Properties Of Polymeric Materials Research Articles

Stereolithography-assisted sodium alginate-collagen hydrogel scaffold with molded internal channels

Fabricating internal vascular networks within a hydrogel scaffold is essential for facilitating the supply of nutrients, oxygen, and metabolism exchange required by the encapsulated cells. The challenges in current hydrogel scaffold fabrication involve the difficulty of building adequate internal channels, poor scaffold geometry precision, and low cell viability caused by the fabrication process and polymer material properties. Stereolithography (SLA) stands out as a 3D printing technique distinguished by its superior production efficiency, advanced precision, and remarkable resolution in crafting intricate custom geometries. These attributes establish it as an innovative approach for templates in scaffold fabrication, potentially surpassing the fused deposition modeling (FDM)-based template strategy. Meanwhile, it exerts less shear stress on the cells compared to the direct bioprinting process. This novel strategy enables the fabrication of hydrogel vascular structure within the precision of 500 µm in both channel diameter and wall thickness. In this paper, various sodium alginate and collagen (SA-Col) composite hydrogels with varying collagen concentrations have been investigated to identify the optimal ratio for fabricating hydrogel scaffolds with channels.

Heat partition evaluation during dry drilling of thick CFRP laminates with polycrystalline diamond drills

Since various material properties of carbon fiber-reinforced polymer (CFRP) are temperature dependent, dry drilling of CFRP is a delicate process. Thermal damage can be caused by a rise in temperature during drilling due to a large portion of heat being transferred into the material. Heat partition is used to quantify this, which represents the percentage of total heat being dissipated into the constituent objects during a machining operation. Drill margin and contact conditions at the tool-workpiece interface significantly affect the drilling of CFRP material. Drilling experiments were performed to measure thrust force, torque, and temperatures for five different sets of feed rates and rotational speeds. This study proposes a method for calculating heat partition values during CFRP drilling by developing a finite element-based thermal model. The FE model employs a Gaussian distributed ring-type heat flux that is a function of the equivalent contact length at the interface between the drill and the material surface and the geometry of the workpiece which operates as a moving heat source, emulating the progress of the drill through the CFRP laminate. The tool implements heat fluxes that use characteristic time-point-based step functions to represent the temperature on the drill as it advances through the workpiece during machining. The temperature profiles obtained from the FE analysis and the experiments for the workpiece and tool were subsequently matched iteratively to determine the corresponding heat partition value.

Effects of electron beam and atomic oxygen irradiation on hypervelocity - Impact tested / polyimide coated carbon fiber-reinforced plates

In a low-Earth orbit, space debris orbit at approximately the first cosmic velocity. When space debris strike a spacecraft, ejecta (fragments) from the spacecraft are widely scattered. The reduction in the number of ejecta (fragments caused by impact) must also be considered when selecting spacecraft materials. The authors’ group has previously examined the size of ejecta (fragments) and reduction in the number of ejecta. In general, the mechanical properties of polymer materials and CFRP plates may be damaged by space environments, such as radiation (gamma rays and electron beams (EBs)), atomic oxygen (AO), ultraviolet rays, temperature, and thermal cycling. The authors suggested an anti-AO coating/polyimide CFRP as a material resistant to space environments. The effects of EB and AO irradiation on the fracture behavior and ejecta of anti-AO coating/polyimide CFRP were examined for hypervelocity impacts. The results of static three-point flexural tests were compared with the fracture behavior and ejecta. A two-stage light-gas gun was used for the impact tests. Spherical projectiles formed of aluminum alloy 2017-T4 with a diameter of 1.6 mm were used. Photographs of the ejecta scattered in front of each polyimide CFRP plate were captured from the side using a high-speed video camera. The number and weight of the ejecta on the front side and perforation holes were examined.

Modeling and Experimental Validation of Cell Morphology in Microcellular-Foamed Polycaprolactone.

