Yuqi Li

Enhanced thermal and mechanical properties of polypropylene composites with hyperbranched polyester grafted sisal microcrystalline

Polypropylene composites were prepared by melt compounding method with hyperbranched polyester grafted sisal microcrystalline and CaCO3. The thermal and mechanical properties of polypropylene composites were investigated by means of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), melt flow indexer (MFI), dynamic mechanical analysis (DMA) and mechanical tests. It was found that the thermal and mechanical properties of PP composites were greatly improved by incorporating MCC-g-HPG-SA. For example, the impact strength, flexural strength, and toughness of the composites with 4 wt% MCC-g-HPG-SA loading were 64.71 kJ/m2, 42.72 MPa, and 2186.69 J/m3, significantly increased by 238.3 %, 18.4 % and 1843.9 % respectively, as compared with PP/MCC/CaCO3 composites. In addition, thermal stability of PP/MCCg-HPG-SA/CaCO3 composites also showed an obvious enhancement compared with PP/MCC/CaCO3 composites.

Y-doped V2O5 with enhanced lithium storage performance

Y-doped V2O5 was prepared by the sol–gel method combined with the freeze drying technique followed by annealing in air. The microstructure of the Y-doped V2O5 was analyzed by XRD, SEM, XPS, and first-principles calculations. The electrochemical performance of the Y-doped V2O5 was characterized by CV, EIS, and charge–discharge tests. The results demonstrated that Y doping had great influence on the morphology and crystalline orientation of the prepared V2O5 sample. In particular, Y formed covalent bonds with the adjacent O atoms within the V2O5 layers and decreased the bond orders of the neighboring V–O bonds. Compared with undoped V2O5, Y-doped V2O5 showed much improved rate capability, higher lithium ion diffusion coefficient, lower electrochemical reaction resistance, and greatly enhanced cycling stability. Y-doped V2O5 could be a promising cathode material for lithium ion batteries.

High performance composites of spinel LiMn2O4/3DG for lithium ion batteries

A highly crystalline nanosized spinel LiMn2O4/3DG composite cathode material for high rate lithium ion batteries was successfully prepared by mixing spinel LiMn2O4 particles with reduced graphene oxide (3DG). Spinel LiMn2O4 and reduced three-dimensional graphene oxide were synthesized using a hydrothermal method and freeze-drying technology, respectively. The structure, morphology and electrochemical performance of the synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge techniques. The results showed that the LiMn2O4/3DG composites exhibited excellent rate capability and stable cycling performance. The discharge capacity was 131 mA h g−1 and the capacity remains at 89.3% after 100 cycles at a 0.5 C rate, while the discharge capacity was 90 mA h g−1 at 10 C. Compared with spinel LiMn2O4 materials, the LiMn2O4/3DG composites showed obvious improvement in electrochemical performance.

High Mechanical and Thermal Properties of Epoxy Composites with Liquid Crystalline Polyurethane Modified Graphene

Graphene nanosheets (GNs) often result in incompatibility with the hydrophobic polymer matrix, and the tendency to form aggregates during processing. Herein, liquid crystalline polyurethane modified GNs (GPLP) were obtained by π–π stacking interactions between GNs and perylene bisimide derivatives, and then in-situ polymerization of liquid-crystalline polyurethane. Spectroscopic studies, elemental analysis, and thermal properties confirmed the successful π–π stacking and the integrated structure of GPLP. The good dispersion state of GPLP in the epoxy matrix (EP), and the strong interactions between GPLP and EP, lead to the significant improvement of the thermal and mechanical performance of the GPLP/EP composites. The impact strength, Young’s modulus, tensile strength, and toughness of the GPLP/EP composites with 1.47 wt % GNs reached the highest values of 54.31 kJ/m2, 530.8 MPa, 112.33 MPa and 863 J/m3, which significantly increased by 210%, 57%, 143%, and 122% compared to that of neat epoxy, respectively. As well, the glass transition temperature increased by a notable 33 °C. It is hoped that this work can be used to exploit more efficient methods to overcome the poor adhesion between GNs and polymers.

