@article {46764, title = {3D printing of semicrystalline polypropylene: towards eliminating warpage of printed objects}, journal = {Bulletin of Materials Science}, volume = {43}, year = {2020}, month = {JUL}, pages = {171}, type = {Article}, abstract = {

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 {\textquoteleft}brim{\textquoteright}, 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.

}, keywords = {3D printing, polypropylene printing, warpage}, issn = {0250-4707}, doi = {10.1007/s12034-020-02097-4}, author = {Bachhar, Nirmalya and Gudadhe, Aniket and Kumar, Anil and Andrade, Prem and Kumaraswamy, Guruswamy} } @article {46836, title = {Enhancing the mechanical properties of 3D printed polylactic acid using nanocellulose}, journal = {Polymer Engineering and Science}, volume = {60}, year = {2020}, month = {AUG}, pages = {1842-1855}, type = {Article}, abstract = {

We report here a systematic investigation of the mechanical properties of polylactic acid (PLA) processed by fused filament fabrication (FFF) 3D printing vs PLA processed by compression molding. Our results show that the tensile strength and modulus of FFF-PLA is 49\% and 41\% lower, respectively, than compression molded samples of PLA. We also demonstrate here an approach to augment the mechanical properties of 3D printed PLA using nanocellulose. Incorporation of a small quantity (1 wt\%) of cellulose nanofibers (CNF) was found to enhance the tensile strength and modulus of 3D printed PLA by 84\% and 63\%, respectively. X-ray microtomography was used to probe the morphology of 3D printed PLA and PLA/CNF composites. 3D printed PLA/CNF composites had significantly lesser voids as compared to neat 3D printed PLA. Differential scanning calorimetry study revealed that CNF can accelerate the nucleation and crystallization of 3D printed PLA leading to enhanced crystallinity. The thermal stability of 3D printed PLA/CNF composites was not compromised by the addition of CNF. The enhanced mechanical properties of 3D printed PLA/CNF composites can be ascribed to higher crystallinity and lesser defects.

}, keywords = {3D printing, Biocomposites, composites, fused filament fabrication (FFF), Nanocellulose, polylactic acid (PLA)}, issn = {0032-3888}, doi = {10.1002/pen.25421, Early Access Date = JUN 2020}, author = {Ambone, Tushar and Torris, Arun and Shanmuganathan, Kadhiravan} } @article {48389, title = {Biodegradable, solvent-free photocrosslinkable PLLA resin formulations for additive manufacturing}, journal = {Macromolecular Chemistry and Physics}, volume = {223}, year = {2022}, month = {NOV}, type = {Article}, abstract = {

Acrylate end-functionalized linear and star poly l-lactide (PLLA) based aliphatic, photocurable oligomeric crosslinkers are developed, which are formulated with hydroxyl (ethyl)methacrylate (HEMA) as a biodegradable reactive diluent to demonstrate successful application for solvent-less 3D printing using digital light processing (DLP) technique as well as a custom-designed direct ink writing 3D printer. The resin formulation for 3D printing is optimized using spot curing, photodifferential scanning calorimetry and cure depth analysis. The 3D printed parts exhibit promising mechanical property along with improved hydrophilicity and biodegradability. The development of new photocurable resin formulations are expected to meet the growing demand for raw materials that can be applied for developing custom designed bio implantable objects.

}, keywords = {3D printing, biodegradable materials, digital light processing, L-Lactide, photocurable materials}, issn = {1022-1352}, doi = {10.1002/macp.202200139}, author = {Pal, Shibam and Asha, S. K.} } @article {48303, title = {Design and synthesis of photocrosslinker and light blocker based on L-Amino acid polyester and their application in solvent-free resin formulation for DLP/SLA 3D printing}, journal = {Polymers}, volume = {270}, year = {2023}, month = {MAR }, pages = {125781}, type = {Article}, abstract = {

Customising material design for new technological applications like additive manufacturing (AM) is a challenging yet promising approach to create a palette of materials suitable for developing eco-friendly products. LGlutamic acid and L-aspartic acid based aliphatic, photocurable polyester crosslinkers were designed and developed and incorporated into a solvent-free photocurable resin formulation with hydroxyl (ethyl)methacrylate (HEMA). Proof-of-concept 3D printing of clear and transparent objects was demonstrated using digital light processing (DLP) and Stereolithography (SLA) techniques. Resolution of the 3D printed objects could be improved by incorporating a Dansyl labelled L-glutamic acid polyester, which not only aided in modulating the viscosity of the resin formulation but could also function as a light blocker, thereby avoiding polymerization of unwanted areas while 3D printing. The curing kinetics of the photocurable formulation was analyzed using photo differential Scanning Calorimetry. Enzymatic degradability studies of 3D printed films were undertaken in PBS buffer containing esterase enzyme and compared with 3D printed samples using HEMA and a commercial crosslinker (Trimethylolpropane triacrylate (TMPTA)). Scanning electron microscopy (SEM) was used to evaluate the morphology of the 3D printed films before and after enzymatic degradation in the PBS buffer for 60 days. The 3D printed amino acid crosslinked films of HEMA presented high degree of degradation in contrast to the near total absence of any degradation in the 3D printed film crosslinked using TMPTA. The availability of new photocurable formulations that are enzymatically degradable are highly sought after for 3D printing applications.

