General Purpose Grades

This group contains non-precrosslinked, sulfur-free, soluble, homo- and copolymers and is the most important in terms of the quantity used. It comprises the standard grades with polymer viscosities of approximately 30-140 Mooney units (ML4 at 100°C) and slight to medium crystallization types. These grades are also known as mercaptan grades. Their property profiles tend to be influenced mainly by polymer viscosity. 

Grades with slight to very slight crystallization should be used in parts intended for low-temperature service. The influence of crystallization tendency on polymer and elastomer properties is listed in Table 1.3. 

XD-grades are produced with a special modifier. Some of them are copolymerized with other monomers to produce copolymers that have only a medium or slight tendency to crystallization. 

Processing behavior They are generally less elastic (reduced nerve ) than M-grades and are, therefore, more easily processed by calendering or extrusion. Additionally, the ram pressure during mixing can be reduced and as a result the compounds have greater scorch resistance. 

Compatibility with fillers and oil Filler dispersion in soft compounds Dimensional stability and shape retention Green strength especially of heavily loaded compounds 

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Development of toughened acetals has recendy dourished. One such grade, Delrin lOOST, boasts a notched-impact strength of 900 J/m (16.86 ft-lb/in.) at 23°C, substantially higher than that of nonmodified, general purpose grades (Table 2). 

The oils from which factices are manufactured are unsaturated vegetable and animal oils, which react with sulphur. Fatty oils with iodine number greater than 80 (iodine number is defined as the number of grammes of iodine absorbed by 100 g of fat/oil) are generally used, i.e., oils with three or more double bonds per triglyceride molecule. Rapeseed oil is the most common oil used for general purpose grades and castor oil is used for oil resistant factice. Other oils are used in preference by other countries due to local availability and cost. 

At low temperatures, general-purpose grades are generally usable down to -10°C but special grades perform well down to -40°C (bumper grades, for example) according to the mechanical constraints experienced. 

Fire resistance is naturally weak. General-purpose grades burn easily, generating flames, even after removing the ignition source. Moreover, polybutene drips while burning. 

At low temperatures, general-purpose grades generally have a brittle point of -65°C down to -80°C. 

The mechanical properties are generally good with a fair rigidity as long as the temperature does not rise too much. However, general-purpose grades have a low impact resistance and... 

The continuous use temperatures in an unstressed state are generally estimated from 90°C up to 125°C for general-purpose grades and up to 140°C for heat-resistant polycarbonates if the softening or melting temperatures are higher. 

Glass transition temperatures are high, roughly 150°C for general-purpose grades and 160-200°C for heat-resistant grades. 

Fire resistance is naturally weak. For general-purpose grades, oxygen indices are roughly 25 up to 27 with a V2 UL94 rating. 

J/m versus 150-250J/m at 20°C for given general-purpose grades... 

General-purpose grades of PTFE are whitish and translucent with a transmittance of 82% for a thickness of 0.1 mm and 40% for a 1-mm thickness. Refractive indices are roughly ... 

General-purpose grades of ETFE are whitish and translucent. However, for certain grades in thin widths, for example a film of 0.025 mm, transmittance is about 95%. Refractive indices are roughly 1.407. 

General-purpose grades have a high coefficient of friction, 0.35-0.45 for example, but special grades are marketed for tribological applications with coefficients of friction ranging from 0.15 up to 0.2. 

General-purpose grades of cellulosics are transparent or translucent. Certain grades in thick films or sheets, 1.5 mm thick for example, have transmittances superior to 90% with a haze inferior to 8%. Refractive indices are roughly 1.47-1.48. 

Glass transition temperatures are roughly 143°C for a general-purpose grade up to 157°C for a special heat-resistant grade. 

Glass transition temperatures are roughly 120°C for a general-purpose grade. 

E-glass the general-purpose grade that represents more than 90% of the reinforcement fibres. 

Flammability. The general-purpose grades are usually recognized as 04 HB according to the requirements of Underwriters Laboratories UL94 and also meet the requirements, dependent on thickness, of the Motor Vfchicle Safety Standard 302. 

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