Increase In Crosslink Density Research Articles

Effect of cross-link density on the performance of polyimine/epoxy vitrimers

Vitrimers are polymers rich in dynamic covalent bonds in cross-link networks. When the dynamic covalent bonds are not activated, the vitrimers show the performance stability of the traditional thermosetting polymer. When the dynamic covalent bonds are activated, the vitrimers can show some novel and unique properties, such as stress relaxation, self-healing and reprocessing. This new type of polymer has attracted wide attention because of its unique properties. As thermoset materials, the degree of cross-link and cross-link density of the materials are very important for the performance of vitrimers. In order to find out the effects of cross-link density on the properties of vitrimers, a series of dynamic polyimine/epoxy cross-link networks with different cross-link densities were designed and prepared, and their properties were characterized. The materials with higher cross-link density show higher thermal properties, mechanical properties and shape fixation ratio. However, due to the increase of cross-link density, the mobility of molecular chain and the exchange of dynamic bonds are limited, so the healing efficiency, shape recovery ratio and shape recovery rate will decrease to a certain extent. This study provides important insights into a deeper understanding of this new type of polymer.

Robust anti-impact, energy absorption and thermal properties of polyurethane nanocomposites modified by phenol-amine chemistry

It is still a considerable challenge for polyurethane elastomers (PUE) to possess outstanding mechanical and thermal performance simultaneously against harsh dynamic impact environment due to their heat accumulation, thermal stress softening and mechanical failure. Thus, this article innovatively prepared binary nanofibers composed of carbon nanofiber (CNFs) and aramid nanofibers (ANFs) to reinforce PUE, where catechol (CC) and polyethyleneimine (PEI) were served as interfacial modifier between nanofibers and polymer matrix. PUE with 1.5 wt% binary nanofibers achieve 31.62 % increase in crosslinking density, 146.8 °C improvement in thermal decomposition temperature compared to Neat PUE. Besides, the absorption energy and dynamic compression strength of composites were increased by 40.36 % and 38.26 %, respectively. Because reinforced nanofibers with crosslinking network structures improve the interface interaction between fillers and matrix, facilitate stress transfer and increase the energy threshold of thermal decomposition. The paper supplements the impact resistance analysis of PUE-based protective materials under impact loads, providing a systematic and scientific reference for the design and manufacture of impact resistant materials.

Advanced corrosion Protection: Development of MnO2@rGO/EP-GTA nanocoating

This study investigates the potential of utilizing reduced graphene nanosheets to enhance the anticorrosion properties of MnO2 coatings. Specifically, the study focuses on the incorporation of reduced graphene oxide (rGO) into MnO2 coatings to improve their anticorrosion performance. The MnO2-decorated graphene oxide nanocomposite (MnO2@rGO) was thoroughly characterized using various analytical techniques, including Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). These analyses elucidated the morphological and structural features of both rGO and MnO2, highlighting the chemical bonding between MnO2 and rGO. Furthermore, the MnO2@rGO nanocomposite underwent additional modification with glycidoxypropyltrimethoxysilane (GTA) before integration into the epoxy resin, resulting in the formation of the epoxy coating (MnO2@rGO/EP-GTA) on steel plates. Electrochemical and potentiometric measurements demonstrated that the inclusion of rGO significantly prolonged the cathodic protection duration of MnO2 within the coatings. This enhancement can be attributed to rGO acting as an impermeable barrier within the coating matrix, thereby enhancing electrical conductivity and facilitating efficient electrical connection between manganese oxide particles and the steel substrate. Additionally, the incorporation of MnO2@rGO and GTA modification led to improved performance of the MnO2@rGO/EP nanocoating, including enhanced resistance to UV aging and salt spraying, effective dispersion of the MnO2@rGO nanocomposite within the epoxy resin, and increased cross-linking density and adhesion strength of the epoxy coating.

Effects of Peroxide and Sulfur Curing Systems on Physical and Mechanical Properties of Nitrile Rubber Composites: A Comparative Study.

