Kuo-Chung Cheng

Thermal Properties and Flammability of Ethylene-Vinyl Acetate Copolymer/Montmorillonite/Polyethylene Nanocomposites with Flame Retardants

Ethylene-vinyl acetate copolymer (EVA)/montmorillonite (MMT) composite was blended with a linear low density polyethylene (LLDPE). X-ray diffraction and transmission electron microscopy (TEM) image of the EVA/MMT composite are in support of an intercalated with partially delaminated nanocomposite. The tensile strength of the nanocomposite is about 20% higher than that without layered silicates, MMT. Furthermore, the incorporation of MMT into polymer blend delays the main thermo-oxidative degradation. Cone calorimeter test points out that the addition of layered silicates into the pristine EVA/LLDPE blend or the blend with a low smoke non-halogen (LSNH) fire retardants, aluminum trihydroxide, and antimony trioxide, can reduce the maximum heat release rate by 30–40%. The smoke suppressing effect of layered silicates is only observed in the nanocomposite containing flame retardants. According to the limiting oxygen index (LOI) data and cone calorimeter test, the addition of the nanodispersed layered silicate and LSNH flame retardants to the EVA/LLDPE exhibits a synergistic effect on the flame retardancy and smoke suppression.

Effect of feed rate on structure of hyperbranched polymers formed by stepwise addition of AB2 monomers into multifunctional cores

Abstract Hyperbranched polymers generated from the copolymerization of AB2-type monomers slowly added into trifunctional C3 cores under various feed rates were investigated by a kinetic model. The dependences of average molecular weight, polydispersity, degree of branching (DB), and number of structural units of the hyperbranched polymers on the feed rate were calculated by a generating function method. It was found that the final PDI can be attained below 1.5 by a slow addition with the parameter of feed rate, φ, less than 1. While the AB2 monomers fed quickly, the system with a lower content of the C3 cores results in a broader molecular weight distribution. A high DB, about 0.66, can be achieved by addition of a small amount of C3 cores at φ lower than 10.

Kinetic model of hyperbranched polymers formed by self-condensing vinyl polymerization of AB∗ monomers in the presence of multifunctional core molecules with different reactivities

Abstract Hyperbranched polymers formed by the self-condensing vinyl polymerization, SCVP, of AB∗ monomers in presence of trifunctional C 3 ∗ cores with various reactivities were studied by means of the kinetic model. The changes of the degree of polymerization, polydispersity, degree of branching, and structural units of the hyperbranched polymers with the conversions were all investigated by the generating function method. By the addition of the cores with higher reactivity, the molecular weight distribution of the hyperbranched polymers can be further narrowed, and the degree of branching is only slightly lower than that without core monomers. At full conversion of A, the polydispersity index of the hyperbranched polymers formed by the SCVP is lower than that by the AB2–C3 copolymerization studied before.

High intensity fluorescence of photoactivated silver oxide from composite thin film with periodic array structure

We have fabricated a composite thin film that exhibits intense photoactivated fluorescence of silver oxide at 522 and 529nm under the irradiation of a 488nm laser. This film consists of a silver coated polymeric periodic array on indium tin oxide glass substrate. By adjusting the column diameters and lattice constants of the array to coincide with the excitation wavelength, an order increase in fluorescence intensity was obtained due to the surface plasmon polariton resonance of silver. This composite film has many potential applications in highly efficient optoelectronic devices.

Kinetic approach for epoxy resins cured with diaminodiphenyl sulfone under non‐isothermal conditions

The curing reactions of epoxy resin basing on diglycidyl ether bisphenol A (DGEBA) with 4,4′-diaminodiphenyl sulfone (DDS) were investigated with a differential scanning calorimeter and gel permeation chromatography. Based on the generating function method and the Monte Carlo simulation procedure, kinetic models for both isothermal and nonisothermal curing conditions were proposed. The apparent activation energy of curing reactions was found to be 14.9 Kcal/mol by the thermal analysis. According to our kinetic models, gel points, the profiles of epoxy conversion, and the molecular weights of polymers were calculated. Good agreement is obtained between the model predictions and experimental data.

Kinetic model of hyperbranched polymers formed by the polymerization of AB2 monomer with a substitution effect

Hyperbranched polymers obtained by the polymerization of AB2-type monomer with a substitution effect on the B2 groups were studied by means of the kinetic model. In this polymerization with the substitution effect, if one of the B2 group reacts first, the reactivity of the remaining unreacted B group will be changed. The profiles of the degree of polymerization, polydispersity, degree of branching, and structural units of the hyperbranched polymers with the conversions were all calculated by the generating function method. It is shown that the weight-average degree of polymerization and the degree of branching of the hyperbranched polymers having substitution effect differ from that with equal reactivity of the B2 groups. If the substitution effect causes an increase in the rate constant after one of the B2 groups has reacted, a broader molecular weight distribution and a higher degree of branching are observed.

