Ultimate mechanical properties of polyethylene and cellulose fibers: Breaking strength, breaking strain, and modulus

The ultimate mechanical properties, such as breaking strengths, breaking strains, and moduli, of ultra-high molecular weight polyethylene and cellulose fibers have been measured and analyzed using the fusion theory of polymer strength proposed by K. J. Smith. The experimental results strongly support the concept of stress-induced melting while polymer fibers fail. Super strong UHMWPE fibers having breaking strength of 7.2 GPa, modulus of 230 GPa, and strain of 3.4% were obtained. The strengths of cellulose fibers have been greatly improved via the mesophase cellulose/MMNO/H{dollar}sb2{dollar}O with additive NH{dollar}sb4{dollar}Cl system to 1.6 GPa (three times the original cellulose fiber) although they are still far from the theoretical strength (the range of 4.3 to 10 GPa) of cellulose due to difficulties of the technology. The viscoelastic model simulations give a new relationship of breaking strength to breaking strain ({dollar}sigmasp*{dollar} = 0.632E{dollar}varepsilonsp*{dollar}) by extending the principle of fiber fracture to imperfect fibers. The activation energy U{dollar}sb{lcub}rm o{rcub}{dollar} = 108 kJ/mol strongly shows that the major factor of polymer fracture is not the breakage of covalent bond. It is the slippage between macromolecules after the stress-induced melting.