Low Degree Of Cross-linking Research Articles

Fabrication of Antiswelling Loose Nanofiltration Membranes via a "Selective-Etching-Induced Reinforcing" Strategy for Bioseparation.

With diverse selectivity, higher permeance, and good antifouling property, loose polyamide nanofiltration (NF) membranes can be potentially deployed in various bioseparation applications. However, the loose NF membrane with a low crosslinking degree generally suffers from the alkali-induced pore swelling during chemical cleaning, resulting in degradation of separation performance with time. In this work, we conceive a novel strategy to tailor the separating layer through alkaline post-etching following the interfacial polymerization process, where piperazine and tannic acid (TA) were used as water-phase monomers, and trimesoyl chloride (TMC) and ferric acetylacetonate were employed as organic monomers in n-hexane. Thereinto, the polyester network formed by TA and TMC was selectively etched by alkaline treatment, thus obtaining a loose NF membrane, whose structure and performance could be facilely tailored by controlling the TA ratio and the etching pH. As a result, the well-designed loose NF membrane exhibited higher flux, better selectivity, and more stable separation performance in a long-term filtration of diluted cane molasses. Interestingly, the obtained loose NF membrane showed excellent antiswelling ability during alkaline cleaning because of network locking induced by Fe3+ chelation, decrease in the carboxyl proportion (more hydroxyl generation due to the ester bond hydrolysis), and enhanced interface interaction between the separation layer and the sublayer attributed to catechol adhesion effect. Therefore, such a "selective-etching-induced reinforcing" strategy could endow the polyamide NF membrane with both loose and antiswelling separation layer in a reliable and scalable way, which provides a new perspective for preparing highly selective and stable NF membrane for resource recovery.

Tuning the Mechanical and Geometric Properties of Electrochemically Aligned Collagen Threads Toward Applications in Biohybrid Robotics.

Electrochemically aligned collagen (ELAC) threads fabricated by the isoelectric focusing (IF) of collagen have previously shown potential in tissue engineering and more recently in the fabrication of biohybrid robot structures. For applications in biohybrid robotics, ELAC structures are needed that are both robust and compliant enough to facilitate muscle actuation. However, studies on the effects of IF parameters, and the interactions of such fabrication parameters, on the mechanical and geometric properties of resulting ELAC threads have not been previously found in literature. Understanding the impact of these manufacturing parameters on the material properties is critical to facilitate biohybrid robot design. In this study, the effects of IF duration, IF voltage, and collagen solution concentration were investigated and showed statistically significant effects on adjusting ELAC properties via single-factor experiments. The interactions between parameters exhibited significant joint effects on ELAC property tuning through two-factor experiments. Scanning electron microscopy and 2,4,6-trinitrobenzenesulfonic (TNBS) assays revealed the correlation between high mechanical properties and a combination of low porosity and high degree of crosslinking. By simply tuning IF parameters without changing other fabrication steps, such as crosslinker concentration, ELAC threads with a wide range of mechanical and geometric properties were fabricated. The average tensile modulus of the resulting ELAC threads ranged from 198 ± 90 to 758 ± 138 MPa. The average cross-sectional area ranged from 7756 ± 1000 to 1775 ± 457 μm2. The resultant mapping between IF parameters and ELAC thread properties enabled the production of strong and flexible threads with customizable properties.

High performance polymer electrolyte membrane with efficient proton pathway over a wide humidity range and effective cross-linking network

