Synthetic thermosetting polymers

Apart from the synthetic thermosetting polymer adhesives, other polymers such as polyvinyl acetate and polyamides are used in... 

Phenol-formaldehyde was reported as the first commercially synthetic polymer (1899) which was introduced as BakeliteT by Baekeland in 1909. This was the period which marked the dawn for the production of commercial synthetic thermosetting polymers. Other advances in the field included the discovery of urea-formaldehyde resins in 1884 and the beginning of their commercialization as Beetle moldable resin in 1928, followed by thiourea-formaldehyde (1920), aniline-formaldehyde (Cibatine by Ciba, 1935) and melamine-formaldehyde (1937) moulding powders. The year 1909 marked the discovery of epoxy compounds by Prileschaiev, which were not used until World War 2. The first thermoset polyesters, invented by Ellis, date back to 1934 and in 1938 was reported their first use in the forms of glass-reinforced materials [1]. 

Synthetic thermosetting polymers used in the construction industry are polyester, vinylester and epoxies these materials are generally used to manufacture parts of the machines that produce sustainable energy generators. In addition, thermoplastic resins, such as polyetheretherketone (PEEK), polyethersulphone (PES) and various liquid crystal polymers (LCP) are also used. The latter high performance polymers also meet stringent out-gassing (relevant to space environments) and flammability requirements. 

Synthetic Resins. Various polymers and resins are utilized to produce some specialty carbon products such as glassy carbon or carbon foam and as treatments for carbon products. Typical resins include phenoHcs, furan-based polymers, and polyurethanes. These materials give good yields of carbon on pyrolysis and generally carbonize directly from the thermoset polymer state. Because they form Httle or no mesophase, the ultimate carbon end product is nongraphitizing. 

Bakelite, the first synthetic polymer, is an example of a thermoset polymer. It is prepared by the polymerization of phenol and formaldehyde in the presence of ail acid. Carbocations produced by protonation of formaldehyde bond to the ortho and para positions of the highly reactive phenol molecules in a Friedel-Crafts alkylation reaction. The benzylic alcohols that are produced in this step react to produce carbocations that then alkylate additional phenol molecules. A mechanism for the first few steps of this polymerization process is shown in Figure 24.4. 

Some synthetic polymers can be recycled and some cannot. So-called thermoplastic polymers, usually composed of hnear or only shghtly branched molecules, can be heated and formed and then reheated and reformed. Therefore, they can be recycled. On the other hand, thermosetting polymers, which consist of molecules with extensive three-dimensional cross-hnking, decompose when heated, so they cannot be reheated and reformed. This makes them more difficult to recycle. 

The first synthetic polymers were produced as by-products of various organic reactions and were regarded as unwanted contaminants. Thus the first preparations of many of the polymers now regarded as essential to our modern lifestyle were thrown away in disgust. One chemist who refused to be defeated by the "tarry" products obtained when he reacted phenol with formaldehyde was the Belgian-American chemist Leo H. Baekeland (1863-1944). Baekeland s work resulted in the first completely synthetic plastic (cal led Bakelite), a substance that when molded to a certain shape under high pressure and temperature cannot be softened again or dissolved. Bakelite is a thermoset polymer. In contrast, cellulose nitrate is a thermoplastic polymer that is, it can be remelted after it has been molded. 

There exists a large number of other solvent-based adhesives derived from synthetic polymers that are soluble in organic solvents. For example, substituted nylons (aliphatic polyamides)—typically, N-methoxymethyl nylons—are soluble in some alcohols and alcoholic mixtures and have been used to provide solution adhesives with good rust resistance. Such soluble nylons may be compounded with many thermosetting polymers to improve their properties to yield such outstanding characteristics as their resilience and peel strength. 

The synthetic polymer industry started in 1910 when the thermoset moulding resin Bakelite was commercialized and has become a global industry in the intervening IOOh- years. The synthetic thermoplastic polymer industry started in Europe and developed in Europe and the Americas and Japan. Then, there was a shift of production and consumption to Asia-Pacific, particularly China, and a shift in production to the Middle East, in the last 30 years. The polyolefin industry has perhaps even led this shift. Five of the major polyolefin producers (in the list of the... 

The combination with fibres has proved difficult however. Often there are issues with compatibility between bio-resins and fibres (both natural and synthetic), which cause defects in the composite structure and ultimately poorer physical properties. Castor-oil polyurethane was compared with phenolic resins when infused over sisal fibres however, the phenolic resins showed better structural performance when compared with the castor oil-based material [52]. This is not always the case, as some improvements have been made. Soybean oil thermoset polymers were used in a glass/flax hybrid composite resulting in improved mechanical performance [73], Thermoset resins were produced from triglyceride oils with a wide range of properties (tensile modulus 1-2 GPa, glass transition temperature Tg 70-120 °C) and glass- and hemp- fibre composites were manufactured [74,75]. 

Polyurethanes are mostly thermosetting polymers [9]. They are used to make foam products (example seats), wheels, tires, hoses, synthetic fibers, etc. and for surface coatings and sealants. Also their foams have some resistance to the damaging effects of visible light. 

Sealants are also known as adhesives with lower strengths , and they mainly comprise synthetic elastomeric thermoplastic or thermosetting polymers (pigmented/unpigmented). 

These thermosetting polymers are synthetic resins containing the amine group (-NHj) in their macromolecules. The major commercial resins in this group are ... 

The first completely synthetic plastic material was made from the condensation of phenol and formaldehyde in the presence of a catalyst. The production of this material was perfected by Leo Hendrik Baekland (1863-1944), a Belgian chemist working in the United States, and it was marketed from 1909 under the name Bakelite. Bakelite is a highly crosslinked three-dimensional thermosetting polymer, and in the 1920s and 1930s a number of similar materials were developed such as urea formaldehyde and melamine formaldehyde. 

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