Thermal Cross-linking Process Research Articles

Ameliorated DC Insulation Performance of EPDM through Chemical Grafting with a Voltage Stabilizer

Ethylene-Propylene-Diene Rubber (EPDM) is widely utilized as a high-performance insulation material in high-voltage direct current (HVDC) cable accessories, owing to its exceptional electrical and thermal properties. In this study, we have successfully synthesized and employed 4-vinyl oxyacetophenone (VPE) as a modification agent to develop the chemically grafted EPDM materials (EPDM-g-VPE) just through thermal crosslinking reaction and melt blending approach. Infrared spectroscopy results reveal that during thermal cross-linking process, VPE efficiently grafted onto EPDM molecular-chains through free radical addition reaction. Following VPE grafting, the DC dielectric breakdown strength and electrical conductivity of EPDM are significantly increased and noticeably decreased respectively. Theoretical electronic structure calculations corroborate that VPE’s electron-affinity and energy-gap enable it to efficiently absorb thermal electron energy without undergoing collision ionization, thereby enhancing EPDM’s breakdown resistance. Simultaneously, VPE molecules exhibit a high affinity for capturing electron charge carriers within EPDM polymer-molecules. Space charge and thermally stimulated current tests demonstrate that the stable and uniformly distributed charge traps can be effectively introduced into EPDM matrix by grafting VPE modification, thereby suppressing transport and injection of charge carriers. Consequently, this approach substantially improves DC electrical insulation performance of EPDM. This research not only successfully enhances the electrical insulation performance of EPDM but also showcases the wide-ranging potential of chemical modification technology in cable accessory materials.

Theoretical, structural, and thermal aspects of nitro-HTPB as a prospective energetic binder–A detailed computational and experimental analysis

This study is focused on several key parameters of nitro-HTPB, such as the theoretical prediction of propulsive performance in composite propellants, determination of microstructural changes on the HTPB backbone before and after nitration, detailed analysis of the thermal decomposition mechanism, and kinetic analysis, to understand its potential as an energetic binder. When compared to conventional AP/Al/HTPB/DOA composition, nitro-HTPB-based propellant with AP/Al/NHTPB/TEGDN composition increases density-specific impulse by 40–50 s, depending on the extent to which the HTPB backbone is nitrated. As evidenced by 2D NMR methods such as 1H–13C HSQC and 1H–1H COSY, nitration only happened on alkene segments via dehydro-nitration, keeping the alkene segment in the process and barely changing the HTPB backbone's olefinic proton percentage (38%). The thermal cross-linking process during the first stage of decomposition of NHTPB begins at about 190 ºC and finishes at about 280 ºC, which is about 130 °C lower than that of HTPB, according to an FTIR analysis of TGA residues. Although nitro-HTPB has a shorter shelf life than HTPB, the kinetic analysis showed that it can be stored for extended periods in tightly packed conditions without degrading its performance, primarily because of its low K (reaction factor) value of 109 min−1. These encouraging results open up new avenues for nitro-HTPB's possible applications as an energetic binder and may eventually encourage other propellant researchers to use it in real-world applications. © 2017 Elsevier Inc. All rights reserved.

Evaluating PAA/PVA thermal crosslinking process during the preparation of in-situ high-drug loading amorphous solid dispersions

Novel high drug loading amorphous solid dispersions (HDASDs) based on the in situ thermal crosslinked polymeric carriers/matrices have been recently introduced as an upcoming class of drug delivery systems. In this set framework, the present article extends the work of previously published studies by scrutinizing the processes and mechanisms involved during the preparation of indomethacin (IND) HDASDs via in-situ thermal crosslinking of poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA). Specifically, the implementation of ATR-FTIR spectroscopy made the elucidation of the thermal crosslinking process feasible revealing that the crosslinking reaction follows a remarkably different pattern when different crosslinking temperatures are used; namely the utilization of elevated temperature leads to a higher degree of crosslinking in the case of neat PAA/PVA matrices. Interestingly, the presence of IND in the system subverts the data, since a slightly higher degree of crosslinking is achieved in the case of the lower annealing temperature (i.e., 150 °C instead of 170 °C). The progress of PAA/PVA crosslinking in the presence or absence of IND was also evaluated with the aid of isothermal thermogravimetric analysis (TGA). The results of TGA studies concerning the dependence of crosslinking density on the selected annealing temperature were in agreement with the ATR-FTIR findings. Nevertheless, a discordance between the ATR-FTIR spectroscopy and TGA results presented, as far as, the progress of the annealing process is concerned. Additionally, given the indisputable correlation between viscosity and the API's molecular mobility, and hence its recrystallization tendency, the rheological behavior of the prepared systems was addressed. Finally, in order to gain an insight into the of elastic mechanical properties of the developed HDASDs, molecular dynamics (MD) simulation models were utilized as realistic representations of the actual systems.

