Search

Resin matrix composites (RCs) have better thermal and chemical stability, so they are widely used in engineering fields. In this study, the aging process and mechanism of two different types of resin-based three-dimensional four-way braided composites (H15 and S15) under different hygrothermal aging conditions were studied. The effect of aging behavior on the mechanical properties of RCs was also studied. Three different aging conditions were studied: Case I, 40 °C Soak; Case II, 70 °C Soak; and Case III, 70 °C-85% relative humidity (RH). It was found that the hygroscopic behavior of RCs in the process of moisture-heat aging conforms to Fick's second law. Higher temperatures and humidity lead to higher water absorption. The equilibrium hygroscopic content of H15 was 1.46% (Case II), and that of S15 was 2.51% (Case II). FT-IR revealed the different hygroscopic mechanisms of H15 and S15 in terms of aging behavior. On the whole, the infiltration behavior of water molecules is mainly exhibited in the process of wet and thermal aging. At the same time, the effect of the aging process on resin matrices was observed using SEM. It was found that the aging process led to the formation of microchannels on the substrate surface of S15, and the formation of these channels was the main reason for the better moisture absorption and lower mechanical strength of S15. At the same time, this study further found that temperature and oxygen content are the core influences on post-aging strength. The LVI experiment also showed that the structural changes and deterioration effects occurring after aging reduced the strength of the studied material. [ABSTRACT FROM AUTHOR]

• Embryonic callus induction is the key of somatic embryogenesis in A. praecox. • Plant hormone signals trigger somatic cell reprogramming. • Lower and moderate levels of stress are beneficial for the acquisition of embryonic ability. • Starch and sucrose metabolism play fundamental and important roles in the acquisition of embryonic ability. Somatic embryogenesis (SE) is an ideal cell model for plant cell totipotency study. The poor frequency of embryogenic callus (EC) induction limits the application of SE in many plants, such as Agapanthus praecox. Herein, we performed transcriptomic and physiological analyses with different callus (Ca) differentiation directions (SE and organogenesis) and stages (initial SE and repetitive SE) to better understand the physiological and molecular characteristics of the acquisition of embryogenic potential in A. praecox. A number of differentially expressed genes (DEGs) were significantly related to plant hormonal signaling transduction, starch and sucrose metabolism, and reactive oxygen species (ROS) responses. Compared to Ca, DEGs including heat shock protein, isoamylase, histone H4, alpha-1,2-mannosyltransferase , and sucrose synthase substantially changed expression levels in EC formation. Corresponding to DEGs, physiological indicators including indole-3-acetic acid, cytokinins, brassinosteroids, ethylene, abscisic acid, ROS, hydrogen peroxide, superoxide dismutase, catalase, starch and sucrose may be responsible for the acquisition of embryogenic potential in A. praecox. Moreover, plant growth regulators, carbon source combination, osmotic regulating substance, and DNA methylation inhibitors in the culture medium significantly affected the acquisition of SE potential. Altogether, our results suggested that plant hormone signal regulation, starch and sucrose metabolism, ROS scavenging, chromatin accessibility and DNA methylation jointly contributed to the activation of embryogenic ability in A. praecox. [ABSTRACT FROM AUTHOR]