Effect of aramid regenerated fibers on thermo-mechanical behaviour of polyamide 12 composites

Aramid regenerated short fibers, obtained from the production scrap of as-produced aramid yarns, were utilized as reinforcement in a commercial polyamide (PA12) at different contents, ranging from 10wt% to 30wt%, in order to evaluate the effect of the fiber loading on the mechanical and dynamic behaviour of the resulting materials. Differential scanning calorimetry tests revealed how the crystallinity slightly decreased with the fiber content, while quasi-static tensile tests evidenced that the introduction of aramid fibers provided an interesting stiffening effect on the resulting composites, proportionally to the filler content. On the other hand, the presence of agglomerated fibers led to an embrittlement of polyamide composites, with a progressive reduction of the deformation at break. Tensile dynamic tests confirmed the stabilizing effect provided by the recycled fibers, while the coefficient of linear thermal expansion was progressively reduced both under and above the glass transition temperature. Isothermal creep compliance of the material was substantially reduced upon fiber addition, especially at elevated testing temperatures. Accordingly, Vicat softening temperature was increased of 10-20? in dependence on the fiber content. Also, the thermal degradation stability was slightly improved upon fiber addition. Morphological analysis on the cryofractured surfaces revealed a quite good fiber-matrix interfacial adhesion.