and oxidation on PTFE surfaces. The degradation reactions of PTFE chains initiated by the pulsed hydrogen plasma were not as vigorous as those by the continuous hydrogen plasma. A combination of the on‐time/off‐time of 30/270μs in the pulsed hydrogen plasma was efficacious in modifying PTFE surfaces. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 340–348, 2002     

Adhesion enhancement of thermally evaporated aluminum to surface graft copolymerized poly(tetrafluoroethylene) film

Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) film via UV-induced graft copolymerization with glycidyl methacrylate (GMA) and 1-vinylimidazole (VIDz) were carried out to improve the adhesion with evaporated aluminum metal. The surface compositions of the graft copolymerized PTFE films were studied by X-ray photoelectron spectroscopy (XPS). The adhesion strength of the evaporated aluminum to the surface graft copolymerized PTFE film was affected by the type of monomer used for graft copolymerization, the graft concentration, the plasma post-treatment of the graft copolymerized PTFE surface prior to metallization, and the extent of thermal treatment after metallization. The optimum T-peel adhesion strengths of the Al/PTFE laminates were in excess of 10 and 5 N/cm, respectively, for the GMA and VIDz graft copolymerized PTFE films. These adhesion strengths are significantly higher than those obtained between the evaporated aluminum and the pristine or plasma-pretreated PTFE film. The mechanism of adhesion enhancement and the failure of the metal-polymer assembly were also investigated. It was observed that the failure occurred within the PTFE film. The strong adhesion between Al and PTFE arises from the charge-transfer interaction between the Al atom and the epoxide moiety of the grafted GMA polymer, as well as from the fact that the graft chains are covalently tethered on the PTFE film surface as a result of the grafting process.     

Interfacial adhesion between polyurethane binder and poly(tetrafluoroethylene) powder in bonded solid lubricant films

Poly(tetrafluoroethylene) (PTFE) powder was irradiated with ⁶⁰Co γ-rays to improve its dispersing ability in polyurethane (PU) as a binder. The bonded solid lubricant films of the irradiated PTFE were prepared on an AISI 1045 steel block by spraying and curing at ambient temperature, with PU as the binder. The tribological properties of bonded solid lubricant films with the PTFE pigment volume fraction were examined on a ring-on-block friction and wear tester. The interfacial adhesion between the PU binder and PTFE powder was investigated using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), immersion heat, and X-ray photoelectron spectroscopy (XPS). It was found that γ-ray irradiation increases the activity of the PTFE powder surface and improves the interfacial adhesion between the PTFE powder and the PU binder, which is helpful for improving the wear resistance of the corresponding bonded solid lubricant films.     

Mechanochemical preparation of a novel polymeric photostabilizer for poly(vinyl chloride)

The preparation of a novel polymeric photostabilizer was carried out via the vibromilling of poly(vinyl chloride) (PVC) powder, a reactive light stabilizer (r‐LS), and a peroxide initiator in ball‐containing jars with a planetary ball mill for a certain time. The effects of the initiator content, milling time, and temperature on the grafting ratio were studied with gravimetric analysis and intrinsic viscosity measurements. Fourier transform infrared and ultraviolet–visible spectra were used to investigate the structural development of the mixture of the r‐LS and PVC during vibromilling. The results showed that the r‐LS was grafted onto PVC chains successfully, and the aforementioned factors had a significant effect on the grafting ratio. The optimum preparation conditions were 0.5 wt % initiator, 8 h, and 20°C. A grafting mechanism is proposed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010