Crystalline Segments Research Articles

A novel photocurable polymeric solid–solid phase change material for intelligent temperature regulators

The advancement of solid–solid phase change materials (SSPCMs) with crystalline segments embedded onto crosslinked polymer backbones offers a promising solution to the leakage problems associated with traditional phase change materials. Despite its potential, this technology faces challenges, including energy-intensive synthesis processes of SSPCMs and difficulties in custom designing materials for confined spaces. Herein, we introduce a novel strategy for the rapid preparation of polyurethane acrylate-based SSPCMs via UV-initiated polymerization. By leveraging crystalline segments from polyethylene glycol, the resulting SSPCM exhibits an impressive enthalpy of 110.4 J⋅g−1, enabling seamless transitions from rigid to soft states during solid–solid phase changes. When applied in portable electronic devices, this SSPCM can be synthesized in-situ to meet various size requirements, demonstrating exceptional temperature regulation performance based on latent thermal energy storage mechanisms. Furthermore, by integrating thin layers of carbon nanotubes (CNTs) onto the rough surfaces of SSPCM films and employing a face-to-face configuration to convert temperature-sensitive mechanical changes into electric resistance variations, we have engineered high-temperature alarms for SSPCM-based temperature regulators. The advantages of this preparation strategy, combined with the thermal regulation capabilities and innovative temperature alarm design, underscore the significant potential for intelligent and adaptive applications of SSPCMs in advanced technological landscapes.

Highly porous layered carbon nanocomposites from the self-assembly of a poly(amic acid) for efficient oxygen reduction reaction catalysis

Porous layered carbon nanomaterials play important role in the efficient loading of electroactive substances for high performance energy conversion techniques. Herein, an intramolecular cyclization induced self-assembly (ICISA) strategy is proposed to prepare three-dimensional highly porous layered carbon nanostructures (LCs) for efficient loading of various transition metal nanoparticles for oxygen reduction reaction (ORR) catalysis. The amphiphilic alternating copolymer poly(amic acid) (PAA) is synthesized by the stepwise polymerization of hydrazine hydrate and pyromellitic dianhydride. Upon heating above 160 °C, the intramolecular cyclization reaction occurs, leading to the formation of rigid, crystalline and non-soluble polyimide segments in the backbone, which induces the self-assembly of the polymer to form dumbbell-shaped assemblies with a high solid content of 15%. After pyrolysis in a nitrogen atmosphere, LCs are obtained. Cobalt (Co), iron (Fe) and FeCo nanoparticles can be efficiently loaded, noted as Co@LCs, Fe@LCs and FeCo@LCs, respectively. The ORR catalytic performance of the catalysts is evaluated to give half wave potentials of 0.791, 0.787 and 0.812 V, and limit current densities of 4.92, 4.73 and 4.71 mA cm−2 for Co@LCs, Fe@LCs and FeCo@LCs, respectively. Overall, we propose an ICISA strategy to facilely prepare three-dimensional carbon nanomaterials with highly porous layered structure for efficient ORR catalysis.

Coarse-Grained Simulations on Polyethylene Crystal Network Formation and Microstructure Analysis.

