Solvent crazing resistance

Solvent crazing resistance Enhances Enhances Initially remains unchanged then deteriorates Enhances Deteriorates... 

EP 323142 (European) 1989 Ternary polyether ketone blend wire insulations Pirelli General PLC, UK CK Alesbury, RJ Murphy Formulation shows excellent stress craze resistance, flexibility and flame resistance Blends of polyarylene ether ketones, polyether imides and polyfimide siloxanes) were coated onto wire for solvent resistance, O index and abrasion resistance. Blends without siloxane-imide copolymer did not meet these properties... 

Polysulfone has a second, low-temperature glass transition at — 101°C similar to other tough, rigid thermoplastic polymers. These polymers also resist aqueous acid and alkaline environments. Properties such as physical aging and solvent crazing can be improved by annealing the parts. This also reduces molded-in stresses. 

Furfuryl alcohol is used as a viscosity reducer for epoxy formulations. The addition of furfuryl alcohol to urea-formaldehyde resins improves the craze resistance and heat stability of the adhesives. Furfuryl alcohol serves as an effective wetting agent and solvent for phenolic resins in the manufacture of phenolic resin abrasive grinding wheels. Other miscellaneous uses of furfuryl alcohol include use in alkaline paint strippers and cleaning formulations, as a solvent and carrier for dyes in textile printing, and as a chemical intermediate. 

A gelcoat designed specifically for use in the manufacture of FRP mould tools. Exhibits high gloss, excellent abrasion and solvent resistance, with superior hardness and exceptional craze resistance. 

In general, polycarbonate resins have fair chemical resistance to aqueous solutions of acids or bases, as well as to fats and oils. Chemical attack by amines or ammonium hydroxide occurs, however, and aUphatic and aromatic hydrocarbons promote crazing of stressed molded samples. Eor these reasons, care must be exercised in the choice of solvents for painting and coating operations. Eor sheet appHcations, polycarbonate is commonly coated with a sihcone—sihcate hardcoat which provides abrasion resistance as well as increased solvent resistance. Coated films are also available. 

As may be expected of an amorphous polymer in the middle range of the solubility parameter table, poly(methyl methacrylate) is soluble in a number of solvents with similar solubility parameters. Some examples were given in the previous section. The polymer is attacked by mineral acids but is resistant to alkalis, water and most aqueous inorganic salt solutions. A number of organic materials although not solvents may cause crazing and cracking, e.g. aliphatic alcohols. 

The other effect of having a stretched area is a reduction in resistance to stress cracking. Crazing is a possibility in such areas such as in polystyrenes, and environmental stress cracking caused by solvent substances will occur in the stretched areas. This is a particularly important consideration in vacuum formed products used for packaging food that frequently has some solvent action on the plastics. 

PCs are processed by conventional injection molding and extrusion. The impact resistance of molded or extruded PCs is decreased when they are exposed to solvents which tend to craze these plastics. Considerable care must % 5,Ji-... 

When chemicals are weak solvents for polystyrene, stress cracks are formed in the products. Chemical resistances to practical chemicals are compared in Table 18.5. HIPS-SPS blend exhibits better resistance to chemicals which are used in the kitchen and bathroom. In HIPS/SPS blend, SPS may work to prevent the formation of crazes and their propagation to cracks initiated from contact with chemicals. 

Of the economical plastics mentioned above, GP polystyrene is becoming less popular, as it is one of the most brittle plastics unless it is impact modified. GP or (GPPS) polystyrene has good clarity, is highly permeable (compared with most other plastics) to moisture and gases, has poor heat and solvent resistance. It crazes then disintegrates in contact with isopropyl myristate (which is used in some pharmaceutical formulations). It is, however, an excellent material to mould (low shrinkage)... 

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