Phenolic thermosets

Different foundry casting techniques are used. Included are plastic-based binders mixed with sand. Various types of molds and cores are produced that include no-bake or cold-box, hot-box, shell, and oven-cured. Usual binders are phenolic, furan, and thermoset polyester. There is the foundry shell casting, also called dry-mix casting. It is a type of process used in the foundry industry, in which a mixture of sand and plastic (phenolic, thermoset polyester, etc.) is placed on to a preheated metal pattern (producing half a mold) causing the plastic to flow and build a thin shell over the pattern. Liquid plastic pre-coated sand is also used. After a short cure time at high temperature, the mold is stripped from its pattern and combined with a similar half produced by the same technique. Finished mold is then ready to receive the molten metal. Blowing a liquid plastic/sand mix in a core-box also produces shell molds. 

In Figure 1 the percentage of reagents which caused less than 25% reduction in tensile strength have been plotted for PPS and five other plastics, including a phenolic thermoset. PPS shows better resistance than even the phenolic resin, which is known for its chemical resistance. 

Plywood is formed from the impregnation of thin sheets of wood with resin that dries after the sheets are pressed together. Phenolic thermosets such as those developed by Bakelite are often used as the resins for plywood. 

Ammonia is used in the fibers and plastic industry as the source of nitrogen for the production of caprolactam, the monomer for nylon 6. Oxidation of propylene with ammonia gives acrylonitrile (qv), used for the manufacture of acryhc fibers, resins, and elastomers. Hexamethylenetetramine (HMTA), produced from ammonia and formaldehyde, is used in the manufacture of phenolic thermosetting resins (see Phenolic RESINS). Toluene 2,4-diisocyanate (TDI), employed in the production of polyurethane foam, indirectiy consumes ammonia because nitric acid is a raw material in the TDI manufacturing process (see Amines Isocyanates). Urea, which is produced from ammonia, is used in the manufacture of urea—formaldehyde synthetic resins (see Amino resins). Melamine is produced by polymerization of dicyanodiamine and high pressure, high temperature pyrolysis of urea, both in the presence of ammonia (see Cyanamides). 

Amino and Phenolic Thermoset Polymers, and their Composites... 

Most amino and phenolic thermosets are used in the production of composites, mainly prepared with wood (wood-plastic composites, WPC) [68]. Particleboard, or the chipboard is a kind of WPC, which is produced from wood particles, such as wood chips or saw dusts, through their glueing together with synthetic resins or other suitable binders, by pressing and extruding afterwards. In most particleboards, the resin used is formaldehyde-based. 

Uses Plasticizer, flame retardant for plastics incl. acrylics, ceiiuiosics, epoxy, nitrile, phenolic, thermoset po ester, PP, PS, PVAc, PVC, clear vinyl films, vinyl-coated fabrics, flexible PU foam, syn. rubber, wire/ cable insulation, plastisols plasticizer, coalescing agent for coatings Manuf./Dlstrlb. Akzo Nobel FMC Rhodia/Phosphorus Perf. Derivs. Trade Names Antiblaze 519... 

Hazardous Decomp. Prods. Heated to decomp., emits very toxic fumes of Cl" and POx Uses Flame retardant, plasticizer for cellulosics, epoxy, phenolics, thermoset polyesters, PS, PVC, PU foams sec. plasticizer Manuf./Distrib. Akzo Nobel http //www.akzonobei.com-,... 

Bondable substrates for aerobic and second-generation acrylics include clean as well as oily or "as received" metal polyurethanes, filled polycarbonates, filled nylon, phenolics, thermosets, wood, concrete, ceramics, glass, and other common materials of manufacture. Some thermoplastic materials are bonded better by using a second-generation acrylic adhesive. Examples are unfilled nylon, ABS, and rubber. 

A low-molecular-weight cross-linking resin, invariably either an epoxy or a phenolic (thermosetting types). 

The major flame-retarded polymers in the electrical industries are polyamides, polyesters (used in electrical connectors), the epoxy and phenolic thermosetting polymers (used in PCBs), and various types of styrenics for consiuner electronics and business machine housings. 

