UV-Curable Transparent Adhesives for Fabricating Precision Optical Components

UV-curable transparent epoxy adhesives have been specifically developed for the fabrication of optical communictions precision devices. The newly developed adhesives using cylohexane type fluoro-epoxy as the base resin and speherical quartz filler have extremely low volume shrinkage of 1.2% during curing and the cured adhesives have low thermal expansion coefficient of less than 2 × 10^-5/°C. Sheets of the adhesives are colorless and transparent to visible light because the refractive index of the epoxy matrix resin is matched to that of the quatz filler. These highly transparent adhesives can be cured to a depth of more than 5 mm by using 10 mW/cm² UV-irradiation for 30 min. They also have high adhesive strength and good durability. Therefore, they can be used in the fabrication of optical components that require submicron positioning accuracy.     

The preparation and performance of high-temperature adhesives for graphite bonding

Two kinds of high-temperature adhesives (HTAs) were prepared. One was composed of phenol-formaldehyde (PF) resin and boron carbide (PF+B₄C), the other was composed of PF resin, B₄C and fumed silica (PF+B₄C+SiO₂). Graphite materials were bonded by the above adhesives and heat-treated at temperatures ranging from 200 to 1500 °C. The joining strength was tested at room temperature. The results show that the graphite joints exhibit satisfactory bonding strength and that ceramics fillers show a marked property modification effect. The strength of graphite joints bonded by PF+B₄C and PF+B₄C+SiO₂ adhesive and treated at 1500 °C are 9.3 and 17.1 MPa, respectively. The property modification mechanism of ceramics fillers is also discussed in this paper. A strong chemical bonding force is introduced at the bonding interface and the volume shrinkage is restrained, which can be responsible for the good adhesive properties of HTAs for graphite bonding.     

Curing Behavior of Wood Adhesives Under High Steam Pressure

Steam-injection pressing is a recent development for manufacturing wood products. The curing mechanism and behavior of wood adhesives during steam-injection heating and hot-platen heating may cause differences in both chemical and physical aspects. The curing of wood adhesives under high steam pressure using an especially designed reaction cell is discussed. The adhesives used in this study were phenol-formaldehyde (PF), urea-formaldehyde (UF), melamine-formaldehyde (MF), and isocyanate (IC) resins. At different curing times, the heating temperature (steam pressure) applied to cure the adhesives was 160°C (6 kgf/cm²). Results were examined by analytical methods using FR-IR, ¹³C-NMR, dynamic mechanical analysis and solvent extraction. (1) By steam-injection heating, PF resin immediately cured to some degree in a few minutes and maintained an equilibrium situation. In this case, the reaction was accompanied by the disappearance of the ether structure. (2) In UF resin, results from IR data clarified different reactions between hot-platen heating and steam-injection heating. During steam-injection heating, as heating time increased, UF resin returned to its liquid state under the influence of hydrolysis. (3) MF resin was almost cured under steam-injection in a short heating time compared with hot-platen heating. (4) IC resin foamed and cured in a short heating time under steam-injection. It was proved that steam-injection heating was more effective than by hot-platen heating for IC resin.     

Fracture toughness of some adhesive cement systems measured in the temperature range 20–700°C

The adhesive fracture energy (G_IC) of several adhesive cement systems has been measured at temperatures extending to 700°C using alumina adherends in the double torsion test geometry. Two commercially available low-temperature curing systems were evaluated together with three laboratory-formulated cements, two of which were cured at 1000°C. The room temperature values of G_IC rangee from 0.6 to 4.9 J m⁻² for the former and from 6.7 to 11.4 J m⁻² for the latter. Despite the adoption of a linear compliance test geometry it was essential to precrack the specimens in order to obtain ‘valid’ G_IC data. Generally the fracture energy of the adhesive cement joints increased with temperature up to a peak between 400 and 600°C, and then decreased. The maximum G_IC value recorded was 40.2 J m⁻². The increase in toughness can be associated with viscous effects in the glassy phases present in the adhesive cements.     

