Higher Crosslinking Density Research Articles

Improving the performance of polyacrylate latex binders for water-based inks through the application of reactive emulsifiers and nanosized zinc oxide

The poor redissolution and low ethanol resistance stability of room temperature self-cross-linking polyacrylate latexes (RTSPLs) made from conventional emulsifiers are the main obstacles for their industrial application in water-based inks. To address these issues, in this study, anionic SR-10 (allyloxy polyoxyethylene ammonium sulfate) /nonionic ER-10 (allyloxy fatty alcohol polyoxyethylene ether) dual-reactive composite emulsifier is developed to replace the conventional 2A1 (sodium dodecyl diphenyl ether disulfonate) /TX-30 (alkyl phenol polyoxyethylene ether) non-reactive composite emulsifier for the synthesis of polyacrylate latexes, and a certain mass of nanosized zinc oxide (ZnO) was added into as-prepared latexes as an ionic cross-linking agent to partially replace the cross-linking monomer of diacetone acrylamide (DAAM). Properties of the latexes and the latex films, with emphasis on redissolution, stability against ethanol, and adhesion on biaxially oriented polypropylene (BOPP) and polyethylene (PE) substrates, were evaluated to study the effect of the reactive emulsifiers and the nanosized ZnO. The application of the reactive composite emulsifier eliminates the disadvantages associated with the desorption from the latex particles and migration during film formation of the non-reactive emulsifier, thus improving the ethanol resistance stability of latexes and adhesion of their inks on BOPP substrate. The introduction of a certain amount of nanosized ZnO to replace DAAM in equimass amounts improves the redissolution but reduces the cross-linking density and water resistance of the latex film. Surprisingly, the addition of nanosized ZnO substantially improves the ethanol stability of latexes. When ZnO replaces DAAM, accounting for approximately 1 wt% of the total monomers, not only the prepared latex exhibits excellent alcohol dilution stability, but also the latex film has a relatively high cross-linking density, good redissolution, and good comprehensive properties. These findings provide an effective, yet simple way to balance the redissolution and high cross-linking degree of latex films while ensuring that the latexes have good ethanol resistance stability.

Dielectric Properties of Benzocyclobutene-Based Resin: A Molecular Dynamics Study.

Benzocyclobutene (BCB)-based resins have garnered considerable attention because of their remarkable dielectric properties and thermal stability. However, in molecular dynamics (MD) simulations, progress in BCB-based resin research has yet to keep pace with experimental advancements, resulting in a shortage of theoretical underpinnings at the molecular level. This study focuses on a novel homopolymer, poly(2-(4-benzocyclobutenyl)-divinylbenzene(DVB-S-BCB)), and devises an interactive methodology suitable for BCB-based resins. We implemented a Python script for the joint relaxation method to construct a three-dimensional model of the cured polymer using MadeA and LAMMPS. We conducted MD simulations to investigate how the cross-linking degree and resin molecular weight influence the dielectric properties of the cured polymer. Furthermore, we analyzed the thermodynamic properties through simulation. The results illustrate that augmenting the cross-linking degree and resin molecular weight results in a higher cross-linking density and reduced free volume, thereby increasing the dielectric constant of the resin. The cross-link density does not increase indefinitely with molecular weight, and after a certain threshold is reached, it cannot have a significant effect on the dielectric constant. The degree of cross-linking exerts a more pronounced impact on the dielectric constant than the molecular weight of the resin. In addition, the simulation results denote the excellent thermodynamic properties of the cured polymer. This study also examines the dielectric and thermodynamic properties of the resin samples that were experimentally prepared. The obtained data successfully confirm the reliability of the simulation results. This study offers novel insights for future simulation research on benzocyclobutene-based resins. Additionally, it provides theoretical support for exploring experimental work on low-dielectric materials in the electronic field.

