As to be expected, impact strength increases at room temperature for all polyamide compounds in this overview as a result of conditioning. Dry impact resistant AKROMID® grades were developed for use in dry climates or as a way to avoid post conditioning steps. Thus in many cases, parts with snap-on connections can be clipped in immediately following injection moulding, which can accelerate the production process. AKROMID® B3 2 RM-D black (3255) – a special PA-ABS blend with good dry-impact properties – is an interesting alternative to conventional impact-modified compounds.

The effect of conditioning is the lowest with the RM (reduced moisture) formulation. A standard PA 6 B3 1 black (2501) was used as the reference product (see fig. 2).

However the impact strength in the conditioned material decreases at -30 °C. This is due to the complex interaction between the impact-strength modifier and the polymer matrix (see fig. 3). 

It is in the nature of polyamides to absorb moisture. Conditioning changes not only toughness, but also strength. The greater the moisture absorption, the more dramatic it is. The impact-strength modifiers themselves absorb very little moisture, which is why moisture absorption and thus the effect of strength due to conditioning are lower in these compounds than in unmodified compounds (see fig. 4).

One of the advantages of AKROMID® B3 1 black (2501) is its greater stiffness when freshly moulded. With a reduction of the tensile modulus by more than 2 GPa, however, moisture absorption has a significantly greater effect than is the case in impact-modified compounds. This must be taken into account when designing parts (see fig. 5).

As can clearly be seen, the yield stress of AKROMID® B3 1 and AKROMID® B3 3 S3 10 natural is approximately the same when conditioned (see fig. 6).