Synthesis of syndiotacticity‐rich high molecular weight poly(vinyl alcohol) by suspension polymerization of vinyl pivalate and saponification

Vinyl pivalate (VPi) was suspension‐polymerized to synthesize high molecular weight (HMW) poly(vinyl pivalate) (PVPi) with a high conversion above 95% for a precursor of syndiotacticity‐rich HMW poly(vinyl alcohol) (PVA). Also, the effects of the polymerization conditions on the conversion, molecular weight, and degree of branching (DB) of PVPi and PVA prepared by the saponification of PVPi were investigated. Bulk polymerization was slightly superior to suspension polymerization in increasing the molecular weight of PVA. On the other hand, the latter was absolutely superior to the former in increasing the conversion of the polymer, indicating that the suspension polymerization rate of VPi was faster than that of the bulk one. These effects could be explained by a kinetic order of a 2,2′‐azobis(2,4‐dimethylvaleronitrile) concentration calculated by the initial rate method. Suspension polymerization of VPi at 55°C by controlling various polymerization factors proved to be successful in preparing PVA of HMW [number‐average degree of polymerization (P_n): 8200–10,500], high syndiotactic diad content (58%), and very high yield (ultimate conversion of VPi into PVPi: 94–98%). In the case of the bulk polymerization of VPi at the same conditions, the maximum P_n and conversion of 10,700–11,800 and 32–43% were obtained, respectively. The DB was lower and the P_n was higher with PVA prepared from PVPi polymerized at lower initiator concentrations. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 832–839, 2003     

Effect of nano‐silica filler on the rheological and morphological properties of polypropylene/liquid‐crystalline polymer blends

A fumed hydrophilic nano‐silica‐filled polypropylene (PP) composite was blended with a liquid‐crystalline polymer (LCP; Rodrun LC5000). The preblended polymer blend was extruded through a capillary die; this was followed by a series of rheological and morphological characterizations. The viscosity of the PP matrix increased with the addition of the hydrophilic nano‐silica. At shear rates between 50 and 200 s^?1, the composite displays marked shear‐thinning characteristics. However, the incorporation of LC5000 in the PP composite eliminated the shear‐thinning characteristic, which suggests that LC5000 destroyed the agglomerated nano‐silica network in the PP matrix. Although the viscosity ratio of LCP/PP was reduced after the addition of nano‐silica fillers, the LCP phases existed as droplets and ellipsoids. The nano‐silicas were concentrated in the LC5000 phase, which hindered the formation of LCP fibers when processed at high shear deformation. We carried out surface modification of the hydrophilic nano‐silica to investigate the effect of modified nano‐silica (M‐silica) on the morphology of the PP/LC5000 blend system. Ethanol was successfully grafted onto the nano‐silica surface with a controlled grafting ratio. The viscosity was reduced for PP filled with ethanol‐M‐silica when compared to the system filled with untreated hydrophilic nano‐silica. The LC5000 in the (PP/M‐silica)/LC5000 blend existed mainly in the form of fibrils. At high shear rates (e.g., 3000 s^?1), the LC5000 fibril network was formed at the skin region of the extrudates. The exclusion of nano‐silica in the LC5000 phase and the increased viscosity of the matrix were responsible for the morphological changes of the LCP phase. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1484–1492, 2003     

Synthesis of novel tri- and tetrasubstituted C<Subscript>18</Subscript> furan fatty esters

