Optimization of acrylonitrile removal by activated carbon‐granular using response surface methodology

A statistical Box–Behnken design of experiments was performed to evaluate the effects of individual operating variables and their interactions on the acrylonitrile (AN) removal of C₀ = 100 mg/L as fixed input parameter. The variables examined in this study included activated carbon‐granular (AC) dosage, w, temperature, T, and time of contact, t. The significant variables and optimum conditions were identified (w = 4 g/L, T = 30°C, and t = 120 min with AN uptake of 23.97 mg/g of AC) from statistical analysis of the experimental results using response surface methodology (RSM).     

Continuous lipase‐catalyzed synthesis of hexyl laurate in a packed‐bed reactor: optimization of the reaction conditions in a solvent‐free system

BACKGROUND: Hexyl laurate has been applied widely in cosmetic industries and is synthesized by chemical methods with problems of cost, environmental pollution, and by‐products. In this study, Lipozyme^® IM77 (from Rhizomucor miehei) was used to catalyze the direct‐esterification of hexanol and lauric acid in a solvent‐free system by utilizing a continuous packed‐bed reactor, wherein the aforementioned difficulties could be overcome. Response surface methodology (RSM) and three‐level‐three‐factor Box‐Behnken design were employed to evaluate the effects of synthesis parameters, such as reaction temperature (45–65 °C), mixture flow rate (0.25–0.75 mL min^?1) and concentration of lauric acid (100–300 mmol L^?1) on the production rate (µmol min^?1) of hexyl laurate by direct esterification. RESULTS: The production rate was affected significantly by the mixture flow rate and lauric acid concentration. On the basis of ridge‐max analysis, the optimum synthesis conditions for hexyl laurate were as follows: 81.58 ± 1.76 µmol min^?1 at 55 °C, 0.5 mL min^?1 flow rate and 0.3 mol L^?1 lauric acid. CONCLUSION: The lipase‐catalyzed synthesis of hexyl laurate by Lipozyme^® IM‐77 in a continuous packed‐bed bioreactor and solvent‐free system was successfully developed; optimization of the reaction parameters was obtained by Box–Behnken design and RSM. Copyright © 2008 Society of Chemical Industry     

Response surface methodology as a tool to study the lipase‐catalyzed synthesis of betulinic acid ester

BACKGROUND: The synthesis of betulinic acid ester using betulinic acid and oleyl alcohol catalyzed by Novozym 435 (immobilized Candida antarctica lipase) was carried out. Response surface methodology (RSM) based on a five‐level, three‐variable, central composite rotatable design (CCRD) was employed to evaluate the interactive effects of various parameters. The parameters were reaction time (8–16 h), temperature (20–60 °C) and enzyme amount (120–160 mg). RESULTS: Simultaneously increasing reaction time, temperature and amount of enzyme increased the yields of betulinic acid ester produced. CONCLUSION: The optimum conditions derived via RSM for the reaction were reaction time of 10.2 h, temperature of 53.1 °C and enzyme amount of 138 mg. The actual experimental yield was 48.5% under optimum conditions, which compared well with the maximum predicted value of 47.6%. Copyright © 2008 Society of Chemical Industry     

Thermogravimetric analysis of chitosan

The thermal degradation of chitosan at different heating rates B in nitrogen was studied by thermogravimetric analysis. The results indicate that the thermal degradation of chitosan in nitrogen is a one‐step reaction. The degradation temperatures increase with B. Experimentally, the initial degradation temperature (T₀) is (1.049B + 326.8)°C; the temperature at the maximum degradation rate, that is, the peak temperature on a differential thermogravimetry curve (T_p), is (1.291B + 355.2)°C; and the final degradation temperature (T_f) is (1.505B + 369.7)°C. The degradation rates at T_p and T_f are not affected by B, and their average values are 50.17% and 72.16%, respectively, the maximum thermal degradation reaction rate, that is, the peak height on a differential thermogravimetry curve (R_p), increases with B. The relationship between B and R_p is R_p = (1.20B + 2.44)% min^?1. The thermal degradation kinetic parameters are calculated with the Ozawa–Flynn–Wall method. The reaction activation energy (E) and frequency factor (A) change with an increasing degree of decomposition, and the variable trends of the two kinetic parameters are similar. The values of E and A increase remarkably during the initial stage of the reaction, then keep relatively steady, and finally reach a peak during the last stage. The velocity constants of the thermal degradation vary with the degree of decomposition and increase with the reaction temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Influence of processing parameters on the degradation of poly(L‐lactide) during extrusion

