Cross-linked Polymeric Materials Research Articles

Development of Low-Molecular-Weight Gelator/Polymer Composite Materials Utilizing the Gelation and Swelling Process of Polymeric Materials.

The creation of polymer composite materials by compositing fillers into polymer materials is an effective method of improving the properties of polymer materials, and the development of new fillers and their novel composite methods is expected to lead to the creation of new polymer composite materials. In this study, we develop a new filler material made of low-molecular-weight gelators by applying a gelation process that simultaneously performs the swelling (gelation) of crosslinked polymer materials and the self-assembly of low-molecular-weight gelators into low-dimensional crystals in organic solvents within polymer materials. The gelation process of crosslinking rubber-based polymers using alkylhydrazides/toluene as the low-molecular-weight gelator allowed us to composite self-assembled sheet-like crystals of alkylhydrazides as fillers in polymeric materials, as suggested by various microscopic observations, including infrared absorption measurements, small-angle X-ray diffraction measurements and thermal analysis, microscopy, and infrared absorption measurements. Furthermore, tensile tests of the composite materials demonstrated that the presence of fillers improved both the Young's modulus and the tensile strength, as well as the elongation at yield. Additionally, heat treatment was shown to facilitate filler dispersion and enhance the mechanical properties. The findings demonstrate the potential of self-assembled sheet-like crystals of low-molecular-weight gelators as novel filler materials for polymers. The study's composite method utilizing gelators via gelation proved effective.

Crosslinked PVA based polymer coatings with shear-thinning behaviour and ultralow hydrogen permeability to prevent hydrogen embrittlement

An economic transition from natural gas to a hydrogen economy will require redeployment of steel pipelines and other infrastructure. Mechanisms are urgently needed to prevent embrittlement of the steel in hydrogen service. In this work, we show that poly vinyl alcohol (PVA) and poly (ethylene glycol) diglycidyl ether (PEGDGE) crosslinked polymer materials can be used as internal coatings to dramatically reduce hydrogen permeation to the steel surface. Unlike other crosslinked PVA systems, these materials are shear-thinning and thixotropic, which is an essential requirement for facile, in situ application onto existing infrastructure. A hydrogen permeability of 0.01 Barrer is achieved, which is up to 100 times lower than commercially available coating materials. Experiments show that increasing concentrations of the alkali catalyst (KOH) do not impact the permeability of the crosslinked films but can benefit the rheology by shortening the reaction time. Higher reaction ratios of PVA to PEGDGE give lower hydrogen permeability due to a higher degree of polymer crystallinity, but less favorable rheology due to slower reaction kinetics. PVA with higher molecular weight gives lower hydrogen permeability and promotes shear-thinning behaviour, while PEGDGE with higher molecular weight increased the film permeability but enhances the shear-thinning behavior with shorter reaction times.

Effect of Crosslinking Conditions on the Transport of Protons and Methanol in Crosslinked Polyvinyl Alcohol Membranes Containing the Phosphoric Acid Group.

In this investigation, we systematically explored the intricate relationship between the structural attributes of polyvinyl alcohol (PVA) membranes and their multifaceted properties relevant to fuel cell applications, encompassing diverse crosslinking conditions. Employing the solution casting technique, we fabricated crosslinked PVA membranes by utilizing phosphoric acid (PA) as the crosslinking agent, modulating the crosslinking temperature across a range of values. This comprehensive approach aimed to optimize the selection of crosslinking parameters for the advancement of crosslinked polymer materials tailored for fuel cell contexts. A series of meticulously tailored crosslinked PVA membranes were synthesized, each varying in PBTCA content (5-30 wt.%) to establish a systematic framework for elucidating chemical interactions, morphological transformations, and physicochemical attributes pertinent to fuel cell utilization. The manipulation of crosslinking agent concentration and crosslinking temperature engendered a discernible impact on the crosslinking degree, leading to a concomitant reduction in crystallinity. Time-resolved attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was harnessed to evaluate the dynamics of liquid water adsorption and ionomer swelling kinetics within the array of fabricated PVA films. Notably, the diffusion of water within the PVA membranes adhered faithfully to Fick's law, with discernible sensitivity to the crosslinking conditions being implemented. Within the evaluated membranes, proton conductivities exhibited a span of between 10-3 and 10-2 S/cm, while methanol permeabilities ranged from 10-8 to 10-7 cm2/s. A remarkable revelation surfaced during the course of this study, as it became evident that the structural attributes and properties of the PVA films, under the influence of distinct crosslinking conditions, underwent coherent modifications. These changes were intrinsically linked to alterations in crosslinking degree and crystallinity, reinforcing the interdependence of these parameters in shaping the characteristics of PVA films intended for diverse fuel cell applications.