This study investigates the modeling and experimental validation of cell morphology in microcellular-foamed polycaprolactone (PCL) using supercritical carbon dioxide (scCO2) as the blowing agent. The microcellular foaming process (MCP) was conducted using a solid-state batch foaming process, where PCL was saturated with scCO2 at 6 to 9 MPa and 313 K, followed by depressurization at a rate of -0.3 and -1 MPa/s. This study utilized the Sanchez-Lacombe equation of state and the Peng-Robinson-Stryjek-Vera equation of state to model the solubility and density of the PCL-CO2 mixture. Classical nucleation theory was modified and combined with numerical analysis to predict cell density, incorporating factors such as gas absorption kinetics, the role of scCO2 in promoting nucleation, and the impact of depressurization rate and saturation pressure on cell growth. The validity of the model was confirmed by comparing the theoretical predictions with experimental and reference data, with the cell density determined through field-emission scanning electron microscopy analysis of foamed PCL samples. This study proposes a method for predicting cell density that can be applied to various polymers, with the potential for wide-ranging applications in biomaterials and industrial settings. This research also introduces a Python-based numerical analysis tool that allows for easy calculation of solubility and cell density based on the material properties of polymers and penetrant gases, offering a practical solution for optimizing MCP conditions in different contexts.

Enhanced Antimicrobial Properties of Polymeric Denture Materials Modified with Zein-Coated Inorganic Nanoparticles.

Polymeric denture materials can be susceptible to colonization by oral microorganisms. Zein-coated magnesium oxide nanoparticles (zMgO NPs) demonstrate antimicrobial activity. The aim of this study was to investigate the antimicrobial effect and adherence of different oral microorganisms on hybrid polymeric denture materials incorporated with zMgO NPs. Five types of polymeric denture materials were used. A total of 480 disc-shaped specimens were divided by material type (n=96/grp), then subdivided by zMgO NPs concentration: control with no nanoparticles and other groups with zMgO NPs concentrations of 0.3%, 0.5% and 1% by weight. Characterization of the polymeric denture materials incorporating zMgO NPs was done, and the antimicrobial activity of all groups was tested against four types of microorganisms: 1) Streptococcus mutans, 2) Staphylococcus aureus, 3) Enterococcus faecalis and 4) Candida albicans. The samples underwent an adherence test and an agar diffusion test. Experiments were done in triplicates. The characterization of the hybrid samples revealed variation in the molecular composition, as well as a uniform distribution of the zMgO NPs in the polymeric denture materials. All hybrid polymeric denture materials groups induced a statistically significant antimicrobial activity, while the control groups showed the least antimicrobial activity. The agar diffusion test revealed no release of the zMgO NPs from the hybrid samples, indicating the NPs did not seep out of the matrix. The zMgO NPs were effective in reducing the adherence of the tested microorganisms and enhancing the antimicrobial activity of the polymeric denture materials. This antimicrobial effect with the polymeric dentures could aid in resisting microbial issues such as denture stomatitis.

The performance of waste glass aggregate concrete GFRP-steel double-skin tubular columns under axial compression: Experimental study

In an attempt to alleviate the problem of growing waste glass and fully utilize the excellent material properties of fiber-reinforced polymer (FRP), a novel composite structure, waste glass aggregate concrete glass fiber reinforced polymer (GFRP)-steel double-skin tubular column (WGAC-DSTC), was proposed based on the FRP-concrete-steel double-skin tubular column (DSTC). In the present research, eight WGAC-DSTCs and four waste glass aggregate concrete-filled GFRP tubular columns (WGAC-CFFTs) were investigated to explore their mechanical performance under axial compression. Effects of diverse replacement ratio of waste glass aggregate, GFRP tube thickness, and hollow ratio of column on the mechanical performance of twelve columns were investigated. Meanwhile, this research analyzed and discussed the failure characteristics of columns, load-displacement relationship, ductility coefficient, stiffness coefficient, parameter analysis, ultimate bearing capacity, load-strain relationship and constraint factor. Besides, predicted formulae for estimating the ultimate bearing capacity of WGAC-CFFTs and WGAC-DSTCs were proposed. The research results indicated that (1) Failure mode of the WGAC-DSTCs displayed axial compression failure or shear failure and failure mode of WGAC-CFFTs exhibited mainly axial compression failure; (2) WGAC-DSTCs with 10 % replacement ratio of waste glass aggregate and hollow ratio of 0.4 indicated an increase in the ultimate bearing capacity by 17.24 % and 45.78 %, respectively, as the GFRP tube thickness increased from 1.5 mm to 2 mm and 3 mm. As the column's hollow ratio enhanced from 0.27 to 0.68, the column's ultimate bearing capacity significantly decreased by 7.08 %-60.55 %. The ultimate bearing capacity of WGAC-CFFTs showed a trend of first increasing by 8.33 %-9.41 % but then decreasing by 1.52 % when the replacement ratio of waste glass aggregate rose from 0 % to 30 %; (3) WGAC could replace natural aggregate concrete in traditional DSTC and the bearing capacity could be guaranteed. Besides, it's recommended to utilize 20 % replacement ratio of waste glass aggregate for the WGAC-DSTC whose ultimate bearing capacity enhanced by 15.17 % and possessing optimal mechanical performance; (4) The results calculated utilizing predicted formulae matched well with results of experiment. The application of waste glass aggregate concrete in DSTC can contribute to economic growth and environmental protection and meet the concept of sustainable development.

