Macromolecular Materials and Engineering最新文献

This study focuses on characterizing the crystallization kinetics of a PLA 4032D filament, specifically investigating the impact of the extrusion process and different thermal protocols. A principal finding reveals that the PLA filament exhibits a significantly faster crystallization rate compared to the original pellets. This acceleration is attributed to the thermomechanical stresses and potential partial degradation that the polymer experiences during filament extrusion. Two distinct calorimetric protocols, “melt” (erasing prior history) and “solid” (preserving nucleation seeds), were employed. The “solid” protocol demonstrated notably faster kinetics, approximately half the time of the “melt” protocol, underscoring the crucial role of pre-existing nuclei—a condition relevant to the short residence time in Fused Filament Fabrication (FFF) liquefiers. The research also confirmed the phase transition between α′ and α crystalline forms in PLA 4032D, which is highly dependent on crystallization temperature. A kinetic model was successfully developed to accurately predict the evolution of crystallinity for both phases, effective for crystallization from the melt and in the presence of nuclei. These results are crucial for optimizing PLA filament production and controlling the final properties of 3D-printed parts, contributing to a deeper understanding of PLA behavior under processing conditions and improving FFF efficiency.

Until now, most results on processing high molecular weight polyethylene (HMWPE) in laser sintering (PBF-LB/P) have been achieved using industrial machines with a CO₂ laser. The use of diode laser sintering machines could make new materials more accessible to a wider audience. In this study, the role of carbon black (CB) concentration and processing strategy in HMWPE processing using diode laser PBF-LB/P machines is investigated. This work reveals that the carbon black concentration strongly influences processing, as it affects both absorption and specific heat capacity. Changes of specific heat capacity impact thermal balance during processing. Due to its narrow sintering window, HMWPE exhibits a high tendency for curling, which can be mitigated by reducing the scanning area and layer thickness. A suitable CB concentration ranges from 0.25 to 0.5 wt.%. In general, mechanical properties improve with volume energy density. This effect is caused by a more pronounced particle coalescence and interlayer bonding. However, the absorption properties of carbon black have a stronger impact on the mechanical properties than the energy input for the tested parameters. Mechanical tests on fabricated tensile bars reveal brittle fracture, which results from the high melt viscosity of HMWPE and the resulting delayed coalescence of particles.

Cross-linked gel polymer electrolytes for lithium-ion batteries were prepared using a unique photocrosslinking technology. Hydroxyethyl cellulose was dissolved in N-vinylpyrrolidone and combined with polyethylene glycol diacrylate, trimethylolpropane triacrylate, and pentaerythritol tetrakis(3-mercaptopropionate), then subjected to UV irradiation to form a semi-interpenetrating network. This cross-linked structure enhanced stability and compatibility with liquid electrolytes and significantly improved ionic conductivity (2.14 × 10⁻³ S cm⁻¹) compared to hydroxyethyl cellulose-based GPEs. The hydrophilic hydroxyethyl cellulose blend and flexible pentaerythritol tetrakis(3-mercaptopropionate) contributed to improved mechanical and thermal stability, increased liquid retention, and reduced electrolyte leakage. The GHPT-3 electrolyte exhibited electrochemical stability up to 4.5 V and delivered excellent cycling performance in a lithium metal cell with a LiFePO₄ cathode, providing a high reversible capacity of 155.8 mAh g⁻¹ at 0.1 C with near-perfect coulombic efficiency. Remarkably, it retained 90.3% of its initial discharge capacity after 100 cycles. GHPT-3 effectively suppressed lithium dendrite formation for over 1000 h, outperforming a commercial liquid electrolyte, which failed within 895 h. These advancements highlighted GHPT-3's potential as a safer, high-performance electrolyte for lithium-ion batteries.

Microneedles offer a minimally invasive alternative to hypodermic needles for drug delivery and point-of-care diagnostics. Previous studies on microneedle insertion force often used human skin with constant mechanical properties. However, this study, for the first time, investigates the combined effect of human age (29–68 years) and other variables such as insertion velocity (3 and 4.5 m/s), material (poly(glycolic acid) (PGA), Vectra MT-1300, and Zeonor 1060R) and geometry (cone-shaped and tapered cone-shaped) on insertion force using finite element analysis (FEA). The results show that insertion force increases significantly with age due to higher stratum corneum (SC) stiffness and failure criteria. For example, for a PGA cone-shaped microneedle at 4.5 m/s, the insertion force is 111.56%, 64.09%, 36.46%, and 10.52% higher for individuals aged 68, 53, 41, and 33 years, respectively, compared to 29 years. Microneedle material also significantly affects insertion force, with stiffer materials requiring less force to penetrate the SC. Cone-shaped microneedles exhibit lower insertion forces than tapered cone-shaped designs due to their smaller tip angle. Increasing insertion velocity substantially reduces the insertion force, with higher velocity having a more evident effect than changes in microneedle geometry. Finally, stress distribution within the microneedle and skin deformation are evaluated.