4D Printed Shape-Memory Elastomer for Thermally Programmable Soft Actuators.

Polymeric shape-memory elastomers can recover to a permeant shape from any programmed deformation under external stimuli. They are mostly cross-linked polymeric materials and can be shaped by three-dimensional (3D) printing. However, 3D printed shape-memory polymers so far only exhibit elasticity above their transition temperature, which results in their programmed shape being inelastic or brittle at lower temperatures. To date, 3D printed shape-memory elastomers with elasticity both below and above their transition temperature remain an elusive goal, which limits the application of shape-memory materials as elastic materials at low temperatures. In this paper, we printed, for the first time, a custom-developed shape-memory elastomer based on polyethylene glycol using digital light processing, which possesses elasticity and stretchability in a wide temperature range, below and above the transition temperature. Young's modulus in these two states can vary significantly, with a difference of up to 2 orders of magnitude. This marked difference in Young's modulus imparts excellent shape-memory properties to the material. The difference in Young's modulus at different temperatures allows for the programming of the pneumatic actuators by heating and softening specific areas. Consequently, a single actuator can exhibit distinct movement modes based on the programming process it undergoes.

Acoustodynamic Covalent Materials Engineering for the Remote Control of Physical Properties Inside Materials.

Advances in vat-photopolymerization (VP) three-dimensional printing (3DP) technology enable the production of highly precise 3D objects. However, it has been a major challenge to create dynamic functionalities and to manipulate the physical properties of the inherently insoluble and infusible crosslinked material generated from VP-3DP without reproduction. Here, we report the fabrication of light- and high-intensity focused ultrasound (HIFU)-responsive crosslinked polymeric materials linked with hexaarylbiimidazole (HABI) in polymer chains based on VP-3DP. Although the photochemistry of HABI produces triphenylimidazolyl radicals (TPIRs) during the process of VP-3DP, the orthogonality of the photochemistry of HABI and photopolymerization enables the introduction of reversible crosslinks derived from HABIs in the resulting 3D printed objects. While photostimulation cleaves a covalent bond between two imidazoles in HABI to generate TPIRs only near the surface of the 3D printed objects, HIFU triggers cleavage in the interior of materials. In addition, HIFU travels beyond an obstacle to induce a response of HABI-embedded crosslinked polymers, which cannot be attainable with photostimulation. The present system would be beneficial for tuning the physical properties and recycling of various polymeric materials, but it will also open the door for pinpoint modification, healing, and reshaping of materials when coupled to various dynamic covalent materials. This article is protected by copyright. All rights reserved.

Improving physical properties of poly(vinyl alcohol)/montmorillonite nanocomposite hydrogels via the Hofmeister effect

Hydrogel is a kind of three-dimensional crosslinked polymer material with high moisture content. However, due to the network defects of polymer gels, traditional hydrogels are usually brittle and fragile, which limits their practical applications. Herein, we present a Hofmeister effect-aided facile strategy to prepare high-performance poly(vinyl alcohol)/montmorillonite nanocomposite hydrogels. Layered montmorillonite nanosheets can not only serve as crosslinking agents to enhance the mechanical properties of the hydrogel but also promote the ion conduction. More importantly, based on the Hofmeister effect, the presence of (NH4)2SO4 can endow nanocomposite hydrogels with excellent mechanical properties by affecting PVA chains' aggregation state and crystallinity. As a result, the as-prepared nanocomposite hydrogels possess unique physical properties, including robust mechanical and electrical properties. The as-prepared hydrogels can be further assembled into a high-performance flexible sensor, which can sensitively detect large-scale and small-scale human activities. The simple design concept of this work is believed to provide a new prospect for developing robust nanocomposite hydrogels and flexible devices in the future.