Understanding and characterizing semi-crystalline models with crystalline and amorphous segments is crucial for industrial applications. A coarse-grained molecular dynamics (CGMD) simulations study probed the crystal network formation in high-density polyethylene (HDPE) from melt, and shed light on tensile properties for microstructure analysis. Modified Paul-Yoon-Smith (PYS/R) forcefield parameters are used to compute the interatomic forces among the PE chains. The isothermal crystallization at 300 K and 1 atm predicts the multi-nucleus crystal growth; moreover, the lamellar crystal stems and amorphous region are alternatively oriented. A one-dimensional density distribution along the alternative lamellar stems further confirms the ordering of the lamellar-stack orientation. Using this plastic model preparation approach, the semi-crystalline model density (ρcr) of ca. 0.913 g·cm-3 and amorphous model density (ρam) of ca. 0.856 g·cm-3 are obtained. Furthermore, the ratio of ρcr/ρam ≈ 1.06 is in good agreement with computational (≈1.096) and experimental (≈1.14) data, ensuring the reliability of the simulations. The degree of crystallinity (χc) of the model is ca. 52% at 300 K. Nevertheless, there is a gradual increase in crystallinity over the specified time, indicating the alignment of the lamellar stems during crystallization. The characteristic stress-strain curve mimicking tensile tests along the z-axis orientation exhibits a reversible sharp elastic regime, tensile strength at yield ca. 100 MPa, and a non-reversible tensile strength at break of 350%. The cavitation mechanism embraces the alignment of lamellar stems along the deformation axis. The study highlights an explanatory model of crystal network formation for the PE model using a PYS/R forcefield, and it produces a microstructure with ordered lamellar and amorphous segments with robust mechanical properties, which aids in predicting the microstructure-mechanical property relationships in plastics under applied forces.

3D printed sequence-controlled copolyimides with high thermal and mechanical performance

Inadequate heat resistance and mechanical property limited the application of 3D printed polymer parts in aerospace industry. To address this restriction, a kind of sequence-controlled copolyimides with both amorphous segment and crystalline segment, suitable for fused deposition modeling 3D printing technique were designed and synthesized. The effect of content and distribution of crystalline segment on melt fluidity and crystallization behavior was disclosed. It was found that copolyimide with crystalline segment only distributed in the end of backbone exhibited good melt fluidity and slow crystallization rate. Microstructure change of the corresponding copolyimide during 3D printing and thermal annealing was revealed. Due to slow crystallization rate of copolyimide, no crystals formed during 3D printing. Thus, the diffusion and entanglement of polymer chain at interface were guaranteed. Thermal annealing at 350 °C facilitated diffusion and arrangement of polymer chain, leading to the enhancement of interfacial bonding and crystallization of copolyimide at interface and in filament. Therefore, the printed copolyimide specimens exhibited high heat resistance, high mechanical property and excellent interfacial bonding performance. The tensile strength of specimens printed in XY plane with 0° infill direction (XY-0), XY plane with 90° infill direction (XY-90) and XZ plane with 90° infill direction (XZ-90) were 110 MPa, 96 MPa and 57 MPa, respectively. The tensile strength of XY-0 printed specimen at 200 °C was 186 % higher than that of XY-0 printed amorphous polyimide specimen, reaching 40 MPa. This study expanded the kinds of polymeric materials suitable for fused deposition modeling, and provided the possibility of printing high performance engineering parts.

Understanding the structural changes, interfacial mechanisms, and mechanical properties of polymer/MWCNT nanocomposites after microwave treatment

AbstractThe use of microwave radiation for the post‐processing treatment of engineering polymers is a recent trend not seen by many. In the case of polymers, their crystalline nature is a significant factor in optimizing the treatment time for maximum improvement in mechanical properties. With the advent of nanomaterials, the aim of the present work is to explore the possibility of post‐processing microwave treatment on the structure and property relationships in MWCNT‐reinforced polymer matrices. The microwave‐activated nucleating tendency of MWCNTs was found to be promoting molecular chain rearrangement in poly‐amide (PA) and poly‐butylene‐terephthalate (PBT) nanocomposites. This considerably improved the mechanical characteristics of the composites by facilitating the rearrangement of the crystalline segments of the polymer matrix. The wear performance of PA nanocomposite increased by 30%, while the elongation of PBT nanocomposite increased by 93%, after a treatment of only 15–20 s. However, comparing with previous studies, it was found that, similar to virgin polymers, the treatment time needed for maximum improvement in polymer/MWCNT nanocomposites is hugely dependent on polymer matrix crystallinity as well. A detailed analysis of the microwave‐treated nanocomposites' structure and mechanical properties illustrates the post‐processing microwave treatment as a time‐efficient, cost‐effective, and environmentally friendly technique.Highlights Direct use of microwave radiation to heat the finished polymeric component. Microwave treatment brings about structural changes resulting in enhanced properties. Instantaneous heating is a key reason for the systematic arrangement of polymeric chains. Microwave‐activated nucleating tendency of MWCNTs also promotes chain arrangement. Properties increase as high as 30% wear rate and 93% elongation.

