Impact-Modified AKROMID® Compounds
In the group of engineering thermoplastics, polyamides are characterised by a good combination of mechanical properties, chemical resistance and ageing resistance. They are filled as required, reinforced or modified.
It is known that the mechanical properties of thermoplastics are significantly influenced by environmental conditions. In addition to temperature, this includes water absorption and humidity, since components made from conditioned polyamides exhibit different strengths than freshly moulded parts. Thermoplastics are modified appropriately to perform under a wide range of am-bient conditions.
AKRO-PLASTIC GmbH have developed a product range of impact-modified compounds for this purpose. These are suited specifically for applications which are exposed to harsh conditions. There are two types of modified compounds: cold-impact-resistant (S1) and dry-impact-resistant (S3) compounds. Non-reinforced and reinforced compounds with differing glass fibre content are available.
AKROMID® HI
The requirements of the material to be used depend on the type of component. The optimal combination of strength and toughness can be formulated based on the composition of impact-modified compounds. Non-reinforced impact-modified compounds can exhibit extremely high impact strengths. By contrast, the glass fibre grades in this product family are designed to provide a good balance of properties at significantly higher strengths.
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).
AKROMID® HI
Impact-modified AKROMID® compounds are used in all industrial sectors.
Components for sports and leisure activities are frequently confronted with high forces or even impact loads. An interesting example is an ice skate from T-Blade, for which an impact-resistant AKROMID® was used to make the blade holder. The blade itself can be replaced with a new one as soon as it is worn out. The material meets the high standards of the component even at the low temperatures at work here.
Highly reinforced compounds are typically used as metal substitutes. Glazpart Ltd. (UK) have replaced a steel design with an intelligently developed plastic part made of a high-impact-modified AKROMID® compound which is used to protect a gas canister valve. It has passed all tests in the -40 °C to +65 °C range required for gas canisters with a gross weight of 100 kg.
In the automotive industry, typical applications include window frame trim, cable ducts, fasteners and housings which may be subjected to impact loads. In these cases, dry-impact-resistant compounds are frequently used to bypass the conditioning step during assembly. Because polyamides are significantly more brittle at low temperatures than at room temperature, cold-impact-modified compounds are used when the requirements call for this.
Disclaimer: All specifications and information given on this website are based on our current knowledge and experience. A legally binding promise of certain characteristics or suitability for a concrete individual case cannot be derived from this information. The information supplied here is not intended to release processors and users from the responsibility of carrying out their own tests and inspections in each concrete individual case. AKRO®, AKROMID®, AKROLEN®, AKROLOY®, AKROTEK®, ICX®, PRECITE® and DIA(hr)LOG® are registered trademarks of AKRO-PLASTIC GmbH.
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