This study compares the effect of sulfur and dicumyl peroxide (DCP) vulcanizing systems on the physical and mechanical properties of rubber compounds based on acrylonitrile butadiene rubber (NBR). NBR compounds cured by different amounts of DCP and NBR vulcanizates filled with various concentrations of carbon black (CB) and a constant amount of sulfur or DCP were prepared. The vulcanizates were characterized by tensile testing, dynamic mechanical thermal analysis (DMTA), and cross-link density determination. The tensile strength and Young's modulus were found to increase with the rising amount of DCP and CB, while elongation at break decreased. The samples vulcanized by the sulfur system and filled with CB show a substantial increase in tensile strength from 13.1 to 21.2 MPa. Higher storage modulus and glass transition temperature were observed with the increase in the amount of peroxide and filler, and consequently, the increase in cross-link density, indicating rigidity increase and lower molecular mobility. The changes in the physical and mechanical properties of the NBR vulcanizates were in correlation with the changes in solvent uptake and cross-link density.

Enhancing corrosion resistance and toughness of solvent-free epoxy coatings with low-viscosity fluorine-containing hyperbranched polyether

In this study, a low-viscosity epoxy-terminated fluorine-containing hyperbranched polyether (FHBPE) was synthesized and incorporated in a solvent-free epoxy coating formulation to enhance coating toughness and corrosion resistance while minimizing the impact on coating viscosity. FHBPE was synthesized by a solvent-free one-pot method with hexafluorobisphenol A (A2 monomer) and trimethylolpropane triglycidyl ether (B3 monomer). Subsequently, FHBPE, E51 epoxy resin, and an alicyclic amine curing agent were blended to create the solvent-free epoxy coating, which was applied onto a steel substrate by a scraping coating method. This research demonstrates that addition of FHBPE did not show adverse effect on coating viscosity; instead, it reduced the viscosity at around 6 wt% loading. The epoxy-terminated FHBPE increased the cross-linking density of neat E51 coating by up to 20.7 %. Furthermore, the introduction of flexible segments enhanced the toughness, leading to a one-grade increase in the coating flexibility from 1 to 0.5 mm. Furthermore, FHBPE significantly improved the corrosion resistance of the coatings, attributed to increased cross-linking density and hydrophobic properties of the coating. Among FHBPE-modified coatings, the coating with 6 wt% loading demonstrated superior overall performance. Over a 60-day immersion period, its electrochemical impedance value remained stable, while the neat E51 coating experienced a two-orders-of-magnitude decrease. Furthermore, the 6 wt% FHBPE-modified coating passed the 750-h salt spray test without obvious rust, outperforming the neat E51 coating (200 h). This study presents a feasible and promising strategy for the formulation design and mass production of solvent-free epoxy coatings.

Self-Healing Sulfonated Poly(ether ether ketone)-Based Polymer Electrolyte Membrane for Direct Methanol Fuel Cells: Effect of Solvent Content.

Proton exchange membranes (PEMs) with superior characteristics are needed to advance fuel cell technology. Nafion, the most used PEM in direct methanol fuel cells (DMFCs), has excellent proton conductivity but suffers from high methanol permeability and long-term performance degradation. Thus, this study aimed to create a healable PEM with improved durability and methanol barrier properties by combining sulfonated poly(ether ether ketone) (SPEEK) and poly-vinyl alcohol (PVA). The effect of changing the N,N-dimethylacetamide (DMAc) solvent concentration during membrane casting was investigated. Lower DMAc concentrations improved water absorption and, thus, membrane proton conductivity, but methanol permeability increased correspondingly. For the best trade-off between these two characteristics, the blend membrane with a 10 wt% DMAc solvent (SP10) exhibited the highest selectivity. SP10 also showed a remarkable self-healing capacity by regaining 88% of its pre-damage methanol-blocking efficiency. The ability to self-heal decreased with the increasing solvent concentration because of the increased crosslinking density and structure compactness, which reduced chain mobility. Optimizing the solvent concentration during membrane preparation is therefore an important factor in improving membrane performance in DMFCs. With its exceptional methanol barrier and self-healing characteristics, the pioneering SPEEK/PVA blend membrane may contribute to efficient and durable fuel cell systems.

