Expandable Resins

Expandable polymeric blends with SAN are conventionally manufactured by incorporating a blowing agent, such as chlorofluoro-carbons. Some of these blowing agents are known to be environmental pollutants. 

It has been found that the incorporation of a small amount of triethylene glycol in expandable SAN beads provides equivalent or better expansion. On the other hand, the reaction is more rapid and less conventional blowing agent is needed. 

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Patent Number US 6127441 A1 20001003 EXPANDABLE RESIN COMPOSITION Sakamoto T Ishihara K Eurukawa T Nippon Unicar Co.Ltd. 

Platen retracted-chemical blowing agent expands resin to fill enlarged cavity. 

Microreticular Resins. Microreticular resins, by contrast, are elastic gels that, in the dry state, avidly absorb water and other polar solvents in which they are immersed. While taking up solvent, the gel structure expands until the retractile stresses of the distended polymer network balance the osmotic effect. In nonpolar solvents, little or no swelling occurs and diffusion is impaired. 

Stabilization of the Cellular State. The increase in surface area corresponding to the formation of many ceUs in the plastic phase is accompanied by an increase in the free energy of the system hence the foamed state is inherently unstable. Methods of stabilizing this foamed state can be classified as chemical, eg, the polymerization of a fluid resin into a three-dimensional thermoset polymer, or physical, eg, the cooling of an expanded thermoplastic polymer to a temperature below its second-order transition temperature or its crystalline melting point to prevent polymer flow. 

CeUular urea—formaldehyde and phenoHc resin foams have been used to some extent in interior sound-absorbing panels and, in Europe, expanded polystyrene has been used in the design of sound-absorbing doors (233). In general, cost, dammabUity, and cleaning difficulties have prevented significant penetration of the acoustical tile market. The low percent of redection of sound waves from plastic foam surfaces has led to their use in anechoic chambers (216). 

Alternatively, gas may be introduced by blending thermally reactive chemicals which release gas into the resin at the extmder. Extmsion heat initiates the reaction to release gas and expand the melt. 

Steam-Chest Expansion. In steam-chest expansion the resin beads in which gas is already present are poured into molds into which steam is injected. The steam increases the temperature close to the melting point and expands within the stmcture to create beads with food cushioning and insulating properties. Expanded polystyrene is widely used in this process for thermal insulation of frozen food packaging. 

Physical Properties. LLDPE is a sernicrystaUine plastic whose chains contain long blocks of ethylene units that crystallize in the same fashion as paraffin waxes or HDPE. The degree of LLDPE crystallinity depends primarily on the a-olefin content in the copolymer (the branching degree of a resin) and is usually below 40—45%. The principal crystalline form of LLDPE is orthorhombic (the same as in HDPE) the cell parameters of nonbranched PE are a = 0.740 nm, b = 0.493 nm, and c (the direction of polymer chains) = 0.2534 nm. Introduction of branching into PE molecules expands the cell slightly thus a increases to 0.77 nm and b to around 0.50 nm. 

The rate of stripping or the stripabiUty on cataly2ed urethane and epoxy resin finishes can be increased by adding formic acid, acetic acid, and phenol. Sodium hydroxide, potassium hydroxide, and trisodium phosphate [10101-89-0] may be added to the formula to increase the stripabiUty on enamel and latex paints. Other activators include oleic acid [112-80-17, trichloroacetic acid [76-85-9], ammonia, triethanolamine [102-71-6], and monoethyl amine. Methylene chloride-type removers are unique in their abiUty to accept cosolvents and activators that allow the solution to be neutral, alkaline, or acidic. This abihty gready expands the number of coatings that can be removed with methylene chloride removers. 

In the paper industry, PEO is widely used as a retention aid and pitch control agent in the newsprint industry (118—135). Typically, a phenol formaldehyde-type resin is added to the substrate before the addition of PEO. The chemical that is added before PEO has been referred to as an enhancer. Recent pubHcations on designing enhancers that work with PEO have resulted in expanding the use of PEO in flocculation of several substrates (128,129). 

Styrene [100-42-5] (phenylethene, viaylben2ene, phenylethylene, styrol, cinnamene), CgH5CH=CH2, is the simplest and by far the most important member of a series of aromatic monomers. Also known commercially as styrene monomer (SM), styrene is produced in large quantities for polymerization. It is a versatile monomer extensively used for the manufacture of plastics, including crystalline polystyrene, mbber-modifted impact polystyrene, expandable polystyrene, acrylonitrile—butadiene—styrene copolymer (ABS), styrene—acrylonitrile resins (SAN), styrene—butadiene latex, styrene—butadiene mbber (qv) (SBR), and unsaturated polyester resins (see Acrylonithile polya rs Styrene plastics). 

The basic resin for EPS is in the form of beads that ate expanded to a desired density before molding. Densities for packaging parts are typically 20—40 kg/m. Once expanded, the beads are fused in a steam-heated mold to form a specific shape. Most parts are molded of standard-white resins, although several pastel colors are available. 

Some of the chemicals mentioned above and others, such as chlorinated mbber or paraffin, antimony trioxide, calcium carbonate, calcium borate, pentaerythrithol, alumina trihydrate, titanium dioxide, and urea—melamine—formaldehyde resin, may be used to formulate fire retardant coatings. Many of these coatings are formulated in such a way that the films intumesce (expand) when exposed to fire, thus insulating the wood surface from further thermal exposure. Fire retardant coatings are mostly used for existing constmction. 

Polymer fibres are produced by forcing molten polymer or polymer in solution through fine nozzles (spinnerettes). The fibres so formed are twisted into a yarn and woven into fabric. Finally, polymers may be expanded into foams by mixing in chemicals that release COj bubbles into the molten polymer or the curing resin, or by expanding a dissolved gas into bubbles by reducing the pressure. 

Incorporation of hollow or expandable spheres of resin or of glass (microballoons). 

The foam effect is achieved by the dispersion of inert gas throughout the molten resin directly before moulding. Introduction of the gas is usually carried out by pre-blending the resin with a chemical blowing agent which releases gas when heated, or by direct injection of the gas (usually nitrogen). When the compressed gas/resin mixture is rapidly injected into the mould cavity, the gas expands explosively and forces the material into all parts of the mould. An internal cellular structure is thus formed within a solid skin. 

When the compressed gas/resin mixture is rapidly injected into the mould cavity, the gas expands explosively and forces the material into all parts of the mould. 

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