Thermal Stability and Flammability of Styrene-Butadiene Rubber-Based (SBR) Ceramifiable Composites
Ceramifiable styrene-butadiene (SBR)-based composites containing low-softening-point-temperature glassy frit promoting ceramification, precipitated silica, one of four thermally stable refractory fillers (halloysite, calcined kaolin, mica or wollastonite) and a sulfur-based curing system were prepared. Kinetics of vulcanization and basic mechanical properties were analyzed and added as Supplementary Materials. Combustibility of the composites was measured by means of cone calorimetry. Their thermal properties were analyzed by means of thermogravimetry and specific heat capacity determination. Activation energy of thermal decomposition was calculated using the Flynn-Wall-Ozawa method. Finally, compression strength of the composites after ceramification was measured and their micromorphology was studied by scanning electron microscopy. The addition of a ceramification-facilitating system resulted in the lowering of combustibility and significant improvement of the thermal stability of the composites. Moreover, the compression strength of the mineral structure formed after ceramification is considerably high. The most promising refractory fillers for SBR-based ceramifiable composites are mica and halloysite.
Thermal degradation kinetics of poly(methylphenylsiloxane) containing methacryloyl groups
Abstract The kinetics of the thermal degradation of polymethylphenylsiloxane containing methacryloyl groups (PMPS-M) were investigated by thermogravimetric analysis (TGA). Thermal degradation of PMPS-M had two different processes: “unzipping degradation” and “rearrangement degradation”. The corresponding kinetic parameters of the two degradation stages were determined by using Friedman and Flynn–Wall–Ozawa methods, respectively. Coats–Redfern and Phadnis–Deshpande methods were also used to discuss the probable degradation mechanisms of the two different stages. The results showed that the activation energy obtained from Friedman method was in good agreement with the value obtained using Flynn–Wall–Ozawa method. The solid-state decomposition mechanism followed by the first degradation stage of PMPS-M was a decelerated D 4 type (three-dimensional diffusion controlled reaction). However, as for the second degradation stage of PMPS-M, its solid-state decomposition mechanism corresponded to a sigmoidal A 3 type, a nucleation and growth mechanism.
Diversity of Electrospinning Approach for Vascular Implants: Multilayered Tubular Scaffolds
Abstract The biomimetics of biological structures found in nature remains one of the most promising approaches to engineer functional tissues from natural or synthetic biocompatible materials for the replacement of damaged or injured parts of the human body. Recently, medical therapeutic regimes have advanced into a new era, overcoming the known mechanical and biological variances that occur when using autologous or synthetic grafts. Basically, the core concept of tissue biofabrication, commonly referred to as tissue engineering, is to find out the favorable cellular microenvironments to grow a living tissue prior to clinical uses. In fact, the ability of stem cells to regenerate is controlled via signaling pathways (growth factors) and supporting materials (scaffolds) that guide the cellular activities. After the first successful experiments to fabricate polymer fibers from their solutions, Cooley proposed the use of an electric field a century ago (Cooley (US 692:631, 1902 ). The electrospinning technique has been continually developed as a fruitful polymer processing technique to draw ultrafine nonwoven fibers. Electrospun polymer fibers have been used for a wide range of technical and biotechnical applications such as filtration, organic solar cells, tissue engineering, and drug releasing implants. In this regard, this review begins with an overview about the various spinning approaches for the fabrication of polymer fibers as well as the basic principles of electrospinning process. In addition, this review will highlight vascular bypass surgery and, in particular, the needs for vascular tissue engineering. Finally, the review includes some of the latest attempts to improve the mechanical and biological properties of electrospun polymeric fibers and summarizes the challenges and prospects for the future. Lay Summary However, vascular defects are treated successfully via bypass surgical bypass grafting using autologous or synthetic vessels. The small-diameter vessels (less than 6) are often associated with high failure rate. This review reports some of the recent features that should be highlighted to fabricate an ideal graft for small-diameter vascular grafts. The review introduces multilayered conduits as an alternative approach to overcome the known mechanical and biological mismatches of single layered vascular grafts of electrospun polymers.