Fused
filament fabrication
(FFF) three-dimensional (3D) printing of semicrystalline polymers
such as high-density polyethylene (HDPE) is challenging because crystallization-induced
shrinkage of the filament, as it cools, results in stresses that warp
the printed part and debond it from the print substrate. Here, we
demonstrate that waste-derived HDPE can be successfully 3D printed
by (i) blending with a small fraction (<0.5% by weight) of dimethyl
dibenzylidene sorbitol (DMDBS) and (∼10%) linear low density
polyethylene (LLDPE) and (ii) printing the object with a thin “brim”
around it that is adhered to the print substrate using common polyvinyl
acetate-based glue. We match our experimental results with FEM simulations
that provide insight into the origin of the stresses developed during
printing. Because HDPE forms a significant fraction of the plastic
waste stream, conversion of waste-derived HDPE to 3D printing filament
has important technological implications.
We report here enhanced vibration and pressure sensing properties of nanocellulose reinforced flexible composite piezoelectric nanogenerators (PENGs). Surface fluorinated nanocellulose crystals (FNC) were incorporated into poly(vinylidene fluoride) (PVDF) and electrospun into composite nanofibers. Incorporation of only 2 wt % FNC in PVDF resulted in a significant enhancement in pressure sensitivity with a very low detectable pressure limit of 10 Pa and a sensitivity of up to 18 mV/kPa. The composite PENGs also demonstrated very high sensitivity for forced continuous vibrations. 2FNC/PVDF composites resulted in an order of magnitude higher voltage response over neat PVDF for a given strain. When PENGs were mounted on a vacuum pump for transduction of mechanical vibrations into electrical energy, 2FNC/PVDF composite devices manifested ∼3.8 times enhanced voltage output over neat PVDF and faster charging of a capacitor. The enhanced piezoelectric properties of PVDF/FNC nanocomposites could be attributed to the tailored interface between PVDF and nanocellulose and enhanced polarizability.
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