All issues / Volume 5 (2011) / Issue 11 (November)
This is an editorial article. It has no abstract.
Maleic anhydride (MA) is incorporated into poly(lactic acid) (PLA)/poly(propylene carbonate) (PPC) blends to modify its properties through melt compounding. It is interesting to note that the toughness of PLA/PPC blends can be improved by 1355% while the strength is almost kept constant by adding very low content (as low as 0.9%) of MA into the blends. However, higher MA content in the blends leads to decrease in strength and further increase in toughness indicating an obvious plasticizing effect, while MA is shown to have no effect on the toughness of neat PLA. Rheological, scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA) studies have been carried out to understand the above results. It is believed that the improvement in mechanical performance originated from the largely retained molecular weight of PPC and improved interfacial interaction after processing. And relative large amount of MA in the blends is shown to mainly plasticize the PPC phase rather than the PLA phase. Such an effective method could provide PLA based biodegradable polymer blends with novel properties for industrial applications.
Poor filling occurs during the injection molding process of micro- or nano- scale patterns mainly because the hot polymer melt rapidly cools and its skin quickly solidifies upon contact with the mold surface. In this study, it is proposed to use Polyethylene terephthalate (PET) film coated with patterned polyurethane acrylate (PUA) as an effective thermal barrier. It can significantly hinder heat transfer into the mold during the molding process and thus may keep the melt viscosity low for longer duration. As a result, the replication would be improved not only during the filling phase but also during the packing phase. In order to verify the validity of the use of polymeric stamper, the melt-film interface temperature was evaluated by numerical simulation. Experimental results indicated that patterns possessing widths within the range of one to tens of micrometers and a height of approximately 10 µm were successfully filled and demolded.
The aim of this work is to investigate the photochromic behavior and nano-structuration capacity of azo-polymers with different architectures and main chain flexibilities, modified with donor/acceptor groups. As a function of the chemical structure and the substitution degree, the azo-polymers can generate physical interactions and lead to different polymer chain conformational re-organization under optical excitation. Nano-structuration experiments were performed on samples with different chemical structures. Surface relief gratings have been realized both in poly(chloromethyl styrene) and polysiloxanes polymers. The complexity of the phenomena that take place under optical excitation of the azo-benzene molecules are reflected by the samples behavior during the nano-structuration process. Preliminary tests to determine the ability of the azo-polysiloxanic films to support cell growth were performed. The films showed remarkable properties to sustain both cell adhesion and proliferation.
Electron beam immobilization of functionalized poly(vinyl methyl ether) thin films on polymer surfaces – Towards stimuli responsive coatings for biomedical purposes
S. Gramm, J. Teichmann, M. Nitschke, U. Gohs, K.-J. Eichhorn, C. Werner
Vol. 5., No.11., Pages 970-976, 2011
Vol. 5., No.11., Pages 970-976, 2011
Thin films of poly(vinyl methyl ether) (PVME) were immobilized on polystyrene surfaces by low energy electron beam cross-linking. Structure retention as well as the thermo-responsive swelling behavior in aqueous media were studied by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and spectroscopic ellipsometry respectively. The physical properties of the thermo-responsive coatings can be controlled in a wide range by adjusting the irradiation parameters. To allow for a variety of biomolecular functionalization strategies, the concept was extended by adding reactive sites to the system. For that purpose a mixture of PVME and the copolymer of PVME and maleic acid was applied, that possesses a similar stimuli-responsive behavior.
