Structural variation of melt-crystallized PTT during the heating process revealed by FTIR and SAXS

Abstract

Time-resolved FTIR, WAXD/SAXS and DSC have been used to investigate the structural variation of non-isothermally crystallized poly(trimethylene terephthalate) (PTT) during the heating process. The three-phase model: the lamellar phase, the mobile amorphous phase (MAP) and the rigid amorphous phase (RAP) between lamellae is suggested to describe the structure of meltcrystallized PTT. According to FTIR results, the conformation of RAP in the constrained state is different from that of MAP. The increased content of amorphous phase in the temperature range from 120 to 192°C is ascribed to the relaxation of RAP, rather than the melting of defective crystals. When the PTT is heated to a temperature above 192°C, the recrystallization/crystal perfection of original defective lamellae occurs without a pre-melting process, which leads to an increase in lamellar thickness and probably connects two adjacent lamellar stacks. This is responsible for an increase in crystallinity as well as a higher major melting temperature. poly(trimethylene terephthalate), relaxation of rigid amorphous phase, recrystallization Citation:Chen Z, Yan S K. Structural variation of melt-crystallized PTT during the heating process revealed by FTIR and SAXS. Chin Sci Bull, 2013, 58: 328335, doi: 10.1007/s11434-012-5589-x Among the family of aromatic polyester, poly(trimethylene terephthalate) (PTT) has been attracting much attention owing to its excellent resilience [1][2][3] and processing characteristics in comparison with poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT). Morphology and thermal behavior of a crystalline PTT are usually very complicated and only one crystal modification with a triclinic unit cell has been identified so far [4,5]. It has been reported that the multiple melting behaviors of PTT vary with their preparation conditions revealed by differential scanning calorimetry (DSC) [6][7][8][9]. The multiple melting peaks are mainly explained by (i) the melting of crystalline entities with different stability and/or (ii) the meltingrecrystallization-remelting of the imperfect crystals. However, for the PTT sample prepared by cooling from melt to room temperature at a rate of 10°C/min, there is little evidence to support the mechanism of melting of crystalline entities with different stability. An ordered exothermal peak between the minor endothermic peak and the major melting peak has been revealed by Pyda et al. [10] during the heating process of PTT with high crystallinity. This report seems to support the melting-recrystallization-remelting mechanism. However, it should be noticed that the structural perfection of polymer crystals depends strongly on the crystallization process. It is well documented that the structure of cold crystallized polymer crystals is generally less perfect compared to those melt-crystallized at relatively higher temperature. Taking this into account, it is easier for the melting-recrystallization-remelting to take place than the melt-crystallized samples. It should be poi...

Comparative study on the properties of poly(trimethylene terephthalate) -based nanocomposites containing multi-walled carbon (MWCNT) and tungsten disulfide (INT-WS2) nanotubes

“…While, WAXS diffractograms of semicrystalline PTT‐based nanocomposites (Fig. b) show characteristic diffraction peaks of PTT and INT‐WS 2 demonstrating that the nanofillers do not influence the crystal structure of PTT. Similar observations were made for nanocomposites based on different polymer matrices with MWCNT and INT‐WS 2 …”

Effect of heat treatment with alternating tension on microstructure and elastic recovery of poly(trimethylene terephthalate) fibers

“…Generally, common PTT has only one crystal structure, so it should be only one melting peak. The multiple melting peaks can be mainly ascribed to the melting of crystalline entities with different stabilities and/or the melting recrystallization‐remelting of the imperfect crystals 21–24 . Alternating actions of heat and tension by AlterTR heat treatment may lead to more crystal growth modes, which may be the main reason for the multiple melting peaks.…”