Influence of interfacial adhesion and the nonequilibrium glassy structure of a polymer on the enthalpy of mixing of polystyrene-based filled composites

For composites based on polystyrene, the styrene-butadiene copolymer, and polybutadiene filled with various kinds of zinc oxide powder, the enthalpy of mixing is calculated in the entire range of filler contents on the basis of calorimetric measurements with the use of the thermochemical cycle. It is shown that, when the polymer is in excess in the composites based on polystyrene and its copolymer, the enthalpy of mixing is negative, whereas at a high content of the filler, this value is positive. The alternating-sign pattern of the concentration dependence of the enthalpy of mixing is interpreted in terms of the superposition of the negative contribution of the enthalpy of the interfacial-adhesion interaction of a polymer matrix with the filler and the positive contribution due to a gain in the level of nonequilibrium of the glassy matrix near the surface. A thermodynamic model that makes it possible to separate these contributions and to describe the experimental curves of the enthalpy of mixing for the composites is advanced.     

Effects of the degree of dispersion and the morphology of zinc powder on the thermodynamics of its interaction with polystyrene in solution and in composite films

The adsorption of block PS on the surface of spherical, round, and flaky particles of highly dispersed Zn powders with dimensions of 3.5–23 μm and the interaction of the polymer with the surface of Zn powders in the composite films are studied by refractometry and isothermal calorimetry. During establishment of adsorption equilibrium, the concentration of PS in the bulk of solution increases, while, near the surface of Zn particles, the concentration of PS decreases, thus indicating the predominance of absorption from solution of the solvent o-xylene. With the use of the thermodynamic cycle, including processes of solution of the polymer and Zn-PS film composite and wetting of the Zn powder, the enthalpies of formation of PS-Zn composites are estimated. The enthalpies of mixing of filled compositions comprise two contributions of opposite signs: In the low-filling region, the negative contribution of adhesion interactions prevails, while in the region of high-filled compositions, a positive structural contribution, which is associated with additional loosening of the glassy packing of PS near the filler surface, plays the decisive role. The contribution of adhesion interaction is largely determined by the dimensions of filler particles, while the structural contribution is controlled by their shape. The experimental evidence suggests that spherical particles possess the highest thermodynamic compatibility with the polymer matrix of the composite material.     

加工工艺对气相生长碳纤维填充聚苯乙烯复合体系导电逾渗与动态流变特性的影响

研究了加工工艺对气相生长碳纤维(VGCF)填充聚苯乙烯(PS)复合体系导电逾渗与动态流变特性的影响.结果表明,低转速、短时间混合有利于VGCF形成较为完善的逾渗网络结构,其复合体系逾渗阈值低、导电性能好.使用作者提出的两相模型描述VGCF/PS复合体系的流变特性,发现低转速、短时间(30 r/min、5 min)混合条...     

Effect of the nature of a polymer matrix on the enthalpy of adhesion interactions in composites filled with nickel nanoparticles

Interfacial interactions in composites filled with nickel nanoparticles are studied experimentally. The concentration dependences of the enthalpy of mixing of rubbery and glassy homo- and copolymers of different polarities with nickel nanoparticles coated with a carbon shell are measured via isothermal calorimetry. On the basis of these data, the values of adhesion and the structural contributions to the enthalpy of mixing are calculated. A decrease in the kinetic flexibility of macromolecular chains with an increase in the glasstransition temperature of the polymer causes a gain in the positive structural contribution to the enthalpy of mixing of the composite. The contribution of adhesion interaction is negative and predominantly determined by electrostatic forces of the induction type. The maximum enthalpy of adhesion is proportional to the squared dipole moment of a polymer unit and independent of the relaxation state of the polymer matrix.     

