Effect of PHB on the properties of biodegradable PLA blends

Blends of biodegradable polymers polylactic acid/thermoplastic starch/polyhydroxybutyrate (PLA/TPS/PHB) were prepared using a twin-screw extruder. The TPS content was constant (50 %) and the PHB content in the blends was gradually changed from 0 mass % to 20 mass %. TPS was prepared by melting, where a mixture of native starch, water and glycerol was fed into the twinscrew extruder. Average temperature of extrusion was 180°C and the concentration of glycerol was 40 mass %. Influence of the PHB concentration in the blend and that of the processing technology on the mechanical and rheological properties of the PLA/PHB composition containing TPS were studied. Mechanical properties were measured 24 h after the film and monofilament preparation and also after the specific storage time to study the effect of storage on the properties. The results indicate that differences in morphology strongly influence the mechanical properties of the studied materials with identical material composition.     

Thermal properties and applications of low molecular weight polyhydroxybutyrate

The properties of the low molecular weight polyhydroxybutyrate (LMWPHB) and LMWPHB plasticized polyhydroxybutyrate (PHB) are studied using differential scanning calorimetry (DSC), thermogravimetric analysis, wide-angle X-ray diffraction (WAXD), polarized optical microscope (POM), mechanical, and biodegradation tests. The results of DSC, WAXD, and POM indicate that LMWPHB has a lower glass transition temperature (T _g), crystallinity, crystallization rate, melting temperature (T _m), and crystal size than PHB due to its much smaller molecular weight. The tensile strength, T _g, T _m, crystallinity, crystallization rate, and thermal stability of LMWPHB plasticized PHB decrease, while the flexibility and biodegradation rate increase with the increasing content of the added LMWPHB. It is confirmed that LMWPHB can be used to improve the brittleness and control the biodegradation rate of PHB.     

Interaction of sodium cholate with dioctadecyldimethylammonium chloride vesicles in aqueous dispersion

Mixtures of dioctadecyldimethylammonium chloride (DODAC) cationic vesicle dispersions with aqueous micelle solutions of the anionic sodium cholate (NaC) were investigated by differential scanning calorimetry, DSC, turbidity and light scattering. Within the concentration range investigated (constant 1.0 mM DODAC and varying NaC concentration up to 4 mM), vesicle → micelle → aggregate transitions were observed. The turbidity of DODAC/NaC/water depends on time and NaC/DODAB molar concentration ratio R. At equilibrium, turbidity initially decreases smoothly with R to a low value (owing to the vesicle–micelle transition) when R = 0.5–0.8 and then increases steeply to a high value (owing to the micelle–aggregate transition) when R = 0.9–1.0. DSC thermograms exhibit a single and sharp endothermic peak at T_m ≈ 49 °C, characteristic of the melting temperature of neat DODAC vesicles in water. Upon addition of NaC, T_m initially decreases to vanish around R = 0.5, and the main transition peak broadens as R increases. For R > 1.0 two new (endo- and exothermic) peaks appear at lower temperatures indicating the formation of large aggregates since the dispersion is turbid. All samples are non-birefringent. Dynamic light scattering (DLS) data indicate that both DODAC and DODAC/NaC dispersions are highly polydisperse, and that the mean size of the aggregates tends to decrease as R increases.     

Efficient barrier properties of mechanically enhanced agro-extracted cellulosic biocomposites

The objective of this work was to prepare the mechanically stable hydrophobic biocomposites by incorporating the cellulose fibers into the polymer matrices for their applications in biomedical and food packaging. Herein, two different types of biocomposites were prepared by mixing polylactic acid (PLA) and polyhydroxybutyrate (PHB) with the agro-extracted cellulose, separately at 170 °C. The influence of the cellulose fibers on the thermal, mechanical, and barrier properties of polymer matrices (PLA and PHB) was observed. With an increase in the cellulose content in PLA and PHB, the tensile strength of the biocomposite materials significantly improved with the enhancement of 24.45% and 32.08%, respectively, compared with the pure PLA and PHB. Furthermore, a decrease of 74.16% and 73.49% in the water vapor transmission rate and oxygen transmission rate, respectively, was observed for cellulose/PHB biocomposites. This study highlights that adding cellulose fibers significantly improves the mechanical and the barrier properties of PLA and PHB, suggesting their biocomposites for use in biodegradable polymer industries.     