A molecular dynamics study of 3C‐SiC/epoxy nanocomposite as a metal‐free friction material

AbstractThe tribological, mechanical, and thermal properties of an epoxy crosslinking network incorporated with 3C‐SiC nanoparticles, serving as a metal‐free friction material were investigated by molecular dynamics simulations. The considered models encompass pure epoxy materials with 35%, 50%, 65%, and 80% crosslinking degrees, as well as 3C‐SiC/epoxy composite materials at the same crosslinking levels. Glass transition temperature (Tg) of the eight models was analyzed, and the result shows augmenting crosslinking density and addition of 3C‐SiC nanofillers improve Tg of all models. Fractional free volume of each model was quantified to reflect the features of epoxy materials and influence the properties at the atomic scale. Frictional force, normal force, and coefficient of friction (COF) were calculated to elucidate the tribological performance of the epoxy‐based materials. The introduction of 3C‐SiC nanofillers reduces COF. With nanofillers, higher crosslinking degree brings lower COF except 80% crosslinking degree, while without nanofillers, higher COFs are obtained with 35% and 80% crosslinking degrees. 3C‐SiC/epoxy composite with heightened crosslinking degree demonstrates superior Young's modulus, elevated tensile stress, and relatively smaller strain. Thermal conductivity analysis highlights the positive impact of both increased crosslinking density and incorporation of 3C‐SiC nanofillers on heat transfer. Temperature elevation further enhances thermal conductivity.

Phytic acid-modified carboxymethyl cellulose hydrogel for uranium adsorption from aqueous solutions

Phytic acid-modified carboxymethyl cellulose (CMC-PA) has been investigated as a promising adsorbent for the removal of uranium from aqueous solutions. The synthesis of CMC-PA involves the hydrogen bonding interaction between CMC and PA, resulting in the incorporation of PA groups onto the cellulose backbone. The hydrophilicity, reusability and adsorption capacity of the prepared CMC-PA hydrogel have improved with the increase of PA content. Moreover, the adsorption experiments were conducted by varying parameters such as pH, initial uranium concentration, and contact time. The results showed that CMC-PA exhibited excellent uranium adsorption performance, with a theoretical maximum adsorption capacity of 436 mg/g. In addition, the material exhibits excellent reusability, and the reusability improves with the increase of crosslinking density, indicating that the crosslinking structure of the polymer gel can effectively enhance the structural stability of the material. Furthermore, CMC-PA also exhibits high selective adsorption performance towards uranium ions in the presence of various competing ions. Its high adsorption capacity, reusability, and selectivity make it a promising candidate for high-performance uranium ion adsorbents.

3D bioprinting of multifunctional alginate dialdehyde (ADA)–gelatin (GEL) (ADA-GEL) hydrogels incorporating ferulic acid

The present work explores the 3D extrusion printing of ferulic acid (FA)-containing alginate dialdehyde (ADA)–gelatin (GEL) scaffolds with a wide spectrum of biophysical and pharmacological properties. The tailored addition of FA (≤0.2 %) increases the crosslinking between FA and GEL in the presence of calcium chloride (CaCl2) and microbial transglutaminase, as confirmed using trinitrobenzenesulfonic acid (TNBS) assay. In agreement with an increase in crosslinking density, a higher viscosity of ADA-GEL with FA incorporation was achieved, leading to better printability. Importantly, FA release, enzymatic degradation and swelling were progressively reduced with an increase in FA loading to ADA-GEL, over 28 days. Similar positive impact on antibacterial properties with S. epidermidis strains as well as antioxidant properties were recorded. Intriguingly, FA incorporated ADA-GEL supported murine pre-osteoblast proliferation with reduced osteosarcoma cell proliferation over 7 days in culture, implicating potential anticancer property. Most importantly, FA-incorporated and cell-encapsulated ADA-GEL can be extrusion printed to shape fidelity-compliant multilayer scaffolds, which also support pre-osteoblast cells over 7 days in culture. Taken together, the present study has confirmed the significant potential of 3D bioprinting of ADA-GEL-FA ink to obtain structurally stable scaffolds with a broad spectrum of biophysical and therapeutically significant properties, for bone tissue engineering applications.

