Engineering a Formate Dehydrogenase for NADPH Regeneration**

Nicotinamide adenine dinucleotide (NADH) and nicotinamide adenine dinucleotide phosphate (NADPH) constitute major hydrogen donors for oxidative/reductive bio-transformations. NAD(P)H regeneration systems coupled with formate dehydrogenases (FDHs) represent a dreamful method. However, most of the native FDHs are NAD⁺-dependent and suffer from insufficient reactivity compared to other enzymatic tools, such as glucose dehydrogenase. An efficient and competitive NADP⁺-utilizing FDH necessitates the availability and robustness of NADPH regeneration systems. Herein, we report the engineering of a new FDH from Candida dubliniensis (CdFDH), which showed no strict NAD⁺ preference by a structure-guided rational/semi-rational design. A combinatorial mutant CdFDH-M4 (D197Q/Y198R/Q199N/A372S/K371T/▵Q375/K167R/H16L/K159R) exhibited 75-fold intensification of catalytic efficiency (k_cat/K_m). Moreover, CdFDH-M4 has been successfully employed in diverse asymmetric oxidative/reductive processes with cofactor total turnover numbers (TTNs) ranging from 135 to 986, making it potentially useful for NADPH-required biocatalytic transformations.     

Hydrophobicity, solubility, and emulsifying properties of soy protein peptides prepared by papain modification and ultrafiltration

Peptide size control is important for obtaining desirable functional properties so that these peptides can be better utilized. Proteolytic enzymatic modification of soy protein isolates (SPI), followed by ultrafiltration, is an effective way to fractionate these proteins into peptides with controlled molecular size. SPI was predenatured by mild alkali at pH 10 and heated at 50°C for 1 h prior to partial hydrolysis by papain at pH 7.0 and 38°C for 10, 30, and 60 min (PMSPI10, PMSPI30, and PMSPI60). The hydrolysate PMSPI60 was further fractionated by ultrafiltration with a stirred cell and disc membranes (100-, 50-, and 20-kDa molecular weight cut-off) into one retentate (R100) and three permeates (P100, P50, and P20). Molecular weight distribution, surface hydrophobicity (S ₀), protein solubility (PS), emulsifying activity index (EAI), and emulsion stability index (ESI) of the control SPI (without added papain), hydrolysates, and ultrafiltrates were investigated. Significant increases (P<0.001) in S ₀, PS, EAI, and ESI were observed in the hydrolysates. Peptides in the permeates had higher PS and EAI but lower S ₀ than the peptides in the retentate and hydrolysate. Soy protein peptides that were prepared from SPI by papain modification and ultrafiltration had lower molecular weight, higher solubility, and higher emulsifying properties. They could find use in products that require these properties, especially in the cosmetic and health food industries.     

Continuous computer controlled production of formate dehydrogenase (FDH) and isolation on a pilot scale

A continuous production process has been developed up to pilot scale (300 l) for FDH production with the methylotrophic yeast Candida boidinii. A high cell mass specific FDH activity (50 U/g) is achieved by process computer controlled supply of pure methanol to operate the reactor at an optimum methanol concentration of 10 g/l. The maximum FDH spacetime yield achievable with this process control involves a residence time of 7 h. The FDH space-time yield (STY) and FDH concentration are a function of the oxygen transfer rate (OTR) of the fermenter (maximum STY = 255 U/(l h) at k_La = 870 l/h). For a reasonable compromise between high FDH space-time yield and high FDH concentration, an optimum residence time is adjustable by regulating the supply of nutrient salt solution in relation to the OTR of the fermenter. On a pilot scale (200 l continuously stirred tank reactor) roughly 4 million U of FDH were produced within 10 days at a residence time of 14.3 h. Isolation of intracellular FDH enzyme was performed using extraction with an aqueous two-phase system (PEG/K₂HPO₄). A technical product quality of 1.2 U/mg FDH was achieved without any chromatographic purification step.     

