摘要
Rubber of high molar mass, like cis-polybutadiene, shows's stress peak on the engineering stress-strain curve during stretching at room temperature. In this work cis-polybutadiene samples were swollen in a poor solvent, CHCl3/EtOH (1/1 v/v), for different times. It was found that both the initial modulus and the stress peak on stretching decreased in magnitude with increasing swelling time and the peak disappeared entirely after 1 hour of swelling. On further swelling the initial modulus increased somewhat and a small stress peak re-appeared after swelling for 2 h. The disappearance of the stress peak after swelling is interpreted as the result of disruption of cohesional entanglements present in the initial rubber sample. The re-appearance of a small stress peak and the increase of modulus on further swelling are interpreted as being of the same nature as the phenomenon of anti-plasticization. It is the result of forming some new cohesional entanglements of larger binding energies through longer range chain segmental motions excited after the disruption of the previously existing cohesional entanglements in the rubber. Thus an understanding of the stress peak on stretching a high molar mass rubber and the phenomenon of anti-plasticization on molecular level has been put forward.
Rubber of high molar mass, like cis-polybutadiene, shows's stress peak on the engineering stress-strain curve during stretching at room temperature. In this work cis-polybutadiene samples were swollen in a poor solvent, CHCl3/EtOH (1/1 v/v), for different times. It was found that both the initial modulus and the stress peak on stretching decreased in magnitude with increasing swelling time and the peak disappeared entirely after 1 hour of swelling. On further swelling the initial modulus increased somewhat and a small stress peak re-appeared after swelling for 2 h. The disappearance of the stress peak after swelling is interpreted as the result of disruption of cohesional entanglements present in the initial rubber sample. The re-appearance of a small stress peak and the increase of modulus on further swelling are interpreted as being of the same nature as the phenomenon of anti-plasticization. It is the result of forming some new cohesional entanglements of larger binding energies through longer range chain segmental motions excited after the disruption of the previously existing cohesional entanglements in the rubber. Thus an understanding of the stress peak on stretching a high molar mass rubber and the phenomenon of anti-plasticization on molecular level has been put forward.