An SKP and EIS investigation of amine adsorption on zinc oxide surfaces

A metal/oxide/polymer ‘interphase’ with mixed organic–inorganic nature insures the high stability and the strength of the adhesive joints in a variety of corrosive environments. To model the interaction of epoxy resin with a metal surface, the interaction of amines of different structure with oxidized zinc surfaces was studied by Scanning Kelvin Probe (SKP), FTIR microscopy in atmospheric conditions, and a.c. and d.c. electrochemical techniques in the aqueous electrolyte. It was shown that bidentate ligand‐ethylendiamine, forming stable chelate complexes reacts with zinc oxide with redeposition of the interphase. In air and water electrolyte, this ligand shifts the potential of Zn/ZnO electrode to the level of the oxide‐free zinc. The amines with low chelating property show low effect on the potential of Zn/ZnO. The SKP was used to measure the potential drop at epoxy resin/zinc interface. On this basis, SKP is proposed as a sensitive nondestructive technique to characterize in situ the interaction of the resin with the metal and the subsequent formation of the interphase in the metal–polymer joints. Copyright © 2010 John Wiley & Sons, Ltd.     

Electrical properties of conductive polymer composites prepared by an innovational method

<正>An innovational method that poly(styrene-co-maleic anhydride)(SMA),a compatibilizer of immiscible nylon6/polystyrene(PA6/PS) blends,was first reacted with carbon black(CB) and then blended with PA6/PS,has been employed to prepare the PA6/PS/(SMA-CB) composites of which CB localized at the interface.In PA6/PS/CB blends,CB was found to preferentially localize in the PA6 phase.However,in the PA6/PS/(SMA-CB) blends,it was found that CB particles can be induced by SMA to localize at the interface.The electrical porperties of PA6/PS/(SMA-CB) composites were investigated.The results showed that the composites exhibited distinct triple percolation behavior,i.e.the percolation is governed by the percolation of CB in SMA phase,the continuity of SMA-CB at the interface and the continuity of PA6/PS interface.The percolation threshold of PA6/PS/(SMA-CB) was only 0.15 wt%,which is much lower than that of PA6/PS/CB.Moreover,the PTC(positive temperature coefficient) intensity of PA6/PS/(SMA-CB) composites was stronger than that of PA6/PS/CB and the negative temperature coefficient(NTC) effect was eliminated.The electrical properties of PA6/PS/(SMA-CB) were explained in terms of its special interface morphology:SMA and CB localize at interphase to form the conductive pathways.     

Isotherm analysis of phenol adsorption on polymeric adsorbents from nonaqueous solution

Macroporous poly(methyl methacrylate-co-divinylbenzene) (PMMA), interpenetrating polymer adsorbent based on poly(styrene-co-divinylbenzene) (PS) and poly(methyl methacrylate-co-divinylbenzene) (PMMA/PS), and macroporous cross-linked poly(N-p-vinylbenzyl acetylamide) (PVBA) were prepared for the adsorption of phenol from cyclohexane. The sorption isotherms of phenol on the three polymeric adsorbents were measured and fitted to Langmuir and Freundlich isotherms. It is shown that the Langmuir isotherm, which is based on a homogeneous surface model, is unsuitable to describe the sorption of phenol on the adsorbents from nonaqueous solution and the Freundlich equation fits the tested three adsorption systems well. The isosteric enthalpy was quantitatively correlated with the fractional loading for the sorption of phenol onto the three polymeric adsorbents. The surface energetic heterogeneity patterns of the adsorbents were described with functions of isosteric enthalpy. The results showed that the tested three polymeric adsorbents exhibited different surface energetic heterogeneity patterns. The initial isosteric enthalpy of phenol sorption on polymeric adsorbent has to do with the surface chemical composition and is free from the pore structure of the polymeric adsorbent matrix. Forming hydrogen bonds between phenol molecules and adsorbent is the main driving force of phenol sorption onto PVBA and PMMA adsorbent from nonaqueous solution. When phenol is adsorbed on PMMA/PS, pi-pi interaction resulting from the stacking of the benzene rings of the adsorbed phenol molecules and the pendant benzene ring of adsorbent is involved.     

Redox Active Two‐Component Films of Palladium and Covalently Linked Zinc Porphyrin–Fullerene Dyad

Redox active films have been generated electrochemically by the reduction of dyads consisting of fullerene C₆₀ covalently linked to zinc meso‐tetraphenyloporphyrin, ZnP? C₆₀, and palladium acetate. The films are believed to consist of a polymeric network formed via covalent bonds between the palladium atoms and the fullerene moieties. In these films, the zinc porphyrin moiety is covalently linked to the polymeric chains through the pyrrolidine ring of the fullerene. The ZnP? C₆₀/Pt films are electrochemically active in both positive and negative potential excursions. At positive potentials, two oxidation steps for the zinc porphyrin are observed. In the negative potential range, electron transfer processes involving the zinc porphyrin and the fullerene entities are observed. Film formation is also accompanied by palladium deposition on the electrode surface. The presence of a metallic phase in the film influences its morphology, structure and electrochemical properties.     