Thermo-Responsive Shape Memory Thermoplastic Elastomer Based on Natural Rubber and Ethylene Octene Copolymer Blends

The shape memory (SM) polymers with superior SM properties were successfully fabricated based on melt blending of natural rubber (NR) and ethylene octene copolymer (EOC) at various crystallinity of EOC phase. The differential scanning calorimetry analysis, mechanical properties, temperature scanning stress relaxation, and shape memory properties were studied. Results revealed that the mechanical and thermal properties of the prepared NR/EOC blends improved as a function of amount of ethylene fraction in the EOC phase. The ethylene segment of EOC in the NR/EOC blend is triggered as a stimulus-sensitive domain. The shape memory properties in terms of shape fixity and shape recovery efficiencies of the blends tended to increase with the increasing of crystalline segments in the blends. The shape memory properties of the prepared blends substantially exceed the best performance (close to 100%) by blending the NR/EOC at 50/50 parts by weight, having 62%–80% of ethylene content in the EOC phase, which corresponds to approximately 3°–16° of crystallinity of EOC phase in the blends.

An intrinsic phase change elastomer with superior stretchability and reparable capabilities for self-thermal managing stretchable electronics

In recent years, phase change materials (PCMs) are gradually developed and utilized for thermal management in wearable electronics due to their autonomous heat absorption ability during the phase change process. However, the high rigidity (elastic modulus ＞ 100 MPa) and stiffness (yield strain ＜ 15%) severely limited the thermal management application of the reported PCMs in stretchable electronics. Herein, we present an intrinsic phase change elastomer (IPCE) combining the function of PCM and elastomer by introducing crystalline polyethylene glycol segments and amorphous polypropylene glycol segments into an elaborately designed chemical cross-linked networks. The fabricated IPCE merges excellent softness (elastic modulus ＜ 20 MPa), stretchability of 900%, elastic mechanical behavior (without yield phenomenon), fantastic thermal management ability, and outstanding thermal repairable capability. Eventually, we fabricated a simple strain sensor with IPCE as substrate by spraying gold nanoparticles on both sides of the IPCE film. The stable sensing ability that repeatedly monitoring the subtle human motion and autonomous thermal management behavior of the strain sensor demonstrated the appealing practicability of our IPCE. This work paved an avenue for fabricating stretchable and self-thermal managing elastomer for stretchable electronics.

Partial crystalline organosilicon-based polysiloxane-polyurethane copolymers

Partial crystalline polysiloxane-based polyurethane copolymers were prepared by using hydroxyethoxypropyl capped polydimethylsiloxane (PDMS) as soft segment and α,ω-(bis (hydroxyethylthioether) ethyl)-disiloxane as chain extender. Due to this partial crystalline structure, the copolymer shows fairly good tensile properties and multiple shape deformation property. Repeated tensile tests revealed that stretch led to crystal destruction, and the microstructure of samples became stable after twice stretches. The lost crystallinity got 85.1% recovered upon treated at 60 °C for 1 h. It was proved that partial crystallization properties of the polysiloxane-polyurethane copolymer were from combined effects of polysiloxane soft segment and disiloxane chain extender. This unique crystallization kinetics of -(Si-O-Si)x- structure coexisting in soft and hard segments is regarded as one main reason to form crystalline hard segment domains in a common two-step synthesis.

