Polyamide maximum modulus

The maximum attainable values for the strength of elementary fibers from LC solutions of polyamides are 400 cN/Tex [40], and the maximum modulus of elasticity is 238 GPa [41]. (In the last case, the fiber was fabricated from a copolyamide containing an equimolar number of benzidine units together with PPTA units.)... 

Polyamides and polyesteramides are more recent arrivals to the commercial biodegradable polymer field. Copolymers of either glycine or serine with e-aminocaproic acid are biodegradable. For example, biodegradable polyaspartic acid was synthesized (95% yield) at low cost [Koskan, 1992]. A copolymer of butylene-adipate and e-caprolactam was recently introduced by Bayer as BAK 1095. The material has T = 125°C, density of 1070 kg/m, tensile modulus of 180 MPa, maximum strain at break of 400%, tensile stress at break of 25 MPa, and it fully degrades in 300 days under the ASTM standard conditions. 

For a variety of technical reasons the development of aromatic polyamides was much slower in comparison. Commercially introduced in 1961, the aromatic polyamides have expanded the maximum temperature well above 200°C. High-tenacity, high-modulus polyamide fibers (aramid fibers) have provided new levels of properties ideally suited for tire reinforcement. More recently there has been considerable interest in some new aromatic glassy polymers, in thermoplastic polyamide elastomers, and in a variety of other novel materials. 

In structural applications for plastics, which generally include those in which the part has to resist substantial static and dynamic loads, one of the problem design areas is the low modulus of elasticity of polymeric materials. Even when such rigid polymers as the ladder types of polyesters and polyamides are considered, the elastic moduli of unfilled polymers are under one million psi as compared to metals where the range is usually 10 to 40 million psi. Ceramic materials also have high moduli. Since shape integrity under load is a major consideration for structural parts, plastics parts must be designed for efficient use of material to afford maximum stiffness. 

The high axial elastic modulus of polyethylene and polyamide 6 is due to the fact that these polymers have a preferred conformation that is fully extended, i.e. all-trans. The elastic deformation is caused by the deformation of bond angles and by bond stretching, both showing high elastic constants. Isotactic polypropylene and polyoxymethylene crystallize in helical conformations and therefore exhibit a maximum stiffness which is only 20% of the maximum stiffness of the all-trans polymers. The elastic deformation of a helical chain involves, in addition to the deformation of bond angles and bond stretching, deformation by torsion about the G bonds. The latter... 

The mechanical properties of the compounds are conqrared on the basis of accelerated tensile tests with Campus tensile bars. Compared to unfilled polyamide, the highly filled compound shows a considerable increase in rigidity in the form of an increase of Yoimg s modulus by a factor of 2 - 3 and concurrent embrittlement of the material leading to a decrease in the maximum tensile stress (Fig. 8, left side). 

---