Rigid foams crosslinking

The benefits of the Sioplas moisture crosslinking process for the manufacture of crosslinked PE foam and the end-uses of such foams are discussed. The process involves grafting of alkoxysilanes onto ethylene homo- or copolymers to provide moisture crosslinkable polymers suitable for the manufacture of flexible, rigid, open-ceUed, closed-cell or very low density foams. 11 refs. 

A rigid foam sheet product is made by heating at least one surface of a crosslinked PE foam sheet material to a temp, sufficient to cause a slight surface post-expansion of the sheet material and contacting the heated, post expanded foam surface with a cold metal element to form a product with the desired, accurate thickness or having a desired three-dimensional design on the sheet material. USA... 

A rigid, foamed crosslinked PUR, usually with closed cells, is formed by the reaction of a diisocyanate and often methane diisocyanate (MDI) or polymeric MDI with polyester or more usually with a polyether polyol. Foaming may result from the water, which reacts with isocyanate groups to form carbon dioxide but is usually the result of using other... 

These compounds can be copolymerized with styrene to form crosslinked copolymers. When polyisocyanates are incorporated in these reaction systems, the resulting polymers are hybrid polymers containing polyurethane linkages. Rigid foams can be obtained by using the above reaction in the presence of a blowing agent. 

The development of highly crosslinked rigid polyisocyanurate foams opens an excellent area of applications for polyester polyols [4-8]. The required polyols do not need high functionality and the plasticising effect of polyester structures is extremely beneficial for these highly crosslinked systems [6]. The first polyester polyols used for these applications were low viscosity polycondensation products of AA with ethyleneglycol (EG) or diethyleneglycol modified with phthalic anhydride or triols. 

Chem. Descrip. Aluminum hydroxide CAS 21645-51-2 EINECS/ELINCS 244-492-7 Uses Eiller, flame retardant for thermoplastics and thermoplastic elastomers (PP, PE and copolymers, EVA), PVC (plasticized, rigid, foam), crosslinked elastomer cable and conveyor belts, powd. coatings Properties Powd. 1.3-2.6 pm median particle size dens. 2.4 g/cc bulk dens. 400 kg/m surf, area 3-5 mVg oil absorp. 25-30 cc/100 g brightness (TAPPI) > 94 ref. index 1.58 pH 9 1 conduct. < 100 pS/cm 99.6% act. 

Chem. Descrip. Aluminum hydroxide CAS 21645-51-2 EINECS/ELINCS 244-492-7 Uses Filler, flame retardant for polyester resins (SMC, BMC, laminates, artificial marble), epoxy, acrylic, crosslinked elastomers (conveyor belts, cables, flooring), PU (flexible and rigid foam, castings), latexes (carpetbacking, wallpaper), aq. disps., paints, varnishes, powd. coatings... 

Plastics — rigid polyurethane foam, expanded polyst3u-ene, honeycomb, crosslinked PVC foam (one of the most important core materials), poljnnethacrylimides, other plastics foams (excellent thermal insulation, weaker and more expensive than paper). 

Polyurethane materials exist in a variety of forms including flexible or rigid foams, chemical resistant coatings, specialty adhesives and sealants, and elastomers. Most polyurethanes are thermoset materials they cannot be melted and reshaped as thermoplastic materials. Once the reactions have ceased the thermoset polyurethanes are cured and cannot be heat shaped without degradation. The thermal stability results from the croslinking degree of polymer chains (the crosslink density) and from the nature and frequency of repeating units within the polymer chains. 

In general, the thermoset material was obtained by heating the N-cyanourea terminated monomer at a temperature above 100 C or at its melting temperature. Depending on the structure, the crosslinking reaction occurred within a few seconds to several minutes, and the final product varied from rigid foam to flexible film. Typically,... 

An interesting class of monomers which polymerize into different polymeric materials at different temperatures was discovered. At room temperature, the linear pol3rmer was obtained either from the polymerization of a dicyanourea monomer or directly from the polymerization of a mixture containing a diisocyanate and cyanamide. At elevated temperature (>100 C), the dicyanourea monomer or the mixture of diisocyanate and cyanamide crosslinked to a rigid foam or flexible film depending on the structure of the monomer. IR, DSC, and NMR were used for characterization of the polymers. 

TDI is used in paints, adhesives, and in making rigid foams. Also, TDI is used as a crosslinking agent for nylon-6. 

Trimerization to isocyanurates (Scheme 4.14) is commonly used as a method for modifying the physical properties of both raw materials and polymeric products. For example, trimerization of aliphatic isocyanates is used to increase monomer functionality and reduce volatility (Section 4.2.2). This is especially important in raw materials for coatings applications where higher functionality is needed for crosslinking and decreased volatility is essential to reduce VOCs. Another application is rigid isocyanurate foams for insulation and structural support (Section 4.1.1) where trimerization is utilized to increase thermal stability and reduce combustibility and smoke formation. Effective trimer catalysts include potassium salts of carboxylic acids and quaternary ammonium salts for aliphatic isocyanates and Mannich bases for aromatic isocyanates. 

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