Development of Poly(acrylamide)-Based Hydrogel Composites with Powdered Activated Carbon for Controlled Sorption of PFOA and PFOS in Aqueous Systems.

Per- and polyfluoroalkyl substances (PFAS) are anthropogenic compounds developed for various applications; some are connected to adverse health impacts including immunosuppression and higher susceptibility to some cancers. Current PFAS remediation treatments from aqueous sources include granular activated carbon (GAC) adsorption, membrane separation, and anion-exchange resin (AER) removal. Each has specific disadvantages, hence the need for a new and efficient technology. Herein, acrylamide-based hydrogel composites were synthesized with powdered activated carbon (PAC) and characterized to determine their affinity for PFAS. Physicochemical characterization included Fourier-Transform infrared spectroscopy (FTIR) to identify chemical composition, thermogravimetric analysis (TGA) to confirm PAC loading percentage, and aqueous swelling studies to measure the effect of crosslinking density. FTIR showed successful conversion of carbonyl and amine groups, and TGA analysis confirmed the presence of PAC within the network. Surface characterization also confirmed carbon-rich areas within composite networks, and the swelling ratio decreased with increasing crosslinking density. Finally, sorption of PFAS was detected via liquid chromatography with tandem mass spectrometry (LC-MS/MS), with removal efficiencies of up to 98% for perfluorooctanoic sulfonic acid (PFOS) and 96% for perfluorooctanoic acid (PFOA). The developed hydrogel composites exhibited great potential as advanced materials with tunable levers that can increase affinity towards specific compounds in water.

Bioactive interpenetrating hybrids of poly(hydroxyethyl methacrylate-co-glycidyl methacrylate): Effect of polysaccharide types on structural peculiarities and multifunctionality

Crosslinked poly(hydroxyethyl methacrylate-co-glycidyl methacrylate) hybrids prepared in the same experimental condition by adding various polysaccharides of different chemical types; inulin, Na-alginate, starch and κ-Carrageenan were qualitatively compared. The results are presented to extract relevant physicochemical properties for qualitative comparison of structures within the same synthesis batch. Elastic properties and swelling degree of hybrids can be tightly regulated using different types of polysaccharides and by controlling effective cross-linking density. Addition of κ-Carrageenan to copolymer network increased elastic modulus by 6.2-fold in as-prepared state, but greatest increase in effective cross-link density through swelling was observed in alginate-doped gels. An overshooting effect was observed for alginate-doped hybrids; swelling first to a maximum, followed by a gradual deswelling until equilibrium was reached. Compressive elasticity of hybrids is mainly controlled by type of polysaccharides and cross-linking density but also depends on polymerization temperature. The obtained hybrid gels displayed excellent adsorption performance for methyl orange (MO). The highest adsorption capacity was reached with inulin-doped hybrids. The rate of adsorption was very fast and reached equilibrium with 98.9 % efficiency at about 90 min. This approach to modify the properties of hybrid gels with various types of polysaccharides may find wide use in biomaterials and water purification applications.

Uterine Collagen Cross-Linking: Biology, Role in Disorders, and Therapeutic Implications.

