Extended foams

Advantage. DHocules] Water-based, ofl-ba or water-extended foam and entrained air control agents maximizes drainage and prod, in brownstock washing systems, screen room systems, bleach (riants. 

SPI, soy fibre, and corn starch together with 0 0 per cent polyetho- polyol were also incorporated into a flexible polyurethane foam formulation. Stress-strain curves of the control foam and foams containing 10-20 per cent biomass material exhibited a considerable plateau stress region, but not for foams extended with 30—40 per cent of them. An increase in the hiomass content produced an increase in the foam density, whereas an increase in the initial water content produced the opposite effect. Foams extended with 30 per cent SPI, as well as those extended with 30 per cent soy fibre, displayed considerably higher resilience values than all other extended foams. The comfort factor increased by increasing the biomass content, and foams containing 10—40 per cent biomass showed significantly lower values in compression-set than the control foam [86]. 

Miscellaneous Applications. CeUular plastics have been used for display and novelty pieces from their eady development. Polystyrene foam combines ease of fabrication with lightweight, attractive appearance, and low cost to make it a favorite in these uses. PhenoHc foam has its principal use in doral displays. Its abiHty to hold large amounts of water for extended periods is used to preserve cut dowers. CeUular poly(vinyl chloride) is used in toys and athletic goods, where its toughness and ease of fabrication into intricate shapes have been valuable. 

Fillers (qv) are occasionally used in flexible slab foams the two most commonly used are calcium carbonate (whiting) and barium sulfate (barytes). Their use level may range up to 150 parts per 100 parts of polyol. Various other ingredients may also be used to modify a flexible foam formulation. Cross-linkers, chain extenders, ignition modifiers, auxiHary blowing agents, etc, are all used to some extent depending on the final product characteristics desired. 

Rigid vinyl foams ia constmction markets have grown substantially due to improved techniques to manufacture articles with controlled densities and smooth outer surfaces. Wood mol ding substitute for door frames and other wood products is an area that has grown. Rigid vinyl foams are also used ia the manufacture of pipes and wines as resia extenders and ia sidings and wiadows as the replacement of wood or wood substitutes. 

There are three basic types of polyethylene foams of importance (/) extmded foams from low density polyethylene (LPDE) (2) foam products from high density polyethylene (HDPE) and (J) cross-linked polyethylene foams. Other polyolefin foams have an insignificant volume as compared to polyethylene foams and most of their uses are as resia extenders. 

The avadabihty of PMDI also led to the development of polyurethane-modified isocyanurate (PUIR) foams by 1967. The PUIR foams have superior thermal stabiUty and combustibiUty characteristics, which extend the use temperature of insulation foams well above 150°C. The PUIR foams are used in pipe, vessel, and solar panel insulation glass-fiber-reinforced PUIR roofing panels having superior dimensional stabiUty have also been developed. More recently, inexpensive polyester polyols based on residues obtained in the production of dimethyl terephthalate (DMT) have been used in the formulation of rigid polyurethane and PUIR foams. 

Adhesives (qv) used to make plywood are classified as either the exterior adhesive or the lesser quaHty interior adhesive. The terms relate to the abUity of the adhesive to survive exposure to moisture and weather. PhenoHc resins (qv) are commonly used as adhesives to make plywood. The difference between interior and exterior phenoHc resin adhesive is the filler level. Exterior rated plywood uses higher resin content adhesives. Interior rated plywood uses either highly extended (below 24% resin soHds) or protein-based adhesives. The adhesive is appHed to the veneer by roU coating, spraying, curtain coating, or foam extmsion. 

The stabihty of a single foam film can be explained by the Gibbs elasticity E which results from the reduction ia equiUbrium surface concentration of adsorbed surfactant molecules when the film is extended (15). This produces an iacrease ia equiUbrium surface tension that acts as a restoring force. The Gibbs elasticity is given by equation 1 where O is surface tension and is surface area of the film. 

The specific ability of certain finely divided, insoluble solids to sta-bihze foam has long been known [Berkman and Egloff, op. cit., p. 133 and Bikerman, op. cit.. Chap. II]. Bartsch [Kolloidchem. Beth, 20, I (1925)] found that the presence of fine galena greatly extended the life of air foam in aqueous isoamyl alcohol, and the finer the sohds, the... 

The hydraulic oil must provide adequate lubrication in the diverse operating conditions associated with the components of the various systems. It must function over an extended temperature range and sometimes under boundary conditions. It will be expected to provide a long, trouble-free service life its chemical stability must therefore be high. Its wear-resisting properties must be capable of handling the high loads in hydraulic pumps. Additionally, the oil must protect metal surfaces from corrosion and it must both resist emulsification and rapidly release entrained air that, on circulation, would produce foam. 

Additional security against foaming over is provided by a glass tube that projects into the neck of the flask and is attached to a water pump. The checkers found it helpful to use a Hersh-berg stirrer with two wire blades the upper blade was adjusted so that its ends extended above the surface of the reaction mixture and into the foam. 

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