摘要
明确橡胶的流变行为对于理解其链结构和加工行为,以及二者之间的关系至关重要.本文中通过流变学测试手段对比研究了仿生天然橡胶和天然橡胶的生胶的线性黏弹行为和非线性流变行为.相比于商品化合成异戊橡胶,文中的仿生天然橡胶和天然橡胶表现出更为相近的线性黏弹行为,主要表现为近乎相同的平台模量、末端弛豫时间、复数黏度,以及在加工窗口区域相同的剪切黏度对剪切速率的依赖性.非线性松弛行为的结果表明,天然橡胶和仿生天然橡胶的松弛模量对于时间均表现为幂律关系,对时间和应变的依赖具有可分离性,二者的衰减函数对应变的依赖性由于链结构和微观精细结构的不同而存在一定差异.
Abstract
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.
维普
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