Phenolic microspheres

Acrylonitrile-butadiene-styrene copolymer USA grade phenolic microspheres Bulk molding compound USSR grade phenolic microspheres Dough molding compound Dinitrosopentamethylenetetramine... 

USSR grade syntactic foam from epoxy resin and phenol microspheres USSR grade syntactic foam from epoxy resin and glass microspheres USSR grade epoxy resin... 

The Philadelphia Quartz Company in USA produces Q-Cel quartz micro-spheres 20,21. These have an apparent density of 300 kg/m3, a bulk density of 100 kg/m3, and an average diameter of 75 pm. They are mechanically very strong and are very cheap (half the price of glass and one third of the price of phenolic microspheres). 

Phenolic microspheres are obtained by feeding the phenolic resin and the other components (e.g. surfactants, see below)27) into a mixer, heating them to the required temperature, and then pumping them via a displacement pump into a disk sprayer. At the top of the spray chamber the condensation products are dispersed and heated... 

At present, phenolic microspheres based on grade B bakelite are produced commercially in the USSR 29). They are similar to those produced in USA (Table 3) U). 

Phenolic microspheres are weaker than glass and they cannot withstand a hydrostatic pressure greater than 2.5 MPa, whereas glass microspheres can stand pressures up to 12 MPa 30). 

Table 2. Process conditions and properties of phenolic microspheres...

The Carbosphere brand of filler is manufactured in USA by carbonizing BJO phenolic microspheres at 900 °C in an inert atmosphere. They are 5-150 pm (average 40 pm) in diameter, have wall thicknesses of 1-4 pm and bulk densities of 130 to 140 kg/m3 38). Four types of Kresosphere microspheres are produced in Japan. They are more than 95 % carbon and made by carbonizing microspheres made from wood resins (pitches) at 800-1100 °C in an inert medium (Table 7) 39). 

Fig. 5. Molding pressure (P) versus binder concentration (C) for BV-01 phenol microspheres and binder viscosities of 1.25 (1) and 10.8 (2) Pa s...

Epoxy syntactic foams are the best known representatives of this type of material. The brands manufactured in the USSR are EDS (with glass microspheres), EDM (with phenol microspheres). Dienic, novolac, bisphenolic, and esteric structured epoxy resins are used... 

A formulation used in USA is 54.7 parts epoxy resin, 10.3 parts aromatic amine, and 30.0 parts BJO phenolic microsphere. It has an apparent density of 336 kg/m3 and is viable for two hours. The mixture is hardened at 71 °C for 2 hours or at 82 °C for 1 hour 88). Recently, Prigozhin and Krasnikova 89) successfully applied simplex planning to the formulation of EDS materials with good properties. In addition to glass and phenolic microspheres, polystrene18), carbon38 40>, and mineral microspheres 18,59) have also been used. 

In the USSR syntactic materials are manufactured from phenolic microspheres and phenolic binders (18-45 vol%) using press-molding at 170-190 °C and at low pressure. They apparent densities of 400-700 kg/m3 1). 

Syntactic materials based on polybenzimidazole and glass or phenolic microspheres (y = 40-500 kg/m3) have been described in the literature109 nl). They have been used as ablation materials that consist of two layers, one of which is a monolithic carbon plastic. Carbon fiber was added to the polyimide binder to improve the mechanical properties of the material. 

Table 9. Formulation and Properties of Carbonized Syntactic Foams Using BJOa Phenolic Microspheres...

Nicholson and Thomas113) reported carbonized plastic foams containing 51% carbon, made from novolac or epoxy oligomers and phenolic microspheres. A dry charge of resin and filler is mixed in a vibrating mill, then placed in a mold, and heated at 150 °C for 3 hours under 2 x 10 Pa. 

Fig. 8. Effect of molding pressure P on the stress in compression (crc) for a carbonized foamed plastic made from a compound binder (wood resin, furfuryl alcohol, maleic anhydride) and phenolic microspheres 381...

Systems in which a polyolefin is the binder have attracted world-wide attention. These include the polyethylene—phenolic microsphere 74,115>, polyethylene or polypropylene—glass microsphere114116), polyethylene or polybutylene—PVC microsphere (containing isobutane)52), and polyethylene/vinyl acetate copolymer—glass microsphere11 systems. Syntactic foams have been made from polystyrene (and its copolymers with chlorostyrene or polychlorostyrene) and microspheres made from polyethylene or polypropylene46115 and foams from styrene/acrylonitrile 1171... 

A family of elastomeric foams has been developed by Rand 129) for use as stress relief coatings on electronic components in encapsulated electronic assemblies. Polysulfide, silicone and polyurethane elastomers blended with glass and phenolic microspheres have been used to formulate syntactic foams (Fig. 10) These foams are used to minimize the stress caused by differential thermal expansion between the component and the encapsulant. 

