All issues / Volume 5 (2011) / Issue 4 (April)
Poly(butylene succinate) (PBSu), poly(2-methyl-1,3-propylene succinate) (PMPSu), and PBSu-rich copolyesters were synthesized using an effective catalyst, titanium tetraisopropoxide. Measurements of intrinsic viscosity (1.20–1.28 dl/g) and gel permeation chromatography demonstrated the success of the preparation of polyesters with high molecular weights. The compositions of the copolyesters were determined in three approaches from 1H and 13C NMR (nuclear magnetic resonance) analyses, and good agreement between the results was obtained. The distributions of the comonomers were found to be random from the spectra of carbonyl carbon. Their thermal properties were elucidated using a differential scanning calorimeter and a thermogravimetric analyzer. No marked difference exists among the thermal stabilities of these polyesters. However, the window between the glass transition and the melting temperatures becomes narrower with the increase in the concentration of 2-methyl-1,3-propylene succinate in the copolymers. Additionally, the cold crystallization ability decreases considerably. Finally, PMPSu is an amorphous homopolymer. Wide-angle X-ray diffractograms of isothermally crystallized copolyesters also follow the same trend.
Processing and characterization of halloysite nanotubes filled polypropylene nanocomposites based on a masterbatch route: effect of halloysites treatment on structural and mechanical properties
K. Prashantha, M. F. Lacrampe, P. Krawczak
Vol. 5., No.4., Pages 295-307, 2011
Vol. 5., No.4., Pages 295-307, 2011
Halloysites/polypropylene nanocomposites with different nanotubes contents were prepared by diluting a masterbatch containing 30 wt.% halloysites with polypropylene (PP). Unmodified (HNTs) and quaternary ammonium salt treated (QM-HNTs) halloysite nanotubes were used. Both degree of crystallinity and crystallization temperature increase upon addition of halloysites into PP, thus indicating a potential nucleation effect induced by the nanotubes. An homogeneous distribution and dispersion of nanotubes was observed throughout the PP matrix, with a slightly better dispersion in the case of modified QM-HNTs compared to unmodified HNTs. Mechanical tests in tension, bending and notched impact demonstrated that strength and modulus of the nanocomposites significantly increase with addition of halloysites without significant loss of ductility. An halloysite content of 6 wt.% appears as an optimum. Modified halloysites (QM-HNTs) lead to globally better performances due to strong interfacial interaction between the polymer matrix and the nanotubes.
Ion exchange (IEX) chromatography is commonly used in separation and purification systems. However, micropore blockage within its resin structure can easily lead to a reduction in the effectiveness of purification. To tackle this problem, we adopted the concept of membrane separation by combining electrospinning techniques with rapid alkaline hydrolysis to prepare a weak acid IEX nanofibrous membrane (AEA-COOH), consisting of polyethyleneterephthalate (PET) meltblown fabric as a supporting layer, with upper and lower IEX layers consisting of polyacrylonitrile (PAN) nanofibrous membranes. To determine the characteristics of the AEA-COOH membrane, we used the commercial product Sartobind© C IEX membrane as the standard of comparison. Results showed that the base weight and thickness of AEACOOH were 33 and 64%, relative to Sartobind© C membrane. The thermo-degradable temperature of AEA-COOH membrane (320°C) was far higher than that of Sartobind© C (115°C), indicating high thermal stability. Finally, comparisons between the lysozyme adsorption rates and capacity of various IEX membranes confirmed that AEA-COOH was lighter, thinner, faster, possessing higher protein adsorption efficiency than Sartobind© C membrane.