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.

Development of poly(vinyl alcohol)/β-cyclodextrin/P(MVE-MA) composite nanofibers as effective and selective adsorbent and filtration material for the removal and separation of cationic dyes from water

The preparation of new smart adsorbent and filtration materials has a great importance for the adsorption and filtration studies. In this study, for the effective adsorption of cationic Basic Yellow 2 (BY2) dye from water and for the selective separation of anionic dye from the anionic and cationic dye mixture solution, a new water-insoluble negatively charged poly(vinyl alcohol) (PVA)/β-cyclodextrin/poly(methyl vinyl ether-alt-maleic anhydride) (P(MVE-MA)) nanofiber membrane was fabricated by using simple electrospinning technique and thermal cross-linking process. The obtained nanofiber composite membrane material was characterized by FTIR, water solubility, mechanical property, SEM, BET specific surface area and pore size distribution measurements. After cross-linking process, maximum tensile stress and Young's modulus of membrane material showed an enhancement from 1.59 MPa to 2.58 MPa and from 66.67 MPa to 146.75 MPa, respectively. For cationic BY2 dye, membrane material exhibited an excellent adsorption capacity value of 2.554 × 10−3 mol g−1 or 775.98 mg g−1. In addition, it did not adsorb anionic Acid Blue 74 (AB74) dye. Kinetic and isotherm data of BY2 followed the pseudo second order and Langmuir models, respectively. For BY2 dye, membrane material displayed a good regeneration performance during the five adsorption/desorption cycles. In the filtration of anionic and cationic dye mixture, PVA/β-cyclodextrin/P(MVE-MA) nanofiber membrane material exhibited a remarkable separation efficiency (99.33%) and showed selective adsorption ability toward cationic BY2 dye. In brief, the fabricated membrane material is of a promising application in the water treatments and separation studies.

Fabrication and characterization of crosslinked pea protein isolated/pullulan/allicin electrospun nanofiber films as potential active packaging material

In this study, pea protein isolated/pullulan electrospun nanofiber films (PPI/PUL NFs) were successfully cross-linked by heating through Maillard reaction. PPI/PUL NFs were characterized by scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and water contact angles (WCAs). The morphological analysis illustrated that the cross-linking degree of these NFs varied with the glucose content, and the maximum glucose content was 3.0% (w/v). The fiber structure was broken down when the glucose content exceeded 3.0% (w/v), which was attributed to partial swelling and fusion of nanofibers after cross-linked by glucose. FTIR results indicated that the Maillard reaction occurred between the PPI and glucose during the thermal crosslinking process. Cross-linking dramatically improved the thermal stability, WCAs, insolubility and barrier properties of PPI/PUL NFs, which were needed to be solved urgently in biobased food packaging material. The cross-linked PPI/PUL NFs with a 2.0% glucose showed the most hydrophobic surface (WCAs of 104.5° and water vapor transmission rate of 29.3%). The antimicrobial activity of allicin-loaded PPI/PUL NFs (PPI/PUL-AC NFs) was evaluated, and the maximum size of the inhibition zone of cross-linked PPI/PUL-AC NFs against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was 16.5 mm and 12.8 mm, respectively. This study not only offered an effective pathway to protect the biological activity of allicin under heating conditions by electrospinning but also provided a reference on novel crosslinking approach of PPI/PUL NFs, which allowed PPI/PUL-AC NFs to be a highly promising platform for antimicrobial food packaging.