Preparation and Properties of Aramid Copolymers Derived from 3,4'-ODA, 4,4'-ODA, IPC and TPC

Two series of wholly aromatic copolyamides (aramid copolymers) derived from (3-aminophenyl) (4-aminophenyl) ether (3,4'-ODA), bis(4-aminophenyl)ether(4,4'-ODA), isophthaloyl chloride (IPC), and terephthaloyl chloride (TPC), having inherent viscosity of 0.63-1.41 dL·g^-1 were synthesized. The thermal and mechanical properties of the cast films were investigated for application as hot-melt adhesives. When the aramid 341 composed of 3,4'-ODA and IPC was used, the value of adhesive joint strength at 20°C was 8.4 MPa and this value was maintained even at 230°C. And when 20 mol % of 3,4'-ODA were replaced by 4,4'-ODA, the value of adhesive joint strength at 20°C was a maximum, 16 MPa.     

Development of solid oxide fuel cells based on a Ce(Gd)O2−x electrolyte film for intermediate temperature operation

Initial tests have been carried out with the fuel cell arrangement La_0.6Sr_0.4Co_0.2Fe_0.8O₃Ce_0.9Gd_0.1O_1.95Ni/YSZ, incorporating dense film (5–10 μm) Ce_0.9Gd_0.1O_1.95 electrolyte tape cast onto the supporting anode, to investigate the feasibility of intermediate temperature operation (500–700°C). A good open circuit voltage of approx. 0.8 V was obtained at 550°C using moist hydrogen as the fuel. Slightly lower open circuit voltages were found at higher temperatures, which may have been caused by minor gas leakage and the electronic conductivity of the electrolyte. Power outputs in excess of 100 mW/cm² were obtained at 650°C, and the cell resistance was 0.8Ω cm² at this temperature. This resistance, and the greater resistance at lower temperature, was predominantly due to the cathode according to AC impedance measurements. Experiments were also carried out at 600°C using direct methanol fuels at the anode; the maximum power output was approximately half of that obtained with hydrogen.     

A Water Soluble Hydrated Metal Oxide primer for Adhesively Bonded Joints

Weight saving and manufacturing cost benefits have led to the increase in use of adhesively-bonded structures in the automotive, aerospace and marine industries. In order to be a viable alternative to, for example, metal fasteners, these adhesive bonds should maintain the strength typical of conventional fastener systems. In many applications, the bonds are put under a variety of environmental and mechanical stresses. For example, frequently these bonds are exposed over long periods of time to wet environments which can result in a loss of bond strength. The loss of strength can result from the extension of cracks and other deformations that occur in the adhesive or metal oxide which are accelerated by the moist environment. As a result of this deficiency, extensive research and development efforts have been undertaken to define methods and identify materials which improve bonded joint performance in humid conditions. For example, it is known that surface preparation is important in the bonding of aluminum and titanium, and cleanliness in the bonding of ceramic articles. Thus, it is essential that, before bonding, the adherend is cleaned and chemically pretreated to produce a surface which in combination with the adhesive develops the bond strengths which meet application requirements. The normal procedure after surface treatment is to apply a corrosion-inhibiting primer by a spray technique for surface protection prior to bonding and to insure resin penetration into the oxide structure which provides improved environmental resistance. A major drawback of spray application is the large volume of organic solvent (normally MEK) emitted to the atmosphere. A successful alternative is the recently-developed electrodeposited primer by Northrup Corp., which consists of water solubilized primer particles which migrate in an electric field to a conductive work piece where they are deposited in a dense, continuous coating.¹ The primer was developed for use with 121°C (250°F) curing epoxy adhesives. An Air Force sponsored contract is currently under way, the objective of which is to develop an electrodeposited water-based primer for use with 177°C (350°F) curing epoxy systems.² A water-based epoxy primer system for application using the more conventional spray techniques has also been decribed.³     