Wood pulp industry by-product valorization for acrylate synthesis and bio-based polymer development via Michael addition reaction

It is crucial to adapt the processing of forest bio-resources into biochemicals and bio-based advanced materials in order to transform the current economic climate into a greener economy. Tall oil, as a by-product of the Kraft process of wood pulp manufacture, is a promising resource for the extraction of various value-added products. Tall oil fatty acids-based multifunctional Michael acceptor acrylates were developed. The suitability of developed acrylates for polymerization with tall oil fatty acids-based Michael donor acetoacetates to form a highly cross-linked polymer material via the Michael addition was investigated. With this novel strategy, valuable chemicals and innovative polymer materials can be produced from tall oil in an entirely new way, making a significant contribution to the development of a forest-based bioeconomy. Two different tall oil-based acrylates were successfully synthesized and characterized. Synthesized acrylates were successfully used in the synthesis of bio-based thermoset polymers. Obtained polymers had a wide variety of mechanical and thermal properties (glass transition temperature from –12.1 to 29.6 °C by dynamic mechanical analysis, Young's modulus from 15 to 1 760 MPa, and stress at break from 0.9 to 16.1 MPa). Gel permeation chromatography, Fourier-transform infrared (FT-IR) spectroscopy, matrix-assisted laser desorption/ionization-time of flight mass spectrometry, and nuclear magnetic resonance were used to analyse the chemical structure of synthesized acrylates. In addition, various titration methods and rheology tests were applied to characterize acrylates. The chemical composition and thermal and mechanical properties of the developed polymers were studied by using FT-IR, solid-state nuclear magnetic resonance, thermal gravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, and universal strength testing apparatus.

Encapsulation of Cadmium-Free InP/ZnSe/ZnS Quantum Dots in Poly(LMA-co-EGDMA) Microparticles via Co-flow Droplet Microfluidics.

Quantum dots (QDs) are semiconductor nanocrystals that are used in optoelectronic applications. Most modern QDs are based on toxic metals, for example Cd, and do not comply with the European Restriction of Hazardous Substances regulation of the European Union. Latest promising developments focus on safer QD alternatives based on elements from the III-V group. However, the InP-based QDs lack an overall photostability under environmental influences. One design path of achieving stability is through encapsulation in cross-linked polymer matrices with the possibility to covalently link the matrix to surface ligands of modified core-shell QDs. The work focuses on the formation of polymer microbeads suitable for InP-based QD encapsulation, allowing for an individual protection of QDs and an improved processibility via this particle-based approach. For this, a microfluidic based method in the co-flow regime is used that consists of an oil-in-water droplet system in a glass capillary environment. The generated monomer droplets are polymerized in-flow into poly(LMA-co-EGDMA) microparticles with embedded InP/ZnSe/ZnS QDs using a UV initiation. They demonstrate how a successful polymer microparticle formation via droplet microfluidics produces optimized matrix structures leading to a distinct photostability improvement of InP-based QDs compared to nonprotected QDs.

