Pressure-induced rapid solidification of polyphenylene sulfide melt

Abstract

In this work, pressure-induced rapid solidification of polyphenylene sulfide (PPS) melt is studied on a pressure-jump apparatus. Five PPS samples under a pressure of 0.1 GPa are heated to 563 K, 573 K, 583 K, 603 K and 613 K, respectively. These samples are rapidly compressed to 2.4 GPa in about 20 ms. The solidified samples are quenched to room temperature and then depressured to ambient pressure. The X-ray diffraction (XRD) analyses of the recovered samples indicate that three PPS samples, prepared at 563 K, 573 K and 583 K, contain crystal phases but their crystallinity is lower than that of the original PPS powder. The remaining two PPS samples, prepared at 603 K and 613 K, are in amorphous state but do not sharp crystal diffraction peaks in the XRD patterns. Differential scanning calorimetry curves of the five PPS samples each display an endothermic step of glass transition at about 325 K and an exothermic peak of recrystallization around 360 K. The glass transition temperature decreases roughly with the increase of preparation temperature. The thermal enthalpy of recrystallization process increases with the increase of preparation temperature, indicating that the content of amorphous phase increases. We speculate that the recovered samples are in a “frozen state” of their parent liquid. At 563 K, 573 K and 583 K, the crystalline phases partially melt. More crystal phases melt with the increase of preparation temperature. The molten part is rapidly solidified into amorphous phase. At a temperature higher than 603 K, the crystalline phase fully melts, and after being rapidly compressed, amorphous PPS sample is obtained. For the amorphous PPS sample prepared at 613 K, we investigate whether the interior of this amorphous PPS sample is also in amorphous state. Micro XRD analysis indicates that the central part of the PPS sample is also in amorphous state, which suggests that this PPS sample is of a fully amorphous bulk. For the amorphous PPS sample prepared at 613 K, we investigate its recrystallization product. After being annealed at 425 K for 2 h, the amorphous phase, which is solidified from the melt of crystal phase, is recrystallized into the orthorhombic crystal phase. The results in this work indicate that the rapid compression can inhibit the PPS melt from being crystalized, so, it is a way to prepare amorphous PPS bulk. Since the solidification of polymer melt is realized by increasing pressure instead of quenching and is not limited by polymer thermal conductivity, it is a promising way to prepare amorphous polymer bulks with large size.