Role of Strain Crystallization in the Fatigue Resistance of Double Network Elastomers

Abstract

Double networks were prepared from guayule rubber (GR), deproteinized natural rubber (DPNR), and styrenebutadiene rubber (SBR), and their properties compared to conventional "single networks" having the same crosslink density. Substantial residual strains (> 150%) were obtained in all double networks, whereby the modulus parallel to the residual strain was enhanced. For the two strain-crystallizing elastomers, the fatigue resistance of the double networks (for extensions parallel to the residual strain) was higher than for their single network counterparts. Moreover, the guayule rubber, which is more strain-crystallizable than DPNR, exhibited the greater enhancement. For the amorphous SBR, on the other hand, the network structure had an insignificant effect on the fatigue life. These results demonstrate that longer mechanical fatigue lifetimes in double network rubbers are a consequence of their intrinsic orientation. This provides the capacity to retain crystallinity at the front of growing cracks, even in the absence of stress. The origin of the improved fatigue resistance is similar to the mechanism responsible for the better performance of strain-crystallizing rubbers subjected to non-relaxing cyclic deformations.

Viscoelastic Behavior of Rubbery Materials

“…Given their higher modulus, this means that double networks can be used to circumvent the usual compromise between stiffness and strength. Moreover, double networks of strain-crystallizing rubbers having substantially larger fatigue lifetimes (Figure 19 [129,137]). This appears to result from retention of crystallinity through the minimum of the strain cycle [137], analogous to the greater fatigue life of crystallizing rubbers subjected to non-relaxing strain cycles [138].…”

Characteristics of mechanical properties of sulphur cross-linked guayule and dandelion natural rubbers

“…4,5,[18][19][20] Guayule (Parthenium argentatum) and rubber dandelion (Taraxacum kok-saghyz, also known as rubber root, Russian dandelion, Kazak dandelion, Buckeye Gold, TKS and TK) have long been known to produce NR, and are the most promising species for the next-generation of NR sources. [21][22][23][24][25][26][27] Up to now, studies have focused on mechanical properties, such as tensile properties, [28][29][30][31] tear strength, 30 hardness, 30 fatigue life, 32,33 dynamic mechanical properties, 34 compression set 35 and rebound properties 30 of cross-linked and uncross-linked guayule NR compared to various kinds of rubber in both lled and unlled systems. Recently, uncross-linked guayule NR, and guayule NR from which the rubber particle membranes were stripped before rubber solidication, showed similar glass transition temperatures (T g ) to uncross-linked Hevea NR.…”

The Payne Effect in Double Network Elastomers

“…For strain-crystallizing rubbers, the benefits are even greater, since substantial improvements in crack-growth and fatigue performance can be realized. [7][8][9][10] Double networks exhibit anisotropic properties, [7][8][9]11,12 and are usually characterized in terms of their residual stretch ratio, λ R , equal to the ratio of their length along the stretch direction of the second cure to the initial length (prior to the second curing, or equivalently, in the uncured state). However, λ R does not uniquely define a double network, as different cure strains and crosslink apportionment between the two networks can yield the same residual strain, but different mechanical properties.…”