Influence of compatibilizer on the structure properties of polylactic acid/natural rubber blends

Polylactic acid (PLA) was toughened by 5–20 wt % of natural rubber (NR). Two different compatibilizers maleated PLA (PLA-g-MA) and maleated NR (NR-g-MA) were used as coupling agent. The blends were prepared using twin screw extruder at varying levels of NR. Mechanical, thermal and morphological analyses were carried out to study the effect of compatibilizer on PLA/NR blends compatibility.     

Melt processing of maleic anhydride grafted poly(lactic acid) and its compatibilizing effect on poly(lactic acid)/poly(butylene adipate-<Emphasis Type="Italic">co</Emphasis>-terephthalate) blend and their composite

Poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT) blends were prepared using melt processing. The effects of maleic anhydride grafted PLA (PLA-g-MA) and calcium carbonate (CaCO₃) content on mechanical, thermal, and morphological properties of the blends were investigated. PLA-g-MA was synthesized by varying monomer and initiator contents using a reactive melt-grafting process. Tensile properties of PLA/PBAT blend were enhanced with adding 2 phr of PLA-g-MA. SEM micrographs exhibited the improvement of interfacial adhesion between PLA and PBAT in the compatibilized blend. Moreover, thermal stability of the blends improved with presence of PLA-g-MA. With increasing CaCO₃ content, Young’s modulus of the composites increased.     

Investigation of polyethylene‐grafted‐maleic anhydride presence as a compatibilizer on various properties of nanocomposite films based on polyethylene/ethylene vinyl alcohol/ nanoclay

High oxygen barrier films were prepared based on low‐density polyethylene (LDPE)/ethylene vinyl alcohol (EVOH)/ nanoclay and polyethylene‐grafted‐maleic anhydride (LDPE‐g‐MA) as a compatibilizer. Box–Behnken statistical experiment design methodology was employed to study the effects of nanoclay, LDPE‐g‐MA, and EVOH presence and their contents on various properties of the final films. The R² parameter varied between 0.89 and 0.99 for all the obtained responses. The morphology of the samples was evaluated. Results of oxygen transfer rate (OTR) test indicated that the addition of EVOH up to 30 wt% to neat LDPE can decrease oxygen permeability significantly. The addition of nanoclay also decreased the permeability of resulting films but, LDPE‐g‐MA reduced the permeability of the films only at an optimal content. Elastic modulus was increased with the addition of nanoclay, EVOH, and LDPE‐g‐MA to the matrix. An increase in EVOH content in the samples improved the tensile strength. Effect of nanoclay on tensile strength was highly dependent on the presence of a compatibilizer. The addition of compatibilizer to the samples and increasing its content enhanced the tensile strength of the specimens. Incorporation of nanoclay, EVOH, and LDPE‐g‐MA to the LDPE matrix and increasing the amount of these components in the samples led to higher storage modulus, zero shear rate viscosity, and shear thinning exponent, but, lowered the terminal slope and the frequency of intersection point of storage modulus (G′) and loss modulus (G″). The only exception was that EVOH increment resulted in a lower shear thinning exponent. Copyright © 2016 John Wiley & Sons, Ltd.     

Correlation of Morphology Evolution with Superior Mechanical Properties in PA6/PS/PP/SEBS Blends Compatibilized by Multi-phase Compatibilizers

In this study,the maleic anhydride(MAH)and styrene(St)dual monomers grafted polypropylene(PP)and poly[styrene-b-(ethylene-co-butylene)-b-styrene](SEBS),i.e.PP-g-(MAH-co-St)and SEBS-g-(MAH-co-St)are prepared as multi-phase compatibilizers and used to compatibilize the PA6/PS/PP/SEBS(70/10/10/10)model quaternary blends.Both PS and SEBS are encapsulated by the hard shell of PP-g-(MAH-co-St)in the dispersed domains(about 2μm)of the PA6/PS/PP-g-(MAH-co-St)/SEBS(70/10/10/10)quaternary blend.In contrast,inside the dispersed domains(about 1μm)of the PA6/PS/PP/SEBS-g-(MAH-co-St)(70/10/10/10)quaternary blend,the soft SEBS-g-(MAH-co-St)encapsulates both the hard PS and PP phases and separates them.With increasing the content of the compatibilizers equally,the morphology of the PA6/PS/(PP+PP-g-(MAH-co-St))/(SEBS+SEBS-g-(MAH-co-St))(70/10/10/10)quaternary blends evolves from the soft(SEBS+SEBS-g-(MAH-co-St))encapsulating PS and partially encapsulating PP(about 1μm),then to PS exclusively encapsulated by the soft SEBS-g-(MAH-co-St)and then separated by PP-g-(MAH-co-St)inside the smaller domains(about 0.6μm).This morphology evolution has been well predicted by spreading coefficients and explained by the reaction between the matrix PA6 and the compatibilizers.The quaternary blends compatibilized by more compatibilizers exhibit stronger hierarchical interfacial adhesions and smaller dispersed domain,which results in the further improved mechanical properties.Compared to the uncompatibilized blend,the blend with both 10 wt%PP-g-(MAH-co-St)and 10 wt%SEBS-g-(MAH-co-St)has the best mechanical properties with the stress at break,strain at break and impact failure energy improved significantly by 97%,71%and 261%,respectively.There is a strong correlation between the structure and property in the blends.     

