Healing of Voids in Crazed Polymers and Their Growths of Craze Phases

<p>The craze has porous structure consisting of fibrils（ fiber bundles） and voids（ pores） with a diameter of several tens of nanometers. Craze differs from crack. In previous work, to control craze formation, we have succeeded that crazing film consists of repeated porous phase and non-porous phase. This porous phase has specific properties. For craze, the temperature required to begin void disappearance was lower than the melting point. There are many reports that estimate this phenomenon due to the melting of polymers or contribution of internal residual stress. On the other hand, the behavior is different from an ordinary thermal relaxation phenomenon. Therefore, in this paper, the phenomenon that void in craze is scale downed and disappear, is defined as“ healing”. It is thought that generation and progression of the healing is caused by interfacial free energy as a driving force. In this study, we reported the balance between“ Laplace-pressure” which is a self-shrinking force acting on void in craze and the widening force such as an external tensile load. From the stress-strain curve, a bending point was confirmed only the crazed film separately from the yield point. The stress at the bending point decreased with an increase in specimen sample temperature. On the other hand, the temperature dependency of strain had not been observed. Based on the above result, it was shown that the appearance of the bending point was a characteristic behavior derived from their voids. In addition, it was revealed that an inflection point in the S-S curve was determined in response to the balance between the void property in craze and an original mechanical strength of raw polymer as used.</p>