High Degree Of Crosslinking Research Articles

Robust loose nanofiltration membrane with fast solute transfer for dye/salt separation

In today's energy crisis and shortage of resources, resource recycling on the premise of saving energy is a crucial topic. Large volumes of wastewater containing dye/salt mixtures in the textile industry are generated. In the process of treating textile wastewater, a membrane with better solute transport properties can be used to selectively remove solutes at constant energy input to save energy. Moreover, due to the challenging environment of typical textile wastewater, the membrane also needs to have a certain robustness. In this study, β-cyclodextrin and mussel-inspired polydopamine were combined using host-guest chemistry and then cross-linked by glutaraldehyde to form a robust loose separation layer. The results show that the membranes obtained by this process have a dye rejection greater than 99% and a salt rejection of about 16%. With the high degree of crosslinking at the surface, the membrane was found to exhibit excellent robustness in corrosive media at different pH values. Due to the high degree of cross-linking of the surface, the modified membrane also has good anti-fouling and anti-bacterial properties. Filtration using different concentrations of dye/salt mixed solutions demonstrated the stability of the membrane for filtration in highly concentrated salt solutions. In addition, a long-term stability test proved that the membrane operates stably for more than 60 h, maintaining its selectivity. This membrane with excellent robustness can provide technical guidance and theoretical support for the large-scale application of loose nanofiltration membranes.

Preparation, characterization, and foaming properties of soy protein nanoparticles by the cross-linking reaction induced by microbial transglutaminase

Native soy proteins have limited surface properties, but fortunately, it is expected that their foaming behaviors can be improved through the enzymatic cross-linking method. In this paper, by using the cross-linking method with microbial transglutaminase (mTG) as the catalyst, soy protein isolate (SPI), soy β-conglycinin (7S), and soy glycinin (11S) nanoparticles (NPs) were prepared in the molten state of the protein induced by dithiothreitol (DTT). We compared the structural characteristics of these nanoparticles, including particle sizes, morphologies, zeta potentials, surface hydrophobicities, changes of spatial structure, and cross-linking degrees. In addition, their foaming properties, including foamabilities, foam stabilities, and bubble diameters, were also tested. The results show that there are no significant differences in the foamabilities between the native soy proteins and their nanoparticles with similar initial foam heights. However, it is found that 11S NPs have enhanced foam stabilities with longer half-lives and smaller changes in bubble size, which is closely related to their high wettability and cross-linking degree. This study may provide references for the application of soy protein nanoparticles as new foam stabilizers to replace the traditional foaming agents in the food industry.

Covalent adaptable networks using boronate linkages by incorporating TetraAzaADamantanes.

Boronic esters prepared by condensation of boronic acids and diols have been widely used as dynamic covalent bonds in the synthesis of both discrete assemblies and polymer networks. In this study we investigate the potential of a new dynamic-covalent motif, derived from TetraAzaADamantanes (TAADs), with their adamantane-like triol structure, in boronic ester-based covalent adaptable networks (CANs). The TetraAzaADamantane-boronic ester linkage has recently been reported as a more hydrolytically stable boronic ester variant, while still having a dynamic pH response: small-molecule studies found little exchange at neutral pH, while fast exchange occurred at pH 3.8. In this work, bi- and trifunctional TetraAzaADamantane linkers were synthesised and crosslinked with boronic acids to form rubber-like materials, with a Young's modulus of 1.75MPa. The dynamic nature of the TetraAzaADamantane networks was confirmed by stress relaxation experiments, revealing Arrhenius-like behaviour, with a corresponding activation energy of 142 ± 10kJ/mol. Increasing the crosslinking density of the material from 10% to 33% resulted in reduced relaxation times, as is consistent with a higher degree of crosslinking within the dynamic networks. In contrast to the reported accelerating effect of acid addition to small-molecule TetraAzaADamantane complexes, within the polymer network the addition of acid increased relaxation times, suggesting unanticipated interactions between the acid and the polymer that cannot occur in the corresponding small-molecules analogues. The obtained boronate-TetraAzaADamantane materials were thermally stable up to 150°C. This thermal stability, in combination with the intrinsically dynamic bonds inside the polymer network, allowed these materials to be reprocessed and healed after damage by hot-pressing.

