Thermoset plastics durability

Melamine is a strong organic base, which is used primarily to produce melamine resin, which when combined with formaldehyde produces a very durable thermoset plastic. This plastic is often used in kitchen utensils or plates (often sold under the brand name Melmac), and is the main constituent of Formica and Arborite . Melamine tile wall panels are known as whiteboards. Melamine is also used to make decorative wall panels and is often used as a laminate. Melamine is produced from urea, mainly by either of two methods catalyzed gas-phase production or high-pressure liquid-phase production. 

Body Panels Plastics can help considerably reduce the mass of body panels while providing better durability, damage resistance, and corrosion resistance. Their first application in body panels was in 1953 [1]. General Motors introduced the Corvette with a fiber-reinforced thermoset plastic body (see Pig. 17.4). At almost the same time, Kaiser introduced a reinforced-plastic body on a sports car. Since then polymers have been used for fenders, hoods, trunk lids, roofs, doors, quarter panels, and lift gates. 

Compared with other thermosetting polymers (i.e. polyester or vinyl ester resins), epoxy resins are more expensive, but show both better mechanical properties and higher resistance to moisture absorption and to corrosive liquids and environments. These good physical properties and their durability in service help to provide a favorable cost-performance ratio when compared to other thermoset plastics. 

The Araldite series of epoxy resins, manufactured by Huntsman, are perhaps the most well-known, typically two-part systems and these epoxy adhesives wonld generally be expected to bond well to epoxy thermoset plastics. Cyanoacrylates showed good results in these trials [3], but would not be expected to offer the same durability as epoxy-based adhesives. Note that there are so many different grades of epoxy materials that it is impossible to give specific data (Table 3.2) is intended as a guideline and tests would always be necessary to confirm adhesion performance. 

Epoxies will show quite good adhesion (and hence durability) to thermoset plastics but many thermoplastics may require careful surface preparation if this type of adhesive is to be used. 

The thermosetting group, shown in Figure 4.2(b), cannot be reheated as it damages the plastic, forming a useless mass. These type of plastics form a network of cross-linked polymer chains and are moulded during their manufacture when the cross links are formed. They have higher thermal durability and resist acid or basic attacks when compared with thermoplastics. 

Nearly all plastics fall into two broad categories thermoplastics and thermosets. The processing and fabrication are very different, but in both cases have a major effect on the durability of the final products. 

The purpose of this chapter is to describe an analytical tool which, when coupled with accelerated material characterization, is capable of predicting the long term durability of reinforced plastics for applications in hostile environments. Throughout the chapter, the words resin and polymer are used interchangeably, and the resin can be thermoplastic or thermosetting, but it must be remembered that thermosetting resins are much less prone to creep and other viscoelastic effects than are thermoplastics. 

Covalent chemical bonds can form across the interface and are Ukely to occur in cross-Unked adhesives and thermoset coatings. This type of bond is usually the strongest and most durable. However, they require that mutually reactive chemical groups should exist. Some surfaces, such as previously coated surfaces, wood, composites, and some plastics, contain various functional groups that under appropriate conditions can produce chemical bonds with the adhesive material. There are ways to intentionally generate these conditions, such as by surface treatment of plastics with techniques like corona or flame treatment. 

The growth in bioplastics can be supported by the development of biobased plastics from non-food-based agricultural sources, the development of durable products in addition to biodegradable products, and the development of new biobased chemicals for thermoplastic and thermoset polymers. 

Plastics are classified as thermoplastics, rubbers, or thermosets. Available in a variety of forms and blends, their advantages include durability, strength, lightness of weight, and excellent thermal and electrical insulating properties. Progress made in the recycling of plastics has added to the acceptance of plastics. 

Bakelite, a durable plastic used for the casing of early radios and TVs, was the first of the thermosetting polymers. It is a highly cross-linked polymCT formed from the acid-catalyzed polymerization of phenol and formaldehyde. Because it is much darker than Melmac, Bakelite s range of colors is limited. Propose a structure for Bakelite. 

Thermosets More Tailored Durability., Plastics Engineering, April 2001, p. 28. 

Epoxies cure to become thermoset adhesives and so show excellent humidity resistance, especially if one of the substrates is metal. For long-term, durable adhesively bonded metal-to-metal joints, toughened epoxies are hard to beat [6] but where plastics are involved, some of the other technology adhesives invariably offer benefits in terms of ease of application and cure speed whilst still retaining satisfactory environmental resistance. Indeed epoxies do not often show good adhesion to elastomers and for the thermoplastic elastomers cyanoacrylates will generally show the best environmental resistance. 

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