Preparation of diacylglycerol‐enriched palm olein by phospholipase A1‐catalyzed partial hydrolysis

Partial hydrolysis of palm olein catalyzed by phospholipase A₁ (Lecitase Ultra) in a solvent‐free system was carried out to produce diacylglycerol (DAG)‐enriched palm olein (DEPO). Four reaction parameters, namely, reaction time (2–10 h), water content (20–60 wt‐% of the oil mass), enzyme load (10–50 U/g of the oil mass), and reaction temperature (30–60 °C), were investigated. The optimal conditions for partial hydrolysis of palm olein catalyzed by Lecitase Ultra were obtained by an orthogonal experiment as follows: 45 °C reaction temperature, 44 wt‐% water content, 8 h reaction time, and an enzyme load of 34 U/g. The upper oil layer of the reaction mixture with an acid value of 54.26 ± 0.86 mg KOH/g was first molecularly distilled at 150 °C to yield a DEPO with 35.51 wt‐% of DAG. The DEPO was distilled again at 250 °C to obtain a DAG oil with 74.52 wt‐% of DAG. The composition of the acylglycerols of palm olein and the DEPO were analyzed and identified by high‐performance liquid chromatography (HPLC) and HPLC/electrospray ionization/mass spectrometry. The released fatty acids from the partial hydrolysis of palm olein catalyzed by phospholipase A₁ showed a higher saturated fatty acid content than that of the raw material.     

Poly(L‐Lactide), 8. High‐Temperature Hydrolysis of Poly(L‐Lactide) Films with Different Crystallinities and Crystalline Thicknesses in Phosphate‐Buffered Solution

Poly(L ‐lactide) (PLLA) films having different crystallinities (X_c's) and crystalline thicknesses (L_c's) were prepared by annealing at different temperatures (T_a's) from the melt and their high‐temperature hydrolysis was investigated at 97°C in phosphate‐buffered solution. The changes in remaining weight, molecular weight distribution, and surface morphology of the PLLA films during hydrolysis revealed that their hydrolysis at the high temperature in phosphate‐buffered solution proceeds homogeneously along the film cross‐section mainly via the bulk erosion mechanism and that the hydrolysis takes place predominantly and randomly at the chains in the amorphous region. The remaining weight was higher for the PLLA films having high initial X_c when compared at the same hydrolysis time above 30 h. However, the difference in the hydrolysis rate between the initially amorphous and crystallized PLLA films at 97°C was smaller than that at 37°C, due to rapid crystallization of the initially amorphous PLLA film by exposure to crystallizable high temperature in phosphate‐buffered solution. The hydrolysis constant (k) values of the films at 97°C for the period of 0–8 h, 0.059–0.085 h^–1 (1.4–2.0 d^–1), were three orders of magnitude higher than those at 37°C for the period of 0–12 months, 2.2–3.4×10^–3 d^–1. The melting temperature (T_m) and X_c of the PLLA films decreased and increased, respectively, monotonously with hydrolysis time, excluding the initial increase in T_m for the PLLA films prepared at T_a = 100, 120, and 140°C in the first 8, 16, and 16 h, respectively. A specific peak that appeared at a low molecular weight around 1×10⁴ in the GPC spectra was ascribed to the component of one fold in the crystalline region. The relationship between T_m and L_c was found to be T_m (K) = 467·[1–1.61/L_c (nm)] for the PLLA films hydrolyzed at 97°C for 40 h.     