Combined effects of NaOH, NaCl, and heat on the characteristics of ovalbumin gel and the exploration of the mechanism of transparent gel formation

Salted preserved eggs are made using poultry eggs under the combined action of NaOH, NaCl, and heat. To elucidate the main basis and mechanism of the formation of salted preserved egg white, the effects of NaOH (0.5–2.5%), NaCl (0–1.2%), and heat (72–100 °C) on the properties of ovalbumin (the most abundant protein in poultry egg whites) gel were studied. With increasing NaOH addition, the pH and the absolute value of zeta potential (TAV-ZP) increased, the opacity and Hunter whiteness decreased, and the relaxation time (T2) initially decreased and then increased. With increasing NaCl addition and heating temperature, the pH and TAV-ZP decreased, the opacity and Hunter whiteness increased, and T2 decreased first and then increased. In addition, the hardness and cohesiveness of the ovalbumin gel were greatly modified by NaOH, NaCl, and heat. NaOH contributed to the formation of the gel network structure. In addition, the surface hydrophobicity (H0) analysis result indicated that the tertiary structure of the ovalbumin had changed during the formation of the ovalbumin gel. The correlation analysis results showed that electrostatic repulsion played a vital role in the formation of the transparent ovalbumin gel, and the transparent ovalbumin gel possessed the following characteristics: low aggregation degree, high cross-linking degree, high immobilized water content, gel network structure, and the fully unfolded structure of ovalbumin molecules. In general, the ovalbumin formed a unique gel under the combined action of NaOH, NaCl, and heat. This study could provide theoretical guidance for the processing and control of salted preserved eggs and a reference for highly transparent egg white gel products.

Film-Formation and Binder-Free Pigment Printing of Fluorosilicone-Modified Polyacrylate/Pigment Hybrid Latex: Effect of Cross-Linking Degree

Binder-free pigment dyeing/printing of textiles is a type of environmentally friendly and clean production technology that utilizes polymer/pigment hybrid latex. Although it has widespread use, the manner in which the nature of the hybrid latex influences the film formation and how systems can be designed to improve softness and air-permeability is still unclear. In this study, we synthesized a series of fluorosilicone-modified polyacrylate/pigment hybrid latexes to explore how cross-linking degree affects film-formation behavior and binder-free pigment printing performance on fabric, where the cross-linking structure is controlled by a silane coupling agent. Our results show that the cross-linking degree of the fluorosilicone-modified polyacrylate chain plays a vital role in chain diffusion, latex particle packing, and deformation. Further, it controls “skin” formation during the process of hybrid latex drying. The dried hybrid films not only have homogeneity and good barrier performance but also exhibit a soft state (low Tg, – 28.3 °C) owing to the silicone chain segment and bound water with a plasticizing effect. Interestingly, our results show that the cross-linking degree of hybrid latex particles changes as a function of the morphology of the printed polyester (PET) fiber. Further, as a result of the improvement of the softness and air-permeability of the binder-free printed PET fabric, the surface of single yarns is uniformly wrapped by hybrid films with a high cross-linking degree. These insights allow for effective development of textile pigment printing technology controlled by the film-formation behavior of hybrid latex.

Effects of partial replacement of unwashed Antarctic krill surimi by Litopenaeus vannamei surimi on the heat-induced gelling and three-dimensional-printing properties.

There is an emerging consumption of the Antarctic krill (AK) muscle-based food due to its excellent nutritional value and enormous biomass storage capacity. However, the coarse texture of the muscle and the weak gelling properties of AK protein impede its expansion in surimi-based products. This investigation successfully prepared heat-induced gels of AK surimi with desirable textural properties by including Litopenaeus vannamei in varying proportions. Higher concentrations of L. vannamei resulted in improved three-dimensional printability, greater water-holding capacity (WHC), larger viscoelastic modulus, and a well-formed microstructural matrix of AK surimi, due to an increased level of myofibrillar protein. Compared with AK, L. vannamei muscle had double the salt-soluble protein content, which was corroborated by increased intensity of bands of actin, paramyosin, tropomyosin, and myosin light chains on reducing SDS-PAGE. DSC results indicated that a high ratio of L. vannamei elevated the denaturation temperature and enthalpy of myosin, sarcoplasmic protein, and actin, suggesting a high degree of cross-linking. It was also found that when hydroxypropyl cassava starch was added at 0.5% (w/w), WHC and gel strength were further improved with a more compact gel matrix. The successful preparation of unwashed mixed surimi with AK meat fully exploited in this study provides an option for AK surimi-based product industrialization.