Preparation and characterization of nanocomposites based on COOH functionalized multi-walled carbon nanotubes and on poly(trimethylene terephthalate)
A. Szymczyk, Z. Roslaniec, M. Zenker, M. C. Garcia-Gutierrez, J. J. Hernandez, D. R. Rueda, A. Nogales, T. A. Ezquerra
Vol. 5., No.11., Pages 977-995, 2011
Vol. 5., No.11., Pages 977-995, 2011
Poly(trimethylene terephthalate) nanocomposites containing COOH functionalized multi-walled nanotubes were synthesized with in situ polymerization method. The microstructure of the nanocomposites was studied by SEM, in terms of the dispersion state of the nanotubes and the polymer–nanotube interface. The thermal behaviour, mechanical properties and conductivity of these resultant PTT/MWCNTs nanocomposites were studied. The effect of the presence of MWCNTs on cold crystallization of PTT was monitored by dielectric spectroscopy. From thermal analysis study, it is found that the melting temperature and glass transition temperature are not significantly affected by the addition of MWCNTs. The crystallization temperature of PTT matrix is affected by the presence of CNTs. Nanocomposites have slightly higher degree of crystallinity than neat PTT and their thermo-oxidative stability is not significantly affected by the addition of MWCNTs. The study of the isothermal cold crystallization of amorphous PTT and its nanocomposites monitored by dielectric spectroscopy reveals that the presence of MWCNTs have influence on crystallization rate, especially at higher concentration (0.3 wt%). In comparison with neat PTT, the MWCNTs reinforced nanocomposites posses higher tensile strength and Young’s modulus at low MWCNTs loading (0.05–0.3 wt%). In addition, all nanocomposites show reduction of brittleness as compared to the neat PTT. The electrical percolation threshold was found between 0.3 and 0.4 wt% loading of MWCNTs.
Porous, poly(D,L-lactide-co-glycolide) (PLGA) materials were prepared by physicochemical solvent/non-solvent method with polyvinyl pyrrolidone (PVP) as a stabilizer and with silicone oil, paraffin, hydrogen peroxide or sodium chloride as a porogen. The obtained PLGA particles without porogens are non-agglomerated, uniform and with particle size on the submicron scale. The formation of intracellular reactive oxygen species (ROS) was measured spectrophotometrically using a fluorescent probe, 2,7-dichlorofluorescein diacetate (DCFH-DA) and it is shown that PLGA nanospheres are not inducers of intracellular formation. Porous PLGA scaffolds obtained in the experiment with sodium chloride as porogen and water as solvent of the porogen had apparently uniform pore morphology with spheroidal pore in shape and well controlled three-dimensional interconnected network. PLGA scaffolds are highly porous with similar porosity values. The degradation of PLGA nanoparticles and PLGA porous materials were studied in phosphate buffered saline as a degradation medium. The samples were characterized by Infrared Spectroscopy (IR), X-ray difractometry, Zeta potential measurements, Scanning Electron Microscopy (SEM) and Ultraviolet Spectroscopy (UV).
While adhesiveness is required for polymer surfaces in special applications, tacky surfaces are generally undesirable in many applications like automotive interior parts. The tackiness of polymer surface results from a combination of composition and additivation, and it can change significantly in natural or accelerated ageing. Since there is no established, uniform method to characterize surface tack, the major focus of the present work was on the development of an objective quantification method. A setup having a soft die tip attached to a standard tensile tester was developed aiming for correlation to the human sense of touch. Three different model thermoplastic polyolefin (TPO) compound formulations based on a high-impact isotactic polypropylene (iPP) composition with varying amounts and types of anti-scratch additives were used for these investigations. As the surface tack phenomenon is related to ageing and weathering, the material’s examination was also performed after various intervals of weathering. The developed method allows a fast assessment of the effect of polymer composition variations and different additive formulations on surface tack and gives identical rankings as the standardized haptic panel.
Polyethylene terephthalate (PET) fibers containing different contents of β-nucleating agent (β-NA) were meltspun from a reconstructive melt flow index rheometer at 270°C, and then blended with polypropylene (iPP). The supermolecular and phase structure of the composite were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD). For the pure PET fiber reinforced iPP, the interfacial region was mainly composed of α-modification, though it has been demonstrated that PET fiber shows weak nucleating ability towards iPP matrix. More interestingly, when the amount of β-NA introduced into the PET fiber exceeds a critical value, the transcrystalline layer will be notably dominated by β-modification. This method to prepare β-transcrystallinity is remarkably different from those through stress or temperature control. The present results provide a facile and promising technique to prepare rich β-transcrystallinity under stress-free conditions.