The effect of filler type and content and the manufacturing process on the performance of multifunctional carbon/poly-lactide composites

Two nanosized carbonaceous fillers, vapor grown carbon nanofibers and exfoliated graphite nanoplatelets, were used to prepare poly(lactide acid) composites at various concentrations from 0 up to 20 wt.%. The two fillers were also combined in order to explore possible synergistic actions. Two compounding processes, melt mixing and polymer dissolution, and two forming methods, injection and compression molding, were used to manufacture the composites. The flexural properties, impact strength, storage and loss modulus, Vicat softening temperature, and electrical conductivity of neat matrix and composites were determined as a function of the filler type and content, and of the processing method used. The filler dispersion within the polymer matrix, the presence of agglomerates and the existence of voids were studied using field-emission scanning electron microscopy. It is concluded that compounding by polymer dissolution followed by compression molding leads to composites with the lowest percolation threshold and surface conductivity and highest storage modulus whereas extrusion injection molding results in composites with the highest mechanical properties. The results can be used to engineer biodegradable composites with specific properties for targeted applications.