In this work, we first synthesized modified cellulose nanocrystals (MCNC) with 2,4-toluene diisocyanate and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide via a two-step in-situ polymerization method, and then incorporated it with shape memory polyurethane (SMPU) to fabricate composite. It was found that the urethane chains and phosphorus-containing flame retardant were covalently grafted onto the cellulose nanocrystals surface, and the MCNC exhibited good dispersion level in the SMPU matrix. Due to the crystallization-induced and flame retardant effects of the prepared MCNC, it could be acted as a multifunctional reinforcer in SMPU composites. Noticeably, the most balanced improvements in crystallization, shape memory, mechanical, thermal stability, and flame retardancy properties of composites were observed with the incorporation of 3 wt% MCNC. Shape memory experiment demonstrated that the SMPU-MCNC3 composite exhibited admirable thermal induced shape memory behavior, and its shape fixity and shape recovery ratios were maintained above 90% after five cycles. More importantly, the SMPU-MCNC3 composite showed well balanced mechanical (σ b = 13.1 MPa, ε b = 189.3%), limiting oxygen index (23.8%), and UL-94 rating (V-2) among the prepared polyurethane films. In addition, the representative SMPU-MCNC3 showed obviously reductions in heat and smoke production during combustion as compared to the neat SMPU. The present work offers a promising route to fabricate shape memory polyurethane composites with versatile functions.

Recently, traditional flame retardant finishing with a single metal compound has been rarely applied owing to its low effectiveness and durability. This study reports metal ion finishing in combination with surface photografting modification (M/P technology) as a novel approach to incorporate an inorganic−organic hybrid structure containing an Fe 3+ ion onto the surface of the polyamide (PA) 66 fabric. Specifically, the PA fabric was first surface-modified in the presence of acrylic acid (AA) and N,N′-methylene bisacrylamide (MBAAn) during photografting pretreatment under UV irradiation (step I), then further reacted with the Fe 3+ ion in the metal ion finishing (step II). After treatment with M/P technology, the fabric exhibits the required excellent flame retardancy and dripping resistance. Here, flame retardant tests show that the treated PA fabric has the highest limiting oxygen index (LOI) value of 33.4 and no melt dripping during combustion. An interesting inorganic/organic composite thermal barrier consisting of an inorganic iron oxide nanoparticle (NP) outer layer and an organic micro-intumescent inner layer can be observed on the surface of the burnt fabric. This structure could be responsible for the significant enhancement in the fire performance of the treated fabric. Importantly, the treated fabric is also highly stable during the laundering procedure, which could retain a high Fe/C ratio and an acceptable LOI value of 27.8 after washing 45 times. This confirms the achievement of durable flame retardancy after treatment with M/P technology, and its possible interaction mechanism has been discussed here.

This paper investigated the fire-retardant mechanism of the nano-LDHs in the intumescent system by the temperature programmed oxidation (TPO). Researches were also conducted to explore the function of the nano-LDHs in the composite fire-retardant agents in air and nitrogen atmosphere, respectively. The results indicated that the nano-LDHs species were responsible for the catalytic oxidation of the rich-carbon compound in oxygen atmosphere. In addition, the nano-LDHs species and their calcinated products at high temperature could increase the carbonaceous residue-shield of the carbon-rich materials, improve the quality and the graphitization degree of the formed char-layer, and accelerate the intumescence and expansion of the melting carbon-rich materials to a certain degree under the oxygen-free condition, leading to the carbonization and expansion of the intumescent layer.nanometer, layer double hydroxides (LDHs), fire-retardant mechanism, intumescent system Since the layered double hydroxides (LDHs) were firstly published to be used as precursors of new catalysts by Miyata S [1] in 1971, many issues on their potential applications were increased year after year. The interstitial layers of LDHs were analogous to the molecular sieve, leading to their direct application to a rigidity support framework for the intumescent coat of the fire-retardant coating with an increasing fire-retardant performance. Moreover, the complex metal oxides, formed by calcination of LDHs at different temperature, exhibited an improvement on the carbonization of intumescent layer of fire-retardant coating in fire. Therefore, the LDHs gradually became an ideal fire-retardant auxiliary agent. It should be noticed that the nanometer layered double hydroxides (nano-LDHs) had received considerable interests owing to their comprehensive applications as fire-retardants in recent years. The thermal stability and thermal degradation process of nano-LDHs were analyzed by Yang W et al. [2][3][4] , and their fire-retardant performance were also investigated by Xu Jianghua et al. [5][6][7] ; however, there were few studies on their fireretardant mechanism. The present work mainly purposed to firstly study the fire-retardant mechanism of nanoLDHs by the temperature programmed oxidation, and investigate their fire-retardant function in the intumescent fire-retardant system. Experimental Reagent and instrumentsThe preparation of the purposed products was carried out on the QM planet-style ball mill (Instrument Factory of Nanjing University). The self-manufactured temperature programmed oxidation (TPO) equipment, whose temperature control was carried out on an AI-708PA artificial intelligence industry adjuster (ÜGU Company), was recorded on the produced gas quantity (Figure 1).

To manufacture transparent waterborne polyurethane composite coatings that possess desirable mechanical and flame retardancy properties is still a challenge. Herein, we first synthesized phosphorus-silicon functionalized cellulose nanocrystals (FCNC) filler, and further introduced it into waterborne polyurethane (WPU) matrix to prepare composite. The phosphorus-silicon-containing components were grafted covalently on the surface of FCNC, and the FCNC showed good dispersion level in water and WPU matrix. Moreover, the inserted FCNC could not only maintain the high transparency of WPU-FCNCs composites, but also remarkably enhancing the mechanical and flame retardancy performances. Noticeably, the WPU-FCNC3 composite containing 3 wt% of FCNC showed balanced mechanical (σ b = 16.7 MPa, ε b = 557.5%), limiting oxygen index (22.9%), and a UL-94 rating of V-2 among prepared films. Additionally, WPU-FCNC3 composite exhibited significantly reductions in heat release during combustion, and also showed a high transmittance of 92.2%. The present research supplies promising way for developing transparent, toughness, and flame retardant composite coatings.

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