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     

Graft copolymerization of acrylic acid onto methylcellulose by potassium permanganate‐p‐xylene redox pair

Poly(acrylic acid) was grafted onto methylcellulose in aqueous media by a potassium permanganate‐p‐xylene redox pair. Within the concentration range from 0.93 × 10^?3 to 9.33 × 10^?3M, p‐xylene, the graft copolymerization reaction exhibited minimum and maximum graft yields and was associated with two precursor‐initiating species, a p‐xylyl radical and its diradical derivative. The efficiency of the graft was low, not higher than 12.9% at a p‐xylene concentration of 0.93 × 10^?3M and suggested the dominance of a competitive homopolymerization reaction under homogeneous conditions. The effect of permanganate on the graft yield was normal and optimal at 135% graft yield, corresponding to a concentration of the latter of 33.3 × 10^?3M over the range from 8.3 × 10^?3 to 66.7 × 10^?3M. The conversion in graft yield showed a negative dependence on temperature in the range 30–60°C and suggested a preponderance of high activation energy transfer reaction processes. The calculated composite activation energy for the graft copolymerization was 7.6 kcal/mol. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 278–281, 2004     

Kinetics and thermodynamics of hydrolytic depolymerization of poly(ethylene terephthalate) at high pressure and temperature

Hydrolytic depolymerization of PET (polyethylene terephthalate) waste in excess of water was studied using a 0.5‐L stirred high‐pressure autoclave at temperatures of 100, 150, 200, and 250°C and at 200, 300, 400, 500, 700, and 800 psi (pounds per square inch) pressure. Velocity constants of hydrolysis were calculated from the experimental data obtained. Maximum depolymerization (91.38%) of PET into monomer was obtained at 250°C and 800 psi. pressure. However, the maximum rate of reaction was recorded at 200°C and 500 psi temperature and pressure, respectively. The energy of activation and frequency factor were calculated, as 64.13 KJ/g mol and 7.336 × 10⁴ min^?1, respectively, for higher pressure and temperature conditions. It was also reported that the hydrolytic depolymerization is first order with the velocity constant 1.773 × 10^?2 min^?1 at 250°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3305–3309, 2003     

Depolymerization of poly(ethylene naphthalate) in fused silica capillary reactor and autoclave reactor from 240 to 280°C in subcritical water

Depolymerization of poly(ethylene naphthalate) (PEN) in subcritical water was performed in a fused silica capillary reactor (FSCR) and an autoclave reactor. The phase behaviors of PEN in water during the heating‐cooling process in the FSCR were observed under microscope and images were captured by digital camera. Reaction conditions for PEN hydrolysis in the autoclave reactor were chosen based on the experimental results obtained from the FSCR. Under autogenous pressures in the autoclave reactor, the effects of the water/PEN mass ratio (8.0 g/1.0 g to 16.0 g/1.0 g), reaction temperature (240–280°C) and reaction time (5–60 min) on the depolymerization yield and products yields were investigated. The main products of depolymerization were identified and quantified as 2,6‐naphthalene dicarboxylic acid (2,6‐NDA) and ethylene glycol (EG). PEN was completely depolymerized at 260°C in 60 min with an optimal water/PEN mass ratio of 12.0 g/1.0 g (12:1). The yields of 2,6‐NDA and EG were optimized to 83.1% and 79.7%, respectively. Reaction kinetics analysis showed that the PEN depolymerization in subcritical water was first‐order and the activation energy was 95 kJ mol^?1. Additionally, a reaction pathway was proposed based on the experimental results. POLYM. ENG. SCI., 57:1382–1388, 2017. © 2017 Society of Plastics Engineers     

Conversion of isopropanol and mixed alcohols to hydrocarbons using HZSM‐5 Catalyst in the MixAlco™ process

HZSM‐5 (SiO₂/Al₂O₃=280 mol/mol) is used to produce hydrocarbons from reagent‐grade isopropanol and mixed alcohols made from lignocellulosic biomass (waste office paper and chicken manure) using the MixAlco? process. All studies were performed at 101 kPa (abs). The experiments were conducted in two sets: (1) vary temperature (300–T_max°C) at weight hourly space velocity (WHSV)=1.31 h^–1, and (2) vary WHSV (0.5–11.5 h^–1) at T=370°C. For isopropanol, T_max=450°C and for mixed alcohols T_max=520°C. For isopropanol, higher temperatures produced more gaseous products and more aromatics. High WHSV gives high concentration of C6+ olefins, whereas low WHSV gives high concentrations of C9 aromatics. For mixed alcohols, changes in temperature affected the product distribution similar to isopropanol. In contrast, WHSV did not affect the concentration of reaction products; only dehydration products were observed. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2549–2557, 2013     