Collagen is an essential constituent of the uterine extracellular matrix that provides biomechanical strength, resilience, structural integrity, and the tensile properties necessary for the normal functioning of the uterus. Cross-linking is a fundamental step in collagen biosynthesis and is critical for its normal biophysical properties. This step occurs enzymatically via lysyl oxidase (LOX) or non-enzymatically with the production of advanced glycation end-products (AGEs). Cross-links found in uterine tissue include the reducible dehydro-dihydroxylysinonorleucine (deH-DHLNL), dehydro-hydroxylysinonorleucine (deH-HLNL), and histidinohydroxymerodesmosine (HHMD); and the non-reducible pyridinoline (PYD), deoxy-pyridinoline (DPD); and a trace of pentosidine (PEN). Collagen cross-links are instrumental for uterine tissue integrity and the continuation of a healthy pregnancy. Decreased cervical cross-link density is observed in preterm birth, whereas increased tissue stiffness caused by increased cross-link density is a pathogenic feature of uterine fibroids. AGEs disrupt embryo development, decidualization, implantation, and trophoblast invasion. Uterine collagen cross-linking regulators include steroid hormones, such as progesterone and estrogen, prostaglandins, proteoglycans, metalloproteinases, lysyl oxidases, nitric oxide, nicotine, and vitamin D. Thus, uterine collagen cross-linking presents an opportunity to design therapeutic targets and warrants further investigation in common uterine disorders, such as uterine fibroids, cervical insufficiency, preterm birth, dystocia, endometriosis, and adenomyosis.

Preparation of EPDM/silicon nanofibers-graphene nanocomposites with enhanced interfacial structure: Highly reinforcing and stabilizing effect

Aiming at designing enhanced interfacial structure, TA@SiNF/PGNs hybrids with hydrogen bonding and π-π conjugation were constructed through wrapping of polyrhodanine on graphene nanosheets (GNs) and self-polymerization of tannic acid (TA) onto SiNF surface. EPDM/TA@SiNF/PGNs nanocomposites were further prepared and the enhanced interfacial interactions were achieved, which promoted good dispersion of the hybrid nanofillers. Compared with EPDM, addition of TA@SiNF/PGNs resulted in a significant increase in mechanical strength and fracture toughness, and the mechanical strength of EPDM/TA@SiNF/PGNs was much better than EPDM/TA@SiNF or EPDM/PGNs due to the increased crosslinking density, indicating remarkably reinforcing and toughening effect of TA@SiNF/PGNs. In addition, the lower compression set and higher contact stress relaxation coefficient were achieved, revealing an improvement of compressive resilience. Moreover, TA@SiNF/PGNs effectively slowed down the deterioration of mechanical properties after thermo-oxidative aging, and the higher retention of crosslinking density and prolonged oxidation induction time confirmed the excellent stabilization effect of TA@SiNF/PGNs.

Effect of novel furan‐based ester reactive diluent on structure and properties of UV‐crosslinked acrylated rapeseed oil

AbstractUnsaturated furan‐based ester (UES) was prepared by green electrosynthesis using a single‐cell setup and inexpensive graphite electrodes. The UES was validated as a reactive diluent for a bio‐based acrylated rapeseed oil (ARO). UV‐light photopolymerization of the bio‐based resin was initiated using a diphenyl (2,4,6‐trimethylbenzoyl)phosphine oxide (TPO) radical photoinitiator. The addition of 20 wt% UES to ARO dropped the resin viscosity by 1.6‐fold. Incorporating 5 wt% UES into the ARO resin increased crosslinking density νe from 1.07 to 1.65 mol/m3. Fourier‐transform infrared spectroscopy (FT‐IR) spectra revealed that ARO has been grafted with UES. The UES functional moieties promote the formation of soft mobile dangling chain end segments in the developed macromolecular network. UV‐cured thermoset polymer reveals distinct morphologies in SEM micrographs, indicating notable structural changes with the addition of UES. A total of 5 wt% UES increased tensile strength from 0.49 to 0.55 MPa and storage modulus from 7.9 to 12.0 MPa at room temperature (22 ± 1 °C). The biodegradability in composting conditions was investigated, and up to 28% of the initial mass was lost after 60 days. UES was shown as to be efficient reactive diluent that can successfully replace fossil‐based acrylate monomers in vegetable oil‐based thermoset polymer synthesis.