PERMEATION THROUGH KAPTON® POLYIMIDE AT ELEVATED TEMPERATURES

The permeabilities of CH₄, CO₂, CH₃OH, H₂O, O₂, and CO through films of Kapton® polyimide were measured at temperatures of 50, 100, 150, 200, and 250°C and pressures below 1 atm. Apparent activation energies for the permeation of the pure components ranged from 31.6kJ mol^-1 for CH₄ to nearly 0 for H₂O under the conditions studied. The ideal permselectivity for methanol relative to methane decreased from over 100 to under 10 as the temperature was increased from 50 to 250°C.     

Optimization of Surface Treatment and Adhesive Selection for Bond Durability in Ti-15-3 Laminates

The promising mechanical performance of a baseline Hybrid Titanium Composite Laminate (HTCL) inspired an investigation into maximizing the strength and environmental performance of this new aerospace material. This research focused upon finding the strongest and most durably combination of three commercially-available titanium surface treatments (i.e., Pasa-Jell 107^TM, Boeing's Sol-Gel, and Turco 5578^R) and two polyimide adhesives (i.e., LaRC^TM-IAX and FM5^R) for use in HTCL. The tests employed the cracked-lap shear (CLS) specimen geometry for fatigue crack growth measurements and also for fracture toughness analyses of the bonded specimens. The CLS geometry models several bonded applications found in the aerospace industry, and it also represents the debonding characteristics of a cracked titanium foil in HTCL.

The environmental performance of these six material combinations has been evaluated after 5,000 hours of continuous exposure to either a Hot/Wet environment that subjected the bonded specimens to 160°F (71°C) with relative humidity in excess of 95%, or to a Hot/Dry environment of 350°F (177°C) with a relative humidity of less than 5%. These two exposure environments utilized in this study are the most aggressive long-term environments that the HTCL is projected to experience while in service.

Test results showed that the best combination of the titanium surface treatments and the polyimide adhesives in the FM^R adhesive used in conjunction with Boeing's Sol-Gel titanium surface treatment. Though the FM5^R/Sol-Gel system was the strongest of all combinations, its performance dropped to less than 50% of its original strength after exposure to the Hot/Dry environment. An important finding is that this bonded system did not significantly degrade after exposure to the Hot/Wet environment. The only other material combination that showed substantial bond strength was the FM5^R/Pasa-Jell 107 system, though its strength also dropped to less than 50% of its original strength after exposure to the Hot/Dry environment.     

Adhesion properties of lactic acid based hot melt adhesives and their storage stability in different packaging applications

Adhesion properties and the stability during the use life of the package for two biodegradable hot melt adhesives were evaluated. Adhesives were based on poly (L-lactide) (PLLA) and poly(-caprolactone) (PCL) with molar ratio 81:19. One sample was stabilized by end-capping the terminal hydroxyl groups with acetic anhydride. The other sample was unmodified. Reference adhesive that was used in the studies, was a conventional non-biodegradable hot melt adhesive based on poly(ethylene-co-vinylacetate) (EVA).

Materials, which were bonded with these hot melt adhesives, were typical biodegradable packaging materials: a pigment-coated cardboard, a similar cardboard extrusion laminated with film type PLLA and an uncoated cardboard. The storage stabilities of the copolyester films and bonded structures were monitored during an eight week period at room (23°C) and at low (−18°C) temperatures.

Changes in molecular weight and crystallinity of the copolyesters were measured with gel permeation chromatography (GPC) and differential scanning calorimetry (DSC), respectively. Mechanical strength of the adhesive bonds was measured by a tensile testing instrument. Fracture surfaces of the adhesive bonds were subjected to microscopic studies.

Initial adhesion properties of the copolyesters were similar to those of EVA and better in case of PLLA-laminated cardboard. Both biodegradable copolyester samples degraded during the studied period; however, end-capping of the copolymer retarded this degradation rate.     

