| With the release of the "National Fitness Program(2021-2025)" and the successful holding of the Beijing 2022 Winter Olympics,people’s enthusiasm for participating in sports is gradually increasing,but the probability of sports injuries is increasing as well.Choosing and using appropriate sports protective gear(SPG)is an effective measure to avoid injuries during sports.Traditional SPG may not be fully suitable for all users due to the invariability of shape,thereby,the flexibility of people’s movement and the protective performance of the protective gear are reduced.As a unique natural polymer material in China,Eucommia Ulmoides Gum(EUG)has a unique "rubber and plastic duality",which can be processed and modified into hard plastic or soft rubber according to the needs of users.Meanwhile,due to its good shape memory properties,it can be shaped into an ideal shape according to different requirements,so EUG is a potential excellent material for the preparation of personalized SPG.In this paper,the hardness of EUG is increased by chemical modification and blending with plastic powder to achieve a better protective effect.Meanwhile,the hardness of EUG is reduced by vulcanization cross-linking and physical or chemical foaming processes,so that it can be used in protective with soft lining,this is of great significance for expanding the application field of EUG and preparing personalized EUG for SPG.The research on this paper is divided into three parts:The first part is the study on the hardening of EUG.The hardness of EUG is increased by chemical modification of unsaturated carboxylate and physical blending of micro-nano powder plastics.The effects of different types and dosages of unsaturated carboxylates and powder plastics on the hardness,mechanical properties,shape memory properties and impact protection properties of EUG were investigated.In terms of chemical modification hardening,it is determined that the in-situ reaction of acrylic acid and zinc oxide to produce zinc acrylate hardening EUG is better than the direct use of commercial unsaturated carboxylates,with the degree of in-situ reaction increasing,the hardness and yield strength of EUG are obviously improved,the rigidity is increased,the resistance of the material to external deformation is enhanced,and the protective performance is better.When the ratio of acrylic acid and zinc oxide is 30/30,the Shore D hardness of EUG is 48 degrees,which is 14% higher than that of unhardened EUG.In terms of physical blending hardening,it is determined that the addition of micro-nano polypropylene(PP)powder can effectively harden the EUG.With the increase of the amount of PP powder added,the hardness of the EUG is obviously increased,and the resistance of the material to deformation is enhanced.When60 phr PP powder is added,the Shore D hardness of EUG is 53 degrees,which was 26% higher than that of unhardened EUG.In addition,these two hardening methods can also improve the shape memory properties of EUG,regulate the hardening time and shorten the time for EUG to return from the temporary shape to the original state.It broadens the design space of personalized EUG shape memory protective gear.The second part is the research on the softening of EUG.By adjusting the crosslinking density,adding physical microsphere foaming agent(Expancel920DU40)or chemical foaming agent(SA5000D),the hardness of EUG is greatly reduced.The results show that the more the amount of foamed microspheres,the lower the hardness of EUG,the greater the deformation,and the smaller the penetration force of the material when it is impacted by the outside force.By adjusting the amount of foaming agent,a lightweight and high-toughness foamed EUG with a foaming ratio of 1-5 times can be obtained.When 30 phr microspheres are added,the Shore A hardness of the material is only 73 degrees,which is far lower than the pure EUG,and the material can reduce the external impact force by 83.2%;When the amount of sulfur is 1.5phr,both excellent foaming effect and better mechanical properties can be achieved.The EUG foaming material with higher foaming degree(2-11times)and lower hardness can be obtained by chemical foaming method.When 25 phr foaming agent and 1.5phr S are added,the Shore A hardness of foaming Eucommia gum is 37 degrees.and the material cells are very uniform and have a good appearance.When the amount of foaming agent is 15 phr,the Shore A hardness of the material is 55 degrees,and the material can reduce the external impact force by 89.5% at most.The third part is the design and preparation of soft-hard gradient composites for sports.The harder EUG can block the external impact process,but the wearing feeling is poor;while the softer foamed EUG can absorb more external impact energy,but its own strength is poor,and it is easy to be deformed and damaged by external force;whether softened,hardened EUG also cannot be used alone in the preparation of protective gear products.Therefore,in this paper,hardened EUG,natural rubber and foamed EUG will be prepared into a hardness gradient composite material with shape memory function through an integrated co-vulcanization process,which will be applied to the preparation of personalized sports protective gear for different human organs and shapes.According to the SEM observation and 180° peel test results,the hardness gradient composites prepared by the co-vulcanization process of three different hardness rubbers material have good bonding effect.The mechanical impact test of the material shows that the composite material per unit thickness can reduce the external impact force by 11.6%.Compared with the two commercial shin guard products on the market,the soft-hard gradient composite material has the highest reduction of external impact force per unit thickness,showing excellent impact protection effect. |
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