Grafting of N‐carbamyl maleamic acid onto a styrene–butadiene–styrene copolymer

A styrene–butadiene–styrene block copolymer (SBS) was functionalized with N‐carbamyl maleamic acid (NCMA) using two peroxide initiators with the aim of grafting polar groups onto the molecular chains of the polymer. The influence of the concentration of benzoyl peroxide (BPO) and 2,5‐dimethyl, 2,5‐diterbuthylperoxihexane (DBPH) was studied. The concentration of peroxy groups ranged between 0.75 and 6 × 10^?4 mol % while the concentration of NCMA was constant at 1 wt %. The reaction temperature was chosen according to the type of peroxide employed, being 140°C for BPO and 190°C for DBPH. FTIR spectra confirmed that NCMA was grafted onto the SBS macromolecules. It was found that the highest grafting level was achieved at a concentration of peroxy groups of about 3 × 10^?4 mol %. Contact angle measurements were used to characterize the surface of the SBS and modified polymers. The contact angle of water drops decreased with the amount of NCMA grafted from 95°, the one corresponding to the SBS, to about 73°. T‐peel strength of polymer/polyurethane adhesive/polymer joints made with the modified polymers was larger than those prepared with the original SBS. The peel strength of SBS modified with 1.5 and 3 × 10^?4 mol % of peroxy groups from BPO were five times larger than that of the original SBS. The materials modified using BPO showed peel strengths higher than the ones obtained with DBPH. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4468–4477, 2006     

Hydrolysis of imidazole and 2‐chloropyridine under subcritical and supercritical water conditions

Imidazole and 2‐chloropyridine were used as model molecules to investigate the acid hydrolysis kinetics of agrochemicals in high‐temperature water in a batch reactor system at 28 MPa. Pseudo‐first‐order hydrolysis reaction rate constants for the acid hydrolysis of Imidazole and 2‐chloropyridine were determined in the temperature ranges 200–600 and 400–575°C, respectively, at 28 MPa. Rate constants for both compounds increased with temperature with a local maximum observed at around 400°C due to changes in the physical properties of the solvent. Imidazole and 2‐chloropyridine conversions of 0.95 and 0.99999 were respectively attained at the highest temperature after 30 min of reaction. © 2012 Canadian Society for Chemical Engineering     

Poly(L‐lactide). X. Enhanced surface hydrophilicity and chain‐scission mechanisms of poly(L‐lactide) film in enzymatic,alkaline, and phosphate‐buffered solutions

Attempts were carried out to enhance the surface hydrophilicity of poly(L ‐lactide), that is, poly(L ‐lactic acid) (PLLA) film, utilizing enzymatic, alkaline, and autocatalytic hydrolyses in a proteinase K/Tris–HCL buffered solution system (37°C), in a 0.01N NaOH solution (37°C), and in a phosphate‐buffered solution (100°C), respectively. Moreover, its chain‐scission mechanisms in these different media were studied. The advancing contact‐angle (θ_a) value of the amorphous‐made PLLA film decreased monotonically with the hydrolysis time from 100° to 75° and 80° without a significant molecular weight decrease, when enzymatic and alkaline hydrolyses were continued for 60 min and 8 h, respectively. In contrast, a negligible change in the θ_a value was observed for the PLLA films even after the autocatalytic hydrolysis was continured for 16 h, when their bulk M_n decreased from 1.2 × 10⁵ to 2.2 × 10⁴ g mol^?1 or the number of hydrophilic terminal groups per unit weight increased from 1.7 × 10^?5 to 9.1 × 10^?5 mol g^?1. These findings, together with the result of gravimetry, revealed that the enzymatic and alkaline hydrolyses are powerful enough to enhance the practical surface hydrophilicity of the PLLA films because of their surface‐erosion mechanisms and that its practical surface hydrophilicity is controllable by varying the hydrolysis time. Moreover, autocatalytic hydrolysis is inappropriate to enhance the surface hydrophilicity, because of its bulk‐erosion mechanism. Alkaline hydrolysis is the best to enhance the hydrophilicity of the PLLA films without hydrolysis of the film cores, while the enzymatic hydrolysis is appropriate and inappropriate to enhance the surface hydrophilicity of bulky and thin PLLA materials, respectively, because a significant weight loss occurs before saturation of θ_a value. The changes in the weight loss and θ_a values during hydrolysis showed that exo chain scission as well as endo chain scission occurs in the presence of proteinase K, while in the alkaline and phosphate‐buffered solutions, hydrolysis proceeds via endo chain scission. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1628–1633, 2003     

