R. Balkova

Plasma surface treatment and modification of glass fibers

New helical coupling plasma system for continuous surface treatment and modification (surface processing) of fiber bundles has been developed and tested for glass fibers. The system enables surface processing of single filaments and flat substrates as well. Surface processed glass fibers and their bundles were examined as reinforcements for glass fiber/polyester composite systems. Processing of fibers comprised a surface treatment using argon gas and a surface modification using hexamethyldisiloxane and vinyltriethoxysilane monomers. Interfacial and interlaminar shear strengths of plasma processed glass fiber/polyester systems were compared with those of untreated and commercially sized fibers.

The influence of surface modifications of glass on glass fiber/polyester interphase properties

Unsized glass fibers and planar glass substrates were subjected to low temperature plasma or wet-chemical process to modify the fiber or substrate surface and thus influence the interphase properties of the glass/polyester system. Plasma-polymerized thin films (interlayers) of organosilicon monomers (hexamethyldisiloxane and vinyltriethoxysilane) were deposited in an RF helical coupling plasma system on the glass surface. Commercial silane coupling agent (vinyltriethoxysilane) was coated onto an unmodified glass surface from an aqueous solution. Bonding at the glass/interlayer interface was analyzed by employing a micro-scratch tester together with an optical polarizing microscope for the planar samples. The results revealed that the adhesion bonding could be controlled by plasma process parameters. Scanning electron and atomic force microscopies enabled characterization of the film surface morphology. Chemical composition and chemical structure of prepared interlayers were characterized using X-ray photoelectron and infrared spectroscopies. Microcomposites (macrocomposites) were tested to evaluate the interfacial shear strength (short-beam strength) of the glass fiber/polyester interphase using the microbond test (short-beam shear). Our study indicated that the most efficient interphase could be prepared by plasma polymerization or wet-chemical process using the vinyltriethoxysilane monomer. The short-beam strength was 110% higher than that for untreated fibers in both cases.

XPS study of siloxane plasma polymer films

Abstract Plasma polymer films were deposited from hexamethyldisiloxane (HMDSO), dichloro(methyl)phenylsilane (DCMPS) and vinyltriethoxysilane (VTEO) on polished silicon wafers using a RF helical coupling deposition system. The composition of elements in the surface region (top 6–8 nm) of the deposited films was studied by X-ray-induced photoelectron spectroscopy (XPS) on an ADES 400 VG Scientific photoelectron spectrometer using MgK α (1253.6 eV) or AlK α (1486.6 eV) photon beams at the normal emission angle. Aging effects of plasma-polymerized (PP) HMDSO and DCMPS films stored under standard laboratory conditions were investigated by employing XPS. Post-deposition contamination and oxidation of pp-DCMPS and pp-HMDSO film was carefully observed. An increase in oxygen atoms on the film surface over time is accompanied by changes in bulk atomic concentrations. Sequential sputtering with an Ar ion-beam, together with XPS analysis, was used to measure concentration depth profiles in pp-HMDSO and pp-DCMPS films.

Functional interlayers in multiphase materials

Properties of a three-dimensional interlayer formed between the reinforcement (fiber) and the matrix are final properties of composite materials. It means that surface properties, chemistry of the coated fiber and the matrix play a very important role for achieving good adhesion (a primary factor for stress transfer from the matrix to the fiber) and strong bonding between the fiber and the matrix (to gain the best possible composite mechanical properties). The aim of this work was to prepare thin films with siloxane structure by glow discharge polymerization technique, and the film serves in the end as an adhesion interlayer between the glass fiber and the polyester resin. Plasma polymerized dichloro(methyl)phenylsilane, hexamethyldisiloxane and vinyltriethoxysilane thin films were deposited on the surface of glass slides, silicon wafers and glass fibers. Chemical composition of the plasma polymers on planar substrates was examined by Fourier transform infrared and X-ray photoelectron spectroscopies, surface morphology was studied by atomic force microscopy and surface properties were evaluated by contact angle measurements as the free surface energy. Adhesion between the plasma polymerized film and the glass slide was tested using fully PC-controlled scratch tester with the Rockwell diamond tip. Performance of glass fiber/polyester composite was assessed using a short beam shear and the test revealed that the plasma-polymerized vinyltriethoxysilane interlayer was the best and the interlaminar shear strength was 75% higher than that for untreated fibers.

The Effect of Processing of Polycaprolactone Films on Degradation Process Initiated by Aspergillus Oryzae Lipase

Poly(ϵ-caprolactone) (PCL) films with Mn = 18 kDa obtained by compression molding (CM) or solution casting (SC) were subjected to Aspergillus oryzae (AO) lipase action in a phosphate buffer at pH 7 at 37°C. The appearance of randomly oriented cracks on the surface of incubated PCL films accompanied by a decrease of the weight-average molecular weight (Mw) by 10% was observed after 42 days. The increase of crystallinity and surface morphology pattern of PCL samples exposed to AO lipase action supported the fact that the degradation proceeded in the amorphous phase of the aged films. SC films were degraded faster, probably due to better accessibility of ester bonds in the amorphous phase of spherulites.

Organoclays with carbosilane dendrimers containing ammonium or phosphonium groups

New composite materials could reveal attractive capabilities and favourable properties. Herein, we present novel layered nanocomposites consisting of inorganic clay (montmorillonite) and cationic carbosilane dendrimers. A comparative study was performed to evaluate cationic moieties (ammonium or phosphonium) and various generations of dendrimers (first, second and third) and their influence on the characteristics of resulting materials. The target nanocomposites were characterized by XRD, TEM, TGA, IR and MAS NMR. Interestingly, with multivalent dendritic cations, as opposed to monovalent cations, we detected a new connection of cationic species to the inorganic matrix by both ammonium and phosphonium dendrimers. To evaluate the mechanism of thermal degradation of the prepared materials, non-oxidative pyrolysis coupled with analysis of the resulting products by IR and MS was performed. To illustrate the catalytic activity of the as-prepared materials, selected samples were tested as catalysts in the cycloaddition of CO2 with epoxide (allyl glycidyl ether).

Degradation of polymeric bellows effecting life cycle of constant-velocity joint

ABSTRACT One broken and three new polymeric constant-velocity boots (bellows) being a spare part of a constant-velocity joint in two military vehicles were analyzed to identify basic composition and to determine if composition or structure of broken bellows differ. Infrared spectroscopy, differential scanning calorimetry, and thermogravimetry were used for analyses. Bellows for both vehicles are produced from thermoplastic elastomer. Broken bellows is chemically degraded and material just from the fracture is deformed plastically. The life cycle of bellows depends especially on applied stress and temperature (that about −20°C seems to be critical due to crystallization of soft segments).

The Impact of Graphite Source and the Synthesis Method on the Properties of Graphene Oxide

The purpose of this study is to insight more thoroughly into the structural properties of graphene oxide (GO) in particular of the type generated by Hummers method in relation with graphite precursor originating from different sources. The systematic study using elemental analysis (EA), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) was performed to reveal the changes of GO microstructure. The results revealed considerable influence of both the original graphite source and isolation procedure of GO by lyophilisation. Further, maintaining of GO in a form of aqueous colloidal dispersion is crucial for preservation of its unique properties. SEM results revealed the occurrence of associated GO blocks formed form identically oriented planes.