Novel Covalently Cross-Linked Attapulgite/Poly(acrylic acid-<i>co</i>-acrylamide) Hybrid Hydrogels by Inverse Suspension Polymerization: Synthesis Optimization and Evaluation as Adsorbents for Toxic Heavy Metals

Novel covalently cross-linked microbeads of attapulgite/poly­(acrylic acid-<i>co</i>-acrylamide) [ATP/P­(AA–AM)] hybrid hydrogels with excellent mechanical stability were synthesized by the inverse suspension copolymerization of acrylic acid (AA) and acrylamide (AM) with multifunctional attapulgite nanorods (MF-ATP) as the sole cross-linker. The synthesis conditions, such as feeding method, neutralization degree of AA, and feed ratio of the comonomers to MF-ATP, were optimized scientifically. The TGA results showed that 96% of the comonomers (AA and AM) were grafted onto the MF-ATP nanorods to form a three-dimensional network skeleton of the hybrid hydrogels, for a feed ratio of MF-ATP nanorods to comonomers of 1:5. The ATP/P­(AA–AM) hybrid hydrogels exhibited selective adsorption toward toxic heavy-metal ions, especially Pb²⁺ and Cu²⁺ ions. In addition, the adsorbed ions could be easily desorbed, indicating the reusability of the ATP/P­(AA–AM) hybrid hydrogels. Their use as an adsorbent for toxic heavy-metal ions can therefore be expected to be economically and technically feasible

Rapid Recovery Double Cross-Linking Hydrogel with Stable Mechanical Properties and High Resilience Triggered by Visible Light

The designed tough hydrogels, depending on energy dissipation mechanism, possess excellent biocompatibility, stimuli-responsiveness, and outstanding mechanical properties. However, the application of hydrogels is greatly limited in actuators and sensors for the lack of instantaneous recovery and resilience. In this work, we synthesized a double cross-linking poly­(acrylic acid) hydrogel via a simple, one-pot, visible-light-trigger polymerization, with carboxymethyl cellulose as initiator and the first cross-linker, <i>N</i>,<i>N</i>′-methylene bis­(acrylamide) (MBA) as the second cross-linker. The tensile strength and elastic modulus are in the range of 724–352 kPa and 115–307 kPa, respectively, depending on the MBA content. The swelling ratio of hydrogels dramatically decreased with increasing the MBA content. DMA results indicate that the internal friction between molecules within the hydrogel decreases with the increase of MBA content. Cyclic tensile tests show that after the structure stabilizes, the resilience, maximum stress, and residual strain of Gel-2 maintains over 93% (95% for successive cyclic tensile test), 115 kPa and less than 3%, respectively, at a strain of 125%. The values of resilience and residual strain are almost constant in both successive and intermittent cyclic tensile tests. Moreover, the swollen hydrogel has higher resilience and lower residual strain than the same hydrogel in the as-prepared state

Facile Construction of Inorganic Phosphorus/Boron-Layered Double Hydroxide Complexes for Highly Efficient Fire-Safety Epoxy Resin

For inorganic flame retardants, facile fabrication and high-efficiency fire safety without compromising the mechanical property of the matrix are still significant challenges. Here, nanolayered double hydroxide containing boron constructed on the surface of ammonium polyphosphate (APP) complexes (B-LDH@APP) is prepared by a simple in situ coprecipitation technology to reduce the fire hazard and improves the mechanical performances of epoxy resin (EP). The as-obtained 4B-LDH@APP/EP achieves the UL-94 V-0 rating and presents superior flame-safety performance. With respect to the 4APP/EP, the fire growth rate (FIGRA), the peak heat release rate (pHRR), and the peak smoke production rate (pSPR) of 4B-LDH@APP/EP decrease by 77.8, 57.3, and 52.6%, respectively. This is mainly attributed to the excellent synergistic flame-retardant effect among boron, LDH, and APP, which can accelerate the generation of compact charring residual with a good microstructure during combustion of B-LDH@APP/EP composites. Furthermore, B-LDH@APP slightly affects the mechanical performances of the EP matrix due to the upgraded interfacial interaction