Increase In Crosslink Density Research Articles

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.

Investigating the Effect of Curing Activators on the Cure Kinetics of Acrylonitrile–Butadiene Rubber Filled with Graphene Oxide and Reduced Graphene Oxides Nanocomposites

For the first time, acrylonitrile–butadiene rubber (NBR)–graphene oxide (GO) and reduced graphene oxide (rGO) composites were prepared without cure activators: zinc oxide/stearic acid (ZnO/SA) and studied. The vulcanization characteristics of the compounds were systematically studied at 160–190°C, with the aid of rheometer and differential scanning calorimetry (DSC) techniques. NBR revealed rapid curing time (t90) with greater cure rate index compared with NBR–GO/rGO composites for the rheometer measurement. This results were in correspondence with the activation energies Ea (kJ/mol) calculated by Ozawa and Kissinger models of vulcanization kinetics. NBR–rGO obtained reduced t90 and Ea (kJ/mol) than NBR–GO, perhaps due to lower oxygenated groups: epoxide (–C–O–C–), carboxyl (–O–C=O), and hydroxyl (–OH) present. Although, the composites delayed in curing, they significantly recorded high tensile properties with high reinforcing factors than NBR. The order of increasing mechanical properties: NBR < NBR–rGO < NBR–GO followed the same order of increasing crosslinking density. In terms of tensile strength, NBR–GO-1 obtained 62.5% and 18.2% increment than NBR and NBR–rGO-1, respectively. The findings from this study indicate that the absence of ZnO/SA in rubber compounds may slow down curing of rubber–GO/rGO composites and lower networks compared with those containing activators ZnO/SA. However, optimization of ZnO/SA and with desired functional groups on graphene and derivative graphene sheets (GDS) including other proposed factors may enhance the curing speed of rubber–GDS based systems, without compromising their mechanical integrity for advanced applications.

A novel approach in wood waste utilization for manufacturing of catalyst-free polyurethane-wood composites (PU-WC)

In recent decades, due to the increase in environmental awareness and noticeable environmental degradation, the area of wood waste management has attracted increasing attention. The purpose of this study is to develop a new type of highly filled polyurethane wood-composite (PU-WC) by the utilization of large amount of wood wastes without addition of a catalyst. Although wood-plastic composites (WPCs) are widely known, there is still a lack of knowledge about WPCs with a polyurethane matrix. Obtained results showed that composites with a wood content of up to 80% show mechanical properties to commonly used MDF boards. This may be caused proper adhesion between polyurethane matrix and the wooden filler which was confirmed by scanning electron microscopy. The flexural strength of the manufactured composites varied between 19.25 and 25.11 MPa, while the flexural modulus varied between 966 and 1255 MPa. Dynamic mechanical analysis (DMA) of the composites showed a shift of Tgβ (from −70.3 to −52.3 °C) and Tgα (from 94.9 to 117.8 °C) to higher temperatures with increasing filler amount. The observed shift could be interpreted as a reduction of polymer chain mobility and an increase in cross-linking density of composites with a higher amount of wood. This is caused by chemical reactions between isocyanates and reactive hydroxyl groups on the wood surface. Thermogravimetric analysis has shown that PU-WC degrades in one step with Tmax at around 360 °C and T2% significantly reduce with greater addition of wood. Water absorption tests that water absorption strongly depends on wood content and varies between 13 and 80%. Moreover, cyclic water absorption tests showed no considerable difference between the water adsorption of samples after each cycle. Our work suggests that PU-WC can be used successfully as a potential substitute for wood or different types of wood-plastic composites (WPC).

Preparation of Cellulose Hydrogels and Hydrogel Nanocomposites Reinforced by Crystalline Cellulose Nanofibers (CNFs) as a Water Reservoir for Agriculture Use

An effective strategy for the management of available water and fertilizers is imperative to improve agricultural production and food quality, including releasing them sustainably to the soil and plants. Polymeric hydrogels with three-dimensional (3D) networks can absorb ample water and soluble fertilizers without network dissolution. Subsequently, the absorbed water and fertilizers can be released to arid and semi-arid agricultural land to furnish enough moisture and nutrients for plant growth. In this study, carboxymethyl cellulose sodium salt (NaCMC)- and hydroxyethyl cellulose (HEC)-based hydrogels have been synthesized using citric acid (CA) as a crosslinker. The Fourier transform infrared (FTIR) spectroscopy study revealed the formation of hydrogels with porous structures depicted by field emission scanning electron microscopy images. The prepared hydrogels have shown a remarkable swelling ratio of ∼1070% for the hydrogel prepared using NaCMC/HEC: 2/1 and ∼840% for NaCMC/HEC: 3/1 and a reduction in the swelling ratio with increasing crosslinking density. Moreover, crystalline (shown by X-ray diffraction) cellulose nanofibers (CNFs: ∼600 nm), prepared by acid (H2SO4) hydrolysis of cotton fibers, have been used to prepare hydrogel nanocomposites. The evaluation of hydrogel nanocomposites’ mechanical properties (universal testing matching test) depicted an improved tensile strength (16.27 MPa using 0.7% CNFs) compared to that of the hydrogel without CNFs. The soil burial test for biodegradation study of prepared hydrogels revealed soil degradation of hydrogel, confirmed by FTIR analysis and visual appearance. The current study provides comprehensive data establishing the potential of hydrogels for agriculture applications.

