| As a kind of military and civilian basic materials,rubber materials,which possess unique high elasticity,can be used as tires,conveyor belts,various seals and vibration damping components.Conventional rubber generally uses sulfur or peroxide to form irreversible covalent chemical cross-linking network,which is difficult to be recycled and self-healed,and has caused serious resource waste and environmental pollution.Therefore,it is particularly important to study the preparation of new rubber materials with self-healing and recyclability.In recent years,researchers have attempted to construct dynamic bond with reversible fracture-regeneration under certain conditions through molecular design,enabling the material recyclable and self-healable properties,and even imparting responsive features to different external stimuli(such as light,heat,pH).This project aims to construct dynamic bonds by molecular design to prepare elastomer with high mechanical strength and can achieve multiple functions under mild conditions,which provides a new strategy for the recycling and functionalization of rubber materials.The innovative work and results are as follows:(1)The catalytic Diels-Alder reaction suitable for melt blending was designed for the first time to prepare epoxy natural rubber(ENR)with thermal reversible and self-healing properties.The epoxy groups of ENR undergo ring-opening reaction with furfuryl amine(FA)to form ENR-FA catalyzed by Yb via one-step melt blending method,EMR-FA could react with bismaleimide(BMI),formin thermally reversible cross-linking ENR(TRENR).The effects of the amount of catalyst(Yb),the amount of FA on the grafting ratio of ring-opening reaction were investigated.Besides,we also studied the decrosslinking,re-crosslinking temperature of DA reaction and the recyclable,self-healable properties of TRENR.The results show that the suitable amount of Yb is 0.2%of the molar ratio of epoxy groups of ENR.As the amount of FA increases,the grafting ratio,tensile strength and elongation at break of TRENR increase.The decrosslinking temperature of TRENR is about 150?,and the temperature of re-crosslinking reaction is about 125?.Based on the temperature of decrosslinking reaction,the self-healing efficiency and the retention rate of tensile strength after the first recycle at 170 ? for 20 min are about 87%and 90%,respectively;and also,the crosslink-density of TRENR almost remains the same after the first recycle,indicating good thermo-reversible,self-healable properties.The preparation of TRENR was carried out in a Haake rheomixer with short reaction time,and it requires no solvent and does not produce a stimulating smell.This new technique is promising in industry for rubber recycling and large-scale preparation of TRENR in an environmentally friendly method(2)The vitrimer dynamic network based on transesterification was designed to prepare epoxy natural rubber(ENR)with photothermal induced self-healable,recyclable and reconfigurable shape memory properties.The triphenylaniline(ACAT)monomer was synthesized and a simple blending-hot pressing method was used to make dodecanedioic acid(DA)and ACAT participate in the covalent crosslinking of ENR to form a transesterification network and trace permanent crosslinks.The co-existing network structure imparts ENR with multi-functional properties.We explored the influence of reaction time on the degree of covalent crosslinking,revealed the relationship between the molar ratio of different DA and ENR to the de-freezing temperature of the topological network(Tv)and mechanical properties,clarified the relationship between ACAT and pH responsive,light-induced self-healiing,shape memory performances.The results show that ENR,DA and ACAT can form dynamic covalent cross-linking network with vitrimer characteristics based on transesterification within 40 min.With the increase of DA/ENR,the Tv increased from 185.2? to 188.7?.The tensile strength increased and the hysteresis loss gradually decreased with the improvement of the cross-linking network.Thermally-induced self-healing and recycling experiments at 200? for 30 min indicates that the self-healing efficiency is approximately 80%and recycling efficiency is approximately 88%after three cycles.The shape memory experiment which was carried out at 80? showed that the fixing rate(Rf)and recovery rate(Rr)were both over 90%.The introduction of ACAT enables the elastomer good pH responsive and NIR-induced self-healing,multi-stage shape memory properties,which will make ENR-DA-ACAT elastomers more widely used in the field of actuators.(3)The vitrimer dynamic network based on dynamic imine bond was designed to prepare polysiloxane(PDMS)elastomer with recyclable,self-healable and water-driven properties.The PDMS elastomer based on dynamic imine bond was prepared via one-step process.The effects of solvent on the structure of the elastomer network,the crosslinking degree on the mechanical properties and the responsiveness to water of the elastomer were investigated.The self-healing and recyclable properties of the elastomer were further studied.The results show that the vitrimer-like PDMS elastomer is solvent-resistant at high temperatures and exhibits recycling efficiency at 100? for 15 min(1st:98%,2nd:99%,3rd:88%)and self-healing efficiency(about 93%).With the increase of crosslinking degree,the tensile strength of the elastomer gradually increases,and the elongation at break gradually decreases.PDMS elastomer possesses water-responsive property because of dynamic imine bonds,which will potentially lead to green processing of the elastomers.(4)The double network with multiple hydrogen bonding interactions was designed to prepare a hydrogel with high strength,self-healing and shape memory performance.The NAGA monomer with two amide groups at the same side group was synthesized,and P(NAGA-co-NBAA)/agar double network hydrogel based on multiple hydrogen bonding interactions was prepared by one-pot method.We investigated the effects of monomer concentration on equilibrium water content(EWCs),pore size and mechanical properties of hydrogels,revealed the relationship between network structure and rheology behavior,shape memory performance of the hydrogel,clarified the de-association,re-association of hydrogen bonds during the heating-cooling cycle.The results show that as the monomer concentration increases,the EWCs and average pore size decrease gradually,the tensile strength and elongation at break increase gradually.The increase of temperature makes the self-healing efficiency increase gradually and the efficiency reaches the highest at 90?(about 95%).The DN hydrogel can possess high stability at low frequencies,achieve dual shape memory quickly(complete shape recovery within 10s)and triple shape memory function.During the heating-cooling cycle,more than 80%of the de-associated hydrogen bonds can be re-associated.In addition,P(NAGA-co-NBAA)/agar hydrogel is completely crosslinked by hydrogen bonds,and can be widely used in the field of biomedical materials as its good biocompatibility.(5)Inspired by mussels,the network structure with multiple hydrogen bonds and ?-? interactions was designed,and nano-composite hydrogel with high stretchability,high toughness and self-healing performance was prepared.PDA-PNAGA-GO hydrogel with high toughness,self-healing,NIR actuated performance and high mechanical strength was prepared by two-step method using NAGA monomer.We explored the effects of different DA/NAGA mass ratios on gelation,NAGA monomer concentration on mechanical properties of hydrogel and toughness,GO concentration on hydrogel photo-thermal effect and driving degree,revealed the mechanism of self-healing and high toughness of hydrogel.The results show that the optimal mass ratio of DA to NAGA is 4 ‰,the polymerization of DA forms large amounts of PDA microfibers,which gives the hydrogel high tensile properties and high toughness.With the increase of NAGA concentration,the tensile strength and fracture energy of hydrogel increase gradually,and the elongation at break decreases slightly.The increase in GO concentration makes the photothermal effect and driving degree of the hydrogel(up to 40%)being enhanced gradually.The hydrogel can be self-healed at 90?(the efficiency is about 87%).These unique properties including highly stretchable,high toughness and self-healing and NIR responsive properties will enable greater application of these hydrogel materials,especially in tissue engineering and soft actuators... |
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