The effects of intracrystalline chain diffusion on the non-linear mechanics of semicrystalline polymers

Large deformability is a specific property of many semicrystalline polymers that is enabled by plastic flow going along with a restructuring of the semicrystalline morphology in combination with strain hardening caused by network forces. This ability has been linked with the intracrystalline chain diffusion (ICD), which allows chains to move within the crystals. However, the influence of ICD on the non-linear mechanics remains unclear. We here study the intrinsic non-linear mechanical properties of two model polymers, namely PEO with fast ICD and PCL without ICD by mechanical testing in plane strain compression in dependence of strain rates and temperature. For both polymers the stress could be decomposed in an elastoplastic contribution and a network contribution. Strong differences in the true stress-true strain curves became evident by comparing the rate dependence at larger deformation. The stress in PEO depends strongly on rate and temperature, indicating relaxation of the network contribution, while the stress in PCL is rate independent. Experiments for PEO with different molecular weights indicate that the relaxation affects entire chains as expected for ICD.