Polyamide-imide mechanical properties

Polyamide-imides are appreciated for good mechanical and electrical properties high service temperatures (up to 220°C with possible long service times at 260°C) rigidity good creep behaviour fatigue endurance low shrinkage and moisture uptake inherent flame retardancy chemical resistance usability down to -196°C. 

Polyimide (PI) caps all other polymers in its temperature range of use (-200 to 260 °C in air short-time even up to 500 °C). Because of its high price, it is used in special cases only, such as space vehicles, nuclear reactors and some electronic parts. Newer developments, related to polyimide, are the polyether imides (e.g. Ultem ), polyester imides and polyamide imides (e.g. Torlon ), all with very good mechanical, thermal and electrical properties and self-extinguishing. 

These polyamide imide films have excellent thermal, mechanical, and electrical properties, and they are used to upgrade other enamel films. Other attractive features of polyamide imide film insulations are a low coefficient of friction and good solvent resistance. These enamels are rated for use at 200 °C. 

The Kinel materials produced by Rhone-Poulenc are polybismaleinimides of the type shown in Figure 4.22. These materials have chain-end double bonds, as explained previously, can be processed like conventional thermosetting plastics. The properties of the cured polymers are broadly similar to the polyimides and polyamide-imides. Molding temperatures are usually from 200°C to 260°C. Post-curing at 250°C for about 8 h is necessary to obtain the optimum mechanical properties. 

This is an engineering plastic designed for thermal/electrical applications requiring high dimensional stability. This material exhibits superior electrical and mechanical performance at continuous use temperatures ranging from -60 to 260 °C. Pyropel HDT polyamide-imide (PAI) produced by Albany International [35] has enhanced properties without the need for post-curing. 

Polyamide-imides and polyimides have very good electrical properties although not as good as those of the fluorocarbons. However, they are much better than fluorocarbons in mechanical and dimensional stability properties. 

Polyamide-imides are thermoplastic amorphous polymers that possess exceptional mechanical, thermal, and chemical- and wear-resistant properties. They are inherently nonflammable, have outstanding electrical properties, and possess enormous temperature stability from cryogenic to 300°C. These properties place polyamide-imides at the top of the price and performance pyramid with polyketones and polyimides. 

Polyamide-imide powders may be compression-molded into standard shapes and geometries. This operation produces parts that may be used as is or further machined into intricate parts. The mechanical properties of compression-molded parts are somewhat less than those of the corresponding injection-molded grades. The tjtpical compression-molding operation uses a fine particle size of polyamide-imide powder. The powder material should have particles which are 100% less than 150 pm and 95% less than 75 pm. Polyamide-imide powders may also be used as an additive or adhesive binder in the sintering of other shapes based on PTFE powders, metal powders, or abrasive materials. 

The highly intractable chemical stmcture vMch. inq)arts the outstanding mechanical properties also makes the PATs very difficult to process (4, 5). In the ftilly imidized form PAI is not processable hence a poly(amic acid) (PAA) precursor is the usual form in which they are supplied and bricated. The precursors themselves have very hi viscosities in the melt state and hence the flow characteristics tend to be very poor. Semicrystalline and amorphous polyamides (6) and aromatic sulfone polymers such as poly(phenylene sulfide), poly(ether sulfone) and polysulfone (7) have been blended with the precursor to PAI, to obtain better flow characteristics. 

In order to improve the mechanical properties and the heat resistance of TPE-A, other links have been investigated. For instance, a poly(ether-6-amide) with an imide link was prepared by reacting polyamide-forming monomers and a diamino polyether together with trimellitic anhydride [61]. Naphthalene-1,2,5-tricarboxylic acid can also be used for this purpose. 

Polyamide-imides (PAIs) are thermoplastic amorphous polymers prepared by the condensation of an aromatic diamine, such as methylene diamine, and an anhydride, such as trimellitic add chloride. PAIs have good mechanical, thermal, chemical resistance, high strength, melt processability, and high heat capacity. They can be processed into a variety of forms, such as injection or compression molded articles, coatings, films, fiber, and adhesives. The typical heat deflection temperature for neat molded PAI is 278°C,but reinforcements are often used to improve mechanical properties. PAIs are generally soluble in strong aprotic solvents such as NMP and DMAc, and thus misdble blends with PBI are feasible. 

PAIs are unique materials that have elements of PA (aka nylon) chemistry, as well as aromatic polyimide chemistry. They have exceptional mechanical, chemical, and thermal properties and are considered by some to be at the top of the thermoplastic performance chart. They have high strength, exceptional high heat capability, and broad chemical resistance. Polyamide-imide polymers are melt processible and can be processed into a wide variety of forms—from injection- or compression-molded parts and ingots— to coatings, films, fibers, and adhesives. PAI is often lower in cost than TPI. 

An all aromatic polyetherimide is made by Du Pont from reaction of pyromellitic dianhydride and 4,4,-oxydianiline and is sold as Kapton. It possesses excellent thermal stability, mechanical characteristics, and electrical properties, as indicated in Table 3. The high heat-deflection temperature of the resin limits its processibility. Kapton is available as general-purpose film and used in applications such as washers and gaskets. Often the resin is not used directly rather, the more tractable polyamide acid intermediate is applied in solution to a surface and then is thermally imidized as the solvent evaporates. 

---