The influence of processing conditions during melt extrusion on the degradation of poly(L ‐lactide) (PLLA) has been investigated. PLLA polymer was processed by melt extrusion in a double screw extruder at 210 and 240°C. For each extrusion temperature, two screw rotation speeds, 20 and 120 rpm, were used. To investigate the influence of moisture on the thermal degradation during processing, the PLLA granules were dried at 100°C for 5 h and then either extruded directly or conditioned at 65% RH, 20°C for 24 h prior to extrusion. The results show that a decrease in molecular weight measured as number‐average (M_n) molecular weight occurs for all combinations of process parameters used. At processing temperature of 210°C, the change in molecular weight for the dry granules was shown to be dependent on the residence time (i.e., screw rotation speed) in the melt. By changing the screw rotation speed from 120 to 20 rpm at 210°C, M_n decreased from 33,600 to 30,200 g/mol. When the processing temperature was increased to 240°C, the dry granules showed an M_n of 25,600 and 13,600 g/mol when extruded at 120 and 20 rpm, respectively. M_n for the conditioned specimens extruded at 210°C was 18,400 g/mol when processed at 120 rpm and 12,300 g/mol at 20 rpm. When processed at 240°C, 20 rpm, M_n is independent of whether the granules were dry or moist prior to extrusion. It is probably due to the fact that the degradation at 240°C is so extensive that the presence of moisture in the polymer does not contribute further to the degradation process. The stress and strain at break decreased due to degradation and were dependent on the molecular weight of the samples. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2128–2135, 2001     

Effects of glycerol and ethylene–acrylic acid on composition optimization of PVOH/starch‐blended biodegradable resin using response surface methodology

Response surface methodology was used to analyze the effect of glycerol (X₁) and ethylene–acrylic acid (EAA) level (X₂) on the objective (water solubility index (WSI), water absorption index (WAI), and tensile strength) attributes of a poly(vinyl alcohol) (PVOH)/starch‐blended plastic resin. A rotable central composite design was used to develop models for the objective responses. The experiments were run with different barrel temperatures, such as zone 1: 100°C, zone 2: 100°C, zone 3: 105°C, and zone 4: 105°C, respectively, with a feed rate of 20 g/min and screw speed of 25 rpm. Responses were most affected by changes in glycerol level (X₁) and to a lesser extent by EAA level (X₂). Individual contour plots of the different responses were overlaid, and regions meeting the optimum WSI of 6.10%, WAI of 5.57 g gel/g dry wt, and tensile strength of 62.14 MPa were identified at the glycerol level of 72.41 mL and the EAA level of 36.03 g, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermogravimetric analysis of methyl methacrylate‐graft‐natural rubber

The thermal degradations of methyl methacrylate‐graft‐natural rubber (MG) at different heating rates (B) in nitrogen were studied by thermogravimetric analysis. The results indicate that the thermal degradation of MG in nitrogen is a one‐step reaction. The degradation temperatures increase along with the increment of heating rates. The temperature of initial degradation (T₀) is 0.448B + 362.4°C, the temperature at maximum degradation rate, that is, the peak temperature on a differential thermogravimetric curve (T_p) is 0.545B + 380.7°C, and the temperature of final degradation (T_f) is 0.476B + 409.4°C. The degradation rate at T_p is not affected by B, and its average value is 48.9%; the degradation rate at T_f is not affected by B either, and its average value is 99.3%. The reaction order (n) is 2.1 and is not affected by B. The reaction activation energy (E) and the frequency factor (A) increase along with B, and the apparent reaction activation energy (E₀) is 254.6 kJ/mol. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2952–2955, 2002     

Polymers based on N,N‐diglycidylaniline. I. Investigations of the curing kinetics by dynamic differential scanning calorimetry measurements

