Studies on crystallization and thermal expansion behavior of PA6/SEBS blends with co-continuous structure

Rubber was used as an additive instead of an inorganic filler to mediate the thermal expansion of plastics. This is based on the fine control of the micro-structure so that the expansion is preferentially along the thickness direction. Reactive extrusion and injection molding processes were employed for deformation of the rubber domains into microlayers. It is found that when the rubber domains are deformed into microlayers and co-continuous with the plastic matrix, the coefficient of linear thermal expansion (CLTE) in directions parallel to the microlayers decreases to a very low value. The relationship between the content of styrene/ethylene-butylene/styrene block copolymer (SEBS), the crystallization behavior of polyamide 6 (PA6) and CLTE for injection-molded PA6/SEBS blends-was investigated. It was found that when the content of SEBS phases exceeded 20 wt%, the CLTE of PA6/SEBS in flow direction decreased drastically. TEM observation showed that both the plastic and rubber phases were elongated and orientated along flow direction (FD), and PA6 crystals were mostly oriented normal to the SI, layers. WAXD measurements demonstrated that b-axis of PA6 unit cells preferred to orientation along FD based on the calculations of the degree of orientation for PA6 crystallographic axes, and the CLTE of PA6 lattice was determined to be 7.0 x 10(-5) K-1 -5.8 x 10(-5) K-1, and 25.8 x 10(-5) K-1 for a, b, and c-axes, respectively, for the injection-molded PA6/SEBS (60/40). Since the b-axis has thermal retraction effect, the orientation of b-axis along FD might provide the second driving force to reduce the CLTE of injection-molded PA6/SEBS.