Bio-Based Waterborne Polyurethane Coatings with High Transparency, Antismudge and Anticorrosive Properties.

Green and environment-friendly preparation are of the utmost relevance to the development of transparent antismudge coatings. To prepare a waterborne polyurethane (WPU) coating with antismudge property, it is challenging to balance the stability of dispersion and the antismudge property of coating. Herein, we prepare a transparent bio-based WPU coating grafted with a minor proportion of poly(dimethylsiloxane) (WPU-g-PDMS) using renewable castor oil, monocarbinol-terminated PDMS, hexamethylene diisocyanate trimer, and 2,2-bis(hydroxymethyl)propionic acid as raw materials. Effects of the dosage of monocarbinol-terminated PDMS, the curing temperature, and the curing time on the antismudge performance were studied. Results showed that rigorous stirring (3000 rpm) is necessary to obtain a stable WPU-g-PDMS dispersion with a storage time longer than 6 months. A high curing temperature (>160 °C) and a period of curing time (>1 h) are indispensable to obtain the excellent antismudge property because they would facilitate the grafted low-surface-tension PDMS chains to migrate from the interior to the coating surface. The facts that simulated contaminated liquids such as water, HCl solution, NaOH solution, artificial blood, and tissue fluid could slide off easily and cleanly, and marker ink lined on the coating surface could shrink, indicated that the WPU-g-PDMS coating has good antismudge properties, which could be self-compensated shortly after deterioration. Due to the high cross-linking degree caused by multifunctional polyol and isocyanate, the WPU-g-PDMS coating has high hardness and good anticorrosive performance. The antismudge functionalization and waterborne technology of bio-based polyurethane coatings proposed in this work could be a promising contribution to the green and sustainable development of functional coatings. This kind of WPU-g-PDMS coating is expected to protect and decorate electronic screens, vehicles, and buildings, especially endoscopes.

Chloride transport resistance of alkali-activated concrete exposed to combined chloride, sulfate and carbonation environment

The chloride transportation in alkali-activated fly ash (AAFA), alkali-activated slag (AAS) and alkali-activated fly ash/slag (AAFS) concrete exposed to the environments of single chloride and combined of chloride, sulfate and carbonation were investigated. The iodide migration, chloride diffusion and capillary absorption tests were carried out before and after exposure, as well as the analysis of their microstructure and compositions. It was found that the initial chloride transport of AAFA concrete was the highest but decreased gradually with the increase of exposure period. For AAFA and AAFS specimens with a relatively lower strength, chloride and sulfate salt crystallization led to the surface spalling and strength reduction. The coupling of carbonation would further accelerate the deterioration of AAFA, but the inhibitory effect was acted for AAFS specimen. Although the appearance of AAS specimens had little change under various aggressive environments, carbonation led to the decalcification of C-(A)-SH gels and deterioration of pore structure, both the porosity and the harmful 10–50 nm pores content of the specimens were higher compared with that before exposure, and their chloride transport increased with time. However, the deterioration of AAFS specimens resulted from carbonation was less serious, due to the formation of C-(N)-ASH gels with a higher degree of cross-linking and polymerization, thereby it had the best long term performance under the combined environment of chloride, sulfate and carbonation.

One-Step Construction of the Positively/Negatively Charged Ultrathin Janus Nanofiltration Membrane for the Separation of Li+ and Mg2+