It is vital to constructing long-term proton transfer channels with sufficient conduction sites in proton exchange membranes. The mPBI-TGDDM/ZrSP polymer electrolyte membranes are prepared by covalent cross-linking with tetrafunctional N,N,N′,N′-tetraglycidy-4,4′- diaminodiphenyl-methane (TGDDM) and doping with the zirconium 3-sulfopropyl phosphonate (ZrSP). The new high-temperature proton conductor ZrSP contains sulfonic acid groups and phosphonic acid groups. TGDDM has high functionality which efficiently enhanced the dimensional stability, mechanical properties, and oxidative resistance of the membranes under low cross-linking degrees (5%–10%). The low cross-linking degree and good mechanical stability also allow high doping levels of ZrSP and consequently high proton conductivity. At 100% relative humidity (RH), 50% RH and 0 RH, the proton conductivity of mPBI-TGDDM(5%)/ZrSP(50%) membrane is 0.127, 0.078 and 0.0186 S cm−1 at 180 °C, respectively. A large number of sulfonic and phosphonic acid groups in the membrane can establish an efficient proton pathway over a wide humidity range. High cross-linking will decrease the conductivity, and high doping will increase the conductivity, thus affecting the performance of the fuel cells. The mPBI-TGDDM/ZrSP membranes exhibited good methanol resistance and good membrane selectivity and thus the membranes have great application potential in direct methanol fuel cells (DMFCs).

Crucial role of side-chain functionality in anion exchange membranes: Properties and alkaline fuel cell performance

Side-chain functionality is critical to achieve highly conductive and chemically stable anion exchange membrane (AEM) materials. Herein, two series of quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) having different lengths (n or m) of cationic side-chains were designed and prepared, including PPO-C-nQA with a triazole-containing linker and PPO-mQA without triazole groups in the side chains. The effect of the side-chain functionality on the properties of AEMs has been systematically investigated. Long cationic side chains in PPO-mQA membranes induced the formation of obvious microphase-separated morphology. However, PPO-C-nQA membranes with a triazole-containing linker showed a considerable higher hydroxide conductivity than that of PPO-mQA membranes, due to the developed hydrogen-bond networks between triazole and water/hydroxide. High retention of conductivity and low degree of crosslinking were observed for the AEMs with longer side-chains (PPO-C-3QA, PPO-C-4QA, PPO-6QA, and PPO-7QA) in the alkaline stability testing under 10 M NaOH at 80 °C for 250 h, indicating their excellent stability. Moreover, a single H2/O2 AEMFC with these side-chain type AEMs demonstrated that PPO-C-1QA with highest conductivity exhibited a peak power density of 141.3 mW cm−2 at a current density of 320 mA cm−2.

Construction of Novel Proton Transport Channels by Triphosphonic Acid Proton Conductor-Doped Crosslinked mPBI-Based High-Temperature and Low-Humidity Proton Exchange Membranes

High proton conductivity and sufficient stability of the polybenzimidazole membrane are important for the application of high-temperature proton exchange membrane fuel cells (HT-PEMFCs). A series of composite membranes based on crosslinked mPBI (cPBI) with cerium 2,4,6-triphosphono-1,3,5-triazine (CeTPT) were resoundingly fabricated. Novel cPBI networks with tetrafunctional N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) were synthesized. It is noteworthy that a new high-temperature proton conductor CeTPT was added. CeTPT contained three phosphonic acid groups, which offered good proton conductivity at moderate-to-low humidity and had good thermal stability. Tetrafunctional crosslinker TGDDM had multiple functional groups. With a relatively low crosslinking degree (CLD), the mechanical properties, dimensional stability, and oxidative resistance of the membranes were efficiently improved. The low CLD and good physicochemical stability also allowed high doping levels of CeTPT (up to 50%) and consequently high proton conductivity. At 180 °C and 50% RH, the proton conductivity of cPBI-5-CeTPT-50 and cPBI-10-CeTPT-50 was 0.072 and 0.068 S cm–¹, respectively. The cPBI-CeTPT membranes showed good methanol resistance and membrane selectivity, and thus the membranes were suitable for direct methanol fuel cells.

Particle Stiffness and Surface Topography Determine Macrophage-Mediated Removal of Surface Adsorbed Particles.