Thermally-triggered multi-shape-memory behavior of binary blends of cross-linked EPDM with various thermoplastic polyethylenes and their potential applications as temperature indicators

Shape-memory polymers (SMPs) are smart materials that can alter their configuration in response to external stimuli. They have shown promise in a number of application areas, including soft robotics or biomedical devices. Frequently, however, the materials needed are expensive, or labor-intensive synthetic processes are involved. In this contribution, we report a versatile and cost-effective manufacturing method for SMPs based on binary elastomer-thermoplastic-blends. These were produced from ethylene-propylene-diene monomer rubber (EPDM) combined with ultra-low-density polyethylene (ULDPE), propylene-ethylene copolymer (PP-c-PE), or high-density polyethylene (HDPE) as thermoplastic components. Atomic force microscopy revealed an immiscible two-phase morphology. Results of dynamic-mechanical thermal analysis showed that all polymer blends with a high thermoplastic load had efficient thermo-responsive dual-shape-memory, also demonstrated on macroscopic specimens. Furthermore, multi-shape-memory of elastomer/thermoplastic (40/60)-blends was investigated. Especially ULDPE-containing blends exhibited particularly promising multi-shape-memory features and stepless, controllable temperature response. Mechanistically, this is based upon the synergistic interaction of the cross-linked elastomer and the thermoplastic switching phase, consisting of different crystalline segments melting over a wide range from 60 to 125 °C. The continuous shape recovery over a broad temperature range could be used to create reusable test strips, e.g., for indicating exposure temperature in transportation chains or overheating protection.

ReaxFF reactive force field model enables accurate prediction of physiochemical and mechanical properties of crystalline and amorphous shape‐memory polyurethane

AbstractWe investigate reactive force field (ReaxFF) prediction of physiochemical and mechanical properties, and stimuli response behavior of a shape‐memory polyurethane (SMPU) rigid segment. We used SMPUs as a platform to link the rigid/hard segment domain crystallinity with properties that can also be experimentally measured. Specifically, we developed models for crystalline and amorphous forms of a common rigid segment of SMPUs, for example, 4,4′‐diphenylmethane diisocyanate (MDI) with n‐butanediol (BDO), denoted as MDI‐BDO. ReaxFF molecular dynamics simulations with equilibrium dynamics are performed by controlling mass, temperature, and pressure or volume to predict the structural and physiochemical properties of crystalline and amorphous rigid segments of SMPU systems, followed by simulating their XRD and FTIR patterns, respectively. Non‐equilibrium ReaxFF simulations are implemented by using uniaxial box deformation technique to study response‐behavior of crystalline SMPU under tensile loading and during stress‐relaxation. The model and simulation scheme presented in this study demonstrates a robust theoretical pathway toward application‐dictated, on‐demand design of high‐performance SMPUs in applications such as soft robotics.

Fast-Tracking of the Segmental Orientation in Poly(ethylene oxide)-based Polyurethane Urea by Mechano-optical (Infrared Dichroism and Birefringence) Properties: Degree of the Soft-Segment Ordering Effect

The orientation behavior of segment-specific chemical groups of NH and CH was investigated for poly(ethylene oxide) (PEO)-based polyurethane urea (PUU) during uniaxial stretching using a uniaxial stretching system integrated with spectral birefringence and ultrafast IR spectrometers that capture two polarization states simultaneously. PUUs with 30% by-weight urethane-urea hard segment content were prepared using PEO oligomers with number average molecular weights of 2000, 4600, and 8000 g/mol. High-molecular weight PEO-based PUUs exhibited microphase morphologies with sharp interfaces between the PEO matrix and urethane-urea hard segments, while low-molecular weight PEO-2000 (2000 g/mol)-based PUU exhibited a gradient interphase. This is primarily due to substantial hydrogen-bonding interactions between the urea hard segments and ether groups of highly amorphous PEO-2000 compared with highly crystalline soft segments in PEO-4600 and PEO-8000, which lack significant hydrogen-bonding interactions with urea groups and hence a sharper interface and improved microphase separation. The segment-specific chemical group orientation study revealed that the relaxation and reorganization behaviors are closely dependent on the initial morphology. In microphase-separated PUU with a gradient interphase, responses of the hard and soft segments to deformation are similar even at lower strain levels. For the microphase-separated PUUs with a sharp interface, the low-strain level orientation is localized in the soft-segment regions until the connection with the hard segments drive the orientation in the chain axis toward the stretching direction. This network transition is also reflected in the mechano-optical behavior as a change from a high-strain optical constant to a lower-strain optical constant.