A new study of the enzymatic hydrolysis of carboxymethyl cellulose with a bulk acoustic wave sensor

A new bulk acoustic wave (BAW) cellulase sensing technique, which is based on the enzymatic hydrolysis process of sodium carboxymethylcellulose (CMC) by cellulase, was established. The frequency shift curves of BAW sensor indicated that the viscosity of the tested solutions decreased during the hydrolysis process. The hydrolysis rate of CMC by cellulase was calculated from the frequency shift curves. The hydrolysis rate of CMC under different pH conditions at 30°C showed that cellulase had high hydrolysis ability approximately at pH 5.0. Kinetic parameters (the Michaelis constant K_m and the maximum rate V_max) of the process were estimated by using a linear method of Lineweaver–Burk plot. K_m is 1.95±0.25 mg ml⁻¹ and V_max is −(4.25±0.58)×10⁻³ g^1/2 cm^−3/2 cP^1/2 min⁻¹. Also the activation energy (E_a) of the enzymatic hydrolysis, with a value of 51.99±1.26 kJ mol⁻¹, was estimated in this work.     

Influence of electronic and steric effects on stability constants and electrochemical reversibility of divalent ion complexes with glycine and sarcosine. A glass electrode potentiometric, sampled direct current polarographic, virtual potentiometric, and molecular modelling study

Cd^II complexes with glycine (gly) and sarcosine (sar) were studied by glass electrode potentiometry, direct current polarography, virtual potentiometry, and molecular modelling. The electrochemically reversible Cd^II–glycine–OH labile system was best described by a model consisting of M(HL), ML, ML₂, ML₃, ML(OH) and ML₂(OH) (M = Cd^II, L = gly) with the overall stability constants, as log β, determined to be 10.30 ± 0.05, 4.21 ± 0.03, 7.30 ± 0.05, 9.84 ± 0.04, 8.9 ± 0.1, and 10.75 ± 0.10, respectively. In case of the electrochemically quasi-reversible Cd^II–sarcosine–OH labile system, only ML, ML₂ and ML₃ (M = Cd^II, L = sar) were found and their stability constants, as log β, were determined to be 3.80 ± 0.03, 6.91 ± 0.07, and 8.9 ± 0.4, respectively. Stability constants for the ML complexes, the prime focus of this work, were thus established with an uncertainty smaller than 0.05 log units. The observed departure from electrochemical reversibility for the Cd–sarcosine–OH system was attributed mainly to the decrease in the transfer coefficient . The MM2 force field, supplemented by additional parameters, reproduced the reported crystal structures of diaqua-bis(glycinato-O,N)nickel(II) and fac-tri(glycinato)-nickelate(II) very well. These parameters were used to predict structures of all possible isomers of (i) [Ni(H₂O)₄(gly)]⁺ and [Ni(H₂O)₄(sar)]⁺; and (ii) [Ni(H₂O)₃(IDA)] and [Ni(H₂O)₃(MIDA)] (IDA = iminodiacetic acid, MIDA = N-methyl iminodiacetic acid) by molecular mechanics/simulated annealing methods. The change in strain energy, ΔU_str, that accompanies the substitution of one ligand by another (ML + L′ → ML′ + L), was computed and a strain energy ΔU_str = +0.28 kcal mol⁻¹ for the reaction [Ni(H₂O)₄(gly)]⁺ + sar → [Ni(H₂O)₄(sar)]⁺ + gly was found. This predicts the monoglycine complex to be marginally more stable. By contrast, for the reaction [Ni(H₂O)₃IDA] + MIDA → [Ni(H₂O)₃MIDA] + IDA, ΔU_str = −0.64 kcal mol⁻¹, and the monoMIDA complex is predicted to be more stable. This correlates well with (i) stability constants for Cd–gly and Cd–sar reported here; and (ii) known stability constants of ML complex for glycine, sarcosine, IDA, and MIDA.     

