Reinforced-plastic molding compound

HDPE, high density polyethylene PP, polypropylene EVA, ethylene—vinyl alcohol SMC, sheet-molding compound ERP, fiber-reinforced plastic LDPE, low density polyethylene PE, polyethylene BMC, bulk mol ding compound TPE, thermoplastic elastomer. 

Uses. Molding compounds surface coatings adhesives laminating or reinforcing plastics... 

The resin matrix can be either thermosetting or thermoplastic. Thermosetting resins such as epoxy, polyimide, polyester, and phenolic are used in applications where physical properties are important. Polyester and epoxy composites make up the bulk of the thermoset composite market. Of these two, polyesters dominate by far. Reinforced with glass fiber, these are known as fiberglass-reinforced plastics (FRPs). FRPs are molded by layup and spray-up methods or by compression molding either a preform or sheet molding compound (SMC). 

To meet fabricated dimensional tolerances different approaches are used. They include use of specific fillers and reinforcements and process control (Chapter 3). Popular filler used is short glass fibers (Chapter 15). Over 50wt% of all types of glass fibers used with different plastics and by different processes are used in injection molding compounds. Table 2.2 shows the shrinkage of different unreinforced plastics ad glass fiber reinforced plastics based on ASTM testing procedures. 

In use are stamping compression molding presses. Plastic used can be TS sheet molding compounds (SMCs) and stampable reinforced thermoplastic sheet (STX) material (STX is a registered tradename Azdel Inc., Shelby, NC). It is usually composed of a glass fiber-thermoplastic RTP (Chapter 15). 

TS plastics in reinforced sheets and compounds are usually used. Also used are reinforced thermoplastic sheets and compounds. With TSs compression molding (CM) can use preheated material (dielectric heater, etc.) that is placed in a heated mold cavity. The mold is closed under pressure causing the material to flow and completely fill the cavity. Chemical crosslinking occurs solidifying the TS molding material. 

Earlier attempts—in the 1970s—to make cellulose-filled thermoplastic compositions had identified a serious obstacle. It became recognized that fillers, particularly cellulose fibers, do not disperse easily throughout the plastic formulations during compounding and molding. Accordingly, the finished products typically do not exhibit the desirable physical characteristics ordinarily associated with fiber-reinforced plastic composites. This problem has been dealt with in a number of patents. 

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