Characterization of calcium-independent cytosolic phospholipase A2 activity in the submucosal regions of rat stomach and small intestine

This study was undertaken to compare the calcium-independent phospholipase A₂ (PLA₂) activities in the cytosols of twelve rat tissues and to determine whether their activities were distinct. 1-O-Alk-1′-enyl-2-[¹⁴C]-oleoyl-sn-glycero-3-phosphocho-line (PlsC) and 1-O-Alk-1′-enyl-2-[¹⁴C]oleoyl-sn-glycero-3-phosphethanolamine (PlsE) were synthesized and used as substrates, instead of phosphatidyl compounds, to exclude hydrolysis by cytosolic PLA₁ activity that could be present in some of the cytosolic preparations. For each tissue, we examined substrate specificity, pH optimum, and effect of adenosine triphosphate (ATP) and ATP analogues. PLA₂ activity was detected in eleven out of the twelve issues examined. Based on substrate specificity and pH optimum, cytosolic calcium-independent PLA₂ were classified in three groups. The first group, which included PLA₂ from small intestine, stomach and spleen, had the highest specific activity with PlsC as substrate (1253, 309 and 75 nmol/mg protein/hour, respectively) and an optimal pH at 6.5. Activity with PlsE as substrate was much lower (20–37%) than with PlsC. The second group of PLA₂ activities included the cytosolic activities from thymus, lung, liver and pancreas that showed lower specific activities for both substrates (14–23 nmol/mg protein/hour with PlsC) and had a broader optimal pH range of 6.1 to 7.5. The cytosols from brain, kidney, heart and muscle comprised the third PLA₂ group that was found to have a higher specific activity with PlsE (5–20 nmol/mg protein/hour) than PlsC and an optimal pH range from 7.4 to 7.9. Since the highest specific activity was found in the cytosol from small intestine, this PLA₂ was examined further. PLA₂ activity was found to be equally distributed in the cytosol of the submucosal portion of duodenum, jejunum and ileum with an optimal pH of 6.1 and a 5-fold higher activity with PlsC than PlsE as substrate. Moreover, this PLA₂ activity was inhibited by treatment with detergents. These results indicate the presence in the submucosal portion of the intestine of a calcium-independent cytosolic PLA₂ with a high specific activity toward PlsC and properties distinct from those described for the PLA₂ found in the intestinal brush-border.     

Guidelines for the Application of NAD(P)H Regenerating Glucose Dehydrogenase in Synthetic Processes

Glucose dehydrogenase (GDH) is frequently used for the reduction of NAD⁺ and NADP⁺ in bench‐ and industrial‐scale syntheses because the coenzyme regenerating system GDH is easy to apply, robust and relatively inexpensive. To optimize the application of this long known coenzyme regeneration system we investigated the commonly applied Bacillus GDH and characterized this enzyme by its kinetic features in the presence of substrates and products at pH 6.4 and 8.0. Three substrates/products were found to inhibit GDH considerably: (i) the reaction product glucono‐1,5‐lactone, (ii) the reduced coenzyme NAD(P)H and (iii) the oxidized coenzyme NAD(P)⁺. The inhibition of GDH under several process conditions was modeled using the determined kinetic constants. It was found that the GDH regeneration system is strongly inhibited by the usually applied conditions. This study provides the rate equation of the GDH reaction and simulations of this coenzyme regenerating system leading to an improved prediction and, thus, to a faster scale‐up and increased efficiency of NAD(P)H‐dependent synthetic processes.     

Catalytic potential of a poly(AAc‐co‐HPMA‐cl MBAm)‐matrix‐immobilized lipase from a thermotolerant Pseudomonas aeruginosa MTCC‐4713

A purified alkaline thermo‐tolerant lipase from Pseudomonas aeruginosa MTCC‐4713 was immobilized on a series of five noble weakly hydrophilic poly(AAc‐co‐HPMA‐cl MBAm) hydrogels. The hydrogel synthesized by copolymerizing acrylic acid and 2‐hydroxy propyl methacrylate in a ratio of 5 : 1 (HG_5:1 matrix) showed maximum binding efficiency for lipase (95.3%, specific activity 1.96 IU mg^?1 of protein). The HG_5:1 immobilized lipase was evaluated for its hydrolytic potential towards p‐NPP by studying the effect of various physical parameters and salt‐ions. The immobilized lipase was highly stable and retained ～92% of its original hydrolytic activity after fifth cycle of reuse for hydrolysis of p‐nitrophenyl palmitate at pH 7.5 and temperature 55°C. However, when the effect of pH and temperature was studied on free and bound lipase, the HG_5:1 immobilized lipase exhibited a shift in optima for pH and temperature from pH 7.5 and 55°C to 8.5 and 65°C in free and immobilized lipase, respectively. At 1 mM concentration, Fe³⁺, Hg²⁺, NH₄⁺, and Al³⁺ ions promoted and Co²⁺ ions inhibited the hydrolytic activities of free as well as immobilized lipase. However, exposure of either free or immobilized lipase to any of these ions at 5 mM concentration strongly increased the hydrolysis of p‐NPP (by ～3–4 times) in comparison to the biocatalysts not exposed to any of the salt ions. The study concluded that HG_5:1 matrix efficiently immobilized lipase of P. aeruginosa MTCC‐4713, improved the stability of the immobilized biocatalyst towards a higher pH and temperature than the free enzyme and interacted with Fe³⁺, Hg²⁺, NH₄⁺, and Al³⁺ ions to promote rapid hydrolysis of the substrate (p‐NPP). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4252–4259, 2006     

