Full length articleTechnical pathways for distributed recycling of polymer composites for distributed manufacturing: Windshield wiper blades
Introduction
Of the composite materials in production, polymer composites dominate in industry and thermoplastic composites have been growing rapidly in use (Yang et al., 2012). Unfortunately, the inherent heterogeneous nature of the composites leads to poor materials recyclability (Yang et al., 2012). As overall polymer recycling is only 9% globally, with the overwhelming majority of global plastic waste being land filled or ending up contaminating the environment in some way (Geyer et al., 2017), it can be safely assumed that polymer composite recycling is nearly non-existent. This is in part due to the technical complexity, but also because these composites are not labeled for recycling in major economies like the U.S. and current law does not enable consumers to be informed about the materials making up their products (Pearce, 2018). Although some countries, like China, have a far more robust recycling code system (SAC, 2008), even if a polymer composite is technically recyclable, it is not marked for recycling from post-consumer waste. This issue is compounded by the recent Chinese import ban on waste plastic (Brooks et al., 2018), which effectively blocks polymer recycling from the largest global recyclers.
One technical area that provides some hope for expanding plastic waste recycling is the new circular economy concept of distributed recycling for additive manufacturing (DRAM) (Zhong and Pearce, 2018). The open source 3-D printing community (De Jong and de Bruijn, 2013) has already started to adopt a complex voluntary recycling code system that can be adapted for polymer composites (Hunt et al., 2015). As distributed manufacturing is still in its infancy, this method does not have a large impact on global plastics end use, however, as the global value chains continue to shift (Laplume et al., 2016), this pathway could become important. This is possible because of the superior economics of distributed manufacturing, where direct production by prosumers offers significant cost savings compared to purchasing mass-manufactured products (Gwamuri et al., 2014; Wittbrodt et al., 2015). Substantial savings are observed for scientists and engineers manufacturing scientific tools (Pearce, 2012, 2014; Baden et al., 2015; Coakley and Hurt, 2016; Beeker et al., 2018; Hietanen et al., 2018), technically-sophisticated prosumers making consumer products (Wittbrodt et al., 2013) as well as average consumers making everyday items (Petersen and Pearce, 2017). Distributed manufacturing savings on the order of 90% or more are found for products ranging from medical supplies and adaptive aids (Gallop et al., 2018) to children's toys (Petersen et al., 2017).
Economic incentives for consumers can be expanded further with the concept of distributed recycling coupled to distributed AM (Zhong and Pearce, 2018). This was first done by upcycling plastic waste into 3-D printing filament with an open source waste plastic extruder known as a recyclebot (Baechler et al., 2013). Using a recyclebot decreases the embodied energy of 3-D printing filament by 90% (Kreiger et al., 2013, Kreiger et al., 2014; Zhong et al., 2017). Following the self-replicating rapid prototyper (RepRap) model (Sells et al., 2007; Jones et al., 2011; Bowyer, 2014) a recyclebot has been designed that is largely itself 3-D printed (Woern et al., 2018). Many recyclebot versions have been developed (Appropedia, 2019). As the use of a recyclebot system introduces a melt and extrude cycle, which is known to impair the mechanical properties (Hyung Lee, et al., 2012; Oblak et al., 2015) and limits the recycles to about five (Cruz Sanchez, et al., 2017; Santander et al., 2018) without using some means of reinforcement or blending with virgin materials. In addition, fused particle fabrication (FPF) or fused granular fabrication (FGF) 3-D printers can fabricate products directly from shredded plastic waste or pellets (Volpato et al., 2015; Beaudoin, 2016; Giberti et al., 2017; Liu et al., 2017; Whyman et al., 2018) and have been used for recycled materials (Woern et al., 2018b; Byard et al., 2019; Reich et al., 2019). Other recent studies have looked at using 3-D printing for recycling of advanced applications like batteries (Singh et al., 2019a) and for multimaterials (2019b).