Shape memory polyurethanes crosslinked with castor oil-based multifunctional polyols

As both the industry and academia become more focused on biomass-based smart materials, they are attracting a lot of attention. There has been a significant effort in the field of polyurethane (PU) synthesis to replace polyols used in synthesis with bio-derived polyols. Bio-derived polyols have limited application potential for bio-based PU due to their low functionality. Here, we reported castor oil (CO) based multifunctional polyols prepared by grafting thiols such as 1-mercaptoethanol or α–thioglycerol via a facile thiol-ene click reaction method (coded as COM and COT, respectively). Subsequently, bio-based shape memory polyurethanes (SMPU) crosslinked with prepared polyols were synthesized using a 2-step prepolymer method. By confirming the functionality of the synthesized polyols, it was determined that COT has an OH value of 380 mg KOH/g, which is approximately three times that of CO. The successful synthesis of SMPUs was confirmed through chemical structural analysis. It was also proved that the phase separation between the soft and hard segments was limited due to the increase in crosslinking density. As compared to SMPU crosslinked with CO, the mechanical strength of SMPU crosslinked with COT was improved by 80%, while the elongation was decreased by about 26%. As a result of shape memory behavior analysis, it was confirmed that the outstanding SMPU can be synthesized using CO-based multifunctional polyols.

Investigations on thermomechanical and structure properties of pure and wet polyimine networks by molecular dynamics simulations

Polyimine polymer is a kind of covalent adaptable networks with excellent reprocessing and self-healing properties. It has attracted wide attentions in recent years because it can release stress by reversible bond exchange reactions without using catalysts. Since polyimines containing -NH- groups are strongly hydrophilic, the influence of water content on their thermomechanical and structure properties is significant. In this study, we establish atomic models involving diamine and dialdehyde monomers combined with triamine cross-linkers to investigate the thermomechanical and structure properties of polyimine networks. Furthermore, different amounts of water molecules are added into networks to explore the interaction between polyimines and water molecules in aqueous polyimine systems. It is concluded that the increase of cross-linking density and conversion degree will improve the thermomechanical properties of polyimines. The water molecules in the aqueous polyimine systems will reduce glass transition temperature and enhance plasticity. Moreover, the diffusion coefficient is found to positively correlate with water content and temperature. Further researches on the structure of polyimines shows that the radius of gyration of polyimines and the radial distribution function of water molecules around the polyimines are also sensitive to temperature and water content. This investigation provides comprehensive information on different factors affecting the thermomechanical properties of pure and wet polyimine networks and contributes toward predicting the evolution of properties of polyimines under different circumstances.

Temperature-directed fluorescent switchable nanoparticles based on P3OT–PNIPAM nanogel composite

Poly(N-isopropylacrylamide) (PNIPAM) is a unique stimuli-responsive material that exhibits a lower critical solution temperature (LCST). Owing to this characteristic temperature-dependent behavior, PNIPAM has found extensive utilization as an active material in various applications, including sensors, drug delivery, and cellular imaging. Herein, we demonstrate temperature-directed fluorescent switchable nanoparticles based on poly(3-octylthiophene-2,5-diyl) (P3OT) nanoaggregate-embedded PNIPAM nanogel composites (POPNs) featuring different crosslinker contents. The amount of P3OT loading in the nanogel composites can be gradually controlled by varying the crosslinking density of the PNIPAM matrix; this may be attributable to the efficient entrapment of P3OT nanoaggregates in case of a dense polymeric network with the increase in crosslinking density. POPNs exhibit dramatic temperature-dependent fluorescence enhancement (by a factor of 2.11). This is based on the environmental changes affecting fluorescent P3OT chains at temperatures below and above the LCST of the PNIPAM matrix. Based on this temperature-directed fluorescent switching capability, POPN could find potential applications in various fields, including biomedical imaging and sensors.