To coordinate the trade-off between the separation and permeation of the nanofiltration membrane for the separation of Mg2+/Li+, we regulated poly(ethyleneimine)/piperazine interface polymerization parameters to construct a positively/negatively charged ultrathin Janus nanofiltration membrane at a free aqueous-organic interface. At the optimized interfacial polymerization parameters, 0.03 wt % of piperazine reacted with trimethylbenzene chloride prior to poly(ethyleneimine), forming a primary polyamide layer with fewer defects or limiting large-scale defects of the polyamide layer. The controlled subsequent reaction of poly(ethyleneimine) and trimethylbenzene chloride results in a Janus nanofiltration membrane, with one side enriched with the carboxyl groups, the other side enriched with the amine groups, and a dense polyamide structure in the middle. Under the optimum conditions, the positive potential of the rear surface of the prepared membrane was 14.57 mV, and the water contact angle reached 71.31°, while the negative potential of the front surface was -25.48 mV, and the water contact angle was 12.93°, confirming a Janus membrane with opposite charges and large hydrophilicity differences in the front and rear surfaces. With a high cross-linking degree, a 40 nm thick polyamide layer is 29.09% more thinner than the traditional polyamide membrane. The ultrathin Janus nanofiltration membrane showed an excellent separation factor (SLi,Mg of 18.26), stability, and water permeability flux (10.6 L·m-2·h-1·bar-1). The rejections to MgCl2, CaCl2, MgSO4, and Na2SO4 are measured above 90% at a nearly constant permeability of 10.6 L·m-2·h-1·bar-1, particularly stable rejections to MgCl2 and Na2SO4.

Improved viability of probiotics encapsulated in soybean protein isolate matrix microcapsules by coacervation and cross-linking modification

The objective of this research was to encapsulate probiotic bacteria based on soy protein isolate (SPI) matrix using either coacervation, cross-linking modification or their combination, and investigate the influences on the survival of probiotic bacteria during spray drying, in vitro gastrointestinal digestion, heating, UV irradiation and storage. A probiotic isolate Lactobacillus plantarum 550 was spray dried in SPI solution combined with either pectin (PEC), transglutaminase (TGase) or their combination. High survival rate and low moisture content were obtained for all the samples. Microcapsules fabricated using either SPI-PEC coacervation or TGase induced cross-linking obtained well cell survival during gastric digestion, heat/UV treatment and storage, however, combination of these two modification methods generated microcapsules with lower cross-linking degree and loose package structure corresponding with significant negative effects to the cell viability during gastric digestion and storage. Among the formulations tested, SPI-PEC microparticles provided the best protection to the probiotic cells, as pectin own well thermal stability and digestion resistibility, could fill the cracks and voids existed in SPI matrix and form hydrogen bond to stabilize cell membrane during processing. In conclusion, the current study demonstrated that SPI based probiotic microcapsules with high structural density and cross-linking degree may provide better protection to adverse external environment.

Effect of MXene Nanosheet Dispersed Phases on the Fabrication of Polyamide Nanofiltration Membranes

The effects of different dispersed phases of MXene nanosheets on polyamide nanofiltration membranes, which was first reported in this investigation, are still unclear. We found that when the MXene nanosheets were dispersed into the aqueous phase, the cross-linking degree of the interfacial polymerization (IP) reaction was low, thereby forming a rough and thin polyamide layer with nanovoids, which increased the pure water flux to 14.1 L m2– h–1 bar–1. When the MXene nanosheets were dispersed into the organic phase, the IP reaction was more thorough with a high degree of cross-linking. Therefore, the salt rejection was higher, with 99.1% of Na2SO4 rejection. We believe that different dispersed phases for 2D nanosheets had different impacts on the IP reaction and polyamide layer and we hope this study can provide ideas for selecting a suitable dispersed phase to develop optimization strategies.

Interfacial Wettability Regulation Enables One-Step Upcycling of the End-of-Life Polymeric Microfiltration Membrane

Polymeric membranes, which are typically synthesized from fossil-based polymers, will reach their end of life (EOL) and then be replaced, due to the inevitable accumulation of membrane fouling even though the periodic cleaning is applied. The conventional disposal methods of the EOL membranes are landfilling and incineration, which will lead to additional carbon emission and fossil resource depletion. Herein, we proposed a surfactant-regulated interfacial polymerization strategy, by adding sodium dodecylbenzene sulfonate (SDBS) in the piperazine (PIP) aqueous solution, for the one-step upcycling of the EOL polymeric microfiltration membrane to obtain a thin-film composite polyamide (PA) nanofiltration (NF) membrane. Revealed by the quartz crystal microbalance with dissipation analysis and molecular dynamics simulation, the presence of SDBS reduced interfacial tension (IFT) and regulated interfacial wettability, thereby facilitating adequate and uniform uptake of PIP monomers. The resulting upcycled NF membrane with 4 critical micelle concentration (CMC) of SDBS addition exhibited a favorable pure water permeance (20.1 ± 0.6 L m–2 h–1 bar–1) and a satisfactory Na2SO4 rejection of 98.6 ± 0.4% owing to the formation of a continuous PA layer with high cross-linking degree (89.3 ± 0.5%). The Na2SO4 permeability of the 4 CMC upcycled NF membrane was more than 1 magnitude lower than that of the upcycled NF membrane without SDBS addition. This study provides a facile, rapid, and cost-effective method for the one-step upcycling of EOL polymeric membranes, which thus improves the sustainability of membrane technology.

