Effect of solution properties on nanofibrous structure of electrospun poly(lactic‐co‐glycolic acid)

Electrospinning of poly(lactic‐co‐glycolic acid) (PLGA) in chloroform or 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) was investigated, focusing on its solution parameters, to develop nonwoven biodegradable nanofibrous structures for tissue engineering. PLGA nanofibers were obtained by electrospinning of 15 wt % PLGA solution and the resulting average fiber diameters were varied with the range of 270–760 nm, depending on solution property. When small amounts of benzyl triethylammonium chloride (BTEAC) was added to the PLGA/chloroform solution, the average diameter was decreased from 760 to 450 nm and the fibers were densely amounted in a straight shape. In addition, the average fiber diameter (270 nm) of nanofibers electrospun from polar HFIP solvent was much smaller than that (760 nm) of nanofibers electrospun from nonpolar chloroform solvent. Therefore, it could be concluded that conductivity or dielectric constant of the PLGA solution was a major parameter affecting the morphology and diameter of the electrospun PLGA fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1214–1221, 2006     

Viscosity effect in polyolefin ternary blends and composites

Ternary blends of PP (80) /rubber (EPM, EPDM) (10) / PE (10) and PP (80) / rubber (10) / CaCO₃ (10) composites were prepared in a twin-screw extruder. With polyethylene (PE) viscosity comparable to, or higher than that of rubber, the dispersed phase formed a reticulate structure with reduced size. On the contrary, when the viscosity of PE was significantly lower than that of rubber, the dispersed phase formed almost homogeneous morphology. With reticulate morphology, PE crystallinity content, hardness, modulus, and elongation at break of the ternary blend increased. In polypropylene (PP) / rubber / CaCO₃ composites, better dispersion of CaCO₃ in the PP matrix was obtained when the viscosity of rubber was significantly higher than that of matrix. With better dispersion, hardness and tensile properties were improved, but the impact strength more or less decreased. © 1993 John Wiley & Sons, Inc.     

Manufacturing and foaming of high melt viscosity of polypropylene by using electron beam radiation technology

The high melt viscosity of polypropylene was studied by grafting bifunctional monomers, 1,6‐hexanediol diacrylate (HDDA) and tripropylene glycol diacrylate (TPGDA), onto homopolypropylene (HPP) and random ter‐polypropylene (RTPP) under electron‐beam irradiation. Creation of the high‐melt‐viscosity polypropylene was possible at low radiation dosage and low monomer content, under a prohibition of both radiation degradation and homopolymerization. TPGDA monomer was more effective in increasing the melt viscosity of HPP compared with RTPP, whereas HDDA monomer was more effective for enhancing the melt viscosity of RTPP. Such different effects of monomers on melt viscosity may arise from different monomer structures, namely, TPGDA has additional three methyl groups, but HDDA has no methyl groups. Electron‐beam radiation technology, on an increase of the melt viscosity, was much more effective in HPP than RTPP, when compared with virgin polymers. Modified RTPP and HPP with high melt viscosity were capable of foaming with numerous fine cells, of which the modified HPP with 1.5 mmol TPGDA and 0.5 kGy could create more spherical foam cells and its bending strength was 1.5 times more than that of the foamed RTPP. POLYM. ENG. SCI., 46:431–437, 2006. © 2006 Society of Plastics Engineers.     

Desulfurization in a plate-type gas-lift photobioreactor using light emitting diodes

Hydrogen sulfide gas was removed in a 2-dimensional gas-lift reactor by the photosynthetic microorganismChlorobium thiosulfatophilum using light emitting diodes (LEDs) as a light source. LEDs saved light energy by 99% compared with the incandescent light source. The plate-type gas-lift reactor removed hydrogen sulfide five times better per unit mg of protein, and performed two times better in the maximum performance per unit luminous flux, compared with cylindrical fermentors.     

Binary blends of nylons with ethylene vinyl alcohol copolymers: Morphological,thermal, rheological,and mechanical behavior

Binary blends of ethylene vinyl alcohol copolymers, containing 62 (EVOH-62) and 71 (EVOH-71) mole percent vinyl alcohols, with nylons (nylon-6, nylon-6/12, and nylon-12) have been prepared from melt mixing in a twin screw compounding machine. Morphological, thermal, rheological, and mechanical properties were determined. EVOH-62/nylon-6 and EVOH-71/nylon-6 blends showed homogeneous phase morphologies in the nylon-6-rich region, and fine phase separations (c.a. 2 × 10^?7 m) in the EVOH-rich region. Melting point depression, positive deviations in viscosity and flexural modulus, and negative deviation in impact strength from the simple additive rule were generally observed. And the results were possibly interpreted in terms of compatibility and increased nylon/EVOH interactions over the nylon/nylon interactions. On the contrary, clean phase separations in large domains were observed from EVOH-71/nylon-6/12 and EVOH-71 /nylon-12 blends. Fibrillation was also obtained from EVOH rich blends. Probably due to the incompatible nature of these blends, yield at low rate of shear and a mechanical property drop were also observed.     