A methylene-interrupted C₁₈ keto-acetylenic fatty ester (methyl 12-oxo-9-octadecynoate) was obtained from methyl ricinoleate by bromination-dehydrobromination followed by oxidation. Reaction of methyl 12-oxo-9-octadecynoate with bis(benzonitrile) palladium(II) chloride, allyl bromide, or methyl-allyl bromide furnished methyl 8-[5-hexyl-3-allyl-furan-2-yl]-octanoate (1, 56%) or methyl 8-[5-hexyl-3-(2-methyl-allyl)-furan-2-yl]-octanoate (2, 55%). Reaction of methyl 12-oxo-11-chloro-or 11-fluoro-9-octadeyynoate (prepared from methyl santalbate-methyl 11-E-9-octadecynoate, found in sandalwood, Santalum album, seed oil) with bis(benzonitrile) palladium(II) chloride gave methyl 8-(4-fluoro-5-hexyl-furan-2-yl)-octanoate (3, 50%) or methyl 8-(4-fluoro-5-hexyl-furan-2-yl)-octanoate (4, 50%), respectively. And when methyl 12-oxo-11-chloro- or 11-fluoro-9-octadecynoate was treated with a mixture of bis(benzonitrile) palladium(II) chloride, allyl bromide, or methyl-allyl bromide, the reaction yielded tetrasubstituted C₁₈ furan derivatives, viz, methyl 8-(3-allyl-4-chloro-5-hexyl-furan-2-yl)-octanoate (5, 54%), methyl 8-[4-chloro-5-hexyl-3-(2-methyl-allyl)-furan-2-yl)-octanoate (6, 54%), methyl 8-(3-allyl-4-fluoro-5-hexyl-furan-2-yl]-octanoate (7, 10%), and methyl 8-[4-fluoro-5-hexyl-3-(2-methyl-allyl)-furan-2-yl]-octanoate (8, 10%). The presence of a fluorine atom in the furan derivatives 4, 7, and 8 was readily characterized by the appearance of doublets for carbon nuclei, which were coupled to the fluorine atom in the ¹³C NMR spectra. All furan fatty derivatives from this work were characterized by NMR spectroscopic and mass spectrometric analyses. The yields of compounds 7 and 8 were very low (10%) despite attempts to improve the procedure by increasing the amounts of the reactants and catalyst.     

Simplified design of rock cavern concrete lining to resist shock loading

A simplified method was proposed for the design of concrete lining in underground rock cavern/tunnel against shock loading. The loading may result from the detonation of explosives on ground surface or ground penetration projectiles exploding adjacent to the cavern/tunnel. The resulting problem necessitates the solution of the dynamics of a beam loaded by a transient pressure uniformly distributed over the span. According to mechanical characteristics of the system with rock bolt and shotcrete, a dynamic support design method based on equivalent single degree of freedom (SDOF) was put forward. The SDOF method was applied to obtaining the maximum displacement at the mid-span of the beam, which is often the controlling factor in the blast-resistant design. In the formulation of the problem, the proposed method combines the phenomena of spalling and structural dynamics theory. An example is provided to demonstrate the applicability of this simplified method.     

Electromechanical behavior of hybrid carbon/glass fiber composites with tension and bending

To understand the smart (i.e., good memory) characteristics of hybrid composites of carbon fibers (CFs) and glass fibers (GFs) with epoxy resin as a matrix, the changes in the electrical resistance of composites with tension and on bending were investigated. The electrical resistance behavior of composites under tension changed with the composition of the CF/GF, as well as with the applied strain. The fractional electrical resistance increased slowly with increasing strain within a relatively low strain region. However, with further loading it increased stepwise with the strain according to the fracture of the CF layers. The strain sensitivity of the samples increased with increasing CF weight percentage, and the samples incorporating more than 40 wt % CF showed a strain sensitivity higher than 1.54 for a single CF. The changes in the fractional electrical resistance with bending were not so dominant as those with tension. This difference was attributed to the action of two cancelling effects, which are the increasing and decreasing fractional electrical resistance due to tension and compression with bending, respectively. On recovery from a large applied bending, the fractional electrical resistance decreased slowly with unloading because of the increase of contacts between the fibers that resulted from the reorganization of ruptured CFs during the recovery. Even the composites incorporating a relatively small CF content showed an irreversible electrical resistance with both tension and bending. However, the strain sensitivity being larger with tension than with bending is ascribed to the difference in their mechanical behaviors. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2447–2453, 2002     

Positivity and stability of mixed fractional‐order systems with unbounded delays: Necessary and sufficient conditions

This article provides a comprehensive study on quantitative properties of linear mixed fractional‐order systems with multiple time‐varying delays. The delays can be bounded or unbounded. We first obtain a result on existence and uniqueness of solutions to these systems. Then, we prove a necessary and sufficient condition for their positivity. Finally, we provide a necessary and sufficient criterion to characterize asymptotic stability of positive linear mixed fractional‐order systems with multiple time‐varying delays.     

