Crystal Polymer Research Articles

β-Phase Crystallinity, Printability, and Piezoelectric Characteristics of Polyvinylidene Fluoride (PVDF)/Poly(methyl methacrylate) (PMMA)/Cyclopentyl-Polyhedral Oligomeric Silsesquioxane (Cp-POSS) Melt-Compounded Blends.

Poly(vinylidene fluoride) (PVDF) is a semicrystalline polymer that exhibits unique piezoelectric characteristics along with good chemical resistance and high thermal stability. Layer-based material extrusion (MEX) 3D printing of PVDF is desired to create complex structures with piezoelectric properties; however, the melt processing of PVDF typically directs the formation of the α crystalline allomorph, which does not contribute to the piezoelectric response. In this work, PVDF was compounded with poly(methyl methacrylate) (PMMA) and cyclopentyl-polyhedral oligomeric silsesquioxane (Cp-POSS) nanostructured additives in binary and ternary blends to improve MEX printability while maintaining piezoelectric performance. Overall crystallinity and β phase content were evaluated and quantified using a combination of attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and differential scanning calorimetry (DSC). Enhancement of MEX printability was measured by quantifying the interlayer adhesion and warpage of printed parts. All blends studied contained a significant percentage of β allomorph, but it could be detected by ATR-FTIR only after the removal of a thin surface layer. Inclusion of 1% Cp-POSS and up to 10% PMMA in blends with PVDF improved interlayer adhesion (2.3-3.6x) and lowered warpage of MEX printed parts compared to neat PVDF. The blend of 1% Cp-POSS/1% PMMA/PVDF was demonstrated to significantly improve the quality of MEX printed parts while showing similar piezoelectric performance to that of neat PVDF (average piezoelectric coefficient 24 pC/N). MEX printing of PVDF blends directly into usable parts with significant piezoelectric performance while reducing the challenges of printing the semicrystalline polymer opens the potential for application in a number of high value sectors.

Anisotropic Semicrystalline Homopolymer Dielectrics for High‐Temperature Capacitive Energy Storage

AbstractHigh‐temperature dielectric polymers are in high demand for powering applications in extreme environments. Here, we have developed high‐temperature homopolymer dielectrics with anisotropy by leveraging the hierarchical structure in semicrystalline polymers. The lamellae have been aligned parallel to the surface in the dielectric films. This structural arrangement resembles the horizontal alignment of nanosheet fillers in polymer nanocomposites and nanosheet‐like lamellae in block copolymers, which has been proven to provide the optimal topological structure for electrical energy storage. The unique ordering of lamellae in our dielectric films endue a significantly increased breakdown strength and a reduced leakage current compared to amorphous films. This novel approach of enhancing the capacitive energy storage properties by controlled orientation of lamellae in homopolymer offers a new perspective for the design of high‐temperature polymer dielectrics.

Anisotropic Semicrystalline Homopolymer Dielectrics for High-Temperature Capacitive Energy Storage.

High-temperature dielectric polymers are in high demand for powering applications in extreme environments. Here, we have developed high-temperature homopolymer dielectrics with anisotropy by leveraging the hierarchical structure in semicrystalline polymers. The lamellae have been aligned parallel to the surface in the dielectric films. This structural arrangement resembles the horizontal alignment of nanosheet fillers in polymer nanocomposites and nanosheet-like lamellae in block copolymers, which has been proven to provide the optimal topological structure for electrical energy storage. The unique ordering of lamellae in our dielectric films endue a significantly increased breakdown strength and a reduced leakage current compared to amorphous films. This novel approach of enhancing the capacitive energy storage properties by controlled orientation of lamellae in homopolymer offers a new perspective for the design of high-temperature polymer dielectrics.

Physical-Entanglements-Supported Polymeric Form Stable Phase Change Materials with Ultrahigh Melting Enthalpy.

With the rapid development of new energy and the upgrading of electronic devices, structurally stable phase change materials (PCMs) have attracted widespread attentions from both academia and industries. Traditional cross-linking, composites, or microencapsulation methods for preparation of form stable PCMs usually sacrifice part of the phase change enthalpy and recyclability. Based on the basic polymer viscoelasticity and crystallization theories, here, a kind of novel recyclable polymeric PCM is developed by simple solution mixing ultrahigh molecular weight of polyethylene oxide (UHMWPEO) with its chemical identical oligomer polyethylene glycol (PEG). Rheological and leakage-proof experiments confirm that, even containing 90% of phase change fraction PEG oligomers, long-term of structure stability of PCMs can be achieved when the molecular weight of UHMWPEO is higher than 7000kg mol-1 due to their ultralong terminal relaxation time and large number of entanglements per chain. Furthermore, because of the reduced overall entanglement concentration, phase change enthalpy of PCMs can be greatly promoted, even reaching to ≈185 J g-1, which is larger than any PEG-based form stable PCMs in literatures. This work provides a new strategy and mechanism for designing physical-entanglements-supported form stable PCMs with ultrahigh phase change enthalpies.