Synergistic effect of nucleation and compatibilization on the polylactide and poly(butylene adipate-<Emphasis Type="Italic">co</Emphasis>-terephthalate) blend films

Polylactide (PLA) films blended with 10 wt% poly(butylene adipate-co-terephthalate) (PBAT) were prepared by using a twin screw extruder in the presence of the nucleating agent of titanium dioxide (TiO₂) and the compatibilizers of toluene diisocyanate (TDI) and PLA-grafted-maleic anhydride (PLA-g-MA). The synergistic effect of the nucleation and compatibilization on the properties and crystallization behavior of the PLA/PBAT (PLB) films was explored. The results showed that the addition of TiO₂ significantly enhanced the tensile strength and the impact tensile resistance of the PLB films while slightly decreased its thermal stability. In addition, the compatibilizers of TDI and PLA-g-MA in the system not only affected the crystallinity and cold crystallization process of the PLB films, but also increased the mechanical properties of them due to the improvement of the interfacial interaction between PLA and PBAT revealed by the morphological measurement. The synergistic effects of the nucleating agent and the compatibilizer afforded the blend films with increased tensile strength and impact tensile toughness, improved cold crystallization property and χ _c.     

Synthesis and Characterization of Butyl Acrylate-based Graft Polymers with Thermo-responsive Branching Sites <Emphasis Type="Italic">via</Emphasis> the Diels-Alder Reaction of Furan/Maleimide

Thermo-responsive butyl acrylate/furfuryl methacrylate copolymer-based (PBF backbone) graft (co)polymers with dynamic covalent linkages between their backbones and side chains via the Diels-Alder reaction of furan/maleimide were synthesized. Atom transfer radical polymerization (ATRP) was used to synthesize graft copolymers with thermo-responsive transformation from graft copolymers to linear polymers with bimodal or wide MWD. The NMR measurements indicated that the Diels-Alder reaction and retro-Diels-Alder reaction occurred, depending on the change of the temperature, meaning that the side chains could be cleaved and reformed according to the variation of the temperature. GPC measurements demonstrated that the molecular weights of the polymers were thermoresponsive. Furthermore, three graft copolymers with various branching chains (PBF-g-PBA, PBF-g-P(BMA-co-MA) and PBF-g-PBMA) were compared to study the influence of compatibility between the backbone and the branching chain on the efficiency of Diels-Alder reaction after the cleavage of the DA linkage. The results showed that the ability of the side chains to come back to the main chain was strongly affected by the compatibility between the backbone and the side chains and the flexibility of the polymer chains.     

Production of <Emphasis Type="Italic">R</Emphasis>-Mandelic Acid Using Nitrilase from Recombinant <Emphasis Type="Italic">E. coli</Emphasis> Cells Immobilized with Tris(Hydroxymethyl)Phosphine

Recombinant Escherichia coli cells harboring nitrilase from Alcaligenes faecalis were immobilized using tris(hydroxymethyl)phosphine (THP) as the coupling agent. The optimal pH and temperature of the THP-immobilized cells were determined at pH 8.0 and 55 °C. The half-lives of THP-immobilized cells measured at 35, 40, and 50 °C were 1800, 965, and 163 h, respectively. The concentration of R-mandelic acid (R-MA) reached 358 mM after merely 1-h conversion by the immobilized cells with 500 mM R,S-mandelonitrile (R,S-MN), affording the highest productivity of 1307 g L^?1 day^?1 and the space-time productivity of 143.2 mmol L^?1 h^?1 g^?1. The immobilized cells with granular shape were successfully recycled for 60 batches using 100 mM R,S-MN as substrate at 40 °C with 64% of relative activity, suggesting that the immobilized E. coli cells obtained in this study are promising for the production of R-MA.     