Effect of thermal crosslinking process on membrane structure and PEM fuel cell applications performed with SPEEK-PVA blend membranes

One of the promising options in the pursuit of clean and sustainable energy is fuel cell technology. PEM fuel cell stands out among fuel cell technologies due to its high efficiency, compactness, and ability to be used in portable applications. SPEEK (with different sulfonation degrees) and PVA blend membranes, which are thought to create a good synergy for PEM fuel cell, were prepared by using the solution casting method. As a result of the weight loss experiments, it was understood that the membranes dissolve in water regardless of the degree of sulfonation. Thermal crosslinking was carried out to prevent the membrane dissolution in water, which is in continuous contact with water in the fuel cell. Dissolution was mostly prevented by means of the thermal crosslinking process. Changes in the physical, chemical, and mechanical structure of the membrane after thermal crosslinking were comparatively determined by fourier transform infrared (FTIR), thermogravimetric analysis – differential thermal analysis (TGA-DTA), differential scanning calorimetry (DSC), water uptake capacity, swelling property, ion exchange capacity (IEC), dynamic mechanical analysis (DMA), electrochemical impedance analysis and oxidative stability. In addition, single-cell performance tests were performed with the membrane that gave the best results in the characterization analyses. Analysis results showed that thermal crosslinking prevented the dissolution of membranes in water ingreat extent. In addition, it was determined that the thermally crosslinked membranes had a more stable structure.

Microwave-induced ultrafast crosslinking of Poly (vinyl alcohol) blended with nanoparticles as wave absorber for pervaporation desalination

Although pervaporation (PV) membranes based on crosslinked polyvinyl alcohol (PVA) exhibit high desalination performance, the thermal crosslinking process often takes several hours. Here, we report a microwave assisted method to reduce the crosslinking duration. Moreover, to the PVA crosslinking system, a MOF particle, UIO-66, was added to increase the microwave absorbing efficiency and improve the desalination property. As a result, the PVA crosslinking time decreased to 2 min and the water flux increased by 67% compared with the plain crosslinked PVA membrane.

Evaluation of the Photocatalytic Activity and Anticorrosion Performance of Electrospun Fibers Doped with Metallic Oxides.

This paper reports the development and characterization of a multifunctional coating that combines anticorrosion and photocatalytic properties, deposited by means of the electrospinning technique. In the first step, a functional electrospun fiber mat composed of poly(acrylic acid) (PAA) and β-cyclodextrin (β-CD) was obtained, showing high water insolubility and great adhesion increased by means of a thermal crosslinking process (denoted as PAA + β-CD). In the second step, the fibers were doped with particles of titanium dioxide (denoted as PAA + β-CD/TiO2) and titanium dioxide plus iron oxide (denoted as PAA + β-CD/TiO2/Fe2O3). The morphology and fiber diameter of the electrospun mats were evaluated by using confocal microscopy, whereas the presence of the metal oxides in the electrospun fibers was corroborated by scanning electron microscopy (SEM) and X-ray fluorescence (XRF), respectively. In addition, electrochemical tests in saline solution revealed that the sample composed of PAA + β-CD/TiO2/Fe2O3 showed the highest corrosion protection efficiency of all the samples, which was directly associated to lower corrosion current density and higher corrosion potential. Furthermore, the paper reports a novel approach to in situ determination of methylene blue (MB) degradation onto the coating. The results revealed complete degradation of MB, which is perfectly appreciated by total discoloration of the film in the irradiated zone (from bluish to a white spot). The main conclusions of this research are the efficiency of the electrospun system PAA + β-CD/TiO2/Fe2O3 for developing photocatalytic activity and corrosion protection and the utility of the dry MB discoloration tests to evaluate photocatalytic activity.