Flexibilized Copolyimide Adhesives

Two copolyimides, LARC-STPI and STPI-LARC-2, with flexible backbones were prepared and characterized as adhesives. The processability and adhesive properties were compared to those of a commercially available form of LARC-TPI.

Lap shear specimens were fabricated using adhesive tape prepared from each of the three polymers. Lap shear tests were performed at room temperature, 177°C, and 204°C before and after exposure to water-boil and to thermal aging at 204°C for up to 1000 hours.

The three adhesive systems possess exceptional lap shear strengths at room temperature and elevated temperatures both before and after thermal exposure. LARC-STPI, because of its high glass transition temperature provided high lap shear strengths up to 260°C. After water-boil, LARC-TPI exhibited the highest lap shear strengths at room temperature and 177°C, whereas the LARC-STPI retained a higher percentage of its original strength when tested at 204°C [68% versus 50% (STPI-LARC-2) and 40% (LARC-TPI)].

These flexible thermoplastic copolyimides show considerable potential as adhesives based on this study and because of the ease of preparation with low cost, commercially available materials.     

Grain boundary characteristics of batio3 PTC thermistor

A method to calculate physical parameters of grain boundaries of BaTio₃ PTC thermistor is presented in this paper. Increasing temperature form 20°C to 200°C, the grain boundary parameters take a sudden change near 130°C., Capacitance of depletion layer decreases form 40 to 15 uF/cm², while barrier height, charge density and depletion layer width increases from 0.05 to 0.03 eV, 3.5 to 8.5 uC/cm², and 0.7 to 2.0 nm, respectively. From TEM observation, three types of grain boundaries have been identified. The calculated parameters are an average of al grain boundaries.     

Preparation of three-dimensional ordered macroporous SiCN ceramic using sacrificing template method

Three-dimensional (3D) long range well ordered macroporous SiCN ceramics were prepared by infiltrating sacrificial colloidal silica templates with the low molecular weight preceramic polymer, polysilazane. This was followed by a thermal curing step, pyrolysis at 1250 °C in a N₂ atmosphere, and finally the removal of the templates by etching with dilute HF. The produced macroporous SiCN ceramics showed high BET surface areas (pore volume) in the range 455 m²/g (0.31 cm³/g)–250 m²/g (0.16 cm³/g) with the pore sizes of 98–578 nm, which could be tailored by controlling the sizes of the sacrificial silica spheres in the range 112–650 nm. The sphere-inversed macropores were interconnected by 50 ± 30 nm windows and 3–5 nm mesopores embedded in the porous SiCN ceramic frameworks, which resulted in a trimodal pore size distribution. The surface of the achieved porous SiCN ceramic was then modified by Pt–Ru nanoparticle depositing under mild chemical conditions.     

Dynamic Contact Angles of Viscous Liquids

An empirical model has been developed which can predict the dynamic contact angle of a spreading drop of viscous liquid on a plane wettable surface from the contact area for contact angles between 90° and 0° within a specified drop size. This range of drop size is restricted to those drops having a contact area at a 90° cap condition (A₉₀) between 0.10 cm² and 0.20 cm² The drop profile was found not to be that of a spherical segment and hence could not allow a simple geometric interpretation. The model strengthens the interpretation that contact angle development in this range of drop size is mainly the geometric result of spreading. The model was found to hold over a wide variety of polymer melt temperatures (155-240°C), molecular weights and molecular weight distributions, which combined would greatly influence drop profile. The time dependency of the dynamic contact angle was also evaluated by combining the present empirical model with a previous viscosity dependent model relating contact area with time. The model was successfully applied to the unrelated systems of silicone oil and glycerol at room temperature indicating its general applicability.     

