Abstract
Extrusion-based additive manufacturing (EBAM) or 3D printing is used to produce customized prototyped parts. The majority of the polymers used with EBAM show moisture sensitivity. However, moisture effects become more pronounced in polymers used for critical applications, such as biomedical stents, sensors, and actuators. The effects of moisture on the manufacturing process and the long-term performance of Shape Memory Polyurethane (SMPU) have not been fully investigated in the literature. This study focuses primarily on block-copolymer SMPUs that have two different hard/soft (h/s) segment ratios. It investigates the effect of moisture on the various properties via studying: (i) the effect of moisture trapping within these polymers and the consequences when manufacturing; (ii) and the effect on end product performance of plasticization by moisture. Results indicate that higher h/s SMPU shows higher microphase separation, which leads to an increase of moisture trapping within the polymer. Understanding moisture trapping is critical for EBAM parts due to an increase in void content and a decrease in printing quality. The results also indicate a stronger plasticizing effect on polymers with lower h/s ratio but with a more forgiving printing behavior compared to the higher h/s ratio.
Highlights
Over the last decade, extrusion-based additive manufacturing (EBAM), commonly referred to as thermoplastic 3D printing, has gained much attention due to the major advantages it offers for producing customized prototyped parts
For the majority of the polymers used with EBAM, including polylactic acid (PLA), acrylonitrile butadiene styrene (ABS) and various grades of polyamide (Nylon® ), moisture is an obstacle during the manufacturing process and later during the part’s life cycle
Moisture trapping within Shape Memory Polyurethane (SMPU) is significant for any melt-extrusion manufacturing process
Summary
Extrusion-based additive manufacturing (EBAM), commonly referred to as thermoplastic 3D printing, has gained much attention due to the major advantages it offers for producing customized prototyped parts. For the majority of the polymers used with EBAM, including polylactic acid (PLA), acrylonitrile butadiene styrene (ABS) and various grades of polyamide (Nylon® ), moisture is an obstacle during the manufacturing process and later during the part’s life cycle. This effect is a more pronounced problem when the printed parts are intended for critical applications, such as in the case of polyurethane-based shape memory polymers (SMPU). Other critical and promising applications include grippers, actuators for soft robotics [4], origami-based self-assembly structures for Materials 2019, 12, 244; doi:10.3390/ma12020244 www.mdpi.com/journal/materials
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