Chin-Lung Chiang

Synthesis, characterization and thermal properties of novel epoxy containing silicon and phosphorus nanocomposites by sol-gel method

Abstract Organic–inorganic hybrids were prepared using diglycidyl ether of bisphenol A (DGEBA) type epoxy and tetraethoxysilane via the sol–gel process. The DGEBA type epoxy was modified by a coupling agent to improve the compatibility of the organic and inorganic phases. The sol–gel technique was used successfully to incorporate silicon and phosphorus into the network of hybrids increasing flame retardance. Fourier transform infrared spectroscopy and 29Si nuclear magnetic resonance spectroscopy were used to characterize the structure of the hybrids. In condensed siloxane species for TEOS, silicon atoms through mono-, di-, tri-, and tetra-substituted siloxane bonds are designated as Q1, Q2, Q3, Q4, respectively. For 3-isocyanatopropyltriethoxysilane and diethylphosphatoethyltriethoxysilane, mono-, di-, tri-, tetra-substituted siloxane bonds are designated as T1, T2, T3. Results revealed that Q4, Q3, T3 are the major environments forming a network structure. The morphology of the ceramer was examined by scanning electron microscopy and Si mapping. Particle sizes were below 100 nm. The hybrids were nanocomposites. The char yield of pure epoxy resin was 14.8 wt.% and that of modified epoxy nanocomposite was 31 wt.% at 800 °C. A higher char yield enhances the flame retardance. Values of limiting oxygen index of pure epoxy and modified epoxy nanocomposites are 24 and 32, respectively, indicating that modified epoxy nanocomposites possess better flame retardance than the pure epoxy resin.

Synthesis, characterization, thermal properties and flame retardance of novel phenolic resin/silica nanocomposites

Novel phenolic/silica hybrid ceramers were synthesized by the sol-gel process. FTIRand 29 Si NMRwere used to characterize the structure of the hybrids. The results revealed that Q 4 ,Q 3 andT 3 are the major microstructures. That is, network structures were formed. SEM, TEM and Si mapping revealed that the hybrids were nanocomposites. The thermal properties were investigated by thermogravimetric analysis (TGA). The char yields of the hybrids increased with TEOS content. Td5 (the degradation temperature at 5% weight loss) of the hybrid that contained 20 wt.% TEOS was 290 � C. The Td5 of the hybrid rose to 312 � C as the TEOS content was increased to 80 wt.%. TEOS inorganic components enhance the thermal stability of the hybrids. The limiting oxygen index (L.O.I.) and the UL-94 test revealed that the hybrid ceramer possesses excellent flame retardance. # 2003 Elsevier Ltd. All rights reserved.

Thermo-oxidative degradation of novel epoxy containing silicon and phosphorous nanocomposites

Abstract Modified epoxy nanocomposites containing silicon and phosphorous was prepared and compared with pure epoxy. The study of thermo-oxidative degradation of modified epoxy nanocomposites and pure epoxy has been utilized by thermal analysis. The thermal stability of modified epoxy nanocomposites is not superior to that of the pure epoxy at low temperature, however, the char yield of modified epoxy nanocomposites is higher than that of the pure epoxy at 800 °C in air atmosphere. The modified epoxy nanocomposites possess better thermal stability at high temperature range. The values of the limiting oxygen index of pure epoxy and modified epoxy nanocomposites are 24 and 32, respectively. This indicates that modified epoxy nanocomposites possesses better flame retardance. By the Kissinger’s method, the activation energies of thermo-oxidative degradation for epoxy nanocomposites are less than those of thermo-oxidative degradation for pure epoxy in first stage of thermo-oxidative degradation. However, the activation energies of thermo-oxidative degradation for epoxy nanocomposites are more than those of thermo-oxidative degradation for pure epoxy in second stage of thermo-oxidative degradation.

Effects of chain extender and hard/soft segment content on the surface and electrical properties of PDMS based polyurea-urethane

A series of PDMS based Poly(urea-urethane) (PUU) polymers with various polar functional groups on their side chains have been prepared by using a prepolymer process. The hydrophilic and hydrophobic characters of PUU films have been investigated. It was found that PUU film possesses different surface properties on the aluminum contacting face and on the air contacting face. Results show that the differences of contact angles between two sides of the PUU film are very significant. Results also indicate that the silicone/nitrogen ratio on the aluminum-contacting surface is higher than that on the air-contacting surface, and the ratio decreases as the hard segment content increased. It was also found that when the sample was in a dry condition, the electrical surface resistance is in the range of 1014 Ω. However, when the sample was conditioned at 70%, 80% and 100% R.H., the electrical surface resistance decreases to 108 Ω.

Prediction of the fracture toughness of fibrous composites

A statistical/micromechanical model is developed for the prediction of the fracture toughness of fibrous composites. The fracture resistance of the material is assumed to be related to the statistical distribution of the fiber pull-out length. The distribution of the fiber pull-out length is derived from the fiber strength distribution. The R-curve behavior of the fibrous composite is predicted and interpreted based on the present model. The limiting fracture toughness is predicted to be proportional to the square root of the ineffective length, or proportional to the square root of the fiber length if the fiber length is less than the ineffective length.

Plastic stress-strain relations of polycrystalline metals

Plastic deformation of polycrystals is investigated on the basis of single-crystal deformation. Slip is assumed to be the only deformation mechanism. Accordingly, an explicit tensile plastic stress-strain relation which contains the relevant microstructure parameters is obtained. As a simple application of the theoretical model, the effect of grain size on the flow stresses of polycrystals is studied. Finally, the general features of the present polycrystal model are summarized. Numerical results are obtained for face-centred cubic polycrystals, and the theoretical predictions are found to be in reasonable agreement with those of Taylor, Bishop, Hill and Hutchinson.

Synthesis, Thermal Properties and Flame Retardance of Novel Phenolic Resin/Silica Nanocomposites

The novel phenolic/silica hybrid ceramers were synthesized by sol-gel process. FTIR and 29 Si NMR were used to characterize the structure of the hybrids. Results revealed that Q 4 , Q 3 , T 3 are the major environments, i.e., it formed network structure. The thermal properties were investigated by thermogravimetric analysis (TGA). The char yields of the hybrids increase with increasing TEOS content. T d5 (the temperature of degradation at which weight loss is 5%) of the hybrid containing 20% TEOS content was 290°C. As the TEOS content increases to 80%, T d5 of the hybrid raises to 312°C. TEOS inorganic components enhance the thermal stability of hybrids. Limiting oxygen index (L.O.I.) and UL-94 test reveals that the hybrid ceramer possesses excellent flame retardance.