All issues / Volume 7 (2013) / Issue 5 (May)
This is an editorial article. It has no abstract.
The morphology of peroxide-cured, styrene crosslinked, bisphenol A-based vinyl ester (VE) resin was investigated by atomic force microscopy (AFM) after ‘physical’ etching with different methods. Etching was achieved by laser ablation, atmospheric plasma treatment and argon ion bombardment. Parameters of the etching were varied to get AFM scans of high topography resolution. VE exhibited a nanoscaled nodular structure the formation of which was ascribed to complex intra- and intermolecular reactions during crosslinking. The microstructure resolved after all the above physical etching techniques was similar provided that optimized etching and suitable AFM scanning conditions were selected. Nevertheless, with respect to the ‘morphology visualization’ these methods follow the power ranking: argon bombardment > plasma treatment > laser ablation.
Poly(ethylene glycol)-poly(tetrahydrofuran)-poly(ethylene glycol) (PEG-PTHF-PEG) triblock copolymer was synthesized by ring-opening polymerization of ethylene oxide using sodium alcoholate of PTHF as the macroinitiator. Its crystallization behavior and formation mechanisms of different crystal structures were studied. The study showed that the molecular weight of PEG-PTHF-PEG exhibited a significant effect on its crystallization: that is, with the increase of the copolymer’s molecular weight, the crystallizability of PTHF blocks decreased gradually, which led to the transition of copolymer from crystalline-crystalline to crystalline-amorphous. By adjusting the total molecular weight of triblock copolymer, the crystallization process can be effectively controlled, and as a result, different spherulite structures were obtained. Particularly, when PTHF blocks became amorphous, novel double concentric spherulites were observed. The morphological structures were studied by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), polarized optical microscopy (POM), and its crystalline process was investigated.
Polylactide (PLA) based nanocomposites of organically modified montmorillonite and micro-talc based microcomposites were prepared with different compositions and were UV-light irradiated under artificial accelerated conditions representative of solar irradiation. The chemical modifications resulting from photo-oxidation were followed by infrared (IR) and ultraviolet (UV)-visible spectroscopies. The infrared analysis of PLA photooxidation shows the formation of a band at 1847 cm–1 due to the formation of anhydrides. The filler addition provokes an increase of anhydride formation rate dependent on filler nature, amount and dispersion degree on the matrix. The main factors that influence oxidation rate are the total extension of polymer/filler interfacial area and the presence of transition metal impurities of clays.
A series of novel acetic acid lignin-containing polyurethane (LPU) films coupled with aminopropyltriethoxy silane (APTS) (LPUSi) or the mixture of APTS and trimethylol propane (TMP) (LPUSiT) were prepared. With 2% APTS addition, the crosslinking density increased, and the resultant films were endowed with good mechanical properties and water resistance. It was also found that the hydrogen bonding interaction between –NH and –C=O of urethane was destroyed, and new hydrogen bonds between APTS and LPU were formed. However, when APTS content was greater than 4%, significant phase aggregation were detected, resulting in poor mechanical properties and water resistance. In contrast, the crosslinking density, tensile strength and water resistance can be further improved with TMP addition at 2% APTS. The simultaneous addition of APTS and TMP was beneficial for phase mixing and the formation of uniform network. And the surface morphology of LPUSiT films became smoother and more homogeneous.
Poly(siloxane-urethane) (PSiU) networks based on a bis(hydroxyorgano) disiloxane chain extender, a trifunctional polyether polyol as a cross-linker, methylene-diphenyl diisocyanate and α,β-hydroxyethoxyethyl polydimethylsiloxane were synthesized in butyl acetate solution. The effect of the chain extenders and the cross-link density was investigated by using thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA), swelling, hardness and tensile strength measurements. Isotherm thermogravimetric analyses were carried out for selected polymer compositions at 120 and 170°C and also the changes in tensile strength were followed. The different chain extenders have a strong effect on the hard segment structure, thus on the thermal and mechanical behaviour. The phase separation of the soft and hard segments was indicated by the two or three well distinguished tanδ peaks, the maxima of which range within wide intervals depending on the polymer composition. The polymers of high cross-link density showed a very good thermal stability, high tensile strength (up to 68.7 MPa) and hardness (80–95 Shore A) even of high 13–36% dimethyl siloxane content. Changing the siloxane soft segment ratio and the cross-link density the physical properties can be adjusted.
The effect of various modifications/intercalations of halloysite and the combination of these modifications with in situ PP matrix modification was investigated with respect to the structure and properties of the polypropylene/halloysite nanocomposites. Hexadecyl-tri-methyl-ammonium-bromide (HEDA), 3-aminopropyltrimethoxysilane and urea were used as the intercalators/modifiers. The best intercalation was found for urea, although an unexpected insignificant impact on the mechanical properties also resulted as a consequence of the urea polarity and the significant decrease in PP crystallinity. However, the simultaneous application of 4,4!-diphenylmethylene dimaleinimide (DBMI) brought about an increase in the mechanical behavior by increasing the halloysite/PP affinity as a result of in situ matrix modification. This effect was further supported by coupling between the PP and halloysite (HNT) in the system containing urea-intercalated HNT. This can be explained by the occurrence of a urea-supported reaction between the imide ring of DBMI and the OH groups of the HNT, which resulted in the best mechanical behaviors achieved in this study.
This paper presents a novel strategy to prepare nano-lignin and its composites with natural rubber. The nanolignin was ontained by fabricating colloidal lignin-Poly (diallyldimethylammonium chloride) (PDADMAC) complexes (LPCs) via self-assembly technology. The characteristics of LPCs were investigated by zeta potential, dynamic light scattering (DLS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and ultraviolet – visible (UV-vis) absorption measurements. The results indicated that PDADMAC intensively interacted with lignin by cation-π and π-π interactions, and lignin particles were stable in aqueous solution with an average particle size less than 100 nm. LPCs accelerated the vulcanization of NR/LPCs nanocomposites. Morphological studies and Dynamic mechanical analysis (DMA) showed the homogeneous dispersion of LPCs in the NR matrix and the strong interfacial adhesion between them. The nanoscale dispersion of LPCs significantly enhanced the thermal stability and mechanical properties of NR/LPCs nanocomposites.