塑料技术手册:Volume 1:发泡成型·压延成型:Foaming·calendering

　　《塑料技术手册 发泡成型·压延成型（1 影印版）》：　　Polyethylene，polyurethane， and polystyrene are the most common foams； however， polypro— pylene （PP） foams can provide favorablc properties at a lower material cost.PP is stiffer than PE and performs better in load bearing and structural applications.The low glass—transition tempera— ture of PP compared to PS provides increased flexibilitv and impact strength （chapter 1）.Use of PP foams includes packaging， automotive， insulation， and protection of underground pipe.　　It is important to know in advance what foam properties will be required for a particular application.As with other plastics or any material， it is not enough to be told that a material is plastic foam with remarkable properties.The following review on examples of different plastics used includes preliminary information on processes and applications.It starts by reviewing the subject of structural foams and reinforced plastic foams.　　STRUCTURAL FOAM　　Structural foam is a term originally used for cellular thermoplastic articles with integral solid skins and possessing high strcngth—to—weight ratios （Table 8.25）.Eventually， the term covered high— density rigid cellular plastics strong enough for structural applications.As an example， thermoset foams， such as polyurethane， are frequently referred to as structural foams.In general， a structural foam can be made from virtually any high molecular weight thermoplastic organic polymer and will have a cellular core and an integral skin on all sides.The skin is relatively nonporous in relation to the cellular core.　　……