Bulk surface photografting process and its application. III. Photolamination of polymer films

This paper introduces a set of new concepts related to the macromolecular design and to the practice in the realm of lamination by photografting, with experimental studies of the synthesis, structure, and performance of various systems, including valence bond adhesion of the organic polymeric materials, hyperbranched macromolecules rooted to the surface of organic substrates, macromolecular networks rooted on and bridged between two organic substrates, and a synthetic route combining primary and secondary photografting processes for the preparation of supermolecular architectures. In successful photolamination experiments based on these ideas, hyperbranched macromolecules of large size (10–20 μm) were obtained after initiation with aromatic ketones, which undergo a photoreduction reaction. A range of different organic polymeric films have been laminated. T-peel tests show most of the laminates broke inside the substrates and not at the interface between adhesive and substrate. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1723–1732, 1997     

Migration Issues and Strategies for Token Ring

This article considers the problems caused by ever increasing traffic on Token Ring LANs. It shows how the new IEEE 802.5 standard for DTR addresses this problem, outlining scenarios and providing a migration strategy for evolving networks, using this new standard. © 1997 John Wiley & Sons, Ltd.     

Photopolymerization of dendritic methacrylated polyesters. I. Synthesis and properties

The so-termed starburst dendritic polyesters differ from classical polymers by their structural symmetry, high degree of branching, and high density of terminal functionality. The divergent synthesis of a series of polydisperse dendritic polyesters based upon pentaerythritol and 1,2,4-benzenetricarboxylic anhydride, modified by glycidvl methacrylate and methacrylic anhydride, is described, proceeding in a stepwise growth manner starting from an “initiator core,” building branched arms. These materials have about eight (two samples), 12, or 16 methacrylate double bonds (indicated as D-1-OH, D-1, D-2, and D-3, respectively) at the chain extremities on each molecule. The rheological behavior was investigated by measuring the dynamic viscosity of the dendritic polyesters. The viscosities of the dendritic polyesters largely decrease in the order D-1-OH, D-1, D-2, and D-3 at lower frequency, but the viscosities of D-1-OH and D-1 decrease dramatically at higher frequency. Using a viscometric cup, the flow time of the dendritic methacrylated polyesters was compared with epoxy acrylate-modified unsaturated polyester of a linear type and it was shown that the flow time for the former is only one-third of that for the latter. The thermal mechanical properties and glass transition temperatures of the UV-cured films increase with the degree of terminal functionality. © 1996 John Wiley & Sons, Inc.     

The influence of EB-crosslinking on barrier properties of HDPE–mica composites

High-density polyethylene (HDPE) was compounded with untreated and surface-treated mica (10, 20, 40 wt %) and composites were injection-molded. The composites were radiation crosslinked (100, 300, 700 kGy) and hydrocarbon permeability, tensile impact strength, and tensile strength at 25 and 80°C of the composites were examined. The permeability of HDPE decreased from 7 to 3.6 g/(d × m²) by compounding the polymer with 20 wt % mica, and the permeability was additionally reduced to 1.3 g/(d × m²) by irradiation of the compounds (700 kGy). When surface-treated mica was used, the permeability of the composite furthermore decreased to about 1.0 g/(d × m²). Upon irradiation, the E modulus measured at 25°C increased 5% when the dose was 300 kGy. At 80°C, the corresponding increase was 40%. The tensile impact strength of an unfilled polymer increased more than three times by an irradiation dose of 700 kGy, and for a polymer with 10 wt % mica, the tensile impact strength was twice the level of an unirradiated composite. © 1996 John Wiley & Sons, Inc.     

Low-Temperature CO Oxidation over a Pt/Al2O3 Monolith Catalyst Investigated by Step-Response Experiments and Simulations

The ignition–extinction processes for CO oxidation over a Pt/Al₂O₃ monolith catalyst have been studied by flow-reactor experiments and simulations. The study was performed by stepwise changes of the inlet O₂ concentration ranging 0–20 vol% while the CO concentration and the inlet gas temperature were kept constant at 1.0 vol% and 423 K, respectively. Several features observed experimentally are qualitatively simulated with our model: (i) the ignition of the CO oxidation demands 8.0vol% O₂ (ii) corresponding to a catalyst ignition temperature of 433 K (due to the exothermicity of the reaction) and (iii) occurs in the rear part of the monolith where (iv) a local reaction zone is formed which (v) moves towards the reactor inlet as a function of time on stream. Additionally, the simulations show first order kinetic phase transitions, i.e. rapid adsorbate concentration changes, where the catalyst surface is predominantly CO covered in the low reactive state and almost completely oxygen covered in the high reactive state. For the ignition process the kinetic phase transition occurs after the actual catalytic ignition. However, the extinction process is more difficult to simulate dynamically without changing the model parameters for O₂ adsorption in the low and high reactive state, respectively. The influence of diffusion limitations and the role of formation of a less reactive Pt state under oxidising conditions is discussed.     