Method for controlling the polypropylene wettability using surfactants

This paper describes a novel approach to imaging polypropylene PP using digital inkjet printing techniques. The low surface energy of PP, and significant hydrophobic properties prevent it from being used for direct coloration by available methods. A number of surfactants (surfactants) have been proposed as pre-coatings to improve the adhesion between the polymer surface and the ink. Due to the amphiphilicity of surfactants, improved coloration and enhanced color rendering are provided. The polymer/surfactants interactions were evaluated by IR spectroscopy. The amount of surfactants was evaluated using TGA analysis. The effect of modifying agent concentration was evaluated using wetting edge angle measurement. The surface morphology was evaluated using scanning electron microscopy. The test scales were printed and their colorimetric performance was investigated. The study demonstrates the high potential of surfactants for tuning the properties of nonwoven polymeric materials.

DFT Modeling of Coordination Polymerization of Polar Olefin Monomers by Molecular Metal Complexes

Introducing polar functional groups into polyolefin chains through polar olefin monomer coordination (co)polymerization can directly and significantly improve the surface properties of polymer materials and expand their application range. Therefore, the related research has always received considerable attention from both academia and industry. Many experimental studies have been reported in this field, and molecular metal complexes have shown high catalytic activity and selectivity in polar olefin monomer polymerizations. Although considerable DFT calculations have also been conducted for better understanding of the (co)polymerization performance, the factors governing the activity, selectivity, and molecular weight of resulting polymers are still ambiguous. This review mainly focuses on the DFT studies of polar olefin monomer coordination (co)polymerization catalyzed by molecular metal complexes in recent years, discussing the chain initiation and propagation, the origin of polymerization activity and selectivity, and the specific role of additives in the (co)polymerization reactions.

Rapid identification of the coefficient of moisture expansion of polymer materials by the employment of plates with asymmetric concentration fields

The paper pursues the development of a novel methodology for the rapid identification of the diffuso-mechanical properties of polymer materials based on the employment of plates subject to asymmetric moisture concentration fields. The study is carried out on epoxy plate samples equipped with a thin aluminium foil on a surface exposed to the environment to promote asymmetric moisture absorption. The asymmetric moisture fields promote deformations of the plate. Mass gain and plate curvatures are measured as a function of time during conditioning. By using a weakly coupled diffuso-mechanical model: 1D Fick’s diffusion model and 2D plane stress hygroelastic model the diffuso-mechanical properties of the material can be then identified. Due to the chosen size of the experimental samples the present study allows the identification of the coefficient of moisture expansion of the epoxy material. For the material under study, the following values can be identified for saturation mass gain, water diffusivity and coefficient of moisture expansion respectively: 1.67%, 0.025 mm2.h−1, 0.1628.

Molecular Dynamics Simulation of Effect of Carbon Nanotube Diameter on Properties of Crosslinked Epichlorohydrin Rubbers.