Mechanism study on char formation of zinc acetylacetonate on ABS resin

The mechanism of char formation effect of zinc acetylacetonate(Zn(acac)2) on acrylonitrile-butadiene-styrene copolymer(ABS) was studied. Thermal gravimetric analysis(TGA) was used to study the mass loss and char yield of ABS composites. In situ temperature-dependent Fourier transform infrared spectroscopy(FTIR) was used to characterize the chemical change during thermal decomposition. Roman spectroscopy and scanning electron microscopy(SEM) were applied to characterize the structure and morphology of the char after combustion. Results showed that the presence of Zn(acac)2 not only slowed down thermal decomposition of the ABS composites, but also increased the charred residue. A more compact and denser char layer with higher graphitization degree was formed for ABS composites with Zn(acac)2. To study the char formation mechanism of Zn(acac)2 on ABS, thermal decomposition was analyzed for the composites of Zn(acac)2 with PB, PS and SAN, respectively. Also, the chemical structure change was investigated for Zn(acac)2 during thermal decomposition. Based on these results, it was deduced that the increase of char yield of ABS composites was probably attributed to the interaction between the units of acrylonitrile in ABS and zinc acetate, produced during the thermal decomposition of Zn(acac)2. A proposed mechanism for crosslinking and the subsequent char formation was presented.     

An antimicrobial zinc based molecule for cross linking poly-acrylic acid

A system for incorporating antimicrobial zinc into polymeric materials, in particular hydrogel type polymers has been developed. Zn(Bipy-(MMOES)₂) a zinc carboxylate monomer was designed with the purpose of mimicking commercial cross linking agents such as ethylene glycol diacrylate, as well as containing antimicrobial zinc ions (Zn²⁺), with the intention that it can be used to cross link into any polymeric material, the example here being polyacrylic acid. Two systems were studied: a homopolymer of the Zn(Bipy-(MMOES)₂) and copolymers of Zn(Bipy-(MMOES)₂) with acrylic acid (AA). The AA – Zn(Bipy-(MMOES)₂) produced water swellable polymers which retained antimicrobial activity. The ability of the polymers to release the zinc ions was shown to be pH responsive and the leachate analysed to give a proposed mechanism of action. The Zn(Bipy-(MMOES)₂) monomer and polymers have shown antibacterial activity against both gram positive Methicillin susceptible staphylococcus aureus (MSSA 476) and gram negative Pseudomonas aeruginosa (PA01).     

Positive‐temperature‐coefficient/negative‐temperature‐coefficient effect of low‐density polyethylene filled with a mixture of carbon black and carbon fiber

Low‐density polyethylene (LDPE) filled with carbon black (CB) and carbon fiber (CF) composites were prepared by a conventional melt‐mixing method. The effects of a mixture of CB and CF on the positive‐temperature‐coefficient (PTC) effect and the negative‐temperature‐coefficient (NTC) effect, as well as the percolation threshold, were examined in detail. A synergy effect between CB and CF occurred, in that continuous conductive pathways formed within the CB/CF‐filled composite. The percolation threshold was moved to a reduced filler content with the addition of CF to an LDPE/CB composite. A model was proposed to explain the difference in the PTC behavior of composites containing CB and CF and composites containing only CB or CF. In addition, the NTC effect was weakened with a mixture of CB and CF, and a relatively small radiation dose was required to eliminate the NTC phenomenon in LDPE/CB/CF composites. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3094–3101, 2003     

Thermally Stimulated Current Spectroscopy of Amorphous and Semi-Crystalline Polymers