}, keywords = {3D printing, Crosslinker, L -Amino acid Polyester, Light blocker, Photocurable}, issn = {0032-3861}, doi = {10.1016/j.polymer.2023.125781}, author = {Kamble, Ganesh N. and Joshi, Dheeraj Chandra and Asha, S. K.} } @article {48790, title = {Luminescent 3D printed poly(lactic acid) nanocomposites with enhanced mechanical properties}, journal = {Polymer Engineering and Science}, volume = {63}, year = {2023}, month = {JUL}, pages = {2059-2072}, type = {Article}, abstract = {

The three-dimensional (3D) printing of functional composite materials has gained tremendous interest in recent years. Nevertheless, research on 3D printing of luminescent composite materials is very limited, and the mechanical properties of such 3D-printed composites are poor. Herein, we report the preparation and characterization of a poly(lactic acid) (PLA) composite that, when 3D printed, exhibits enhanced toughness and high solid-state fluorescence quantum yield. Incorporation of only 1 wt\% pyrene butyric acid modified cellulose nanofibers (PBA-m-CNF) and l0 wt\% thermoplastic polyurethane (TPU) into PLA led to 223\% increase in toughness and 21\% increase in tensile modulus of PLA. Scanning electron microscopy (SEM) and X-ray microcomputed tomography (mu-CT) analysis of the fractured cross-sections of 3D printed composites revealed a ductile failure mode. The PLA/PBA-m-CNF1/TPU10 3D printed composite also exhibited a high solid-state fluorescence quantum yield of 38.35\%. To the best of our knowledge, this is the first report to show both enhanced mechanical properties and high solid-state fluorescence emission for 3D printable PLA. Such functional PLA composites could have potential applications in the fabrication of complex-shaped sensors, optical light pipes, etc.

}, keywords = {3D printing, Composite, fluorescence, Nanocellulose, poly(lactic acid), toughness}, issn = {0032-3888}, doi = {10.1002/pen.26345}, author = {Kothavade, Premkumar Anil and Yadav, Prashant and Nidhankar, Aakash D. and Torris, Arun and Pol, Harshawardhan and Kafi, Abdullah and Bateman, Stuart and Sukumaran, Santosh Babu and Shanmuganathan, Kadhiravan} } @article {48758, title = {Thermally activated delayed fluorescent solvent-free organic liquid hybrids for tunable emission applications}, journal = {Chemistry-An Asian Journal}, volume = {18}, year = {2023}, month = {JUL }, type = {Article}, abstract = {

The synthetic feasibility and excellent luminescence features of organic molecules attracted much attention and were eventually found useful in lighting applications. In this context, a solvent-free organic liquid having attractive thermally activated delayed fluorescence features in bulk along with high processability has prime importance. Herein, we report a series of naphthalene monoimide-based solvent-free organic liquids exhibiting cyan to red thermally activated delayed fluorescence with luminescence quantum yields up to 80\% and lifetimes between 10 to 45 mu s. An effective approach explored energy transfer between liquid donors with various emitters exhibiting tunable emission colors, including white. The high processability of liquid emitters improved the compatibility with polylactic acid and was used for developing multicolor emissive objects using 3D printing. Our demonstration of the thermally activated delayed fluorescence liquid will be much appreciated as a processable alternate emissive material suitable for large-area lighting, display, and related applications.

}, keywords = {3D printing, Energy Transfer, OLED, Organic Liquids, TADF}, issn = {1861-4728}, doi = {10.1002/asia.202300276}, author = {Nidhankar, Aakash D. D. and Goudappagouda and Kothavade, Premkumar D. and Dongre, Sangram D. and Veer, Sairam Dnyaneshwar and Dash, Soumya Ranjan and Rajeev, Kavya and Unni, K. N. Narayanan and Shanmuganathan, Kadhiravan and Babu, Sukumaran Santhosh} } @article {49069, title = {Highly electrostrictive salt cocrystal and the piezoelectric nanogenerator application of its 3D-printed polymer composite}, journal = {ACS Applied Materials and Interfaces }, volume = {16}, year = {2024}, month = {MAY}, pages = {26406-26416}, type = {Article}, abstract = {

