Cast into Mold

Once the prepolymer and catalyst are added together, the chain extension (curing) reactions will commence. The time taken to mix must be carefully monitored. It must be sufficient to allow complete mixing, but there must be enough pot life left to allow pouring into the mold while the material is at the lowest viscosity possible. This is to allow the polyurethane to fill the mold completely and any entrapped bubbles to reach the surface. 

Polyurethanes tend to trap air very easily. The method of pouring must be such that the mix will flow down a surface and across the bottom and fill the mold upward, displacing the air ahead of it. The pouring should be in one continuous stream. It may be advantageous to raise the height slowly during the pour to improve the flow of the material into the mold. 

Any exposed bubbles may be gently popped using a soft gas flame or a hot air gun. The heat source must be used to a minimum and kept moving to prevent damage to the surface. 

When the material has gelled sufficiently for the mold to be moved, it should be placed in an oven heated to the curing temperature for the initial curing to 

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The zinc is normally melted in a gas, oU, or coal-fired reverberatory furnace with a capacity up to 100 tons or in a low frequency induction furnace with a capacity of a few tons. The more highly aUoyed compositions are more effectively melted and mixed in low frequency induction furnaces. The furnace must be refractory-lined to eliminate iron pickup by the molten metal. The metal temperature is maintained below 500°C to minimize loss by oxidation. A ladle is used to transfer the metal for casting into molds the pouring temperature is usuaUy ca 440°C. Zinc scrap is not generaUy suitable for remelting because it may contain undesirable impurities. 

PVC plastisol propellant may be formed into the required size and shape to make the desired grains either by screw extrusion or by casting into molds. No exotherm or volume change is observed as a result of curing (16). Molds are normally bottom-filled, the propellant being forced into them from a pressurized casting pot. Heat to raise the propellant to curing temperature may be supplied by many means. The filled... 

The step 3 product (9 mmol), 2-hydroxyethyl methacrylate (4.8 mmol), and tetrapro-poxy zirconium (35 mg) were blended together and the solution cast into molds then UV-cured to give clear, hard plastic parts. 

Both series of polyurethanes were prepared using a prepolymer technique in which reactants were mixed at 70 °C/1 hour, cast into molds at 105 °C/2 hours, and cured at 80 °C/14 hours. The BD/MDI hard segment contents ranged from 0% (transparent, colorless homopolyurethanes) to 30% w/w (opaque, white copolyurethanes). All elastomers were characterized using DSC, dynamic mechanical, and tensile stress-strain measurements. 

For the AIA-SEM analyses, the raw and clean coal samples were prepared by mixing 2 g of the sample with an epoxy resin and casting into molds 1 in. in diameter. The hardened pellets were polished to reveal a cross section and finished by polishing with 0.3-ym alumina powder. Then the pellets were coated with approximately 500 A of carbon to render sample surfaces electrically conductive for examination in the SEM unit. 

Several silica aerogel coupons were fabricated and consisted of quartz fiber felt, various concentrations of 1 pm Ti02 powder, quartz powder, and fumed silica powder. For the most part, all the constituents were kept the same except for the concentration of Ti02 powder. Basically, the powders were combined in acetonitrile, agitated and combined with the two-step sol-gel process described in Sect. 32.2.2. The sol was then cast into molds prefilled with the quartz fiber felt, allowed to gel, aged for 24 h, supercritically dried, and the thermal conductivity was measured. 

TPU MWCNT MWCNT-HPU 0.5,1 One-pot polycondensation to graft HPU to CNTs 40-60/- CNTs added to P(EO-THF), mixed with aliphatic polyisocyanate, dibutyltin dilaurate, degassed, cast into molds = 0.5 >1 l.MO-12 1.210-7 [376]... 

Transparent Soaps The early commercial transparent soap bars were based on conventional fat charges of tallow and coconut and also contained solubility enhancers such as potassium soap and rosin, in addition to glycerol and ethanol. These products were cast into molds and allowed to set and then stored for an extended period of time to allow the ethanol to evaporate. It is only after evaporation of the ethanol that transparency is achieved. This overall process can take several weeks and coupled with the alcohol evaporation is a slow and costly process. The best known product of this type still exists today and is sold by Unilever under the name Pears soap. ... 

Once mixed, the paste must be cast into molds quickly if the catalyst is of the room temperature curing type. Alternatively, a premix or masterbatch of all ingredients other than catalyst is made first to ensure a long shelf life. Portions of this masterbatch are weighed out and the prescribed amount of eatalyst is added just prior to easting. 

Two copolymers, a poly(styrene-6-isoprene-7>-styrene) (SIS) triblock (60 wt% S Mn=100,000, Mw/Mn=1.04) and a poly(styrene-Wsoprene) (SI) diblock (70 wt% S Mn=50,000, Mw/Mn=1.05), were synthesized by anionic polymerization. The selective solvent used here was an aliphatic white mineral oil (MO) produced by Witco (380PO). Specific masses of each copolymer and MO weae dissolved in cyclohexane and cast into molds. Upon solvent evaporation, the resultant films were vacuum-dried for up to 7 h at 120 C. Steady-shear tests were performed on a Rheometrics dynamic stress rheometer (DSR) as a function of shear stress (x) to measure the solution viscosity (q), while dynamic tests were performed here to discern G and G" as functions of x, oo and temperature. 

Efficient dispersion of nanoparticles was achieved by sonicating with an ultrasound probe the PDMS and the appropriate amount of clay for 6 min, at room temperature. The crosslinking system was then added and dispersed into the mixture and the samples were cast into molds for subsequent cure at room temperature for 12 hours. 

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