Understanding the Impact of Chain Mobility on Conformational Evolution and Kinetics of Mesophase Formation in Poly(ʟ-lactide) under Low-Pressure CO2.

Although the mesomorphic phase as an intermediate state has been introduced to understand polymer crystallization, the understanding of the mesomorphic phase is far from complete. Here, the effect of chain mobility on the mesophase structuring in melt-quenched poly(ʟ-lactide) (PLLA) treated in low-pressure CO2 at 1.6-2.0 MPa and 0 °C was investigated using infrared (IR) spectroscopy, differential scanning calorimetry (DSC), and atomic force microscopy (AFM). The IR and AFM results demonstrated that the final degree of order and the kinetics of structural evolution during the CO2-induced mesophase formation were critically dependent on the CO2 pressure. This was attributed to the distinct dynamics of conformational evolution (gg to gt conformer transition) due to the different CO2 pressures. The thermal behavior from the DSC results showed that CO2 pressure dominated both the scale and dynamics of the chain motion of PLLA. At a lower CO2 pressure of 1.6 MPa, smaller-scale segmental motion was not replaced by the larger-scale cooperative motion that occurred at a relatively higher CO2 pressure of 2 MPa, which was favorable for faster mesophase formation. Consequently, by inhibiting direct crystallization under limited mobility conditions, it was demonstrated that different chain mobility controlled by CO2 pressure and thus CO2 solubility impacted the dynamics of the mesophase formation of PLLA. The present results have implications for understanding the role of chain mobility in determining the intermediate structural phases in semicrystalline polymers.

Exploiting flow manipulation to engineer the electroactive phase for improved piezo response in size tunable PVDF microspheres via microfluidic technology

Polyvinylidene fluoride (PVDF), a semi-crystalline polymer with remarkable piezo-, ferro-, and pyroelectric properties in its electroactive phase (EA), holds significant potential. Microfluidic-based techniques, particularly droplet-microfluidics, have become a preferred method for producing PVDF microspheres, offering advantages like size and shape adjustability, simplicity, efficiency, and effective heat dissipation. This article focuses on employing a microfluidic flow focussing device (MFFD) with thermal initiated off-chip polymerization to process PVDF microspheres. The MFFD disperses uniform droplets into an oil bath, initiating polymerization and yielding microspheres ranging from 126 to 754 µm. Fine-tuning flow rates achieves precise control over microparticle uniformity, monodispersity, size, and spherical shape. Optimization of reaction temperature (Toil) significantly enhances the EA phase, reaching 82.05 % at Toil = 60 °C. The resulting microspheres are comprehensively characterized for structure, morphology, composition, phase, hydrophobicity, biocompatibility, thermal, and piezoelectric properties. Additionally, machine learning analysis is employed to predict the mean diameter as well as the EA and β-phase of PVDF microspheres. A flexible piezoelectric device made from PVDF microspheres, demonstrating an open circuit voltage of ∼23.5 V in response to finger and foot tapping movements, showcases potential for self-powered wearable sensors and devices. This study underscores the synergy of microfluidics, polymer science, and artificial intelligence in advancing smart materials.

Photopolymerizable semi-crystalline polymers for thermally reversible, 3D printable cast molds

ObjectivesThis study demonstrates the use of photopolymerization to create semi-crystalline linear polymers suitable for thermally reversible materials in dental cast moldings produced from 3D printing. MethodsAn aromatic diallyl, aliphatic dithiol chain extender, and monofunctional thiol were used in a photoinitiated system. The photopolymerization and crystallization kinetics as a function of chemistry and temperature were investigated using spectroscopy and calorimetry. These insights were used to realize vat photopolymerization-based 3D printing of functional objects that could be remotely melted and thereby removed using induction heating. ResultsThe addition of monothiol was shown to decrease the polymer molecular weight which correspondingly increased the crystallization rate. Photopolymerization kinetics are independent of temperature while crystallization was slowed as the temperature approaches the melting point of the materials. Through inclusion of chromium oxide, semicrystalline materials could be melted through induction heating. These materials were implemented in vat photopolymerization 3D printing to realize high-resolution objects that could be used as releasable dental molds following printing and induction heating. SignificanceThis work demonstrates a proof-of-concept methodology to realize directly printable, thermally reversible semicrystalline materials for potential use as dental molding materials.

