Fracture behaviour and micromechanical processes in novel rubber toughened polystyrene materials

P. FRONTINI; F. RUEDA; H. DE SANTIS; L. FASCE; V. PETTARÍN; R. DIAZ DE LEÓN; G. MORALES; P. ACUÑA

Kerkrade, The Netherlands

Conferencia; 14th International Conference on Deformation, Yield, and Fracture of Polymers (DYFP2009); 2009

In this work experimental modified HIPS products were synthesized. Changes in SBR weight concentration (8 and 12 % weight) and the incorporation of small amounts of AN monomer (2 and 6% weight) induced different morphologies as revealed by TEM analysis. For 8% weight SBR materials, rubber particles exhibited a “salami” structure with a few PS sub-inclusions. Incorporation of 2 % AN lead to an important increase in the effective rubber volume fraction in contrast to 0 % and 6 % AN materials. For 12 % weight SBR materials, the addition of 2 % AN lead to a quasi co-continuous structure while the other AN compositions exhibited typical  “salami” structures and mean particle sizes about 1 mm, which were twice larger than the ones obtained for HIPS based on 8 % SBR and 2 % AN. As expected, elastic modulus and yield stress decreased with the increase in the effective volume fraction. Fracture toughness (JIC) was determined by means of the J-Integral approach using the Load Separation Parameter methodology under both quasi-static and dynamic conditions. The highest impact toughness (10 N/mm) was displayed by HIPS based on 8% SBR with the highest effective volume fraction. Under quasi-static loads HIPS based on 12% SBR and 6% AN displayed the highest initiation parameter (6 N/mm). Differences in fracture behavior indicate that different micromechanical processes were activated depending on loading conditions. Post-mortem SEM inspection of fracture surfaces together with OM and TEM analysis of the deformed region around an arrested crack were carried out to reveal the involved micromechanical processes. The most striking result is that the material that exhibited the quasi-co-continuous structure was able to spontaneously recover the stress whitening after unloading.