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Foams described

This technique eliminates the long induction period at 0° and the violent foaming described in the preparation of thio-phenol.8 However, in a larger-scale operation it would be advisable to check the rate of addition of the zinc dust somewhat, lest an exception arise. [Pg.25]

The so-called bi-liquid foams described by Sebba and Vincent [17-20] will not be discussed since they are not true colloidal emulsions, but resemble conventional foams more closely, possessing polyhedral cells of centimetre dimensions. [Pg.165]

Turn to Chapter 1 and look at the structures of the dyes in the shaving foam described on p. 7.-Comment on the structures in comparison with those in Problem 6 and suggest where-they get their colour from and why they too have extra functional grodps fhen turn to the beginning of Chapter 1 (p. 3) and look at the structures of the compounds in the - spectrum of molecules . Can you see what kind of absorption leads to each colour You will want to think.-, about the conjugation in each molecule but you should not expect to correlate structures with. wavelengths in any even roughly quantitative way. - —. ... [Pg.42]

The following are thermoplastic foams that are frequently grouped under structural foams, but do not always have the integral-skin properties of the structural foams described above. [Pg.228]

Covers prefoamed polyurethane foams, both rigid and flexible, for packaging applications. The foams described are intended for use as... [Pg.430]

Superabsorbents. Water-sweUable polymers are used extensively in consumer articles and for industrial appUcations. Most of these polymers are cross-linked acryUc copolymers of metal salts of acryUc acid and acrylamide or other monomers such as 2-acrylamido-2-methylpropanesulfonic acid. These hydrogel forming systems can have high gel strength as measured by the shear modulus (134). Sometimes inorganic water-insoluble powder is blended with the polymer to increase gel strength (135). Patents describe processes for making cross-linked polyurethane foams which contain superabsorbent polymers (136,137). [Pg.144]

Antagonism between antimony oxide and phosphoms flame retardants has been reported in several polymer systems, and has been explained on the basis of phosphoms interfering with the formation or volatilization of antimony haUdes, perhaps by forming antimony phosphate (12,13). This phenomenon is also not universal, and depends on the relative amounts of antimony and phosphoms. Some useful commercial poly(vinyl chloride) (PVC) formulations have been described for antimony oxide and triaryl phosphates (42). Combinations of antimony oxide, halogen compounds, and phosphates have also been found useful in commercial flexible urethane foams (43). [Pg.475]

Nonreactive additive flame retardants dominate the flexible urethane foam field. However, auto seating appHcations exist, particularly in Europe, for a reactive polyol for flexible foams, Hoechst-Celanese ExoHt 413, a polyol mixture containing 13% P and 19.5% Cl. The patent beHeved to describe it (114) shows a reaction of ethylene oxide and a prereacted product of tris(2-chloroethyl) phosphate and polyphosphoric acid. An advantage of the reactive flame retardant is avoidance of windshield fogging, which can be caused by vapors from the more volatile additive flame retardants. [Pg.479]

Low deasity polyethyleae foam products (thin sheets, planks, rounds, tubes) ia the range of 32—160 kg/m (2—10 lbs/ft ) have beea prepared by an extmsion technique usiag various gaseous fluorocarboa blowiag ageats (100,101). The techniques are similar to those described earlier for produciag extmded polystyreae foam planks and foam sheets. [Pg.406]

Compression Set. The compression set is an important property ki cushioning appHcations. It has been studied for polyurethane foams (185,186), and has been discussed ki reviews (32,60,156). Compression set has been described as flex fatigue and creep as weU. [Pg.413]

Another type of polyol often used in the manufacture of flexible polyurethane foams contains a dispersed soHd phase of organic chemical particles (234—236). The continuous phase is one of the polyols described above for either slab or molded foam as required. The dispersed phase reacts in the polyol using an addition reaction with styrene and acrylonitrile monomers in one type or a coupling reaction with an amine such as hydrazine and isocyanate in another. The soHds content ranges from about 21% with either system to nearly 40% in the styrene—acrylonitrile system. The dispersed soHds confer increased load bearing and in the case of flexible molded foams also act as a ceU opener. [Pg.417]

Process and Equipment. Rigid polyurethane foam processes use the same high or low pressure pumping, metering, and mixing equipment as earher described for flexible foams. Subsequent handling of the mixture is deterrnined by the end product desired. [Pg.418]