Fig. 10. Compression stress-strain properties of various elastomeric syntactic foams129> (l)urethane elastomer binder and glass microspheres y = 640 kg/m3, void fraction 0.321 (2) polysulfide elastomer binder and phenolic microspheres y = 1500 kg/m3, void fraction 0.133 (3) silicone elastomer binder and glass microspheres y = 610 kg/m3, void fraction 0.407...

Unsaturated polyester syntactic foams are cheaper than epoxy foams, although the latter are stronger, more water resistant, and shrink less if cured at room or high temperatures 83,136). One merit of polyester syntactic foams is the low apparent density that can be obtained. But the mechanical characteristics depend upon the apparent density e.g. for the Soviet polyester syntactic foams (SPB), using phenolic microspheres (BV-01)1 ... 

Table 16. Properties of carbonized syntactic foams (phenolicbinder and phenolic microspheres)...

Fig. 17. Heat Conductivity (X.) versus temperature and apparent density for a carbonized phenolic foam with phenolic microspheres, (1) 200, (2) 250, (3) 300 and (4) 350 kg/m3 U3)...

The strength of adhesion also depends on the filler, being better with glass than with phenolic microspheres. This is due to better adhesion at the binder-filler interface (See Sect. 5.2.2) 6-124). 

Dementyev and Tarakanov 8 160) used another approach by adopting a macrostructural model of syntactic foam morphology161 to calculate the strength properties of an epoxy foam with phenolic microspheres. They made two restrictive assumptions, i.e. that the mechanical properties of the microsphere walls and the binder are the same, and that the volume fraction of filler is substantially smaller than that of the matrix. The macrostructural parameters of the syntactic foam are then defined in terms of the dimensions of the microspheres, and their displacements have the same nature as the deformations of the nodes and edges of an imaginary latice. We then get ... 

Fig. 20. Calculated and experimental (dotted and solid curves respectively) values of (1) elastic modulus (E) and (2) ultimate compression strength (crj versus phenolic microsphere concentration (C) in an epoxy syntactic foam at 23 °C 162)...

Fig. 21. Compression diagram for (1) an epoxy syntactic foam with phenolic microspheres and (2) unfilled epoxy resin 1611...

Fig. 22a and b. Behavior of syntactic foams during thermal treatment. Key a Thermogram of the hardening process for (1) Unfilled epoxy and (2) Epoxy syntactic foam with phenolic microspheres, b Glass transition temperature of the epoxy binder versus concentration of phenolic microspheres 1621... 

Typical fillers calcium carbonate, talc, glass fiber, glass beads, glass flakes, silica flour, wollastonite, mica, sepiolite, magnesium hydroxide, carbon black, clay, metal powders (aluminum, iron, nickel), steel fiber, si-licium carbide, phenolic microspheres, wood fiber and flour, antimony trioxide, hydrotalcite, zinc borate, bismuth carbonate, red phosphorus, potassium-magnesium aluminosilicate, fly ash, hydromagnesite-huntite... 

Syntactic foam is made by dispersing hollow microballoons into a liquid polymer and then solidifying it. Microballoons are typically hollow glass or hollow phenolic microspheres, and the most common liquid polymer is an epoxy prepolymer, which is then cured. Although some products are notably woodlike in their properties and machinability, primary applications are high-performance products such as deep-sea instrumentation. 

Suppliers of thermoexpandable microspheres are Expancel (Eka Chemicals AB, Akzo Nobel), Sweden Matsumoto Yushi-Seiyaku Co. Ltd, Japan Sekisui Chemical Company Ltd, J apan, and Kureha Chemical Industry Co. Ltd, Japan. Suppliers of solid microspheres are Microbeads AS, Norway Matsumoto Yushi-Seiyaku Co. Ltd, Japan, and Sekisui Chemical Company Ltd, Japan. Supplier of microcapsules for release purposes is Microbeads AS, Norway. Supplier of phenolic microspheres is Asia Pacific Microspheres, Malaysia. Supplier of EPS particles Kaucuk a,s-Unipetrol Group, Czech Republic Dow Chemical Company, Michigan, USA BASF SE, Germany. Suppliers of metal coated microspheres Microbeads AS, Norway and Sekisui Ghemical Gompany Ltd, Japan. 

Gas-injection molding n. A specialized technique for molding low-density structures in which a mixture containing cork particles, or glass or phenolic microspheres, glass fibers, and a thermosetting resin is injected into a mold by fluidizing it in a gas stream. 

Emerson Gumming, Inc., eventually bought the rights to the Sohio process and produced a variety of microspheres. Union Carbide was licensed to produce the phenolic microspheres offered under the name Phenolic Microballoons (Table 15). When Phenolic Microballoons are introduced into a crude-oil storage tank, they form a fluid seal that rises and falls with the level of the oil. A continuous vapor-barrier seal is formed, which reduces evaporational losses up to 90%. Tests have been conducted under various mechanical and weather conditions and with crude oils of varying vapor pressure. 

---