β-cyclodextrin-scaffolded crosslinked poly(ionic liquid)s for ultrafast removal of multiple pollutants: Insight into adsorption performance and mechanism

The design of highly rapid and efficient cross-linked polymer materials is essential for developing adsorption of pollutant methods based on cyclodextrin to replace currently used slow trapping activated carbons. It is rarely possible to achieve rapid and complete adsorption at high concentrations, even though available adsorbents have developed high adsorption capacity. Herein, a beta-cyclodextrin cross-linked poly(ionic liquid) adsorbents (CD-PILs), was facilely fabricated through one-pot radical polymerization for fast, high-capacity and selective removal of pollutants from water, including organic dyes, pharmaceutical and personal care products, heavy metal ions as well as microbial contamination. It could be completely removed from water within a short period ranging from seconds to minutes at a wide range of high-load anionic dyes (1 mM). Theoretical maximum adsorption capacity of CD-PILs for CR, MO, DS, SD, K2Cr2O7, and CA is 2058.2, 1338.6, 903.7, 1661.4, 878.2, and 343.6 mg/g, respectively. The adsorption rate of ionic CD-PILs superior than those of most of reported synthetic adsorbent materials with the highest adsorption capacity so far, especially for heavy metals. Moreover, after being regenerated five times, the water-remediation performance of CD-PILs remained almost the same as fresh ones, demonstrating the great potential of CD-PILs in industrial water remediation.

Formation of lamellar domains in liquid crystal elastomers under compression

Liquid crystal elastomers (LCEs) are lightly cross-linked polymer materials containing liquid crystal (LC) molecules with unique strain-induced director reorientation properties. Compressive studies on LCEs have been very little given the difficulty synthesizing sufficiently large monodomain block samples. Based on the continuum mechanics model of LCEs, the compressive behaviors of monodomain LCE blocks in plane stain with different initial directors between two rigid plates are systematically studied in this paper. The rotation of the director, especially the formation of lamellar domains, significantly changes the characteristics of the compressive stress-strain curves. Compression along the initial director will induce the formation of lamellar domains orthogonal to the loading axis due to the alternating rotation of the director after loading to a critical strain. The rotation of the director also leads to the stress plateau on the stress-strain curves. When the initial director is nearly parallel to the compression axis, the lamellar domains can still be observed in the central region of the sample bonded to the rigid plates, which is also related to the deformed morphology of the stress-free boundaries. If the initial director is slightly deviated from the loading axis, almost uniform rotation occurs in the central region of the sample, while the stress increases monotonically with strain hardening. The formation of lamellar domains is not only related to the angles between the initial director and the compressive loading axis, but also strongly depends on the geometrical and material parameters of the samples. For large aspect ratios or small anisotropy constants, the formation of lamellar domains may require compression sufficiently parallel to the initial director. Our work provides a deeper understanding of the behavior of LCEs under compression.

Dual Nanofillers-Reinforced Noncovalently Cross-Linked Polymeric Composites with Unprecedented Mechanical Strength

Open AccessCCS ChemistryRESEARCH ARTICLES9 Dec 2022Dual Nanofillers-Reinforced Noncovalently Cross-Linked Polymeric Composites with Unprecedented Mechanical Strength Ni An, Youliang Zhu, Xiaohan Wang, Yixuan Li, Junjun Liu, Xu Fang, Zhongyuan Lu, Bai Yang and Junqi Sun Ni An Google Scholar More articles by this author , Youliang Zhu Google Scholar More articles by this author , Xiaohan Wang Google Scholar More articles by this author , Yixuan Li Google Scholar More articles by this author , Junjun Liu Google Scholar More articles by this author , Xu Fang Google Scholar More articles by this author , Zhongyuan Lu Google Scholar More articles by this author , Bai Yang Google Scholar More articles by this author and Junqi Sun Google Scholar More articles by this author https://doi.org/10.31635/ccschem.022.202202496 SectionsSupplemental MaterialAboutPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Noncovalently cross-linked polymer materials can reduce materials consumption and alleviate environmental pollution through healing, recycling, and reprocessing. However, it remains a huge challenge to fabricate superstrong noncovalently cross-linked polymer materials with mechanical strength comparable to highperformance engineering polymers. Herein, healable and reprocessable noncovalently cross-linked polymer composites with an unprecedented mechanical strength are fabricated by complexation of polyacrylic acid (PAA), polyvinylpyrrolidone (PVPON) and carbonized polymer dots (CPDs) (denoted as PAA-PVPON-CPDs). The incorporation of 15 wt% CPDs generates PAA-PVPON-CPDs composites with a tensile strength of ~158 MPa and Young’s modulus of ~8.2 GPa. Serving as nanofillers, the CPDs can establish strong interactions with polymers in PAA-PVPON composites. The CPDs and the in situ-formed PAA-PVPON nanoparticles work in concert to significantly strengthen the PAA-PVPON-CPDs composites to an unprecedented strength. The PAAPVPON-CPDs composites exhibit excellent impact resistance and damage tolerance because of the high mechanical strength of the composites and the energy dissipation mechanism of the CPDs and PAA-PVPON nanoparticles. Moreover, the fractured PAA-PVPON-CPDs composites can be healed to restore their original mechanical strength. Download figure Download PowerPoint Previous articleNext article FiguresReferencesRelatedDetails Issue AssignmentVolume 0Issue jaPage: 1-27Supporting Information Copyright & Permissions© 2022 Chinese Chemical Society Downloaded 53 times PDF downloadLoading ...

