title: Enhanced nucleation rate of polylactide in composites assisted by surface acid oxidized carbon nanotubes of different aspect ratios.
abstract: Biodegradable polylactide (PLA) composites added with acid oxidized multiwalled carbon nanotubes (A-MWCNTs) of two different aspect ratios (length to diameter) were prepared by coagulation. The aspect ratios and surface structures of A-MWCNTs were characterized by TGA, Raman, and SEM measurements. The percolation thresholds for gelation in the PLA composites with A-MWCNTs of large and small aspect ratios are 2.5 and 4.0 wt %, respectively, which were determined by a rheological method, and in turn, the rheological result confirms the aspect ratio differences for the added two types of A-MWCNTs in the composites. Isothermal crystallization kinetics of neat PLA and its composites were further investigated by using polarized optical microscope (POM) and differential scanning calorimetry (DSC) to clarify the effects of A-MWCNTs of different aspect ratios and concentrations. The different aspect ratio A-MWCNTs with the same carboxyl group mass percent show substantial effects on PLA crystallization kinetics. Those with smaller aspect ratios enhance nucleation rate for PLA spherulites much more than those with larger aspect ratios. This phenomenon can be attributed to fewer sidewall carboxyl groups on the surfaces of A-MWCNTs with smaller aspect ratios, which provides more nucleation sites for PLA crystallization than those with larger aspect ratios at the same concentration, resulting in faster PLA nucleation rates for the former one.
authors.affiliation: CAS Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui Province 230026, P. R. China.
authors.forename: Zhaohua
authors.initials: Z
authors.lastname: Xu
authors.forename: Yanhua
authors.initials: Y
authors.lastname: Niu
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Wang
authors.forename: Heng
authors.initials: H
authors.lastname: Li
authors.forename: Liang
authors.initials: L
authors.lastname: Yang
authors.forename: Jie
authors.initials: J
authors.lastname: Qiu
authors.forename: Howard
authors.initials: H
authors.lastname: Wang
mesh_terms: D002152:Calorimetry, Differential Scanning; D003460:Crystallization; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000648:ultrastructure; D010084:Oxidation-Reduction; D011091:Polyesters / Q000737:chemistry*; D013059:Spectrum Analysis, Raman; D013499:Surface Properties; D013818:Thermogravimetry
chemical_list: D037742:Nanotubes, Carbon; D011091:Polyesters; C033616:poly(lactide)