Hyperbranched Liquid Crystals Modified with Sisal Cellulose Fibers for Reinforcement of Epoxy Composites

Well-defined functionalized sisal cellulose fibers (SCFs) grafted on hyperbranched liquid crystals (HLP) were synthesized to improve the compatibility between SCFs and epoxy resin (EP). The influence of SCFs-HLP on the mechanical and thermal properties of SCFs-HLP/EP composites was studied. The results show that the mechanical properties of SCFs-HLP/EP composites were enhanced distinctly. Particularly, compared with EP, impact strength, tensile strength, and flexural strength of composites with 4.0 wt % SCFs-HLP were 38.3 KJ·m−2, 86.2 MPa, and 150.7 MPa, increasing by 118.7%, 55.6%, and 89.6%, respectively. As well, the glass transition temperature of the composite material increased by 25 °C. It is hope that this work will inform ongoing efforts to exploit more efficient methods to overcome the poor natural fiber/polymer adhesion in the interface region.

A Combined Self-Consistent Method to Estimate the Effective Properties of Polypropylene/Calcium Carbonate Composites

In this work, trying to avoid difficulty of application due to the irregular filler shapes in experiments, self-consistent and differential self-consistent methods were combined to obtain a decoupled equation. The combined method suggests a tenor γ independent of filler-contents being an important connection between high and low filler-contents. On one hand, the constant parameter can be calculated by Eshelby’s inclusion theory or the Mori–Tanaka method to predict effective properties of composites coinciding with its hypothesis. On the other hand, the parameter can be calculated with several experimental results to estimate the effective properties of prepared composites of other different contents. In addition, an evaluation index σf′ of the interactional strength between matrix and fillers is proposed based on experiments. In experiments, a hyper-dispersant was synthesized to prepare polypropylene/calcium carbonate (PP/CaCO3) composites up to 70 wt % of filler-content with dispersion, whose dosage was only 5 wt % of the CaCO3 contents. Based on several verifications, it is hoped that the combined self-consistent method is valid for other two-phase composites in experiments with the same application progress as in this work.

Water-Induced shape memory effect of nanocellulose papers from sisal cellulose nanofibers with graphene oxide

A novel water-induced shape memory nanocomposites were prepared by introducing graphene oxide (GO), which was based on microcrystalline cellulose nanofibers (MSF-g-COOH) extracting from sisal fibers. The results showed that the water-induced shape memory properties of MSF-g-COOH were significantly improved by the strong hydrogen bonding interaction between MSF-g-COOH and GO, It leads to some additional physically cross-linked points in MSF-g-COOH. On the other hand, at 0.5wt% GO loading, tensile strength and Young modulus of the nanocomposite increased from 139 to 184MPa, and from 5.77 to 8.54GPa, respectively, compared to those of pure MSF-g-COOH. Furthermore, a water-induced model was proposed to discuss the water-induced shape memory behaviors of the MSF-g-COOH/GO nanocomposites. This study provides a framework for developing a cellulose based shape memory polymers (CSMPs) and better understanding the shape recovery mechanism in water-induced CSMPs.

Preparation and model of high-performance shape-memory polyurethane with hydroxylated perylene bisimide

3,4,9,10-Perylene tetracarboxylic anhydride (PTCDA) was reacted with tris(hydroxymethyl)methyl aminomethane (THAM) to form the corresponding hydroxylated perylene bisimide (PBI). Different weight ratios of PBI were used as the reactive filler with hexamethylene diisocyanate (HDI) and polycaprolactone (PCL) to prepare shape-memory PBI/polyurethane composites (PSMPs). Thermogravimetric analyses were carried out to identify the thermal properties of the PSMPs. The shape-memory behaviors of the PSMPs were characterized by dynamic mechanical analysis (DMA). It was revealed that the PSMP with 5.5 wt% PBI exhibited good shape-memory properties with high shape-fixity ratios (Rf) above 94% and shape-recovery ratios (Rr) above 97%. Additionally, compared to the samples without PBI, the PSMP with 5.5 wt% PBI showed better tensile properties with an elongation at break (er) of 932.8% and tensile strength (σm) of 52.76 MPa, which were 333.3% and 18.09 MPa higher than those of the samples without PBI, respectively. Furthermore, a three-element model was proposed to discuss the shape-memory behaviors of the PSMPs. The current work is expected to inform ongoing efforts to develop more efficient methods to study the shape-memory behaviors of polymers and has broad implications for the development of shape-memory polyurethanes for engineering applications.