Junping Zheng

Synthesis and biological evaluation of PMMA/MMT nanocomposite as denture base material.

Inorganic-polymer nanocomposites are of significant interest for emerging materials due to their improved properties and unique combination of properties. Poly (methylmethacrylate) (PMMA)/montmorillonite (MMT) nanocomposites were prepared by in situ suspension polymerization with dodecylamine used as MMT-modifier. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the structures of the nanocomposites. Cytotoxicity test, hemolysis test, acute systemic toxicity test, oral mucous membrane irritation test, guinea-pig maximization test and mouse bone-marrow micronucleus test were used to evaluate the biocompatibility of PMMA/MMT nanocomposites. The results indicated that an exfoliated nanocomposite was achieved, and the resulting nanocomposites exhibited excellent biocompatibility as denture base material and had potential application in dental materials.

Construction of a Different Polymer Chain Structure to Study π-π Interaction between Polymer and Reduced Graphene Oxide

In this work, a different polymer chain structure was synthesized to study π-π interactions between polymer and reduced graphene oxide (RGO). Polymers with different chain structures were obtained from free radical copolymerization of styrene with 4-cyanostyrene (containing substituted phenyl rings) and 2-vinylnaphthalene (containing naphthalene rings). In this work, the polystyrene, poly(styrene-co-4-cyanostyrene) and poly(styrene-co-2-vinylnaphthalene) were named as PS, PSCN and PSNP, respectively. RGO was prepared through modified Hummers’ method and further thermal reduction, and nanocomposites were prepared by solution blending. Thus, different π-π interactions were formed between polymers and RGO. Raman and thermal gravimetric analysis (TGA) were used to characterize the interfacial interaction, showing that the trend of the interfacial interaction should be in the order of RGO/PSCN, RGO/PS, and RGO/PSNP. The differential scanning calorimetry (DSC) measurement showed that, compared with polymer matrix, the glass transition temperature (Tg) of RGO/PS, RGO/PSCN and RGO/PSNP nanocomposites with the addition of 4.0 wt% RGO are increased by 14.3 °C, 25.2 °C and 4.4 °C, respectively. Compared with π-π interaction only formed through aromatic rings, substituent groups changed the densities of electron clouds on the phenyl rings. This change resulted in the formation of donor-acceptor interaction and reinforcement of the π-π interaction at the interface, which leads to increased value of Tg. This comparative study can be useful for selecting appropriate interaction groups, as well as suitable monomers, to prepare high performance nanocomposites.

Polymer/carbon nanotubes nanocomposites: relationship between interfacial adhesion and performance of nanocomposites

Understanding the relationship between interfacial adhesion and performance of nanocomposites is crucial for further designing and preparation of polymer/carbon nanotubes (CNTs) nanocomposites. In this work, we designed three auxiliary comonomers (ACMs) to construct different interfacial interaction between CNTs and polymer matrix. Raw CNTs were first oxidized by blended acids, and then three ACMs were introduced to copolymerize with methyl methacrylate (MMA) to prepare polymethyl methacrylate (PMMA)/CNTs nanocomposites via in situ polymerization. The relationship between interfacial adhesion and performance of nanocomposites was investigated in detail. The results indicated that, the enhanced interfacial adhesion led to improved thermal stability, tensile strength and modulus of nanocomposites, while the elongation at break displayed a totally opposite variation with increased interfacial adhesion. When interfacial adhesion is overwhelmingly strong, the elongation at break of nanocomposites may be even lower than that of polymer matrix. In a word, this study provides a significant reference value on constructing different interfacial interaction for obtaining polymer/CNTs nanocomposites with desired properties.

The effect of silica nanotubes on mechanical performance of polymethyl methacrylate nanocomposites: Comparison to spherical nano-silica

Silica nanotubes (SNTs) were synthesized via sol–gel method using ammonium tartrate as template, and then spherical nano-silica (SiO2) and SNTs which have different geometric morphology were introduced into polymer matrix to obtain polymethyl methacrylate (PMMA)/SiO2 and PMMA/SNTs microspheres via in situ suspension polymerization, respectively. The morphology of synthesized SNTs and microspheres were observed by scanning electron microscope (SEM), while the structure of SiO2 and SNTs, as well as the interaction between PMMA and SiO2 or SNTs were characterized by Fourier transform infrared spectroscopy. The dispersion of SiO2 in the PMMA/SiO2 nanocomposites was observed by transmission electron microscopy (TEM). The molecular weight of the extracted PMMA was measured by gel permeation chromatograph. Finally, the mechanical properties were studied in detail and the tensile fracture surface was studied by SEM. The result indicated that, SNTs with uniform size and high aspect ratio were prepared successfully, and the mechanical properties of PMMA/SNTs nanocomposites were improved greatly due to the introducing of SNTs. However, the mechanical properties of the PMMA/SiO2 nanocomposites decreased overall. Due to the special tubular structure of SNTs, it is much easier for them to be dispersed in polymer matrix compared with spherical SiO2. This work reveals the potential application of SNTs in polymer-based nanocomposites.