Polyethylene terephthalate (PET) is a commodity thermoplastic that is predominately used in drink bottles. Forecasted production of bottles are expected to reach 583.3-billion in 2021. Waste PET plastic bottles also accumulate rapidly on Forward Operating Bases (FOBs), and are currently disposed of by burning, which compromises the respiratory health of U.S. soldiers and residents of locales adjacent to FOBs. Fortunately, recycled PET (rPET) as well as its glass fiber (GF) reinforced composites have potential application as a cheap, local feedstock for fused filament fabrication (FFF) additive manufacturing (AM), which could be used to fabricate repair parts on an FOB and thus reduce time required to obtain parts. The objectives of this study were (i) to explore the use of PET as a feedstock for FFF and (ii) to explore the effects of glass-fiber (GF) reinforcement on PET processability and final printed part properties.
A streamline recycled PET bottle flakes were first compounded with different amount of short GF using twin-screw mixing followed by pelletizing, then filaments with different loadings of GF were extruded with Filabot EX2 filament extruder. Rheological measurements were conducted to understand the influence of GF on the composite’s rheological behavior. A custom-made FFF three-dimensional printer was used to print filaments produced from recycled PET (rPET) and GF at varying concentrations, and quality of printed parts were confirmed by scanning electron microscopy (SEM). The GF inside printed samples was recovered with TGA burn off and length distribution was analyzed by optical microscopy. Mechanical test was used to examine the performance of reinforcement, and finally differential scanning calorimetry (DSC) was used to calculate the crystallinity of printed parts.
It was found that 20 wt.% of short GF tripled the viscosity of rPET as well as enhanced the shear thinning effect, and printed tensile bars showed a decreasing trend in crystallinity with glass fiber loading. It is shown that GF leads to an increase in both modulus and tensile strength of the printed parts. However, compared with the modulus increase (71%), the increase in tensile strength is relatively small (25%), mainly due to the significant fiber break down as shown by the glass fiber length distribution. Qualitative evaluation of the printability of this recycled PET as well as its glass fiber reinforced composite is demonstrated by printing several complex geometries, including components for an autonomous air vehicle (drone).
These results suggest a promising future for this technique to be applied in resource-poor areas or forward operating base (FOB) as a method to turn waste water bottles directly into printed functional parts, which could greatly shorten the wait time for repair parts delivery and reduce raw material demand on site.