The effect of random branching on the balance between flow and mechanical properties of polyamide-6

The rheological and mechanical properties of a series of linear and randomly branched polyamide 6 samples, with varying molar mass and varying degree of moderate branching, have been investigated.As expected, it was found that random long-chain branching has a pronounced effect on the rheological behaviour of the materials in both shear and extensional flow. The zero shear viscosity increases with branching while the flow curve becomes more shear thinning. Randomly branched materials have an enhanced melt strength in elongational flow. Although branched, the materials show perfect melt stability in their rheology.The mechanical properties show minor differences between the linear and the moderately branched samples and are mainly dependent on the weight average molar mass. A small increase in modulus, yield stress and failure stress and a decrease in the strain at break are found, which is probably due to increased molecular orientation in the plane of injection moulding. The IZOD impact strength is similar to what is normally found for linear polyamide-6, and independent of branching. Also the fracture toughness K_IC is not affected by the incorporation of random branching. However, it is clearly dependent on the weight average molar mass.By using random branched polyamide-6, molecular weights and related mechanical properties can be obtained that are out of reach for linear polyamide-6.