Proteins and phospholipids play crucial roles in the physical properties of natural rubber(NR),including ultra-high tensile strength,stress at 300％elongation,and excellent elasticity.Accordingly,a biomimetic rubber(BMR)was synthesized by grafting some proteins/phospholipids into poly(cis-1,4-isoprene)(PI)chain ends,endowing it with high mechanical performances that are identical to NR.It is of great importance to understand the chain structure and processing behavior of rubber materials,and their relationship.In this work,BMRs with～0.5％and～2.0％proteins grafting into PI chain ends were synthesized,and the linear viscoelasticity(LVE)and nonlinear rheological behavior of these BMRs were studied,comparison with that of a high-grade NR and a commercial IR.For the BMR sample with～2.0％proteins(which is named BMR-H),its plateau modulus is nearly the same as that of NR,and the chain relaxation time is much larger than that of the IR sample.Moreover,the viscoelastic behavior of both BMR and NR deviate from Williams-Landel-Ferry(WLF)-like at temperatures above 30 ℃,indicating that the associations/disassociation of the physical cross-links from proteins affect and finally predominate chain relaxation behavior.The shear modulus G(t,y)of the samples all exhibit separable time-and strain-dependent.Damping function,h(y)=G(t,y)/G(t,y)was reviewed,and all the h(y)of the samples deviate from Doi-Edwards'prediction,showing a weak type-B relaxation behavior.The weaker damping indicates that the degree of disassociation is lower than that of the prediction of Doi-Edwards model,and it is probably to be related to long-chain branched structure in the samples.This work shows that BMR is a more effective approach to preparing rubbers that possess identical high performance to NR by incorporating proteins and phospholipids into PI chain ends.
Biomimetic rubberNatural rubberLinear viscoelasticityDamping function
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