Entanglement in Smart Hydrogels: Fast Response Time, Anti‐Freezing and Anti‐Drying

AbstractThe common techniques to improve hydrogel's mechanical properties include increasing crosslinking density and forming crosslinked double‐network hydrogel, which may cause some hydrogels to lose their smart functionalities. Inspired by entanglement‐induced strengthening, a simple approach to introducing hydroxypropyl cellulose (HPC) fibers entangled with different smart hydrogel matrix systems are reported. Different from the conventional methods which hinder the movement of the polymer network, through entanglement with HPC fibers, the composite hydrogel shows both improved Young's modulus and toughness and more importantly improved smart functionalities including response speed, anti‐drying, and anti‐freezing capabilities and cycle stability. This strategy provides a new design rule to fabricate durable and strengthened smart hydrogels which can be used in smart windows, sensors, and soft robots.

Chemical Modification of Human Decellularized Extracellular Matrix for Incorporation into Phototunable Hybrid-Hydrogel Models of Tissue Fibrosis.

Tissue fibrosis remains a serious health condition with high morbidity and mortality rates. There is a critical need to engineer model systems that better recapitulate the spatial and temporal changes in the fibrotic extracellular microenvironment and enable study of the cellular and molecular alterations that occur during pathogenesis. Here, we present a process for chemically modifying human decellularized extracellular matrix (dECM) and incorporating it into a dynamically tunable hybrid-hydrogel system containing a poly(ethylene glycol)-α methacrylate (PEGαMA) backbone. Following modification and characterization, an off-stoichiometry thiol-ene Michael addition reaction resulted in hybrid-hydrogels with mechanical properties that could be tuned to recapitulate many healthy tissue types. Next, photoinitiated, free-radical homopolymerization of excess α-methacrylates increased crosslinking density and hybrid-hydrogel elastic modulus to mimic a fibrotic microenvironment. The incorporation of dECM into the PEGαMA hydrogel decreased the elastic modulus and, relative to fully synthetic hydrogels, increased the swelling ratio, the average molecular weight between crosslinks, and the mesh size of hybrid-hydrogel networks. These changes were proportional to the amount of dECM incorporated into the network. Dynamic stiffening increased the elastic modulus and decreased the swelling ratio, average molecular weight between crosslinks, and the mesh size of hybrid-hydrogels, as expected. Stiffening also activated human fibroblasts, as measured by increases in average cellular aspect ratio (1.59 ± 0.02 to 2.98 ± 0.20) and expression of α-smooth muscle actin (αSMA). Fibroblasts expressing αSMA increased from 25.8 to 49.1% upon dynamic stiffening, demonstrating that hybrid-hydrogels containing human dECM support investigation of dynamic mechanosensing. These results improve our understanding of the biomolecular networks formed within hybrid-hydrogels: this fully human phototunable hybrid-hydrogel system will enable researchers to control and decouple the biochemical changes that occur during fibrotic pathogenesis from the resulting increases in stiffness to study the dynamic cell-matrix interactions that perpetuate fibrotic diseases.

Improvement in alkali‐resistance of basalt fiber‐reinforced polymer by Ti3C2TX (MXene) modified matrix

AbstractFiber‐reinforced polymer (FRP) is a kind of potential construction material due to its low density and strong mechanical properties, but its weak alkali stability impedes its widespread use. MXene nanosheets' two‐dimensional (2D) property makes them an attractive contender as a nanofiller for polymer‐based composites. Here, a basalt fiber‐reinforced polymer (BFRP) laminate with a matrix modified with MXene nanosheets was made using a vacuum‐assisted resin‐transfer molding (VaRTM) process. The flexural strength (530.1 MPa) and flexural modulus (26.7 GPa) of the M0.5/BFRP composite were superior to those of the BFRP laminate, increasing by 39.4% and 4.6%, respectively. According to DMA examination, the MXene/BFRP composite exhibited increased crosslinking density, which could improve stability as well as aid in energy dissipation. As anticipated, the BFRP composites enhanced with MXene nanosheets demonstrated exceptional long‐term stability in a hostile alkali environment. After being submerged in alkali solution at 40°C for 60 days, the M0.5/BFRP's flexural strength reached 398.0 MPa, exceeding that of pristine BFRP that had not been submerged in alkali solution. This study gives an insight into the effect of MXene Ti3C2TX nanosheets modified resin on the durability of BFRP in strong alkali environment.

