Showing papers by "Ming Qiu Zhang published in 2003"

Mechanical properties of low nano‐silica filled high density polyethylene composites

Abstract: Modification of nanoparticles through graft polymerization is able to change the chemical nature of the particles' surfaces and provides an effective means for the preparation of nano-fillers specified for composites manufacturing. The present work focuses on the mechanical role of grafted nano-SiO 2 particles in high density polyethylene composites prepared by melt compounding. The experimental results show that at a content of 0.75 vol%, the modified nano-silica results in a rise in tensile stiffness, tensile strength and impact strength of the composites. The grafted nanoparticles can improve the mechanical performance of the matrix polymer more effectively than the untreated version. In addition, a further enhancement of the composites stiffness and strength can be achieved by crosslinking the concentrated masterbatches, which has not yet been revealed in the authors' previous works on grafted nano-SiO 2 particles/polypropylene composites. It is thus revealed that the introduction of the grafting polymers onto the nanoparticles increases the tailorability of the composites.

Preparation of Binary Conductive Polymer Composites with Very Low Percolation Threshold by Latex Blending

Abstract: The communication reports a way to prepare carbon black (CB)/waterborne polyurethane conducting composites with percolation thresholds as low as 0.2 vol.-% through conventional latex blending. CB particles in the composites appear segregated in their distribution and are located in the two-dimensional interstices among the polymer domains. The intimate filler/matrix interaction also improves the tensile strength of the matrix at the CB content corresponding to the electrical percolation threshold

All-plant fiber composites. II: Water absorption behavior and biodegradability of unidirectional sisal fiber reinforced benzylated wood

Abstract: Sisal fiber reinforced benzylated fir sawdust composites belong to a new category of composite materials, in which both the reinforcement and matrix are based on plant fibers, i.e. renewable resources. The present paper discusses the water absorption behavior of the composites and its influence on the mechanical properties of the composites. In addition, biodegradability of the composites is assessed by using enzyme and fungi tests, respectively. The experimental results indicate that water absorption behavior of the composites is mainly controlled by the reinforcing fiber and the fiber/matrix interfacial characteristics. The inherent biodegradability of the raw materials of the all-plant fiber composites proves to be retained. During the tests of enzymolysis and biodeterioration in soil, damage of the composites was initiated either inside the sisal fiber or at the surface of the composites.

Electrical Response to Organic Vapor of Conductive Composites from Amorphous Polymer/Carbon Black Prepared by Polymerization Filling

Abstract: In recent years, conductive polymer composites have found applications as gas sensors because of their sudden change in electric resistance of magnitude when the materials are exposed to certain solvent vapors. However, the composites having this function reported so far are mostly based on crystalline polimeric matrice, which factually sets a limit to materials section. The present work prepares polystyrene/carbon black composite through polymerization filling and proves that the amorphous polymer composites can also serve as gas sensing materials. The composite'percolation threshold is much lower than that of the composite produced by dispersive mixing. In addition, high responsivity to some organic vapors coupled with sufficient reproducibility is acquired. The experimental data show that molecular weight and molecular weight distribution of the matrix polymer and conducting filler content exert great influence on the electrical response behavior of the composite. As the result, composites performance can be purposely tailored accordingly. Compared with the approaches of melt-blending and solution-blending, the current technique is characterized by many advantages, such as simplicity, low cost, and easy to be controlled.

A novel sensor for organic solvent vapors based on conductive amorphous polymer composites: carbon black/poly(butyl methacrylate)

Abstract: Conductive composites from carbon black/poly(butyl methacrylate) (CBPBMA) are synthesized through polymerization filling. The experimental results indicate that relatively low percolation threshold (∼6wt%) is associated with the composites. When the composites are exposed to good solvent vapors of the matrix polymer, the electric resistance of the composites drastically increases by over lo4 times. In the case of poor solvent vapor, however, the electrical response of the composites is rather weak, demonstrating selective gas sensibility. In addition, environment temperature exerts great influence on the responsivity of the composites against organic vapors. The higher the temperature, the faster and the stronger the electrical response. It was also found that the response of electric resistance of the composites against good solvent vapors is provided with sufficient reproducibility and stability. It can thus be concluded that the CB/PBMA composites can be used as promising gas sensing materials in practice.