Flexible and rigid block copolymers from recyclable polyesters

The paper addresses a study on the thermoplastic elastomers (TPE) that can be synthesized using monomers retrieved from the chemically recycled semi-aromatic polyesters, such as terephthalic acid from low value stream recyclable polyethylene terephthalate (rPET). In contrast to PET, because of their physical and mechanical properties, TPEs are often used as an engineering polymer in automotive and consumer goods. The understanding of the crystallization and phase behavior of these materials is crucial to fine-tune the molecular structure and properties. We explore the interplay between the crystallization and phase separation in these materials by performing experiments on model thermoplastic elastomers consisting of polybutylene terephthalate (PBT) and polytetrahydrofuran (PTHF). A common denominator in the synthesis of PBT is terephthalic acid that can be obtained from Dimethyl Terephthalate (DMT) or recycling used PET. We show that by varying the compositions and block length of different blocks, in PBT-PTHF block copolymers, morphological variations from spherulites to dendrites can be induced, which could be captured using optical microscopy. By performing rheological and small angle X-ray scattering studies, we correlate these morphological variations at microscopic length scales, to the chain architecture at nanometer length scales. Our observations reveal that at the higher rigid PBT content, the process of phase separation strongly influences the crystallization kinetics that promotes the lamellar structure of the semi-crystalline polymer, observed at room temperature. On the other hand, in the presence of higher soft block content, the crystal growth occurs with minimal influence of the microphase separation. In broader generality, no morphological differences in the TPEs synthesized using the terephthalic acid from rPET are found. However, when the monomer from rPET is used, enhancement in crystallization rate occurs in the TPEs having similar molar mass and molecular configuration. We attribute the enhanced crystallization rate to the catalyst residues present in the terephthalic acid obtained fom rPET.

Polymer Crystallization Kinetics and Thermodynamics of Some Industrial Polyamides

A comprehensive non-isothermal kinetics study on polymer crystallization processes taking place in a set of industrial polyamides comprising nylon 6, nylon 6,6, nylon 11 and nylon 12, individually, is reported. The kinetics studies elucidated that the phenomena of nucleation/diffusion underlying the nylons crystallization go to completion in a single-step. Notwithstanding, the nylons diffusion activation energies do not correspond to the universal value of segmental jump activation energy signifying polymer chains diffusion processes. The polymer chain transport phenomenon was probably the slowest one in the case of nylon 6 and nylon 6,6, and the fastest in the case of nylon 12, while intermediate for nylon 11. Furthermore, the nucleation barrier during the course of polymer crystallization was the highest for nylon 6,6, followed by nylon 6, nylon 11 and nylon 12. Our kinetics studies further predict that the crystallization of nylon 12 and nylon 11 follows, respectively, diffusion-controlled 2D growth of spherulites and a somewhat complicated nucleation/growth phenomenon. The thermodynamics of the nylons crystallization suggests that the highest structural orientation of the activated complex was attained in the case of the nylon 12 crystallization process. Interestingly, while the thermodynamics and majority of the kinetic parameters of nylon 6 and nylon 6,6 were similar/comparable, the two follow widely differing crystallization mechanisms. The most probable physical meanings of the obtained kinetics and thermodynamics parameters and their practical significance are given and discussed.

Strength and toughness of semicrystalline polymer fibers: Influence of molecular chain entanglement

The mechanical properties of oriented semicrystalline polymers fibers are mainly determined by the semicrystalline morphology in which lamellar crystals and disordered amorphous layers are in staggered arrangement. As a stress transmission channel, amorphous entanglement network can affect the strength and toughness of fiber together with crystalline phase. In this study, the relationship between mechanical properties and amorphous entanglement of oriented poly (l-lactic acid) fibers was clarified by studying the cyclic loading characteristics. Based on the Haward-Thakray model of semi-crystalline polymers, the energy contributions of the crystalline phase and the amorphous phase are separated. During the deformation of oriented fiber, the crystal will be broken under the action of tight entanglement network, and the entanglement network can transfer stress well without failure under the action of straight chain. Therefore, although the crystalline phase and the amorphous phase jointly bear the strength, the toughness and fracture behavior mainly affected by the entangled network of the amorphous phase.

