Jörg Friedrich

Surface Modification of Ultra-high Molecular Weight Polyethylene Membranes Using Underwater Plasma Polymerization

Ultra-high molecular weight polyethylene membranes were modified and subsequently polymer coated using the underwater plasma produced by glow discharge electrolysis. This plasma pretreatment generated various O-functional groups among them OH groups have dominated. This modified inner (pore) surface of membranes showed complete wetting and strong adhesion to a hydrogel copolymerized by glow discharge electrolysis also. The deposited hydrogel consists of plasma polymerized acrylic acid crosslinked by copolymerization with the bifunctional N,N′-methylenebis(acrylamide). Tuning the hydrogel hydrophilicity and bio-compatibility poly(ethylene glycol) was chemically inserted into the copolymer. Such saturated polymer could only be inserted on a non-classic way by (partial) fragmentation and recombination thus demonstrating the exotic properties of the underwater plasma. The modification of membrane was achieved by squeezing the reactive plasma solution into the pores by plasma-induced shock waves and supported by intense stirring. The deposited copolymer hydrogel has filled all pores also in the inner of membrane as shown by scanning electron microscopy of cross-sections. The copolymer shows the characteristic units of acrylic acid and ethylene glycol as demonstrated by infrared spectroscopy. A minimum loss in carboxylic groups of acrylic acid during the plasma polymerization process was confirmed by X-ray photoelectron spectroscopy. Additional cell adhesion tests on copolymer coated polyethylene using IEC-6 cells demonstrated the bio-compatibility of the plasma-deposited hydrogel.

Influence of water addition on the structure of plasma-deposited allyl alcohol polymer films

One hundred and fifty nanometre thick polymer films made of allyl alcohol and H2O addition were deposited onto aluminium substrates using the radio-frequency (rf) pulsed plasma mode. The structure–property relationships of polymer films were studied in dependence on the precursor ratio allyl alcohol-water. Both the regularity of structure and composition of such thin films in comparison to chemically polymerized allyl alcohol were investigated using by bulk-sensitive Fourier transform infrared spectroscopy (FTIR) in the spectral range of 4000–500 cm−1 as well as surface-sensitive X-ray photoelectron spectroscopy (XPS). The intention of this work was to increase the yield in OH groups by addition of water to the allyl alcohol precursor. For an unambiguous identification of the functionality of the deposited films, the OH groups were labelled with trifluoroacetic anhydride and subsequently measured by XPS as well as quantitatively by FTIR. As expected, the O/C ratio grew with increasing water admixture by oxidation of both the plasma polymerized allyl alcohol layer to preferably aldehyde and/or carboxylic acid groups. In contrary, the concentration of OH groups in the deposited polymer film decreases dramatically with increasing admixture of water to the allyl alcohol plasma. It has been shown that the additional water has produced preferably higher oxidized C-Ox species with two or three C–O bonds. This fits also very well with the observation that almost no deuterium is introduced into the surface of plasma polymer if D2O was added instead of H2O.

Plasma deposition of adhesion-promoting polymer layers onto polypropylene for subsequent covering with thick fire retardant coatings

Melamine resins were used as 50-μm-thick fire retardant coatings for polypropylene (PP). Preceding deposition, low-pressure plasma polymer films of allyl alcohol were coated onto PP to improve the adhesion between PP and melamine resin coatings. The efficiency of such fire retardant coatings was confirmed by flame tests. The plasma-deposited polymer and the dip-coated melamine resin films were characterized by Fourier transform infrared-attenuated total reflectance spectroscopy and X-ray photoelectron spectroscopy (XPS). The adhesion of coatings was measured using a 90° peel test with a doubled-faced adhesive tape. To detect the locus of failure, the peeled layer surfaces were inspected using optical microscopy and XPS. Thermal properties of PP thick melamine resin-coated films were analyzed by thermogravimetric analysis.

Cured melamine systems as thick fire-retardant layers deposited by combination of plasma technology and dip-coating

Melamine and melamine resins are widely used as fire-retardants for polymer building materials. Cured melamine systems are used in heat-sensitive items, such as furniture and window frames and sills. In this work, differently cured methylated poly(melamine-co-formaldehyde) (cmPMF) resins were used as fire-retardant coverage for poly(styrene) (PS) and poly(ethylene) (PE) building materials. Such polymer layers should have several tenths of micrometers thickness to produce sufficient fire retardancy. These thick layers were produced by dip-coating. To promote sufficient adhesion of such thick coating to the polyolefin substrates, also in the case of high temperatures occurring at fire exposure, the polymer substrates were firstly coated with a few hundred nanometer thick adhesion-promoting plasma polymer layer. Such thin plasma polymer layers were deposited by low-pressure plasma polymerization of allyl alcohol (ppAAl). It was assumed that the hydroxyl groups of ppAAl interact with the melamine resin; therefore, ppAAl was well suited as adhesion promoter for thick melamine resin coatings. Chemical structure and composition of polymer films were investigated using infrared-attenuated total reflectance and X-ray photoelectron spectroscopy (XPS). Peel strengths of coatings were measured. After peeling, the peeled polymer surfaces were also investigated using optical microscopy and XPS the layers for identification of the locus of peel front propagation. Thermal properties were analyzed using TGA (thermo-gravimetric analyses). Finally, the fire-retardant properties of such thick coated polymers were evaluated by exposure to flames.

