Bei Liu,Kai Jin,Jie Tao,Hao Wang,Dan He,Huaguan Li
In this study, we proposed a machine learning (ML) method to optimize the comprehensive performance of shape memory epoxy polymers (SMEPs) based on experimental data as samples. Firstly, a series of SMEPs specimens were prepared, and their properties were evaluated respectively by testing four indexes including the glass transition temperature ( T g ), bending strength, strain fixation rate ( R f ), and strain recovery rate ( R r ). Subsequently, ML used these experimental data as samples for feature learning to investigate the influence of each component on these properties. The results indicated that methyltetrahydrophthalic anhydride was more favorable to T g and bending strength than methylhexahydrophthalic anhydride (MHHPA) as a curing agent. However, a certain amount of MHHPA must be included in the system to guarantee a higher R f and R r . Moreover, the right amount of bisphenol A cyanate ester in the system improved the comprehensive properties of SMEPs, especially the shape memory effect. Finally, a SMEPs system with superior properties was acquired through the optimization of four indexes of T g , bending strength, R f and R r . Therefore, this study shows that ML methods can also be used to investigate SMEPs that require more specific excellent performance.
A novel thermoplastic vulcanizate (TPV) based on poly (vinylidene fluoride)/poly (ethylene–butylacrylate–glycidyl methacrylate) (PVDF/PTW) (30/70 w/w) blends has been fabricated by dynamic vulcanization due to selective cross-linking of PTW by adding small amount of 3-(2-Aminoethylamino) propyldimethoxymethylsilane (KH602). The blends with KH602 had the solid-like behavior at low frequency and enhanced viscosities and dynamic modulus. The TPV exhibited a quasi co-continuous morphology with PVDF dispersed in PTW matrix, which was different from that of PVDF/PTW blend, exhibiting phase-separated morphology with PVDF dispersed in unvulcanized PTW matrix. The resulted TPVs displayed excellent mechanical properties, and excellent strain recovery, which will be a promising coating material, especially wire and cable applications.
A six-coordination stable structure of Ni2+ with two carboxylate ligands and two sulfur atoms in side chains of ethylene-propylene copolymers can be constructed to form 3D physically cross-linked networks according to a density functional theory simulation. The reversibly cross-linked polar ethylene/propylene/5-ethylidene-2-norbornene copolymer elastomers (rcEPDMs) with triple noncovalent cross-linking sites of hydrogen bonds, ionic aggregation, and 6-coordination Ni2+ bonds can be successfully in situ prepared by the reaction of carboxyl functionalized EPDM with NiCl2·6H2O in the presence of tetrabutylammonium hydroxide. The rcEPDM networks with Ni2+ having a coordination number of 6 (rcEPDM-Ni2+) show much higher cross-linking density than their analogues with Zn2+ having a coordination number of 4 (rcEPDM-Zn2+), which is confirmed by swelling experiments and Mooney–Rivlin analysis. The rcEPDM-Ni2+ networks exhibit a much higher tensile strength of 19.0 MPa at an elongation of 587% than rcEPDM-Zn2+ networks (6.8 MPa at 777%). The mechanical properties of rcEPDM-Ni2+ networks containing triple cross-linking sites are superior to those of networks containing hydrogen and coordination bonds as well as those containing ionic aggregation and coordination bonds. The hysteresis energy of rcEPDM-Ni2+ networks increases by 19 times, and the strain recovery reaches 95% when the strain gradually increases from 50% to 400%, which is attributed to the synergy of noncovalent cross-linking sites. The hysteresis energy of rcEPDM-Ni2+ network is 66% higher than that of rcEPDM-Zn2+ networks at 400% strain, due to the formation of a more stable and dense six-coordination structure of rcEPDM-Ni2+ networks. To the best of our knowledge, this is the first example of renewable triple noncovalently cross-linked polar EPDM with high strength and outstanding strain recovery using Ni2+-carboxylate coordination bonds. The renewable cross-linked EPDM elastomers would have potential applications in organic–inorganic composite materials, bonding agents, sealing parts, and reusable elastomers.
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