Investigating the effect of methacrylic acid on the properties of waterborne epoxy-acrylate core-shell emulsion, film and coating

Waterborne coating has recently become a trend in research, with extensive studies focusing on waterborne epoxy-acrylate (WEA) emulsion. However, the understanding of the role of methacrylic acid (MAA) in the core-shell structure, affecting film and coating performance, is still limited. Here, we investigate the effect of MAA addition on the properties of the WEA core-shell emulsion, film and coating. The WEA core-shell emulsion was synthesized through semi-continuous emulsion polymerization and subsequently cast into WEA film. Two types of crosslinking systems were established by introducing MAA to either the shell layer (interlayer crosslinking) or the core layer (intralayer crosslinking). The interlayer crosslinking provides a high crosslinking density (7.01 × 10−4 mol cm−3), involving the crosslinking of polymer chains between the core and shell layers. Consequently, the film has a compact structure and high modulus (489 MPa) but low elongation at break (3.20 %). Conversely, the intralayer crosslinking has a low crosslinking density (1.59 × 10−4 mol cm−3). Hence, the film has a loose structure and low modulus (0.38 MPa) but high elongation at break (225 %). This occurs because it involves crosslinking with the polymer chains within the same layer, resulting in reduced compatibility between the layers. The inclusion of MAA enhances the clarity in discerning two glass transition temperatures (Tg). Lastly, the stability (shelf-life) of the WEA emulsion remains unaffected by the MAA, with the decisive factor being the presence of the oxirane ring in the Epoxy (EP). We believe that this finding can significantly contribute to a better understanding of the role of MAA in crosslinking systems within WEA core-shell coatings for researchers.

Hydrosilylation Adducts to Produce Wide-Temperature Flexible Polysiloxane Aerogel under Ambient Temperature and Pressure Drying.

Despite incorporation of organic groups into silica-based aerogels to enhance their mechanical flexibility, the wide temperature reliability of the modified silicone aerogel is inevitably degraded. Therefore, facile synthesis of soft silicone aerogels with wide-temperature stability remains challenging. Herein, novel silicone aerogels containing a high content of Siare reported by using polydimethylvinylsiloxane (PDMVS), a hydrosilylation adduct with water-repellent groups, as a "flexible chain segment" embedded within the aerogel network. The poly(2-dimethoxymethylsilyl)ethylmethylvinylsiloxane (PDEMSEMVS) aerogelis fabricated through a cost-effective ambient temperature/pressure drying process. The optimizedaerogel exhibits exceptional performance, such as ultra-low density (50mg cm-3), wide-temperature mechanical flexibility, and super-hydrophobicity, in comparison to the previous polysiloxane aerogels. A significant reduction in the density of these aerogels is achieved while maintaining a high crosslinking density by synthesizing gel networks with well-defined macromolecules through hydrolytic polycondensation crosslinking of PDEMSEMVS. Notably, the pore/nanoparticle size of aerogels can be fine-tuned by optimizing the gel solvent type. The as-prepared silicone aerogels demonstrate selective absorption, efficient oil-water separation, and excellent thermal insulation properties, showing promising applications in oil/water separation and thermal protection.

The effect of composite curing agent ratio on the photooxidative aging behavior of epoxy asphalt based on molecular dynamics simulation

In order to explore the effect of composite curing agent ratio on the photooxidative aging behavior of epoxy asphalt with an acidic composite curing system, three curing agent ratios of epoxy asphalt were prepared to obtain different cross-linking network densities. The prepared epoxy asphalt was subjected to photooxidation aging for 240 h at 60 ℃. Fourier transform infrared (FTIR) and elemental analysis tests were conducted to determine the evolution of chemical components during photooxidative aging. Based on the chemical components before and after aging, molecular models of photooxidation aged epoxy asphalt with different curing agent ratios were constructed. The mean square displacement (MSD) of oxygen atoms and the oxygen uptake of each component were calculated to study the diffusion behavior of oxygen atoms and the oxidation degree of each component under various cross-linking networks. Glass transition temperature (Tg) and interaction energy were determined to characterize the thermodynamic properties and interaction between asphalt phase and epoxy resin phase of epoxy asphalt before and after aging. The radial distribution function (RDF) was determined to simulate the distribution of asphaltene and epoxy resin crosslinked networks in different cross-linking networks. The results show that the formation of carbonyl groups, alcohol hydroxyl groups, and the fracture of methylene groups was observed during the photooxidative aging process of epoxy asphalt. The rise in the proportion of anhydride curing agents improved the stability of the chemical components in epoxy asphalt under photooxidation aging. High cross-linking density and methylene fracture weakened the diffusion ability of oxygen atoms in epoxy asphalt due to a reduction in free volume. In addition, photooxidation aging had a negative impact on the low-temperature performance and interaction between asphalt phase and epoxy resin phase of epoxy asphalt. However, a high content of acid anhydride alleviated the damage of photooxidation aging to low-temperature performance. Photooxidation aging developed the polar functional groups of epoxy asphalt, promoting the stacking of asphaltene under a high content of dicarboxylic acid curing agent, while breaking the stacking of asphaltene under a high content of acid anhydride curing agent.

