Effect of isothermal aging on post-imidization and glass transition temperature of LaRC-IA polyimide resin

The isothermal aging of partilly imidized NASA Langley Research Center, LaRC-IA polymide resin containing 70 wt% N-methyl pyrrolidone, NMP was performed in a vacuum oven at 65, 95, 135, 165 and 200°C for 0.5, 1.0, 1.5 and 2 h. The weight loss and chemical changes that occurred during aging was determined gravimetrically and by FTIR spectroscopy, respectively. The imide absorption peak at 1778 cm⁻¹, increased in intensity as the aging temperature was increased from 65 to 200°C. The expulsion of NMP (70 wt%) was completed after ∼2.5 h of aging at 135°C. Additional weight loss ≤4 wt%, after the expulsion of NMP, was attributed to post-imidization. The imide carbonyl peak absorption at 1721 and 1778 cm⁻¹, respectively, were broadened after aging at 200°C. The broadening of the imide absorption peaks was marked by the disappearance of the amide peak near 1660 cm⁻¹ and is attributable to post-imidization of the partially imidized polyamic-acid. Dissolution of the polyimide aged at T ≥ 165°C in dimethyl formamide, DMF, was unsuccessful even after long times of stirring (∼12 h) at elevated temperature (T ∼ 85°C). The DSC thermogram for the LaRC-IA resin showed a series of broad endothermic peaks between 150–180°C and narrow endothermic peaks at 210°C. The low temperature endotherm disappeared after aging at T ≥ 135°C for t ≥ 1 h. The high temperature endotherm decreased with increased aging temperature and time. The glass transition temperature of the polyimide increased with increased aging temperature and time.     

Comparative Assessment of Crystallographic Phase Stability of Anatase and Rutile TiO2 at Dynamic Shock Wave Loaded Conditions

In the present research article, authors have experimentally evaluated the shock wave resistant properties of technologically potential materials of the anatase and the rutile phase TiO₂ nanoparticles at the dynamic shock wave loaded conditions. The shock wave resistant behavior has been quantitatively drawn utilizing the crystallographic phase stability of the test samples for which the required crystallographic information has been extracted from the powder XRD patterns. Based on our observed experimental results as well as the respective interpretations, it is strongly authenticated that Rutile TiO₂ NPs are suitable candidates for aerospace and defense industrial applications of materials fabrications because of the outstanding shock resistant properties than that of Anatase TiO₂ NPs which undergo the crystallographic phase transition of rutile-TiO₂ at shocked conditions.

     

Negative Regulation of Innate Immune Signaling by Components of the Button Mushroom Agaricus bisporus

Scope: Mushrooms are valued as an edible and medical resource for millennia. As macrofungi, they possess conserved molecular components recognized by innate immune cells like macrophages, yet unlike pathogenic fungi, they do not trigger the immune system in the same way. That these well-tolerated foods both avoid immuno-surveillance and have positive health benefits, highlights the dearth of information on the interactions of mushroom-derived products with the immune system. Methods and results: Using powders produced from the common white button mushroom, Agaricus bisporus, it is observed that pre-treatment of mouse and human macrophages with mushroom powders attenuates innate immune signaling triggered by microbial ligands like LPS and  β-glucans, including NFκB activation and pro-inflammatory cytokine production. This effect of mushroom powders is observed at lower doses of TLR ligands, suggesting a model of competitive inhibition whereby mushroom compounds bind and occupy innate immune receptors, precluding activation by microbial stimuli. This effect is preserved following simulated digestion of the powders. Moreover, in vivo delivery of mushroom powders attenuates the development of colitis in a DSS-mouse model. Conclusion: This data highlights an important anti-inflammatory role for powdered A. bisporus mushrooms, which can be further utilized to develop complementary approaches to modulate chronic inflammation and disease.