Changping Yin

A new resin with improved processability and thermal stability

To maintain outstanding thermal stability, amino- and hydroxyl-containing phthalonitrile monomers, 4-(4-aminophenoxy)-phthalonitrile (APN) and 4-(4-hydroxyphenoxy)-phthalonitrile (HPN) were selected and synthesized. Their structures were confirmed by proton nuclear magnetic resonance spectroscopy. Their curing polymers were characterized by Fourier transform infrared spectroscopy. The self-catalytic curing behaviors of the monomers were investigated by differential scanning calorimetry (DSC) at different heating rates. From the results, APN exhibits a higher curing temperature, while HPN exhibits a longer curing time. Then, mixtures of these monomers were investigated by DSC. The result shows that the 50/50 mixture exhibits different autocatalytic behaviors: the curing temperature is lower than that of APN and the curing time of the mixture is shorter than that of HPN. Furthermore, thermogravimetric analysis shows that the polymer from the mixture exhibits higher temperature of 5% weight loss (T5%) and char yield value at 800°C than those of the polymers from each monomer. All these results indicate that the new mixture resin exhibits improved processability with excellent thermal stability, attributed to the synergistic effect between similar monomers; the synergistic effect optimizes the cure reaction kinetics and promotes cross-linking reactions, thereby producing an excellent resin; this approach is a new method for improving the processability without sacrificing thermal stability.

Composite sandwich panel with multifunction of load bearing, heat insulation, and thermal protection

Integrative sandwich panels with multifunction of load bearing, thermal protection, and heat insulation are manufactured through co-injection resin transfer molding process. These panels have a polymethacrylimide foam core for heat insulation and two composite layers made of carbon/epoxy for load bearing and carbon/phenolic for thermal protection. In co-injection resin transfer molding process, the epoxy resin and phenolic resin are synchronously injected and cured in order to make integrative structures and improve the properties of the interface between different layers. The influence of main factors in the process of co-injection is investigated: the vacuum assistance is indispensable to improve the efficiency of manufacture and guarantee the properties of the products, volume fraction of carbon fiber plays the main role in determining size accuracy of the product, adjusting injection pressure is a simple and efficient way to adjust the infusion time of resin, while injection temperature has smaller influence in the features of manufacture. The mechanical properties of sandwich panels manufactured through co-injection resin transfer molding process and multi-step process are tested and compared to validate the advantage of the co-injection resin transfer molding process. The test shows that the in-plane compressive strength, three-point flexural strength, and interface shear strength are all improved by the co-injection resin transfer molding process. Co-injection resin transfer molding process is proved to be a feasible and efficient way to manufacture the integrative sandwich panel with good interface features.