NIR-II live imaging study on the degradation pattern of collagen in the mouse model.

The degradation of collagen in different body parts is a critical point for designing collagen-based biomedical products. Here, three kinds of collagens labeled by second near-infrared (NIR-II) quantum dots (QDs), including collagen with low crosslinking degree (LC), middle crosslinking degree (MC) and high crosslinking degree (HC), were injected into the subcutaneous tissue, muscle and joints of the mouse model, respectively, in order to investigate the in vivo degradation pattern of collagen by NIR-II live imaging. The results of NIR-II imaging indicated that all tested collagens could be fully degraded after 35 days in the subcutaneous tissue, muscle and joints of the mouse model. However, the average degradation rate of subcutaneous tissue (k = 0.13) and muscle (k = 0.23) was slower than that of the joints (shoulder: k = 0.42, knee: k = 0.55). Specifically, the degradation rate of HC (k = 0.13) was slower than LC (k = 0.30) in muscle, while HC showed the fastest degradation rate in the shoulder and knee joints. In summary, NIR-II imaging could precisely identify the in vivo degradation rate of collagen. Moreover, the degradation rate of collagen was more closely related to the implanted body parts rather than the crosslinking degree of collagen, which was slower in the subcutaneous tissue and muscle compared to the joints in the mouse model.

The effect of crosslinking concentration, time, temperature and pH on the characteristic of genipin-crosslinked small intestinal submucosa

In an attempt to prepare genipin-crosslinked collagen scaffolds with different crosslinking characteristics for experimental and clinical applications, the porcine small intestinal submucosa (SIS) was crosslinked with genipin under different conditions (concentrations, duration times, temperatures, pHs), and their crosslinking degree, macroscopic morphology, microstructure, swelling ratio, shrinkage temperature, degradation degree, maximum stress and cytotoxicity were determined respectively. SIS was efficiently crosslinked with all genipin concentrations, yielding genipin-crosslinked small intestinal submucosa (GP-SIS) with a high crosslinking degree (≥60%) and shrinkage temperature (≥80 °C), as well as a low swelling ratio (≤85%) and degradation degree (≤5%). However, only the concentration greater than or equal to 0.12% did significantly increase the maximum stress. Additionally, the fixation of different concentrations of genipin did not introduce cytotoxicity in SIS. As for the effect of duration times, enough crosslinking time was required for high crosslinking efficiency. When the crosslinking time was less than 24 h, GP-SIS had a crosslinking degree of less than 60%, and there was no significant decrease in swelling ratio in comparison to native SIS. When the crosslinking time was less than 24 h, the maximum stress did not reach 7 MPa. Only 3 h-fixed GP-SIS had a shrinkage temperature of less than 75 °C and a degradation degree of more than 6%. GP-SIS prepared at all temperatures and pHs, except for 4 °C, 25 °C and pH 4.0, had a crosslinking degree greater than 80%, a swelling ratio less than 50%, a shrinkage temperature greater than 80 °C, a degradation degree less than 4%, and a maximum stress greater than 8 MPa. Notably, only the fixation at alkaline conditions can increase crosslinking degree and maximum stress of SIS to 90% and 11 MPa respectively.

Self‐healing and reprocess of crosslinked polyurethane based on dynamic oxime‐carbamate bond

AbstractPolymer materials containing oxime‐carbamate bonds show superior self‐healing ability under certain conditions. In this study, a series of dynamic oxime‐carbamate based PU‐D‐x (Polyurethane‐Dimethylglyoxime‐x) with different crosslinking degrees (x indicates the content of crosslinker based on the weight of solid content) were prepared, and the self‐healing together with the reprocessing characteristic was investigated. In situ variable temperature FTIR spectroscopy shows that the dissociation of oxime‐carbamate bonds occurred at 80°C and can be accelerated by the increasing temperature. With relatively lower cross‐linking degrees, these types of PU can be healed at low temperature and in a short time, for example, PU‐D‐0.3 can be completely healed at 80°C in 6 h, and PU‐D‐0.45 can be almost completely healed at 80°C in 9 h. With the increase of cross‐linking degree, the self‐repair of this kind of PU needs to be carried out at higher temperature and needs an extension of time. However, when the temperature increased to 100°C, the self‐healing time is greatly reduced to 3–5 h. Most interestingly, these types of crosslinked PUs showed expected reusing and reprocessing characteristics, even the PU‐D‐1.2 sample with the highest crosslinking degree can be completely reshaped and reprocessed under 120°C and 10 MPa pressure.