Designing conductive nanocomposites by localizing/trapping a conductive nanofiller at the polymer/polymer interface is quite challenging and considered very dynamic. In this work, the interface developed in poly(ethylene furanoate)/polyethylene (PEF/PE) blends is studied and evaluated for strategic localization of graphene at the interface. The trapping of graphene at the interface was confirmed by extraction of individual components as well as a sharp increase in the electrical conductivity of the PEF/PE/graphene nanocomposites. The sequence of mixing PEF, PE, and graphene showed significant effects on graphene's localization. The inclusion of graphene reduced the characteristic domain size by inducing compatibility in PEF/PE. The PEF/PE interface acts as an energy well that does not allow diffusion of graphene nanosheets into or away from the interface by annealing at high temperatures. Furthermore, adding a compatibilizer affected conductivity negatively, attributed to the altered morphology in blends. The PEF/PE/graphene nanocomposites achieved a low percolation threshold of 0.97 vol%, whereas electrical percolation in PEF/GNP and PE/GNP nanocomposites was observed at 6–7 vol%. A 3D graphene network was confirmed in PEF/PE/GNP nanocomposites via power-law conductivity model. This is the first report on electrically conductive PEF-blends highlighting the potential of interfacially-localized graphene in optimizing the multifunctional properties of bio-based PEF.

The cooperative gelation of sPS with the short PEGDME molecules (molecular weight M_W = 1.5 kg mol⁻¹) from a common THF solution is driven by the gelation tendency of sPS at a temperature around 40°C. The crystalline junctions in the wet gel are fibrillar morphologies, which are typically composed of sPS and PEG molecules, as shown by contrast variation SANS, and consist of sPS, which co-crystallizes in d-form with the solvent molecules, and to a certain extent with PEGDME molecules, as demonstrated by the conformational change of both polymer types from an amorphous to a helical form when the gelation temperature is exceeded, which was observed by in situ FTIR. XRD and SEM on drying gels have shown that the large-scale morphology of dry gels, when the polymer strands collapse and crystalline polymer strands are formed, is determined by the presence and length of the PEGDME molecules. While the sPS dry gel exhibits a more homogeneous distribution of polymer strands and well-defined pores, the polymer strands of the gel with short PEGDME connect at one end to form “tufted” macroassemblies, which, due to the additional co-crystallization of PEGDME with sPS, leads to very large pores and voids.

The demand for corneal tissue replacements increases due to corneal diseases, prompting the exploration of tissue engineering (TE) solutions using biopolymers. Poly (glycerol sebacate) (PGS) is one of the promising biomaterials to be explored in the ocular TE, not only because of its biocompatibility, biodegradability, and elasticity, but also its transparency. However, its low molecular weight and low glass transition temperature (Tg) make PGS scaffold fabrication via electrospinning challenging. Here, we fabricated fibrous membranes by electrospinning of PGS and poly (vinyl alcohol) (PVA) blend and obtained a membrane composed of homogenous fibers with a diameter of 4 µm and a porosity of 28%. In addition, the membrane exhibited a stiffness of 12 MPa and strain of 20%. The permeability of the membrane closely resembled that of the natural cornea with 9.8E-07 cm²/s. Most of the PVA was successfully washed off, resulting in biocompatible scaffold that was able to support the proliferation of human corneal epithelial cells (HCEC) and human corneal endothelial cells (HCEndC) for a week. According to the in vitro biocompatibility assay, HCEC has demonstrated an 88% and HCEndC a 96% viability on electrospun PGS membranes. These results demonstrate the suitability of electrospun PGS membrane for cornea tissue engineering.

Anion exchange membranes (AEMs), which serve as one of the key components in fuel cells, fulfill dual functions: conducting hydroxide ions and blocking the anode and cathode. To balance the relationship between ionic conductivity, mechanical properties, and dimensional stability, quaternized polydopamine (QPDA) nanoparticles were synthesized via a three-step process, including dopamine self-polymerization, grafting with branched polyethylenimine, and quaternization. These QPDA nanoparticles were subsequently used as a novel nanofiller to modify a blend quaternized chitosan (QCS) and polyvinyl alcohol (PVA) polymer, resulting in the QPDA/QCS-PVA composite membranes. The composite samples exhibited improved water uptake, dimensional stability, and ionic conductivity. With the optimal QPDA loading of 6%, the composite membrane achieved a conductivity of 48.4 mS cm⁻¹ at 80°C, which was 2.27 times that of the pure membrane (21.3 mS cm⁻¹). The membranes also demonstrated enhanced mechanical properties and alkaline stability, benefiting from the uniform dispersion of QPDA nanoparticles and chemical cross-linking within the composite system. These QPDA/QCS-PVA composite membranes with an optimal balance between performance and stability can be expected to be novel biomass-based AEMs.

The integration of advanced materials with new fabrication techniques is crucial for advancing bioelectronics. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is a widely used conductive polymer, but its printability remains challenging due to low viscosity in aqueous solutions. Here, we present 3D freeze-printing to fabricate binder-free, high-conductivity PEDOT:PSS structures. Utilizing a temperature-controlled plate, 3D structures can be formed by direct extrusion printing of dimethyl sulfoxide (DMSO)-doped PEDOT:PSS solutions that are typically unprintable using conventional methods due to spreading and poor shape retention. Freeze-printing at temperatures just below 0 °C increases PEDOT:PSS conductivity by more than 350% compared to room temperature printing. Characterizations using Raman spectroscopy, XRD, and XPS indicate the presence of freezing-induced phase separation and polymer chain alignment, contributing to enhanced conductivity. Critically, our mild fabrication approach enables direct printing onto thermally sensitive materials, such as alginate hydrogels, achieving ∼50% reduction in interfacial impedance at 1 kHz. Unlike other methods requiring multi-day pre- or post-processing under harsh conditions, our approach enables rapid fabrication within a few hours, without the use of harsh chemicals. This work introduces a broadly applicable strategy for patterning conducting polymers with mixed conductivities on soft substrates, suitable for applications in bioelectronics, soft robotics, and wearable sensing devices.