低毒锌类催化剂制备聚乳酸的研究

采用低毒锌类催化剂制备了一系列具有高分子量、不同光学纯度及热力学性质的聚乳酸材料. 以金属锌作催化剂制备丙交酯, 研究了不同裂解温度对产物光学纯度的影响. 随后在低毒催化剂乳酸锌的作用下使丙交酯开环聚合, 进一步研究了单体的光学纯度对聚乳酸立体规整性的影响, 以及聚合过程中的结晶对聚合物分子量和热力学行为的影响. 并用旋光仪、核磁共振氢谱(1H NMR)、凝胶渗透色谱(GPC)、差示扫描量热分析(DSC)等方法对产物进行表征. 结果表明, 合适的裂解温度有利于合成高光学纯度的丙交酯; 在低毒乳酸锌的催化作用下, 高光学纯度的单体以及聚合过程中的结晶都有利于制备高分子量聚乳酸.     

Mechanical and biodegradation performance of short natural fibre polyhydroxybutyrate composites

The work outlined in this paper describes the evaluation of polyhydroxybutyrate (PHB) based natural fibre composites via an extrusion – injection moulding process. Virgin PHB was compounded with two different naturally occuring plant fibres, hemp and jute, and a third, regenerated cellulose fibre, lyocell. Composite materials containing 10–30 wt% of each type of fibre were obtained by twin screw extrusion and the resultant material was injection moulded to produce tensile samples suitable for mechanical characterisation. Mechanical properties were determined using tensile, impact and flexural testing. Melt flow index and water absorption studies were also carried out on the biocomposite materials, and Fourier transform infrared spectroscopy was used to examine the bonding between the polymer and each fibre type. The rate of biodegradation was also observed by placing composite samples in compost and measuring weight loss weekly. The biocomposites produced using this method were shown to have increased rates of biodegradation whilst exhibiting significantly improved flexural properties.     

Thermal stability and related thermodynamic properties of N-ethylthiourea

The enthalpy and entropy of sublimation of N-ethylthiourea were obtained from the temperature dependence of its vapour pressure measured by both the torsion–effusion and the Knudsen effusion method in the temperature range 360–380 K. The compound undergoes no solid-to-solid phase transition or decomposition below 380 K. The pressure against reciprocal temperature resulted in lg(p, kPa) = (13.40 ± 0.27) − (6067 ± 102) /T(K). The molar sublimation enthalpy and entropy at the mid interval temperature were Δ_subH_m(370 K) = (116.1 ± 2.0) kJ mol⁻¹ and Δ_subS_m(370 K) = (218.0 ± 5.2) J mol⁻¹ K⁻¹, respectively. The same quantities derived at 298.15 K were (118.8 ± 2.1) kJ mol⁻¹ and (226.1 ± 5.5) J mol⁻¹ K⁻¹, respectively.     

Experimental studies of pressure/temperature dependence of protein adsorption equilibrium in reversed-phase high-performance liquid chromatography

The effect of the average pressure and temperature of the column on the adsorption equilibrium of insulin variants on a C₈ bonded silica was studied in isocratic reversed-phase HPLC. Analytical injections of samples of four different insulins (bovine, porcine, Lys–Pro and human recombinant) were carried out at constant flow-rate but under increased average pressure. The temperature dependence of the retention parameters over the range 25–50 °C was studied under two different average column pressures (47 and 147 bar). Substantial increases of the retention time (up to 300%) were observed when the pressure and/or the temperature were increased. Similar adsorption-induced changes in the partial molar volume at constant temperature (ΔV_m≈102 ml/mol) were found for all the variants studied. Furthermore, ΔV_m was revealed to be practically independent of the temperature, which suggests that the temperature has no or very little influence on the mechanism of the pressure induced perturbations in the molecular structure of the solute. This conclusion was also derived from the observed temperature dependence of the logarithm of the retention factor (k) measured under different pressures. The relation between the temperature and ln k was nonlinear with a parabolic shape. Moreover, the shapes of the plots corresponding to the low and high pressures were found to be exactly the same, except that the curves were vertically shifted, due to the difference between the two average column pressures. These results indicate that pressure and temperature affect the retention behavior of insulins in a different and separate way.     