Effect of deacetylation on sorption of dyes and chromium on chitin

Deacetylated chitins (10.7–67.2%) were prepared by alkaline hydrolysis to determine an optimal degree of deacetylation (DD) which can effectively remove four dyes and chromium ions from textile effluent. Sorption isotherms were carried by varying the treatment time, pH, and initial concentration of dyes or chromium ions. Experimental results were analyzed in three ways: (1) equilibrium sorption capacity and sorption rate constant, (2) Langmuir isotherms, and (3) separation factor. Results indicated that except for the chitin with a 67.2% DD, rate and capacity of the dye sorption on the chitin increased with the increase of the DD in chitin for each pH but decreased with the increase of pH for each deacetylated chitin. This was mainly due to the increase of—NH⁺₃ groups in chitin with a high DD and the low pH of the system. On the contrary, dye desorption from the deacetylated chitin was highly effective at 80° and pH ≥ 10, which could facilitate the reduction of—NH⁺₃ ions and the increase of electrostatic repulsion. The number of chromium ions sorbed on the chitin also increased with the increase of the DD at a specific time. Therefore, by controlling the DD of the deacetylated chitin maximum efficiency can be achieved in the removal of dyes and metal ions from textile effluent.     

Aryl and heteroaryl azo dyes derived from 6, 8‐dichloro‐4‐hydroxyquinolin‐2 (1H)‐one: synthesis,characterisation, solvatochromism and spectroscopic properties

In this research study, 6, 8‐dichloro‐4‐hydroxyquinolin‐2(1H)‐one was prepared by the thermal cyclocondensation of 2‐(2, 4‐dichlorophenylcarbamoyl) acetic acid or N, N?‐bis(2,4‐dichlorophenyl)malonamide at 140‐150°C in polyphosphoric acid, resulting in a yield of 48%. This compound was then coupled with a series of diazonium salts derived from aromatic and heteroaromatic amines for synthesis of the corresponding azo dyes. The structures of the compounds were confirmed using elemental analysis as well as ultraviolet‐visible, Fourier Transform‐infrared and proton nuclear magnetic resonance spectroscopy. The effects of organic solvents with different polarities, pH values and substituents of the diazotising components on the maximum absorption wavelength of the colorants were discussed and evaluated in detail. The acidity constants (pK_a) of the dyes were also determined using the spectrophotometric method in an ethanol‐water mixture (80:20, v/v) at 20‐23°C.     

Stereo-Divergent Enzyme Cascades to Convert Racemic 4-Phenyl-2-Butanol into either (S)- or (R)-Corresponding Chiral Amine

The synthesis of enantiopure chiral amines from racemic alcohols is a key transformation in the chemical industry, e. g., in the production of active pharmaceutical ingredients (APIs). However, this reaction remains challenging. In this work, we propose a one-pot enzymatic cascade for the direct conversion of a racemic alcohol into either (S)- or (R)-enantiomers of the corresponding amine, with in-situ cofactor recycling. This enzymatic cascade consists of two enantio-complementary alcohol dehydrogenases, both NADH and NADPH oxidase for in-situ recycling of NAD(P)⁺ cofactors, and either (S)- or (R)-enantioselective transaminase. This cell-free biocatalytic system has been successfully applied to the conversion of racemic 4-phenyl-2-butanol into the high value (S)- or (R)-enantiomers of the amine reaching good (73 % (S)) and excellent (>99 % (R)) enantioselectivities.     