Cellular surface recognition and behavior are driven by a host of physical and chemical features which have been exploited to influence particle-cell interactions. Mechanical and topographical cues define the physical milieu which plays an important role in defining a range of cellular activities such as material recognition, adhesion, and migration through cytoskeletal organization and signaling. In order to elucidate the effect of local mechanical and topographical features generated by the adsorption of particles to an underlying surface on primary human monocyte-derived macrophages (MDM), a series of poly(N-isopropylacrylamide) (pNIPAM) particles with differing rigidity are self-assembled to form a defined particle-decorated surface. Assembly of particle-decorated surfaces is facilitated by modification of the underlying glass to possess a positive charge through functionalization using 3-aminopropyltriethoxysilane (APTES) or coating with poly(L-lysine) (PLL). MDMs are noted to preferentially remove particles with higher degrees of crosslinking (stiffer) than those with lower degrees of crosslinking (softer). Alterations to the surface density of particles enabled a greater area of the particle-decorated surface to be cleared. Uniquely, the impact of particle adsorption is evinced to have a direct impact on topographical recognition of the surface, suggesting a novel approach for controllably affecting cell-surface recognition and response.

A chondrogenesis induction system based on a functionalized hyaluronic acid hydrogel sequentially promoting hMSC proliferation, condensation, differentiation, and matrix deposition

Hydrogel scaffolds are widely used in cartilage tissue engineering as a natural stem cell niche. In particular, hydrogels based on multiple biological signals can guide behaviors of mesenchymal stem cells (MSCs) during neo-chondrogenesis. In the first phase of this study, we showed that functionalized hydrogels with grafted arginine-glycine-aspartate (RGD) peptides and lower degree of crosslinking can promote the proliferation of human mesenchymal stem cells (hMSCs) and upregulate the expression of cell receptor proteins. Moreover, grafted RGD and histidine-alanine-valine (HAV) peptides in hydrogel scaffolds can regulate the adhesion of the intercellular at an early stage. In the second phase, we confirmed that simultaneous use of HAV and RGD peptides led to greater chondrogenic differentiation compared to the blank control and single-peptide groups. Furthermore, the controlled release of kartogenin (KGN) can better facilitate cell chondrogenesis compared to other groups. Interestingly, with longer culture time, cell condensation was clearly observed in the groups with RGD and HAV peptide. In all groups with RGD peptide, significant matrix deposition was observed, accompanied by glycosaminoglycan (GAG) and collagen (Coll) production. Through in vitro and in vivo experiments, this study confirmed that our hydrogel system can sequentially promote the proliferation, adhesion, condensation, chondrogenic differentiation of hMSCs, by mimicking the cell microenvironment during neo-chondrogenesis.

Qualitative and quantitative evaluation of epoxy systems by Fourier transform infrared spectroscopy and the flexibilizing effect of mercaptans.

Epoxy systems are widely applied as adhesives in the aerospace industry. They have excellent adhesion properties, however, being thermosetting, epoxy systems show fracture brittleness characteristics. Polysulfide and polymercaptans are good options to increase the flexibility of the epoxy adhesive. Thermal analysis techniques are generally used to evaluate the curing degree of epoxy systems. In most cases, when infrared (IR) analysis is used, it is employed qualitatively. This paper presents the reaction study of a DGEBA epoxy prepolymer with diethylenetriamine (DETA) and linear and branched dodecyl mercaptans as flexibilizers. Conversion data and curing time were assessed qualitatively and quantitatively by Fourier Transform Infrared Spectroscopy (FT-IR) in the medium infrared region (MIR) and in the near infrared region, using near infrared reflectance accessory (NIRA). NIRA methodology showed satisfactory results, with errors between 3 and 7%, especially in samples with lower amine contents. Mechanical tests confirmed the flexibilization of the cured epoxy system by the addition of mercaptans, indicating a lower crosslinking degree in the matrix. Young's modulus (E) significantly decreased from 2017 MPa to 578 MPa with the addition of approximately 20 wt% of normal dodecyl mercaptan to the epoxy system.