Purification and Properties of an Extracellular Polyhydroxybutyrate Depolymerase from Pseudomonas mendocina DSWY0601

An extracellular polyhydroxybutyrate(PHB) depolymerase was purified to homogeneity from the culture supernatant of a PHB-degrading bacterium, Pseudomonas mendocina DSWY0601, which was isolated from brewery sewage for the ability to form clear zones on the PHB mineral agar plates. The molecular weight of the purified PHB depolymerase as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE) was approximately 59800 at the optimal temperature and pH value being 50 ℃ and 8.5, respectively. PHB depolymerase was stable in a temperature range of 20―50 ℃ and sensitive to pH value within a pH range of 8.0―9.5. PHB depolymerase degraded poly-3-hydroxybutyrate-co-4-hydroxybutyrate(P3/4HB) and poly-3-hydroxybutyrate-co-3- hydroxyvalerate(PHBV) but did not degrade poly(lactic acid)(PLA), poly(butylene succinate)(PBS) or poly- (caprolactone)(PCL). PHB depolymerase was sensitive to phenylmethylsulfonyl fluoride(PMSF), H₂O₂ and SDS. The main product after enzymatic degradation of PHB was indentified as 3-hydroxbutyrate monomer(3HB) by mass spectrometric analysis, suggesting that PHB depolymerase acted as an exo-type hydrolase. Analysis of phaZ_pm gene reveals that PHB depolymerase is a typical denatured short-chain-length PHA(dPHA_SCL, PHA=polyhydroxyalkanoate) depolymerase containing catalytic domain, linker and substrate-binding domain.     

(Trifluoromethyl)sulfanyl sulfinylimine, CF3SNSO. Structure and conformation in the electronic ground and excited states

The molecular structure of (trifluoromethyl)sulfanyl sulfinylimine, CF₃---S---N=S=O, was determined by gas electron diffraction (GED) and ab initio calculations (HF/3–21G*, HF/6–31+G* and MP2/6–31+G*). Experimental and theoretical methods result in a structure with planar C---S---N=S=O skeleton (C_s symmetry), anti orientation of the S---C bond relative to the N=S bond and syn orientation of the S---N bond relative to the S=O double bond (anti-syn structure). The following skeletal parameters (r_a values with 3σ uncertainties) were derived in the GED analysis: S---C, 1.831(4) Å; S---N, 1.684(5) Å; N=S, 1.538(6) Å; S=O, 1.453(6) Å; C---S---N, 94.6(8)°; S---N=S, 120.6(6)°; N=S=O: 116.5(8)°. A normal coordinate analysis based on FTIR (gas), FTIR (matrix) and Raman (liquid) spectra was performed. The UV (gas) spectrum was recorded and interpretation of the resonance Raman effect leads to the conclusion that the molecular symmetry (C_s) is retained upon electronic excitation.     

Thermal degradation studies of methacrylonitrile polymers and copolymers—3. Polymers capable of chain end-initiated colouration

Polymethacrylonitrile (PMAN) prepared by free-radical polymerisation with the initiator 4,4′-azo-bis(4-cyanovaleric acid) (ACVA) has chain ends from the initiator fragment which incorporate carboxyl groups. These ends are found to act as reactive sites for initiation of colouration in the polymer at temperatures from 140 °C. Several polymers, with different chain-end concentrations, have been made and the thermal degradation behaviour has been studied under programmed heating in the absence of air to 500 °C, with full product characterisation. In contrast with pure PMAN prepared with 2,2′-azo-bis(isobutyronitrile) (AIBN) as initiator, which degrades quantitatively to monomer, these ACVA-initiated polymers give very much reduced monomer yields, an important tar/wax fraction and a substantial amount of residue, amounting to 32–48% of the sample weight, dependent on the initial molecular weight of the polymer. The infrared spectral changes at the onset of the colouration reaction have been examined at 160 °C. Mechanisms are suggested to account for the observed products.     

