Thermoset polyimide resins

On the other hand, clays modified with salts of aromatic amines, in which the N atom is directly linked to aromatic ring, exhibited higher thermal stability then those modified with alkylammonium compounds [117, 118]. The use of a combination of aromatic and aliphatic ammonium compounds was an effective strategy for synthesis of clays with sufficient thermal stability for thermoset polyimide resin (PI) [117]. In that case, the aromatic component of OLS provided higher thermal stability and the aliphatic component promoted intercalation. The benefits of combining aromatic and aliphatic surfactants to treat clay are also reported by other authors [ 119]. It was shown that clay treated with a 1 1 molar mixture of methylene dianihne (MDA) and dodecylamine resulted in an improvement in thermooxidative stability of Pl-based nanocomposites. 

The polyimide shown is a tme thermosetting resin, but the general reaction procedure, coupling the dianhydride with the diamine, is extremely important throughout polyimide chemistry. The intermediate polyamic acid polymers form the basis for many of the polyimide resins used in advanced composites. 

Bis-maleimide resins composed of BMI and diamines have been reported in the early 1960s in the patent literature. Since that time, a number of patents have appeared describing improvements in their properties and uses [3]. Although many bis-maleimide resins are commercially developed, relatively few reports of their use as adhesives are to be found in scientific journals [4-10]. Improvements of maleimide resins are mirrored in the improvements of thermosetting polyimides. For example, the method of in situ polymerization of monomer reactants (PMR method) was developed [6]. 

One resin based on the BTDA/ODA backbone and 2-aminobiphenylene as an endcapper was thought to be such a resin (126). High quality laminates could be fabricated, but the Tg of the crosslinked polymer was lower than expected and therefore thermal oxidative stability was poor. The chemical structure of this thermosetting polyimide is given in Fig. 42. 

In Table 1, the moisture uptake of cured and uncured Navy P3-2300-PE resin after 24 hours of immersion is compared to a number of other high-temperature polymer resins. The moisture uptake of the Navy P3 oligomer is nearly identical to that of the commercial P3 thermoplastic. Other commercial thermoplastics, such as poly(ether ether ketone), with very similar chemical compositions, exhibit similarly low levels of moisture uptake. On the other hand, the Navy P3 resins absorbs about 85% less water than the commercial polyimide Kapton HN. Since thermosetting phenyl ethynyl end-capped polyimides have moisture uptake characteristics that are similar to Kapton HN, with around 3% weight gain on exposure to 95% relative humidity (77), void-free composites based on Navy P3 resins should exhibit greatly reduced moisture uptake compared to those based on thermosetting polyimides. 

Organic matrices are divided into thermosets and thermoplastics. The main thermoset matrices are polyesters, epoxies, phenolics, and polyimides, polyesters being the most widely used in commercial applications (3,4). Epoxy and polyimide resins are applied in advanced composites for structural aerospace applications (1,5). Thermoplastics Uke polyolefins, nylons, and polyesters are reinforced with short fibers (3). They are known as traditional polymeric matrices. Advanced thermoplastic polymeric matrices like poly(ether ketones) and polysulfones have a higher service temperature than the traditional ones (1,6). They have service properties similar to those of thermoset matrices and are reinforced with continuous fibers. Of course, composites reinforced with discontinuous fibers have weaker mechanical properties than those with continuous fibers. Elastomers are generally reinforced by the addition of carbon black or silica. Although they are reinforced polymers, traditionally they are studied separately due to their singular properties (see Chap. 3). 

The fibres are surface treated during manufacture to prepare adhesion with the polymer matrix, whether thermosetting (epoxy, polyester, phenoUc and polyimide resins) or thermoplastic (polypropylene. Nylon 6.6, PMMA, PEEK). The fibre surface is roughened by chemical etching and then coated with an appropriate size to aid bonding to the specified matrix. Whereas composite tensile strength is primarily a function of fibre... 

KINEL molding powders and KERIMID 601 leuninating resins dre based on a thermosetting polyimide, which cures without evolution of volatiles. KINEL compounds are transformed by compression, transfer, or extrusion molding into void-free parts, whose thermomechanical properties exceed those attainable from conventional thermoplastics or thermosets. 

Kimura [37] selected three kinds of thermosetting resins—furan, diphenylether-formaldehyde and polyimide resins—as matrix precursors to fabricate carbon fiber reinforced carbon composites (C/C composites). After heat treatment at 2000-3000°C, the graphitization process of the matrix was examined by optical microscopy and X-ray diffraction. In the C/C composite derived from a polyimide, the graphite structure was not as well developed as the others. This retarded development is attributed to less internal stress between fibers and matrix as well as to less stretching of the matrix. 

Polyimide parts can be joined with mechanical fasteners. Self-tapping screws must be strong enough to withstand distortion when they are inserted into the polyimide resin which is very hard. Polyimide parts can be bonded with epo adhesives. Only abrasion and solvent cleaning is necessary to treat the substrate prior to bonding. Tbe plastic part will usually have a hi er thermal rating than the adhesive. Thermosetting polyimides carmot be heat welded or solvent cemented. 

The most common thermosetting laminating resins are phenolics, melamines, epoxies, polyesters, silicones, and polyimides. Thermoplastic resins used in making laminates include polysulfone, polyphenylene sulfide, polyetheretherketone, polyamide-imide, polybutylene terephthalate, nylon 6, and polypropylene. 

Thermosetting epoxy and acrylic resin Hot-melt-type polyimide resin Pressure-sensitive adhesives (PSAs)... 

ASP Water-washed kaolin, Engelhard Aspun Fiber grade resins, Dow Astrawax Amide wax, additive lubricant, AlliedSignal Adac Thermoset polyester, Reichhold Attain ULDPE, Dow Aurum Polyimide resin, Mitsui Auto-Grader Online melt flow indexer, Brabender Autofiroth Pressurized rigid froth polyurethane foam systems, BASF Autoguage Automatic die. 

Thermosetting polyimides are commercially available as uncured resins, thin sheets, and laminates. Thermoplastic polyimides are very often called pseudothermoplastic. There are two general types of polyimides. One type is linear polyimides which are made by combining imides into long chains. Aromatic heterocyclic polyimides are the other usual kind, where R and R" are two carbon atoms of an aromatic ring. Examples of polyimide films include Apical, Kapton, and Kaptrex. Polyimide parts and shapes include Meldin, Vespel, and Plavis. Polyimides have been in mass production since 1955. 

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