Molecular dynamics simulation (MD) technology can be used to simulate and study the physicochemical properties of polymer materials on the basis of material data obtained in traditional experiments. In this study, we use MD to construct models of crosslinked carbon nanotubes/epichlorohydrin rubber composites with different carbon nanotube diameters and study the effect of CNT tube diameter on crosslinked ECO. The results show that with the increase in CNT tube diameter, the contact area between the CNTs and rubber matrix increases, the interaction force is enhanced, the free volume fraction of rubber matrix decreases by 21.36%, the glass transition temperature increases by 6.5%, the mean square displacement decreases, the radius of gyration decreases by 3.18 Å, and the radial distribution function of the C-atom group and the H-atom group in the system gradually decreases. The binding energy between the two is elevated, which in turn verifies the enhancement of the interaction force.

Combining linear and cyclic sulfones as a strategy for elaborating more efficient high-dielectric polymer materials: A second case of dipolar glass copolymers

Motivated by the excellent features exhibited by sulfone functional groups in the development of high-dielectric polymer materials, this work assesses the combination of linear and cyclic sulfone structures through copolymerization to prepare novel polymer materials exhibiting high dielectric constants (ԑr'), low dissipative behavior, and improved thermal properties. Five new polymethacrylate-based copolymers with varying compositions were synthesized through reversible addition-fragmentation chain transfer (RAFT) polymerization. The correct structure and macromolecular nature of the devised materials were confirmed by infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H/13C NMR), and gel permeation chromatography (GPC), while their thermal properties were evaluated using thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). All specimens exhibited adequate thermal properties for most capacitor applications in terms of onset degradation (Ti) and glass transition (Tg) temperatures. All materials degraded well above 250 °C, with increased Ti and Tg values depending on the final composition of the cyclic sulfone monomer in the material. The incorporation of cyclic sulfones not only increased the thermal robustness of the specimens but also raised their Tg values to as high as 189 °C, notably expanding the range of temperatures where these systems can operate without dissipative phenomena. More importantly, broadband dielectric spectroscopy (BDS) revealed that all samples exhibited dielectric properties notably superior to those of conventional polymer materials, with high ԑr' values between 6.0 and 8.9 (at 25 °C and 1 Hz) and low loss factors (Tan(δ) < 0.018). Overall, the present work successfully demonstrates the advantages of including cyclic structures with high dipole moments in polymeric backbones, offering a new strategy to enhance the thermal and dielectric properties of high-dielectric polymer materials.

Structural, optical, and morphological properties of PVC-BaTiO3 nanocomposite films

This work aims to fabricate barium titanate (BaTiO3) nanoparticles and study the effect of adding different contents of BaTiO3 nanoparticles on the structural, optical, and electrical properties of PVC polymer matrices. The PVC/BaTiO3 nanocomposite films were characterized by X-ray diffraction, FT-IR spectroscopy, and SEM. In addition, dielectric properties were studied within the frequency range of 0.1 KHz–6 MHZ. The XRD analysis reveals an amorphous nature of pure PVC with two characteristic peaks at 2θ = 17.09° and 2θ = 23.25°, and it reveals that BaTiO3 has sharp and narrow peaks. In PVC/BaTiO3 nanocomposite films, all XRD peaks of BaTiO3 appeared in all the samples with an increase in the average particle size from ∼46 nm to 55 nm. There is no shift of IR position in PVC bands, but the decreased intensity of some bands suggests complexation between PVC and BaTiO3. The UV–visible absorption spectrum of pure PVC has a band at λ = 278 nm. This band was shifted to 252 nm after adding BaTiO3 content. UV–visible transmission spectra demonstrate a decrease in the transmittance as an increase of BaTiO3 content from 89.23 % for pure PVC to 5.23 % for 0.1 wt% of BaTiO3. The values of the optical bandgap decrease with increasing BaTiO3 contents due to defect formation in PVC matrices. The optical parameters of the prepared nanocomposite films were also enhanced. The AC conductivity shows an increase with both frequency and BaTiO3 concentration, leading to enhanced movement of charge carriers and relaxation of interface polarization.