Assembly of multidimensional MXene-carbon nanotube ultrathin membranes with an enhanced anti-swelling property for water purification

Severe stacking and swelling properties are critical issues in two-dimensional (2D) lamellar membrane fabrication and separation processes that can result in low flux and poor rejection. Herein, we propose the assembly of multidimensional MXene-carbon nanotube (CNT) ultrathin membranes by loading a MXene intercalated with CNTs onto a tubular ceramic membrane. Benefiting from the modes of van der Waals interactions (hydrogen bond) and repulsion forces between the MXene and functionalized CNTs, the one-dimensional (1D) CNTs are well dispersed and intercalated into the 2D MXene nanosheets, forming a uniform network and continuous three-dimensional (3D) labyrinthine short mass transfer channels, which can considerably improve the permeability and rejection performance of the membranes. Furthermore, the membranes exhibit a distinct suppressed swelling property via a facile thermal crosslinking process (-OH + -OH = -O- + H2O and -COOH + -OH = -COO + H2O), accompanied by the formation of new chemical bonds (Ti-O-C and Ti-COO-C) due to dehydroxylation between the neighboring MXene nanosheets and CNTs. Additionally, 50 h long-term operation studies also indicate the promising anti-swelling property and stability of the MXene-CNT membranes. This multidimensional (1D and 2D) assembly and thermal crosslinking strategy represents a new avenue for the facile and scalable development of MXene-based and other 2D material-derived high-performance membranes for water purification.

Fabrication of a Floating Device of Domperidone Tablets Using 3D-Printing Technologies

Gastro-retentive drug delivery systems (GRDDS) have been developed with the aim of prolonging drug release. In this study, floating device systems (FDS) were developed and incorporated with a domperidone tablet (Motilium-M®). The FDSs were made of polyvinyl alcohol (PVA) using a fused deposition modelling (FDM) 3D-printer and crosslinked by thermal crosslinking process. The morphology, water insolubilization, water uptake, thermal analysis, FT-IR, floating time and drug release were investigated. The results showed that thermal crosslinking caused the structural change of PVA. Increasing the crosslinking time increased the crystallinity of the polymer resulted in the decreased water solubility, water uptake, and swelling property. An optimal crosslinking condition for the FDS was heating at 120 °C for 6 h. Floating time of the FDS decreased after the crosslinking process. However, the sustained drug release of domperidone from the FDSs were observed after the thermal crosslinking process.

Enhancing physical properties of chitosan/pullulan electrospinning nanofibers via green crosslinking strategies

In this study, electrospun chitosan/pullulan composite nanofiber films were crosslinked by two green methods (heating and cinnamaldehyde). With the increase of chitosan content, the morphology results indicated that the nanostructures of thermal crosslinking chitosan/pullulan (TCP) and cinnamaldehyde crosslinking chitosan/pullulan (CCP) nanofiber films became more stable. The decreases in weight loss (83.65 % to 43.85 % for TCP and 23.42 % to 15.58 % for CCP) and the increases in water contact angle (31.8° to 54.1° for TCP and 83.65 % to 43.85 % for CCP) confirmed the improved water stability. The decreases in water vapor permeability indicated that the crosslinking processes significantly improved the barrier properties of the films. Mechanical and thermal properties of TCP and CCP films were enhanced respectively. Furthermore, the corresponding properties of CCP films were more excellent than TCP films. FTIR results indicated the occurrence of Maillard reaction during the thermal crosslinking process and Schiff base reaction during the cinnamaldehyde crosslinking process.

Fabrication of floating capsule-in- 3D-printed devices as gastro-retentive delivery systems of amoxicillin

Gastro-retentive drug delivery systems (GRDDS) provide prolonged drug release in the stomach for the treatment of some diseases located in the gastric area, and can improve patient compliance by reducing the required dosing frequency. In this study, floating 3D-printed devices combined with a commercial capsule of amoxicillin (Sia-Mox®) were developed for the treatment of H. Pylori infection. The floating 3D-printed devices (FPD) were fabricated using fused deposition modeling (FDM) 3D-printer with PVA filament followed by thermal crosslinking process. The morphology of the FPD was investigated by microscope. The water insolubilization, TGA and FT-IR were analyzed to confirm the successful crosslinking of the FPD. In vitro floating time and drug release in a simulated gastric fluid were determined using the USP dissolution apparatus II. The results showed that the floating time of the Sia-Mox® incorporated FPD was significantly longer than that of the conventional Sia-Mox® capsule, and that the floating time increased after the FPD was crosslinked. The optimal condition for the crosslinking of FPD was 140 °C for 6 h (FPD4). In vivo floating study in rabbit showed that the floating time of FPD4 was more than 10 h. The release of the drug from the Sia-Mox® in FPD4 fitted with the Higuchi model. Our results demonstrated that the development of FPD for GRDDS was successful, which the FPDs were able to float and prolong drug release.

