Toughness optimization of glass‐fiber reinforced PA 6/PA 66‐based composites: Effect of matrix composition and colorants

Abstract

Mixing of polyamide 6 (PA 6) and polyamide 66 (PA 66) is integrated in the trend of development of new and improved materials by combination of different polymers and some reinforcing materials to polymer composites. The specific polymer composite PA 6/PA 66 reinforced with short glass-fibers combines the good coloring of PA 6, and the small moisture absorption of PA 66. Technical applications of PA 6/PA 66 composites are mainly used in the automotive industry. Specific requirements of this industry lead to the necessity to optimize the material resistance against crack propagation of the PA 6/ PA 66 composites, using mechanical and fracture mechanical methods. So, the present investigations focus on fracture mechanics toughness optimization of the PA 6/PA 66 composites, including unstable and stable crack growth. The aim of this toughness optimization is to find out the optimal mixing ratio of PA 6/PA 66. Applications of PA 6/PA 66 in the automotive industry and specific client wishes are the main reasons for black-coloring of the PA materials. The influence of several black-colorants (carbon black, nigrosine, spinel, iron oxide) on mechanical and fracture mechanical properties of the PA composites is also investigated using fracture mechanical methods. As experimental fracture mechanical method, preferentially, the instrumented Charpy impact test (ICIT) and the new cut method to determine the stable crack growth of glassfiber reinforced materials was used.

The influence of carbon black batches on the fracture behavior of glass fiber reinforced PA6/PA66 blends

“…The batch polymer PA6 only slightly changes the blend's PA6/PA66 ratio. This has no significant effect on morphology or properties in the case of very small variations, as was shown by Nase et al1 PE as a third immiscible blend component does decisively change morphology and fracture behavior. It becomes obvious in Figure 11 that PE does appear in a spherical morphology with good adhesion to the polyamide matrix.…”

“…This method is not appropriate when highly reinforced materials are investigated, because the measurement of Δ a is complicated by the roughness of fracture surfaces of reinforced materials. Different methods to gain R‐curves can be found in the literature 1, 37, 38…”

“…The combination of the good processability and higher surface quality of Polyamide 6 with the enhanced temperature resistance of Polyamide 66 leads to application‐specific compounds, primarily for visible parts or assemblies within engine bays or interiors. Blending PA6 and PA66, the influence of the relationship between the mass fractions of these two miscible components as well as the influence of an additional inhibition of a toughening modifier are well described in the literature 1–3. The blend properties are frequently compared to the properties of in situ polymerized PA6/PA66 composites, where the molecular composites often provide very specific characteristics and relatively high effects at very low PA66 mass fraction levels 4–6.…”

“…Generally, the presence of CB leads to a reduction in mechanical properties such as elongation at break or impact toughness whereas material stiffness is increased 7–11. In comparison to other available polyamide colorants such as spinel or iron oxide, CB provides higher strength and hardness values 1. There are several reasons for property changes with increasing CB concentration.…”

Effects of fiber characteristics on the mechanical and rheological properties of poly(butylene terephthalate)/glass fiber composites

“…For example, the PBT/GF (50 wt %) composite is mainly used for the outside mirror of automobiles, and can be utilized in a nonhalogen flame retardant PBT system. Other polymer systems of poly(ethylene terephthalate),19–23 nylon,24, 25 poly(phenylene sulfide),26 and polyolefins26–29 with fillers such as GF, graphite, and carbon nanotubes can be coordinated. However, problems associated with surface troubles during the extrusion process can occur when the content of GF reaches about 50% by weight.…”