Structural behavior and ion dynamics of methylcellulose/tri-potassium phosphate-based solid biopolymeric electrolytes

In this article, the complexation of methylcellulose (MC) with tri-potassium phosphate (K3PO4) is investigated using an ultrasonication-assisted solution cast process. X-ray diffraction (XRD) analysis indicates that varying concentrations of K3PO4 salt (7–35 wt.%) disrupt the crystalline segment of the MC host matrix. The considerable shift in the intensity and orientation of the Fourier transforms infrared spectroscopy (FTIR) transmittance bands indicate the establishment of a charge-transfer entanglement between the polymer host and the dispersed salt. The optimum sample (28 wt.%) exhibits a high ionic conductivity of 1.74 × 10−5 S cm−1, potential stability of 3.48 V, and a cation transference number (ti ) of 0.945. These findings show the relevance of the developed SPEs for possible application in electrochemical devices.

Structural design and properties of crystalline polyarylene ether nitrile copolymer

In this paper, the bisphenol A segment is introduced into the molecular chain by molecular design to avoid high molecular weight crystalline PEN, while having good crystallization ability due to the internal plasticization of the bisphenol A segment. Three PEN copolymers with different structures were synthesized by adjusting the structures of the crystalline segments. Firstly, the crystallization ability, thermal and mechanical properties of PEN with different structures were studied. Then, for the hydroquinone/bisphenol A copolymerized PEN with a tensile strength of 121.7 MPa, an elongation at break of 9.94%, stable dielectric properties and good crystallization ability, the effects of hot-pressing conditions on the properties were investigated. The results show that temperature and pressure have a synergistic effect while the temperature factor dominates. Finally, the best processing conditions were confirmed. This is a guideline for the study of semi-crystalline PEN and provides a theoretical basis for application.

Fatigue Characteristics of Poly(ether-b-amide) Elastomers during Cyclic Dynamic Tests and the Underlying Microstructural Evolution

The dynamic fatigue behavior of the poly(ether-b-amide) (PEBA) elastomers was characterized by a combination of step increase load test (SILT), step increase strain test (SIST), and single load dynamic creep (SLDC). PEBA had crystalline hard segments of polyamide 12 (PA12) and soft segments of poly(tetramethylene oxide) (PTMO). The crystalline morphologies before and after the tests were studied by ex situ wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). Fast stress relaxation can be seen under the applied strain well below than the elongation at break. Remarkable dynamic creep can be observed under the applied load triggering yielding of the specimen, which is substantially less than the ultimate tensile strength. Although the presence of high content of amorphous PTMO renders high entropic elasticity, the disintegration of the crystalline hard domains of PA12 is expected to determine the relaxation rate, creep rate, and modulus, as strain-induced crystallization in soft domains did not occur and no trace was found by WAXD. SAXS patterns showed that the orientation of the PA12 lamellae at lower stresses or strains can largely be restored. However, the fractured and highly aligned PA12 lamellae resulted in classic four-point or two-lobe SAXS patterns, which implied the underlying microstructural changes after the cyclic dynamic tests.

Crystalline Carbosilane‐Based Block Copolymers: Synthesis by Anionic Polymerization and Morphology Evaluation in the Bulk State

