Synthesis And Anti-counterfeiting Packaging Application Of Toughness And Self-healing Stimulus-response Hydrogel

Intelligent packaging anti-counterfeiting technology is an important tool to ensure the security and circulation of production.To date,the substrate materials of intelligent anti-counterfeiting packaging materials are mainly paper,metal,and plastics.However,during the use and transportation process,the anti-counterfeiting packaging materials are easily wiped,resulting in a decrease in anti-counterfeiting quality and a shortened service life.Therefore,the development of smart packaging materials with high-strength,self-healing properties will help promote the application of intelligent anti-counterfeiting packaging.As a typical flexible material,hydrogel is a polymer with three-dimensional network,high water content,chemical crosslinking network,and self-healing properties.Through reasonable design of hydrogel network structure,the hydrogel can meet the requirements of intelligent packaging materials.More important,stimuli-responsive hydrogels have attracted widespread attention in the field of smart packaging anti-counterfeiting in recent years due to their excellent performance.Therefore,in this paper,we will devote to the preparation of high-strength,self-healing,and stimulus-responsive hydrogels,and to explore its application in intelligent packaging anti-counterfeiting.the research content of this paper includes the following three aspects:(1)Preparation of agar/pAM@PCD fluorescent nanocomposite hydrogel:We firstly prepared blue ang green fluorescent carbon dots(CD)using citric acid as a carbon source and ethylenediamine or urea as a nitrogen source by microwave method.In this way,abundant amino groups were anchored on the surface of the prepared CD,which can be further reacted with methacrylic acid glycidyl to form double bond-modified polymerizable carbon dot(PCD).The prepared polymerizable carbon dot were copolymerized with acrylamide monomer and agar to form a nanocomposite double-network hydrogel through heating-cooling and photo-initiated polymerization processes.The nanocomposite double network exhibited excellent fluorescent properties and high mechanical strength with tensile strength of 1.6 MPa at a stretch of 1400%.These results indicate that the addition of PCD can form a chemical cross-linking network to increase the cross-linker density of agar/PAM hydrogel.Under 365 nm,the nanocomposite double network exhibited blue and green fluorescent.More importing,the prepared nano-composite double-network hydrogel has Fe3+ sensing capability.Based on this property,the as-obtained nanocomposite hydrogel can further construct fluorescent anti-counterfeiting patterns.(2)Agar/pHEAA@MPS-CSNPs hydrogels with toughness and tunable full-color fluorescence for anti-counterfeiting:Three types of NaREF4:Ln3+ @NaYF4 core-shell upconversion nanoparticles(CSNPs)with red,green and blue primary fluorescence were successfully synthesized by using thermal decomposition method.Then,3-(trimethoxysilyl)propyl methacrylate(MPS)functionalized upconversion(UC)fluorescence NaREF4:Ln3+@NaYF4 core-shell nanoparticles(MPS-CSNPs)were prepared through a reverse microemulsion method.Finally,we developed three typical tough and upconversion fluorescence hydrogels by incorporating MPS-CSNPs into agar/poly(N-hydroxyethyl acrylamide)(agar/pHEAA)double-network hydrogels to produce agar/pHEAA@MPS-CSNPs gels.The obtained agar/pHEAA@MPS-CSNPs gels with RGB-emitting fluorescence were fabricated to exhibit a combination of superior mechanical properties,including high strength(tensile stress of 2.4 MPa),extensibility(tensile strain of 560%),and toughness(tearing energy of 11000 J/m2).More important,the obtained agar/pHEAA@MPS-CSNPs gels showed fast toughness/stiffness recovery of 47%/23%,good self-healed tensile stress/strain of 0.9 MPa/0.9.In parallel,the full-color UC fluorescence of the hydrogels can be readily tuned from primary RGB colors to any secondary color(even to white color)by simply changing the types and relative ratios of single or multiple MPS-CSNPs.Taking advantage of highly tough,surface adhesion,and self-healing properties,we further fabricated agar/pHEAA hydrogel film containing fluorescence-responsive patterns for potential anti-counterfeiting.The fluorescence-responsive patterns only can be seen by naked eye under 980 nm laser irradiation.(3)Preparation of spiropyran-based mechanoresponsive double network hydrogel:A mechanochromic and mechanofluorescent double-network hydrogels(poly(AM-co-MA/SP))based on spiropyran(SP)was prepared by micellar-copolymerization of SP cross-linker in the presence of methyl acrylate and acrylamide.The effect of components on the mechanical properties and force response properties of hydrogels was systematically investigated.Under optimal conditions,the obtained poly(AM-co-MA/SP)hydrogel exhibited a combination of superior mechanical properties,including high strength(tensile stress of 1.8 MPa),extensibility(tensile strain of 800%).Due to force responses of SP crosslinkers,the hydrogels exhibited the reversible changes in color.Based on the fast,reversible,force-induced color change behavior of SP,the obtained poly(AM-co-MA/SP)hydrogel showed excellent self-recovery performance(more than 90%recovery ratio).This approach for a new mechanoresponsive hydrogel is easily transformative to the construction of mechanophore-based hydrogels.At the same time,we hope that this type reversible force-sensitive hydrogels can be applied to the field of anti-counterfeiting packaging.