Composite catalytic materials based on k-carrageenan and CaO used on the transesterification of soybean oil for the process of biodiesel obtention

Composite materials based on CaO obtained from egg shells and k-carrageenan, an anionic sulfated linear polysaccharide obtained from red seaweeds was used as an efficient, environmentally friendly heterogeneous catalyst for the transesterification of soybean oil with methanol at 60 °C.The different composite samples were produced through the dissolution of the biopolymer in an ionic liquid (IL) derived from imidazolium ion and by further addition of CaO. The samples were characterized by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM) and Termogravimetry (TGA). The materials exhibit an internal structure consisting of meso and macropores which widen with the addition of small amounts of Hexamethylene diisocyanate (HMDI) that acts as a crosslinker. The composite materials present a similar thermal behaviour to k-carrageenan, without loss of stability.The catalytic activity of the prepared composite materials was evaluated in the transesterification reaction of soybean oil with methanol through catalytic runs in batch conditions. It was found that both CaO loading and polymer cross-linking affect the sorption capacity and the transport properties of the prepared catalytic materials, with best results obtained for the intermediate CaO concentration in membrane and a lower crosslinking degree.

Eucommia ulmoides gum-based engineering materials: fascinating platforms for advanced applications

Eucommia ulmoides gum (EUG) exhibits good rubber–plastic duality and great application potential in biomedicine, textiles, aerospace, and other fields. The extraction methods of EUG include mechanical (high-temperature cooking), alkali extraction, solvent, microbial (enzymatic hydrolysis), and comprehensive methods. However, the complicated preparation process and high cost of EUG greatly limit its application. EUG is composed mainly of trans-isoprene, and the high crystallinity of EUG at room temperature showing rigid plastics is due to the relatively regular and short identity period of its molecular chain. Through regulating the ratio of the three-phase structure of EUG (regular crystal region, completely irregular amorphous region, and intermediate region of transition pattern between the crystallized and amorphous regions), it exhibits rubber elasticity at room temperature. The application of EUG is closely related to its crystallinity and cross-linking degree. The double-bond modification of EUG by physical or chemical method can regulate its crystalline structure and cross-linking structure, so that EUG engineering materials that meet the performance requirements of multiple fields can be obtained. EUG with zero cross-linking degree is linear thermoplastic material, which is usually used in artificial limb, medical composite scaffold, composites denture soft lining, and modified plastic. EUG with low cross-linking degree is thermoelastic material, which is frequently used in the preparation of shape memory material, interfacial compatibilizer, and composite film. EUG with critical cross-linking degree is rubber-type material, which is regularly used in elastomer, self-healing material, and modified rubber. In this article, the extraction technology of EUG and its pros and cons and the structure and properties of EUG and their corresponding material states in the past 10 years were systematically discussed. The research progress of engineering materials in different states was introduced, and the effect of modification on the structure and properties of EUG was discussed. The future development direction of the materials was prospected.

Biobased furan-based epoxy/TiO2 nanocomposites for the preparation of coatings with improved chemical resistance

Biobased, solvent-free thermosetting coating systems are developed from epoxidized hydroxymethylfuran (BOMF) crosslinked with methyl nadic anhydride (MNA) filled with TiO2 nanoparticles. The effect of 1 to 5 wt% of TiO2 on the curing behavior of the resin and the overall performance of the resulting coatings is studied by means of rheological, thermal, mechanical, morphological, and chemical resistance tests. TiO2 particles shift the curing reaction to higher temperatures and reduce the reaction enthalpy, resulting in lower crosslinking degrees and glass transition temperatures. The resins are applied as tinplate coatings, exhibiting optimal adhesion to the metal substrate (5A according to ASTM D3359), and performing well in pencil hardness tests (9H and 7H in gouge and scratch hardness, respectively). Morphological characterization highlights homogeneous distribution of TiO2 nanoparticles even at the highest loading. Finally, the chemical resistance of the coatings to ethanol and acetic acid solutions used as simulants is significantly enhanced by the addition of TiO2, resulting in an efficient protection of the tinplate from corrosion. Overall, these results demonstrate that the proposed furan-based thermosets show potential for use as coatings.