Cyano-substituted polyamides and polyimides prepared from 2,6-bis(3-aminobenzylidene)-1-dicyanomethylene-cyclohexane

Cyclohexanone was condensed with 3-nitrobenzaldehyde in the presence of dry HCl as catalyst to afford 2,6-bis(3-nitrobenzylidene)cyclohexane. The condensation of the latter with malononitrile yielded 2,6-bis(3-nitrobenzylidene)-l-dicyanomethylene-cyclohexane that was hydrogenated to the corresponding diamine. The latter was used as a reagent for preparing various unsaturated polyamides and polyimides bearing dicyanomethylene segments. In addition, a model diamide and diimide were synthesized. The polymers were soluble in polar aprotic solvents and certain strong inorganic and organic acids. They were crosslinked upon heating at 300°C for 20 hr. The crosslinked polymers were stable up to 377–408°C in N₂ or air and afforded anaerobic char yields of 65–70° at 800°C.     

[(Me3Sn)2(Me3Sb)M(CN)6]∞ (M = Fe, Ru): Neuartige Organo-Sn/Sb-Polymere von besonderer chemischer und thermischer stabilität

The thermally (decomp. temp. 300°C) and completely air stable, novel coordination polymers [(Me₃Sn^IV)₂(Me₃Sb^V)M^II(CN)₆]_∞ with M = Fe and Ru can be prepared by co-precipitation from aqueous solutions of Me₃SnCl, Me₃SbBr₂ and K₄[(M(CN)₆], or, alternatively, by the ion-exchange-like reaction of the polymers [A(Me₃Sn)₃M(CN)₆]_∞ (A⁺ = Et₄N⁺, Cp₂Co⁺, Me₃Sn⁺ etc.) with Me₃SbBr₂. IR-spectroscopic findings suggest a statistical distribution of quasi-octahedral M(CN-Sn··)_6-x(CNSb ··)_x building blocks (with x = 0–6) within a three-dimensional network.     

Phase behavior, conformations, thermodynamic properties, and molecular motion of multicomponent paraffin waxes: A Raman spectroscopy study

Variable-temperature (72–20 °C) studies of Raman spectra (3100–800 cm⁻¹) and thermal analysis of multicomponent paraffin wax have been carried out. The disorder–order transition under liquid–solid transition was observed and their temperature ranges were obtained through the S_lateral order parameter as a function of temperature. From 56 to 43 °C, the paraffin undergoes a conformational state transition of non-extended chain state (NECS) to extended chain state (ECS). The enthalpy and entropy change for the transition obtained by van’t Hoff analysis were 214.286 ± 21 kJ/mol and 0.661 ± 0.066 kJ/mol/K, respectively. The enthalpy determined by differential scanning calorimetry (DSC) was 52.165 ± 5.2 kJ/mol, which is smaller than the van’t Hoff enthalpy due to larger effective non-extended chain state. The variation of Raman spectra with decreasing temperature presents the structure evolution and molecular motion during the crystallization of paraffin wax.     

Molecular structure of 3-methylthiophene studied by gas electron diffraction combined with microwave spectroscopic data

The molecular structure of 3-methylthiophene

has been determined by gas electron diffraction (GED) combined with microwave (MW) spectroscopic data. Ab initio calculations at the HF/3–21G* level were carried out and used as structural constraints in the data analysis. The torsional vibration of the methyl group was treated as a large-amplitude motion. The structural parameters were determined to be: r_g(S---C₂) = 1.719(2) Å, r_g(C₂=C₃) = 1.370(3) Å, r_g(C₃---C₆) = 1.497(6) Å, r_g(C₂---H) = 1.101(5) Å, CSC = 91.6(2)°, SC₂C₃ = 113.3(5)°, SC₅C₄ = 111.3(3)°, C₂C₃C₆ = 123.2(11)° and C₃C₆H = 112(2)°. The values of r(S---C₂) − r(S---C₅) and r(C₂=C₃) − r(C₄=C₅) were fixed at the 3–21G* value of 0.002Å. Parenthesized values are the estimated limits of error (3σ) referring to the last significant digit.     

