Thermal degradation mechanism of highly filled nano-SiO2 and polybenzoxazine

Effects of high nano-SiO₂ loading (up to 30 mass%) on polybenzoxazine (PBA-a) thermal degradation kinetics have been investigated using nonisothermal thermogravimetric analysis (TG). The DTG curves revealed three stages of thermal decomposition process in the neat PBA-a, while the first peak at low temperature was absent in its nanocomposites. As a consequence, the maximum degradation temperature of the nanocomposites shifted significantly to higher temperature as a function of the nano-SiO₂ contents. Moreover, the degradation rate for every degradation stage was found to decrease with the increasing amount of the nano-SiO₂. From the kinetics analysis, dependence of activation energy (E _a) of the nanocomposites on conversion (α) suggests a complex reaction with the participation of at least two different mechanisms. From Coats–Redfern and integral master plot methods, the average E _a and pre-exponential factor (A) of the nanocomposites showed systematically higher value than that of the PBA-a, likely from the shielding effect of the nanoparticles. The main degradation mechanism of the PBA-a was determined to be a random nucleation type with one nucleus on the individual particle (F1 model), while that of the PBA-a nanocomposite was the best described by diffusion-controlled reaction (D3 model).     

Curing kinetics of arylamine-based polyfunctional benzoxazine resins by dynamic differential scanning calorimetry

In this study, the curing kinetics of polyfunctional benzoxazine resins based on arylamine, i.e. aniline and 3,5-xylidine, designated as BA-a and BA-35x, respectively, were investigated. Non-isothermal differential scanning calorimetry (DSC) at different heating rates is used to determine the kinetic parameters and the kinetic models of the curing processes of the arylamine-based polyfunctional benzoxazine resins were proposed. Kissinger, Ozawa, Friedman, and Flynn-Wall-Ozawa methods were utilized to determine the kinetic parameters of the curing reaction. BA-a resin shows only one dominant autocatalytic curing process with the average activation energy of 81-85 kJ mol⁻¹, whereas BA-35x exhibits two dominant curing processes signified by the clear split of the curing exotherms. The average activation energies of low-temperature curing (reaction (1)) and high-temperature curing (reaction (2)) were found to be 81-87 and 111-113 kJ mol⁻¹, respectively. The reaction (1) is found to be autocatalytic in nature, while the reaction (2) exhibits nth-order curing kinetics. In addition, the predicted curves from our kinetic models fit well with the non-isothermal DSC thermogram.     

Thermosetting Shape Memory Polymers and Composites Based on Polybenzoxazine Blends,Alloys and Copolymers

When dealing with smart polymers, in particular with shape memory polymers, the polymer type and composition specify the overall material properties and in particular the extent of the shape memory effect. Polybenzoxazines as a polymer with high potential for structural applications represent a promising component for materials with both shape memory effect and structurally interesting material properties. This minireview gives insight into how the shape memory effect, in particular the shape recovery event, is influenced by internal factors such as polymer structure, morphology and external factors such as filler addition.     

Property enhancement of polybenzoxazine modified with dianhydride

A novel bisphenol-A-aniline type polybenzoxazine (PBA-a) modified with dianhydride was successfully prepared by reacting bisphenol-A-aniline based benzoxazine (BA-a) resin with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) in 1-methyl-2-pyrrolidone (NMP) solvent. The miscible monomer mixture was easily transformed into transparent PBA-a/BTDA copolymers by thermal cure. Fourier-transform infrared spectroscopy reveals the formation of ester linkage which is a covalent interaction between hydroxyl group of the PBA-a and the carbonyl group in the dianhydride. The PBA-a/BTDA copolymers show only one glass transition temperature (Tg) with the value as high as 263 °C at BA-a:BTDA = 1.5:1 mol ratio. The value is remarkably higher than that of the unmodified PBA-a, i.e. 160 °C. In addition, the resulting PBA-a/BTDA copolymers display relatively high degradation temperature up to 364 °C and substantial enhancement in char yield with a value of up to 61% by weight. Moreover, flexibility of the PBA-a/BTDA copolymer samples is also significantly enhanced compared to the unmodified PBA-a. The obtained copolymer demonstrates high potential for those applications that require high thermal and mechanical properties with fire resistant characteristics.