Biocompatible and antimicrobial chitosan/PVP/PEO/PAA/AgNP composite hydrogels synthesized by e-beam cross-linking

Novel biocompatible composite hydrogels with good elastic and antimicrobial properties have been fabricated by e-beam cross-linking using chitosan and water-soluble polymers mixed with commercial silver nanoparticles (AgNP). Hydrogels having different formulations were characterized by rheological, swelling, FTIR, SEM, and biodegradation measurements. The network structure, biocompatibility, and antimicrobial properties were evaluated as well. The composite hydrogels showed higher stability and absorb large amounts of fluids specific to an infected wound without losing structural integrity. The rheological, SEM, and network structure results demonstrate that at above 0.1 mg/mL AgNP, hydrogels with high cross-linking density are obtained. The in vitro response of fibroblasts proved the high biocompatibility of the hydrogel's composites. The antimicrobial activity is directly influenced by the amount of AgNP and cross-linking degree of the hydrogel. Significant antimicrobial activity was recorded against Gram-negative bacteria, while for the Gram-positive ones, the growth inhibition seems to require a decrease of the cross-linking degree.

Curing Kinetics and Structure-Property Relationship of Moisture-Cured One-Component Polyurethane Adhesives

Moisture-curable polyurethane (PU) adhesives have been exploited in the automotive industry because of their usability, non-toxicity without the use of volatile organic compounds (VOC), outstanding solvent resistance, and adhesiveness. However, there has been a lack of quantitative and comprehensive analyses related to the chemical and thermomechanical properties of moisture-curable PU adhesives depending on the applied curing conditions. Herein, we systematically investigated the effects of curing conditions, including relative humidities (25, 35, 45, 55, 65, and 75%RH) and curing duration (0, 0.25, 0.5, 1, 2, 3, 4, 5, 6, and 7 days), on the structure–property relationships of moisture-cured PU adhesives. As the relative humidity increased, the chemical reaction of the PU adhesives accelerated, and they exhibited a high crosslinking density and storage modulus. However, even prolonged curing time and higher relative humidity did not lead to a continuous enhancement in the mechanical properties of the PU adhesive. After a sufficient curing time, the storage modulus of the PU adhesive reached saturation, and the PU adhesives cured above 65%RH demonstrated a comparable saturated storage modulus. This structure–property relationship of PU adhesives will provide fundamental understanding and insights for quality control and optimization of processing time in the industry.

The Coordination Nanocages-Integrated Polymer Brush Networks for Flexible Microporous Membranes with Exceptional H2 /CO2 Separation Performance.

The emergence of polymers with intrinsic microporosity provides solutions for flexible gas separation membranes with both high gas permeability and selectivity. However, their applications are significantly hindered by the costly synthetic efforts, limited availability of chemical systems, and narrow window of microporosity sizes. Herein, flexible mixed matrix membranes with tunable intrinsic microporosity can be facilely fabricated from the coordination assembly of polymer brushes and coordination nanocages. Polymer brushes bearing isophthalic acid side groups can coordinate with Cu2+ to assemble into polymer networks crosslinked by 2nm nanocages. The semi-flexible feature of the polymer brush and the high crosslinking density of the network prevent the network from collapsing during solvent removal and the obtained aerogels demonstrate hierarchical structure with dual porosity from the crosslinked polymer network and coordination nanocage, respectively. The porosity can be facilely tuned via the amount of Cu2+ by regulating the network crosslinking density and nanocage loadings, and finally, optimized gas separation that surpasses Robeson upper bound for H2 /CO2 can be achieved. The coordination-driven assembly protocol paves a new avenue for the cost-effective synthesis of polymers with intrinsic microporosity and the fabrication of flexible gas separation membranes.