Shear-Thickening Covalent Adaptive Networks for Bifunctional Impact-Protective and Post-Tunable Tactile Sensors

Shear-thickening materials have been widely applied in fields related to smart impact protection due to their ability to absorb large amounts of energy during sudden shock. Shear-thickening materials with multifunctional properties are expanding their applications in wearable electronics, where tactile sensors require interconnected networks. However, current bifunctional shear-thickening cross-linked polymer materials depend on supramolecular networks or slightly dynamic covalently cross-linked networks, which usually exhibit lower energy-absorption density than the highly dynamic covalently cross-linked networks. Herein, we employed boric ester-based covalent adaptive networks (CANs) to elucidate the shear-thickening property and the mechanism of energy dissipation during sudden shock. Guided by the enhanced energy-absorption capability of double networks and the requirements of the conductive networks for the wearable tactile sensors, tungsten powders (W) were incorporated into the boric ester polymer matrix to form a second network. The W networks make the materials stiffer, with a 13-fold increase in Young's modulus. Additionally, the energy-absorption capacity increased nearly 7 times. Finally, we applied these excellent energy-absorbing and conductive materials to bifunctional shock-protective and strain rate-dependent tactile sensors. Considering the self-healable and recyclable properties, we believe that these anti-impact and tactile sensing materials will be of great interest in wearable devices, smart impact-protective systems, post-tunable materials, etc.

Tuning mechanical behavior of polymer materials via multi-arm crosslinked network architectures

Crosslinked polymer materials provide tremendous opportunities for delivering unique material properties for a wide variety of applications such as shape-memory and self-healing materials, aerospace materials, and biomedical systems. Most crosslinked polymer networks investigated to date are designed based on covalent or noncovalent crosslinkers that include two-ended connections to the backbone polymer base. In this paper, we investigate the topic of multi-arm crosslinking of polymer materials using a computational platform. We take advantage of molecular dynamics simulations and graph theory to define computational models that describe potential architectures for multi-arm crosslinked polymer networks. We also discuss feasible experimental routes for implementation of these approaches. We investigate how the polymer network architecture affects the mechanical and self-healing behavior of the material. Our results show that the angular stiffness of multi-arm crosslinkers can be adjusted to control the mechanical strength of the overall polymer network. Additionally, using graph theory, we find that the complex connections that exist between the crosslinkers and the backbone polymer chains define the overall connectivity of the polymer network, which in turn dictates the mechanical behavior of the material. Furthermore, we find that increasing the number of crosslinking arms may improve the self-healing behavior, but it can reduce the overall mechanical strength of the polymer network. The findings of this paper can motivate future experimental and data-driven studies to realize more sophisticated crosslinked polymer materials with a large number of degrees of freedom to deliver a variety of tunable properties.

