Ultraviolet-curable Silicone/Urethane Elastomer and Its Selective Modulus Enhancement

Department of Chemical EngineeringThermosets usually have brittle structure, but thermosetting polyurethane (PU) is classified as elastomer due to its urethane linkage in the backbone. Polyurethanes are used in many areas in a form of foam, adhesive and especially as an elastomer. To utilize elastomers in various applications without being fractured, various methods to control the mechanical properties of elastomers have been investigated such as incorporating fillers and additives or creating multiple networks. In this study, ultraviolet-curable silicone containing polyurethane acrylate was synthesized from poly(tetrahydrofuran) (PTH), hydroxy-terminated poly(dimethyl siloxane) (PDMS) and isophorone diisocyanate. The polyurethane chain was terminated with acrylate to fabricate modulus tunable and rapidly crosslinkable silicone/urethane composite elastomer. By adding 3-(trimethoxysilyl)propyl acrylate to the silicone/urethane elastomer network, the mechanical properties of silicone/urethane elastomer can be enhanced by creating additional covalent bonds at elevated temperature. The mechanical properties of the silicone-contained PUA elastomer can be enhanced even after complete photopolymerization, and local modulus enhancement is also possible by heating only desired area of the elastomer. We believe that the silicone/urethane elastomer can be used to fabricate flexible devices, force sensor, etc.clos

Fexible curtain shields equipment from intense heat fluxes

Flexible, high strength curtain made of fiber glass silicone elastomer laminate provides thermal shielding for equipment

Vacuum-stripped silicone binder for thermal-control paint

Silicone elastomer is placed in evacuating system, heated to 160 C and held at this temperature for 24 hours. Elastomer is then cooled to room temperature in vacuum, producing upgraded, low outgassing polymer of increased molecular weight

Flexible diaphragm-extreme temperature usage

A diaphragm suitable for extreme temperature usage, such as encountered in critical aerospace applications, is fabricated by a unique method, and of a unique combination of materials. The materials include multilayered lay-ups of diaphragm materials sandwiched between layers of bleeder fabrics. After being formed in the desired shape on a mold, they are vacuum sealed and then cured under pressure, in a heated autoclave. A bond capable of withstanding extreme temperatures are produced

EXOhSPEC collimator mechanical design

The Exoplanet High-Resolution Spectrograph (EXOhSPEC) is a high-resolution spectrograph for the characterisation of exoplanets with the Thai National Telescope. The folded version of this instrument comprises one triplet lens to collimate the beam incident on the grating and to focus the beam reflected by the grating onto the camera. This collimator comprises three lenses L1, L2 and L3 of diameter varying between 50 mm and 60 mm. We specified the barrel to guarantee a maximum decenter of the lenses equal to 25 μm. The maximum error in the orientation of each single lens is specified to be lower than 0.03º. The proposed concept is based on a semi-kinematic mounting which is used to restrain these lenses with 6 and 30 N of preloads on the axial and lateral directions to ensure their stability. These preloads are applied to the lenses using the elastic pushing force of silicone elastomers and spring force from ball-plungers. We present the design of the collimator and the assembly method. Our Finite Element Analyses show that the maximum surface error induced by the preloads is lower than 60 nm Peak-To-Valley on each optical surface of L1, L2, and L3. We describe our manufacturing process using NARIT’s CNC machine and its validation using our Coordinate-Measuring Machine

Role of uncrosslinked chains in droplets dynamics on silicone elastomers

We report an unexpected behavior in wetting dynamics on soft silicone substrates: the dynamics of aqueous droplets deposited on vertical plates of such elastomers exhibits two successive speed regimes. This macroscopic observation is found to be closely related to microscopic phenomena occurring at the scale of the polymer network: we show that uncrosslinked chains found in most widely used commercial silicone elastomers are responsible for this surprising behavior. A direct visualization of the uncrosslinked oligomers collected by water droplets is performed, evidencing that a capillarity-induced phase separation occurs: uncrosslinked oligomers are extracted from the silicone elastomer network by the water-glycerol mixture droplet. The sharp speed change is shown to coincide with an abrupt transition in surface tension of the droplets, when a critical surface concentration in uncrosslinked oligomer chains is reached. We infer that a droplet shifts to a second regime with a faster speed when it is completely covered with a homogeneous oil film

ZnO as a cheap and effective filler for high breakdown strength elastomers

Cheap, high-performance dielectric elastomers are in high demand from industry concerning new products based on dielectric elastomer transducers. However, formulating an elastomer that fulfils all the requirements for dielectric elastomers is difficult and, first and foremost, not cheap. In this article, we explore the use of a cheap and abundant metal oxide filler, namely ZnO, as a filler in silicone-based dielectric elastomers. The electro-mechanical properties of the elastomer composites are investigated, and their performance is evaluated by means of figures of merit. Various commercial silicone elastomers and a self-formulated silicone elastomer are utilised as elastomer matrices, the effects of which on the final properties of the elastomer composite are investigate

Development of specifications for polymeric materials Monthly technical progress report no. 14, Jul. 10 - Aug. 9, 1965

Weight analysis - trial run of specification test procedures using silicone elastomer in vacuum weight loss uni

Selection of elastomeric membranes for the removal of volatile organics from water

A wide range of homogeneous elastomeric membranes has been prepared using dicumylperoxide as a general cross-linking agent. The membranes have been used for both equilibrium sorption measurements and steady-state pervaporation experiments to study solution-diffusion phenomena in the removal of volatile organic components from aqueous solutions. Pervaporation experiments have been performed under identical hydrodynamic conditions in order to fix the boundary layer mass transfer coefficient at a constant and known value. For comparison of the permeabilities of different pervaporation membrane materials, this is of utmost importance. A wide range of selectivity factors up to a value of 100,000 are obtained, whereas usually the permeabilities for the organic component are in the range of 10-10-10-9m2/s and 10-14-10-12m2/s for water. The permeation and sorption data obtained for the various elastomers have been related to the chemical and physical nature of the elastomers through the solubility parameter and the glass transition temperature, respectively. Both diffusional and sorption effects seem to be important, determining the water-transport behavior in the elastomeric membranes. The solubility of the organic component appears to be independent of this combined solubility parameter. Differences in the permeabilities of the organic component can primarily be ascribed to structural parameters in the membrane material, like degree of unsaturation and presence of steric side groups