Vanillin and organosilicon functionalized graphene oxide modified ester resin composite coatings with excellent anti-corrosion properties

Epoxy vinyl ester resin is widely used in the field of corrosion protection because of its excellent corrosion resistance and mechanical properties. However, due to the ease of hydrolysis of the ester group in the ester resin, the barrier ability of the coating is reduced, which will accelerate metal corrosion. The existing literature shows that the use of nano-sheet materials such as graphene oxide (GO) can effectively enhance the barrier properties of the coating. In order to solve the poor compatibility and electrical corrosion phenomenon of GO, in this work, renewable vanillin and silicone with excellent anti-corrosive properties were grafted to GO (APGO) by insertion reaction and D-A reaction. Subsequently, a series of new APGO-based epoxy vinyl ester resin composites with excellent mechanical properties and anti-corrosion properties were prepared by thermal crosslinking polymerization. The results showed that when the additive amount of APGO was 0.1 wt%, the comprehensive performance of the composite was the best: the conductivity (1.9 × 10−13–5.6 × 10−13 S/cm) of the composite was far lower than the critical electrical insulation value (10−9 S/cm), the breaking strength was improved by 38.0 %, the contact angle was increased by 65.7 %, and its anti-corrosion efficiency was up to 99.03 %. After 70 days of immersion in 3.5 wt% salt water, the impedance modulus of the composite at low frequency (Zf = 0.01 Hz) remained 2.23 × 1010 Ω cm2, which was 2 orders of magnitude higher than that of pure epoxy vinyl ester resin (2.43 × 108 Ω cm2). The above results were not only related to the maze effect formed by APGO, but also related to the increased crosslinking density of the system. This work provided a novel strategy for preparing GO-based composites with excellent comprehensive properties.

Computationally developed acrylated epoxidized methyl ester based pressure-sensitive adhesives

Healthcare sector is increasingly demanding pressure-sensitive adhesives (PSAs) to be bio-sourced and biodegradable to replace petro-based PSAs, which are neither renewable nor sustainable. This investigation employs MD simulations to develop bio-based PSAs by replacing low Tg monomers such as 2-ethylhexyl acrylate partially and fully with acrylated epoxidized methyl ester (AEME). The simulation procedures used in this study were verified by comparing specific properties with published literature. The glass transition temperatures of all developed systems show insignificant differences and are well below application as desirable for developing PSA products. Also, these values closely match Fox equation estimates and are in good accord with experimental values. Surface characteristics like surface energy and interfacial adhesion with Al substrate have been predicted. A ∼79 % increment in surface energy with AEME content ensures good substrate wettability and thermodynamic work of adhesion. The interaction energy with Al substrate has been increased by ∼365 % with addition of AEME reflecting improved adhesion strength and enhanced tackiness of the PSA copolymer. AEME provides polar groups like acrylate and hydroxyl groups, which helps improve adhesion strength. The polar groups associated with AEME and increased crosslinking density enhanced mechanical properties of developed PSA systems. This computational research lays the path for developing innovative bio-based PSAs used in adhesive bandages and transdermal patches.

Ageing behaviour and molecular/network structure evolution of EPDM/carbon black composites under compression and in thermal-oxidative environments

EPDM/carbon black (CB) composites were first prepared using sulfur as vulcanizing system, and the mechanical properties of EPDM/CB composites gradually increased with increasing CB content. Compressive stress-thermo oxidative ageing was performed in terms of three compressive stress levels and temperature conditions. During ageing process, two typical reactions of chains scission and crosslinking were deduced. On the one hand, degradation reaction of EPDM molecules occurred and unstable free radicals were produced under thermo/stress effect, which were oxidized to generate oxygenated compounds, leading to the increase of dangling chains ratio and the breakage of CB network with two-phase separation. On the other hand, the active free radicals were further consumed to initiate secondary crosslinking reaction, resulting in increase of crosslinking density and restriction of chains mobility. During the whole ageing process, the crosslinking reaction was dominant over chain scission reaction, resulting in the increase of crosslinking density and poor uniformity of network structure. Consequently, the surface/fractured surface morphologies of aged EPDM showed coarse features with obvious CB aggregates and the rupture of continuous CB network due to interfacial debonding, eventually leading to the remarkable deterioration of mechanical properties and decline of sealing resilience.