High-Tg bio-based polybenzoxazine derived from renewable anethole and furfurylamine

The exploration of high-performance benzoxazine thermosets from easily processable monomers is still a challenge with the enhancement on the concept of sustainable development from worldwide. In this contribution, a new bio-based benzoxazine monomer (DA-FBz) with two functionality was successfully prepared from renewable trans-anethole and furfurylamine. DA-FBz showed a low melting temperature (Tm) of 60 °C and could be easily converted into polybenzoxazine (poly(DA-FBz)) through ring-opening thermal polymerization. The curing behavior was characterized by differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) analysis. After thermal curing, the obtained poly(DA-FBz) exhibited high thermal stability with a 5 wt% loss temperature of 404 °C. In particular, this thermoset showed a high glass transition temperature of 334 °C due to the high crosslinking density constructed from the reactive furan structure during thermal polymerization. In addition, poly(DA-FBz) also exhibited high thermal mechanical strength with a storage modulus of 3 GPa at room temperature, which was still up to 1.2 GPa at 300 °C. This highly crosslinked framework also resulted into a low thermal expansion and low water absorption. All these results indicated this polybenzoxazine would be potential candidate used in high-performance engineering applications.

Study on reduction potential of curing agent in sustainable bio-based controlled release coatings

Sustainable polyurethane coated fertilizer is attracting much attention. Reducing the amount of curing agent is promising to improve the bio-content and biodegradability of coating material. In order to achieve the aim, the research attempted to select palm oil with balanced unsaturation as feedstock, hydrochloric acid as both catalyst and nucleophilic reagent for bio-polyols with low hydroxyl values by the epoxidation/ring-opening reaction. The chemical structures of palm oil-based polyols and properties of polyurethanes were tailored by controlling hydrochloric acid amount, and the effect was investigated by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), etc. With the increase of hydrochloric acid amount, hydroxyl value, functionality and viscosity of palm oil-based polyol were gradually increased. The resultant coatings prepared by the palm oil-based polyol with hydroxyl value exceeding 120 mg KOH g−1 and functionality of more than 2 had good macroscopic performances including controlled nutrient release property as a result of high crosslinking density. The optimum amount was 10%, for the viscosity of the relative palm oil-based polyol was beneficial to the coating process. The bio-content of the coating was 67% and the nitrogen release duration of the coated urea was 73 days at the coating rate of 7% even without paraffin. Overall, the way offers a bio-based platform to create a variety of polyurethane coated fertilizer that promises economic and environmental benefits.

Low defect and high mechanical properties POSS copolymerization phthalonitrile resin prepared by powder hot isostatic pressing

The high melting point of high-temperature resistant phthalonitrile resin is often prone to defects in traditional hot melt manufacturing. And its high cross-linking density leads to poor toughness of the resin. In this work, we report for the first time a novel densifying processing, powder hot isostatic pressing (PHIP), for phthalonitrile resin with low defect and high mechanical performance. The bending strength and impact strength of the pure phthalonitrile resin (PBAPN) by PHIP reached to 108.5 MPa and 9.1 kJ·m−2, respectively, increasing by 186.3% and 405.6% than PBAPN by hot melt method. The epoxycyclohexyl polyhedral oligomeric silsesquioxane (EP-POSS) with excellent heat resistance was used to achieve synchronous improvement of thermal and mechanical properties of phthalonitrile resin. The bending strength and impact strength of the phthalonitrile resin containing 1 wt% POSS (PBAPNPOSS-1) further increased to 120.1 MPa and 13.0 kJ·m−2. In addition, the glass transition temperature of PBAPNPOSS-5 increased by 40 °C compared with PBAPN.