N,N‐Diglycidylaniline was reacted with aniline (yielding polymer EP‐1) and the newly synthesized chromophore 4‐(phenylazo)aniline (yielding polymer EP‐2). The curing kinetics of these two epoxy resin systems was studied in dynamic experiments by means of differential scanning calorimetry. Kinetic parameters such as the activation energy and frequency factor were estimated with the Ozawa method [E(O) and A(O), respectively], the Kissinger method [E(K) and A(K), respectively], and the modified Avrami method [E(A) and A(A), respectively]. The activation energy and frequency factor of EP‐1 were much lower than those of EP‐2 estimated with the Ozawa, Kissinger, and Avrami methods. The activation energy and frequency factor for EP‐1 determined with the Ozawa method [E(O) = 55.8 kJ/mol, A(O) = 10 × 10³ 1/s] and the Avrami method [E(A) = 56.4 kJ/mol, A(A) = 9.2 × 10³ 1/s] were higher than those determined with the Kissinger method [E(K) = 51.0 kJ/mol, A(K) = 2 × 10³ 1/s]. In the case of EP‐2, the kinetic parameters calculated with the Ozawa model [E(O) = 140.4 kJ/mol, A(O) = 12.3 × 10¹³ 1/s] and the Kissinger model [E(K) = 139.9 kJ/mol, A(K) = 10.9 × 10¹³ 1/s] were higher than those calculated with the Avrami model [E(A) = 130.4 kJ/mol, A(A) = 7.9 × 10¹² 1/s]. The obtained polymers were characterized with Fourier transform infrared, ¹H‐NMR, differential scanning calorimetry, and ultraviolet–visible spectroscopy. The polymers exhibited low glass‐transition temperatures in the range of 57–79°C and good solubility in common organic solvents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and properties of fluorinated aromatic poly(amide imide)s based on 4,4′‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzophenone and various bis(trimellitimide)s

A CF₃‐containing diamine, 4,4′‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzophenone ( 2 ), was synthesized from 4,4′‐dihydroxybenzophenone and 2‐chloro‐5‐nitrobenzotrifluoride. Imide‐containing diacids ( 3 and 5B_a – 5B_g ) were prepared by the condensation reaction of aromatic diamines and trimellitic anhydride. Then, two series of novel soluble aromatic poly(amide imide)s (PAIs; 6A_a – 6A_k and 6B_a – 6B_g ) were synthesized from a diamine ( 4A_a – 4A_k or 2 ) with the imide‐containing diacids ( 3 and 5B_a – 5B_g ) via direct polycondensation with triphenyl phosphate and pyridine. The aromatic PAIs had inherent viscosities of 0.74–1.76 dL/g. All of the synthesized polymers showed excellent solubility in amide‐type solvents, such as N‐methyl‐2‐pyrrolidone and N,N‐dimethylacetamide (DMAc), and afforded transparent and tough films by DMAc solvent casting. These polymer films had tensile strengths of 90–113 MPa, elongations at break of 8–15%, and initial moduli of 2.0–2.9 GPa. The glass‐transition temperatures of the aromatic PAIs were in the range 242–279°C. They had 10% weight losses at temperatures above 500°C and showed excellent thermal stabilities. The 6B series exhibited less coloring and showed lower yellowness index values than the corresponding 6A series. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3641–3653, 2006     

Thermogravimetric analysis of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

The thermal degradation of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [P(HB‐HV)] was studied using thermogravimetry (TG). In the thermal degradation of PHB, the temperature at the onset of weight loss (T_o) was derived by T_o = 0.97B + 259, where B represents the heating rate (°C/min). The temperature at which the weight loss rate was maximum (T_p) was T_p = 1.07B + 273, and the final temperature (T_f) at which degradation was completed was T_f = 1.10B + 280. The percentage of the weight loss at temperature T_p (C_p) was 69 ± 1% whereas the percentage of the weight loss at temperature T_f (C_f) was 96 ± 1%. In the thermal degradation of P(HB‐HV) (7:3), T_o = 0.98B + 262, T_p = 1.00B + 278, and T_f = 1.12B + 285. The values of C_p and C_f were 62 ± 7 and 93 ± 1%, respectively. The derivative thermogravimetric (DTG) curves of PHB confirmed only one weight loss step change because the polymer mainly consisted of the HB monomer only. The DTG curves of P(HB‐HV), however, suggested multiple weight loss step changes; this was probably due to the different evaporation rates of the two monomers. The incorporation of 10 and 30 mol % of the HV component into the polyester increased the various thermal temperatures (T_o, T_p, andT_f) by 7–12°C (measured at B = 20°C/min). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2237–2244, 2001     

One‐pot synthesis of hyperbranched poly(aryl ether ketone)s for the modification of bismaleimide resins