In-depth investigation on the factors affecting the performance of high oil-absorption resin by response surface method

A series of high oil-absorption resins with low cross-linking degree were synthesized by suspension polymerization using stearyl methacrylate (SMA), 2-Ethylhexyl methacrylate (EHMA), and styrene (St) as monomers. Response surface methodology (RSM) with central composite design (CCD) was also applied to determine the optimal parameters that are mainly known to affect their synthesis. Thus, the effects of the monomer mass ratio (EHMA:SMA), the rigid monomer (St) dosage, the porous agent (acetone) dosage, and their pairwise interaction on the resin's oil-absorption capacity were analyzed, highlighting PSES-R 2 as the resin with the optimum performance. The pure oil-absorption rates of PSES-R 2 for gasoline, diesel, and kerosene were 11.19 g·g −1 , 16.25 g·g −1 , and 14.84 g·g −1 , respectively, while the oil removal rates from oily wastewater were 98.82%, 65.11%, and 99.63%, respectively. • A series of high oil-absorption resins with low cross-linking degree were synthesized by suspension polymerization. • The optimal parameters were determined by response surface methodology (RSM) with central composite design. • The optimized sample PSES-R 2 exhibited the excellent oil-absorption performance.

Physicochemical changes of MTGase cross-linked surimi gels subjected to liquid nitrogen spray freezing

Physicochemical properties of microbial transglutaminase (MTGase) cross-linked surimi gels subjected to liquid nitrogen (LN) spray freezing with different temperatures and cross-linking degrees were investigated. Gels with lower LN spray temperature (−90 °C) were found taking less time in cooling down themselves to maximum-ice-crystal generating temperature. Microstructure images showed the pores of gels became smaller and the structure gradually became denser, as freezing temperature decreased and cross-linking degree increased. It also revealed T22 relaxation time of gels decreased significantly with surimi gels cross-linking degree increasing, indicating the binding ability of gels to moisture was enhanced accordingly. Meanwhile, the proton density weighted image brightness declined along with the LN spray temperature decreasing, and the image brightness showed a decreasing trend from outside to inside, indicating that water migrated and permeated easier from the inside of the gel network to the outside undergone higher LN temperature and lower cross-linking degree. Besides, the L⁎ and W values of LN groups decreased along with LN spray temperature and cross-linking degree increasing. Moreover, −90 °C LN group with 46.70% cross-linking degree presented the highest breaking force which ascribed to their synergistic efforts in maintaining a stable and dense structure of gels via controlling ice crystals and cross-linkages' generation.

A viscoelastic PEGylated poly(glycerol sebacate)-based bilayer scaffold for cartilage regeneration in full-thickness osteochondral defect

Defects of either articular cartilage or subchondral bone would destroy the structural integrity and functionality of the joint. Reconstruction of osteochondral defects requires difunctional scaffolds that simultaneously induce cartilage and subchondral bone morphogenesis, however, high-performance cartilage reconstructive scaffolds remain a considerable challenge. In this study, a solvent-free urethane crosslinking and spontaneous pore-forming procedure under room temperature was proposed and optimized to produce PEGylated poly(glycerol sebacate) (PEGS) scaffolds with controllable crosslinking degrees and hierarchical macro-/micro-porosities. Based on the economical and feasible preparative approach, the viscoelastic PEGS-12h with low crosslinking degree was demonstrated to significantly stimulate chondrogenic differentiation, maintain chondrocyte phenotype and enhance cartilage matrix secretion compared to elastic polymer with high crosslinking degree, emphasizing the importance of matrix viscoelasticity in cartilage regeneration. On this basis, the viscoelastic low-crosslinked PEGS-12h was combined with the well-acknowledged osteoinductive mesoporous bioactive glass (MBG) to construct a difunctional PEGS/MBG bilayer scaffold, and evaluated in a full-thickness osteochondral defect model in vivo. The PEGS/MBG bilayer scaffold successfully reconstructed well-integrated articular hyaline cartilage and its subchondral bone in 12 weeks, exhibiting extraordinary regenerative efficiency. The results indicated that the viscoelastic PEGS scaffold and PEGS/MBG bilayer scaffold proposed in this study made an excellent candidate for cartilage and osteochondral regeneration, and was expected for clinical translation in the future.