Cofactor Regeneration of NAD+ from NADH: Novel Water‐Forming NADH Oxidases

Dehydrogenases with their superb enantioselectivity can be employed advantageously to prepare enantiomerically pure alcohols, hydroxy acids, and amino acids. For economic syntheses, however, the co‐substrate of dehydrogenases, the NAD(P)(H) cofactor, has to be regenerated. Whereas the problem of regenerating NADH from NAD⁺ can be considered solved, the inverse problem of regenerating NAD⁺ from NADH still awaits a definitive and practical solution. A possible solution is the oxidation of NADH to NAD⁺ with concomitant reduction of oxygen catalyzed by NADH oxidase (E.C. 1.6.‐.‐) which can reduce O₂ either to undesirable H₂O₂ or to innocuous H₂O. We have found and cloned two novel genes from Borrelia burgdorferi and Lactobacillus sanfranciscensis with hitherto only machine‐annotated NADH oxidase function. We have overexpressed the corresponding proteins and could prove the annotated function to be correct. As demonstrated with a more sensitive assay than employed previously, the two novel NADH oxidases reduce O₂ to H₂O.     

Cellulose/polyaniline derivatives nanocomposites: Synthesis and their performance in removal of anionic dyes from simulated industrial effluents

A series of cellulose/polyaniline derivatives [polyaniline (PANI), poly(N‐methylaniline) (PNMANI), and poly(N‐ethylaniline) (PNEANI)] nanocomposites were synthesized by in situ chemical oxidation polymerization method and successfully applied for removal of acid red 4 and direct red 23 dyes from simulated industrial effluents. The synthesized nanocomposites were analyzed using Fourier transform infrared and ultraviolet‐visible spectroscopies, thermogravimetric analysis and scanning electron microscope. The effect of some parameters including pH, adsorbent amount, and initial dyes concentrations on adsorption processes were evaluated. The maximum adsorption capacities (Q_m) for the synthesized nanocomposites were calculated, and among them the Cell/PANI sample showed the highest Q_m for both AR4 (117 mg g^–1) and DR23 (56 mg g^–1) dyes. The regeneration and reusability tests exhibited that the synthesized nanocomposites had the relatively good reusability after five repetitions of the adsorption–desorption cycles. According to results, we envision that these nanocomposites, especially Cell/PANI, find application for removal of anionic dyes from industrial effluents mainly due to their low production costs, high adsorption effectiveness, and relatively good reusability. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45352.     

Synthesis and in vitro degradation of copolymers of glycolide and 6 (R,S)-methylmorpholine-2,5-dione

Copolymerization of glycolide (GA) and 6(R,S)-methylmorpholine-2,5-dione (MMD) was carried out in bulk using stannous octoate as an initiator. The effects of temperature, time, concentration of stannous octoate, and the feed composition on the copolymerization were investigated. DSC analysis showed that glass transition temperature (T_g) of the resulting copolymers (PGM) increased with increase of MMD content in the copolymers, while melting temperature (T_m) and heat of fusion (ΔH) decreased. In vitro degradation was performed in two media: PBS buffer (pH 7.4) and distilled water (pH 6.8). It showed that the erosion rates increased with increasing MMD content in the original copolymers, and the degradation proceeded more rapidly in PBS buffer than in distilled water. Based on the changes of composition and crystallinity of the samples during the degradation, it is suggested that the degradation proceeded through two main stages: first, mainly in amorphous regions and then in crystalline ones. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 643–650, 1997     

Batch kinetics and modelling of propionic acid fermentation

Batch propionic acid fermentation kinetics was studied using five different initial concentrations of lactose (i.e., 37 g/L, 45g/L, 50g/L, 57 g/L and 73 g/L) at constant temperature (30°C) and pH (6.5) under anaerobic conditions using Propionibacterium acidipropionici (ATCC 4875). When the initial substrate concentration was 37 g/L, 45 g/L, 50 g/L, 57 g/L and 73 g/L, then, correspondingly, 16 g/L, 19 g/L, 22.25 g/L, 25.3 g/L and 26.3 g/L of propionic acid was accumulated in the fermentation broth. Increasing the supply of lactose in the fermentation medium led to the accumulation of by products succinate, acetate and pyruvate. Maximum propionate yield (0.44 g/g) and comparatively lesser impurities (byproducts) were achieved with 57 g/L initial lactose concentration. The batch growth kinetics was eventually used to develop and test a mathematical model for propionic acid fermentation by P. acidipropionici at pH 6.5 and S_o = 57 g/L. Y_X/S^max was found to be the most sensitive parameter of the model. The same model also successfully simulated the batch kinetics observed at S_o = 37 g/L. However the model failed to simulate the fermentation kinetics observed at S_o = 73 g/L. The developed model can be used for process optimization studies.     

