Investigation of recycling effects on the mechanical properties of short carbon and glass fiber reinforced polyetherimide composites

Considering the increasing composite waste accumulation, this work explores the feasibility of replacing virginal carbon fibers (VCFs) and virginal glass fibers (VGFs) with recycled fibers for injection molded polyetherimide (PEI) composites. Extensive characterizations were conducted to reveal effects of sulfuric acid recycling process on mechanical properties of fibers and their composites. It was shown that strength retention rates of recycled carbon fibers (RCFs) and recycled glass fibers (RGFs) were 81.6% and 55.7%. The reinforcing factor of RCFs increased from 0.120 of VCFs to 0.147 due to the enhanced interfacial bonding while the reinforcing factor of RGFs decreased from 0.080 of VGFs to 0.065 owing to the glass fiber strength reduction. As a result, the composite tensile strength (152.8 MPa) of RCF/PEI was comparable to that (155.3 MPa) of VCF/ PEI and RGF/PEI tensile strength (102.5 MPa) was lower than that (112.3 MPa) of VGF/PEI. Moreover, the tensile modulus of RCF/PEI and RGF/PEI were also approximatively comparable to those of VCF/PEI and VGF/PEI since recycling process showed a slight effect on fiber modulus. Although there exists an impact of recycling on fiber mechanical properties, the introduction of recycled fibers (especially RCFs) by injection molding process can promisingly enhance PEI composites.