Ductile‐to‐brittle transition behavior of low molecular weight polycarbonate under carbon dioxide

Abstract

We investigated the stress-strain behavior of low molecular weight polycarbonate for optical disc grade (OD-PC) under carbon dioxide (CO 2 ) at various pressures, and compared the results with that under ambient pressure at various temperatures. Elongation at break decreased sharply with increased CO 2 pressure at around 2 MPa, while the elastic modulus decreased gradually up to 6 MPa. These results indicate that the tensile property changed from ductile to brittle with increased CO 2 pressure, although the molecular motion is accelerated due to the plasticization effect of CO 2 . Such ductile-to-brittle transition is similar to that observed under elevated temperatures caused by chain disentanglement due to accelerated molecular motion. Although the changes of tensile properties were similar, the craze structure obtained by the brittle behavior was different, i.e., a filamented-craze structure was obtained under high-pressure CO 2 , while a lace-like one was obtained under elevated temperatures. POLYM. ENG. SCI., 58:683-690, 2018.

Evolution of Filament-Shaped Porous Structure in Polycarbonate by Stretching under Carbon Dioxide

“…In situ observation of the structural change of the film specimens during the stretching under compressed CO 2 was performed using a specially designed stretching instrument with a stainless steel pressure vessel (Figure 1), as mentioned in the details of our previous papers [20,21]. The structure was observed under a high-fidelity digital microscope (MX-5030SZII, and KH-1300, Hirox Co., Ltd., Tokyo, Japan) equipped above a pressure vessel through a sapphire window.…”

“…Next, the specimen was stretched at a stretching speed of 0.05 s −1 under CO 2 . It was noted that the tensile properties of the OD-PC films did not change by absorbing CO 2 for longer than 1 h, so 1 h was sufficient for absorbing the CO 2 in the specimen [21]. In situ observation under CO 2 was carried out at a stretching speed of 8.33 × 10 −2 s −1 where the porous structure obtained was almost the same as that obtained by stretching at a stretching speed of 0.05 s −1 , to obtain the structure image during the measurement of the stress–strain behavior at small strain.…”

“…Our recent study on the stress–strain behavior of poly(methyl methacrylate) under compressed CO 2 revealed that molecular orientation was enhanced and the elongation at break increased with the increased pressure of CO 2 due to the plasticization effect when the amount of gas absorbed into the polymers was large at high CO 2 pressure [20]. On the other hand, the elongation at break was found to be decreased with increased pressure of CO 2 in low molecular weight polycarbonate for optical disc grade (OD-PC) [21]. In addition to the plasticization effect, compressed CO 2 caused the hydrostatic pressure effect, which is the resistance to deformation caused by the vitrification resulting from the reduction of free volume.…”

“…In crystalline polymers, voids are formed in the intercrystalline amorphous region by stretching [46] and the void formation is enhanced by stretching under CO 2 [10,47]. On the other hand, in amorphous polymers, we found that a filament-shaped porous structure with periodic distance was obtained macroscopically throughout the whole specimen in OD-PC by stretching under compressed CO 2 [21]. Such a filament-shaped porous structure was not obtained by conventional stretching under air at atmospheric pressure, but by a specially designed continuous three-point bending method [48,49,50].…”

Structural Evolution of Two-Phase Blends of Polycarbonate and PMMA by Simultaneous Biaxial Stretching

“…On the other hand, poly(methyl methacrylate) (PMMA) has poor toughness, but exhibits high scratch-resistance due to high surface hardness; its pencil hardness is 4H. The tensile property of glassy PMMA changes from brittle to ductile with increasing temperature [41], while that of glassy PC changes from ductile to brittle when the molecular weight is low [42,43]. Fracture toughness of PMMA and PC abruptly increases at very high loading rates [44].…”