Evaluation of carbon fibers structure and morphology after their recycling via pyro-gassification of CFRPs

Abstract

The present work presents the evaluation of the performance of single carbon fibers after pyro-gassification treatment in different gasification conditions, i.e. 500°C for 30' and 60', and 600°C for 20', in order to evaluate the intrinsic fiber properties that might contribute to the overall composite behavior when re-impregnated with a polymeric matrix. Such investigation, carried with different analytic techniques such as Raman spectroscopy, XRD diffractometry, SEM Microscopy with EDX atimic mapping and finally mechanical tensile test carried out on single fibers, proves that convenient pyro-gassification conditions might lead to recovery of carbon fibers with properties not far from the pristine ones. While some further tuning of the gasification condition might still be required, 500°C proved to be the optimal temperature for treatment, where the structure and morphology are practically untouched and mechanical properties are well comparable with pristine fibers in terms of Young's Modulus with just a slight drop in ultimate properties.

Recycling of carbon fiber reinforced composite waste to close their life cycle in a cradle-to-cradle approach

“…recently introduced an innovative static-bed batch pilot reactor [55,56] which soon afterwards was modified into continuous process in two steps able to combine at 500-550°C both the pyrolysis and the oxidation step, drawing the main advantages of the different disposal techniques (Figure 3). In such a plant, pyrolysis can be carried out on the whole parts, up to 2m in diameter, in order to save the energy costs of shredding the feed wastes, and simultaneously recovering energy and materials with Re-CF retaining 95% of their original tensile strength [57,58]. In these conditions the obtained Re-CF maintain the original arrangement they had in the waste part, as depicted in Figure 3.…”

Adenine as Epoxy Resin Hardener for Sustainable Composites Production with Recycled Carbon Fibers and Cellulosic Fibers

“…Although SFRCs usually exhibit lower mechanical properties than long fiber counterparts, they can nonetheless be applied in a variety of fields, as they exhibit lightness and isotropic properties and allow a simpler manufacturing process than for long fiber composites [ 56 , 57 , 58 , 59 , 60 ]. Moreover, it must be considered that when recycled carbon fibers (rCFs) are specifically used for composite production, there is no preliminary control over their shape and size: they are indeed a secondary raw material, which, as previously reported, can maintain mechanical properties up to about 80%/90% of the virgin ones, depending on the applied recycling process [ 30 , 43 , 61 , 62 , 63 ]. In the case of rCFs, SFRCs—analogue composites with virgin carbon fibers (vCFs)—were also produced, for the sake of comparison, using in both cases a 45:55 matrix fiber ratio.…”

“…Virgin chopped carbon fibers (vCF) (25 mm) were obtained cutting down Unidirectional Fabric UC 301 based on Toray T700S 12K dry fibers (Toray Industries Inc., Tokyo, Japan). Recycled chopped carbon fibers (rCF) (25 mm) were obtained by pyrolysis (500 °C for 150 min) of Toray T700S 12K-based carbon fiber composites post-treated at 500 °C for 60 min under oxidizing atmosphere in collaboration with Curti SpA (Curti Spa, Castel Bolognese, Italy) [ 30 , 43 ]. Both virgin and recycled carbon fibers were used without any other treatment.…”

“…While their average performance can be acceptable for standard applications, which simply pursues light-weighting as goal, when a composite needs to withstand a relevant mechanical performance, such as in primary load bearing structures, the use of natural fibers is still not enough to match the target [ 40 , 41 , 42 ]. In the latter case, the performance of glass or carbon fibers is required and a viable approach for making the composite more sustainable is the use of recycled fibers [ 4 , 43 ]. A particularly positive approach for recycling CF from CFRP (end-of-life wastes or production scraps) is the pyrolysis, a thermochemical process able to reach already industrial application, even if in a still limited dimension.…”

“…Pyrolysis is indeed a flexible and reliable process able to treat different complex substrates and recover the reinforcing fraction, irrespective of its shape a material [ 4 , 30 , 32 , 44 ]. This technique is not suitable for recovering natural fibers, but when optimized is able to give back both glass and carbon fibers [ 30 , 32 , 44 ], with the latter reinforcement that is proved to keep 85–90% of the original CF mechanical properties [ 4 , 43 ].…”