The Density of Chemical Crosslinks and Chain Entanglements in Unfilled EPDM Vulcanizates as Studied with Low Resolution, Solid State 1H NMR

Abstract

The network density in unfilled EPDM vulcanizates was studied by the following methods: low resolution, proton T2 NMR relaxation, Mooney—Rivlin analysis of stress—strain curves, and equilibrium swelling experiments. For the vulcanizates as such, the NMR method measures the total network density, which is composed of chemical crosslinks (CC) and of temporary (EN/TE) and trapped chain entanglements (EN/TR). The estimated molar mass of EPDM chains between apparent chain entanglements (EN) is 1900 ± 200 g/mol. For partially swollen samples, the NMR method determines the network density composed of CC and EN/TR. The CC density is obtained from the total density of network junctions and the measured entanglement density assuming that CC and chain entanglements are decoupled and additive. The contribution of CC, EN/TE and EN/TR to the total network density is estimated.

Influence of PE/PP ratio and ENB content on the degradation kinetics of γ-irradiated EPDM

“…C. Note that using a different statistical approach, Macosko found in equation 56 of reference [46] a similar expression, except for a difference in the values of the coefficients, which is not coherent with the previous equations of the same paper, and likely due to typing error. D. The M e value chosen in our study is 2400 g/mol, which is the upper bound of all the M e values proposed in the literature [47,48]; it is generally assumed that the critical molecular weight enabling the presence of entanglements is around 2*M e , which is much lower than the initial average molecular weight of our nonirradiated samples (12,000 g/mol for A, and 52,000 g/mol for SC); moreover, our statistical analysis suggests that the highest radiation dose (1000 kGy) generates, in average, about one scission per chain. Thus, whatever the radiation dose, the molecular weight of the chains in the network should enable the formation of entanglements.…”

NMR measurements of gaseous sulfur hexafluoride (SF6) to probe the cross‐linking of EPDM rubber

“…One has to remember, however, that total inaccuracy, originated from experimental error and unavoidable multiparametric fitting procedure uncertainties, is a priori estimated to be 25% for both methods. 5,17 Taking this into account, the matching between cross-linking density values determined by both methods can be considered as adequate. However, to remove the ambiguity of the absolute values of cross-link density more sensitive and reliable methods of its determination are needed.…”

“…18 The T rl 2 value measured below the glass transition point for swollen samples is related to the strength of inter-chain 1 H dipolar coupling in rigid lattice. 19 The T rl 2 value for EPDM swollen with C 2 Cl 4 was measured to be 10.4 š 0.2 µs at 140 K. 17 The detailed description of the procedure as well as its theoretical background can be found in Ref 5.…”

Review of the Reclaiming of Rubber Waste and Recent Work on the Recycling of Ethylene–propylene–diene Rubber Waste

“…[95][96][97][98][99][100] As an illustration, Moldovan et al 99 studied the dynamic heterogeneities of polymer chains for a series of EPDM rubbers with carbon black N683 filler content varying from 20 to 70 parts per hundred rubber by weight (phr). Proton…”