FACTORS INFLUENCING THE MECHANICAL-BEHAVIOR OF RAW UNFILLED NATURAL-RUBBER

The influence of gel and soluble nonrubbers on the relaxation behavior of raw, bale NR (natural rubber) has been studied by testing fractionated and solvent-extracted rubber. The fractionation was carried out by progressive dissolution, each fraction being recovered by evaporation of the solvent. The tests were performed in tension for extensions up to 70%. The experiments have shown that gel and soluble nonrubbers have a marked influence on the relaxation behavior of NR. The gel has a predominantly stiffening effect: it produces a comparatively slight decrease of the rate of relaxation. Whether the gel is present as a macrogel phase or as individual microgel particles appears to be of secondary importance. The soluble nonrubbers, on the other hand, influence mainly the time variation of the relaxation modulus: at longer relaxation times they increase the rate of relaxation quite markedly.