EPR study of the nature of the impurity centers responsible for the scintillation properties of the Li<Subscript>2</Subscript>Zn<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> crystal

The binary molybdate Li₂Zn₂(MoO₄)₃ of a new crystal type was characterized by EPR, optical spectroscopy, and X-ray diffraction methods. The crystals have the Pnma symmetry group and the lattice parameters a = 5.1139(5) Å, b = 10.4926(13) Å, c = 17.6445(22) Å; Z = 4. The crystals possess scintillation properties; emission is caused by the presence of impurity levels in the forbidden band. The EPR studies of the nature of the impurity centers responsible for the scintillation characteristics of the crystal showed that the centers were Cu²⁺ ions substituted for zinc ions in the oxygen octahedra. The directions of the main values of the g and tensors (g _zz , A _zz ) correspond to the direction of O-Cu-O of the oxygen octahedron distorted along the Z axis. The EPR spectra of the copper ions are described by the spin Hamiltonian with the parameters g _‖ = 2.38, g _⊥ = 2.06; A _‖ = 116 G, A _⊥ = 0 G.     

Induction of radiative forbidden transitions in an oxygen molecule in O<Subscript>2</Subscript>–H<Subscript>2</Subscript>O collision complexes

By the DFT/B3LYP method the equilibrium structures of oxygen complexes with water are calculated in various geometric conformations with symmetries C _2v and C _s . By the MRCI/CASSCF method potential energy surface cross-sections of the ^1.3[O₂–H₂O] complexation reaction are constructed. With taking into account the spin-orbit coupling, the forbidden transition moments a ¹Δ _g –X ³Σ _g ^?, b ¹Σ _g ⁺–a ¹Δ _g , c ¹Σ _u ^?–a ¹Δ _g , A ³Σ _u ⁺–X ³Σ _g ^? of the complexes are calculated and changes in their intensities at different geometric configurations of the complex are revealed.     

Study on anti-UV aging mechanism of PP-<Emphasis Type="Italic">g</Emphasis>-AN in the PP/PP-<Emphasis Type="Italic">g</Emphasis>-AN blend

In order to verify the anti-UV aging mechanism about polypropylene-grafting-acrylonitrile (PP-g-AN) to polypropylene (PP), the structural analysis of the PP/PP-g-AN blend before and after aging was carried out via the X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared Spectrometry (FTIR) and UV-visible Absorbance Spectrum (UV–Vis). Inference on PP-g-AN anti-aging process was proposed and confirmed.     

Asymmetric Synthesis of 3-Substituted 4-Oxoesters Using the SAMP-/RAMP-Hydrazone Method

Based on aldehydes 1a—f or ketone 1g, 3-substituted 4-oxo esters 6a—g were synthesized in three steps in moderate to good overall yield (12—50%) and in excellent enantiomeric excesses (ee >90—>95%) by an Umpolung-strategy employing the SAMP-/RAMP-hydrazone method. The key step in the synthesis is the highly diastereoselective alkylation of lithiated SAMP-hydrazones 3a—g (chiral d²-nucleophiles) with tert-butyl bromoacetate (4) (a²-electrophile) to furnish the alkylated 3-hydrazono tert-butylesters 5a—g in good yields (58—91%) and in excellent diastereomeric excesses (de >90—>98%). Regeneration of the carbonyl functionality by cleavage of the hydrazones 5a—g was accomplished either by acidic hydrolysis or ozonolysis to give the acid labile and oxidation-sensitive 3-substituted 4-oxo esters 6a—g in moderate yields (19—63%) and in excellent enantiomeric excesses (ee >90—>95%). The absolute configuration of compounds 6a—g were assigned by conversion of 4-oxo esters (S)-6d and (R)-6e into their corresponding known 3-substituted λ-butyrolactones (S)-7d and (R)-7e.     

Molecular dynamics simulations of the characteristics of sodium carboxymethyl cellulose with different degrees of substitution in a salt solution