Ionic cocrystals with hydrogen bonding can form exciting materials with enhanced optical and electronic properties. We present a highly moisture-stable ammonium salt cocrystal [CH3C6H4CH(CH3)NH2][CH3C6H4CH(CH3)NH3][PF6] ((p-TEA)(p-TEAH)PF6) crystallizing in the polar monoclinic C2 space group. The asymmetry in (p-TEA)(p-TEAH)PF6 was induced by its chiral substituents, while the polar order and structural stability were achieved by using the octahedral PF6- anion and the consequent formation of salt cocrystal. The ferroelectric properties of (p-TEA)(p-TEAH)PF6 were confirmed through P-E loop measurements. Piezoresponse force microscopy (PFM) enabled the visualization of its domain structure with characteristic {\textquoteleft}{\textquoteleft}butterfly{\textquoteright}{\textquoteright} and hysteresis loops associated with ferro- and piezoelectric properties. Notably, (p-TEA)(p-TEAH)PF6 exhibits a large electrostrictive coefficient (Q(33)) value of 2.02 m(4) C-2, higher than those found for ceramic-based materials and comparable to that of polyvinylidene difluoride. Furthermore, the composite films of (p-TEA)(p-TEAH)PF6 with polycaprolactone (PCL) polymer and its gyroid-shaped 3D-printed composite scaled-up device, 3DP-Gy, were prepared and evaluated for piezoelectric energy-harvesting functionality. A high output voltage of 22.8 V and a power density of 118.5 mu W cm(-3) have been recorded for the 3DP-Gy device. Remarkably, no loss in voltage outputs was observed for the (p-TEA)(p-TEAH)PF6 devices even after exposure to 99\% relative humidity, showcasing their utility under extremely humid conditions.

}, keywords = {3D printing, cocrystals, energy harvesting, ferroelectricity, Piezoelectricity}, issn = {1944-8244}, doi = {10.1021/acsami.4c03349}, author = {Sahoo, Supriya and Panday, Rishukumar and Kothavade, Premkumar and Sharma, Vijay Bhan and Sowmiyanarayanan, Anirudh and Praveenkumar, Balu and Zareba, Jan K. and Kabra, Dinesh and Shanmuganathan, Kadhiravan and Boomishankar, Ramamoorthy} } @article {49039, title = {Thiol-ene-based degradable 3D printed network from bio resource derived monomers ethyl-lactate and isosorbide}, journal = {European Polymer Journal}, volume = {205}, year = {2024}, month = {FEB }, type = {Article}, abstract = {

A polymeric ene-based thiol-ene network is reported that was demonstrated for light-based 3D printing. Allyl poly (acrylate ethyl lactate) (PAEL) was synthesized starting from ethyl lactate in an efficient and scalable manner. Ethyl lactate is a biobased material obtained naturally or chemically in high yields in the form of ethyl ester of lactic acid. Isosorbide, which is also a bio based resource was converted into thiol derivative and was used along with Pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) as multifunctional thiol. The polymeric nature of the ene (i.e. PAEL) imparted exceptionally high mechanical properties like Young{\textquoteright}s modulus of 1.75 GPa as well as high thermal stability with a decomposition temperature (Td,10\%) exceeding 350 C for all the networks studied. The properties could also be customized by fine tuning the type and stoichiometric ratio of the thiol crosslinked employed. For instance, the Young{\textquoteright}s modulus range from 1.75 GPa to 1.03 GPa and glass transition temperature range from 44 C to 54 C could be achieved. DLP 3D printing was used to demonstrate the printability of the resins with high resolution and structural fidelity. The study also highlights the basemediated rapid hydrolytic degradation efficiency of the 3D printed parts, demonstrating the applicability of these novel polymeric ene based thiol-ene for sustainable and eco-friendly 3D printable formulations.

}, keywords = {3D printing, Degradation, digital light processing, Poly (acrylate ethyl lactate), Thiol-ene}, issn = {0014-3057}, doi = {10.1016/j.eurpolymj.2024.112761}, author = {Pal, Shibam and Asha, S. K.} } @article {49711, title = {Carbohydrate-based polyester and amino acid polyester photocrosslinker and their resin formulation for 3D printing applications}, journal = {Chemistry-An Asian Journal}, volume = {20}, year = {2025}, month = {JUN}, type = {Article}, abstract = {

Fully bio-based polyester was designed and synthesized using the carbohydrate-based diol 2,4:3,5-di-O-methylene-D-mannitol (Manx) and dimethyl ester of 2,3:4,5-di-O-methylene-galactaric acid (Galx). Photocurable resin formulations were prepared by incorporating up to 15 wt\% of the carbohydrate polyester into hydroxyl ethyl methacrylate (HEMA) along with polyacrylamide crosslinker derived from L-glutamic acid. Complex 3D structures with good shape fidelity could be 3D printed using these novel polyester resin formulations. The incorporation of the carbohydrate polyester improved the glass transition temperature of the 3D-printed objects. Enzymatic erosion studies conducted using esterase enzyme revealed a higher degradation rate for the 3D-printed films containing the carbohydrate polyester. The hydrolytic degradation analysis conducted in both acidic and basic environments revealed that the 3D-printed polymer network exhibits stability and resilience in acidic conditions, while it undergoes complete degradation in basic conditions. This finding underscores the possibility of tailoring degradation processes under regulated circumstances.

}, keywords = {3D printing, Amino acid, Carbohydrate polyester, Enzymatic degradation, Resin formulation}, issn = {1861-4728}, doi = {10.1002/asia.202401474}, author = {Kamble, Ganesh N. and Joshi, Dheeraj Chandra and Gavhane, Utreshwar A. and Asha, S. K.} }