Thermally Stimulated Current (TSC) spectrometry has been applied to the characterization of polymeric materials. The study of a series of amorphous polymers having different physical structures has shown that the compensation parameters are independent of physical aging; contrarily, the activation enthalpy distribution reflects the evolution of the heterogeneity of the amorphous phase. In copolymers, TSC allows us to identify segregated amorphous phases. In semi-crystalline polymers, with semi-rigid chains, we have shown the existence of an amorphous crystalline interphase characterized by a plateau in the temperature distribution of activation enthalpy. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phase Chemistry and Thermochemstry on Coordination Behavior of Zinc Chloride with Leucine

The solubility property of the ZnCl2-Leu-H2O(Leu=L-a-leucine) system at 298.15K in the whole concentration range was investigatey by the semimicro-phase equilibrium method.The corresponding solubility diagram and refractive index diagram were constructed.The results indicated that there was one complex formed in this system.namely,Zn(Leu)Cl2.The complex is congruently soluble in water.Based on Phase equilibrium data,the complex was prepared.Its composition and properties were characterized by chemical analysis,elemental analysis,IR spectra,and TG-DTG.The thermochemical properties of coordination reaction of zinc chloride with L-a-leucine were investigated by a microcalorimeter.The enthalpies of solution of L-a-leucine in water and its zinc complex at infinite dilution and the enthalpy change of solid-liquid reaction wrer determined at 298.15K.The enthalpy change of soild phase reaction and the standard enthalpy of formation of zinc complex were claculated.On the basis of experimental and calculated results,three thermodynamic parameters(the activation enthalpy,the activation entropy and the activation free energy),the rate constant and three kinetic parameters(the activation energy,the preexponential constant and the reaction order) of the reaction,and the standard enthalpy of formation of Zn(Leu)^2 (aq) were obtained.The results showed that the title reaction took place easily at studied temperature.     

Thermodynamic study of poly(N-vinyl caprolactam) hydration at temperatures close to lower critical solution temperature

The lower critical solution temperature of aqueous solutions of poly(N-vinyl caprolactam) falls in the 305–307 K range and depends on the molecular weight of the polymer. The thermodynamic functions of mixing at 298 K have been calculated from measurements of vapor pressures and heats of dissolution and dilution. Partial Gibbs energy, partial enthalpy, and partial entropy of mixing were negative over the entire range of composition. Increasing temperature resulted in a decrease in the exothermal character of mixing. Excessive heat capacity values, calculated from the dependencies of enthalpy of mixing on temperature, were positive over the entire composition range. Heat capacity of dilute solutions was measured at 298 K and partial heat capacity of poly(N-vinyl caprolactam) at infinite dilution was shown to be positive. The data obtained point out the hydrophilic and hydrophobic hydration of poly(N-vinyl caprolactam) in aqueous solutions. Hydrophobic hydration dominates at temperatures close to binodal curve. As a result, the mutual mixing of the polymer with water is decreased and phase separation takes place.     

A novel model for quantification of the moisture absorption of polymeric laminated composites

In the present study, a new model was developed that considers the amount of the environmental fluid absorption by different constituents of polymeric laminated composites including fibers, resin, fiber-matrix interphase region, ply interface region, and voids. By knowing the fluid absorption behavior of the composite constituents, the present model can predict the amount of fluid absorption of different constituents of polymeric laminated composites with an arbitrary resin volume fraction and stacking sequence. Test specimens were fabricated by glass fibers and vinyl ester resin. The environmental fluids, examined in this study, were distilled and saline water under different temperatures and salt concentrations. To investigate the absorption behavior of different constituents of polymeric composite, various tests were conducted on fibers, pure cured resin, unidirectional composite specimens, and laminated composites. Based on the results of the tests, a new theoretical model was developed to quantify and predict the amount of fluid absorption of different constituents of laminated polymeric composites. The thickness of the interphase region between the fiber and matrix was also measured using the scanning electron microscope (SEM) images and nano-indentation tests. The consistency of experimental results with the outcomes of the theoretical model indicates the accuracy of the model.     

