Mei Fang Zhu

Preparation and Characterization of TPU Toughened PLA Elastic Fibers

Poly (lactic acid) (PLA) elastic fibers were prepared by melt spinning using Thermoplastic polyurethane (TPU) as a toughing agent and PLA-g-MA(Maleic anhydride) as a compatibilizer. Thermal properties and thermal stability of PLA/TPU composites, as well as the cross section morphology and mechanical properties of fibers were studied in the present investigation. DSC results showed that PLA was immiscible with TPU. In addition, the incorporation of TPU decreased the melting enthalpy of PLA/TPU composites. TG results indicated that the initial degradation temperatures of composites were also decreased by the appearance of TPU, and it decreased by 9°Cwhen TPU content was up to 20wt%. FESEM results confirmed that strong interactions were existed between PLA and TPU phases, which were benefit for the improvement of PLA/TPU fibers’ mechanical properties. Results of tensile testing demonstrated that TPU could improve the toughness of fibers effectively and the elongation-at-break of fibers increased from 2.2% of PLA to 203.9% of PLA/TPU.

Effect of Filler Ratio on Properties of Nanohydroxyapatite/SiO2 Based Bioactive Dental Resin Composites

Hydroxyapatite (HAP), as an essential component of bone and tooth, is one of the promising bioactive materials. The purpose of this study was to investigate the effects of incorporation of nanoHAP and SiO2 particles on the properties of bioactive dental composite. Silanized HAP and SiO2 were mixed with BisGMA/TEGDMA (1/1 wt/wt) monomers at various HAP/SiO2 mass ratios of 0:7 (no HAP), 5.25/1.75, 3.5/3.5, 1.75/5.25, 7:0 (no SiO2) to yield a series of pastes all containing 70 wt% filler loading. The results showed that flexural strength, elastic modulus and compressive strength gradually decreased with increasing amount of HAP particles, as well as curing depth and polymerization shrinkage, which resulted from the nature of HAP particle material. Water sorption and solubility in water increased slightly with addition of HAP particles. Degree of conversion test could support results above well. Remineralization test in SBF demonstrated dental composite with HAP particles had a good apatite-forming ability. Consequently, dental composite filled with lower amount of nanoHAP (HAP/SiO2 around 0.25) particles would possess better comprehensive performances.

Synthesis and Characteristics of Dental Composites with Novel Bis-GMA Derivate as a Resin Base

2,2-bis [4-(2-hydroxy-3-methacryloyloxypropoxy) pheny propane (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) have been commonly used as a viscous monomer and a reactive diluent in the organic phase of dental restorative composites, respectively. The purpose of addition of TEGDMA is mainly to decrease the high viscosity of Bis-GMA caused by hydrogen bonding between hydroxyl groups. However, some adverse effects will accompany with increased amounts of the TEGDMA, such as higher values of polymerization shrinkage, which is not undesirable for the clinical application. Therefore, substituting hydroxyl groups of Bis-GMA might be an appropriate and effective way to reduce the amount of diluents and weaken the accompanied adverse effects. This work focuses on the synthesis of a novel Bis-GMA derivate, substituting acetyl groups for hydroxyl groups in Bis-GMA. The viscosity of Bis-GMA characterized with rotational rheometer was significantly decreased from 820 Pa.s to 11 Pa.s by substitution of acetyl group, leading to the low amount of TEGDMA in resin matrix. Differential Scanning Calorimeter (DSC) was used for investigating the reaction kinetics of this novel monomer with different mass ratios of TEGDMA. The results suggested that the maximum conversion of the Ac-Bis-GMA can reach 88% while the corresponding value for Bis-GMA is 75%. Dental composites were prepared from 2,2-bis [4-(2-acetyl-3-methacryloyloxypropoxy) pheny propane (Ac-Bis-GMA) or Bis-GMA resin mixtures with TEGDMA filled with 70 wt% silica co-fillers. The results presented that dental composites prepared from new resin matrixes exhibited adequate mechanical properties.

Crystallization Behavior of Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate) with WS2 as Nucleating Agent

Poly (3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) is one of the aliphatic polyesters that are completely synthesized by microorganisms. Owing to the physical and chemical properties of PHA being similar with those of polypropylene, PHBV is expected to be able to partially replace petroleum-based polymers, and to reduce the pollution of environment at the same time. However, many inherent defects, including slow crystallization rate, large-size spherulite and secondary crystallization phenomenon, restrict the development of PHBV. In the present study, PHBV/WS2 hybrid materials where the tungsten disulphide (WS2) acted as nucleating agent were produced, and then its accelerated crystallization effect on PHBV was evaluated. Mo’s methods were employed to describe the non-isothermal crystallization kinetics of the nucleated PHBV hybrid materials. The activation energy (ΔE) of hybrid material was calculated by Kissinger formula. It was found that the addition of low WS2 loadings strongly increased the crystallization rate of PHBV and correspondingly the crystallization half time (t1/2) decreased from 97s to 38s with only 1wt.% WS2 added. Meanwhile, the crystallization temperature (Tc) increased from 81.9°C to 112 °C. The results reported here are expected to be of great interest for the practical application of PHBV.

