Multifunctional Shape Memory Materials And Robust Elastomers Based On Eucommia Ulmoides Gum

In recent years,driven by carbon peaking and carbon neutrality goals,it has become a new trend to replace traditional petroleum-based polymer materials with green bio-based polymer materials.As an isomer of natural rubber（NR）,Eucommia ulmoides gum（EUG）exists in the bark,leaves,roots,fruits and seeds of Eucommia ulmoides Oliver with a structure of trans-1,4-polyisoprene.It possesses unique and excellent duality of both rubber and plastic owing to crystallization.Thus,it can be used as a high-performance plastic,shape memory polymer（SMP）or high elastic rubber.Although a series of important progress has been made in the application of EUG,there are still some issues to be solved.In terms of the application of shape memory materials,the stimuli ways of EUG-based SMPs are limited,and their permanent shape is difficult to reconfigure.In addition,they are unable to achieve bidirectional reversible shape transformation,and don’t possess self-healing properties and recyclability.In terms of the application of elastomers,EUG-based elastomers usually need to be vulcanized by sulfur or DCP before using,and the formation of covalent network makes them recycle very difficult.Besides,these EUG-based elastomers do not have strain-induced crystallization（SIC）properites,resulting in poorer performance than NR.In order to solve the above issues,this paper focuses on two aspects of multi-functional shape memory materials and high-performance elastomers.The detailed research content is as follow.（1）We prepared a series of EUG/silica hybrids（ESH）through a facile one-pot process,in which EUG was epoxied and then self-crosslinked with Si O₂by epoxy ring-open reaction.Varying the amount of H₂O₂,the shape memory transition temperature(T_trans)of ESH was adjusted from 47.4℃to 36.6℃,which is close to human body temperature（37℃）.Among them,ESH-17 exhibited the best body temperature triggering shape memory ability(T_trans=36.6℃),which can restore the permanent shape within 60s at 37℃with shape fixity ratio of99%and shape recovery ratio near 100%.In addition,we discuss the shape memory mechanism and show some application scenarios of ESHs.The as-produced materials can be used as smart biomaterials such as self-tightening sutures,self-sealing root canal filling materials and so on.（2）We prepared a kind of multifunctional SMPs by constructing a dynamic boronic ester bond cross-linking network using sustainable EUG as a raw material.Thanks to the crystallization and wide melting temperature range,this kind of SMPs has thermal-triggered one-way shape memory performance and shows two-way shape memory properties,whether under constant stress or stress-free conditions.Owing to the dynamic nature of the boronic ester bond,it exhibits good self-healing properties（near 100%at 80℃）,shape reconfigurability,and chemical recyclability.In addition,by incorporating multi-walled carbon nanotubes（MWCNTs）,the formed composite is responsive to 808 nm near-infrared light.Its applications are further exploited,including photo-responsive actuators,vascular stents,and light-driven switches.This chapter provides a simple way for fabricating multifunctional SMPs,and the as-prepared materials have potential applications in diverse fields,such as biomedicine,intelligent sensing,and soft robotics.（3）We demonstrate a simple way to prepare a multifunctional EUG elastomer by constructing a semi-interpenetrating dynamic network（semi-IDN）.This kind of EUG elastomer possessed high stretchability（～876%）,high tensile strength（～12.1 MPa）as well as good self-healing,solid plasticity and shape memory properties.Moreover,it can not only be reprocessed by hot pressing（tensile strength remains 92%after three times reprocessing）,but also can be recycled by dissolving with little effect on the structure and properties.In addition,a flexible electronic device is prepared by spraying hydroxylated multiwalled carbon nanotubes（MWCNTs-OH）on its surface,which exhibited good self-healing of electrical conductivity after damage.The concept of semi-IDN provides a new way to prepare recyclable materials,and the as prepared elastomer has broad application prospects in new generation green rubber and flexible wearable devices.（4）A high-performance elastomer was prepared by the simple epoxidation modification of EUG.For the first time,we found that epoxidized EUG（EEUG）with epoxy degree of 12.3～17.4%no longer crystallized at room temperature but had the ability to strain-induced crystallization（SIC）.As a result,its vulcanizates showed excellent tensile strength（17 MPa）,toughness(37.8 MJ m^-3)and elasticity（strain recovery values>97%）without filler reinforcement,which is comparable with vulcanized NR.The SIC of EEUG was studied by synchrotron radiation wide-angle X-ray diffraction（SR-WAXD）,and its performance was also compared with NR under the reinforcement of carbon black.In addition,through cross-linking by disulfide bonds,EEUG could be used to prepare high-performance（tensile strength of 10.5 MPa,toughness of 30.7MJ/m³）,recyclable green elastomers.This new kind of elastomer can be used as the second natural rubber,which is of great significance to solve the problem of insufficient production and difficult recovery of NR.（5）Inspired by the isomerization of unsaturated phospholipids in cell membranes,we report a novel method of preparing stereo-controlled polymer using sustainable EUG as a raw material.Under the catalysis of thiyl radical,EUG with 100%trans-1,4-polyisoprene structure isomerized to cis-configuration partly in a controllable way,thus achieving the rational modulate of thermomechanical properties.The isomerization mechanism was verified by density functional theoretical（DFT）calculation.The isomerized EUG（IEUG）with low cis content（≤8.7%）can serve as plastics or shape memory materials,while high cis content（≥10.7%）IEUG transferred into elastomer materials.Especially for IEUG-10.7%,its vulcanizates without filler reinforcement show high tensile strength（15.5 MPa）and elasticity（97%）comparable to natural rubber due to strain-induced crystallization（SIC）ability,which has the potential to be the second natural rubber.This chapter provides a new strategy for stereo-control of polymer properties,and the prepared materials have broad application prospects in the intelligent sensing and rubber industry.