Thermosets such as phenolic thermosets are brittle at room temperature and usually have poor mechanical properties. However, due to the presence of cross-links, thermosets can be used at higher temperatures, as they have higher softening temperatures and better creep properties than thermoplastics. Thermosets are also usually more resistant to chemical attack than most thermoplastics, among other characteristics (Paiva and Frollini, 2000). In applications where good mechanical properties are required in addition to these intrinsic properties of thermosets, the thermosets can be combined with reinforcements to improve these properties. 

Phenolic composites reinforced with CF are also used for load-bearing materials. Phenolics have good resistance to seizure and work well with steel or bronze journals when lubricants such as oil or water are used. In these applications, the low thermal conductivity of phenolics is overcome by the presence of CF because the phenolic thermoset usually has a thermal conductivity of approximately 0.35 W/m K, i.e., approximately 1/150 that of steel, which may lead to bearing failure by charring (Kim et al, 2009). 

Mathur et al. (2010) used multi-walled carbon nanotubes (MWCNTs) to reinforce phenolic resins using both the wet and dry dispersion techniques before molding. The phenolic composites reinforced with 5% MWCNTs exhibited a flexural strength 158% higher than those of neat phenolic thermosets. 

TGA and DSC indicate that the residual cure stage of the phenolic thermoset hes between 100 and 200°C and releases water and other volatile by-products. The cure stage is observed as an exothermic peak in the DSC curves (Siegmann and Narkis, 1977). The condensation stage involving two phenolic hydroxyls may occur around 300°C and form diphenyl-ether type bonds with consequent mass loss (Pilato, 2010a Vazquez et al., 2002 El Mansouri et al., 2011). This event corresponds to an endothermic peak in DSC curves (Siegmann and Narkis, 1977). 

Phenolic thermosets are known to be resistant to high temperatures and generate high amounts of char during pyrolysis (Knop and Pilato, 1985). The thermal decomposition of phenolic thermosets can be divided into three... 

Thermosets such as phenolic thermosets cannot be melted or solubilized because they form a cross-linked stmcture after curing, unlike thermoplastics that can be melted several times (Goto and Santorelli, 2010). 

Phenolic thermosets can be recycled using a mechanical recycling system such as milling or crushing, and the obtained powder material can be used as a filler or additive for new thermosets (Goto and Santorelli, 2010). 

Phenolic thermosets and phenolic composites are solid, combustible materials with caloric values similar to that of coal. Therefore, products based on phenolic resins can be used as an alternative solid fuel to coal (Goto and Santorelli, 2010). Depending on the fiber thermal stability, thermal processes can be used to recover fibers. The composites are heated to high temperatures, causing the separation of the fibers from the polymers (Conroy et at., 2006). 

Trindade W G, Hoareau W, Razera IA T, Ruggiero R, Frollini E and Castellan A (2004), Phenolic thermoset matrix reinforced with sugar cane bagasse fibers Attempt to develop a new fiber surface chemical modification involving formation of quinones followed by reaction with furfuryl alcohol , Macromol Mater Eng, 289, 728-736. 

Phenolic thermoset resins are the oldest thermoset materials. They do not find as wide an application in the corrosion-resistant field as do the epoxies, vinyl esters, polyesters, and furans. As with other thermoset resins, they can be formulated to meet certain properties, but in general they do not have the range of corrosion resistance of the other thermosets. Table 8.6 shows their resistance to atmospheric corrosion and Table 8.7 gives their operating temperature range. 

Recently Ensinger has introduced PEEK/PBI for compression vanes in a new line of high-rotation pneumatic tools. The vanes needed exceptional wear resistance and modulus at high temperatures together with excellent resistance to oils and grease. The vanes were previously made from a phenolic thermoset which was more expensive and time consuming to process and required lubrication inside the compression chamber. 

The net result is that the polymer extends in many directions forming a three-dimensional crosslinked network of the thermoset polymer. Note that, in contrast to the phenolic thermosets, no water is evolved in the cure step. 

For molding common thermoplastics such as ABS, PVC, and polycarbonate, cold forming compacts by a factor of 3-6 a granular charge at 3000-5000 psi (21-34 MPa) but without heat into a preform [1]. This preform is not mechanically strong with inferior dimensional control and surface quality, but any air has been forced out, and it is ready to be further processed. Phenolic thermosetting material is cold molded then cured in an oven. 

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