Study on the Properties of Melamine Cyanurate Modified Polyamide 6 Nanocomposites with Different Dimensional Siliciferous Particles

Different dimensional siliciferous particles including silica (0D), halloysite nanotubes (HNTs,1D) and montmorillonite (MMT,2D) were melt blending with certain amount of melamine cyanurate and polyamide 6(PA6) by a twin-screw extruder. Characterization of the PA6 composites has been investigated using scan electron microscopy (SEM), thermal gravimetric analyzer (TGA), universal testing machine and limiting oxygen index instrument. SEM images indicate that the nanoparticles were uniformly dispersed in the PA6 but there was some aggregation of MCA in the composites. The incorporation of silica exerted a negative effect on the flame retardancy of PA6/MCA composite, whereas adding HNTs and MMT lead to the improvements of LOI value of 30.4 and 30.9 respectively. TGA results show that PA6/MCA/silica, PA6/MCA/HNTs and PA6/MCA/OMMT exhibit two degradation stages. Higher Tmax1 and Tmax2 appeared comparing with PA6/MCA. Char residue of PA6/MCA/OMMT at 600°C were elevated most. HNTs and OMMT can increase the tensile strength and elongation of PA6/MCA by universal testing machine results, even higher than pure PA6, showing enhanced effects of these 1D and 2D fillers. These could enhance strength of the char and finally increase the flame retardancy of PA6.

Conductive Polypyrrole/Polyurethane Composite Fibers for Chloroform Gas Detection

Flexible conductive fibers were fabricated by in-situ chemical polymerization of pyrrole monomers on the surface of polyurethane (PU) fibers. Compact polypyrrole (PPy) surface layer were observed, and moreover, high structural stability of the composite fibers can be obtained due to interpenetrating interface formation and strong interaction between PPy layers and PU matrix. More importantly, the composite fibers exhibited high sensitivity with relative fast response and recovery time, and good reproducibility for chloroform vapor detection.

Synthesis and characterization of the PANI/ITO conducting nanocomposites

The PANI/ITO conducting nanocomposites have been synthesized by in-situ polymerization. The obtained nanocomposites were characterized by X-ray diffraction pattern, scanning electron microscopy and Fourier transform infrared. Electrical conductivity measurements on the samples pressed into pellets showed that the maximum conductivity attained 2.0 ± 0.05 S/cm for PANI/ITO nanocomposites, at ITO doping concentration of 10 wt%. The results of the present work may provide a simple, rapid and efficient approach for preparing PANI/ITO nanocomposites.

Synthetic Comb-Like Phase-Change Material Poly(Acrylonitrile-co-Lauric Acid) Copolymer for Low Temperature Energy Management

Comb-like poly(acrylonitrile-co-lauric acid) (PANLA) phase change materials with low phase change temperature were synthesized via mixed solvent precipitation polymerization where acrylonitrile (AN) and dodecyl acrylate (DA) were employed as monomers. Fourier transform infrared spectroscopy (FTIR) and 13C nuclear magnetic resonance spectroscopy (13C NMR) were used to characterize the chemical structure of the resultant PANLA. Differential scanning calorimetry (DSC) and thermogravimetry analyzer (TG) were adapted to evaluate the energy storage performance and thermal reliability of PANLA materials. Thermal analysis revealed that comb-like PANLA had a good energy storage performance and cyclic stability. The crystallization temperature of PANLA was around -8 °C with a crystallization enthalpy range of 3.77~41.30 J/g which was intended to apply in an environment with a relatively low temperature.

Synthesis of Biotinylated pH-Sensitive Glycopolymer with Different Architectures

Two pH-sensitive Glycopolymers with the same components but with different construction tailored biotin functionalities were developed for controlled release of bortezomib (BTZ).The initiator brominate biotin and glyco-monomer were synthesized precedently to produce the block-and random-biotinylated poly (2-Gluconamidoethyl methacrylate)-poly (2-Diethylaminoethyl methacrylate) (block/random Biotin-PGAMA-PDEA) via atom transfer radical polymerization (ATRP). The construction and composition of compounds and polymers were characterized by 1H NMR Spectroscopy. The block copolymer self-assembled into micelle according to the pH-response ability of the copolymer while the random one did not under certain conditions.

Functionalization of α-ZrP by 1,2-Epoxypropane for Further Modification

To prepare alpha zirconium phosphate (α-ZrP) with high interlayer distance, grafting ratio and thermal stability, 1,2-epoxypropane was used to modify α-ZrP as the epoxy group reacting with P-OH on the external and internal surfaces of α-ZrP to form P-O-C bonds after small amines pre-intercalation. Different characterization techniques were used, including X-ray Powder Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Thermo-Gravimetric Analysis (TGA) and Carbon Mass Nuclear Magnetic Resonance (13C MAS NMR). The results of XRD confirmed the pre-intercalation of amino-propane and the intercalation of 1,2-epoxypropane, as the interlayer distance increased from 7.5 Å to 16.9 Å and 15.3 Å, respectively. FT-IR and 13C MAS NMR results confirmed the formation of P-O-C bonds between 1,2-epoxypropane and α-ZrP. TGA analysis showed that the grafting ratio of 1,2-epoxypropane was 19.44%.