Hyperbranched poly(aryl ether ketone)s with hydroxyl end groups (HBP‐OH) and high degree of branching value (83%) were synthesized via an A₂ + B₃ approach. The polymerization conditions (e.g., polymerization temperature and time, monomer concentration, stoichiometric ratio of functional groups) were explored to avoid the gelation. Allyl‐terminated hyperbranched PAEKs (HBP‐AL) with low molecular weight (M_n = 3.4 × 10³) and narrow polydispersity (PDI = 1.65) were obtained via the etherification of HBP‐OH and it has been used for the modification of bismaleimide (BMI) resins. The prepolymers showed good processibilities with a viscosity below 0.6 Pa s at 110°C, though the viscosities slightly increased as the increase of HBP‐AL contents. The cured BMI resins showed high glass transition temperatures (T_g > 320°C) and good thermal stabilities (T_d > 400°C, both in nitrogen and air). It is inspiring to note that the incorporation of HBP‐AL into BMI matrix results in a significant enhancement of toughness without any noticeable loss in modulus, processibility, and T_g. POLYM. ENG. SCI., 54:1675–1685, 2014. © 2013 Society of Plastics Engineers     

Measurement and Prediction of the Solubility of Stearic Acid Polymorphs by the UNIQUAC Equation

The solubility of stearic acid polymorphs B and C in methanol, 2‐butanone, decane and hexane was measured using a precise gravimetric method. Stearic acid is a molecule with 18 carbons that is highly nonideal in solutions and experimental data show strong deviations from the solubility prediction for ideal systems. It is soluble in both polar and nonpolar organic solvents. From experimental solubility, data the solvent mediated polymorphic transition temperature was found around 30°C. From thermal analysis, temperature and heat of transition from form B to form C and also heat of fusion of form C were found to be 49°C, 20 J/g and 240 J/g, respectively. From experimental solubility data the binary parameters of the universal quasi‐chemical (UNIQUAC) model, for stearic acid were calculated. The UNIQUAC solubility predictions compared very closely with the experimental data.     

Structural evolution of the R‐T phase boundary in KNN‐based ceramics

Although a rhombohedral‐tetragonal (R‐T) phase boundary is known to substantially enhance the piezoelectric properties of potassium‐sodium niobate ceramics, the structural evolution of the R‐T phase boundary itself is still unclear. In this work, the structural evolution of R‐T phase boundary from ?150°C to 200°C is investigated in (0.99?x)K_0.5Na_0.5Nb_1?ySb_yO₃–0.01CaSnO₃–xBi_0.5K_0.5HfO₃ (where x = 0‐0.05 with y = 0.035, and y = 0‐0.07 with x = 0.03) ceramics. Through temperature‐dependent powder X‐ray diffraction (XRD) patterns and Raman spectra, the structural evolution was determined to be Rhombohedral (R, <?125°C)→Rhombohedral + Orthorhombic (R + O, ?125°C to 0°C)→Rhombohedral + Tetragonal (R + T, 0 °C to 150°C)→dominating Tetragonal (T, 200°C to Curie temperature (T_C)) → Cubic (C, >T_C). In addition, the enhanced electrical properties (e.g., a direct piezoelectric coefficient (d₃₃) of ~450 ± 5 pC/N, a conversion piezoelectric coefficient () of ~580 ± 5 pm/V, an electromechanical coupling factor (k_p) of ~0.50 ± 0.02, and T_C~250°C), fatigue‐free behavior, and good thermal stability were exhibited by the ceramics possessing the R‐T phase boundary. This work improves understanding of the physical mechanism behind the R‐T phase boundary in KNN‐based ceramics and is an important step toward their adoption in practical applications.     

Determination of the Optimum Conditions for Leaching of Malachite Ore in H2SO4 Solutions

The Taguchi method has been used to determine the optimum conditions for the dissolution of malachite ore in H₂SO₄ solutions. The chosen experimental parameters and their range were (i) reaction temperature: 15 to 45 °C, (ii) solid‐to‐liquid ratio: 1/10 to 1/3 g cm^–3, (iii) acid concentration (in weight): 2 % to 10 %, (iv) particle size: –40 to –3.5 mesh, (v) stirring speed: 240 to 720 rpm, and (vi) reaction time: 5 to 45 minutes. The optimum conditions were found to be reaction temperature: 40 °C, solid‐to‐liquid ratio: 1/3 g cm^–3, acid concentration (in weight): 10 %, particle size: –30 mesh, stirring speed: 480 rpm, and reaction time: 45 minutes. Under these optimum working conditions, the dissolution of copper and iron in malachite ore was 100 % and 58 %, respectively. Besides, alternative working conditions reducing the total cost and dissolution of iron were found.     