Advancing spin-coating technique for semi-crystalline low-density polyethylene thin films

Polymeric thin films are widely used for coating substrates or as freestanding materials. They are prepared using physical/chemical vapor deposition, dip coating, solution casting, or spin coating. Among these, spin-coated films offer uniform thickness and reproducible results. These films are typically made from amorphous polymers, which are soluble in solvents at ambient temperature, making it easier to coat the polymer solution on the substrate. Despite the advantages of this technique, it has hardly been used for semi-crystalline polymers. In this work, we report the synthesis of freestanding porous thin films using semi-crystalline polymers, specifically low-density polyethylene (LDPE), through the utilization of spin coating. The effect of polymer concentration and porosity on thickness and strength was investigated. The as-prepared thin film was characterized by XRD, XPS, FTIR, and SEM techniques. The increase in crystallinity (14 % change) of the thin film was attributed to the rearrangement and uniform alignment of the polymer chains, which further resulted in relatively higher tensile strength.

Morphological structure and mechanical properties of a nucleated Polyoxymethylene (POM) homopolymer resin processed under conventional injection molding conditions

When injection molding semi-crystalline polymers, it is known that the resulting morphological and mechanical properties are strongly dependent on the processing conditions. Selectively influencing the performance of the final part as early as during processing is of great interest for industrial applications. To investigate the processing-structure-property correlation for a POM hompolymer resin, tensile specimens were manufactured under conventional injection molding conditions following a Design of Experimets (DoE). Morphological characterization was carried out by microscopy and X-ray measurements. Crystallinity was also measured by differential scanning calorimetry (DSC). Additionally, the (fracture) mechanical behaviour of the samples was assessed. Influences of the processing parameters on the crystalline structure and orientations within the material were identified. Furthermore, tensile tests were found to be sensitive to changes in morphology and processing, whereas the fracture behaviour did not change significantly despite the structural changes within the samples.

Influence of Polymer Surface Roughness on the Fractions of Transmitted, Reflected and Absorbed Energy in Operation of Laser Transmission Welding

The study of energy fractions plays a fundamental role in laser joining operations: from their knowledge, it is possible to calculate the amount of laser beam energy that is effectively available during the formation of chemical and physical bonds, and how much energy is dissipated. This study examines semi-crystalline polymers of polyamide 6.6 (PA), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), and polypropylene (PP), semitransparent to light radiation, with the aim of studying the influence of surface roughness on the distribution of energy fractions, and in particular on the reflection portion. For this purpose, polymeric samples with different surface finishing were prepared and characterized by profilometric analysis. Subsequently, an experimental setup was implemented to directly measure the transmitted ratio, obtaining the reflected energy fraction from the Beer-Lambert law, and the absorbed ratio by energy balance. The results showed a decrease in the power transmitted by polymers subjected to surface treatment, due to an increase in the reflection fraction, a phenomenon particularly evident for PET, for which the reflection share increased from ~ 0.5% to ~ 15.3%, following P240 treatment. A lower influence was verified for PA and especially PTFE, due to a lower influence of the treatment on surface morphology. On the basis of the experimental results, it is hypothesised that roughening the lower section of the irradiated polymer could allow an increase in the total internal reflection fraction, favouring the joint at the interface point.Graphical

Comparison of Three Grafting Options for Anterior Cervical Corpectomy and Fusion: A Retrospective 3-Arms Case Control Study

Anterior cervical corpectomy and fusion achieves foraminal radicular and central medullary decompression and spinal stabilization in staged lesions. Many bone graft materials have been developed for the reconstruction of cervical lordosis and the restoration of intervertebral height after corpectomy. The PolyEtherKetoneEtherKetoneKetone (PEKEKK) is a semicrystalline thermoplastic polymer that can be reinforced with carbon fibers to create long and highly fenestrated rectangular cervical cages for corpectomy. This study aimed to evaluate the radiological outcomes of an innovative PEKEEKK cage compared with others grafting options. Forty-five consecutive patients who underwent surgery with PEKEKK cages between 2017 and 2019 at a spine institution, were matched with 15 patients with a titanium mesh cylindrical cage (TMC) and 15 patients with a tricortical structural iliac bone graft. The restoration of vertebral height and cervical lordosis postoperatively, and subsidence of the construct were evaluated. Complications were reported. The minimal follow-up was 5.1±2years. A better, but nonsignificant, postoperative gain in height was observed for PEKEKK (+8.1 ± 20%) and TMC cages (+8.2 ± 16%) than for iliac crest autograft reconstruction (+2.3 ± 15%, P= 0.119). The mean subsidence at the last follow-up was greater for TMC cages (-10.2 ± 13%), but was not significant, with -6.1 ± 10% for PEKEKK cages and -4.1 ± 7% for iliac crest autografts (P= 0.223). The gain in segmental cervical lordosis was significant (P < 0.001) and remained stable in all the groups. Although an improvement in radiologic anatomical parameters can be achieved with all cage groups, the PEKEKK cage can be considered as a safe alternative for reducing subsidence.