Sodium carboxymethyl cellulose (SCMC) with different degrees of substitution (DS) possesses structural characteristics and physicochemical properties that are important in broad areas of industrial applications. This reported work investigated the structural characteristics, including the effective length (L _ef), the radius of gyration (R _g), and the hydrodynamic radius (R _H), and the physicochemical properties, including intrinsic viscosity ([η]) and salt tolerance, of SCMC with a DS more than 1.0 in NaCl solution using molecular dynamics (MD) simulations. In the MD simulations, the DS of SCMC varied from 1.2 to 2.8, and the NaCl concentration varied from 0 to 1.4 mol/L. MD simulation results showed that with the increment of NaCl concentration, the L _ef (or R _g or R _H) of SCMC decreased; with the increment of the DS, the L _ef of SCMC increased. Also, the variation tendency of [η] in the NaCl solution was consistent with its L _ef (or R _g or R _H). It was noted that the salt tolerance (represented by D) of SCMC increased as the DS increased. In addition, the sharp variation of the D value of SCMC occurred in the range of DS of 1.6 to 2.0, which agreed with the reported experimental results. Radial distribution function analyses showed that the Na⁺ cations had a stronger interaction with the carboxyl groups in SCMC with lower DS when it was present in a salt solution of higher concentration, which also reasonably explained the variation of L _ef, R _g, R _H, [η], and D of SCMC in NaCl solution.     

Dielectric properties of films of Ag-ED20 epoxy nanocomposite synthesized in situ. Temperature dependence of direct current conductivity

The influence of silver myristate used as a precursor of silver nanoparticles on the direct current conductivity σ _dc of epoxy polymer within the concentration range of ≤0.8 wt % was investigated. The value of direct current conductivity was determined on the basis of analysis of the frequency dependence of complex permittivity within the frequency range of 10^?2–10⁵ Hz. The temperature dependence of σ _dc is composed of two regions. The dependence corresponds to the Vogel-Fulcher-Tammann empirical law σ _dc = σ _dc0exp{?DT ₀/(T-T ₀)} (where T ₀ is the Vogel temperature and D is the strength parameter) at temperatures higher than the glass transition temperature T _g. At the same time, T ₀ does not depend on the concentration of nanoparticles. The Arrhenius temperature dependence characterized by activation energy about 1.2 eV is observed at temperatures lower than T _g. The observed shape of the temperature dependence is related to the change in the mechanism of conductivity after “freezing” of ionic mobility at temperatures lower than T _g. The value of σ _dc is increased as the concentration of nanoparticles is raised within the temperature range of T > T _g. The obtained dependence of σ _dc on silver myristate concentration is similar to the root one, indicating the absence of percolation within the studied range of concentrations.     

Interaction of active particles of oxygen plasma with polypropylene

Changes in the chemical composition of surface were studied and the rates of formation of gaseous degradation products during polypropylene treatment in oxygen plasma and its flowing afterglow were determined by means of attenuated total internal reflectance IR spectroscopy and mass spectrometry. It was found that surface oxidation at minimal degradation rates is reached upon the joint action of O₂(a ¹Δ _g ) molecules and ground-state oxygen molecules, whereas O(³ P) atoms participate in both oxidation processes and the processes of degradation of oxygen-containing groups leading to the formation of gaseous products. It was shown that only the action of plasma leads to the formation of vinyl and vinylidene double bonds, which disappear in reactions with O₂(a ¹Δ _g ) molecules and O(³ P) atoms.     

Thermal and dielectric characterization of multi-walled carbon nanotubes−thermoplastic polyurethanes composites

Multi-walled carbon nanotubes–thermoplastic polyurethanes composites were characterized by means of differential scanning calorimetry and dielectric relaxation spectroscopy. The composite is characterized by two glass transition temperatures T _g . The T _g associated with the soft segment decreases by increasing of carbon nanotubes content, while carbon nanotubes content has practically no effect on the value of the T _g associated with the hard segments. It was observed that rising the temperature and carbon nanotubes content resulted in the increased of both the dielectric permittivity and the loss factor. The presence of carbon nanotubes produces an enhancement of charge carriers trapping, increasing the electrical conductivity. The electrical conductivity of the composite was found to exhibit an insulator to conductor transition at a carbon nanotubes critical content, i.e., the percolation threshold, near 6 wt %.     

Thermal Rearrangements of 3<Emphasis Type="Italic">H</Emphasis>- and 4<Emphasis Type="Italic">H</Emphasis>-Pyrazoles Prepared by Reactions of 9-Diazofluoren with Methyl Tetrolate and Methyl 3-Phenylpropiolate

9-Diazofluoren adds in Et₂O at 20°C to methyltetrolate in keeping with Auwers rule and nonregioselectively adds to methyl-3-phenylpropiolate with the formation of spirocyclic 3H-pyrazoles. The methyltetrolate adduct at boiling in toluene converts into methyl 3a-methyl-3aH-dibenzo[e,g]indazole-3-carboxylate, at 190°C in benzene, into methyl 3-methyl-2H-dibenzo[e,g]indazole-2-carboxylate, and at 160°C in methanol, into 3-methyl-2H-dibenzo[e,g]indazole. Auwers adduct of methyl 3-phenylpropiolate at boiling in benzene gives cyclopropene derivative and at boiling in methanol isomerizes into methyl 3a-phenyl-3aHdibenzo[e,g]indazole-3-carboxylate. Anti-Auwers adduct at boiling in benzene isomerizes into methyl 2-phenylpyrazolo[1,5-f]phenanthridine-3-carboxylate.     

