Effect of chemical and physical crosslinks on strength of rubber and plastics-a theoretical approach

For rupture of rubber and plastics, three types are proposed: (a) elastic, (b) plastic, and (c) brittle. For (a) the rupture takes place at the ultimate elongation of chains between crosslinks. Strength f is proportional to the number of crosslinks and also the fraction of effective chains giving the optimum degree of vulcanization ν. Both ν and f at the maximum strength decrease with increasing the bond energy D of crosslinks. The rupture in (b) occurs for filled rubbers. The maximum reinforcement with filler is expected to be attained at 20% volume fraction of filler from the pseudo‐link model in which the number of links are proportional to the specific surface area, the fraction, and the adsorption ability of the filler particles. For (c) the craze occurs due to the breakdown of pseudo‐crosslinks of the smallest size b, and b is 2 at the glass transition temperature. Impact strength is improved by the dispersion of rubber particles at the optimum fraction of 13% and under the small distance of neighboring particles, which is 0.4 μm and is corresponding to the relaxation distance. © 1994 Wiley & Sons, Inc.