Synthesis and Physico-Chemical Characterization of Halogenated Partly Aromatic Cardo Copolyesters

Copolyesters of 1,1′-bis(3-methyl-5-chloro-4-hydroxy phenyl) cyclohexane (0.0025 mol), ethylene glycol/propylene glycol/1, 4-butanediol/1,6-hexanediol (0.0025 mol) and terephthaloyl chloride (0.005 mol) have been synthesized by interfacial polycondensation technique by using water-chloroform (4:1 v/v) as an interphase, sodium hydroxide (0.125 mol) as an acid acceptor and cetyl trimethyl ammonium bromide (50 mg) as an emulsifier. The reaction time and temperature were 3 h and 0°C, respectively. The yield of copolymers was 85–87%. Copolyesters are soluble in common solvents and possess moderate molecular weights. The structures of copolyesters are supported by FT-IR and ¹HNMR spectral data. Copolyesters are characterized for their viscosity in chloroform and 1,2-dichloroethane at 30, 35 and 40°C, densities by floatation method (1.139–1.2775 g cm^?3). It is observed that both [η] and density of copolyesters decreased with increase in alkyl chain length. Copolyesters possess excellent hydrolytic stability against water and 10% each of acids, alkalis and salt at room temperature. The observed wt. % change is ±3.15% in the selected environments. A 30 μm thick C1MPT film has 17.8 MPa tensile strength, 50.1 kV mm^?1 electric strength and 2.2 × 10¹² ohm cm volume resistivity. Copolyesters possess high T_g (148–172°C) and are thermally stable up to about 411–426°C and followed single step degradation kinetics involving 70–75% weight loss with 20–24% residual weight above 650°C. Copolyesters followed 1.19–1.94 order degradation kinetics. Activation energy and frequency factors are increased with alkyl chain length.     

Treatment of dyehouse waste‐water by supercritical water oxidation: a case study

BACKGROUND: Supercritical water oxidation (SCWO) of dyehouse waste‐water containing several organic pollutants has been studied. The removal of these organic components with unknown proportions is considered in terms of total organic carbon concentration (TOC), with an initial value of 856.9 mg L^?1. Oxidation reactions were performed using diluted hydrogen peroxide. The reaction conditions ranged between temperatures of 400–600 °C and residence times of 8–16 s under 25 MPa of pressure. RESULTS: TOC removal efficiencies using SCWO and hydrothermal decomposition were between 92.0 and 100% and 6.6 and 93.8%, respectively. An overall reaction rate, which consists of hydrothermal decomposition and the oxidation reaction, was determined for the hydrothermal decomposition of the waste‐water with an activation energy of 104.12 ( ± 2.6) kJ mol^?1 and a pre‐exponential factor of 1.59( ± 0.5) × 10⁵ s^?1. The oxidation reaction rate orders for the TOC and the oxidant were 1.169 ( ± 0.3) and 0.075 ( ± 0.04) with activation energies of 18.194 ( ± 1.09) kJ mol^?1, and pre‐exponential factor of 5.181 ( ± 1.3) L^0.244 mmol^?0.244 s^?1 at the 95% confidence level. CONCLUSION: Results demonstrate that the SCWO process decreased TOC content by up to 100% in residence times between 8 and 16 s under various reaction conditions. The treatment efficiency increased remarkably with increasing temperature and the presence of excess oxygen in the reaction medium. Color of the waste‐water was removed completely at temperatures of 450 °C and above. Copyright © 2010 Society of Chemical Industry     