Surface modification of magnetic metal nanoparticles and its influence on the performance of polymer composites

Abstract: To control the interfacial interaction in magnetic metal nanoparticles-filled polymer composites, surfaces of iron, cobalt, and nickel nanoparticles were grafted by irradiation-induced polymerization. On the basis of the study of dynamical mechanical behavior, thermal stability, and magnetic performance of the composites prepared by either solution mixing or in situ polymerization, the structure–property relationships of the composites are a function of interfacial interaction and the dispersion state of the nanoparticles. In addition, grafting of polymers onto the surface of the metal nanoparticles changed the surface magnetic state, leading to the possibility of purposely tailoring the magnetic behavior of the composites. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1070–1084, 2003

Blends of liquid crystalline polyester–polyurethane and epoxy: Preparation and properties

Abstract: A novel liquid crystalline polyester–polyurethane (LCPU) that contains polyester mesogenic units was synthesized in the present work. Through a careful investigation of the structure and morphology of the LCPU, it was found that the home-synthesized LCPU is a highly birefringent thermotropic nematic liquid crystal. After being blended with bisphenol-A epoxy, the liquid crystalline polymer can, simultaneously, improve the impact strength and the glass transition temperature as well as the tensile strength and the tensile modulus of the blends. It was proved to be an efficient toughening agent for epoxy without the expense of other properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 783–787, 2003

Performance stabilization of conductive polymer composites

Abstract: Conductive polymer composites used as candidates for positive temperature coefficient (PTC) materials are faced with performance decay characterized by gradually increased room-temperature resistivity and decreased PTC intensity. Considering that deterioration of the properties is mainly related to the capability of conductive networks established by conductive fillers to recover from the effect of repeated expansion/contraction in a timely manner, the present work introduces chemical bonding into the filler/matrix interphase. The experimental results indicate that in the composites consisting of conductive carbon black (CB), low-density polyethylene (LDPE), and ethylene–vinyl acetate copolymer, CB particles can be covalently connected with LDPE through melt grafting of acrylic acid. As a result, the composites are provided with reduced room-temperature resistivity and significantly increased PTC intensity. Compared with the composites filled with untreated CB, the present composites possess reproducible PTC behavior and demonstrate stable electrothermal output in association with negligible contact resistance at the composites/metallic electrodes contacts. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2438–2445, 2003

Gas sensing materials from carbon black/poly(methyl methacrylate) composites

Abstract: In this work, the electrical conductivity of carbon black/poly(methyl methacrylate) composites and its responsiveness to organic solvent vapors were investigated The carbon black-polymer conducting composites were synthesized by in-situ polymerization They exhibited a low electrical percolation threshold (∼33wt% of carbon black) The electric resistance of the composites increased drastically by over 10 4 times when they were exposed to good solvent vapours such as chloroform, tetrahydrafuran and ethyl acetate, and it recovered when the composites were transferred to air The effect of temperature on the vapour responsivity of the composites was notable An elevated temperature accelerated the vapour-induced variation in electrical resistance of the composites The experimental data also indicate that the composites possessed a good reproducibility of vapour responsivity These results suggest that they can be regarded as promising gas sensors characterized by easy processability and cost effectiveness

Carbon black‐filled polyolefins as positive temperature coefficient materials: The effect of in situ grafting during melt compounding

Abstract: For the production of polymer-based conducting composites serving as positive temperature coefficient (PTC) materials with lower room-temperature resistivity and sufficiently high PTC intensity, carbon black has been pretreated with acrylic acid and some initiator and then melt-mixed with low-density polyethylene. Because of the in situ formation of covalent bonding at the filler/matrix interface, the distribution status and thermally induced displacement habit of the conductive fillers have changed accordingly. As a result, the electrical performance of the composites can be tailored as desired. The amount of acrylic acid and the treatment sequence of carbon black exert an important influence on the effectiveness of the modification.

