TAILIEUCHUNG - Modern Plastics Handbook 2011 Part 2

Tham khảo tài liệu 'modern plastics handbook 2011 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Thermoplastics If higher stiffness is required short glass reinforcement can be added. The use of a coupling agent can dramatically improve the properties of glass-filled Other fillers for polypropylene include calcium carbonate and talc which can also improve the stiffness of PP. Other additives such as pigments antioxidants and nucleating agents can be blended into polypropylene to give the desired properties. Carbon black is often added to polypropylene to impart UV resistance in outdoor applications. Antiblocking and slip agents may be added for film applications to decrease friction and prevent sticking. In packaging applications antistatic agents may be incorporated. The addition of rubber to polypropylene can lead to improvements in impact resistance. One of the most commonly added elastomers is ethylene-propylene rubber. The elastomer is blended with polypropylene forming a separate elastomer phase. Rubber can be added in excess of 50 to give elastomeric compositions. Compounds with less than 50 added rubber are of considerable interest as modified thermoplastics. Impact grades of PP can be formed into films with good puncture resistance. Copolymers of polypropylene with other monomers are also available the most common monomer being ethylene. Copolymers usually contain between 1 and 7 wt of ethylene randomly placed in the polypropylene backbone. This disrupts the ability of the polymer chain to crystallize giving more flexible products. This also improves the impact resistance of the polymer decreases the melting point and increases flexibility. The degree of flexibility increases with ethylene content eventually turning the polymer into an elastomer ethylene propylene rubber . The copolymers also exhibit increased clarity and are used in blow molding injection molding and extrusion. Polypropylene has many applications. Injection-molding applications cover a broad range from automotive uses such as dome lights kick panels and car battery cases

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