Core/shell rubber toughened polyamide 6: an effective way to get good balance between toughness and yield strength

Abstract

We have recently shown that by adding 10 to 30 wt% core/shell toughener with a low density polyethylene (LDPE) core and a polybutadiene-g-maleic anhydride (PB-g-MAH) rubber shell to polyamide 6 (PA6), the impact strength of PA6 matrix can be significantly increased by 600–1000%. However, this is at the expense of quite large losses in elastic modulus of 10–25% and tensile yield strength of 30–55%, especially at high core/shell rubber loading (e.g., 30 wt%). In this study, we have redressed this problem by replacing the LDPE core with a polypropylene (PP) core, which has both higher elastic modulus and yield strength than that of LDPE, forming a new core/shell (PP/PB-g-MAH) toughener. When this core/shell toughener containing 5 wt% PB-g-MAH is blended with PA6 in the weight ratios of 10/90 and 30/70, the Izod impact strengths are 390 and 480 J m⁻¹ (which are 330 and 550% increases compared to neat PA6), and the modulus are 2.37 and 2.13 GPa, and yield strength are 60.2 and 54 MPa, respectively (which represent only 6 and 15% loss of modulus, and 5 and 13% decrease in yield strength relative to neat PA6). These improved results confirm that although the decrease of tensile modulus cannot be avoided with increasing impact strength, increasing the elastic modulus and yield strength of the core material in the rigid core/soft rubber shell toughener is an effective way to obtain a good balance of elastic modulus, tensile yield strength and impact strength.