Dyeing of poly(lactic acid) fibres with synthesised novel heterocyclic disazo disperse dyes

Poly(lactic acid) (PLA) is the first melt‐processable, renewable, sustainable and biodegradable natural‐based synthetic fibre. It has a broad range of uses and combines ecological advantages with outstanding performance in textiles. PLA fibre, as an aliphatic polyester, can be dyed with disperse dyes. Apart from the limited number of commercial disperse dyes, disperse dye exhaustion on PLA is generally lower than that on  poly(ethylene terephthalate) (PET). In this study, new heterocyclic disazo disperse dyes, substituted with methyl, nitro and chloro groups at their ortho‐, meta‐ and para‐ positions, synthesised in our previous study, were applied to PLA and PET fibres to examine their dyeing performance, and colour fastness and dye exhaustion properties. Different shades of yellow, orange, reddish brown and brown were obtained. Most of the synthesised novel heterocyclic disazo disperse dyes exhibited good build‐up properties with high K/S levels on both fibres. Para‐ bonding substituent provided higher K/S values than meta‐ and ortho‐ positions for –NO₂ and –Cl substituents for both fibres. Overall, the most synthesised novel heterocyclic disazo disperse dyes in this study exhibited good build‐up properties with high K/S, exhaustion and wet fastness levels on both PLA and PET fibres.      

Chitosan intercalated montmorillonite: Preparation, characterization and cationic dye adsorption

Chitosan intercalated montmorillonite (Chi-MMT) was prepared by dispersing sodium montmorillonite (Na⁺-MMT) into chitosan solution at 60 °C for 24 h. The Chi-MMT was characterized by XRD, XRF and FT-IR. The intercalation was accomplished via the ion-exchange of Na⁺ ions with –NH₃⁺ of chitosan, resulting in the expansion of d₀₀₁ from 1.42 nm of Na⁺-MMT to 2.21 nm of Chi-MMT. The chitosan content in the Chi-MMT measured by TGA was about 17 mass%. The adsorption capacity of Chi-MMT was investigated in comparison with the starting Na⁺-MMT and chitosan using three different cationic dyes, i.e. basic blue 9 (BB9), basic blue 66 (BB66) and basic yellow 1 (BY1). The Chi-MMT showed the highest adsorption capacity in the range of 46–49 mg/g when the initial dye concentration was 500 mg/L, being equivalent to 92–99 wt.% of dye removal. The adsorption capacities of Chi-MMT for all basic dyes increased with an increase of initial dye concentration. An increase of adsorption capability of Chi-MMT was attributed to the existence of intercalate-chitosan. It could enlarge the pore structure of Chi-MMT, facilitating the penetration of macromolecular dyes, and also electrostatically interact with the applied dyes. These results indicated the competency of Chi-MMT adsorbent for basic dye adsorption.     

Photofading of phenylazo‐aniline, ‐pyridone and ‐quinolone disperse dyes on a nylon 6 substrate

The photofading of phenylazo‐aniline, ‐pyridone and ‐quinolone disperse dyes on nylon fabric was analysed using the Kubelka–Munk (K/S) spectra of fabrics exposed to a carbon arc in air. The exposure of dyed fabric through ultraviolet and coloured filters, which do not shield the main absorption band, showed a large decrease in the initial rate (K_PA) of fading. Compared with the K_PA values without filters, the values using filters were half as large for dyes without the nitro groups and a quarter as large for dyes with the nitro groups. The K_PA values may be qualitatively explained by the sum of azo scission (decrease of K/S value at λ_max) and the conversion of nitro groups to nitroso groups. These phenomena occur, respectively, via thermal disproportionation reactions between hydrazinyl radicals (from the azo group) and the reaction between hydrazinyl and N‐centred nitrosyl hydroxide radicals (from the nitro group). The azo scission is promoted by N‐centred nitrosyl hydroxide radicals via the latter reactions.     

Reactivity of disulfide peptide l-cystine with iodido (diethylenetriamine)platinum(II) and synthesis of products in the presence of an iodide ion

Substitution reactions of complex [PtI(dien)]⁺ (where, dien=diethylenetriamine ) with sulfur-containing peptide l-cystine has been studied in 1.0×10^?1 M aqueous perchlorate or acetate medium between 298≤T (K)≤323 and 2.30≤pH≤4.45 using a UV–visible spectrophotometer. Products obtained have characterized from their physico-chemical and spectroscopic methods at various pH and temperatures. From this characterization, products have indicated that [PtI(dien)]⁺ has formed a complex with l-cystine and acts as a bidentate ligand, through Pt–S bond at 2.30≤pH≤3.30 and through Pt–N and Pt–S bond of cystine in 3.95≤pH≤4.45. At 2.30≤pH≤3.30, ring opening and closing of dien have occurred at 308 and 323 K, respectively, and the same has happened at pH≥3.95. All reactions have followed the rate law – d[mixture]/dt=(k ₁+k ₂ [cystine]) [Pt(II)], where k ₂ denotes the second-order rate constant. Activation parameters E _a , Δ H ^# and Δ S ^# have been determined. Product formation and reversible and forward reaction rate constants have also been evaluated.     