Octylamine regulating the mechanical robustness of natural rubber by involving in the construction of crosslinking network

The formation of three dimensional network structure is critical in determining mechanical properties of natural rubber (NR). Consequently, it is vital to regulate crosslinking network of NR by controlling vulcanization process. Inspired by our previous studies on contribution of non-rubber components (NRCs) to the excellent properties of NR, we find octylamine in NRCs decreases the activation energy (Ea) of vulcanization from 82.73 kJ/mol to 44.34 kJ/mol, thereby reducing vulcanization time from 18.67 min to 2.71 min. From microscopic perspective, octylamine tends to coordinate with zinc ions to improve dispersion of ZnO in NR. And octylamine promotes ring-opening reaction of S8 to favor formation of polysulfide intermediates.Therefore, the incorporation of octylamine remarkably improves vulcanization efficiency, which contributes to the formation of a more homogeneous network with higher crosslinking density, enhancing remarkably the strength and toughness of NR. As a result, the tensile strength and fracture energy of samples are as high as 31.15 MPa and 68.88 kJ/m2, respectively. In addition, even with a 60 % reduction in ZnO content, the NR samples still maintain high vulcanization efficiency and excellent mechanical properties after the addition of octylamine, which provides a green and feasible way to alleviate the environmental pollution caused by ZnO.

Impacts of BaO additives on the mechanical, optical and radiation shielding properties of BaO–K2O– CoO–Al2O3–B2O3 glasses

This article reports the influence of barium oxide (BaO) on mechanical and radiation protection characteristics of BaO–K2O– CoO–Al2O3–B2O3 glass. The obtained results confirmed the enhanced the elastic moduli, confirming a high cross-linked density, high impact resistance, and toughness of the network, with the good mechanical stability of samples with further additives of BaO. In detail, with increasing BaO contents, it is observed that the shear modulus increased from 33.8 GPa reaching 37.7 GPa (increased by about 11.5%), while the longitudinal modulus enhanced from 100.5 GPa up to 117.4 GPa (enhanced by ⁓ 16.8%), besides Young's modulus augmented from 84.4 GPa to 95.3 GPa (augmented by ⁓ 13%), and bulk modulus is increased from 55.4 GPa reaching 67.2 GPa (increased by ⁓ 21.3%). These enhancements in the elastic moduli are attributed to the increased tetrahedral units (BO4 and AlO4 units) inside the glass matrix with increasing BaO additives. On the other hand, with increasing BaO, optical band gaps increase from 3.07 eV to 3.58 eV, and ligand field strength values decrease from 3494 cm−1 to 3273 cm−1. Furthermore, the addition of BaO reduces the linear and nonlinear refractive indices. Moreover, the obtained radiation shielding parameters were studied and compared to those of well-known shielding materials. The comparison confirmed that the glass specimen with the highest barium oxide content has better radiation shielding ability than others and is suitable for radiation shielding applications.

Stoichiometric effect on the structural transformation and spatial variation of polyamide reverse osmosis membranes: A molecular dynamics study

Reverse osmosis based on polyamide membranes is currently the leading technology for desalination and water purification. However, the spatial variation of polyamide architecture, especially regarding stoichiometric criteria at the real reaction interface during membrane fabrication, is poorly understood. Here we conducted equilibrium molecular dynamic simulations, mimicking the practical construction of polyamide matrices using a variety of monomer component stoichiometries, to investigate resulting differences in both the morphological transformation and mass transport through the polymer network. Our simulations indicated that an equal stoichiometry of the reactive functional groups predominantly resulted in favorable polyamide matrix qualities such as a high crosslinking density, uniform pore size distribution, and adequate layer compactness. Despite the thickness-dependent water diffusion across the active layer, an analysis of polyamide membrane density revealed depth heterogeneity, particularly for membranes constructed under unequal concentrations. Consequently, uncontrollable defects are likely to be created, as evidenced by the partial penetration of Na+ across such membranes. In addition, the residual functional groups in the polyamide matrices (–COOH and –NH2) influenced the transport behavior of ions near the membrane surface. Overall, our simulations provide a visual platform for understanding the stoichiometry-induced relationship between membrane structure and performance, which may guide the future design of defect-free and scaling-resistant reverse osmosis membranes.

