Epoxides laminates

As mentioned in the introduction, epoxide resin laminates are much less important in tonnage terms than those for polyesters. However, in terms of value the epoxide laminates are significant. 

Tritolyl phosphate (TTP) has been examined as a pretreatment for E-glass in epoxide laminates and thermoplastic adhesives for bonding poly(vinyl chloride) to aluminum, steel to zinc, and acrylonitrile butadiene styrene to aluminum [59]. Mono- and diphosphate esters have been claimed to be suitable adhesion-promoting primers for acrylic adhesives on metal [60,61], unsaturated acid phosphates have been suggested as primers for use on metals to be bonded with free radical initiated adhesives [42], and thiopho-sphate esters have been suggested for adhesives to be used on plastics, ceramics, and metals [62]. 

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. 

NB Daia for the three important ihermosetting materials (phenolics, aminoplastics and epoxide resins) were not covered in the 1998 review on which the 1997 data was based. The 1987 figures for these materials do include a substantial percentage of use in adhesive, surface coating and laminate applications. 

Because of their favourable price, polyesters are preferred to epoxide and furane resins for general purpose laminates and account for at least 95% of the low-pressure laminates produced. The epoxide resins find specialised uses for chemical, electrical and heat-resistant applications and for optimum mechanical properties. The furane resins have a limited use in chemical plant. The use of high-pressure laminates from phenolic, aminoplastic and silicone resins is discussed elsewhere in this book. 

About half of epoxide resin production is used for surface coating applications, with the rest divided approximately equally between electronic applications (particularly for printed circuit boards and encapsulation), the building sector and miscellaneous uses. In tonnage terms consumption of epoxide-fibre laminates is only about one-tenth that of polyester laminates, but in terms of value it is much greater. 

Epoxide resin laminates are of particular importance in the aircraft industry. It has been stated that the Boeing 757 and 767 aircraft use 1800 kg of carbon fibre/ epoxide resin composites for structural purposes per aeroplane. The resin has also been used with Aramid fibres for filament-wound rocket motors and pressure vessels. The AV-18 fighter aircraft is also said to be 18% epoxide resin/cc bon fibre composite. The resins are also widely used both with fibres and with honeycomb structures for such parts as helicopter blades. 

Epoxide resins reinforced with carbon and Aramid fibres have been used in small boats, where it is claimed that products of equal stiffness and more useable space may be produced with a 40% saving in weight over traditional polyester/ glass fibre composites. Aramid fibre-reinforced epoxide resins have been developed in the United States to replace steel helmets for military purposes. Printed circuit board bases also provide a substantial outlet for epoxide resins. One recent survey indicates that over one-quarter of epoxide resin production in Western Europe is used for this application. The laminates also find some use in chermical engineering plant and in tooling. 

Laminates have been prepared for the manufacture of chemical plant. They have better heat and chemical resistance than the polyester- epoxide- phenolic- or aminoplastic-based laminates but because of the low viscosity of the resins were not easy to handle. Because they were also somewhat brittle, furan-based laminates have been limited in their applications. 

The highest mechanical strengths are usually obtained when the fibre is used in fine fabric form but for many purposes the fibres may be used in mat form, particularly glass fibre. The chemical properties of the laminates are largely determined by the nature of the polymer but capillary attraction along the fibre-resin interface can occur when some of these interfaces are exposed at a laminate surface. In such circumstances the resistance of both reinforcement and matrix must be considered when assessing the suitability of a laminate for use in chemical plant. Glass fibres are most commonly used for chemical plant, in conjunction with phenolic resins, and the latter with furane, epoxide and, sometimes, polyester resins. 

As an additional component, various thermoplastic polymers can be used. As a binder for copper clad laminates, a solution of solid epoxide resin (Epikote 1001), BPA/DC prepolymer, Zn acetate and poly(phenylene sulfide) was used [83], Other binders for reinforced plastics contain polysulfone. Such compositions consist of liquid BPA/ECH epoxide resin, BPA/DC prepolymer, polysulfone and bis(4-hydro-xyphenyl)sulfone [85]. Bis(4-aminophenyl)sulfone can be also added [86]. In such systems the bisphenol reacts with the epoxide resin as a chain extension agent, whereas the diamine crosslinks the diepoxide. The Tg values are close to 200 °C. They can be increased a little, if the BPA/ECH epoxide resin is replaced by the tetra-epoxide A,A,A, A -tetrakis(2,3-epoxypropyl)diaminodiphenylmethane [87]. 