Thin-film nanocomposite membranes incorporated with UiO-66-NH2 nanoparticles for brackish water and seawater desalination

In this work, UiO-66-NH2 nanoparticles, a type of metal-organic frameworks (MOFs) with an average size of ~100 nm, were incorporated into the polyamide-based thin-film nanocomposite (TFN) RO membranes. Their inherent porous structure, suitable triangular aperture size, hydrophilic nature, and high chemical and water stability endow the TFN membranes with greater surface hydrophilicity, lower degree of cross-linking and preferential pathways for water molecules across the selective layers. Herein, we introduce UiO-66-NH2 nanoparticles in the TFN layer via spray assisted pre-disposition. The UiO-66-NH2 TFN membranes with a spray duration of 3 min show a ~50% increase in pure water permeance while maintaining a similar rejection compared with the thin-film composite (TFC) membranes in brackish water desalination tests. The former also displays higher chlorine resistance than the latter. In the stimulated seawater desalination tests, TFN membranes also exhibit a higher water flux and salt rejection than the benchmark membranes.

A high-strength and healable shape memory supramolecular polymer based on pyrene-naphthalene diimide complexes

Dynamic interaction plays an important role in the design of smart materials, but how to utilize it to realize multifunction without sacrificing performance is also pursued goal. Herein, we report a shape memory network (PTMEG-Py@PEA-NDI) with excellent healability and high-strength by simply blending flexible poly(tetramethylene ether glycol) (PTMEG) and polyether amine (PEA), which contained the complementary recognized groups π-electron-rich pyrene (Py) and π-electron-poor naphthalene diimide (NDI), respectively. The existence of CT interactions between NDI and Py was confirmed by color change, UV–vis spectrum and fluorescence spectrum, and its reversibility can be driven by changing the temperature. Tuning the CT interactions between two precursors by varying the Py content, the mechanical properties of supramolecular polymer can increase from 2.8 MPa to 34.5 MPa. All the samples present excellent shape memory properties with high Rf (98%) and Rr (98%). And the highest self-healing efficiency (95%) was achieved in the sample PTMEG-Py0.25@PEA-NDI which own relative low crosslinking degree.

Emulsion Copolymerization of Vinyl Acetate and Vinyl Silanes: Kinetics and Development of Microstructure

AbstractThe batch emulsion copolymerization of vinyl acetate with different vinyl silane functional monomers (vinyl trimethoxysilane [VTMS], vinyl triethoxysilane [VTES], and vinyl silanetriol [VSTO]) is studied. The nature of the silane strongly affects the development of the microstructure and crosslinking ability of the latexes. A combination of techniques (Soxhlet extraction, centrifugation, assymetric‐flow field flow fractionation AF4/MALS/RI) shows that the factor controlling the molar mass and crosslinking density is the degree of hydrolysis of the alkoxysilane, producing higher molar masses and degrees of crosslinking when the degree of hydrolysis is high. Thus, the copolymer containing VSTO produced a very crosslinked latex, the one with VTMS produced a latex with a low degree of crosslinking in the wet state that can yield high degrees of crosslinking upon drying, and the latex with VTES do not produce significant amounts of crosslinking neither before nor after drying.

A Chondrogenesis Induction System Based on Functionalized Hyaluronic Acid Hydrogel Sequentially Promoting hMSC Proliferation, Condensation, and Differentiation and Matrix Deposition

Hydrogel scaffolds are widely used in cartilage tissue engineering as a natural stem cell niche. In particular, hydrogels based on multiple biological signals can guide behaviors of mesenchymal stem cells (MSCs) during neo-chondrogenesis. In the first phase of this study, we showed that functionalized hydrogels with grafted arginine-glycine-aspartate (RGD) peptides and lower degree of crosslinking can promote the proliferation of human mesenchymal stem cells (hMSCs) and upregulate the expression of cell receptor proteins. Moreover, grafted RGD and histidine-alanine-valine (HAV) peptides in hydrogel scaffolds can regulate the viscosity of the intercellular at an early stage. In the second phase, we confirmed that simultaneous use of HAV and RGD peptides led to greater chondrogenic differentiation compared to the blank control and single-peptide groups. Furthermore, the controlled release of kartogenin (KGN) can better facilitate cell chondrogenesis compared to other groups. Interestingly, with longer culture time, cell condensation was clearly observed in the groups with RGD and HAV peptide. In all groups with RGD peptide, significant matrix deposition was observed, accompanied by glycosaminoglycan (GAG) and collagen (Coll) production. Through in vitro and in vivo experiments, this study confirmed that our hydrogel system can sequentially promote the proliferation, adhesion, condensation, chondrogenic differentiation of hMSCs, by mimicking the complex cell microenvironment during neo-chondrogenesis.

