The Temperature Shift of the Second Order Transition of Natural Rubber by Crosslinking

Abstract

The present article reports on dynamic mechanical and infrared spectroscopic tests of natural rubber crosslinked by sulfur, peroxide or high energy radiation. The effect of these vulcanization methods upon the rate of crosslinking, the position of the second order transition temperature and the double bond structure is discussed. Whereas the temperature displacement of the transition range from the second order transition phase to the rubber elastic state during crosslinking by high energy radiation or by peroxide arises from the increasing hindrance of chain movement by the crosslinks, the intramolecular addition of sulfur predominantly is responsible for the much greater temperature displacement—related to the same crosslink density—during sulfur vulcanization. The change of the double bonds which proceeds in the sulfur vulcanization at a much faster rate than in the crosslinking by irradiation also can be considered as indication of intramolecular rings being formed along the chain during sulfur vulcanization. Vulcanization by sulfur and crosslinking by irradiation appear, principally, to be based on the same mechanism. The influence of oxidation on the mechanical properties of the vulcanizates is studied in natural rubber irradiated in an oxygen atmosphere. The two damping maxima observed at the dynamic mechanical test can be ascribed, with the aid of infrared spectroscopy, to the influence of crosslinks and oxidation products on the chain mobility.

Phase behavior and some calorimetric and physical properties of diurethanes from perfluoropolyether macromonomers

“…39 Some theoretical treatments on the dependence of T g on crosslinking degree are found in the literature 40 -42 ; all are of the form: (10) where M c and n c are the molecular weight and the number of chain atoms of the segment between two crosslinks, respectively, and the constants K and KЈ depend on the theoretical approach. Nielsen 39 analyzed the literature data and determined an average value of K Х 3.9 10 4 , while Heinze et al 43 reported KЈ ϭ 788. The regression analysis carried out on our T g data measured after cooling at Ϫ5°C/min (ZDOLU-2 was considered to be practically a two-phase system) gives K ϭ 2.74 10 4 and KЈ ϭ 752, which compares favorably with the datum of Heinze.…”

Molecular Structure and Cohesive Properties of Polymeric Adhesives.

“…When exposed to moisture the latter is disturbed by the inter- This equation in terms of compliance can be written as , Finally , Figure A.ll depicts the retardation spectra for the wet and dry sample at 43 .7°c. The function (L) was calculated using a computer program ( 65 ) based on Schwarzl and Staverman 's (66) second order apprac imation. The shape of the curve presented in the graph is such that when it is used to back calculate S the reduced creep compliance function 3(t) , it gives da ta which are wi thi n e xperimental error .…”

Dynamic shear compliance of polymer melts and networks in dependence on crosslinking density

“…(16) and (17) For some polymers (polyisoprene and polysiloxane), the viscosity of molten fractions below M c follows 1/o -M. This is the consequence, via Eq. (16) and (17) For some polymers (polyisoprene and polysiloxane), the viscosity of molten fractions below M c follows 1/o -M. This is the consequence, via Eq.…”

“…cs/c~ with e ~ Q~, (2ye -1) taken at To = 273 K (by a least-square fit to the activation curve), r = 2 " 10 -4 K -1 being the expansion coefficient of the glass, and ~ ~ 0.6 signifying the intermolecular part of Qx, which may depend on T similar to cs. Further experiments on sulfur-crosslinked IR are expected to show Tg -Pc [16] and will shed new light on the strong Tg-shift in the case of sulfur vulcanization. free energy of formation es of the segment dislocation.…”