A self-healing and anticorrosion epoxy coating based on the novel polymer filler containing a side-linked grafting 2-mercaptobenzothiazole

The healing mechanism of traditional self-healing coatings can be divided into “extrinsic” and “intrinsic” types according to the reactants, among which intrinsic restorations can be recycled multiple times and have great potential for applications. But epoxy resin is difficult to achieve intrinsic healing process through secondary bonding and reaction between polymers owing to the high chain rigidity and cross-linking density. In this study, a composite coating combining both “extrinsic” and “intrinsic” healing methods has been fabricated by adding a novel polymer filler (MBT-PGMS), which was synthesized via grafting copolymerization of glycidyl-methacrylate, styrene, methyl-methacrylate and 2-mercaptobenzothiazole (MBT). Multiple analytical techniques have been used to characterize the structure and properties of fillers, and the effect on the anti-corrosion performance and self-healing efficiency of epoxy coatings in 3 wt.% NaCl solution has been studied by electrochemistry measurements and mechanical analysis. Results indicated that the intact coating containing MBT-PGMS (MBT-PGMS/EP) showed prominent corrosion resistance during the immersion of 90 days. Once the coating was scratched, the impedance of MBT-PGMS/EP increased gradually with increasing the immersion time, and reached the optimal performance as the filler amount at 5 wt.%, while the impedance modulus was about 2.8 × 108 Ω cm2 after immersion for 144 h. A dynamic crosslinking model in MBT-PGMS/EP has been proposed to explain the self-healing mechanism.

Fabrication of UV-curable waterborne polyurethane coatings with self-cleaning, anti-graffiti performance, and corrosion resistance

A novel UV-curable anti-smudge coating based on waterborne polyurethane (WPU) was constructed by using polydimethylsiloxane (PDMS) as hydrophobic material and pentaerythritol triacrylate (PETA) as UV-curable cross-linking agent. At the same time, the effect of PDMS loading and the cross-linking density on the transparency, hydrophobicity, as well as graffiti resistance of the coating, were investigated. Due to the high cross-linking density, the obtained coating possessed desirable optical transparency. The synergistic effect of hydrophobic side chains and dense cross-linking imparts the coating favorable repellency to pollutant liquids such as water, coffee, muddy water, ink, hexadecane, ethanol, fingerprint liquid and others. The coating showed good anti-graffiti properties on a variety of substrates, including glass, tinplate, ceramics, wood, and paper sheet. In addition, aside from protecting the substrate against strong acid, alkali, and salt solutions, the coatings remained stain resistant despite being folded and curled. This study provides a new strategy for the design of WPU UV-curable anti-smudge coatings.

Characterization of Heat-Resistant Insulating Impregnating Varnish Based on Bismaleimide/Diamine Copolymer

With the development of high-voltage electrical equipment towards the direction of higher power density and higher voltage level, it will resulting in the temperature-resistant grade of insulating dip varnish. Bismaleimide (BMI) resin used as the matrix resin of dip varnish solution is widely applied due to its good aging resistance, mechanical properties and dielectric properties. Due to the imide ring structure in BMI resin structure, the bonding energy of chemical bonds in the molecule is higher. The resin reacts less at lower temperatures, resulting in the difficulty of forming and processing. The high crosslinking density of condensates results in unsatisfactory mechanical properties of BMI resin and presents a poor toughness. Therefore, this paper uses Michael addition reaction to prepare branched resin with large free volume from binary amine and BMI resin, and explores various properties of its cured products. The results show that: Using different kinds and different contents of binary amines, its insulation performance was further improved. MT-cured sample had the best comprehensive performance, with a minimum dielectric constant of 3.24. The minimum dielectric loss of BAPP cured sample was 0.00135. The maximum volume resistivity of FDA sample was 2.46×1015 Ω·m and the maximum breakdown field strength of BAPP sample was 29.83 kV/mm; The mechanical properties were significantly improved, and the maximum mechanical strength of the MT samples reached 174.63 MPa.

