No abstract

In modern society, the multifarious polymeric material polyurethane (PU) is used in household appliances and commercial sectors. Statistics shows the usage of PU as rigid and flexible foams is the highest among different PU-based materials. Industrially viable synthesis, tailor-made porosity and pore morphology, robustness to micro-organisms, weathering, hydrolytic degradation, and resistance to a wide range of chemicals are the excellent attributes of PU foams. Despite achieving significant attention in academia and industries, the prominent tendency to fire-catching or flammability and rapid-fire spread on ignition are the serious concerns of PU foams at their end-use. The figures on home fire accidents and associated fire injuries, loss of civilians, and properties primarily due to fire-catching of furniture are highly devastating. Therefore, a large volume of efforts has been dedicated to decorating flame retardancy in PU foams using a wide range of flame retardants (FRs) (in-situ or post-synthesis). Hence, the focus of this review is to summarize various FRs for rigid and flexible PU foams. The mechanism of flame retardancy, advantages and limitations of various FRs, and the past decade’s advancements achieved concerning the flame retardancy of PU foams have been explored.

Porous poly(ε-caprolactone) (PCL) scaffolds were fabricated using the high internal polymerization emulsion (HIPE) technique. Bis(ε-caprolactone-4-yl) (BCY) was utilized as crosslinker. The crosslinking density and the volume fraction of the dispersed phase were varied in order to study the potential effect of these parameters on the hydrolytic degradation at 37 °C and 60 °C. After different hydrolysis times the remaining solid samples were analyzed by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), while the degradation products in the aqueous aging solutions were analyzed by laser desorption ionization-mass spectrometry (LDI-MS). The effect of temperature on the degradation process and release of degradation products was, as expected, significant. The temperature effect was also shown by FTIR analysis that displayed a pronounced increase in the intensity of the hydroxyl-group absorption band after 70 days of hydrolysis at 60 °C indicating significant cleavage of the polymer chains. LDI-MS analysis proved the release of oligomers ranging from dimers to hexamers. The product patterns were similar, but the relative m/z signal intensities increased with increasing time, temperature and crosslinking density, indicating larger amounts of released products. The latter is probably due to the decreasing degree of crystallinity as a function of amount of crosslinker. The porous structure and morphology of the scaffolds were lost during the aging. The higher the crosslinking density, the longer the scaffolds retained their original porous structure and morphology.

Role of poly(ɛ-caprolactone) (PCL) and its 3D-scaffolds in tissue engineering has already been established due to its ease of processing into long term degradable implants and approval from FDA. This...

Cellulose-derived nanographene oxide (nGO)-type carbon dot reinforced porous scaffolds of poly­(ε-caprolactone) (PCL) were developed as templates from high internal phase emulsions (HIPE). The mechanical strength, structural integrity, and reusability of the scaffolds were enhanced via in situ cross-linking. An oil-in-oil (o/o) HIPE of ε-caprolactone monomer (CL) was made for this purpose, and the ring-opening polymerization of a continuous phase comprised of CL, catalyst (Sn­(Oct)2), and cross-linker (bis­(caprolactone-4-yl)) (BCY) was carried out. The functionalization of scaffolds with nGO was assessed along with its role as an effective Pickering stabilizer of the HIPEs. The pore size and porosity of the scaffolds were governed by HIPE morphology, which in turn was controlled by the amount of nGO and the volume fraction of the dispersed phase. The nGO-functionalized scaffolds of cross-linked PCL thus prepared were characterized for their morphological structure, mechanical strength, and oil sorption capacity. Enhanced oil adsorption of nGO-functionalized scaffolds proved them to be of higher potency compared to those made of neat PCL. Superior compressive strength and reusability of scaffolds for oil adsorption up to 40 times while maintaining the structural integrity for ≥25 sorption–desorption cycles added extra value to such scaffolds. The scaffolds also had excellent cell viability as evaluated by MG63 osteoblast-like cells and some bioactivity in the form of calcium phosphate mineralization on the surface of the scaffolds.