The physical toxicity of chemicals. VI. Relationships between the boiling points of liquids and the toxicities of their vapours

The following equation gives the relation between the toxic concentration C_t of the vapour to the absolute boiling point T_B of a physically toxic liquid: log₁₀C_t (at 25°) = log₁₀C_B-1.43 × 10^?4T_b^1.7-E_A+0.09 Here, C_B is a measure of the intensity of the toxicity and E_A accounts for any difference between molecular interaction in the vapour and in the biophase involved in the toxicity. The equation is useful for the estimation of toxicities and for the classification of toxic substances. It is deduced that compounds with boiling points (°K ) above 509(E_A - log₁₀C_B+1.22)^0.588 will show no physical toxicity.     

Synthesis,characterization, and thermo‐optical properties of azobenzene polyurethane containing chiral units

An optically active levoazobenzene polyurethane (PU) was synthesized and was based on the chromophore 4‐(4′‐nitrophenylazo) phenylamine, the chiral reagent L (?)‐tartaric acid, and toluene diisocyanate. The chemical structure and thermal properties were characterized by ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, ¹H‐NMR spectroscopy, and differential scanning calorimetry. The PU had high number‐ and weight‐average molecular weights up to 52 300, a large glass‐transition temperature of 235.7°C, and an optical rotation of ?18.06°, The optical parameters, including the refractive index (n) and thermo‐optic coefficient (dn/dT); the dielectric constant (?) and its variation with temperature; and the thermal volume expansion coefficient and its variation with temperature of PU were obtained. The dn/dT and ? values for the polymer were in the range ?4.1200 to 3.6257 × 10^?4 °C^?1 and 2.00 ± 0.11, respectively. The dn/dT values were one order of magnitude larger than those of inorganic glasses, such as zinc silicate glass (5.5 × 10^?6 °C^?1) and borosilicate glass (4.1 × 10^?6 °C^?1), and were larger than organic materials, such as polystyrene (?1.23 × 10^?4 °C^?1) and poly(methyl methacrylate) (?1.20 × 10^?4 °C^?1). The ? values were lower than that of alicyclic polyimide and semiaromatic polyimide. The obtained PU is expected to be useful for optical switching and optical waveguide areas. The conclusion has a little significance for the development of a new digital optical switch. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Extraction,purification and characterization of wax from flax (Linum usitatissimum) straw

The chemical composition and selected physical parameters of wax extracted from flax straw with supercritical CO₂ (SC‐CO₂) and hexane have been determined. From the GC/MS results, clear variations in composition and component distributions were observed between SC‐CO₂‐ and hexane‐extracted samples. The major components of the SC‐CO₂ and hexane extracts from three flax cultivars were: fatty acids (36–49%), fatty alcohols (20–26%), aldehydes (10–14%), wax esters (5–12%), sterols (7–9%) and alkanes (4–5%). Purification of SC‐CO₂‐extracted wax with silica gel chromatography yielded 0.4–0.5% (dry matter) and was composed primarily of wax esters (C₄₄, C₄₆ and C₄₈) and alkanes (C₂₇, C₂₉ and C₃₁). UV‐Vis scans of the purified wax samples exhibited two main peaks indicating the presence of conjugated dienes and carotenoids or related compounds. Fourier transform infrared results showed prominent peaks at 2918 (‐C‐H), 2849 (‐C‐H), 1745 (‐C=O), 1462 (‐C‐H), 1169 (‐C‐O) and 719 cm^–1 (‐(CH₂)_n‐), with NorLin wax showing a slightly deviating pattern compared to the other samples. Thermal analysis by differential scanning calorimetry revealed a mean melting point of 55–56 °C and oxidation temperatures of 146–153 °C for purified wax from flax straw processed using different procedures.     