Submicron aerosol filtration performance of centrifugally spun nanofibrous polyvinylpyrrolidone media

In this study, polyvinylpyrrolidone-based nanofibrous air filter media were produced via centrifugal spinning and subsequently stabilized by thermal cross-linking process. Samples were produced using solutions with three different polymer concentrations (5, 10 and 20 wt.%) and three different rotational speeds (4000, 6000 and 8000 r/min). After obtaining the optimum web structure with the lowest average fiber diameter and the most uniform distribution, the webs were later thermally cross-linked in order to stabilize polyvinylpyrrolidone against the degradative effects of water. In addition, the webs were subjected to dissolvability tests to see the efficacy of cross-linking treatment. Morphological, structural and chemical characterizations of the polyvinylpyrrolidone webs were performed by SEM, XRD and FTIR, respectively. Finally, filter efficiency and pressure drop were measured to assess filter performance. The results have shown that the lowest average fiber diameter is obtained at the highest rotational speeds. Subsequent thermal cross-linking treatment has been found to prevent fibers from dissolving in water. The produced water-resistant, environmentally friendly polyvinylpyrrolidone nanofibrous filter media has had a satisfactory filtration performance with a high filter efficiency of 99.995% and a high quality factor of 0.39 mm H2O−1.

Fabrication of carboxymethyl chitosan–hemicellulose resin for adsorptive removal of heavy metals from wastewater

Carboxymethyl chitosan–hemicellulose resin (CMCH) was synthesized by thermal cross-linking process and characterized by FTIR, TGA, and SEM. Subsequently, the adsorption properties of CMCH toward Ni(II), Cd(II), Cu(II), Hg(II), Mn(VII) and Cr(VI) were evaluated. Various factors affecting the uptake behavior such as pH, temperature, contact time and the initial concentration of the metal ions were investigated. The results showed that all adsorption processes fit the pseudo-second-order model and Langmuir isotherm equation. Significantly, the regeneration experiments showed CMCH can be used as a potentially recyclable and effective adsorbent for the removal and recovery of metal ions from wastewater.

Biosorption study of copper and zinc by particles produced from silk sericin – alginate blend: evaluation of blend proportion and thermal cross-linking process in particles production

Sericin is a protein present in the cocoon of silkworm silk (Bombyx mori), usually discarded in the effluent from the spinning process, and alginate is a linear natural polysaccharide, extracted mainly from brown algae. Both biomaterials have been attracting attention due to their properties. Sericin isolated present weak structural properties, but its strongly polar side groups enable easy cross-linking, polymerization and blending. The use of blends provides an improvement in the physical characteristics of the materials produced with the protein, and the use of alginate has an advantage because it has affinity for a variety of cations. The aim of this paper is to evaluate the particles produced from the blend between sericin and alginate and its properties. The gelation technique, dripping blends in aqueous and alcoholic solutions of CaCl2, was applied to produce particles with 1%, 2% and 3% w/V of alginate in sericin solution (2.5% w/V). Posteriorly, the thermal cross-linking process at 40, 100, 125 and 150 °C was performed in sericin-alginate particles and the biosorption processes of these particles for zinc and copper metals were investigated. The evaluation of the data was carried out through the measurement of water solubility, Scanning Electron Microscopy (SEM) images, Fourier Transform Infrared Spectrometry (FTIR) spectra and adsorption capacity. Water solubility of particles decreased when they were produced in alcoholic solution, which is probably related to the formation of β-sheet structure confirmed by FTIT analyses. Also, it was observed that adsorption capacity increased when the particles were produced in alcohol solution. The thermal cross-linking process increased the adsorption capacity until 100 °C, with values around 75% and 65% of reduction of Cu2+ and Zn2+, respectively. From temperature 100 °C all particles got higher degree of browning with an increase of solubility and decrease of adsorption capacity by particles because of the degradation of protein/polysaccharide.