Sustainable and recyclable thermosets with performances for high technology sectors. An environmental friendly alternative to toxic derivatives

This study focuses on the development of environmentally friendly and chemically recyclable thermosets using or a renewable based monomer, the triglycidyl ether of phloroglucinol (TGPh), or a commercial non-toxic tris(4-hydroxyphenyl) methane triglycidyl ether (THPMTGE) monomer. The recyclable polyester thermosets were prepared by crosslinking the two monomers with hexahydro-4-methylphthalic anhydride (HMPA) or methyl nadic anhydride The TGPh-based formulations exhibited lower reaction temperatures and narrower reaction intervals. Additionally, these systems showed higher tan δ values (189°C–199°C), higher crosslinking densities (7.6–7.8 mmol cm−3) and compact networks, crucial for high-performance industries. Tensile tests demonstrated the remarkable mechanical properties of the thermosets, including high Young modulus (1.3–1.4 GPa), tensile stress (55–69 MPa), and an elongation at break around 3%–8%. Moreover, the thermosets exhibited complete dissolution at a temperature of 170°C, with depolymerization times of approximately 2.5 h for TGPh-based resins and 4.5 h for THPMTGE-based formulations. In conclusion, this study shows that sustainable and eco-friendly thermosets with excellent physico-chemical and thermo-mechanical properties, low hydrophilicity, and rapid dissolution capacity can be developed. These thermosets offer a viable alternative to non-recyclable and toxic resins in high-end industrial applications.

Tuning the properties of bio-based epoxy resins by varying the structural unit rigidity in oligomers and curing procedures

Bio-based epoxy resins, which will replace petroleum-based ones, are gaining attention. In this work, three magnolol-based epoxy oligomers with varied structural unit rigidities (biphenyl, monophenyl, and aliphatic chains) were synthesized. Both the processability and the reactive activation of curing systems improved as structure unit rigidity decreased. “First-time curing resins” had only an epoxy-amine curing network, while “second-time curing resins” had dual curing networks. The structural unit rigidity regulated the thermal properties of first-time curing resins, which decreased with decreasing rigidity. However, P-MHQ-EP-n/DDM-1 had better mechanical properties than DGEBA/DDM, e.g., its impact strength (6.2 kJ/m2 vs. 4.5 kJ/m2) increased by 37.8%, indicating that moderate structural unit rigidity allows for good deformation and absorbs impact energy due to chain mobility. The second-time curing resins with increased crosslinking sites had better heat resistance (with a Tg increase of over 71.6%), thermal stability, and char residue in comparison to the first-time curing resins. More impressively, P-MBP-EP-n/DDM-2 and P-MHQ-EP-n/DDM-2 obtain a LOI values greater than 39.0% and UL 94V-0 ratings because they have high-rigidity structural units and high crosslinking densities. In conclusion, well-balanced biobased epoxy resins could be made by regulating the structure-unit rigidity of epoxy oligomers and curing procedures.

Insights into network rearrangement of konjac glucomannan gel induced by post-gelation soaking

Post-gelation soaking is a critical step in gel-based foods processing, which plays an important role in the physicochemical properties of konjac glucomannan (KGM) gels, and the related structural changes are yet less explored. Here we compared the gel network, KGM aggregates and molecular chemistry of pre-soaking (PS), hot water soaking (HWS), hot acid soaking (HAS) and cold acid soaking (CAS) gels. Our findings indicated that post-gelation soaking promoted the network rearrangement, resulting in greater elasticity and higher cross-linking density. The average pore size of the network of soaking gels was twice that of PS gel, and the fibril diameter of HWS, HAS and CAS gels increased to 46.86 ± 9.18 nm, 46.12 ± 11.76 nm and 38.99 ± 6.12 nm, respectively, contributing to the higher degree of anisotropy in gel network. Post-gelation soaking also favored molecular aggregation by increasing df and decreasing Rg of KGM aggregates. Molecular chemistry analysis suggested that the molecular structure of KGM remained unchanged, and the strengthened hydrogen bonds and hydrophobic interactions improved the compactness of aggregate structures. Moreover, heating accelerated the rearrangement of gel network, and the presence of acid enhanced its heterogeneity. These findings shed light on the structural changes that occur during post-gelation soaking, which can help to optimize the processing conditions of gel-based foods.