Nowadays, the use of macromolecular photoinitiators provides for a good compatibility of the initiator in the formulation. Moreover, the migration of the initiator to the surface of the material is prevented, which results in low-odor and non-toxic coatings. In the present study, it has been demonstrated that polyvinylchloride macrophotoinitiator (PVC-TX) containing side chain thioxanthone (2%) moieties were successfully prepared by 'click chemistry'. For this purpose, propargyl thioxanthone and polyvinylchloride with side chain azide moieties were reacted in N,N-dimethylformamide for 24 hours at 25°C in order to give corresponding macrophotoinitiator. The synthesized polymer was characterized by 1H-NMR (nuclear magnetic resonance), UV (ultraviolet) and fluorescence spectroscopies and water based gel permeation chromatography. Obtained macrophotoinitiator has similar absorption characteristics compared to parent thioxanthone. Its capabilities to act as initiator for the photopolymerization of methacrylic acid, methyl methacrylate, N-vinyl pyrrolidone and styrene in various solvents in the absence and presence of triethylamine media were also examined.
Intramolecular phase separation is usually associated with block-copolymers, but the same phenomenon is also obtainable by random-copolymers. In this article, evidence of intramolecular phase separation is reported for a linear octadecene-ethene copolymer, which shows an evolving 'yield point' at a long time and low frequency. This is attributed to a partial phase separation of the long short-chain branches. In creep recovery, this behavior is evident as increasing elastic steady-state creep recovery compliance Je 0. In contrast to 'normal' block-copolymers, this special polymer has an increase in phase separation with temperature, which is caused by the chemical composition and the short chain segments in the side chain domain, leading to a high surface fraction.
Chitosan is soluble in most acids. The protonation of the amino groups on the chitosan backbone inhibits the electrospinnability of pure chitosan. Recently, electrospinning of nanofibers based on chitosan has been widely researched and numerous nanofibers containing chitosan have been prepared by decreasing the number of the free amino groups of chitosan as the nanofibiers have enormous possibilities for better utilization in various areas. This article reviews the preparations and properties of the nanofibers which were electrospun from pure chitosan, blends of chitosan and synthetic polymers, blends of chitosan and protein, chitosan derivatives, as well as blends of chitosan and inorganic nanoparticles, respectively. The applications of the nanofibers containing chitosan such as enzyme immobilization, filtration, wound dressing, tissue engineering, drug delivery and catalysis are also summarized in detail.
New waterborne polyurethane (WPU)-based nanocomposites were prepared by incorporating low loading levels of chitin whiskers (ChWs) as the nanophase. The resultant WPU/ChW nanocomposites exhibited prominent enhancement in both strength and Young's modulus, and maintained an elongation of greater than ca. 500%. The ChW loading level of 3 wt% showed the maximum tensile strength (28.8 MPa) and enhanced Young's modulus (6.5 MPa), ca.1.8- and 2.2-fold over those of neat WPU. The active surface and rigidity of ChW facilitated formation of the interface for stress transferring and contributed to higher stress-endurance. As the ChW loading level increased, self-aggregation of ChWs resulted in a decrease in strength; however, the rigidity of ChW still supported the increase in Young's modulus, and the nanocompositescontaining 5 wt% ChWs had the highest Young's modulus (9.6 MPa). This work enriches the research into achieving high mechanical performance of waterborne polyurethane-based nanocomposites by introducing a natural nanofiller, and this high performance 'green' bionanocomposites will likely have promising prospects.
Self-assembly of block copolymer/nanoparticle blends has promising applications in the design and fabrication of novel functional nanomaterials. Precise control of the spatial positions of nanoparticles within block copolymer-based nanomaterials is crucial to achieve some special physical properties and functions. Here, we employ the self-consistent field method to theoretically investigate the self-assembly of polymer grafted-nanoparticles in a diblock copolymer. It is found that by varying the size and selectivity of nanoparticles, one can not only produce various self-assembled nanostructures but also modulate the spatial positions of the nanoparticles, either at the copolymer interfaces or in the center of one copolymer phase, within the nanostructures. A denser grafted polymer brush plays a role of shielding effect on nanoparticles and can position them into the center of one copolymer phase. The nanostructural transition we observed is dictated by the competition between entropy and enthalpy. On the basis of a number of simulations, two phase diagrams of self-assembled nanostructures are constructed. This study may be helpful for optimal design of advanced materials with desired nanostructures and enhanced performance.