Showing papers by "Ming Qiu Zhang published in 2009"

A thermally remendable epoxy resin

Abstract: To provide epoxy resin with crack healing capability, an epoxy containing both furan and epoxide groups, N,N-diglycidyl-furfurylamine (DGFA), was synthesized through a two-step approach. When it reacted with N,N′-(4,4′-diphenylmethane) bismaleimide (DPMBMI) and methylhexahydrophthalic anhydride (MHHPA), respectively, a crosslinked polymer with two types of intermonomer linkage was yielded. That is, thermally reversible Diels–Alder (DA) bonds from the reaction between furan and maleimide groups, and thermally stable bonds from the reaction between epoxide and anhydride groups. In this way, cured DGFA possessed not only similar mechanical properties as commercial epoxy, but also thermal remendability that enabled elimination of cracks. The latter function took effect as a result of successive retro-DA and DA reactions, which led to crack healing in a controlled manner through chain reconnection.

A Facile Strategy for Preparing Self-Healing Polymer Composites by Incorporation of Cationic Catalyst-Loaded Vegetable Fibers

Abstract: A two-component healing agent, consisting of epoxy-loaded microcapsules and an extremely active catalyst (boron trifluoride diethyl etherate, (C 2 H 5 ) 2 O · BF 3 )), is incorporated into epoxy composites to provide the latter with rapid self-healing capability To avoid deactivation of the catalyst during composite manufacturing, (C 2 H 5 ) 2 O · BF 3 is firstly absorbed by fibrous carriers (ie, short sisal fibers), and then the fibers are coated with polystyrene and embedded in the epoxy matrix together with the encapsulated epoxy monomer Because of gradual diffusion of the absorbed (C 2 H 5 ) 2 O · BF 3 from the sisal into the surrounding matrix, the catalyst is eventually distributed throughout the composites and acts as a latent hardener Upon cracking of the composites, the epoxy monomer is released from the broken capsules, spreading over the cracked planes As a result, polymerization, triggered by the dispersed (C 2 H 5 ) 2 O · BF 3 , takes place and the damaged sites are rebonded Since the epoxy―BF 3 cure belongs to a cationic chain polymerization, the exact stoichiometric ratio of the reaction components required by other healing chemistries is no longer necessary Only a small amount of (C 2 H 5 ) 2 O · BF 3 is sufficient to initiate very fast healing (eg, a 76% recovery of impact strength is observed within 30 min at 20 °C)

Imparting Ultra‐Low Friction and Wear Rate to Epoxy by the Incorporation of Microencapsulated Lubricant?

Abstract: The incorporation of microcapsules containing lubricant oil into epoxy composites leads to materials with ultra-low friction and wear performance. During sliding wear tests, the capsules are damaged by the asperities of the counterface, releasing the oil to the contact area. The lubrication effect of the released oil and the entrapment of wear particles in the cavities left by the ruptured capsules leads to a significant reduction of both the frictional coefficient and the specific wear rate. The approach provides the merits of fluid lubrication but excludes the drawbacks of external lubrication. A minute amount of lubricant oil is sufficient to improve the tribological properties significantly.

Microencapsulation of styrene with melamine-formaldehyde resin

Abstract: Melamine-formaldehyde (MF) resin-walled microcapsules containing styrene were prepared by in situ polymerization in an oil-in-water emulsion. In response to the characteristics of styrene (i.e., high volatility, non-polarity, low molecular weight, and low viscosity), the synthesis method was improved by optimizing the reaction conditions accordingly. It was found that utilization of macromolecular emulsifier of lower molecular weight, moderate dispersion rate, and higher feeding weight ratio of core/shell monomers is critical for the fast formation of capsules’ wall. The highest loading of styrene in the resultant microcapsules can be about 60%, and mean diameter of the capsules fell in the range of 20∼71 μm, which can be adjusted by changing processing parameters. It is believed that the present work provides a feasible approach to encapsulate monomers for manufacturing polyester based self-healing composites.

Durability of self-healing woven glass fabric/epoxy composites

Abstract: In this work, the durability of the healing capability of self-healing woven glass fabric/epoxy laminates was investigated. The composites contained a two-component healing system with epoxy-loaded urea-formaldehyde microcapsules as the polymerizable binder and CuBr2(2-methylimidazole)4 (CuBr2(2-MeIm)4) as the latent hardener. It was found that the healing efficiency of the laminates firstly decreased with storage time at room temperature, and then leveled off for over two months. By means of a systematic investigation and particularly verification tests with dynamic mechanical analysis (DMA), diffusion of epoxy monomer from the microcapsules due to volumetric contraction of the composites during manufacturing was found to be the probable cause. The diffusing sites on the microcapsules were eventually blocked because the penetrated resin was gradually cured by the remnant amine curing agent in the composites' matrix, and eventually the healing ability was no longer reduced after a longer storage time. The results should help to develop approaches for improving the service stability of the laminates.

Study of Phase Separation of Poly(vinyl methyl ether) Aqueous Solutions with Rayleigh Scattering Technique

Abstract: Phase separation and its kinetics of poly (vinyl methyl ether) (PVME) aqueous solutions was investigated by Rayleigh scattering (RS) technique in this work. Concentration dependence of the lower critical solution temperature and time dependence of phase separation were collected, respectively. The RS spectra revealed the transition of molecular conformation and aggregation of molecular chains in the course of phase separation. It was found that upon heating PVME chains changed from expanded coils to collapsed globules and then aggregated. In contrast, during cooling, the chain aggregates were initially swelled and followed by gradual dissociation, while the conformation of molecular chains finally returned to its original state. By means of Avrami equation and Arrhenius formula, apparent activation energy of phase separation of PVME aqueous solutions was estimated. Moreover, a model was proposed to describe the phase separation process.

Plant oil-based biofoam composites with balanced performance

Abstract: BACKGROUND: Biofoam composites were prepared using short sisal fibers as reinforcement and acrylated epoxidized soybean oil as matrix, aiming at replacing traditional unsaturated polyester foams in structural applications. The compressive properties of the composites were examined as a function of fiber loading, fiber length and foam density. RESULTS: The foam composite with 10 phr (parts per hundred of base resin by weight) sisal fiber possessed properties similar to those of commercial unsaturated polyester foams. A study of the failure mechanism revealed that debonding between fiber and matrix was a key issue responsible for catastrophic damage of the composites. According to this finding, surface pre-treatment of the sisal using an alkali or silane coupling agent was carried out. This brought about positive effects on interfacial interaction and compressive strength of the composites, as desired. Also, soil burial tests proved that the foam composites could be biodegraded, and the incorporated sisal fibers accelerated the biodegradation of the composites. CONCLUSION: This work shows the feasibility of making rigid biofoams from natural resources, which could be potential candidates for structural foams. Copyright © 2009 Society of Chemical Industry

Association behaviors between carboxymethyl cellulose and polylactic acid revealed by resonance light scattering spectra

Abstract: Resonance light scattering (RLS) spectra were used to study the formation of complexes of carboxymethyl cellulose (CMC) and polylactic acid (PLA) in a mixed solvent of 10% DMSO/90% H2O(V/V). The RLS results showed that the CMC and PLA could form a steady homogeneous complex due to the interaction of hydrogen bonding. With the increasing of CMC mass fraction in the complex, the observed durative enhancement RLS signal with two inflexion points indicated the forming of complexes and aggregation of complexes. The aggregation equilibrium and thermo stability of the complexes were also investigated based on RLS values.