Dielectric and ferroelectric properties of lead indium niobate ceramic prepared by wolframite method

The dielectric and ferroelectric properties of lead indium niobate (Pb(In_1/2Nb_1/2)O₃, PIN) ceramic prepared by an oxide-mixing method via wolframite route were investigated. The 98.5% perovskite fine-grained PIN ceramics with average grain sizes of 1–2 μm were obtained by sintering at 1050 °C for 2 h. The dielectric properties of the PIN were of relaxor ferroelectric behavior with temperature of dielectric maximum (T_m) 53 °C and dielectric constant (_r) 4300 (at 1 kHz). The P–E hysteresis loop measurements at various temperatures showed that the ferroelectric properties of the PIN ceramic changed gradually from the paraelectric behavior at temperature above T_m to slim-loop type relaxor behavior at temperature below T_m. Moreover, the P–E loop became more open at temperatures much lower than T_m. At −25 °C, the maximum polarization is found to be 8 μm/cm² at a field of 30 kV/cm, with P_r value of 2.5 μm/cm² and E_c of +7.5 kV/cm.     

Redox behavior of palladium at start-up in the Perovskite-type LaFePdOx automotive catalysts showing a self-regenerative function

In order to elucidate the superior start-up activity of LaFePdO_x catalysts in practical automotive emission control, the redox property of Pd species in a Perovskite-type LaFe_0.95Pd_0.05O₃ catalyst was studied at temperatures ranging from 100 to 400 °C using X-ray spectroscopic techniques. In a reductive atmosphere, and even at temperatures as low as 100 °C, Pd⁰ species is partially segregated out onto the catalyst surface from the B-site of the Perovskite-type matrix of LaFe_0.95Pd_0.05O₃. Passing through successive oxidizing atmospheres, the segregated Pd⁰ species is re-oxidized into Pd²⁺ at 200–300 °C. The formation of a solid solution between the re-oxidized Pd species and the Perovskite-type matrix begins to be seen at around 400 °C and accelerates at higher temperatures. Thus a quasi-reversible redox reaction between the surface Pd⁰ and the cationic Pd in the LaFe_0.95Pd_0.05O₃ matrix takes place. The start-up activity of LaFePd_xO_x catalysts can be attributed to Pd⁰ that segregates under the reductive atmosphere which is a natural part of the redox fluctuation in automotive exhaust gases at 100–200 °C.     

Soluble and colorless polyimides with polyalicyclic structures [1]

Two tetracarboxylic dianhydrides with polyalicyclic structure, bicyclo[2.2.2]octane-2-endo, 3-endo, 5-exo, 6-exo-2,3:5,6-dianhydride (5a) and the all-exo isomer (5b), were synthesized in six steps using phthalic acid as a starting material. The dianhydrides were polymerized at 85–105°C in well-purified DMAc with aromatic diamines which were purified by two recrystallizations and then sublimation. The polyimides formed flexible and tough films, and were soluble in aprotic polar solvents such as DMAc. The 5%-weight loss temperatures were over 450°C. The polyimides possessed glass-transition temperatures in the range from 211 to 385°C. The polyimides films had a tensile modulus range of 1.5–2.6 GPa, a tensile strength range of 52–96 MPa, and an elongation range at break of 3–11%. The polyimide films showed cutoffs at wavelengths shorter than 320 nm and were entirely colorless. The colorlessness of the polyimide films was maintained up to 200°C when heated in air and to 400°C in a N₂ atmosphere.     

Room Temperature Curing Epoxy Adhesives for Elevated Temperature Service

Room Temperature curing compositions of epoxy resins with high temperature service capability (95-120°C) were formulated and evaluated. The compositions were based on selected high functionality atomatic epoxy polymers and multicomponent poly amine curing agent systems. Toughening was achieved by addition of a rubbery phase either by prereaction of the epoxy resin with carboxyl terminated (CTBN) or by amine terminated (ATBN) poly butadiene acrylonitrile. The latter elastomeric component served as a part of the poly amine curing agent.

Best results were achieved with an adhesive formulation comprising tetra glycidyl-4-4'-diaminodiphenylmethane (TGDDM) and triglycidyl ether of p-aminophenol with triethylenetetramine and addition of ATBN with a felt carrier.