Дослідження полімерних плівок на основі суміші дисперсій стирол-акрилових сополімерів

The article presents the results of a study of the physical, mechanical, structural and chemical properties of polymer films based on a mixture of styrene acrylic aqueous dispersions Akratam AS 02.1 and Akratam AS 03.1. The physical and mechanical properties of individual and combined polymer films were evaluated in terms of transparency, stickiness, thickness, surface density and elongation at break. Individual styrene acrylic film Akratam AS 02.1 is characterized by high elasticity and stickiness, and Akratam AS 03.1. dispersion forms a strong, hard and brittle film. It was found that an increase in the concentration of Akratam AS 03.1 in the polymer mixture Akratam AS 02.1 / Akratam AS 03.1 leads to a decrease in stickiness, thickness, surface density and the degree of deformation of the combined film. Changes in the structural parameters of the network of combined polymer films depending on the concentration of the components in the mixture were studied using the sol-gel method. It was determined that the individual film Akratam AS 02.1 has a high content of the soluble fraction (28.5%), which is due to the low degree of intermolecular crosslinking (1.221). For films of the composition Akratam AS 02.1 / Akratam AS 03.1 90:10 and 50:50, an increase in the degree of crosslinking and a decrease in the sol fraction to 27.6 and 27.3% are observed, respectively. The obtained data on the structural characteristics of the polymer network of the studied films correlate with the results of determining the effect of the composition of the polymer mixture on the hydrolytic stability of the combined film. The greatest indicators of resistance to the action of cold, hot water and soap-soda solution are characteristic for the film of the composition Akratam AS 02.1 / Akratam AS 03.1 50:50 and are 98.3, 97.8 and 98.7%, respectively. Thus, the mixed styrene acrylic films of the composition Akratam AS 02.1 / Akratam AS 03.1 90:10 and 50:50 can be used to form a polymer coating on a textile material with improved performance properties. Key words: polymer film, styrene acrylic dispersion, polymer mixture, physical and mechanical properties, structural parameters of the network, hydrolytic stability.

The effect of radiation exposure on carbon fiber-reinforced Rohacell® core laminate structural composites

Two equivalent density foams with identical shear strengths were used to manufacture carbon-fiber reinforced composite sandwich structures. One foam core system (Rohacell® 71 WF) has a cell diameter of 1117 µm and a wall thickness of 29 µm, while the second one (Rohacell® 71 HERO) has cell diameter of 146 µm and a wall thickness of 3 µm. A 60Co source was used to expose composites from 0 to 12 Mrads of radiation. Tests were used to evaluate the effect of radiation on the core shear strength and failure mechanism for both types of composites. The WF composites experienced a 75% decrease in core shear strength, while the HERO only exhibited an 8% decrease. The fracture behavior of the WF composites changed from a more compliant to a brittle fracture path with increased radiation. The fracture modes for the HERO were similar and did not change characteristics, even with maximum radiation dosage. Thermal analysis also showed that even after composite thermal processing, the WF foam retained a lower Tg in comparison to the HERO foam. Dynamic mechanical analyzer also indicated a faster rate of Tg degradation for the WF foam composites as a function of radiation, suggesting a lower degree of crosslinking which resulted in fragmentation of the network. Thermal gravimetric analysis and size exclusion chromatography also exhibited an earlier onset of thermal degradation for the WF foams with radiation. This investigation suggests that changes in composite mechanical properties with radiation are related to both foam macrostructure and the degree of crosslinking of the polymer foam. Careful evaluation must be performed to establish proper selection of the composite core material based on end of life environmental exposure.