Biphenyl liquid crystalline epoxy resin as a low-shrinkage resin-based dental restorative nanocomposite

Low-shrinkage resin-based photocurable liquid crystalline epoxy nanocomposite has been investigated with regard to its application as a dental restoration material. The nanocomposite consists of an organic matrix and an inorganic reinforcing filler. The organic matrix is made of liquid crystalline biphenyl epoxy resin (BP), an epoxy resin consisting of cyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (ECH), the photoinitiator 4-octylphenyl phenyliodonium hexafluoroantimonate and the photosensitizer champhorquinone. The inorganic filler is silica nanoparticles (∼70-100 nm). The nanoparticles were modified by an epoxy silane of γ-glycidoxypropyltrimethoxysilane to be compatible with the organic matrix and to chemically bond with the organic matrix after photo curing. By incorporating the BP liquid crystalline (LC) epoxy resin into conventional ECH epoxy resin, the nanocomposite has improved hardness, flexural modulus, water absorption and coefficient of thermal expansion. Although the incorporation of silica filler may dilute the reinforcing effect of crystalline BP, a high silica filler content (∼42 vol.%) was found to increase the physical and chemical properties of the nanocomposite due to the formation of unique microstructures. The microstructure of nanoparticle embedded layers was observed in the nanocomposite using scanning and transmission electron microscopy. This unique microstructure indicates that the crystalline BP and nanoparticles support each other and result in outstanding mechanical properties. The crystalline BP in the LC epoxy resin-based nanocomposite was partially melted during exothermic photopolymerization, and the resin expanded via an order-to-disorder transition. Thus, the post-gelation shrinkage of the LC epoxy resin-based nanocomposite is greatly reduced, ∼50.6% less than in commercialized methacrylate resin-based composites. This LC epoxy nanocomposite demonstrates good physical and chemical properties and good biocompatibility, comparable to commercialized composites. The results indicate that this novel LC nanocomposite is worthy of development and has potential for further applications in clinical dentistry.

Nanolithography made from water-based spin-coatable LSMO resist

A dual functional and water soluble spin-coatable lanthanum strontium manganese oxide (LSMO) resist has been developed that consists of lanthanum nitrate, strontium nitrate, manganese nitrate, polyvinyl alcohol and water. Energetic nitrates plus polyvinyl alcohol fuel promote autoignition and produce nanopatterns (<60 nm) upon mild electron beam exposure (< 2m C cm −2 ). The formation of cubic perovskite LSMO has been confirmed by micro-IR spectroscopy, elemental analysis, x-ray diffraction and transmission electron microscopy. The patterned LSMO film can be developed using nontoxic and environmentally friendly pure water, and the resist can fabricate active magnetic patterns directly by electron beam exposure. The spin-coatable LSMO resist can be fabricated into either positive or negative patterns easily by varying the electron doses. It can change from negative resist to positive resist and then finally negative resist with the increase of electron dose. The positive and negative dual functional mechanism of spin-coatable LSMO resist is reported. A resist with simultaneous positive and negative capabilities patterning will benefit the direct writing technology of an electron beam. The active magnetic characteristics and high refractive index of the material are useful for the direct fabrication of magnetic and optical devices. (Some figures in this article are in colour only in the electronic version)

Effect of polar interactions on the structure and rheology of EVA/Montmorillonite nanocomposites:

In this study we utilized X-ray diffraction, transmission electron microscopy (TEM) and various types of simple shear flow experiments to investigate the effect of the polar-polar interaction between ethylene-vinyl acetate co-polymers (EVA) and organo-silicates on the nanoscale structures and rheological properties of their melt blends. The WAXS intensities and TEM micrographs demonstrate that the exfoliation and the intercalation of nanoclays respectively prevail in EVA/Cloisite 30B nanocomposites and EVA/Cloisite 15A nanocomposites, respectively. The master curves obtained from transient shear flow tests and their Arrhenius plot demonstrate the formation of side-tethered structure in the melt blends of EVA/ Cloisite 30B nanoclay. Finally, by means of performing a series of large-strain relaxation tests and regression techniques, the single integral Wagner model, that is expected to appropriately describe the rheometric experiment data of melt blends, was established, and then a comparison of the calculated and measured viscosity and first normal stress is presented.

Chemorheology of epoxy resin

A secondary hydroxyl group containing epoxy resin was reacted and cross-linked with polyurethane (PU). This PU-cross-linked epoxy resin was cured with a tertiary amine and the viscosity and dynamic mechanical properties were determined by a cone-and-plate rheometer. A dual Arrhenius viscosity model was modified to predict the viscosity profile with time before gelation during non-isothermal curing, and the calculated values coincided with the experimental data. The activation energy of this system (NCO/OH ratio=30 mol%) calculated by the modified model was 13kcal mol−1 for the initial region, and 16.8 kcal mol−1 for the final region. After gelation, the dynamic complex modulus was correlated to the reaction kinetics according to the rubber elasticity theory, and the activation energy calculated was 5.2 kcal mol−1. These activation energies are all lower than those of the unmodified epoxy resin system. Consequently, the reaction rate of the PU-cross-linked epoxide system was less affected by temperature than that of the unmodified epoxide system. It was also found that the rate of increase of viscosity and dynamic moduli decreased with increasing PU content. The gelling point was estimated by rheological measurements.