Thermosetting epoxid

The purpose of this paper is to present a technique whereby manufacturing process dynamics for structural polymers can be accurately defined through efficient laboratory rheological characterization. Structural polymers, in this paper, refer principally to the thermosetting epoxides, phenolics and polyimides. This type of test pattern, however, is generally applicable to the production and utilization of most polymers. The engineering applications associated with these polymers involves primary and secondary aerospace articles. In this situation, failure to meet performance criteria could result in catastrophic loss of the vehicle and associated cargo. 

As has already been stated in Chapter 5, the principal method used for the plastic encapsulation of electronic devices is transfer moulding with thermosetting epoxide resin based moulding compounds. A number of other thermosetting compounds are also occasionally used but until recently no thermoplastic materials capable of being injection moulded were suitable for the encapsulation of electronic components because of the high pressures required. One thermoplastic material that has been successfully developed for the packaging of electronic components is polyphenylene sulphide. 

It was evident from post-treatment surface tensions in this study that iiquid adhesives using thermosetting epoxide polymers mixed with catalyzing agents wet significantly in atmospheric plasma-based pretreatments because the differential surface free energies are at a minimum of 20 dynes/cm, twice the benchmark industry requirement. 

Thermosetting Reactive Polymers. Materials used as thermosetting polymers include reactive monomers such as urea—formaldehyde, phenoHcs, polyesters, epoxides, and vinyls, which form a polymerized material when mixed with a catalyst. The treated waste forms a sponge-like material which traps the soHd particles, but not the Hquid fraction the waste must usually be dried and placed in containers for disposal. Because the urea—formaldehyde catalysts are strongly acidic, urea-based materials are generally not suitable for metals that can leach in the untrapped Hquid fractions. Thermosetting processes have greater utiHty for radioactive materials and acid wastes. 

Epoxy Resins. Epoxy resins (qv) or polyether resins are thermosets used as the binder for terrazzo dooring. The epoxy resin often is made from epichlorohydrin and bisphenol A. An excess of epichlorohydrin is used to assure that the intermediate product contains terminal epoxide groups. 

Interesting developments were also taking place in the field of thermosetting resins. The melamine-formaldehyde materials appeared commercially in 1940 whilst soon afterwards in the United States the first contact resins were used. With these materials, the forerunners of today s polyester laminating resins, it was found possible to produce laminates without the need for application of external pressure. The first experiments in epoxide resins were also taking place during this period. 

The so-called phenoxy resins were a development of epoxide resin technology which had hitherto been used exclusively in the thermosetting resin field (see Chapter 26). As with the most important epoxide resins they are prepared by reacting bis-phenol A with epichlorohydrin to give the following structure (Figure 21.9) ... 

Although phenolic and amino moulding powders remain by far the most important of the thermosetting moulding compositions a number of new materials have been introduced" over the last 30 years based on polyester, epoxide and silicone resins. 

Important thermosetting plastics include the phenolics, melamine-formaldehyde, epoxides and polyester resins used in glass-reinforced plastics. (See also Sections 14.5 and 14.9.)... 

Well-known thermosetting plastics include the phenolics, urea-formaldehyde and melamine-formaldehyde plastics, polyesters and epoxides. 

Epoxy resins are thermosetting matrix resins, characterized by the epoxide group [48,193], as shown in Figure 2.9. 

Epoxy Resins The term epoxy refers to an epoxide group which is a three-membered oxide ring. An epoxy resin is defined as a molecule containing more than one epoxy group capable of being converted into a thermoset (cured) form. The simple structure of epoxy resin [Structure (4.37)] is ... 

The great utility of epoxy resins lies in the fact that the epoxide group is reactive with a large number of molecules which form tough thermoset networks without the evolution of by-products. The reactants can be classified as either direct participants in the crosslinked network or those which promote crosslinking catalytically. 

This substantial toughening effect of CTBN on the cycloaliphatic epoxide ERL-4221, coupled with significant increase of the strength of the resin without seriously lowering the heat distortion temperature, is quite unusual for thermosetting systems. 

ATMET of a triglyceride-based multifunctional monomer [125]. The ring opening of epoxidized soybean oil with 4-vinyl benzene sulfonic acid provided monomers suitable for metathesis polymerization. The bulk reaction of this monomer in the presence of C5 afforded a thermosetting material with a Tg of — 1.6°C. 

Low clamping pressures only are needed, and this in turn means that quite large products can be made on inexpensive plant. By varying the raw materials it is possible to produce either rigid or flexible articles, microcellular or otherwise, and (if required) to include fillers or reinforcing sections. Thermosets other than polyurethane can be used—like epoxides and polyesters (with the latter, the process is known also as resin transfer moulding ). 

Epoxy resins, which are used as adhesives, are also thermoset polymers that form by cross-linking when the two components of the resin are mixed. One component is a low-molecular-mass linear polymer formed by the reaction of the conjugate base of bisphenol A with epichlorohydrin. The nucleophilic oxygens of the phenolate dianion can either displace the chlorine or open the epoxide ring of epichlorohydrin. A slight excess of epichlorohydrin is used to keep these polymer chains short and to ensure that the linear molecules have epoxide groups at their ends. 

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