Controlling the microphase morphology and performance of cross-linked highly sulfonated polyimide membranes by varying the molecular structure and volume of the hydrophobic cross-linkable diamine monomers

Morphological control is essential for tuning the performance of polymer electrolyte membranes (PEMs). Block copolymerization is an effective but complicated way to control the morphology of PEMs. It is urgent to explore a simple alternative method to achieve this target. Herein, the molecular engineering strategy that changes the molecular structure and volume of hydrophobic cross-linkable diamine and introduces a hydrophobic network structure was used to optimize the microphase morphology of sulfonated polyimides (SPIs). Three diamine monomers containing tetrafluorostyrol pendant groups have been synthesized (4-(2,3,5,6-tetrafluoro-4-vinylphenoxy)benzene-1,3-diamine (TFVPDM), 1,3-bis(2-trifluoromethyl-4-amino-phenoxy)-5-(2,3,5,6-tetrafluoro-4-vinylphenoxy)benzene (6FTFPB), 2,2-bis(3-amino-4-(2,3,5,6-tetrafluoro-4-vinylphenoxy)phenyl)hexafluoropropane (6FATFVP)). Based on these monomers, 4,4′-diaminostilbene-2,2′-disulfonic acid (DASDSA) and 1,4,5,8-naphthalenetetracarboxylicdianhydride (NTDA), three cross-linked SPIs (CSPIs: CSPI-T-10, CSPI-TP-10, CSPI-AP-10) with similar ion-exchange capacity (IEC) value of 2.29–2.46 meq. g−1 but different main-chain structures were prepared through polycondensation and thermal cross-linking process. The introduced hydrophobic cross-linked structure improves the oxidative stability and methanol resistance of CSPI membranes. The CSPI membranes prepared from cross-linkable hydrophobic diamine with larger molecular volume and containing hydrophobic structural units in the main chain exhibit more pronounced phase separation morphology and higher proton conductivity. Moreover, the methanol resistance of CSPI membranes is dependent on the combined effect of IEC, degree of crosslinking (DC), and main-chain structure. The higher DC and main-chain containing hydrophobic structure are beneficial for enhancing the methanol resistance. The CSPI-AP-10, which was prepared from the 6FATFVP with the largest molecular volume, more hydrophobic cross-linkable pendant groups and hydrophobic linkages, exhibits the best performance. The CSPI-AP-10 membranes showed high proton conductivity and excellent methanol resistance. The direct methanol fuel cells (DMFCs) assembled from CSPI-AP-10 have a high max power density (PDmax) of 106.2 mW cm−2 in 2 M methanol and 75.1 mW cm−2 in 10 M methanol. The results indicated that the CSPI-AP-10 was a promising candidate as a PEM in DMFC application.

Porosity of Molecularly Imprinted Polymers Investigated by 129Xe NMR Spectroscopy.

Molecularly imprinted polymers (MIPs) display intriguing recognition properties and can be used as sensor recognition elements or in separation. In this work, we investigated the formation of hierarchical porosity of compositionally varied MIPs using 129Xe Nuclear Magnetic Resonance (NMR) and 1H Time Domain Nuclear Magnetic Resonance (TD-NMR). Variable temperature 129Xe NMR established the morphological variation with respect to the degree of cross-linking, supported by 1H TD-NMR determination of polymer chain mobility. Together, the results indicate that a high degree of cross-linking stabilizes the porous structure: highly cross-linked samples display a significant amount of accessible mesopores that instead collapse in less structured polymers. No significant differences can be detected due to the presence of templated pores in molecularly imprinted polymers: in the dry state, these specific shapes are too small to accommodate xenon atoms, which, instead, probe higher levels in the porous structure, allowing their study in detail. Additional resonances at a high chemical shift are detected in the 129Xe NMR spectra. Even though their chemical shifts are compatible with xenon dissolved in bulk polymers, variable temperature experiments rule out this possibility. The combination of 129Xe and TD-NMR data allows attribution of these resonances to softer superficial regions probed by xenon in the NMR time scale. This can contribute to the understanding of the surface dynamics of polymers.