Many research groups and companies have demonstrated that pre-consumer and post-consumer waste polymers can be recycled into 3-D printing filaments or directly printed, including: polylactic acid (PLA) (Cruz Sanchez, et al., 2015, 2017; Anderson, 2017; Pakkanen et al., 2017; Woern et al., 2018), acrylonitrile butadiene styrene (ABS) (Mohammed et al., 2017a,b; Zhong et al., 2018), high-density polyethylene (HDPE) (Baechler et al., 2013; Chong et al., 2017; Pepi et al., 2018), polypropylene (PP) and polystyrene (PS) (Pepi et al., 2018), thermoplastic polyurethane (TPU) (Woern and Pearce, 2017); polyethylene terephthalate (PET) (Zander, et al., 2019; Zander et al., 2018), linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) (Hart et al., 2018), polycarbonate (PC) (Reich et al., 2019). These studies focused on single types of polymers. Only a few studies have looked at making filament from polymer composites using carbon reinforced plastic (Tian et al., 2017), fiber filled composites (Parandoush and Lin, 2017; Heller et al., 2019) and various types of waste wood (Pringle et al., 2018; Zander, 2019).
This study explores the technical pathways for distributed recycling of polymer composites for distributed manufacturing, which is summarized in Fig. 1. To illustrate the options for these pathways a case study is performed on windshield wiper blades, which are a thermoplastic composite made up of a soft (more flexible) and hard material to meet the exacting needs of the automobile industry. First, the percentages of each sub-material are quantified and particle size analysis is performed on the mechanically sized-reduced composite waste. The angle of repose is calculated for the material. Then the thermal and rheological properties are characterized for the two sub-materials to help define the conditions for the extrusion. In addition, the viscosity with the storage (elastic - G') and loss (viscous - G") modulus is characterized. The sub-materials are analyzed using the following techniques: differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), thermomechanical analysis (TMA), thermal gravimetric analysis (TGA), and rheological analysis. Then, the composite material waste is tested in each of the pathways shown in Fig. 1. These include first mechanical grinding, then the particles are (1) converted to filament using a recyclebot and 3-D printed using fused filament fabrication (FFF), (2) the particles are directly printed with FPF, (3) the particles are directly printed using a syringe printer and (4) the particles are injection molded in a custom 3-D printed mold. The results are discussed and conclusions are drawn in the context of distributed recycling and manufacturing using AM for complex composite polymer materials.
Section snippets
Materials
Fig. 2 shows the starting material of a windshield wiper blade with the two materials labeled. It was industrial waste from a automobile component manufacturer. Material 1, which is against the windshield glass in operation, is more flexible and then the rigid material 2 is used to connect to the wind shield wiper frame. Mechanically ground windshield wiper blade (both materials combined) was provided by McDunnough Plastics, Fenton MI for $1/lb ($2.20/kg). The ground combination of material had
Results
After the separation and mass tests the composite material was found to be 29.5% hard material and 70.5% soft material by mass. Fig. 5 shows the distribution of particle size of the windshield wiper components with a separation between particles smaller than an area of 1.153 mm2 and larger than 1.153 mm2 of a particular sample.
Three trials were performed to find the angle of repose using the funnel method shown in Fig. 6a and for the petri dish method shown in Fig. 6b. Using the funnel method,
Discussion
The global additive manufacturing market is expected to grow to US$ 36.61 billion/year by 2027 from US$ 8.44 billion/year in 2018 (RB, 2019). Other estimates expect the AM market to reach over US$ 41 billion from a current value of US$9.3 billion (3D Natives, 2018). Of the total market, the vast majority of 3-D printing is still thermoplastic-based, and in 2018 polymeric additive manufacturing has reached nearly US$5.5 billion (3D Natives, 2018). If the materials fraction of the market grows as
Conclusions
This study successfully explored the technical pathways for distributed recycling of complex polymer composites made up of windshield wiper waste for distributed manufacturing, from mechanical grinding to filament production in a recyclebot to FFF or FGF, syringe printing, or 3-D printed molds to injection molding. A successful pathway was found to convert scrap windshield wiper blades into useful, high-value, bespoke biomedical products of fingertip grips for hand prosthetic and a reflex
CRediT authorship contribution statement
Samantha C. Dertinger: Investigation, Data curation, Writing - original draft, Writing - review & editing, Visualization. Nicole Gallup: Investigation, Data curation, Writing - original draft, Writing - review & editing, Visualization, Funding acquisition. Nagendra G. Tanikella: Formal analysis, Investigation, Data curation, Writing - review & editing, Visualization. Marzio Grasso: Methodology, Validation, Formal analysis, Investigation, Data curation, Writing - review & editing, Visualization.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This research was supported by Aleph Objects, Devlieg Foundation Internship, Portage Foundation Internship and the Richard Witte Endowment.
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