Effective immobilization of lipase onto a porous gelatin‐co‐Poly(vinyl alcohol) copolymer and evaluation of its hydrolytic properties

Crosslinked copolymers of gelatin and poly(vinyl alcohol) (PVA) with excellent water absorption and water retention abilities were successfully synthesized using ⁶⁰Co γ radiation. Ammonium persulfate (APS), as a water‐soluble initiator and sodium bicarbonate (NaHCO₃) as a foaming agent were used. The best synthesis conditions were evaluated with regard to the maximum percentage of swelling as a function of the APS concentration, NaHCO₃ concentration, amount of water, and reaction time. The maximum swelling percentage (1694.59%) of the copolymer gelatin‐co‐PVA, was obtained at the optimum parameters [APS] = 2.92 × 10^?1 mol/L, [NaHCO₃] = 7.94 × 10^?2 mol/L, and 1.5 mL of water with 31.104 kGy of the γ radiation dose. The copolymer was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) methods. The SEM analysis showed a highly nanoporous and cellular structure of the copolymer. The copolymer was used as a support for lipase immobilization. The optimization of the reaction conditions, including the pH and temperature for immobilization, on the basis of the hydrolysis of p‐nitrophenyl palmitate, was carried out. An excellent efficiency for protein loading (70%) at pH 8.5 by the copolymer was observed. The results observed during the evaluation of the hydrolytic properties showed excellent activity of the bound lipase. The porous gelatin‐co‐PVA bound lipase was found to be stable at 75°C and pH 8.5; it displayed 2.326 ± 0.005 U/g of lipase activity. The stability and activity of the copolymer‐bound lipase were also studied as a function of the time at 75°C, and the biocatalyst was found to be stable and active up to 1 h, beyond which the activity decreased. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39622.     

Synthesis and comparative physicochemical investigation of partly aromatic cardo copolyesters

Copolyesters were synthesized through the condensation of 0.0025 mol of 1,1′‐bis(3‐methyl‐4‐hydroxyphenyl)cyclohexane, 0.0025 mol of ethylene glycol/propylene glycol/1,4‐butanediol/1,6‐hexane diol, and 0.005 mol of terephthaloyl chloride with water/chloroform (4:1 v/v) as an interphase, 0.0125 mol of sodium hydroxide as an acid acceptor, and 50 mg of cetyl trimethyl ammonium bromide as an emulsifier. The reaction time and temperature were 2 h and 0°C, respectively. The yields of the copolyesters were 81–96%. The structures of the copolyesters were supported by Fourier transform infrared and ¹H‐NMR spectral data and were characterized with the solution viscosity and density by a floatation method (1.1011–1.2697 g/cm³). Both the intrinsic viscosity and density of the copolyesters decreased with the nature and alkyl chain length of the diol. The copolyesters possessed fairly good hydrolytic stability against water and 10% solutions of acids, alkalis, and salts at room temperature. The copolyesters possessed moderate‐to‐good tensile strength (11–37.5 MPa), good‐to‐excellent electric strength (19–45.6 kV/mm), excellent volume resistivity (3.8 × 10¹⁵ to 2.56 × 10¹⁷ Ω cm), and high glass‐transition temperatures (148–195°C) and were thermally stable up to about 408–427°C in a nitrogen atmosphere; they followed single‐step degradation kinetics involving 38–58% weight losses and 34–59% residues. The copolyesters followed 2.6–2.9‐order degradation kinetics. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Formation of thermosensitive water‐soluble copolymers with phosphinic acid groups and the thermosensitivity of the copolymers and copolymer/metal complexes