Lap shear strengths of aluminum/aluminum specimens primed by silane coupling agent in the order of 22 MPa at 25°C and 11 MPa at 120°C with T-Peel strengths of 1.6N/mm at 25°C and 0.52 N/mm at 120°C, were obtained.

The thermal behaviour and transitions, the chemical and mechanical properties, the microstructure and morphology of the selected adhesive formulation were studied, using DSC, Gehman, FTIR, mechanical testing and SEM analysis, respectively.

Experimental results showed that the selected compositions could develop good high temperature (120°C) properties while cured at room temperature. Furthermore, their high temperature performance compares favorably or even exceeds that of commercially available room-temperature-curing adhesive compounds, and are competitive with elevated temperature cured film adhesives.     

Catalytic decomposition of nitrous oxide over Ru-exchanged zeolites

We report that ultrastable faujasite-based ruthenium zeolites are highly active catalysts for N₂O decomposition at low temperature (120–200°C). The faujasite-based ruthenium catalysts showed activity for the decomposition of N₂O per Ru³⁺ cation equivalent to the ZSM-5 based ruthenium catalysts at much lower temperatures (TOF at 0.05 vol.-% N₂O: 5.132 × 10⁻⁴ s⁻¹ Ru⁻¹ of Ru-HNaUSY at 200°C versus 5.609 × 10⁻⁴ s⁻¹ Ru⁻¹ of Ru-NaZSM-5 at 300°C). The kinetics of decomposition of N₂O over a Ru-NaZSM-5 (Ru: 0.99 wt.-%), a Ru-HNaUSY (Ru: 1.45 wt.-%) and a Ru-free, Na-ZSM-5 catalyst were studied over the temperature range from 40 to 700°C using a temperature-programmed micro-reactor system. With partial pressures of N₂O and O₂ up to 0.5 vol.-% and 5 vol.-%, respectively, the decomposition rate data are represented by: −dN₂O/dt=itk(P_N2O) (P_O2)^−0.5 for Ru-HNaUSY, −dN₂O/dt=k(P_N2O) (P_O2)^−0.1 for Ru-NaZSM-5, and −dN₂O/dt=k(P_N2O)^−0.2 (P_O2)^−0.1 for Na-ZSM-5. Oxygen had a stronger inhibition effect on the Ru-HNaUSY catalyst than on Ru-NaZSM-5. The oxygen inhibition effect was more pronounced at low temperature than at high temperature. We propose that the negative effect of oxygen on the rate of N₂O decomposition over Ru-HNaUSY is stronger than Ru-NaZSM-5 because at the lower temperatures (<200°C) the desorption of oxygen is a rate-limiting step over the faujasite-based catalyst. The apparent activation energy for N₂O decomposition in the absence of oxygen is much lower on Ru-HNaUSY (E_a: 46 kJ mol⁻¹) than on Ru-NaZSM-5 (E_a: 220 kJ mol⁻¹).     

EQUILIBRIUM CONCENTRATION AND WATER AND SUCROSE DIFFUSIVITY IN OSMOTIC DEHYDRATION OF PINEAPPLE SLABS

The weight and water loss of 6 mm thick pineapple slabs (one of a six part of slice) were analyzed during osmotic dehydration in sucrose solution at different temperatures (50, 60 and 70°C), sucrose concentrations (50, 60 and 70°Bx) and pH's (6, 7 and 8), in 3³ experimental design. These results were fitted to a modified Azuara equation to obtain water and sucrose diffusivity results at equilibrium condition. Mean result of water diffusivity was 1.717 × 10^-5 cm²/s and sucrose diffusivity varied from 2.0 to 4.6 × 10^-5 cm²/s. The results of water loss at equilibrium in pineapple slabs varied between 0.6 to 0.67 g/g of initial sample weight. The results of sucrose gain at equilibrium varied between 0.15 and 0.21 g/g of initial sample weight. The results from mathematical modeling were compared to experimental results with r² = 0.94.