Effects of Processing on Electric Response of Carbon Black Filled Poly(methyl methacrylate) Composites against Organic Solvent Vapors

Abstract: Carbon black filled poly(methyl methacrylate) (CB/PMMA) composites were fabricated by solution mixing and polymerization filling, respectively. The effects of processing conditions on electrical conductivity of the composites and their electric responsivity against organic solvent vapors were investigated. The experimental results showed that molecular weight of the polymer matrix, carbon black content, and the composite film thickness greatly influence the response behaviors of the composites in solvent vapors. Furthermore, the composites prepared by polymerization filling have higher gas sensitivity, response rate, recovery rate, and reproducibility as compared to the composites by solution mixing. The sensing performance of the composites is found to be closely related to the microstructure of the materials, which provides possibilities for further improve the overall properties of the composites by altering the processing parameters.

Deformation characteristics of nano-SiO2 filled polypropylene composites

Abstract: Surfaces of nano-silica particles can be effectively modified by means of irradiation graft polymerization. When polypropylene (PP) was compounded with these treated nanoparticles, an overall improvement in the mechanical properties of the composites at rather low filler content was acquired. The present work observed the deformation characteristics of the PP nanocomposites using transmission electron microscope. Due to the interfacial entanglement between the grafting polymers attached to the nanoparticles and the matrix polymer, the grafted nano-SiO 2 exhibits much greater extensibility in the composites than the nanoparticles as-received. It is believed to be the main cause of extensive plastic drawing of the matrix polymer surrounding the treated nanoparticles, and it provides the composites with higher static ductility.

Functionalisation of polypropylene by solid phase graft polymerisation and its effect on mechanical properties of silica nanocomposites

Abstract: To prepare macromolecular compatibiliser for grafted nano-SiO2 /polypropylene (PP) composites, solid phase graft copolymers of PP with styrene and ethyl acrylate were synthesised, respectively. It was found that both per cent grafting and grafting efficiency can be adjusted by changing initiator concentration, reaction temperature and reaction time. As a result of partial chain scission and deterioration of ordered structure of PP during the graft polymerisation, the grafted PP exhibits poorer thermal stability and crystallisability than the unmodified PP. Mechanical tests of grafted nano-SiO2 /PP composites indicated that the addition of PP copolymer with the same species of grafting polymer as that on the nanoparticles further improves the ductility of the composites. Molecular rigidity of the grafting polymers, presence of the homopolymer produced during the graft polymerisation, and strain rate of the load applied have an important influence on the toughening effect of the functionalised PP.

Enzyme degradability of benzylated sisal and its self-reinforced composites

Abstract: To produce natural polymer based composite materials, sisal fibers were slightly benzylated and then molded into sheets. Because the modified skin portions of the fibers acquired certain thermoplasticity and the unmodified core parts remain constant, the resultant composites fall into the category of self-reinforced ones. The present article is devoted to the evaluation of the materials biodegradability with the help of cellulase. It was found that the inherent biodegradability of plant fibers is still associated with the benzylated sisal and the molded composites, as characterized by structural variation, weight loss and deterioration of mechanical performance of the materials. Reaction temperature and time, pH value of the enzyme solution, and dosage of the enzyme had significant influences on the decomposition behavior of the materials. In principle, the enzymolysis of sisal and its self-reinforced composites is a diffusion-controlled process. Due to the insusceptibility of lignin to cellulase and the hindrance of it to the cellulase solution, the degradation rates of the materials are gradually slowed down with an increase in time. Copyright © 2003 John Wiley & Sons, Ltd.

Highly filled nano-CdS/polystyrene nanocomposite film with self-organization behavior

Abstract: Highly filled polystyrene (PS) composite film with a nano-CdS loading of 20wt.% can be obtained when a certain mercaptan is applied to the particles' surfaces. Because of a strong electron transfer interaction between the modified CdS nanoparticles and the aliphatic carbons in PS, self-organization of the nanoparticles is perceivable in the composites. As a result, the ultraviolet/visible absorption edge of the treated nano-CdS/ PS composites is blue-shifted in addition to the shift caused by quantum size effect. The fluorescence emission peak is accompanied by some fine structures and becomes redshifted and narrower. Unlike conventional nanocomposites that generally contain low concentrations of nanoparticles (less than 10wt.%), the present approach greatly improves the scope for cooperative behavior of the nanoparticles.