Thermosensitive and water‐soluble copolymers were prepared through the copolymerization of acryloyloxypropyl phosphinic acid (APPA) and N‐isopropyl acrylamide (NIPAAm). The thermosensitivity of the copolymers and copolymer/metal complexes was studied. The APPA–NIPAAm copolymers with less than 11 mol % APPA moiety had a lower critical solution temperature (LCST) of approximately 45°C, but the APPA–NIPAAm copolymers with greater than 21 mol % APPA moiety had no LCST from 25 to 55°C. The APPA–NIPAAm copolymers had a higher adsorption capacity for Sm³⁺, Nd³⁺, and La³⁺ than for Cu²⁺, Ni²⁺ and Co²⁺. The APPA–NIPAAm (10:90) copolymer/metal (Sm³⁺, Nd³⁺, or La³⁺) complexes became water‐insoluble above 45°C at pH 6–7, but the APPA–NIPAAm (10:90) copolymer/metal (Cu²⁺,Ni²⁺, or Co²⁺) complexes were water‐soluble from 25 to 55°C at pH 6–7. The temperature at which both the APPA–NIPAAm copolymers and the copolymer/metal complexes became water‐insoluble increased as the pH values of the solutions increased. The APPA–NIPAAm copolymers were able to separate metal ions from their mixed solutions when the temperature of the solutions was changed; this was followed by centrifugation of the copolymer/metal complexes after the copolymers were added to the metal solutions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 116–125, 2004     

Lipase‐catalyzed esterification of cinnamic acid and oleyl alcohol in organic solvent media

The esterification of cinnamic acid (CA) and oleyl alcohol (OA) in organic solvent media by immobilized lipase Novozym 435 was optimized in terms of selected parameters, including the logarithm of the 1‐octanol/water partition coefficient of the organic solvent (log P, 0.29–4.5), initial water activity (a_w, 0.05–0.75), agitation speed (0–200 rpm), temperature (35–65 °C) and ratio of substrates (CA/OA, 1.0:0.5–1.0:6.0). The results showed that the more hydrophobic solvent mixtures and lower initial a_w values resulted in a higher enzymatic activity and bioconversion yield. The most appropriate solvent medium and initial a_w value was the mixture of iso‐octane/2‐butanone (85:15, v/v) and 0.05, respectively. The results also showed that an agitation speed of 150 rpm and a reaction temperature of 55 °C were optimal for the reaction system. The activation energy (E_a) of the esterification reaction was calculated as 43.6 kJ mol^?1. The optimal ratio of CA to OA was 1.0:6.0, with the absence of any inhibition by OA. Using the optimized conditions, the maximum enzymatic activity was 390.3 nmol g^?1 min^?1, with a bioconversion yield of 100% after 12 days of reaction. In addition, the electrospray ionization‐mass spectroscopy analysis confirmed that the major end product of the esterification reaction was oleyl cinnamate. Copyright © 2005 Society of Chemical Industry     

Thermal decomposition kinetics of thermotropic copolyesters made from trans‐p‐hydroxycinnamic acid and p‐hydroxybenzoic acid

A series of thermotropic copolyesters were synthesized by direct thermal melt polycondensation of p‐acetoxybenzoic acid (PHB) with trans‐p‐acetoxycinnamic acid (PHC). The dynamic thermogravimetric kinetics of the copolyesters in nitrogen were analyzed by four single heating‐rate techniques and three multiple heating‐rate techniques. The effects of the heating rate, copolyester composition, degradation stage, and the calculating techniques on the thermostability and degradation kinetic parameters of the copolyesters are systematically discussed. The four single heating‐rate techniques used in this work include Friedman, Freeman–Carroll, Chang, and the second Kissinger techniques, whereas the three multiple heating‐rate techniques are the first Kissinger, Kim–Park, and Flynn–Wall techniques. The decomposition temperature of the copolyesters increases monotonically with increasing PHB content from 40 to 60 mol %, whereas their activation energy exhibits a maximal value at the PHB content of 50 mol %. The decomposition temperature, activation energy, the order, and the frequency factor of the degradation reaction for the thermotropic copolyester with PHB/PHC feed ratio of 50/50 mol % were determined to be 374°C, 408 kJ/mol, 7.2, and 1.25 × 10²⁹ min^?1, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 445–454, 2004     

Graft copolymerization of acrylic acid on methylcellulose by ceric ion/p‐xylene redox pair