Constructing a temperature transferable coarse-grained model of cis-1,4-polyisoprene with the structural and thermodynamic consistency aided by machine learning

Polyisoprene (PI) is a widely used polymer and constructing a systematic coarse-grained (CG) PI model with the structural and thermodynamic consistency with the underlying atomic model over a wide range of thermodynamic conditions is very important for the predictive capability of CG model on overall properties of PI polymer materials and the establishment of their structure-property relationship. However, as the number of tunable CG potential parameters and target properties grows, traditional parameter tuning methods become impractical. In this work, we present a novel approach for determining the optimal CGPI non-bonded potential parameters by employing Particle Swarm Optimization as the calibrator with machine learning-based models trained using molecular dynamics data. The resulting CG model is further augmented with temperature factors through a multistate parameterization approach. This enhancement ensures the model's temperature transferability of structure and thermodynamics in a wide temperature of 150K∼750K.

Synergistic effects of cellulose nanocrystal on the mechanical and shape memory properties of TPU composites

Cellulose nanocrystal is a nanomaterial that has a large specific surface area, high surface energy, and high strength. As well, it is biocompatible, environmentally friendly, nontoxic, and can be extracted from biomass resources. Because of these features, cellulose nanocrystals can be used to improve the mechanical properties of polymer matrices with a shape memory effect and as a shape memory switch. In this study, a polytrimethylene ether glycol-based thermoplastic polyurethane (TPU)/cellulose nanocrystal (CNC) composite was prepared via an in-situ polymerization process to create a self-healing polymer matrix. Also, the effect of CNC doses in low concentrations (≤2 wt%) on the different properties of the resulting bio-nanocomposite was investigated. The results showed that the introduction of CNCs affects the hydrogen bonding within the polymer matrix and provides better thermal stability in the high temperature range than pure TPU. Furthermore, the samples with 0 wt%, 0.75 wt%, 1 wt%, and 2 wt% of CNC exhibited an increasing trend in tensile strength with values of 11.71 MPa, 18.95 MPa, 17.88 MPa, and 26.18 MPa, respectively, which indicates a remarkable improvement in mechanical strength. The shape memory behavior was also notably prominent in this polymer composite, where the composite containing 2 wt% of CNC showed the fastest recovery time (240 s) at 75 °C with the highest shape retention. Moreover, their flow behavior and deformation capacity were examined through rheology tests. Besides, docking simulations were conducted in silico to assess the interaction of the TPU/CNC composite with the DNA gyrase enzyme. The interaction between CNC/TPU composite and DNA gyrase was meticulously analyzed across 10 distinct conformations, yielding docking scores ranging from −6.5 Kcal/mol to −5.3 Kcal/mol. Overall, the physico-mechanical properties of the TPU/CNC composites were substantially enhanced with the incorporation of nanofillers.

Combining Injection Molding and 3D Printing for Tailoring Polymer Material Properties

Combining Injection Molding and 3D Printing for Tailoring Polymer Material Properties

Machine learning prediction of the mechanical properties of injection-molded polypropylene through X-ray diffraction analysis

ABSTRACT Predicting the mechanical properties of polymer materials using machine learning is essential for the design of next-generation of polymers. However, the strong relationship between the higher-order structure of polymers and their mechanical properties hinders the mechanical property predictions based on their primary structures. To incorporate information on higher-order structures into the prediction model, X-ray diffraction (XRD) can be used. This study proposes a strategy to generate appropriate descriptors from the XRD analysis of the injection-molded polypropylene samples, which were prepared under almost the same injection molding conditions. To this end, first, Bayesian spectral deconvolution is used to automatically create high-dimensional descriptors. Second, informative descriptors are selected to achieve highly accurate predictions by implementing the black-box optimization method using Ising machine. This approach was applied to custom-built polymer datasets containing data on homo- polypropylene and derived composite polymers with the addition of elastomers. Results show that reasonable accuracy of predictions for seven mechanical properties can be achieved using only XRD.

