Band 36, Heft 1

Infections by microorganisms are a major problem in public health throughout the world. Artificial materials, including biomedical goods, inherently lack defense against microbial development. Therefore, microbial cells can adhere on any type of artificial surface, particularly in a moist environment, and start to multiply to form a huge population. In this review, we will discuss a strategy for designing antimicrobial polymers and antimicrobial surfaces. Generally, there are five types of antimicrobial polymers: (a) polymeric biocides, (b) biocidal polymers, (c) biocide-releasing polymers, (d) bioactive oligopeptides, and (e) antimicrobial surfaces. Antimicrobial surfaces preventing the growth of microorganisms are a promising method to inhibit the spread of microbial infections. The antimicrobial surfaces can reject the attachment of microbes and/or kill microbes in the vicinity and can be designed to kill microbes on contact. It is recommended that the material surface not release biocidal substances, therefore preventing exhaustion of biocide release to kill microbes. Furthermore, the antimicrobial surfaces are desired to be nontoxic to human cells. The development of contact-active antimicrobial surfaces by grafting antimicrobial nanosegments onto the material surface will be an important topic in the future.

The fundamental cause of the proppant suspension behavior in hydraulic fracturing fluids lies in its internal microcosmic network structure and structural strength. In addition to chemical crosslinking, another method to form a network structure is established in this paper. Hydrophobically associating polyacrylamide and an anionic surfactant self-assembly process was applied to form a network structure. Compared with crosslinked hydroxypropyl guar gel, the new fracturing fluid even has better proppant suspending properties in static conditions. The capability does not result from crosslinkage but from reinforced physical associations between chains. The performance of this new fracturing fluid was tested and the results showed that it can fully satisfy the requirement of fracturing fluid. Field test shows excellent stimulation effects during its applications in 400 wells in eight oilfields in China.

Multiwalled carbon nanotubes (MWCNTs) and silicon dioxide microparticles (SiO 2 -MPs) were co-incorporated in poly(methyl methacrylate) (PMMA) matrices to form PMMA/MWCNT-SiO 2 -MP nanocomposite films. The SiO 2 -MP content in the nanocomposite films was varied at a fixed MWCNT content of 4 wt% to investigate the effect of SiO 2 -MP content on the electrical and tribological properties of the PMMA/MWCNT-SiO 2 -MP nanocomposite films. The co-incorporation of MWCNTs and SiO 2 -MPs dramatically lowered the electrical resistance of the nanocomposite films compared to that of the PMMA film, while higher fractions of SiO 2 -MPs more effectively promoted the decrease in the electrical resistance of the nanocomposite films by improving the conductive networks formed by the MWCNTs in the PMMA matrices. Although the friction of the nanocomposite films significantly increased with increased SiO 2 -MP content due to the promoted mechanical interlocking between the surface asperities of two mating surfaces, the wear of the nanocomposite films was much less severe than that of the PMMA film during ball-on-disc tribological tests.

The effect of two commercial melt strength enhancer additives, Paraloid BPMS-250 (BPMS) and Biostrength 700 (BIOS), on the thermal, rheological and morphological properties of polylactide (PLA) was studied. Thermal analyses showed that both the BPMS and BIOS additives decreased the ability of PLA to crystallize. The rheological tests indicated that zero-shear viscosity and storage modulus of the PLA/BPMS and PLA/BIOS blends were significantly increased with the additive content. These could be attributed to the entanglements between the PLA chains with those of the high molecular weight additive, creating a physical network which reduces the segmental mobility of PLA and improves the melt elasticity of the blend. The entanglement molecular weights ( M e ) of PLA/BPMS and PLA/BIOS blends were lower than those of unprocessed and processed PLA ( M e ≈4×10 4 g/mol), which suggests greater chain entanglements and a higher entanglement density ( v e ). The elongational viscosity ( η E ) and melt strength values were estimated using a screw-extrusion capillary rheometer, where the PLA/BIOS blends presented the highest values. Finally, scanning electron microscopy on the samples was carried out to assess the blend morphology.

The present work investigates the effect of organomodified nanoclay (ZW1) and butadiene-acrylonitrile copolymer terminated with different amine groups (amine-terminated butadiene-acrylonitrile, ATBN) on the properties and morphology of epoxy resin. The morphologies of the nanocomposites were analyzed by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The nanocomposites structure was confirmed by Fourier transform infrared (FTIR) spectroscopy, XRD and TEM. The properties evaluation showed that the polymeric modifier and nanoclays strongly influence the fracture toughness and flexural properties of the nanocomposites. Hybrid epoxy composites containing 1% ZW1 and ATBN rubbers showed improved fracture toughness and flexural properties in comparison with unmodified epoxy resin. FTIR spectra showed an increase in the hydroxyl peak height peak height of 3360 cm -1 due to reactive rubber incorporation. SEM micrographs of hybrid epoxy resin nanocomposites showed significant plastic yielding of the polymer matrix with stratified structures and more cavitations, explaining thus the enhancement of fracture toughness and flexural strength of the nanocomposites.

