Qingsheng Liu

Nonisothermal Crystallization Kinetics of Poly(lactic acid)/Nanosilica Composites

Poly(lactic acid) (PLA)/nanosilica composites were prepared by blending the PLA and nanosilica in chloroform and then evaporating the solvent to form the composite films in a dish. The Ozawa and Mo equations were used to characterize the nonisothermal cold crystallization kinetics of the PLA/nanosilica composites. The results indicated that the Ozawa equation was not successful while the Mo equation was successful to describe the nonisothermal crystallization kinetics of PLA/nanosilica composites. The values of crystallization activation energy (E c) of the samples were calculated by the Kissinger method. Although the sample crystallization rates were enhanced with the increase of nanosilica content, the samples exhibited increased E c in the presence of nanosilica. The results showed that nanosilica had an effect on both the nucleation and the crystal growth of PLA, promoting the nucleation but interfering with the molecular motion of PLA in the crystallization process.

Blends of Polylactide/Thermoplactic Elastomer: Miscibility, Physical Aging and Crystallization Behaviors

The PLA/PAE blends with four different weight ratios were prepared by melt mixing. PLA and PAE in PLA/PAE blends were almost immiscible while the weak interaction between PLA and PAE existed. The sub-micrometer PAE domains were dispersed in PLA matrix uniformly. The physical aging of PLA could be inhibited by introducing PAE. For PLA/PAE, the structure formed by physical aging at room temperature induced the accelerated crystallization of PLA during heating. However, for neat PLA, the structure formed by physical aging had a negligible effect on the crystallization of PLA during heating. The isothermal crystallization kinetics of neat PLA and PLA/PAE were analyzed by Avrami theory. The values of Avrami exponent were within the range 2.1–3.0. The crystallization rate of PLA was enhanced significantly by addition of PAE.

Poly(3-hydroxybutyrate) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate): Structure, Property, and Fiber

Poly(3-hydroxybutyrate) [P(3HB)] and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] are produced by various microorganisms as an intracellular carbon and energy reserve from agricultural feedstocks such as sugars and plant oils under unbalanced growth conditions. P(3HB) and P(3HB-co-3HV) have attracted the attention of academia and industry because of its biodegradability, biocompatibility, thermoplasticity, and plastic-like properties. This review first introduced the isodimorphism, spherulites, and molecular interaction of P(3HB) and P(3HB-co-3HV). In addition, the effects of 3HV content on the melting temperature and crystallization rate were discussed. Then the drawbacks of P(3HB) and P(3HB-co-3HV) including brittleness, narrow melt processing window, low crystallization rate, slow biodegradation rate in body, and so on were summarized. At last, the preparation, structure, and properties of P(3HB) and P(3HB-co-3HV) fiber were introduced.

Rheology and crystallisation of PLA containing PLA-grafted nanosilica

Abstract PLA/SiO2 nanocomposites (PLAS) were prepared by premixing in chloroform solution and then melt extrusion. SiO2 were surface grafted via ring-opening polymerisation of L-Lactide before blending. Crystallisation and rheological properties of PLAS were investigated as a function of SiO2 content. It was identified from differential scanning calorimetry cooling plots that the addition of SiO2 could improve crystallisation rate and relative crystallinity of PLA. Meanwhile, SiO2 had affected rheological properties of PLA. Pure PLA and PLAS were both typical shear-thinning fluid, and shear viscosity of PLAS was higher than pure PLA. In dynamic sweep test, the linear viscoelastic regions with critical strains of PLAS decreased with the increasing SiO2 content compared with pure PLA. The G′, G″ and tan δ versus ω of PLAS were all improved. The results of rheological tests indicated that the addition of SiO2 had effect on the structure of PLA molecular chain and had formed network structure in PLA matrix.

Viscoelastic behavior and crystallization property of poly(lactic acid)/silica nanocomposite

The rheological properties of poly(lactic acid)/silica nanocomposite are important to practical industry application, but little research is available regarding this field. In this study, SiO2 nanoparticles were first surface-modified by silane coupling agent KH570 and then melt blending with poly(lactic acid) in a twin-screw extruder to prepare poly(lactic acid)/SiO2 nanocomposites. The effect of the SiO2 content on the viscoelasticity of the nanocomposites was studied. The results showed that the complex viscosity of the nanocomposites decreased with the addition of the SiO2 nanoparticles. The storage modulus was enhanced and the loss modulus was weakened at low frequencies. Both the critical strain and modulus depended on the content of the nanoparticles. The good dispersion of the SiO2 nanoparticles in poly(lactic acid) matrix was identified from field emission scanning electron microscopy. The dispersibility was improved after surface modified by KH570, in comparison to the original nanoparticles. The crystallization property analyzed by differential scanning calorimetry indicated that the presence of the SiO2 nanoparticles had effect on the crystallization behavior and the crystallinity (Xc) of poly(lactic acid)/SiO2 nanocomposites. The Xc of the nanocomposites was bigger than those of pure poly(lactic acid), since the SiO2 nanoparticles dispersed in poly(lactic acid) matrix served as a nucleating agent.

