Epoxies amorphous thermoplastics

Test TGDDM epoxy Toughened epoxy Amorphous thermoplastic... 

Cycloahphatic diamines react with dicarboxyUc acids or their chlorides, dianhydrides, diisocyanates and di- (or poly-)epoxides as comonomers to form high molecular weight polyamides, polyimides, polyureas, and epoxies. Polymer property dependence on diamine stmcture is greater in the linear amorphous thermoplastic polyamides and elastomeric polyureas than in the highly crosslinked thermo set epoxies (2—4). 

A number of amorphous thermoplastics are presently employed as matrices in long fiber composites, including polyethersulfone (PES), polysulfone (PSU), and polyetherimide (PEI). AH offer superior resistance to impact loading and higher interlaminar fracture toughnesses than do most epoxies. However, the amorphous nature of such polymers results in a lower solvent resistance, clearly a limitation if composites based on such polymers are to be used in aggressive environments. 

The less simple polymers (like the epoxies, the polyesters and the formaldehyde-based resins) are networks each chain is cross-linked in many places to other chains, so that, if stretched out, the array would look like a piece of Belgian lace, somehow woven in three dimensions. These are the thermosets if heated, the structure softens but it does not melt the cross-links prevent viscous flow. Thermosets are usually a bit stiffer than amorphous thermoplastics because of the cross-links, but they cannot easily be crystallised or oriented, so there is less scope for changing their properties by processing. 

Experimental results are presented that show that high doses of electron radiation combined with thermal cycling can significantly change the mechanical and physical properties of graphite fiber-reinforced polymer-matrix composites. Polymeric materials examined have included 121 °C and 177°C cure epoxies, polyimide, amorphous thermoplastic, and semicrystalline thermoplastics. Composite panels fabricated and tested included four-ply unidirectional, four-ply [0,90, 90,0] and eight-ply quasi-isotropic [0/ 45/90]s. Test specimens with fiber orientations of [10] and [45] were cut from the unidirectional panels to determine shear properties. Mechanical and physical property tests were conducted at cold (-157°C), room (24°C) and elevated (121°C) temperatures. 

A good agreement was found for thermosets, as demonstrated by Yamini and Young (1980) and Cook et al. (1998). The exponent n for all amorphous thermoplastics was about 1.6 and about 1.9 for epoxy thermosets (Fig. 12.7). As n is significantly higher than 1, Brown s rule cannot be applied. 

Figure 12.10 Evolution of In y/Goo) versus T/Tg for amorphous thermoplastics (PS, PMMA). The different points correspond to various epoxy networks. (Reprinted from Perez and Lefebvre, 1995 with kind permission of INPL.)...

The thermoplastics which have been reported as efficient modifiers for epoxy resin can be classified as a) engineering thermoplastics b) amorphous thermoplastics and c) crystalline thermoplastics. 

Epoxies generally have excellent adhesion to metals, ceramics and glass, although on most amorphous thermoplastics epoxies will usually he outperformed by MMA, UV adhesives or cyanoacrylates. Epoxies will bond well to thermoset plastics and are widely used for bonding sheet moulding compound door and body panels in the transportation industries. Epoxies do not adhere well to elastomers, fluoropolymers or polyolefin plastics. 

Thermoplastic resins, development of, 10 172, 19 536, 537-539 packaging requirements for, 19 538 Thermoplastics, 15 407, 2 620. See also Engineering thermoplastics amorphous, 19 537 as embedding materials, 10 8 epoxy-based, 10 365 fabrication of, 26 765-766 in hazardous waste management, 25 824... 

However, similar structures were observed with etched surfaces of amorphous linear thermoplastics, such as polystyrene and poly(methyl methacrylate). Moreover, the small-angle X-ray scattering (SAXS) spectra of simple epoxy networks based on diepoxy and diamine monomers were... 

Carbon black is the most widely used conducting filler in composite industry. Carbon black filled immiscible blends based on polar/polar (65), polar/nonpolar (63,66), nonpolar/nonpolar thermoplastics (67,68), plastic/rubber and rubber/mbber blends (69,70) have already been reported in the literature. The properties of carbon black filled immiscible PP/epoxy were reported recently by Li et al. (60). The blend system was interesting because one of the components is semicrystalline and the other is an amorphous polar material with different percolation thresholds. The volume resistivity of carbon black filled individual polymers is shown in Fig. 21.23. 

Although epoxies are mainly classified as thermosets, it is also possible to produce linear epoxy polymers using comonomers with two reactive sites per molecule. These linear polymers behave as thermoplastics and can be amorphous or semicrystalline. They exhibit some outstanding optical and barrier properties. Similarly, PUs can be either thermoplastics or thermosets depending on the number of reactive sites per molecule of monomers and comonomers. 

In practice, it is necessary to avoid using amorphous resins in structural applications above, or even near to, the T. (This restriction applies to all thermosets, because they are invariably amorphous, but it does not apply to crystalline thermoplastics, otherwise polypropylene chairs, with a of around -15°C, could only be used safely in Alaska and in Siberian winters). A margin of safety of 20°C is required for reasonable durability, and a much larger one in humid conditions. Traces of water, or any other solvent, lower the Tg to below its usual value, so the maximum safe working temperature of a load-bearing amorphous resin is lower in humid conditions than in a dry environment. There is a widely quoted rule of thumb that each 1% moisture absorbed by the matrix lowers the Tg by 20°C. This comes from epoxy resin data in wet atmospheres and different figures apply to other resins and liquids. 

Chem. Descrip. Amorphous hydrophobic fatty acid amide wax Uses Surf, modifier, surf. tens, modifier, slipagenL antiblocking agent for coatings, inks, piastics, thermoset/thermoplastic polyesters and acrylics, thermosetting aikyds and epoxies, thermoplastic PVC food-contact coatings... 

Linear Elastic and Rubber Elastic Behavior. Although stiffening is quite noticeable in the glassy regime of the amorphous phase, the most spectacular effect is seen in the rubber elastic regime phase, as already evoked in the case of reinforcement by cellulose whiskers (2). The PA6-clay hybrids example presented in Table 3 is quite representative of the situation encoimtered with semi crystalline thermoplastics, but elastomeric networks benefit as well of clay layer dispersion with a two- to threefold increase in modulus for polyurethane or epoxy networks... 

Table 13.12 first emphasizes rubber-toughened plastics. In each of these cases a low Tg elastomer is dispersed in a plastic. Examples are given of amorphous (HIPS and ABS) and crystalline (nylon) thermoplastics, and a thermoset (epoxy). Usually it is desirable to have some limited grafting between the elastomer and plastic phases, to increase interfacial strength. 

Polymer Morphology. Most epoxy thermoplastics are amorphous, glassy polymers with glass transition temperatures (Tg) that range from about 25 °C to over 200 °C (5,5). As is the case with all thermoplastics, Tg in polymers 2, 3 and 5-7 are heavily... 

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