All issues / Volume 6 (2012) / Issue 1 (January)
This is an editorial article. It has no abstract.
Hybrid thin films containing nano-sized inorganic domains were synthesized from UV-curable acrylate-modified waterborne polyurethane (WPU-AC) and monodispersed colloidal silica with coupling agent. The coupling agent, 3-(trimethoxysilyl)propyl methacrylate (MSMA), was bonded onto colloidal silica first, and then mixed with WPU-AC to form a precursor solution. This precursor was spin coated, dried and UV-cured to generate the hybrid films. The silica content in the hybrid thin films was varied from 0 to 30 wt%. Experimental results showed the aggregation of silica particles in the hybrid films. Thus, the silica domain in the hybrid films was varied from 30 to 50 nm by the different ratios of MSMAsilica to WPU-AC. The prepared hybrid films from the crosslinked WPU-AC/MSMA-silica showed much better thermal stability and mechanical properties than pure WPU-AC.
Nanocrystalline cellulose was modified by 3-aminopropyl-triethoxysilane (KH550). The modified nanocrystalline cellulose (MNCC) was further investigated to partially replace silica in natural rubber (NR) composites via coagulation. NR/MNCC/silica and NR/nanocrystalline cellulose (NCC)/silica nanocomposites were prepared. Through the comparison of vulcanization characteristics, processing properties of compounds and mechanical properties, compression fatigue properties, dynamic mechanical performance of NR/MNCC/silica and NR/NCC/silica nanocomposites, MNCC was proved to be more efficient than NCC. MNCC could activate the vulcanization process, suppress Payne effect, increase 300% modulus, tear strength and hardness, and reduce the heat build-up and compression set. Moreover, fine MNCC dispersion and strong interfacial interaction were achieved in NR/MNCC/silica nanocomposites. The observed reinforcement effects were evaluated based on the results of apparent crosslinking density (Vr), thermo-gravimetric (TG) and scanning electron microscopic (SEM) analyses of NR/MNCC/silica in comparison with NR/NCC/silica nanocomposites.
Thermo-sensitive shape-memory polymers (SMP), which are capable of memorizing two or more different shapes, have generated significant research and technological interest. A triple-shape effect (TSE) of SMP can be activated e.g. by increasing the environmental temperature (Tenv), whereby two switching temperatures (Tsw) have to be exceeded to enable the subsequent shape changes from shape (A) to shape (B) and finally the original shape (C). In this work, we explored the thermally and magnetically initiated shape-memory properties of triple-shape nanocomposites with various compositions and particle contents using different shape-memory creation procedures (SMCP). The nanocomposites were prepared by the incorporation of magnetite nanoparticles into a multiphase polymer network matrix with grafted polymer network architecture containing crystallizable poly(ethylene glycol) (PEG) side chains and poly(ε-caprolactone) (PCL) crosslinks named CLEGC. Excellent triple-shape properties were achieved for nanocomposites with high PEG weight fraction when two-step programming procedures were applied. In contrast, single-step programming resulted in dual-shape properties for all investigated materials as here the temporary shape (A) was predominantly fixed by PCL crystallites.
A simple approach for synthesis, characterization and bioactivity of bovine bones to fabricate the polyurethane nanofiber containing hydroxyapatite nanoparticles
F. A. Sheikh, M. A. Kanjwal, J. Macossay, N. A. M. Barakat, H. Y. Kim
Vol. 6., No.1., Pages 41-53, 2012
Vol. 6., No.1., Pages 41-53, 2012
In the present study, we had introduced polyurethane (PU) nanofibers that contain hydroxyapatite (HAp) nanoparticles (NPs) as a result of an electrospinning process. A simple method that does not depend on additional foreign chemicals had been employed to synthesize HAp NPs through the calcination of bovine bones. Typically, a colloidal gel consisting of HAp/PU had been electrospun to form nanofibers. In this communication, physiochemical aspects of prepared nanofibers were characterized by FE-SEM, TEM and TEM-EDS, which confirmed that nanofibers were well-oriented and good dispersion of HAp NPs, over the prepared nanofibers. Parameters, affecting the utilization of the prepared nanofibers in various nano-biotechnological fields have been studied; for instance, the bioactivity of the produced nanofiber mats was investigated while incubating in simulated body fluid (SBF). The results from incubation of nanofibers, indicated that incorporation of HAp strongly activates the precipitation of the apatite-like particles, because of the HAp NPs act as seed, that accelerate crystallization of the biological HAp from the utilized SBF.
Supermolecular structure of welded seams prepared by friction stir welding (FSW) of polypropylene sheets has been studied by optical and electron microscopy. It has been shown that in the central parts of the seam spherulitic structures similar to that of the base material are formed, while at the borderline of the seam, a complex supermolecular structure could be identified. Lower welding rotation speed resulted in a border transition zone of more complex feature than the higher rotation speed during FSW. This was accompanied by reduced joint efficiency.
Molded flexible polyurethane (PU) foams have been synthesized from polypropylene glycol (PPG) with different molecular weights (Mw) and functionalities (f), and 2,4/2,6-toluene diisocyanate (TDI-80) with water as blowing agent. It was found that the glassy state properties of the foam mainly depended on the urethane group content while the rubbery state properties on the crosslink density. That is, PPG of low MW and low f (more urethane groups) provided superior glass state modulus, strength, density, shape fixity and glass transition temperature (Tg), while that of high Mw and high f (higher crosslink density) showed high rubbery modulus and shape recovery. Consequently shape fixity of low Mw PPG decreased from 85 to 72% while shape recovery increased from 52 to 63% as the content of high Mw PPG increased from 0 to 40%.
The encapsulation of octadecane (OD) as heat storage material was studied. The core-shell polydivinylbenzene (PDVB)/natural rubber (NR) capsules encapsulating OD was prepared using the Self-assembling of Phase Separated Polymer (SaPSeP) method by suspension polymerization. The mixture of dispersed phase consisting of DVB, NR, OD and benzoyl peroxide was added in polyvinyl alcohol aqueous solution and then homogenized at 5,000 rpm for 5 minutes. The obtained monomer droplet emulsion was subsequently polymerized at 80°C for 8 hours resulting in PDVB/NR capsule encapsulating OD. The influence of molecular weight and content of NR on the encapsulation efficiency and thermal properties of the encapsulated OD were investigated. It was found that both factors affected on the preparation of PDVB/NR/OD capsule. High molecular weight NR restricted phase separation of formed PDVB. High NR content also reduced phase separation of PDVB due to the increase of internal viscosity. Then, only the incorporation of appropriate molecular weight and content of NR resulted in the formation of PDVB/NR/OD capsule.
Three different, multifunctional acrylic monomers were photopolymerized in a matrix of poly(lactic acid), PLA, using 2-hydroxy-2-methyl-1-phenyl-propan-1-one as a photoinitiator. The kinetics of the photopolymerization of monomers in PLA, studied with Fourier Transform Infrared Spectroscopy, has been compared to analogous processes of pure monomers under the same conditions (room temperature, air atmosphere). Additionally, poly(ethylene glycol) was added to acrylate/PLA blends as plasticizer.The highly crosslinked networks obtained were characterized by FTIR and optical microscopy. The amount of insoluble gel has been estimated gravimetrically. It was found that the studied systems are characterized by very high polymerization rate, moreover, efficient grafting of polyacrylates on PLA takes place. The observed morphology indicates the heterogeneity of formed networks. The glass transition temperature of PLA in studied blends has been determined by differential scanning calorimetry.