AbstractBlock copolymers (BCPs) in the bulk state are known to self‐assemble into different morphologies depending on their polymer segment ratio. For polymers with amorphous and crystalline BCP segments, the crystallization process can be influenced significantly by the corresponding bulk morphology. Herein, the synthesis of the amorphous‐crystalline BCP poly(dimethyl silacyclobutane)‐block‐poly(2vinyl pyridine), (PDMSB‐b‐P2VP), by living anionic polymerization is reported. Polymers with overall molar masses ranging from 17 400 g to 592 200 g mol−1 and PDMSB contents of 4.8–83.9 vol% are synthesized and characterized by size‐exclusion chromatography and NMR spectroscopy. The bulk morphology of the obtained polymers is investigated by means of transmission electron microscopy and small angle X‐ray scattering, revealing a plethora of self‐assembled structures, providing confined and nonconfined conditions. Subsequently, the influence of the previously determined morphologies and their resulting confinement on the crystallinity and crystallization behavior of PDMSB is analyzed via differential scanning calorimetry and powder X‐ray diffraction. Here, fractionated crystallization and supercooling effects are observable as well as different diffraction patterns of the PDMSB crystallites for confined and nonconfined domains.

Influence of the Nature of Aliphatic Hydrophobic Physical Crosslinks on Water Crystallization in Copolymer Hydrogels.

The local environment within a hydrogel influences the properties of water, including the propensity for ice crystallization. Water-swollen amphiphilic copolymers produce tunable nanoscale environments, which are defined by hydrophobic associations, for the water molecules. Here, the antifreeze properties for equilibrium-swollen amphiphilic copolymers with a common hydrophilic component, hydroxyethyl acrylate (HEA), but associated through crystalline (octadecyl acrylate, ODA) or rubbery (ethylhexyl acrylate, EHA) hydrophobic segments, are examined. Differences in the efficacy of the associations can be clearly enunciated from compositional solubility limits for the copolymers in water (<2.6 mol % ODA vs ≤14 mol % EHA), and these differences can be attributed to the strength of the association. The equilibrium-swollen HEA-ODA copolymers are viscoelastic solids, while the swollen HEA-EHA copolymers are viscoelastic liquids. Cooling these swollen copolymers to nearly 200 K induces some crystallization of the water, where the fraction of water frozen depends on the details of the nanostructure. Decreasing the mean free path of water by increasing the ODA composition from 10 to 25 mol % leads to fractionally more unfrozen water (66-87%). The swollen HEA-EHA copolymers only marginally inhibit ice (<13%) except with 45 mol % EHA, where nearly 60% of the water remains amorphous on cooling to 200 K. In general, the addition of the EHA leads to less effective ice inhibition than analogous covalently crosslinked HEA hydrogels (19.9 ± 1.8%). These results illustrate that fluidity of confining surfaces can provide pathways for critical nuclei to form and crystal growth to proceed.

High-Strength Heat-Elongated Thermoplastic Polyurethane Elastomer Consisting of a Stacked Domain Structure.

We found that a high-strength elastomer was obtained by the heat elongation of a thermoplastic polyurethane (TPU) film consisting of a high content of crystalline hard segments (HS). The stress upturn continuously increased with the elongation ratio without a decrease in the strain recovery by heat elongation, i.e., the stress at break of a quenched TPU film was increased from 55 to 136 MPa by heat elongation at an elongation ratio of 300%. The results of small-angle X-ray scattering, DSC, and AFM observations revealed that: (1) anisotropically shaped HS domains were stacked at a nanometer scale and the longer direction of the HS domains was arranged perpendicular to the elongated direction due to the heat elongation, (2) the densification of the HS domains increased with increases in the elongation ratio without a significant increase in the crystallinity, and (3) the stacked domain structure remained during the stretching at 23 °C. Thus, the strengthening of the elongated TPU might be attributed to the densification of the HS domains in the stacked structure, which prevents the fracture of the HS domains during the stretching.