Conceptual and basic designs of the Mobile Harbor crane based on topology and shape optimization

The Mobile Harbor (MH) has been recently proposed as a novel maritime cargo transfer system that can move to a container ship anchored in the deep sea and handle containers directly at sea with the aid of a stabilized MH crane. Because this system operates under at-sea conditions, the MH crane must be designed to support an inertia load and wind force, as well as its self-weight. The wave-induced motions of the MH, e.g. rolling, pitching, and heaving, generate a significant amount of inertia load, which has not been considered in the design of conventional quayside cranes installed on stable ground. Wind force is also a critical design factor due to the higher wind velocity in the open sea. In addition to the aforementioned structural rigidity, mass minimization is also important in the structural design of MH cranes because it reduces the overturning moment and therefore enhances ship stability. In this paper, the sensitivities of the design-dependent loads (i.e. self-weight, inertia load, and wind force) are derived with respect to the design variables, and then a topology optimization is conducted with the derived sensitivities in order to obtain a conceptual design. Then, the conceptual design is elaborated into a three-dimensional basic design through shape optimization with design regulations for offshore cranes. Through the integrated design process with the topology and shape optimizations, a conceptual and basic design is successfully obtained for the MH crane.     

Synthesis and luminescence properties of new blue‐light‐emitting polyconjugated poly{1,1′‐biphenyl‐4,4′‐diyl‐[1‐(4‐t‐butylphenyl)]vinylene} polymers and copolymers

Three new soluble polyconjugated polymers, all of which emitted blue light in photoluminescence and electroluminescence, were synthesized, and their luminescence properties were studied. The polymers were poly{1,1′‐biphenyl‐4,4′‐diyl‐[1‐(4‐t‐butylphenyl)]vinylene}, poly((9,9‐dioctylfluorene‐2,7‐diyl)‐alt‐{1,4‐phenylene‐[1‐(4‐t‐butylphenyl)vinylene‐1,4‐phenylene]}) [P(DOF‐PVP)], and poly([N‐(2‐ethyl) hexylcarbazole‐3,6‐diyl]‐alt‐{1,4‐phenylene‐[1‐(4‐t‐butylphenyl)]vinylene‐1,4‐phenylene}). The last two polymers had alternating sequences of the two structural units. Among the three polymers, P(DOF‐PVP) performed best in the light‐emitting diode devices of indium–tin oxide/poly(ethylenedioxythiophene) doped with poly(styrene sulfonate) (30 nm)/polymer (150 nm)/Li:Al (100 nm). This might have been correlated with the balance in and magnitude of the mobility of the charge carriers, that is, positive holes and electrons, and also the electronic structure, that is, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels, of the polymers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 307–317, 2006     

Influence of mixing cycle on the degree of mixing of calcite‐filled polyethylene upon stretching

The mixing cycle‐dependent degree of dispersion and degree of mixing of a calcite (calcium carbonate) agglomerate in high‐density polyethylene (HDPE), low‐density polyethylene (LDPE), and linear low‐density polyethylene (LLDPE) matrices upon stretching was investigated using three different techniques: mechanical property, morphological behavior, and image analyzer analyses. The mechanical properties analyzed in terms of the tensile strength and maximum elongation resulted in that the second mixing was the best for giving a better property for all systems except the LDPE system, which exhibited no significant difference between the second and third mixings. The morphological behavior of the three compounds were different, but no distinctive difference was observed to differentiate the degree of mixing from system to system. The number‐, weight‐, and z + 1‐average diameters of the air hole and the aspect ratio upon the stretching and mixing cycle were calculated to analyze the degree of mixing of the calcite‐filled composites. As a consequence, no difference in the average diameter of the air hole was obtained among the three systems, but the aspect ratios of the air hole varied significantly. Thus, the degree of dispersion and the degree of mixing may be influenced by the average calcite agglomerate size, the average diameter of the air hole, and the aspect ratio upon stretching and mixing cycles. Those factors would be formed by the difference in chemical characteristics upon various microstructures of polyethylene and its molecular weight and molecular weight distribution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 311–321, 2003     

Effect of low molecular weight polybutadiene as processing aid on properties of silica‐filled styrene–butadiene rubber compounds

Because silica has strong filler–filler interactions, a silica‐filled rubber compound shows a poor filler dispersion compared to a carbon black‐filled one. Improvement of the filler dispersion in silica‐filled styrene–butadiene rubber (SBR) compounds was studied using low molecular weight polybutadiene (liquid PBD) with the high content of 1,2‐unit. By adding the liquid PBD to the silica‐filled SBR compound, the filler dispersion and flow property are improved. The cure time and cure rate become faster as the 1,2‐unit content of the liquid PBD increases for the compounds containing the liquid PBD. The crosslink density increases linearly with increase in the 1,2‐unit content of the liquid PBD. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3135–3140, 2003     

Sequence analysis and fiber properties of a blend of poly(ethylene terephthalate) and poly(ethylene terephthalate‐co‐4,4′‐bibenzoate)

Blends of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate‐co‐4,4′‐ bibenzoate) (PETBB) are prepared by coextrusion. Analysis by ¹³C‐NMR spectroscopy shows that little transesterification occurs during the blending process. Additional heat treatment of the blend leads to more transesterification and a corresponding increase in the degree of randomness, R. Analysis by differential scanning calorimetry shows that the as‐extruded blend is semicrystalline, unlike PETBB15, a random copolymer with the same composition as the non‐ random blend. Additional heat treatment of the blend leads to a decrease in the melting point, T_m, and an increase in glass transition temperature, T_g. The T_m and T_g of the blend reach minimum and maximum values, respectively, after 15 min at 270°C, at which point the blend has not been fully randomized. The blend has a lower crystallization rate than PET and PETBB55 (a copolymer containing 55 mol % bibenzoate). The PET/PETBB55 (70/30 w/w) blend shows a secondary endothermic peak at 15°C above an isothermal crystallization temperature. The secondary peak was confirmed to be the melting of small and/or imperfect crystals resulting from secondary crystallization. The blend exhibits the crystal structure of PET. Tensile properties of the fibers prepared from the blend are comparable to those of PET fiber, whereas PETBB55 fibers display higher performance. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1793–1803, 2004