Effect of atmosphere on the thermal decomposition of chlorinated natural rubber from latex

The kinetics of the thermal decompositions of chlorinated natural rubber (CNR) from latex under both air and nitrogen atmospheres were studied with thermogravimetric analysis (TGA). The thermooxidative decomposition of CNR had two weight-loss step changes in the TGA curves, which occurred at the two distinct temperature ranges of about 160–390 and 390–850°C, respectively. The gaseous products of the first step change were mainly HCl with a little CO₂, and the apparent reaction order (n) was 1.1. The reaction activation energy (E) increased linearly with the increment of heating rate (B), and the apparent activation energy (E₀), calculated by extrapolation back to zero B, was 101.7 kJ/mol. Bs ranging from 5 to 30°C/min were used. The initial temperature of weight loss (T₀) was 1.31B + 252°C, where B is in degrees Celsius per minute. The final temperature of weight loss (T_f) was 0.93B + 310°C, and the temperature of maximum weight-loss rate (T_p) was 1.03B + 287°C. The decomposition weight-loss percentage at T_p (C_p) and that at T_f (C_f) were not affected by B, and the average values were 38 and 60%, respectively. The second weight-loss step change was an oxidative decomposition of the molecular main chain. The value of n was 1.1. E increased linearly with the increment of B, and E₀ was 125.0 kJ/mol. C_f after the second step approached 100%, which indicated complete decomposition. The thermal decomposition of CNR in a N₂ atmosphere had only one weight-loss step change with an n of 1.1. E increased linearly with the increment of B, and E₀ was 98.6 kJ/mol. T₀ was 1.25B + 251°C, T_f was 0.91B + 315°C, and T_p was 1.09B + 286°C. C_p and C_f were not affected by B, and the average values were 37 and 68%, respectively. The weight percentage of more stable, nonthermal decomposed residue was about 30%. The thermal decompositions of CNR in both atmospheres were similar, mainly by dehydrochlorination, at the low temperature range (160–390°C) but were different at the high temperature range (390–850°C). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2590–2598, 2001     

Synthesis and characterization of chitosan‐g‐methacrylic acid and studies of its additional physicochemical properties,such as swelling,metal‐ion sorption,and flocculation behavior

The aim of this study was to examine the synthesis of a graft copolymer of chitosan and methacrylic acid (MAA) by free‐radical polymerization with a potassium peroxymonosulfate/cyclohexanone (CY) redox system in an inert atmosphere. The optimum reaction conditions affording maximum grafting ratio (%G), grafting efficiency (%E), add on (%A), and conversion (%C) were determined. The grafting parameters were found to increase with increasing concentration of MAA up to 24 × 10^?2 mol/dm³, but thereafter, these parameters decreased. With increasing concentration of peroxymonosulfate from 0.6 × 10^?2 to 1.2 × 10^?2 mol/dm³, %G, %A, and %E increased continuously. All of these grafting parameters increased with increasing concentration of CY up to 1.2 × 10^?2 mol/dm³, but beyond this concentration, the grafting parameters decreased. With various concentrations of chitosan from 0.6 to 1.4 g/dm³, the maximum %G, %A, and %E were obtained at 1.4 g/dm³. %G, %A, and %C decreased continuously with various concentrations of hydrogen ions from 2 × 10^?3 to 6 × 10^?3 mol/dm³. The grafting parameters increased with increasing temperature up to 35°C, but thereafter, these parameters decreased. With increasing time period of reaction from 60 to 180 min, %G, %A, and %E increased up to 120 min, but thereafter, these parameters decreased. The graft copolymer was characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Gelation of poly(vinyl alcohol) solutions at low temperatures (20 to −78°C) and properties of gels

The flow points of atactic poly(vinyl alcohol) (a-PVA) gels with H₂O/dimethyl sulfoxide (DMSO) = 90/10 (v/v) chilled at 20 to ?78°C for 24 h depended on the chilling temperature and were 0–30°C for gels with the initial polymer concentrations (C_i) of 2–5 g/dL, whereas those for H₂O/DMSO = 50/50 chilled at 0 to ?78°C were independent of the chilling temperature and were 70–75°C. Syneresis occurred after eight cycles of freezing (?24°C) and thawing (20°C) for a-PVA hydrogels at concentrations above C_i = 4 g/dL and two such cycles for syndiotacticity-rich PVA (s-PVA) hydrogels at concentrations above C_i = 1 g/dL. The extent of syneresis per one cycle for s-PVA hydrogels was higher than that for a-PVA hydrogels at the initial cycles. In the a-PVA hydrogels with an initial polymer concentration of ca. 30 g/dL, syneresis was expected not to occur even after 20 cycles. If all the free water in the gels is assumed to have transuded by syneresis after 20 cycles, the residual water is bound water and is estimated to be six water molecules per one vinyl alcohol monomer unit. © 1994 John Wiley & Sons, Inc.