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Materials Science in Additive Manufacturing MEX optimization printing of rHPDE from milk jugs

plastic, in 2017, thereby impacting Singapore as a major down the packaging plastics into smaller pieces and then
destination for exporting plastic recyclables. 4 remelting and extruding them into a filament form for
Since 2009, plastic has consistently accounted for use in MEX systems. This approach not only enhances
the largest percentage of Singapore’s disposed waste. the eco-friendliness of MEX printing but also aligns with
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Significant use of plastic packaging resulting in domestic sustainable goals. However, it is important to fully assess
waste is the main contributor to this trend. Concerns have the feasibility, viability, and potential benefits of this
been raised about the adverse impact of China’s ban on methodology.
Singapore’s domestic recycling sector, leading to an increase This study examines the process of recycling HDPE
in the incineration of domestic plastic recyclables. It is packaging materials by breaking them down into small
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crucial, therefore, to develop new capabilities to ensure that pieces for extrusion. The goal is to produce rHDPE
used plastics remain a valuable resource in the economic filaments for MEX printing that can yield quality prints.
loop for as long as possible, thereby allowing Singapore to The key objectives include (i) converting used milk
become more “plastic-resource efficient.” 4 jugs into rHDPE filaments suitable for MEX printing,
To address the abundance of plastic waste, a more (ii) identifying challenges related to printing with rHDPE
eco-effective approach will involve using recycled plastics filaments, and (iii) determining suitable MEX printing
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in sustainable manufacturing. This approach, as Tee parameters to achieve good print results with rHDPE,
illustrated, emphasizes transitioning from the traditional while ensuring the following two conditions: the initial
cradle-to-grave linear material flow model to a Cradle-to- layer of the print must remain attached or adhered to the
cradle® cyclical system, where materials are continuously print bed throughout the entire printing process and the
circulated in regenerative, closed-loop cycles, driven by print bed adhesion should facilitate easy part removal,
renewable energy sources. This means that materials are preferably by hand, after the printing process is completed.
reused and recycled, minimizing waste and environmental
impact, while also reducing the reliance on limited 2. Materials and methods
resources. Additive manufacturing, commonly known as 2.1. Materials
3D printing, is a promising technology that builds parts
using a bottom-up strategy and aligns with the approach. The materials used in this work are used and emptied HDPE
Chong et al. expanded on the Cradle-to-cradle® model milk jugs (bottles) from Meji Co. (Japan) obtained from
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and proposed a recycling and reclamation framework for a recycling center in Singapore. Decon 90 surfactant was
3D printing. The framework connects five main elements: obtained from Sigma-Aldrich (United States of America
plastic recycling, pre-treatment, filament extrusion, 3D [USA]). Virgin HDPE (vHDPE) sheets were obtained from
printing, and user participation. RS Component Pte. Ltd., (Singapore).
The rise of open-source 3D printing technology has 2.2. Processing milk jugs for filament extrusion
significantly enhanced the accessibility, popularity, and The process began by collecting HDPE milk jugs from
ownership of 3D printers. This has sparked the development Meiji Co. at a recycling center in Singapore. After thorough
of various 3D printing technologies, including vat cleaning with water and removal of labels and caps, 16
photopolymerization like stereolithography, powder bed milk jugs (Figure 1) were cut into large pieces and soaked
fusion like selective laser sintering, and material extrusion overnight in diluted Decon 90 surfactant. Following this,
(MEX) like fused deposition modeling (FDM). Among the pieces were rinsed with water to remove any potential
these, MEX is the most prevalent technology used in user- contaminations that might affect the quality of the
friendly, desktop 3D printers. Consumer-grade MEX filaments produced and also to facilitate smooth extrusion
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printers can print a variety of polymeric or plastic filaments, of the filaments.
with acrylonitrile butadiene styrene (ABS) and polylactic
acid (PLA) being the most favored choices. Subsequently, the cleaned pieces were oven-dried at 60
– 70°C for 1 h using a vacuum oven (Binder Oven - Model
High-density polyethylene (HDPE) is a widely used
packaging plastic, particularly in the foods and chemicals VD23; BINDER GmbH, Germany) to reduce moisture-
related defects in the filament to be produced. The large
industries, 1,2,9,10 and there is increasing interest in pieces of milk jug fragments were further cut manually
exploring recycled HDPE (rHDPE) as a feasible material into 6 × 6 mm flakes using a box cutter.
to make filament for MEX printing. This choice is driven
by the relatively straightforward process of recycling The flakes were then oven-dried at 60 – 70°C for 1 h
and converting the packaging materials into filaments to ensure complete drying before feeding into a Filabot
for MEX printing. 11,12 This process involves breaking Original extruder hopper (Vermont USA) (Figure 2). The

Volume 3 Issue 3 (2024) 2 doi: 10.36922/msam.4084