One-step synthesis of silver nanoparticles embedded with polyethylene glycol as thin films

Abstract Silver nanoparticles (Ag NPs) embedded and stabilized with polyethylene glycol (PEG) were synthesized as colloids by heating and exposure to sunlight (direct and indirect) irradiation as green method. The deposition of Ag NP-PEGs onto Si-wafers was also made using the electrospray ionization deposition technique. The generating of Ag NP-PEGs as colloids was examined by UV–visible spectroscopy (UV–Vis) and transmission electron microscopy (TEM). The chemical composition of the resulted nanocomposites was evaluated by Fourier transform infrared (FTIR) and that of thin-film surfaces by X-ray photoelectron spectroscopy. Structure–property relationships of Ag-PEG nanocomposites prepared by heating were discussed in dependence on the time of heating. The UV–visible results confirmed the successful synthesis of spherical Ag NPs with absorption peaks at a wavelength of λ = 413 nm for the heating method and at λ = 418 as well as 449 nm for direct and indirect exposure to the sunlight. Ag-PEG nanocomposite thin films showed excellent antimicrobial activity. These results revealed that the Ag-PEG nanocomposites thin films can be used as potential materials in biomedical applications.

Carbonaceous nanostructures in hydrocarbons and polymeric aerobic oxidation mediums

Abstract The presumptive antioxidative activity of fullerenes C 60 /C 70 , original and purified multiwalled carbon nanotubes, carbon nanofibers of platelet and herringbone structures was studied using model reaction based on a liquid-phase oxidation of cumene initiated by 2,2′-azobisisobutyronitrile. Kinetic measurements of oxidation rates clearly showed that the effect of inhibition in the model oxidative reaction in the presence of the nanoparticulated carbon samples strongly depends on the presence of metallic traces (Co, Fe, Ni). The effective rate constants for the addition of cumyl radicals (R•) to the central nervous system (CNS) have been precisely determined. The obtained kinetic data make it possible to specify the level of intrinsic antioxidative activity of the CNS and scope of their rational use in polymer composites. Polyethylene composites appropriately filled with CNS exhibit extremely heightened thermal and thermo-oxidative stability.

Tuned interactions of silver nanoparticles with ZSM-5 zeolite by adhesion-promoting poly(acrylic acid) deposited by electrospray ionization (ESI)

Abstract The electrospray ionization (ESI) method was used for deposition of thin films of poly(acrylic acid) (PAA) on Cu/ZSM-5 (5 wt.% Cu) and Ag–Cu/ZSM-5 (1 wt.% Ag and 4 wt.% Cu) composites. For comparative purposes, the ZSM-5 zeolite was synthesized under hydrothermal conditions and loaded with PAA under the same treating conditions as the composites. This method allowed the formation of uniform polymer films of controlled thickness on conductive substrates. The structural characteristics were characterized by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, atomic force microscopy and X-ray diffraction (XRD). The deposited PAA layer over ZSM-5 acts as a common dispersing and stabilizing agent through coordination-driven guest-templated polymer via interaction of Ag+ and Cu2+ with carboxylic acid groups, thus increasing and controlling the adhesion and the release of metallic species. A short exposure to light and temperature has reduced the metal ions to Cu0 and Ag0 metallic nanoparticles. The results of XRD analysis let suggest that the interaction of Cu and Ag with carboxylic groups of PAA inhibits the formation of large metallic silver particles. These samples were being studied for their potential as antibacterial agents toward the bacterial strains such as Staphylococcus pneumonia, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa as Gram positive and Gram negative bacteria, respectively. Aspergillus fumigatus and Candida albicans as Fungi were also evaluated. The Cu/ZSM-5 and Ag–Cu/ZSM-5 nanocomposites coated with a 10 nm thick PAA layer exhibit significant antibacterial activity.

The peculiar behavior of functionalized carbon nanotubes in hydrocarbons and polymeric oxidation environments

Abstract It has been shown that selected types of substituents are able to vary the oxidative behavior of multi-walled carbon nanotubes. Such substituents investigated were sterically hindered secondary amino groups bonded in grafted piperidine units and covalently bonded bromine groups. Their interference and activity was preliminary determined in the model cumene and then in oil diesel fraction and low density polyethylene oxidation reactions. Results obtained indicate that chemical linking of amine moieties containing –NH groups directly to the carbon nanotubes core significantly increases their intrinsic anti-oxidative capacity while the grafting of Br-groups provokes the opposite functioning of the pristine samples. This inference was proved by thermogravimetric and differential thermal analysis of the polyethylene composites and experiments on profound aerobic oxidation of petroleum naphthenic fraction derived from the commercial Baku oils blend diesel cut.