The Use of Iron(II,III) Oxide (Fe3O4) as a Cross-Linking Agent for Unfilled and Filled Chlorosulfonated Polyethylene (CSM) and Study of the Vulcanizates Properties.

This paper discusses the cross-linking behaviors, mechanical and dynamical properties, and flammability of elastomeric composites containing unconventionally cured chlorosulfonated polyethylene (CSM). The purpose of this work was to verify the CSM ability to cross-link with iron(II,III) oxide (Fe3O4) and to produce flame retardant materials. During the first series of tests, three types of CSM were used, differing in the content of bound chlorine (29–43%). The results showed that the CSM with 43% bound chlorine (Hypalon 30, CSM43) was the most advantageous type of chlorosulfonated polyethylene in terms of its properties. It exhibited a short vulcanization time, a high degree of cross-linking, and very good mechanical properties. In the next stage, the CSM composites with various fillers (talc, arsil, kaolin, chalcedonite, or carbon black) were prepared, because filled rubber materials are of the greatest practical importance. The cross-linking kinetics, equilibrium swelling, mechanical and dynamic properties as well as flammability were studied. It was found that the addition of fillers led to a decrease in the degree of cross-linking, an increase in the vulcanization time (in the case of talc, arsil, or kaolin), an increase in the overall mechanical strength (in the case of carbon black, arsil or talc). All filled vulcanizates proved to be non-flammable, as the specific oxygen index value exceeded 37.5%.

Construction of a fluorine-free anti-smudge waterborne polyurethane coating

A fluorine-free anti-smudge waterborne polyurethane coating was constructed via the dispersion of hexamethylene diisocyanate trimer into organosilicon-grafted waterborne polyurethane. In the film-forming process, the interaction among carboxyl, hydroxyl and isocyanate groups blocked the hydrophilic groups and improved the density of the coating, thereby preventing contaminants from penetrating into it. Furthermore, the organosilicon side chain migrated onto the coating surface to form a low surface energy amphiphobic layer, which endowed the coating with superior anti-graffiti performance. The surface energy of the as-constructed coating was 24 mN m−1. The water, diiodomethane and hexadecane contact angles were 95°, 70° and 36°, respectively, with corresponding sliding angles of 35°, 10° and 1°, thereby showing that the coating had no affinity to oil- and water-based ink graffiti. More strikingly, the anti-graffiti performance remained after 400 abrasion cycles under a pressure of 110 kPa and under harsh chemical treatment (strong acids, bases and salts). The constructed coating also showed an optical transparency as high as 93 % due to the high crosslinking degree.

Synthesis and application of new core-shell structure via Pickering emulsion polymerization stabilized by graphene oxide

Pickering structures significantly improve the compatibility and stability of composite polymer emulsions by virtue of their unique nanoparticle interfaces. An innovative application of Pickering structures to the synthesis of core-shell emulsions is proposed in this paper, two Pickering emulsions containing polystyrene acrylate-polysiloxane core-shell structures stabilized by graphene oxide (GO) were designed. The synthesized Pickering emulsions have excellent dispersibility and physical stability, while its particle size distribution is uniform and below 120 nm. The Pickering structure improves the grafting proportion between the PSA and polysiloxane components to over 87.8%. The GO interface gives the core-shell structure a desirable molecular configuration and high crosslinking degree, facilitating the formation of complete shielding films and stable hydrophobic layer on the cement hydrates. With a contact angle of over 130° and surface energy of below 15 mJ/m2, the capillary water absorption of the concrete decreased by 98.3% with the Pickering emulsions. Meanwhile, the Pickering coatings have the high corrosion potentials under chloride and sulfate attack, weakening the formation of Friedel's salts, gypsum, and ettringite in the cement substrates. Furthermore, the Pickering coating films are resistant to attack by aggressive ions and free radicals under acid/alkaline corrosion and photo-oxidative aging, effectively inhibiting the degradation of polymer molecules and adhesion failure on the cementitious materials.