Effects of Trefoil Knots on the Initiation of Polymer Crystallization

Effects of Trefoil Knots on the Initiation of Polymer Crystallization

Influence of printing parameters and hinge structure on shape memory performance at the hinge in 4D origami structures

Four-dimensionally (4D) printing technology effectively demonstrates the advantages of portability, foldability, and improved mechanical properties in origami structures. This study highlights the significance of printing process parameters and origami hinge structures in ensuring rapid and complete deployment of origami structures. Polylactic acid based semicrystalline shape memory polymer was utilized to produce 4D printed origami structures. Through response surface analysis methods and bending tests, optimal printing parameters were determined, including layer thickness of 0.31 mm, extrusion speed of 17 mm s−1, and infill percentage of 71%. Additionally, the study designed a U-shaped hinge and analyzed its recovery mechanism through micromorphology of bending hinges and recovery experiments.

Industrially relevant injection moulding apparatus for in situ time-resolving small-angle X-ray scattering measurements

This work presents the design and construction of an automated industrial injection moulding apparatus that can be used with a typical multi-user beamline such as the NCD-SWEET small-angle X-ray scattering at the ALBA Synchrotron Light Source. This apparatus is focused on developing an understanding of how the mould temperature and the injection temperature and pressure affect both the orientation and morphology of the semi-crystalline polymer used to fabricate the injected parts. The system design follows current industrial practice and enables the collection of time-resolved X-ray scattering data at several points within the mould cavity, so we can understand the 4D morphology. In this work we show the effectiveness of the equipment using some results from the injection moulding of a random copolymer of polypropylene and that it can be used with a more demanding material such as polyhydroxybutyrate. This can be seen as the first step toward a multiscale digital twin for injection moulding.

Strain Rate Dependence of Amorphous Phase Instability in Semicrystalline Polymers: Insights from the Scale of Lamellar Stacks

Strain Rate Dependence of Amorphous Phase Instability in Semicrystalline Polymers: Insights from the Scale of Lamellar Stacks

Crystallization of Polymers with a Reduced Density of Entanglements

Since methods for reducing macromolecule entanglements have been developed, it has become possible to better understand the impact of polymer chain entanglement on the crystallization process. The article presents basic information about the disentangling of macromolecules and the characterization of the degree of entanglement. The basic knowledge of polymer crystallization was also presented. Then, it was discussed how polymers crystallize during their disentangling. Non-isothermal and isothermal crystallization experiments using disentangled polymers, and for comparison using entangled polymers, are described in more detail. The influence of disentangling on both nucleation and crystal growth is highlighted. It is also shown how the crystallization of polymers changes when macromolecules re-entangle.

Additive Manufacturing of Composite Polymers: Thermomechanical FEA and Experimental Study.

This study presents a comprehensive approach for simulating the additive manufacturing process of semi-crystalline composite polymers using Fused Deposition Modeling (FDM). By combining thermomechanical Finite Element Analysis (FEA) with experimental validation, our main objective is to comprehend and model the complex behaviors of 50 wt.% carbon fiber-reinforced Polyphenylene Sulfide (CF PPS) during FDM printing. The simulations of the FDM process encompass various theoretical aspects, including heat transfer, orthotropic thermal properties, thermal dissipation mechanisms, polymer crystallization, anisotropic viscoelasticity, and material shrinkage. We utilize Abaqus user subroutines such as UMATHT for thermal orthotropic constitutive behavior, UEPACTIVATIONVOL for progressive activation of elements, and ORIENT for material orientation. Mechanical behavior is characterized using a Maxwell model for viscoelastic materials, incorporating a dual non-isothermal crystallization kinetics model within the UMAT subroutine. Our approach is validated by comparing nodal temperature distributions obtained from both the Abaqus built-in AM Modeler and our user subroutines, showing close agreement and demonstrating the effectiveness of our simulation methods. Experimental verification further confirms the accuracy of our simulation techniques. The mechanical analysis investigates residual stresses and distortions, with particular emphasis on the critical transverse in-plane stress component. This study offers valuable insights into accurately simulating thermomechanical behaviors in additive manufacturing of composite polymers.