Utilization of paper mill sludge for removal of cationic textile dyes from aqueous solutions

ABSTRACT

The present study is concerned usage of paper mill sludge (PMS) as an effective adsorbent to remove the two cationic character dyes (Basic Blue 3 [BB3] and Basic Yellow 28 [BY28]) from aqueous solutions. The surface morphology and some characteristics of PMS were determined by Fouirer Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Brunauer Emmett Teller (BET). The parameters affecting the process – temperature (10–55°C), adsorbent dose (0.5–10 g/l), initial pH (2–10 pH), initial concentration (50–250 mg/l) and contact time (0–24 h) – were examined in the batch adsorption experiments. Maximum adsorption capacities (q_max) of two dyes at 1 g/l dose and pH value of 7 were also calculated as 89.35 and 79.81, respectively. Adsorption phenomena of BB3 and BY28 cationic dyes onto PMS is controlled by pseudo-second-order model. Thereafter, equilibrium experimental data were applied to Langmuir, Freundlich and Dubinin–Redushkevich (D-R) isotherms, and Langmuir isotherm is the best represent the equilibrium adsorption process for both dyes. The processes occurred by physical adsorption because of calculated activation values (E_a) of BB3 and BY28 dyes were 19.43 and 9.35 kJ/mol, respectively. In addition, based on thermodynamic calculations such as free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°), the results clearly demonstrated that the adsorption process were of exothermic and spontaneous nature for both dyes. At the light of obtained findings, it can be stated that PMS can be used effectively in removal of cationic dyes from textile wastewaters and is an alternative to commercial adsorbents due to its low-cost and abundance in the paper industries.     

A novel chloro-bridged tetranuclear cadmium(II) cluster with pyridyl-substituted nitronyl nitroxide: structure and magnetic properties

A tetranuclear cadmium(II) complex of 2(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1 H-imidazol-1-oxy 3-N-oxide (NIToPy) with CdCl₂,[Cd₄Cl₈(NIToPy)₄], has been structurally and magnetically characterized. The structure is based on a novel chloro-bridged tetranuclear cadmium quasi-cubane cluster, in which each cadmium atom is chelated by one NIToPy radical, and coordinated with four bridging chlorine atoms. The temperature dependence of the magnetic susceptibility measurements shows a weak ferromagnetic coupling between the radicals. An excellent simulation of the experimental data with the prism type four spins Hamiltonian H=−2J₁(S₁S₂+S₂S₃+S₃S₄+S₁S₄)−2J₂S₂S₄ obtained the parameters: J₁=1.12 cm⁻¹, J₂=−0.20 cm⁻¹, and g=2.04.     

Effects of alkaline conditioning and temperature on the properties of glass fiber polymer composite rebar

This article investigated long term alkaline conditioning and temperature on the physical and mechanical properties of glass fiber‐reinforced polymer (GFRP) composite rebar for structural applications. The GFRP rebar was immersed in alkaline solution (pH ≈ 13) for 23 months at 23°C, and for 24 months at 60°C. The moisture absorption was found to be 0.34% at 23°C after 23 months, and 0.76% at 60°C after 24 months. At both temperatures, moisture absorption did not reach equilibrium which was attributed to two stages non‐Fickian behavior. Glass transition temperature (T_g) of the polymer matrix of rebar that conditioned at 23°C was found to be decreased because of plasticization, whereas T_g of the rebar that conditioned at 60°C was remained greater than the T_g of control rebar due to nonplasticization effect. Shear strength was retained by 83.5% at 23°C and 80.5% at 60°C, flexural strength was retained by 81% at 23°C and 69% at 60°C, and tensile strength was retained by 91.2% at 23°C and 74.3% at 60°C. It was revealed that durability of GFRP rebar in alkaline environment was controlled by the absorbed moisture; this was because the load transfer efficiency of fiber/matrix interface is vulnerable to moisture. POLYM. COMPOS., 37:3181–3190, 2016. © 2015 Society of Plastics Engineers