Tham khảo tài liệu 'materials handbook 15th ed - g. brady_ h. clauser_ j. vaccari (mcgraw-hill_ 2002) ww part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 700 PHENOL-FORMALDEHYDE RESIN Juvelite was made in Germany by condensing the phenol and formaldehyde with the aid of mineral acids and Laccain was made under an English patent by using organic acids as catalysts. A Russian phenol resin under the name of Karbolite employed an equal amount of naphthalenesulfonic acid C10H7SO3H with the formaldehyde. The hundreds of different phenolic molding compounds can be divided into six groups on the basis of major performance characteristics. General-purpose phenolics are low-cost compounds with fillers such as wood flour and flock and they are formulated for noncritical functional requirements. They provide a balance of moderately good mechanical and electrical properties and are generally suitable in temperatures up to 300 F 149 C . Impact-resistant grades are higher in cost. They are designed for use in electrical and structural components subject to impact loads. The fillers are usually paper chopped fabric or glass fibers. Electrical grades with mineral fillers have high electrical resistivity plus good arc resistance and they retain their resistivity under high-temperature and high-humidity conditions. Heat-resistant grades are usually mineral- or glass-filled compounds that retain their mechanical properties in the 375 to 500 F 190 to 260 C temperature range. Some of these such as phenylsilanes provide long-term stability at temperatures up to 550 F 288 C . Special-purpose grades are formulated for service applications requiring exceptional resistance to chemicals or water or combinations of conditions such as impact loading and a chemical environment. The chemical-resistant grades for example are inert to most common solvents and weak acids and their alkali resistance is good. Nonbleeding grades are compounded specially for use in container closures and for cosmetic cases. The resins are marketed usually in granular form partly polymerized for molding under heat and pressure which complete the polymerization making the