Closed-loop chemical recycling of cross-linked polymeric materials based on reversible amidation chemistry

Closed-loop chemical recycling provides a solution to the end-of-use problem of synthetic polymers. However, it remains a major challenge to design dynamic bonds, capable of effective bonding and reversible cleaving, for preparing chemically recyclable cross-linked polymers. Herein, we report a dynamic maleic acid tertiary amide bond based upon reversible amidation reaction between maleic anhydrides and secondary amines. This dynamic bond allows for the construction of polymer networks with tailorable and robust mechanical properties, covering strong elastomers with a tensile strength of 22.3 MPa and rigid plastics with a yield strength of 38.3 MPa. Impressively, these robust polymeric materials can be completely depolymerized in an acidic aqueous solution at ambient temperature, leading to efficient monomer recovery with >94% separation yields. Meanwhile, the recovered monomers can be used to remanufacture cross-linked polymeric materials without losing their original mechanical performance. This work unveils a general approach to design polymer networks with tunable mechanical performance and closed-loop recyclability, which will open a new avenue for sustainable polymeric materials.

Synthesis, characterisation and optimisation of bulk molecularly imprinted polymers from nonsteroidal anti-inflammatory drugs

The scope of this study was to synthesise and characterise the multi-template molecularly imprinted polymer (MIP) and to use target compounds, naproxen, ibuprofen, diclofenac, fenoprofen and gemfibrozil as templates so as to achieve all maximum extraction efficiency for all compounds. These compounds are a class of nonsteroidal anti-inflammatory drugs (NSAIDs) generally used by humans, as they have pain-relieving activities. MlPs are cross-linked polymeric materials that display high binding capacity and selectivity towards templates of interest. The synthesis consisted of a bulk polymerisation process at 60 °C by using NSAIDs as multi-templates, ethylene glycol dimethacrylate (EGDMA), 2-vinyl pyridine (2VP) and toluene as cross-linker, functional monomer and porogen, respectively. Nonimprinted polymer (NIP) was synthesised in a similar manner with the omission of the templates. Characteristics of the polymers were analysed using Scanning Electron Microscopy (SEM), Fourier Transformed Infrared Spectroscopy (FTIR), Solid State Nuclear Magnetic Resonance Spectroscopy (NMR) and Thermal Gravimetric Analysis (TGA). An adsorption method of NSAIDs using the bulk polymerised MIP was investigated under various pH, mass, concentration and time conditions. Other parameters included adsorption kinetics and adsorption isotherms. Uptake of NSAIDs from an aqueous medium was achieved with 40 mg of MIP at pH 4.0 within 10 min of contact time. The extraction efficiencies achieved for NSAIDs in aqueous solutions ranged from 90-98% for all compounds tested. The adsorption capacity obtained for MIP ranged from 1.230-1.249 mg g-1 and 0.90-1.136 mg g-1 for NIP, whereas the selectivity values ranged from 1.12-2.4. A kinetic study revealed that adsorption obeys a second-order rate, and the Langmuir model explains adsorption isotherm data. This work showed that the multi-template approach for all the target compounds has the potential to give maximum extraction efficiencies in MIP extraction systems from aqueous samples.

Interlocked Covalent Adaptable Networks and Composites Relying on Parallel Connection of Aromatic Disulfide and Aromatic Imine Cross-Links in Epoxy

Covalent adaptable networks (CANs) relying on dynamic cross-links have been developed to make the cross-linked polymeric materials and composites degradable. However, due to the reversibility of dynamic bonds, the CANs and composites suffer accidental degradation and failure upon a certain stimulus (moisture, acid/base, reductant/oxidant, etc.) in the application environment. Herein, inspired by parallel circuits, interlocked covalent adaptable networks (ICANs) were prepared by one-pot reactions from epoxy monomers and two curing agents that contained different dynamic bonds of aromatic disulfide and aromatic imine bonds, resulting in dual dynamic parallel cross-links in homogeneous epoxy networks. The ICANs exhibited outstanding mechanical properties and improved stability, relying on the topological interlocking structure. The ICANs could be unlocked and became degradable only when two stimuli were both applied to completely break the cross-links of disulfide bonds and imine bonds. When applying ICANs as a matrix to form carbon fiber-reinforced polymer (CFRP) composites, the resulted CFRP inherited the interlocking properties from the ICANs, exhibiting improved stability and nondestructive recyclability. Maintaining the degradable properties, the interlocking structure of networks provided a facile way to optimize the stability of CANs and their composites.