The nature of thermodynamic compatibility of components of aqueous solutions of starch and cellulose carboxymethyl derivatives

The Gibbs free energy, enthalpy, and entropy of mixing of starch and carboxymethyl derivatives of starch and cellulose with water were determined by sorption and calorimetry methods at 25°C throughout the entire range of compositions. The contributions due to the equilibrium intermolecular interactions and relaxation of a metastable glassy structure were separated. The relaxation of the metastable structure taking place during physical adsorption of the first portions of water on polymers makes a negative contribution to all thermodynamic functions of mixing. The contribution of equilibrium interactions, which includes pair nonviolent interactions of units and water molecules and electrostatic interactions of ions, is positive for the enthalpy and entropy of mixing. In this case, the positive entropy values exceed those of enthalpy, which is responsible for the thermodynamic compatibility. Thermodynamic analysis of the processes of dissolution of starch, carboxymethyl starch and carboxymethyl cellulose sodium salts showed that, contrary to the popular point of view, the compatibility of polysaccharides and their derivatives with water is based not on the enthalpy, but entropy nature and is strengthened additionally owing to relaxation of the metastable glassy structure of polymers.     

Core–shell morphology as a model for the study of gas permeation in composite systems

Structured latex particles prepared by emulsion polymerization were used as a model to simulate the interphase region between two phases. Multiphase polymer films comprised of high and low permeability polymers of various compositions were used. The model system consisted of a poly(n-butyl methacrylate) (PBMA) matrix and a discontinuous phase with core and shell morphology. The structured particle had a PBMA core and a vinylidene chloride – n-butyl methacrylate (VDC–BMA) copolymer shell. The shell transport characteristics wer altered by changing the (VDC–BMA) copolymer molar ratio. The physical and transport properties for each individual component were measured. Nitrogen was the probe gas. Films used for permeation experiments were prepared by latex casting. The results showed that the morphology of a heterogeneous polymeric system and the transport characteristics of their components had a considerable effect on the magnitude of the transport properties. Experimental data also showed the dependence of the gas global permeability coefficient on the nature of the simulated interphase region, the shell, and the weight percentage of such interphase in the heterogeneous polymeric films. Upon increasing the VDC content in the VDC–BMA copolymer, the gas permeability decreased. The data were fitted to the electrical analogs of conductivity in composite systems. For the matrix filled with structured particles the overall permeability coefficient could best be described when the individual permeabilities were considered as the inverse resistances in parallel.     

The influence of the fractional composition of a filler on thermal conductivity of a polymer composition

The dependence of thermal conductivity of polymer composites based on Viksint PK-68 on the dispersion composition of such fillers as powders of silicon carbide and microdiamonds has been studied. It has been shown that the thermal conductivity of polymeric compositions depends on the gradient of fractions in the powders of fillers.     

PS/MWNT复合材料界面上的化学反应性

利用悬浮聚合法制备了可溶于甲苯的聚苯乙烯／多壁碳纳米管（PS／MWNT）复合材料,通过透射电镜观察到MWNT完全或部分被PS包裹。拉曼光谱分析表明,复合材料中MWNT的两个特征峰D峰和G峰的位置均发生了红移,且D峰的强度及ID／IG值也较MWNT明显增大。凝胶渗透色谱测得复合材料的分子量相对于纯PS的分子量有较大幅度提高。同时比较共混法与悬浮聚合法制得的复合材料在甲苯中的溶解性。可以认为悬浮聚合法制备复合材料的过程中,MWNT参与了PS的聚合反应,与PS形成了化学键从而完全或部分地被PS包裹。     

Evaluating of reinforcing effect of Ceratonia Siliqua for polypropylene: Tensile,flexural and other properties

The aim of this study is to investigate the reinforcing effect of Ceratonia siliqua (CS) powder as a novel natural filler for polypropylene (PP) based composites. CS powder up to 20 wt% was filled into PP matrix by using high speed thermo kinetic mixer. Mechanical and thermal properties of CS filled PP based composites were investigated by tensile and three point bending test, dynamic mechanical analysis, thermogravimetric analysis, differential scanning calorimetry analysis, fourier transform infrared analysis, and thermomechanical analysis. Morphology of the composites was also investigated by scanning electron microscopy. By filling 5% and 10% of CS into PP, tensile strength and flexural strength of PP increased by about 32 and 23%, respectively. This indicates that CS has a great potential to be used as reinforcing filler for PP composites. CS filling into PP led to lower coefficient of thermal expansion values which could help preventing the thermal expansion.