Material BehaviourCrystallization behavior of poly(trimethylene terephthalate)-poly(ethylene glycol) segmented copolyesters/multi-walled carbon nanotube nanocomposites
Introduction
Poly(trimethylene terephthalate) (PTT) is a newly commercialized aromatic polyester, which has a combination of the excellent properties of poly(ethylene terephthalate) (PET) and the processing characteristics of poly(butylene terephthalate) (PBT). It has recently become one of the most important polyesters for fibers and thermoplastics [1], [2], [3], [4], [5]. To improve the properties of polyester material, copolymerization using various amounts of a second glycol or diacid comonomer is an effective approach to attain new linear thermoplastic polyesters with modified properties. Recently, the authors reported investigations of the composition dependence of thermal properties of poly(trimethylene-co-ethylene terephthalate) and poly (trimethylene isophthalate-co-terephthalate) [6], [7]. Poly(trimethylene terephthalate)-poly(ethylene glycol) (PEG) segmented copolyesters (PTEG) were also presented in which PTT was used as the rigid segment in multiblock copoly(ether-ester)s, while PEG was used as the flexible segment [8].
As a typical semicrystalline polymer, the applicability and processing condition of PTEG are determined by its crystallization behavior. However, we have found that this potential biodegradable polyester has limited improvements in crystallization and, when the PEG content in the copolyesters is higher than 5 wt%, the crystallization rate is lower than that of neat PTT. In the present work, we attempt to improve the crystallization ability of PTEG copolyesters by incorporating carbon nanotubes (CNTs) into the matrix to fabricate composites.
On the basis of the remarkable mechanical and electrical properties of CNTs, polymer composites reinforced by CNTs have been extensively researched [9], [10], [11], [12]. However, to date, very few reports [13], [14] have appeared for polymer crystallization promoted by CNTs and these mainly involve single-walled carbon nanotube (SWCNT) filled isotactic polypropylene (iPP) due to various crystal modifications and potential industrial applications of iPP. For instance, Bhattacharyya et al. [13] reported that purified SWCNTs exhibited poor dispersion when melt blended with PP. SWCNTs, even with poor dispersion, can act as nucleating agents for PP crystallization. In this study, nanocomposites comprising PTEG copolyesters and MWCNTs, in which the nanotube consists of several layers of coaxial carbon tubes [15], [16], [17], have been fabricated and the influence of MWCNTs on PTEG crystallization is presented.
Section snippets
Materials and fabrication of composites
PTEG copolyesters and neat PTT used in this study were made by esterification and subsequent polycondensation and are the same polymers that have been described in two of our previous articles [8], [18], respectively. The molecular characteristics of these polymers are listed in Table 1 (Table 1 is abstracted from the tables of Refs. [8], [18]). In this study, the PEG used for polymerization into PTT was PEG2000, i.e. it has a number-average molecular weight of about 2000. MWCNTs were purchased
Dynamic crystallization from melt
Fig. 1 shows DSC cooling thermograms of polyesters and the nanocomposites from the melt after keeping them at 530 K for 3 min to erase their thermal history. It can be seen that neat PTEG97.39/2.61 has a dynamic crystallization peak (Tmc) (459.5 K) higher than that of neat PTT (455.3 K), indicating that a small amount of PEG incorporating into the PTT can prompt its crystallization. As for neat PTEG72.22/27.78, it has a lower Tmc (453.2 K) compared with neat PTT and this may be attributed to
Conclusions
Nanocomposites based on poly(trimethylene terephthalate)-poly(ethylene glycol) (PEG) segmented copolyesters (PTEG) and multi-walled carbon nanotubes (MWCNTs) have been fabricated and the dynamic and isothermal crystallization behavior of the nanocomposites was investigated by DSC and DLI technique, respectively. The secondary crystallization process of the nanocomposites crystallization has been found to be much more important than that of the neat PTEG copolyester crystallization and the
Acknowledgments
The work was supported by a grant (Economic Production of Carbon Nanotubes) of The Hong Kong Polytechnic University, a grant from Ph.D. Programs Foundation of Ministry of Education of China (No. 200802881030) and a grant from the Advanced Research and Development Program of NJUST (No. XKF07011).
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