Bond Scission in a Perfect Polyethylene Chain and the Consequences for the Ultimate Strength

Abstract

We present ab initio calculations concerning the bond scission rate in a polyethylene chain. The energy barrier for scission is calculated both by using an effective potential scheme based on ab initio data and from the ab initio transition state itself. In the latter case the prefactor for scission is calculated. In both methods the relaxation of the polymer chain is taken into account, leading to a strong strain dependence of the energy barrier. The two schemes agree quantitatively. The barrier is reduced from 3.9 eV at zero strain to 1.7 eV at a strain of 5%. The calculated scission rate is used to estimate the strength of a polyethylene fiber consisting of perfectly aligned, independent chains in a constant strain rate experiment resulting in 18 GPa at a strain of 8%. This value of the ultimate strength is a factor 2 larger than found in experiments. This contrasts previously reported quantum chemical calculations, which reported values a factor 5-10 larger than the experimental values.

Strong materials – a structural view of material strength down to a molecular scale: Concept of a novel strong and extremely light weight molecular space frame-polymer

“…However, this value does not differ too much from the results of the more advanced modelling by J.C.L. Hageman et al [4], who found a value of about 300GPa at room temperature. The highest experimental value was about 280 GPa at 77K.…”

“…These predict lower values. An example is the model by J. C. L. Hageman et al [4], which predicts an ultimate strength of about 18GPa at room temperature. Ultra drawn polyethylene fibres are indeed very strong.…”

Predicting experimental results for polyethylene by computer simulation

“…In addition, many commercial and open-source computational codes are available for QM and DFT calculations [394,395]. Some of the applications of firstprinciple methods, mainly DFT, to PE models are conformational and mechanical properties of single chain models [240,245,246,248,[396][397][398][399][400][401][402][403][404][405][406][407][408], equilibrium unit cell, [239, 245-249, 396, 409], electronic properties [238,401,402,407,[409][410][411][412][413][414][415][416][417], infrared and/or Raman spectra of the crystal state [243,246,263,415,418], inelastic neutron scattering spectra [245,419], and Shock Hugoniot studies of PE crystals (studies of the material's behaviour under extreme conditions) [420,421].…”

A molecular model for the electrical aging of XLPE

“…Zhurkov and co-workers [9] have proposed long ago that mechanical breakdown was a kinetic bond scission process and in support of their affirmation they detected free radicals during the aging and breakdown processes. Assuming that strained bonds might relax during deformation, results in a C-C bonds strength value reduced to 30-40% of its original value [10].…”