Synergistic thermodynamic compatibility of polydimethylsiloxane block in thermoplastic polyurethane for flame retardant materials: Super flexible, highly flame retardant and low smoke release

The improvement of flame retardancy and compatibility of PBAT/PLLA via a hybrid polyurethane

Poly (butylene adipate-co-terephthalate)/poly (L-lactic acid) (PBAT/PLLA) is one of the most important biodegradable polymer combinations; however, they are flammable with heavy melt dripping and incompatible. To achieve the objective of flame retardation and compatibility, a hybrid polyurethane (PU) with multiple flame retardation elements is synthesized via a new ring-opening polymerization (ROP) method and integrated into PBAT/PLLA film. The PU not only dissolves in different organic solvents at mild temperature but also improves the compatibility of PBAT/PLLA. As PU with respect to PBAT/PLLA is 20 wt%, the limiting oxygen index (LOI) and UL-94 reach 25.5 % and V-0 rating, respectively. In cone calorimeter test, the peak heat release rate (pHRR) of PU/PBAT/PLLA is ahead of PBAT/PLLA, and the total heat release (THR) decreases to 25.85 MJ/m2. The fire safety is achieved successfully. The initial pyrolysis of PU promotes the formation of a seed carbon layer; it continuously breaks down into a series of phosphorus‑oxygen radicals and generates different inert gases, while the pyrolytic solid products accelerate the carbonization to form the carbon/silicon composite layer. Then the polymeric combustion is braked completely. Besides, the PU can also tune the mechanical properties of PBAT/PLLA film and enhance its hydrophobicity. This work opens a new window for developing multifunctional flame retardant and paves the way for the richening engineering application of PBAT/PLLA.

Polysiloxane-Based Polyurethanes with High Strength and Recyclability

Polysiloxanes have attracted considerable attention in biomedical engineering, owing to their inherent properties, including good flexibility and biocompatibility. However, their low mechanical strength limits their application scope. In this study, we synthesized a polysiloxane-based polyurethane by chemical copolymerization. A series of thermoplastic polysiloxane-polyurethanes (Si-TPUs) was synthesized using hydroxyl-terminated polydimethylsiloxane containing two carbamate groups at the tail of the polymer chains 4,4′-dicyclohexylmethane diisocyanate (HMDI) and 1,4-butanediol as raw materials. The effects of the hard-segment content and soft-segment number average molecular weight on the properties of the resulting TPUs were investigated. The prepared HMDI-based Si-TPUs exhibited good microphase separation, excellent mechanical properties, and acceptable repeatable processability. The tensile strength of SiTPU-2K-39 reached 21.5 MPa, which is significantly higher than that of other flexible polysiloxane materials. Moreover, the tensile strength and breaking elongation of SiTPU-2K-39 were maintained at 80.9% and 94.6%, respectively, after three cycles of regeneration. The Si-TPUs prepared in this work may potentially be used in gas separation, medical materials, antifouling coatings, and other applications.

Development of thermoplastic vulcanizates based on in situ synthesized thermoplastic polyurethane and acrylonitrile-butadiene rubber: the influence of the curing system

We prepared different thermoplastic elastomers (TPEs) using an internal mixer. We investigated the properties of thermoplastic polyurethanes (TPUs) produced from prepolymers with various isocyanate content and two different chain extenders to select the most appropriate TPU matrix for preparing thermoplastic vulcanizates (TPVs). Based on the results, we selected a prepolymer with moderate isocyanate content (10%) and the more flexible 1,6-hexanediol as a chain extender and prepared TPVs by dynamic vulcanization with in situ produced TPU. The rubber phase was acrylonitrile-butadiene rubber (NBR) with peroxidic and sulfuric curing with different accelerators. Dynamical mechanical analysis (DMA) results show that the room temperature storage modulus of the TPVs decreases due to the rubber phase. The TPU/NBR-CBS TPV with delayed action accelerator yields the highest tensile and tear strength and elongation at break. TPU/NBR-DCP made with a peroxide-based rubber blend shows similar tensile strength with significantly lower elongation at break and tear strength. The good mechanical properties of TPU/NBR-CBS can be explained by the long induction period, which allowed the rubber phase to disperse before vulcanization took place. In the TPU/NBR-DCP, the peroxide formed bonds not only in the rubber phase but also between the rubber and TPU phases, which is manifested in the high mixing torque and the result of the thermogravimetric analysis (TGA).