Highly stable “pore-filling” tubular composite membrane by self-crosslinkable hyperbranched polymers for toluene/n-heptane separation

The stability of membrane is a key issue for pervaporation separation of aromatic/aliphatic hydrocarbon mixtures. In this study, in order to enhance the stability, composite membrane with “pore-filling” structure was formed on porous ceramic tubular substrate. A simple self-crosslinking strategy based on the unique hyperbranched macromolecule, Boltorn W3000, was utilized in the preparation procedure. The hydroxyl and carboxyl groups on Boltorn W3000 molecules reacted at intramolecular and intermolecular during thermal cross-linking process, and then hyperbranched polymers were assembled onto the top layer and sublayer of the ceramic substrate. The morphologies and structures of “pore-filling” composite membrane were characterized by FTIR, SEM, and Nano Indenter. Moreover, “non-pore-filling” membrane was also prepared by the same method with an additional “plugging-holes” step. Both of these two composite membranes were used for separating toluene/n-heptane mixtures. The results indicated that the “pore-filling” membrane showed more stable separation performance, due to its excellent anti-swelling properties. This work thus not only illustrated a new approach for the preparation of “pore-filling” membrane, but also produced a potentially useful organic/inorganic composite membrane for aromatic/aliphatic hydrocarbon mixtures separation.

Enzymatic removal of paracetamol from aqueous phase: horseradish peroxidase immobilized on nanofibrous membranes.

Paracetamol is a widely used as an analgesic and an antipyretic that can easily accumulate in aquatic environments. This study aimed to enhance paracetamol removal efficiency from water by combining the biocatalytic activity of horseradish peroxidase (HRP) with the adsorption of nanofibrous membrane. Poly(vinyl alcohol)/poly(acrylic acid)/SiO2 electrospinning nanofibrous membrane was prepared with fiber diameters of 200 to 300 nm. The membrane was made insoluble by the thermal cross-linking process. HRP, which was previously activated by 1,1'-carbonyldiimidazole, was covalently immobilized on the surface of nanofibers. Immobilized HRP retained 79.4 % of the activity of free HRP. The physical, chemical, and biochemical properties of the immobilized HRP and its application in paracetamol removal were comprehensively investigated. Immobilized HRP showed better storage capability and higher tolerance to the changes in pH and temperature than free HRP. Paracetamol removal rate by immobilized HRP (83.5 %) was similar to that of free HRP (84.4 %), but immobilized HRP showed excellent reusability. The results signify that enzyme immobilized on nanofibers has great application potential in water treatment.

New Organic–Inorganic Hybrids with Azo-dye Content

Five new organic–inorganic hybrids were generated from their corresponding co-polymer structures using thermal cross-linking process. The hybrid structures contain covalently-linked azobenzene units provided by the previous co-polymerization step between 3-methacryloxypropyl trimethoxy-silane and five novel azo-monomers. All structures have been characterized by FT-IR spectroscopy and TGA-MS analysis. The soluble co-polymers have also been characterized by SEC, elemental analysis and 1H-NMR spectroscopy. It has been found that the thermal stability of the hybrid structures was enhanced, as compared to the soluble co-polymers, due to the newly generated Si–O–Si bonds. The newly prepared structures show a high content in chromophore units, as indicated by 1H-NMR spectra and elemental analyses.

Mechanism of the Acid-Catalyzed Crosslinking of Poly(4-hydroxystyrene) by Polyfunctional Benzylic Alcohols: A Model Study

The mechanism responsible for the acid-catalyzed cross-linking of a photoresist based on poly(4-hydroxystyrene) was studied by 1 H NMR spectroscopy. The reaction involving cross-linkers that contain benzylic alcohol groups is proposed to proceed via both a direct C-alkylation as well as an initial O-alkylation followed by a subsequent acid-catalyzed rearrangement to the final C-alkylated product. The study reveals that a thermal cross-linking process is competing to a significant extent with the acid-catalyzed one. Two mechanisms involving different intermediates, quinone methides and carbocationic species, are proposed for these two competitive processes