Effect of Oxygen Loss on Densification When Hot Isostatic Pressing YBa2Cu3O7−δ

Hot isostatic pressing of the high-T_c superconductor YBa₂Cu₃O_7−δ can lead to loss of oxygen and transformation of the material from the high-T_c orthorhombic phase to the nonsuperconducting tetragonal phase. It is shown that glass encapsulation helps retain the orthorhombic structure, whereas steel encapsulation resulted in formation of the tetragonal phase. Reasons for this phenomenon are discussed. The equilibrium oxygen gas pressure for the oxygen decomposition reaction in YBa₂Cu₃O₇, however, prevents full densification of this material in glass when employing hot isostatic pressing conditions of 200 MPa and 845°C.     

Surface photografting polymerization of vinyl acetate (VAc), maleic anhydride (MAH), and their charge transfer complex (CTC). III. VAc(3)

Vinyl acetate (VAc) was grafted onto low‐density polyethylene (LDPE) substrates by UV irradiation with benzophenone (BP) as the photoinitiator. BP preabsorbed film samples and BP precoated film samples were prepared in advance and applied as the substrates onto which VAc was photografted, together with the method in which BP was dissolved in VAc directly. In addition, the efficiency of the polymerizations applying the preirradiation technology was examined. The conversion percent, grafting percent, and grafting efficiency were determined by a gravimetric method. The contact angles of the grafted films against water were also measured. The results show that BP preabsorbing and precoating were favorable to grafting polymerization, especially the BP precoating method, which was due to its simple operation and the ease of controlling the amount of BP. The diffusion of BP and VAc through the substrates proved to be an important factor for grafting polymerization. Through UV irradiation, dormant groups can be introduced onto LDPE film, which may be activated again by UV irradiation or by heating, leading to the formation of free radicals. Grafting polymerization can be initiated during the activation process in the presence of monomer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1426–1433, 2001     

Graft copolymerization onto starch. III. Grafting of acrylonitrile to gelatinized potato starch by manganic pyrophosphate initiation

Recent development of synthesis and applications in grafting of acrylonitrile (AN) to gelatinized starch by Ce⁴⁺ initiation have been briefly reviewed. Using the Mn³⁺ method, the effects of starch pretreatment temperature on grafting parameters in grafting of AN onto starch have been studied. Total conversion of AN to PAN and % add-on were almost constant and showed only slight variation with increasing starch pretreatment temperature. Average molecular weight of grafts showed, however, an increase by a factor of nearly 10 (i.e., from 0.4 X 10⁵ to 4 X 10⁵) after swelling and gelatinization of the starch, and the grafting frequency (anhydroglucose units per grafted chain) increased in proportion. In grafting of AN onto gelatinized starch, increasing Mn³⁺ concentration increased the conversion of monomer and % add-on, whereas the average molecular weight of grafts and the grafting frequency (AGU/chain) decreased. An increase in the amount of starch also increased the conversion of monomer and the grafting frequency (AGU/chain) but decreased the % add-on and the average molecular weight of the grafts. Selective solution of PAN homopolymer by dimethylformamide indicated that grafting efficiencies were high in all cases. The results are interpreted in terms of slow termination rates due to high viscosity of gelatinized starch.     

Performance Analysis of Aluminum and Graphite Foam Heat Exchangers Under Countercurrent Arrangement

Due to the increasing power requirement and the limited available space in the vehicles, a countercurrent heat exchanger (HEX) is proposed for the position on the roof of the vehicle compartment. Furthermore, a new material, graphite foam with high thermal conductivity and low density, is a potential material for HEXs in vehicles. In order to evaluate the performance of the graphite foam HEX, the CFD computational fluid dynamics (CFD) approach is applied in a comparative study between the graphite foam and the aluminum HEXs under countercurrent flow condition. The analysis is conducted for the thermal performance (heat transfer coefficient) and the pressure loss. The simulation results show that the graphite foam HEX proves higher thermal performance than the aluminum HEX. However, due to the high pressure loss in the graphite foam HEX, the coefficient of performance in the graphite foam HEX is much lower than that of the aluminum HEX. A specific case study is carried out to evaluate the performance of graphite foam HEX as well. Useful recommendations are highlighted and provided to promote the development of the countercurrent flow HEXs in vehicles.     

Aqueous lipid phases of relevance to intestinal fat digestion and absorption

The phase behavior of monoglyceride/water systems, with oleic and linoleic acid as the dominating fatty acid residues, was investigated. Increased solubilization of triglycerides (oil) or oleic acid in the cubic liquid-crystalline phase formed by monoglyceride and water resulted in the formation of a reversed hexagonal liquid-crystalline phase followed by an L2-phase. The liquid-crystalline phases have different dispersion properties compared to each other in dilute micellar bile salt solutions. The cubic phase is found to be easily dispersed. The relevance of aqueous lipid phases other thah micellar is discussed in relation to intestinal lipid digestion and absorption.