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• Two curing stages occurred in the curing process of silicone rubber at 6 MPa CO 2. • Pressure facilitates the initial reaction stages but hinders the later stages. • Solvation effect of CO 2 on accelerating the curing reaction process. • The high-pressure curing kinetics of silicone rubber are obtained and verified. In this study, high-pressure differential scanning calorimetry (HP-DSC) was used to examine the curing process of a peroxide-cured silicone rubber (SR) system under compressed CO 2 to investigate the influence of pressure and CO 2 on the curing process. We found that the curing reaction occurred in two parts, described as cure separation, because of the dual effect of CO 2 pressure and solvation at 6 MPa CO 2. Consequently, peak fitting was used to calculate the kinetic parameters of the two-part reaction at 6 MPa CO 2. Results indicate that pressure and CO 2 exerted a combined effect on the curing reaction. In particular, pressure and CO 2 solvation effects changed with varying conversion rates and CO 2 pressures. This study provides an effective analysis methodology and an accurate kinetic model for characterizing and predicting high-pressure cure kinetics and unexpected cure separation in a peroxide-cured SR system under compressed CO 2. A model-free isoconversional method was used to investigate the high-pressure curing kinetics of SR. f(α) was determined to be autocatalytic for all the reactions occurring at different CO 2 pressures according to the compensation effect. The impact of pressure on the curing reaction was examined using N 2 as the reference gas. The results indicate that an increase in pressure facilitates the initial stages of the reaction but hinders the later stages. Moreover, CO 2 solvation enhances the mobility of molecular chains and reduces the E α of the entire reaction, thereby accelerating the curing process. The solvation effect is gradually enhanced with increasing CO 2 pressure. E α decreases by ∼30.43 % at 6 MPa CO 2. However, with increasing conversion, the viscosity of the system increases and the density of CO 2 in SR decreases, resulting in a tendency for E α to increase gradually. A Gaussian multiple-peak fitting method was used to analyze and isolate the exothermic peaks at 6 MPa CO 2. Kinetic models were established and validated at various CO 2 pressures. The validity of these kinetic models was verified, demonstrating the effective simulation of the reaction by the curing kinetic model under compressed CO 2. [Display omitted] [ABSTRACT FROM AUTHOR]

This work reports the design and fabrication of strong tough poly(lactic acid) (PLA) foam by combining pressure-induced-flow (PIF) processing with supercritical CO 2 foaming. PIF processing widened the foaming window of PLA to 40–120 °C, while supercritical CO 2 foaming released the undesired internal stress of PLA samples with PIF processing (P-PLA). The prepared PLA foams displayed a unique microfibrillated bimodal micro/nano cellular structure which is strongly affected by saturation temperature (T s). Both micron and nano cells showed decreasing cells size and increasing cell density as T s elevated. The orientation factor as well as internal stress of PLA foams decreased with increased T s. Compared with P-PLA samples, PLA foam prepared at T s of 40 °C showed negligible reduction of orientation from 0.45 to 0.41 and release of internal stress characterized by the rightward shift of Raman peak (stretching vibration of C O bond from 1763 to 1766 cm−1). Furthermore, PLA foam prepared at T s of 40 °C presented excellent impact strength (32.3 kJ/m2), tensile strength (42.0 MPa), and ductility (14.2%). The combination of PIF processing and supercritical CO 2 foaming provides a facile and effective method to prepare strong tough PLA foam that has immense potential in biomedical, aerospace, automotive, and other structural applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Crystallinity decreased with increasing annealing temperature or saturation pressure. • Ring-banded spherulites were formed by crystallization under compressed CO 2. • Cellular structure was affected by both crystallinity and crystal morphology. • A suitable foaming window as a function of temperature was proposed. Abstract Using a batch foaming technique, the effects of supercritical carbon dioxide on the formation of crystals under different saturation conditions (i.e. temperature or pressure) and subsequently on the cellular structure of the PLA foams were investigated. The crystallinity decreased with increasing annealing temperature or pressure, meanwhile, crystal morphologies were varied by controlling the temperature or pressure. It was found that a uniform closed cell structure was obtained by specifically controlling the foaming temperature in the range of (80–100) °C, in which only the ring-banded spherulites were formed. A suitable foaming window as a function of temperature was proposed. A number of stamen-like cell structure was observed because of formation of irregular-banded spherulites under 8 MPa. However, an opened and interconnected cell structure was obtained at 24 MPa. The results indicated that not only the crystallinity but also the crystalline morphology played an important role in the cellular structure. [ABSTRACT FROM AUTHOR]