Trends in Polymer Degradation Across All Scales

AbstractThe development of sustainable plastic materials will be flanked with conscious resource management, waste recovery frameworks, and social change. Nonetheless, developing strategies toward controlled polymer degradation remains a key challenge—whether as a failsafe mechanism for materials that escape the resource recovery cycle, or where distinct degradation pathways are required for specific applications such as in the biomedical realm. This perspective highlights recent trends, challenges, and future strategies on three levels: 1) On the materials level, by the incorporation of enzymes into polymer materials that catalyze polymer degradation under benign conditions; 2) On the domain level, crystalline segments of polymer materials are often inert, even to enzymatically catalyzed degradation. Gaining an understanding of the mode of interaction between enzymes and polymer chains is key to controlling degradation of all polymer morphologies within materials. Processive depolymerization mechanisms, where the enzyme binds polymer chain ends and depolymerizes along the chain are extremely promising for efficient polymer degradation; 3) On the molecular level, where polyesters exhibit enzymatic targets of ester bonds through their polymer backbone, poly(alkene)s c of all carbon backbones. To enable degradation of this most abundant class of polymers, strategies must be developed to incorporate enzymatic targets into the backbone.

End-Terminated Poly(urethane-urea) Hybrid Approach toward Nanoporous/Microfilament Morphology.

In the present work, the effect of heteroatomic hydrogen bonding on the properties of −OH/–NH-terminated soft-segment-free polymers, viz, polyurethane (P-UT), polyurea (P-UR), and their hybrid (P-UT–UR), is explored. P-UT was synthesized from phloroglucinol and P-UR was synthesized from 1,3,5-triazine-2,4,6-triamine by employing hexamethylene diisocyanate as a counterpart. P-UT exhibited a spherulitic structure with varying sizes, whereas P-UR displayed a fibrillar structure characteristic as that of crystalline hard segments. The P-UT–UR hybrid exhibited a fine nanospherulitic structure with a high order of interconnectivity. Negative surface skewness values of −0.47 and −0.18 were measured (by AFM) for P-UT and P-UT–UR, respectively, which revealed that the surface is not smooth and is covered with features. Due to the increased H-bonding (−N–H···O–H) in P-UT–UR, its transparency decreased. A block copolymer hybrid of urethane–urea was synthesized, which preferred homoatomic H-bonding, whereas random urethane/urea bridges favored hetreoheteroatom H-bonding. A pentafluorophenyl end-functional hybrid (PFI–P-UT–UR) was synthesized, which displayed filaments of ∼2–3 μm length in contrast to the interconnected nanospherulitic structure observed for P-UT–UR. The self-aggregation and end folding led to the formation of a filament structure. By altering the chemical structure slightly, nano-ordered polyurethanes or their hybrids can be achieved.

Rapid Carbon Dioxide Foaming of 3D Printed Thermoplastic Polyurethane Elastomers

Polymeric foam preparation using the carbon dioxide (CO2) foaming technique is fascinating. Until now, the CO2-based foaming process has been carried out for a long saturation time. Once it is possible to produce a polymeric foam in a low saturation time, it can enhance foam production. This study investigates the foaming behavior of 3D printed TPU samples with three different hardness values. The variation of infill density in 3D printed samples provides a macroporous range in the sample and creates a path for the gas molecules to reach the polymer. Such a gas flow path expands the foam processing technique to be carried out at low saturation time and pressure. The foaming process carried out here follows two steps: first, CO2 gas saturation in a high-pressure stainless-steel vessel; second, then hierarchical microporous generation by devising a thermodynamically unstable condition by placing the gas saturated sample in a hot water bath set up. The results showed that the increase in saturation time and pressure increases the expansion behavior of the foam samples, whereas an increase in infill density restricts the foam expansion behavior. The crystalline hard segment (HS) enhances the heterogeneous cell nucleation and reduces the shrinkage of the foam samples. The foam sample with low infill density showed low compression strength. It could be improved by filling the macroporous gap with hydrogel during printing. This hydrogel-packed low infill density foam showed an increased compression strength of 0.8 MPa at 80% strain than the neat foam sample (without hydrogel) 0.12 MPa at 80% strain, confirmed through the cyclic compression test. Hence, this 3D printing integrated subcritical solid-state foaming system offers unparalleled freedom to design and create foam and increase its production. The one-pot preparation of low-density higher compression strength foam using hydrogel makes this technique more feasible for high-end applications.