Thermo-Mechanical Behavior of Polyamide12—Polyamide 66 Recycled Fiber Composites

Postconsumed polyamide 66 (PA66) short fibers derived from carpets were utilized as reinforcement in a commercial polyamide (PA12) matrix at different concentrations, ranging from 10 wt% to 30 wt%, in order to evaluate the effect of PA66 content on the mechanical and dynamic behavior of the resulting materials. DSC tests revealed that both melting and crystallization behavior of PA12 matrix was slightly affected by the presence of the fibers, showing a somewhat nucleation effect of PA66. Quasi-static tensile tests evidenced that the introduction of PA66 fibers provided a slight stiffening effect on the resulting composites, increasing the elastic modulus with the filler content, especially at testing temperatures above Tg. On the other hand, the presence of agglomerated fibers led to an embrittlement of polyamide composites, showing a significant reduction of the tensile properties at break increasing the PA66 fibers content. Tensile dynamic tests confirmed the stiffening effect provided by the recycled fibers, increasing both dynamic moduli (Eâ and E″) with PA66 content over the whole range of considered temperatures. Glass transition temperature of PA12 was substantially increased by the presence of the fibers, while the coefficient of linear thermal expansion above T g was progressively reduced with the filler content. Interestingly, isothermal creep compliance of the material above Tg was substantially reduced by the presence of PA66 fibers. Morphological analysis on the cryofractured surfaces revealed a quite good fiber-matrix interfacial adhesion, with the presence of some nucleating phenomena on the pulled out surfaces.