Imparting Fire Retardancy and Smoke Suppression to Leather during Tanning Processes.

Leather is considered a luxury good when used in seating and upholstery. To improve safety, flame retardancy in leather is usually achieved through various finishing processes such as spray or roller coating. These treatments require processing steps that cost time and are labor-intensive. One avenue to achieving flame retardancy in leather is to add flame retardants during the tanning process. However, the influence on flame retardancy exerted by specific intumescent additives specifically added during leather tanning has yet to be investigated. This work explores the roles played by intumescent additive compounds in flame retarding leather when they are added during tanning instead of applied as a coating. Via a systematic investigation of various compound mixtures, the flame retardant effects in the condensed and the gas phases are elucidated. The results show a strong impact of melamine in the gas phase and of polyphosphates in the condensed phase. Their impact was quantified in fire and smoke analysis, showing a 14% reduction in the peak of heat release rate, strongly reduced burning lengths, and a 20% reduction in total smoke release compared to nontreated leather. These results illuminate the key role played by specific compounds in the flame retardancy of leather, particularly when they are added specifically during the tanning process instead of being applied as a coating. This method has great potential to reduce processing steps, lower costs, and improve material safety.

Investigation of the Thermal Stability of Proteinase K for the Melt Processing of Poly(l-lactide).

The enzymatic degradation of aliphatic polyesters offers unique opportunities for various use cases in materials science. Although evidently desirable, the implementation of enzymes in technical applications of polyesters is generally challenging due to the thermal lability of enzymes. To prospectively overcome this intrinsic limitation, we here explored the thermal stability of proteinase K at conditions applicable for polymer melt processing, given that this hydrolytic enzyme is well established for its ability to degrade poly(l-lactide) (PLLA). Using assorted spectroscopic methods and enzymatic assays, we investigated the effects of high temperatures on the structure and specific activity of proteinase K. Whereas in solution, irreversible unfolding occurred at temperatures above 75-80 °C, in the dry, bulk state, proteinase K withstood prolonged incubation at elevated temperatures. Unexpectedly little activity loss occurred during incubation at up to 130 °C, and intermediate levels of catalytic activity were preserved at up to 150 °C. The resistance of bulk proteinase K to thermal treatment was slightly enhanced by absorption into polyacrylamide (PAM) particles. Under these conditions, after 5 min at a temperature of 200 °C, which is required for the melt processing of PLLA, proteinase K was not completely denatured but retained around 2% enzymatic activity. Our findings reveal that the thermal processing of proteinase K in the dry state is principally feasible, but equally, they also identify needs and prospects for improvement. The experimental pipeline we establish for proteinase K analysis stands to benefit efforts directed to this end. More broadly, our work sheds light on enzymatically degradable polymers and the thermal processing of enzymes, which are of increasing economical and societal relevance.

Aromatic vs. Aliphatic Hyperbranched Polyphosphoesters as Flame Retardants in Epoxy Resins.

The current trend for future flame retardants (FRs) goes to novel efficient halogen-free materials, due to the ban of several halogenated FRs. Among the most promising alternatives are phosphorus-based FRs, and of those, polymeric materials with complex shape have been recently reported. Herein, we present novel halogen-free aromatic and aliphatic hyperbranched polyphosphoesters (hbPPEs), which were synthesized by olefin metathesis polymerization and investigated them as a FR in epoxy resins. We compare their efficiency (aliphatic vs. aromatic) and further assess the differences between the monomeric compounds and the hbPPEs. The decomposition and vaporizing behavior of a compound is an important factor in its flame-retardant behavior, but also the interaction with the pyrolyzing matrix has a significant influence on the performance. Therefore, the challenge in designing a FR is to optimize the chemical structure and its decomposition pathway to the matrix, with regards to time and temperature. This behavior becomes obvious in this study, and explains the superior gas phase activity of the aliphatic FRs.

Molecular Firefighting-How Modern Phosphorus Chemistry Can Help Solve the Challenge of Flame Retardancy.

The ubiquity of polymeric materials in daily life comes with an increased fire risk, and sustained research into efficient flame retardants is key to ensuring the safety of the populace and material goods from accidental fires. Phosphorus, a versatile and effective element for use in flame retardants, has the potential to supersede the halogenated variants that are still widely used today: current formulations employ a variety of modes of action and methods of implementation, as additives or as reactants, to solve the task of developing flame-retarding polymeric materials. Phosphorus-based flame retardants can act in both the gas and condensed phase during a fire. This Review investigates how current phosphorus chemistry helps in reducing the flammability of polymers, and addresses the future of sustainable, efficient, and safe phosphorus-based flame-retardants from renewable sources.

Biological evaluation of degradable, stimuli-sensitive multiblock copolymers having polydepsipeptide- and poly(ε-caprolactone) segments in vitro.

Polydepsipeptides, alternating copolymers consisting of α-amino acids and α-hydroxy acids, are degradable polymers. Depsipeptide-based polymers of varied architectures can be synthesized via ring-opening polymerization of various morpholine-2,5-dione derivatives. Thermoplastic phase-segregated multiblock copolymers with poly(ε-caprolactone) (PCL) and poly(iso-butyl-morpholinedione) segments have been synthesized from the macrodiols and an aliphatic diisocyanate as a coupling agent. The respective multiblock copolymers showed shape-memory capabilities and good elastic properties, making them attractive candidates for potential application as biomaterials for controlled drug release systems, scaffolds to be applied in tissue engineering or biofunctional implants. Thus, these abilities cumulate to form multifunctional materials, combining degradability with shape-memory capability. The advantages of depsipeptide-based multiblock copolymers compared to previously reported poly(ether)ester-derived biomaterials having shape-memory property may result from their different degradation products, as the resulting α-amino acids may act as a buffer for the hydroxy acids, thereby stabilizing pH values. In this context, we report on the biological evaluation of material samples in accordance with international standards (EN DIN ISO 10993-5 and 10993-12). Here, extracts of the substrates were exposed to a continuous fibroblast like cell line (L929) to study cytocompatibility of extractable substrates. Cell viability, morphology, LDH-release (as a parameter for the functional integrity of the cell membrane), activity of the mitochondrial dehydrogenases (as a parameter of the cell activity) and assembly of the actin- and vinculin cytoskeleton indicated no incompatibilities between the extracts and L929 cells. These results suggest that depsipeptide-based multiblock copolymers are promising candidates for soft, multifunctional implant materials.