Effect of benzimidazolium salt on dispersion and properties of polyphenylene sulfide/organic clay nanocomposites via melt intercalation

Nanocomposites of polyphenylene sulfide (PPS) were prepared with a benzimidazolium surfactant used as organic modification for the montmorillonite (MMT) by melt blending. The benzimidazolium-modifided MMT (Bz-MMT) exhibited a large interlayer spacing of 3.26 nm and showed a high thermal stability compared to the commonly used clay modified by alkyl ammonium salts (DK-1N). The morphology of the polyphenylene sulfide (PPS)/Bz-MMT nanocomposites were evaluated by X-ray diffraction (XRD) and transmission electron microscope (TEM). The results showed good overall dispersion of the MMT in PPS matrix. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to evaluate the thermal properties of polymer/clay nanocomposites. The results of DSC showed the addition of MMT resulted in heterogeneous nucleation crystallization of PPS. The results of TGA showed the thermal stability of the polymer/clay nanocomposits was enhanced. The rheological properties of nanocomposites were also evaluated by a Anton Paar rheometer. The results indicated that the addition of Bz-MMT nanoplatelets affected the linear viscoelastic behavior of the PPS matrix by increasing the viscosity.

Structure and filtration performance of fibrous composite membranes containing environmentally friendly materials for water purification

A fibrous composite membrane consisting of a chitosan (CS) barrier layer and a poly(hydroxybutyrate-cohydroxyvalerate) (PHBV) fibrous substrate was manufactured as a filter for water purification. The PHBV fibrous supporting layer was fabricated via electrospinning technique, and then the CS solution cast on the PHBV fibers to form the top barrier layer. The structural morphology, mechanical property and adsorption capability of the PHBV/CS membranes were thoroughly investigated. Three heavy metal ions were used to evaluate the equilibrium absorption capacities of the chosen membranes. The equilibrium absorption capacities for Cu(II), Pb(II) and Cd(II) were 64.08 mg/g, 90.32 mg/g and 148.96 mg/ g, respectively. Meanwhile, the rejection ratio of PHBV/CS composite membrane for two disperse dyes could reach to 99 %. The results indicated that PHBV fibrous substrate could not only enhance the mechanical strength of the top barrier layer, but also improve the water permeation of the membrane. This study extended the application of an environmentally friendly material in the water purification without causing much trouble about scrap film.

Miscibility and Phase Morphology of Polylactide/Poly(vinyl acetate-co-vinyl alcohol) Blends Obtained by Melt Mixing

Poly(vinyl acetate-co-vinyl alcohol)s (P(VAc-co-VA)s) with different degree of hydrolysis (DH) were blended with polylactide (PLA) by melt mixing to prepare PLA/P(VAc-co-VA) blends with various weight ratios. PLA and PVAc were miscible. For blends of PLA and P(VAc-co-VA) with DH from 13.8 ∼ 55.1%, PLA and P(VAc-co-VA)s were partly miscible. For PLA/P(VAc-co-VA14) blends with P(VAc-co-VA14) of 5–50 wt.%, PLA/P(VAc-co-VA33) with P(VAc-co-VA33) of 5–50 wt.%, and PLA/P(VAc-co-VA55) with P(VAc-co-VA55) of 5–20 wt.%, P(VAc-co-VA)s were dispersed in PLA uniformly. The size of dispersed phase changed with the content and DH of P(VAc-co-VA). When the content of P(VAc-co-VA55) in PLA/P(VAc-co-VA55) blends was above 30 wt.%, the dual continuous phase formed.

Preparation and thermal properties of polyphenylene sulfide/organic montmorillonite composites

Cetyl trimethyl ammonium bromide (CTAB) was used for the intercalation modification of nano-montmorillonite (MMT). The spectra of Fourier transform infrared spectrometer (FTIR) and X-ray diffraction (XRD) suggested that CTAB had intercalated into the layers of MMT. And the interlayer spacing of MMT increased from 1.198 to 3.616 nm. The thermogravimetric analysis (TGA) curves of organic montmorillonite (OMMT) showed three-step degradation. The scanning electron microscope (SEM) photographs showed that surface morphology of MMT remained unchanged. Then polyphenylene sulfide (PPS)/organic montmorillonite (OMMT) composites were prepared by melt blending. And composites were treated at 180 °C for 24 h. The results of SEM showed that OMMT had good dispersion behavior and adhesion with PPS. The results of differential scanning calorimetry (DSC) showed the addition of OMMT resulted in heterogeneous nucleation crystallization of PPS. The results of TGA showed there was a good improvement of the thermal stability of PPS. The FTIR and color measurement analysis showed the addition of OMMT could improve the thermal oxidation stability.

Experimental study and prediction of the diameter of melt-electrospinning polypropylene fiber

Firstly, the effects of the spinning temperature, spinning voltage, tip-to-collector distance and ambient temperature on the diameter of melt-electrospinning polypropylene (PP) fibers were studied. The results showed that with the increase of the spinning temperature, spinning voltage and tip-to-collector distance, the fiber diameters first decreased and then increased. However, when the ambient temperature increased, the fiber diameters increased gradually. Secondly, based on the previous results, the response surface methodology (RSM) was used to investigate the combined effects of processing parameters on fiber diameters and establish a second-order polynomial equation to predict the fiber diameter. The results showed that the effect order of four factors on fiber diameter was as follows: spinning temperature > tip-to-collector distance > ambient temperature > spinning voltage. Moreover, the fiber diameter predicted by response surface analysis fitted well with the experimental result. Finally, three layer melt-electrospinning PP webs with different fiber diameters were online compounded with conventional non