The graft copolymerization of acrylic acid onto methylcellulose by ceric ion/p‐xylene redox pair was investigated in aqueous media under homogeneous conditions. The graft yield dependency on p‐xylene concentration in the range 1.8–45.0 × 10^?5M showed a minimum and an enhanced yield when the methylcellulose interacted with ceric ion and p‐xylene for an initial period of 10 min (preoxidation time) prior to addition of monomer to the reaction medium. This was attributed to the presence of two kinetically controlled reactions initiated by p‐xylyl radical and diradical species. At prolonged preoxidation times of 30 and 60 min, the graft yield dependency on p‐xylene concentration was normal and suggested the presence of only one initiating species. The effect of ceric ion on the graft reaction in the concentration range of 8.33–83.3 × 10^?3M was optimal at 131% graft yield for ceric ion concentration of 16.7 × 10^?3M and was reduced significantly by as much as 75% at the highest concentration of the latter. The temperature dependency of graft yield was negative in the region 30–50°C. At 50°C the initial rate of graft was only 37% of the value at 30°C. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 500–504, 2002; DOI 10.1002/app.10200     

Graft copolymerization of acrylic acid onto cocoyam starch by ceric ion in the presence of N,N′‐dimethylacetamide

Grafting of acrylic acid onto cocoyam starch, Xanthosoma sagittitolium was initiated by ceric ion—N,N′‐dimethylacetamide redox pair in aqueous media. The reaction was characterized by high graft yields of up to 676%, and infrared spectroscopy affirmed the presence of grafted polymer. Graft yield was enhanced by N,N′‐dimethylacetamide (DMAc) in the concentration range, 9.0–36.0 × 10^?4M but lower concentrations were more favorable with the ratio of percentage graft, P_g/P_g0, in the presence and absence of DMAc respectively, of up to 1.34 at 9.0 × 10^?4M of the latter. Ceric ion was nonterminating of the graft reaction and a 10‐fold increase in its concentration of 4.16 × 10^?3M resulted in high efficiency of graft of 50.2% in monomer conversion to grafted polymer. Enhanced homopolymer formation and low efficiency of graft were observed at monomer concentration greater than 0.69M. Long reaction time, greater than 30 min, was unfavorable to the graft reaction and the latter showed negative dependence on temperature in the range, 30–50°C. At 30‐min reaction time, the graft yield at 50°C was not more than 70% of the corresponding value at 30°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Characterization of modulus and glass transition phenomena in poly(L‐lactide)/hydroxyapatite composites

In order to study the dynamic‐mechanical properties of Poly(L‐lactide)/Hydroxyapatite (PLLA/HA) composites, two different molecular weight (inherent viscosity (η_inh): 4.0 (dL/g), and 7.8 (dL/g)) poly(L‐lactide) (PLLA) were synthesized by bulk polymerization and filled with 10%, 30%, and 50% (w/w) with medical grade HA (size range: 25–45 μm and Ca/P = 1.69). The plain PLLA polymers and PLLA/HA composites were compression molded and machined to yield 50 × 3 × 2 mm³ specimens. The composites were investigated by dynamic mechanical thermal analyzer (DMTA) of imposed bending load on rectangular specimens over a temperature range from 30 to 120°C using multiple frequencies (0.3–50 Hz). The results showed that the bending storage modulus (E′) of the composites increased linearly with the percentage of the filler, reaching at 37°C and 0.1 Hz about 2.5, 3.7 and 5.0 GPa with 10, 30 and 50% of HA respectively. The glass transition temperature, evaluated at the tan δ peaks, were in the range 70–80°C and 50–70°C for PLLA matrix and PLLA composites respectively. The activation energies at the glass transition temperature were calculated from the Arrhenius plot in the range of 102–111 Kcal/mol for the composites, whereas 132 and 148 Kcal/mol were found for low and high molecular weight of PLLA respectively. The content of amorphous phase was evaluated from the intensity of tan δ peak. Results showed that HA causes an amorphous phase with a greater mobility with respect to the pure PLLA.