Mechanical properties of multi-walled carbon nanotubes (CNT) reinforced epoxy nanocomposites, with and without any structural defect, were investigated using different weight percent values of pristine and covalently functionalized CNT. First, nickel ferrite (NiFe 2 O 4 ) catalyst nanoparticles were prepared using the co-precipitate method followed by CNT growth via chemical vapor deposition, using acetylene as carbon feedstock. Through a combination of magnetic stirring and ultrasound vibration treatments in acetone, pristine, COOH-, or NH 2 -functionalized CNTs at 0.15, 0.60, 1.10 and 1.50 wt% were added to the Epon 828 epoxy. During each stage, extensive materials characterization was carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA)/differential thermal analysis (DTA) techniques. Tensile testing of the specimens revealed an increase in the elastic modulus and tensile strength values with maximum increase registered in the case of nanocomposites made from 1.1 wt% CNT-NH 2 (+73%) or CNT-COOH (67%) addition. The energy absorbed during impact testing also increased by 86% upon addition of 1.50 wt% CNT-NH 2 . The presence of a small notch in the nanocomposite specimens yielded superior mechanical properties to those of the neat epoxy. Such enhancement in the mechanical properties can be attributed to better CNT dispersion in the nanocomposites and good interfacial bonding, as confirmed from microstructural examination of the fractured surfaces.

Asymmetric mixed matrix membranes (MMMs) incorporating Cloisite15A (C15A) clay particles were prepared using solvent evaporation and phase inversion with polyethersulfone (PES) as the membrane matrix. C15A loadings varied at 1 wt% and 5 wt%. Membrane morphological and thermal properties were evaluated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Addition of the C15A favorably altered the microscopic structure of membranes from finger-like to homogeneous sponge-like structure as the loading increased. While the amorphous nature of MMMs was retained, the thermal stability was also found to be improved with a slight decrease in glass transition temperature ( T g ). PES/C15A1 MMM showed the best gas transport properties, with 37% and 65% improvement in CO 2 permeance and CO 2 /CH 4 selectivity, respectively. Unlike 1 wt%, the loss in selectivity shown by 5 wt% clay loadings suggested that the interphase voids and extent of silicate layers dispersion play a significant role in the overall performance of MMMs.

The resistance of three different types of masonry mortar, namely Portland cement mortar (CM), epoxy resin-based polymer CM (PCM) and polymer mortar (PM) to corrosive aqueous media have been presented in this study. Assessment was carried out on the basis of relative loss in mass and compressive strength of the mortar specimens after immersion in different corrosive solutions such as 10 vol% sulphuric acid, 10 vol% sodium hydroxide solutions and 10 wt% brine for various periods. CM specimens were found to be vulnerable in brine, acidic and alkaline mediums, while the mortar modified with epoxy resin showed excellent resistance to the above mentioned mediums. By contrast, PM evidenced appreciable stability even after immersion for a longer period in the same environment. Experimental results suggest that the epoxy-based masonry mortars can be used as a promising external rendering material to build infrastructures.

Three different poly(N-isopropylacrylamide-co-acrylic acid) [p(NIPAM-AA)] microgel samples were prepared using a precipitation polymerization method by varying the concentration of NIPAM and AA in aqueous medium. The microgels were used as microreactors to fabricate Ag nanoparticles (NPs) by in situ a reduction method. Fourier transform infrared (FTIR) and UV-visible spectroscopy were used to characterize the pure and hybrid microgels. The hybrid microgels with different AA content were used as catalysts for reduction of nitrobenzene (NB) into aniline. The progress of the reaction was monitored by a UV-visible spectrophotometer. The results show that the value of the apparent rate constant for catalytic reduction of NB decreases from 0.431 min -1 to 0.227 min -1 by increasing AA content from 3 mol% to 7 mol%, respectively. Decrease in apparent rate constant with increase of AA content can be attributed to an increase in hydrophilicity with increase of AA contents of the microgels. The increase in induction period with increase of AA contents indicates that diffusion of NB towards the catalytic surface becomes difficult due to an increase of hydrophilicity.

In this study, we propose a novel method for preparing continuous ultrahigh molecular weight polyethylene (UHMWPE) filaments by flash-spinning. The filaments were processed by calendaring to obtain the sheets. The morphology of the filaments and the sheets, the forming process, the optimal fabrication conditions, mechanical properties, spinning speed, and the rate of spinning of the filaments were investigated. The results showed that the filaments were composed of bunches of microfibers and the diameter of the filaments and the microfibers ranged from 0.15 mm to 0.22 mm and 0.2 μm to 5 μm, respectively. For a given concentration of 5 wt% of the UHMWPE, optimal specimens were obtained only when the temperature was in the range 150–210°C and the pressure was in the range 8–20 MPa. The spinning speed and the polymer consumption increased with enhancement in the pressure and the value reached as high as 47.2 m/s and 116.7 g/min, respectively. The properties and the spinning efficiency of the filaments revealed that flash-spinning is a potential method for manufacturing commercial products in various fields of application.

Indentation size effects have been observed in both polymers and metals but, unlike in metals, the origin of size effects in polymers is not well understood. To clarify the role of second order gradients of displacements, a model polymer is examined with spherical and Berkovich tips at probing depths between 5 and 25 μm. Applying different theories to determine the elastic modulus, it is found that with a pyramidal tip, the elastic modulus increases with decreasing indentation depth, while tests with the spherical tip yielded essentially constant values for the elastic modulus independent of indentation depth. The differences between these tips are attributed to second order displacement gradients, as they remain essentially constant with a spherical tip while they increase in magnitude with decreasing indentation depth applying a Berkovich tip.