Haiping Xing

Dependence of microstructures and melt behaviour of polypropylene/fullerene C60 nanocomposites on in situ interfacial reaction

Polypropylene (PP)/fullerene C60 nanocomposites, in which the interfacial reaction between two components was in situ mediated by peroxide, were prepared by a melt mixing method. Structural characterization showed that the interfacial reaction strongly affected the microstructures of PP/C60 nanocomposites at different scales, such as improving the dispersion state of C60 nanoparticles and forming long chain branched structures in which C60 acts as a branching point. This was ascribed to the ability of C60 (as a reactive nanoparticle) for preferentially trapping carbon-centred macroradicals of PP to in situ form long chain branched structures of PP on the surface of C60 during melt mixing. As a result, the shear-responsive sensitivity of the nanocomposite melts in low shear frequency regions was dramatically enhanced compared to parent PP and the nanocomposites without interfacial reaction. The nanocomposites also showed high melt strength. In addition, the transition from the melt state to solid state (crystallization process) occurred at higher temperature after the interfacial reaction between PP and C60 took place.

Interplay between the composition of LLDPE/PS blends and their compatibilization with polyethylene- graft -polystyrene in the foaming behaviour

Polyethylene-g-polystyrene (PE-g-PS) copolymers, which were prepared by the combination of the ROMP and ATRP method, were utilized to compatibilize LLDPE/PS blends. On one hand, the effect of PE-g-PS on the morphologies of LLDPE/PS blends was investigated. On the other hand, the influences of branch length and added amount of PE-g-PS on the cell morphology of foamed LLDPE/PS blends with different compositions were studied using supercritical CO2 as a physical foaming agent in a batch foaming process. It was found that the presence of PE-g-PS in the LLDPE/PS blends showed different influences on the foaming behaviour, strongly depending on the composition of the blends (i.e. the weight ratio of LLDPE and PS). How the interplay of compatibilization and composition of the LLDPE/PS blends affected the foaming behaviour of the LLDPE/PS blends was studied. A reasonable explanation was ascribed to consecutive states of the interfacial region, resulting from different phase structures of the blends. Compared to pristine LLDPE and PS, the blends with a sea-island phase structure showed the improved foam morphology, but the presence of PE-g-PS did not strongly influence the foaming behaviours of these blends. In contrast, the presence of PE-g-PS dramatically promoted the foaming ability of LLDPE/PS blends with a co-continuous phase structure. It was ascribed to the strengthened interfacial adhesion blocking the channel between two components through which CO2 was released, and the viscoelasticity of the blends was not the key factor to determine the foaming behaviour under the same foaming conditions in this work.

Novel Method for Preparing Auxetic Foam from Closed-Cell Polymer Foam Based on the Steam Penetration and Condensation Process

Auxetic materials are a class of materials possessing a negative Poissons ratio. Here, we established a novel method for preparing auxetic foam from closed-cell polymer foam based on the steam penetration and condensation (SPC) process. Using polyethylene (PE) closed-cell foam as an example, the foams treated by the SPC process presented a negative Poissons ratio during stretching and compression testing. The effect of steam-treated temperature and time on the conversion efficiency of negative-Poissons ratio foam was investigated, and the mechanism of the SPC method for forming a reentrant structure was discussed. The results indicated that the presence of enough steam within the cells was a critical factor for the negative Poissons ratio conversion in the SPC process. The pressure difference caused by steam condensation was the driving force for the conversion from conventional closed-cell foam to the negative-Poissons ratio foam. Furthermore, the applicability of the SPC process for fabricating auxetic foam was studied by replacing PE foam by polyvinyl chloride foam with a closed-cell structure or replacing water steam by ethanol steam. The results verified the universality of the SPC process for fabricating auxetic foams from conventional foams with a closed-cell structure. In addition, we explored the potential application of the obtained auxetic foams by the SPC process in the fabrication of shape-memory polymer materials.