Tensile and Swelling Behaviors

The strain-stress measurements were carried out at room temperature on strips of 50 x 5 x 0.3 mm3 between two clamps by means of a sequence of increasing weights attached to the lower clamp. The distance between two marks on the sample was measured with a cathetometer after allowing sufficient time (10 min after adding a weight) for equilibration. 

The stress-strain curve for unfilled NR exhibits a large increase in stress at higher deformations. NR displays, due to its uniform microstructure, a very unique important characteristic, that is, the ability to crystallise under strain, a phenomenon known as strain-induced crystallization. This phenomenon is responsible for the large and abrupt increase in the reduced stress observed at higher deformation corresponding, in fact, to a self-toughening of the elastomer because the crystallites act as additional cross-links in the network. This process can be better visualized by using a Mooney-Rivlin representation, based on the so-called Mooney-Rivlin equation  

To interpret the variation of stiffness of the polymeric composites with the MWNTs amount, the 100% modulus results are fitted to 

The Halpin-Tsai model (64) yields, for aligned fibre composites and in conditions where the modulus of the fiber, E(, is much higher than that of the unfilled matrix (as in elastomeric composites)  

The degree of adhesion between polymer chains and filler particles can be evaluated from equilibrium swelling of the composites 

---

Swollen tensile and compression techniques avoid both of these problems since equilibrium swelling is not required, and the method is based on interfacial bond release and plasticization rather than solution thermodynamics. The technique relies upon the approach to ideal rubberlike behavior which results when lightly crosslinked polymers are swelled. At small to moderate elongations, the stress-strain properties of rubbers... 

Cyclic behavior in fiber composite plastics is determined by tensile/compressive-swell or by cyclic flexural tests. While normal stress or also deformation can be kept constant for tensile/compressive swell tests, in cyclic flexural tests a flexural strain is typically set and the damage state defined by a certain stress reduction. 

The two network precursors and solvent (if present) were combined with 20 ppm catalyst and reacted under argon at 75°C to produce the desired networks. The sol fractions, ws, and equilibrium swelling ratio In benzene, V2m, of these networks were determined according to established procedures ( 1, 4. Equilibrium tensile stress-strain Isotherms were obtained at 25 C on dumbbell shaped specimens according to procedures described elsewhere (1, 4). The data were well correlated by linear regression to the empirical Mooney-Rivlin (6 ) relationship. The tensile behavior of the networks formed In solution was measured both on networks with the solvent present and on networks from which the oligomeric PEMS had been extracted. 

There have been continuing works by Suto et al. [213-217] on the preparation of cholesteric solid films of hydroxypropyl cellulose (HPC) crosslinked preferably with glutaraldehyde. Coloring conditions [213,217], swelling [215, 216], and tensile-creep behavior [214] of the crosslinked HPC films were examined. Also, the permselectivity of O2/N2 gasses for such liquid-crystalline cellulosic films was reported to become greater than that for the corresponding amorphous ones [218]. 

---