Effects of anodizing voltage on the anodized and hydrothermally treated titanium surface

Anodic oxidation is the process of creating a titanium oxide layer with various defects more dense and stable. In this study, a dense, stable and porous oxide layer was formed using anodic spark oxidation on pure titanium surface and hydroxyapatite crystals were formed on its surface via a hydrothermal treatment. A mixture of 0.02M−GP (Glycerolphosphate disodium salt) and 0.2M-CA (Calcium acetate) was used as an electrolyte. By increasing the anodizing voltage to 220, 260, 300, and 360 V, the effects of the anodizing voltage were examined by evaluating the film properties after anodization and a hydrothermal treatment. Breakdown occurred around 230 V. As the voltage increased after breakdown, the pore size increased. After the hydrothermal treatment, the amount of HA crystal precipitation was also increased as the voltage increased. The mean surface roughness (Ra) of the anodizing surface was also increased as the voltage increased. The Ra value was larger in the hydrothermally treated group compared with the group treated with anodization as a result of the HA crystals present on the surface after the hydrothermal treatment. Corrosion resistance of the surface modified by anodization was significantly increased in a saline solution compared to that for the non-treated group; this increased further after the hydrothermal treatment. These increases were most likely due to a thick stable oxide layer formed through anodization. Thus, it is believed that titanium with its surface modified through anodic spark oxidation would be a suitable biomaterial due to its corrosion resistance and biocompatibility.     

The preparation of tantalum powder using a MR-EMR combination process

In the conventional metallothermic reduction (MR) process used to obtain tantalum powder in batch-type operation, it is difficult to control the morphology and location of the tantalum deposits. In contrast, an electronically mediated reaction (EMR) process is capable of overcoming this difficulty. It has the advantage of being a continuous process, but has the disadvantage of a poor reduction yield. A process known as the MR-EMR combination process is able to overcome the shortcomings of the MR and EMR processes. In this study, an MR-EMR combination process is applied to the production of tantalum powder via sodium reduction of K₂TaF₇. In the MR-EMR combination process, the total charge passed through an external circuit and the average particle size (FSSS) increase as the reduction temperature increases. In addition, the proportion of fine particles (−325 mesh) decreases as the reduction temperature increasess. The tantalum yield improved from 65 to 74% as the reduction temperature increased. Taking into account the charge, impurities, morphology, particle size and yield, a reduction temperature of 1123 K was found to be optimum for the MR-EMR combination process.     

Micro cam system driven by electrostatic comb-drive actuators based on SOI-MEMS technology

Microsystem Technologies - This paper reports a design and fabrication process of a micro cam system (MCS) with a flat-faced translating follower. The cam rim with cover diameter of 2.4&nbsp;mm...     

Pseudo‐predictor feedback control of discrete‐time linear systems with a single input delay

This paper studies the problems of stabilization of discrete‐time linear systems with a single input delay. By developing the methodology of pseudo‐predictor feedback, which uses the (artificial) closed‐loop system dynamics to predict the future state, memoryless state feedback control laws are constructed to solve the problem. Necessary and sufficient conditions are obtained to guarantee the stability of the closed‐loop system in terms of the stability of a class‐difference equations. It is also shown that the proposed controller achieves semi‐global stabilization of the system if its actuator is subject to either magnitude saturation or energy constraints under the condition that the open‐loop system is only polynomially unstable. Numerical examples have been worked out to illustrate the effectiveness of the proposed approaches. Copyright © 2015 John Wiley & Sons, Ltd.