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Wang Y.,Yangzhou University | Cheng Y.,Yangzhou University | Chen J.,Yangzhou University | Chen J.,Provincial Key Laboratories of Environmental Engineering and Materials | And 6 more authors.
Polymer (United Kingdom) | Year: 2015

The polylactide (PLA) composites with various layered graphite particles were prepared by the approach of solution mixing for the viscoelasticity study. Four kinds of particles with various layered structures, including natural graphite flakes, and graphite nanosheets with the thickness of ∼25 nm and ∼5 nm, as well as graphene were used as the filler, aiming at establishing the relationship between viscoelasticity of composites and filler structure and networks. The results reveal that transient rheological response of PLA composites shows evident sheet thickness dependence, and the stress overshoot behavior is closely related to the percolation network density during startup and reverse flow. But the strain-scaling characteristic of overshoots is independent of thickness of nanosheets and their networks. The linear dynamic rheology (molten state) and creep measurements (solid state) as well as thermal analyses were then performed to further explore the difference in dispersion and distribution among those layered graphite fillers. © 2015 Elsevier Inc. All rights reserved.

Wu D.,Yangzhou University | Wu D.,Provincial Key Laboratories of Environmental Engineering and Materials | Cheng Y.,Yangzhou University | Feng S.,Yangzhou University | And 3 more authors.
Industrial and Engineering Chemistry Research | Year: 2013

Polylactide (PLA) composites containing graphene nanosheets were prepared by the approach of solution mixing for a crystallization study. The results revealed that the graphene nanosheets are well distributed in the PLA matrix, leading to an evident viscosity increase despite their dispersion as multilayered structures in stack form. Both the cold and melt crystallization behaviors of PLA were found to depend strongly on the presence of the graphene nanosheets. During cold crystallization, the graphene nanosheets merely act as an inert filler, and the increased viscosity results in a decrease of the overall crystallization rate of the composite relative to neat PLA. However, the graphene nanosheets can act as a heterogeneous nucleating agent, which is their dominant role during melt crystallization. As a result, the composite shows a higher crystallization rate than neat PLA under these conditions. © 2013 American Chemical Society.

Lv Q.,Yangzhou University | Wu D.,Yangzhou University | Wu D.,Provincial Key Laboratories of Environmental Engineering and Materials | Qiu Y.,Yangzhou University | And 5 more authors.
Thermochimica Acta | Year: 2015

Poly(ε-caprolactone) (PCL) composites containing graphite with various layered platelet structures were prepared by solution mixing for crystallization study. The results reveal that the crystallization of PCL is highly dependent on the graphite structure. All three kinds of graphite particles, including graphene nanosheets, graphite nanoplatelets and natural graphite flakes, show evident nucleating effect on the PCL crystallization. But their nucleation activity reduces with increased platelet thickness. However, the presence of graphite particles, especially graphite nanoplatelets and graphene nanosheets, also impedes the movements of PCL chain and increases the system viscosity, resulting in an evident increase of crystallization activation energy. But the nucleating effect is dominant role in the current system because all composites show higher crystallization rates than the neat PCL. The obtained results of this work can provide additional way to design or to control crystallization of PCL composites. © 2015 Elsevier B.V. All rights reserved.

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