3D Bioprinting Technology and Hydrogels Used in the Process.

3D bioprinting has gained visibility in regenerative medicine and tissue engineering due to its applicability. Over time, this technology has been optimized and adapted to ensure a better printability of bioinks and biomaterial inks, contributing to developing structures that mimic human anatomy. Therefore, cross-linked polymeric materials, such as hydrogels, have been highly targeted for the elaboration of bioinks, as they guarantee cell proliferation and adhesion. Thus, this short review offers a brief evolution of the 3D bioprinting technology and elucidates the main hydrogels used in the process.

Sodium polyacrylate hydrogel fixed bed to treat Water-Contaminated cloudy diesel

The applications of hydrogels in industry and academia are numerous and well known. However, the use of these cross-linked polymer materials is presented in this article with a particular purpose that is unexplored in the literature: to reduce water content from diesel aiming at meeting commercial specifications for turbidity in a continuous process. Currently, there are different processes in the industry to reduce water content in fuels, such as coalescing filters (for non-soluble water) and distillation (with high energy demand). However, this work showed the potential application of hydrogel as an alternative technology, being able to remove soluble water with ease of installation and low energy consumption. Sodium polyacrylate (SPA) hydrogel was chosen among others - polyacrylamide (PAAm) and poly(acrylic acid) (PAA) hydrogels - to treat cloudy diesel in a fixed bed. This polymer was characterized in terms of morphology and chemical composition and the swelling degree kinetics was studied considering different lyophilisation conditions and particle diameters. Also, the effect of type of external media and temperature on the equilibrium swelling degree were assessed. The lyophilized SPA hydrogel reduced the water content of diesel from around 630 ppm to near 100 ppm and the turbidity from Haze 6 down to Haze 1. These results demonstrate that the new technology has a potential use in petroleum refineries, storage and distribution facilities and also in small scale applications, such as in gas stations.

Understanding the role of cross-link density in the segmental dynamics and elastic properties of cross-linked thermosets.

Cross-linking is known to play a pivotal role in the relaxation dynamics and mechanical properties of thermoset polymers, which are commonly used in structural applications because of their light weight and inherently strong nature. Here, we employ a coarse-grained (CG) polymer model to systematically explore the effect of cross-link density on basic thermodynamic properties as well as corresponding changes in the segmental dynamics and elastic properties of these network materials upon approaching their glass transition temperatures (Tg). Increasing the cross-link density unsurprisingly leads to a significant slowing down of the segmental dynamics, and the fragility K of glass formation shifts in lockstep with Tg, as often found in linear polymer melts when the polymer mass is varied. As a consequence, the segmental relaxation time τα becomes almost a universal function of reduced temperature, (T - Tg)/Tg, a phenomenon that underlies the applicability of the "universal" Williams-Landel-Ferry (WLF) relation to many polymer materials. We also test a mathematical model of the temperature dependence of the linear elastic moduli based on a simple rigidity percolation theory and quantify the fluctuations in the local stiffness of the network material. The moduli and distribution of the local stiffness likewise exhibit a universal scaling behavior for materials having different cross-link densities but fixed (T - Tg)/Tg. Evidently, Tg dominates both τα and the mechanical properties of our model cross-linked polymer materials. Our work provides physical insights into how the cross-link density affects glass formation, aiding in the design of cross-linked thermosets and other structurally complex glass-forming materials.

Analysis of the New Technology of Recycling Waste Cross-linked Polymer Materials with Difficult Recovery

Analysis of the New Technology of Recycling Waste Cross-linked Polymer Materials with Difficult Recovery