Bun Stock. By pouriag the reaction mixture on a continuous belt a long bun can be produced like the flexible slab foam previously described. After curiag, the bun can be cut iato slabs or blocks as required by the end use. [Pg.419]

One simple rheological model that is often used to describe the behavior of foams is that of a Bingham plastic. This appHes for flows over length scales sufficiently large that the foam can be reasonably considered as a continuous medium. The Bingham plastic model combines the properties of a yield stress like that of a soHd with the viscous flow of a Hquid. In simple Newtonian fluids, the shear stress T is proportional to the strain rate y, with the constant of proportionaHty being the fluid viscosity. In Bingham plastics, by contrast, the relation between stress and strain rate is r = where is... [Pg.430]

Although aH these models provide a description of the rheological behavior of very dry foams, they do not adequately describe the behavior of foams that have more fluid in them. The shear modulus of wet foams must ultimately go to zero as the volume fraction of the bubbles decreases. The foam only attains a solid-like behavior when the bubbles are packed at a sufficiently large volume fraction that they begin to deform. In fact, it is the additional energy of the bubbles caused by their deformation that must lead to the development of a shear modulus. However, exactly how this modulus develops, and its dependence on the volume fraction of gas, is not fuHy understood. [Pg.430]

Commercially, polymeric MDI is trimerized duting the manufacture of rigid foam to provide improved thermal stabiUty and flammabiUty performance. Numerous catalysts are known to promote the reaction. Tertiary amines and alkaU salts of carboxyUc acids are among the most effective. The common step ia all catalyzed trimerizations is the activatioa of the C=N double boad of the isocyanate group. The example (18) highlights the alkoxide assisted formation of the cycHc dimer and the importance of the subsequent iatermediates. Similar oligomerization steps have beea described previously for other catalysts (61). [Pg.451]

Abbreviations of prominent use properties of the various classes of commercial surfactants are shown in Table 1. Antimicrobial activity includes germicidal, bactericidal, and bacteriostatic effects emolliency describes lubrication or a soft feel imparted to skin by surfactants a hair conditioner is a substantive surfactant appHed from aqueous solution to impart a lubricating or antistatic effect and opacifters are used to thicken hand-dishwashing products and cosmetic preparations to convey an appearance of high concentration and to retard solvent drainage from foam. [Pg.233]

Sweetness is primarily a function of the levels of dextrose and maltose present and therefore is related to DE. Other properties that increase with increasing DE value are flavor enhancement, flavor transfer, freezing-point depression, and osmotic pressure. Properties that increase with decreasing DE value are bodying contribution, cohesiveness, foam stabilization, and prevention of sugar crystallization. Com symp functional properties have been described in detail (52). [Pg.295]

Anionic Surfactants. PVP also interacts with anionic detergents, another class of large anions (108). This interaction has generated considerable interest because addition of PVP results in the formation of micelles at lower concentration than the critical micelle concentration (CMC) of the free surfactant the mechanism is described as a "necklace" of hemimicelles along the polymer chain, the hemimicelles being surrounded to some extent with PVP (109). The effective lowering of the CMC increases the surfactant s apparent activity at interfaces. PVP will increase foaming of anionic surfactants for this reason. [Pg.532]

Further developments have brought forth polymeric quats having antimicrobial properties (158—160). Different kinds of polyquats have been described with molecular weight from 2,000 to 60,000 (153). Polymeric quats have two characteristics that make them uniquely different from the monomeric quats. One is the absence of foaming, even at high concentrations. The other is their remarkably low toxicity in skin and eye irritation tests and... [Pg.129]


See other pages where Foams described is mentioned: [Pg.282]    [Pg.180]    [Pg.180]    [Pg.180]    [Pg.180]    [Pg.194]    [Pg.354]    [Pg.355]    [Pg.89]    [Pg.590]    [Pg.282]    [Pg.180]    [Pg.180]    [Pg.180]    [Pg.180]    [Pg.194]    [Pg.354]    [Pg.355]    [Pg.89]    [Pg.590]    [Pg.196]    [Pg.922]    [Pg.234]    [Pg.476]    [Pg.299]    [Pg.405]    [Pg.413]    [Pg.428]    [Pg.428]    [Pg.428]    [Pg.287]    [Pg.99]    [Pg.138]    [Pg.527]    [Pg.528]    [Pg.410]    [Pg.326]    [Pg.336]    [Pg.457]   
See also in sourсe #XX -- [ Pg.631 , Pg.632 ]




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