Regulation of Dihedral Angle on Molecular Engineering for Enhancing Triboelectric Performance

AbstractThe performance of triboelectric polymers relies on their molecular structure. Therefore, investigating how to construct high‐performance molecular structures of triboelectric polymers becomes imperative, yet the relationship between microscopic structural parameters and triboelectric performance remains unclear. In this study, the relationship is studied between dihedral angles of adjacent conjugated planes and triboelectric performance. Various polyimide monomers are synthesized to manipulate the conjugated dihedral angles within the molecular chains. Introducing larger dihedral angles in polyimides (PIs) reduces the conjugation between molecular chains, suppressing the formation of charge transfer complexes (CTCs), and widening the energy gap between molecular orbitals. With the increase in dihedral angles, the output performance improved by 100%. The surface charge density of 335 µC·m−2 is achieved through the synergistic effect of the high charge retention capability of the PI film and the high triboelectric properties of the corona‐polarized fluorinated ethylene propylene (FEP). A large dihedral angle can form numerous deep traps and effectively prevent charge escaping while ensuring stable output. This study provides a feasible strategy for investigating the construction of high triboelectric performance molecular structures, enriching the understanding of how molecular structures influence the triboelectric properties of polymer materials and promote high‐performance fluorine‐free and environmentally friendly polymers.

Modeling and solution of eigenvalue problems of laminated cylindrical shells consisting of nanocomposite plies in thermal environments

This work is dedicated to the modeling and solution of eigenvalue problems within shear deformation theory (SDT) of laminated cylindrical shells containing nanocomposite plies subjected to axial compressive load in thermal environments. In this study, the shear deformation theory for homogeneous laminated shells is extended to laminated shells consisting of functionally graded (FG) nanocomposite layers. The nanocomposite plies of laminated cylindrical shells (LCSs) are arranged in a piecewise FG distribution along the thickness direction. Temperature-dependent material properties of FG-nanocomposite plies are estimated through a micromechanical model, and CNT efficiency parameters are calibrated based on polymer material properties obtained from molecular dynamics simulations. After mathematical modeling, second-order time-dependent and fourth-order coordinate-dependent partial differential equations are derived within SDT, and a closed-form solution for the dimensionless frequency parameter and critical axial load is obtained for first time. After the accuracy of the applied methodology is confirmed by numerical comparisons, the unique influences of ply models, the number and sequence of plies and the temperature on the critical axial load and vibration frequency parameter within SDT and Kirchhoff–Love theory (KLT) are presented with numerical examples.

Obtaining unsaturated polyester resins using products of recycled polyethylene terephthalate solvolysis

A technique for obtaining an unsaturated polyester resin based on recycled polyethylene terephthalate has been developed. The process of curing an unsaturated polyester resin under the action of styrene, a peroxide compound (Butanox 50M) and an accelerator (cobalt ortoate) has been studied. The physical and mechanical properties of polymeric materials based on the developed resin have been studied, it was found that their strength depends on the mass fraction of recycled polyethylene terephthalate in the oligoether polyol used in the synthesis.

Graphene nanoribbon hydrogel scaffold for highly conductive and robust polyimide nanocomposite

Although highly loaded graphitic nanocarbon materials effectively enhance the electrical, mechanical, and thermal properties of polymeric materials, their practical implementation has been hindered by severe aggregation issues. Here, we propose a method to achieve homogeneous nanocarbon-polyimide (PI) composites by integrating graphene oxide nanoribbons (GONRs) with polyamic acid ammonium (PAA) salt, a precursor of PI. Self-assembled scaffold structure of GONRs hydrogel enables the uniform integration and immobilization of PAA within the GONR scaffold, mitigating aggregation concerns. The resulting GONR/PAA hydrogel, formed through physical interactions, can be coated onto substrates via a shear stress-induced bar coating method due to its viscoelastic rheological properties. Subsequent heat treatment at 400 °C triggers the imidization reaction of PAA and the reduction of GONR, facilitating the formation of uniformly integrated GNR/PI nanocomposite coatings. Under optimized conditions, incorporating a high-loading GONR content in PAA (95 wt% of GONR and 5 wt% of PAA) yielded GNR/PI composites with excellent mechanical properties, exhibiting a hardness of 0.75 GPa and an elastic modulus of 8.3 GPa. Additionally, this GNR/PI composite displayed a good electrical conductivity of 3890 S/m, attributed to the electrical pathways formed by GNRs within the PI matrix.