The electrolyte NRTL model and speciation approach as applied to multicomponent aqueous solutions of H2SO4, Fe2(SO4)3, MgSO4 and Al2(SO4)3 at 230–270 °C

This work presents chemical modeling of solubilities of metal sulfates in aqueous solutions of sulfuric acid at high temperatures. Calculations were compared with experimental solubility measurements of hematite (Fe₂O₃) in aqueous ternary and quaternary systems of H₂SO₄, MgSO₄ and Al₂(SO₄)₃ at high temperatures. A hybrid model of ion-association and electrolyte non-random two liquid (ENRTL) theory was employed to fit solubility data in three ternary systems H₂SO₄–MgSO₄–H₂O, H₂SO₄–Al₂(SO₄)₃–H₂O at 235–270 °C and H₂SO₄–Fe₂(SO₄)₃–H₂O at 150–270 °C. Employing the Aspen Plus™ property program, the electrolyte NRTL local composition model was used for calculating activity coefficients of the ions Al³⁺, Mg²⁺ Fe³⁺ and SO₄²⁻, HSO₄⁻, OH⁻, H₃O⁺, respectively, as well as molecular species. The solid phases were hydronium alunite (H₃O)Al₃(SO₄)₂(OH)₆, hematite Fe₂O₃ and magnesium sulfate monohydrate (MgSO₄)·H₂O which were employed as constraint precipitation solids in calculating the metal sulfate solubilities. A correlation for the equilibrium constants of the association reactions of complex species versus temperature was implemented. Based on the maximum-likelihood principle, the binary interaction energy parameters for the ionic species as well as the coefficients for equilibrium constants of the reactions were obtained simultaneously using the solubility data of the ternary systems. Following that, the solubilities of metal sulfates in the quaternary systems H₂SO₄–Fe₂(SO₄)₃–MgSO₄–H₂O, H₂SO₄–Fe₂(SO₄)₃–Al₂(SO₄)₃–H₂O at 250 °C and H₂SO₄–Al₂(SO₄)₃–MgSO₄–H₂O at 230–270 °C were predicted. The calculated results were in excellent agreement with the experimental data.     

Heat capacity, enthalpy and entropy of strontium bismuth niobate and strontium bismuth tantalate

The heat capacities and enthalpy increments of strontium bismuth niobate SrBi₂Nb₂O₉ (SBN) and strontium bismuth tantalate SrBi₂Ta₂O₉ (SBT) were measured by the relaxation method (2–150 K), Calvet-type heat-conduction calorimetry (305–570 K) and drop calorimetry (773–1373 K). The temperature dependences of non-transition heat capacities in the form C_pm = 324.47 + 0.06371T − 5.0755 × 10⁶/T² J K⁻¹ mol⁻¹ (298–1400 K) and C_pm = 320.22 + 0.06451T − 4.7001 × 10⁶/T² J K⁻¹ mol⁻¹ (298–1400 K) were derived for SBN and SBT, respectively, by the least-squares method from the experimental data. Furthermore, the standard molar entropies at 298.15 K S_m°(SBN)=327.15±0.80 and S_m°(SBT)=339.23±0.72 J K⁻¹ mol⁻¹ were evaluated from the low-temperature heat capacity measurements.     

Potentiometric study of Cd(II) and Pb(II) complexation with two high molecular weight poly(acrylic acids); comparison with Cu(II) and Ni(II)

The cadmium (II) or lead (II) complex formation with two poly(acrylic acids) of high molecular weight (Mw=2.5×10⁵ and 3×10⁶) was investigated in dilute aqueous solution (NaNO₃ 0.1 mol l⁻¹; 25°C). Potentiometric titrations were carried out to determine the stability constants of the MA and MA₂ complex species formed. Bjerrum’s method, modified by Gregor et al. (J. Phys. Chem. 59 (1955) 34–39), for the study of polymeric acids was used. The results were compared to those previously obtained in the same conditions with copper (II) and nickel (II) . It appeared that the two polymers under study present similar binding properties and that the stability constants of the complex species formed increased in the following order, depending on the metal ion: Ni(II)β₁₀₂ was found to be close to 7.0) and allowed the formation of the predominant PbA₂ species in a quite large pH domain. Finally, the greater stability of PAA complexes compared to those of their monomeric analogs, glutaric and acetic acids, was confirmed.