Adjustable crystalline stereocomplexes from enantiopure gradient polycarbonates

Stereoselective interaction was observed in the mixture of enantiopure gradient polycarbonate (denoted as PCOPC-g-PCPC, originated from the enantioselective terpolymerization of CO₂, 3,4-epoxytetrahydrofuran (COPO) and cyclopentene oxide (CPO)) and various isotactic polycarbonates with opposite configuration in chloroform solution. The resultant crystalline stereocomplexes exhibit enhanced thermal stability and new crystalline behaviors, significantly distinct from their parent polymers. It was found that the cocrystallization selectively occurred between (R)-PCOPC (CO₂/COPO copolymer) and (S)-PCOPC-enriched segment in the gradient terpolymer (S)-PCOPC-g-PCPC, while (R)-PCPC (CO₂/CPO copolymer) selectively complexed with (S)-PCPC-enriched segment. No stereocomplexation was observed between (S)-PCOPC-g-PCPC and (S)-PCOPC or (S)-PCPC. This study is beneficial to finding new routes to prepare various semicrystalline materials having a wide variety of physical properties and degradability.     

Paramagnetic centers related to Al,Sc, In,and Nb impurities in KTiOAsO<Subscript>4</Subscript>crystals

Electron paramagnetic resonance (EPR) is applied to study Al-, Sc-, In-, and Nb-doped KTiOAsO₄ (KTA) crystals. Paramagnetic hole centers O^? are observed after ionizing irradiation of KTA crystals. These centers are, as a rule, unstable at room temperature and are slowly annealed for about two weeks. Oxygen ions are bridging two cations in KTA. Near the impurity, two p-orbitals of oxygen atoms participate in covalent bonding with cations, whereas the third p-orbital remains free and under the radiation effect captures the hole thus forming the paramagnetic center of M ⁿ⁺-O^?-M^(n?1)+ (here M ⁿ⁺ is the lattice cation and M^(n?1)+ is the impurity cation of Al, In, Sc, or Nb). In the centers investigated the specific principal direction of the g-factor g ～ 2 is normal to the M ⁿ⁺-O^?-M^(n?1)+ plane, and the main value of g _max falls in this plane. The direction of the O^?-M^(n?1)+ bond is close to the selected direction of the hyperfine interaction with the impurity ion. The models of six hole centers and the found parameters of EPR spectra are discussed.     

<Emphasis Type="Italic">Ab initio</Emphasis> quantum-chemical study of vinylation of pyrrole and 2-phenylazopyrrole with acetylene in a KOH/DMSO system

Interaction between pyrrole and its 2-vinyl, 2-azo, and 2-phenylazo derivatives with acetylene in the gas phase and DMSO was studied using the MP2/6-311++G**//MP2/6-31G* ab initio approach and including the solvation effects within the framework of the continuum model. Possible reasons are considered for the hindered character of direct vinylation of azopyrroles with acetylene in superbasic media. The introduction of the azo group in the 2 position of the pyrrole ring leads to the increased stability of the pyrrole anion and increased acidity from pK _a = 22.1 for pyrrole and pK _a = 20.5 for vinylpyrrole to pK _a = 16.6 and 16.4 for 2-azopyrrole and 2-phenylazopyrrole, respectively. The binding energy between the pyrrole anion and the acetylene molecule decreases concurrently. The heat of formation of the pyrrole anion adducts with acetylene changes from ΔH = 4.8 kcal/mol for pyrrole to ΔH = 22.4 kcal/mol for 2-phenylazopyrrole. For all anion adducts under study, preferable isomers are Z isomers formed by the interaction of pyrrole anions with the cis-distorted acetylene molecule, but the formation of the E isomers corresponds to a lower activation barrier, which explains known Z stereoselectivity of the nucleophilic addition to monosubstituted acetylenes. When an azo group is introduced, the reaction becomes more endothermal, and the energy barriers to the formation of both Z and E isomers increase. Among other reasons for lowering of the activity of 2-arylazopyrroles during vinylation we consider possible reaction of acetylene addition at the most remote nitrogen atom of the azo group and participation of the anion center in cation chelation (K⁺ in the calculation).