Thermal and Mechanical Characterization of Epoxy/Polyimide Blends via Postcuring Process

In this study, the effects of polyimide (PI) content and postcuring on thermal and mechanical properties in PI and epoxy (EP) blending systems were investigated. EP/PI (EPI) blending reduced the crosslinking density and improved the flexural and impact strength due to ductility. On the other hand, in the postcuring of EPI, the thermal resistance improved due to the increased crosslinking density and the flexural strength increased by up to 57.89% due to the enhanced stiffness, but the impact strength decreased by up to 59.54%. EPI blending induced the improvement in the mechanical properties of EP, and the postcuring process of EPI was shown to be an effective method to improve heat resistance. It was confirmed that EPI blending induces improvement in the mechanical properties of EP, and the postcuring process of EPI is an effective method for improving heat resistance.

Performance Enhancement of Kaolin/Chitosan Composite-Based Membranes by Cross-Linking with Sodium Tripolyphosphate: Preparation and Characterization.

A new family of environmentally friendly and low-cost membranes based on readily available mineral and polymeric materials has been developed from cast suspensions of kaolin and chitosan using aqueous phase separation and polyethylene glycol as a pore-forming agent. The as-fabricated membranes were further cross-linked with sodium tripolyphosphate (STPP) in order to strengthen the properties of the obtained samples. The functional groups determined by FTIR and EDX confirmed that the reaction occurred. A detailed study of the effects of cross-linking time on the physicochemical, surface and permeation properties showed that a 30-minute reaction enabled the composite membrane to be stable in acidic media (up to pH 2) and increased the mechanical strength twofold compared to the non-cross-linked membrane. A similar morphology to that generally observed in polymeric membranes was obtained, with a sponge-like surface overlaying a finger-like through structure. The top layer and cross-section thicknesses of the membranes increased during STPP post-treatment, while the pore size decreased from 160 to 15 nm. At the same time, the molecular weight cut-off and permeance decreased due to the increase in cross-linking density. These results observed in a series of kaolin/chitosan composite membranes showed that STPP reaction can provide control over the separation capability range, from microfiltration to ultrafiltration.

Co‐catalytic system design for deriving reactive diluent to construct robust benzoxazine resin with microphase‐separated structure

AbstractExploitation a facile and effective strategy for preparing benzoxazine resins with outstanding processability and robust mechanical properties still exists a challenge. In this work, a co‐catalytic concept was proposed to fabricate high‐performance benzoxazine resin by employing curing agent to derive reactive diluent to construct microphase‐separated system. Given on the design, the reactive diluent dissolved solid benzoxazine into a low‐viscosity solution, after which the curing agent presented a catalytic effect on diluent and benzoxazine to optimize the curing crosslinking reactions. As a result, it not only increased crosslinking density for a stable mechanical network, but also induced a microphase‐separated structure to effectively dissipate energy for a strong yet tough resin system, as proved by Fourier transform infrared, differential scanning calorimetry, and dynamic mechanical analyses measurements. Moreover, the as‐prepared modified benzoxazine resin showed great potential to fabricated composites with glass fiber, in which the values of tensile strength, elongation at break, and toughness presented an improvement of 212.1%, 106.8%, and 75.0% compared to composite with pristine PH‐ddm and glass fiber, respectively. These results suggested an effective path to improve the processability and overall mechanical properties of benzoxazine resins, opening a new strategy to develop high‐performance benzoxazine materials.

The study of composition-properties relationships for composite hydrogels based on poly(methacrylic acid) and high concentrations of MFI zeolite

High concentrations of hydrophobic MFI zeolite (26.0–51.3 wt%) were successfully embedded in poly(methacrylic acid) (PMAA) network in simple, one-pot synthesis of PMAA-MFI composite hydrogels. The effects of zeolite concentration regarding pure PMAA xerogel, for all of the investigated properties (primary structural parameters, morphological properties, water swelling ability, thermal degradation mechanism and stability, and mechanical properties) were determined and discussed. The PMAA-MFI composite hydrogels had remarkably higher density than PMAA xerogel (1660/1420 kg m−3), higher crosslinking density (29/1.0 × 10−4), improved mechanics in the dry and swollen state (up to 4.9 times higher storage modulus) and lower swelling degree (42/420 g g−1), average molar mass between the network crosslinks (3.6/110 × 104 g mol−1), and distance between the macromolecular chains (64/710 nm). Despite high zeolite concentration, the composites kept porous hydrogel structure with uniformly dispersed zeolite particles. FTIR spectra disclosed the existence of functional groups of PMAA network and MFI zeolite that interacted mutually and led to increased crosslinking density. The effect of zeolite concentration on the thermal degradation mechanism was established. The composition-properties correlations were determined and described by the adequate linear or power law equations revealing the additive nature of the composites and the fractal structure of the networks. These correlations enable the achievement of desired properties by simple adjustment of the initial composition, i.e. zeolite concentration. Therefore, this work presents the base for further development of tailor-made PMAA-MFI composite hydrogels aimed for specific application.