As mentioned above, the main application of the epoxide /dicyanate systems are copper clad laminates. Other important uses are conductive materials with silver... 

A binder for copper clad laminates contains the prepolymer from BPA/DC and A -(3,5-dimethyl-4-vinylphenyl)maleimide in methylethylketone, an epoxynovolak resin, Zn acetate and tert.butyl peroxide [100], In a similar composition, a prepolymer obtained from epoxide resin, BMI and bis(4-aminophenyl)methane was mixed with BPA/DC, Zn acetate and tert.butyl peroxide in solution [101]. 

Two-layered GRPs for copper clad laminates are obtained with one layer consisting of the three-component system (e.g. BPA/DC, BMI, brominated epoxide resin, Zn octoate and triethylenediamine in methylethylketone). The other layer has the usual epoxy matrix (brominated epoxide resin, dicyandiamide as a hardener and 2-ethyl-4-methylimidazole as curing accelerator) [119]. As similar two-layered laminate contains BPA/DC, BMI, epoxynovolak resin, Zn acetate and triethylenediamine in the first layer and BPA/DC only with the same catalysts in the second layer [120]. 

The three-component cyanate/maleimide/epoxide compositions are mainly used as polymer matrix in copper clad laminates and in carbon fiber composites for engineering purposes. High heat resistance, water and solvent resistance, mechanical and impact strength is claimed. A composition for copper wire enamelling [121] and a resin for electric motor coil windings impregnation were described [107]. 

N-alkylated valine may be slmllarlly synthesized from an epoxide and valine. Figure 15A. Synthesis of DL-mlxtures of N-(2-hydroxyethyl)- and N-(2-hydroxypropyl)-vallne have been performed using o-bromo-lsovalerlc acid and the appropriate alky lamine, Figure 15B (2 ). The reactions of propylene oxide and N-acetyl-cystelne methyl ester, valine methyl ester and N-benzoyl-hlstldlne methyl ester respectively were recently thoroughly Investigated and the stereochemistry discussed (257). 

Exposed to hydrolytic conditions at different pH (2, 6,10), tetraethyl oxiranylidene-l,l-diphos-phonate reacts very slowly with water. " The reaction of tetraethyl oxiranyhdene-l,l-diphosphonate with several primary amines, including -propylamine, cyclohexylamine, benzylamine, and ally-lamine, has been examined, and the phosphonyl phosphates were isolated as the major products in 40-63% yields (Scheme 4.38). It seems very likely that the formation of phosphonyl phosphates is the result of a rearrangement either in concert with (path a) or subsequent to (path b) the opening of the epoxide with amine and generation of an intermediate alkoxide ion. When di- -propylamine was used, a second product, ethenylidene-1-phosphonyl-1-phosphate, corresponding to the loss of amine by elimination, is formed (32%) in addition to aminoethyl-l-phosphonyl-1-phosphate (20%). ... 

Laminating is, furthermore, important as a manufacturing process for composite materials by means of so-called laminating resins (unsaturated polyester, epoxides with substrates such as glass and carbon fibers) for example, in aeroplanes, vehicles and in shipbuilding. In these applications, however, bonded joints in the true sense of the meaning do not occur. 

Inhibition of the polymerization by air was controlled by use of 1 1 diacrylate-poly (methyl methacrylate) mixtures or by using the acrylate in a laminate between two glass plates. These cost-effective cures use no external energy and no lamps. Composites of glass fiber and epoxides from vegetable oils have been cured in sunlight with di-aryliodinium and triaryl sulfonium salts in 25 min.311 Further work is needed to speed up this photocationic cure. 

Epoxy polymers (ako known as epoxides or epoxylines) were first developed in the 1930s by Pierre Castan and were commerciaUy produced in 1939 (Mossman, 1997). The high early production costs compared with those of polyesters have limited their applications but they are established as protective coatings, laminates and construction materiak. 

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