01752nas a2200241 4500008004100000022001400041245006800055210006600123260000800189300001400197490000600211520100700217653003801224653001801262653001801280653001201298100002001310700002201330700001601352700001801368700002701386856009701413 2019 eng d a2637-610500aThree-dimensional printing with waste high-density polyethylene0 aThreedimensional printing with waste highdensity polyethylene cNOV a3157-31640 v13 a

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 (similar to 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.

10a3d printing polyethylene printing10apolymer blend10aRecyclability10awarpage1 aGudadhe, Aniket1 aBachhar, Nirmalya1 aKumar, Anil1 aAndrade, Prem1 aKumaraswamy, Guruswamy uhttp://library.ncl.res.in/content/three-dimensional-printing-waste-high-density-polyethylene02469nas a2200229 4500008004100000022001400041245009700055210006900152260000800221300000800229490000700237520171300244653001601957653002701973653001202000100002202012700002002034700001602054700001802070700002702088856012402115 2020 eng d a0250-470700a3D printing of semicrystalline polypropylene: towards eliminating warpage of printed objects0 a3D printing of semicrystalline polypropylene towards eliminating cJUL a1710 v433 a

Fused filament fabrication (FFF) is an extrusion-based 3D printing technique for thermoplastic polymers. In this technique, molten polymer is extruded through a print nozzle and is laid down layer by layer to build up the printed object. Currently, FFF is used primarily to print amorphous or low-crystallinity polymers, such as acrylonitrile butadiene styrene copolymer (ABS) or polylactic acid (PLA). Printing of semicrystalline polymers, such as polyethylene or polypropylene remains particularly challenging. During FFF of semicrystalline polymers, large thermomechanical stresses are generated when the polymer solidifies on cooling. These stresses result in warpage of the printed part. Here, we analyse the factors that influence stresses generated during FFF 3D printing of a commercial semicrystalline polymer, isotactic polypropylene. We investigate the effect of height of the printed object on part warpage, as well the effect of infilling during printing. We demonstrate that the stresses generated during FFF can be substantially decreased by incorporation of a `brim', viz. a thin layer at the base of the printed object, and by adhering the brim to the print substrate using common polyvinyl acetate-based glue. We systematically investigate the effect of the brim size on the warpage of the printed object. We support our experimental findings with finite element method (FEM) simulations that explain the mechanism of stress buildup during printing. The trend in stresses calculated in the FEM simulations parallel the warpage measured in the experiments. Thus, this work represents an important methodological advance towards warpage-free FFF printing of semicrystalline polymers.

10a3D printing10apolypropylene printing10awarpage1 aBachhar, Nirmalya1 aGudadhe, Aniket1 aKumar, Anil1 aAndrade, Prem1 aKumaraswamy, Guruswamy uhttp://library.ncl.res.in/content/3d-printing-semicrystalline-polypropylene-towards-eliminating-warpage-printed-objects02706nas a2200241 4500008004100000022001400041245011300055210006900168260000900237300001400246490000600260520184600266653002002112653002002132653006402152653001402216653001202230100001902242700002002261700002302281700003102304856012902335 2025 eng d a2637-610500aUpcycling of postconsumer recyclate polypropylene into low warping and high toughness 3D printable filaments0 aUpcycling of postconsumer recyclate polypropylene into low warpi cJUN  a7373-73810 v73 a

Polypropylene (PP) is widely used in commodity applications owing to its chemical stability, mechanical properties and low cost. However, almost 50% of the produced PP ends up as postconsumer waste (PCW) within a short period of usage. Being a non-biodegradable polymer, recycling PCW PP is important to mitigate plastic waste in landfills. Nonetheless, recycling or upcycling postconsumer recyclate (PCR) PP into valuable resources without deterioration in physical and mechanical properties is a challenge. This report presents an approach to upcycle PCR polypropylene (rPP) into high quality 3D printing filament that not only prints with very low warpage but with significantly high elongation at break and toughness. Incorporation of poly(butylene adipate-co-terephthalate) (PBAT) along with maleic anhydride grafted polypropylene (MAPP) in specific proportions led to a significant enhancement in mechanical properties, miscibility, crystallization behavior, and 3D printability. rPP/PBAT blends with 20 wt % PBAT and 10 wt % MAPP exhibited a 62-fold enhancement in elongation at break over rPP (from 1.88 to 118.29%) and a 72-fold increase in toughness (from 2 to 143.60 kJ/m3) with almost similar tensile strength. The final printed components had better layer adhesion and structural stability with a dramatic decrease in warpage, from 25.82% for pristine rPP to only 7.86% for rPP/PBAT blend. Isothermal crystallization studies and data analysis using the Avrami equation showed that crystallization half-time (t 1/2), which measures the duration needed for half of the total crystallinity to form, increased from 12.6 s for rPP to 66 s for the rPP/PBAT blend. This report demonstrates an approach to upcycle PCR PP, a positive step toward realizing the goals of circular economy and sustainable additive manufacturing.

10aCrystallization10aFFF 3D printing10apolypropylene/poly(butylene adipate-co-terephthalate)blends10atoughness10awarpage1 aGopal, Animesh1 aPatil, Prashant1 aPol, Harshawardhan1 aShanmuganathan, Kadhiravan uhttp://library.ncl.res.in/content/upcycling-postconsumer-recyclate-polypropylene-low-warping-and-high-toughness-3d-printable