Yongli Liu

Polymer-Nanoparticle Composites Composed of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and Coated Silver Nanoparticles

The effects of addition of synthesized organic-suspension silver nanoparticles on the crystallization and thermal stability of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were studied by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (XRD), UV-Vis absorption spectroscopy, polarized optical microscopy (POM), and thermal gravimetric analysis (TGA). The TEM images showed the average primary size of the as-synthesized silver nanoparticles, coated with a monolayer of the surfactants consisting of oleic acid and an alkylamine, was about 5 nm with narrow distribution, and that they were uniformly dispersed in n-heptane. PHBV/silver nanocomposites were prepared by melt mixing in an internal mixer and then injection molded into rectangle-shaped specimens by a labscale injection molding device. The coated silver nanoparticles showed a homogenuous dispersion in the PHBV matrix when the content of coated silver nanoparticles was about 1%. Both the DSC and POM data showed the efficient heterogeneous nucleation by the coated silver nanoparticles for facilitating PHBV crystallization. The thermal stability of the PHBV/silver nanocomposites improved with the increase in the content of the coated silver nanoparticles.

Effect of Barium Sulfate Nanoparticles on Mechanical Properties and Crystallization Behaviour of HDPE

High density polyethylene (HDPE)-based composites were prepared by blending HDPE with BaSO4 nanoparticles, which had been treated with sodium stearate. Variations in crystallization behaviour, mechanical properties, storage modulus and damping parameter (tan d) with the addition of BaSO4 nanoparticles were investigated by SEM, XRD, DSC, DMA, etc. The crystallization rate steadily increased with the content of BaSO4 nanoparticles because of these nanoparticles acting as a heterogeneous nucleation agent. The impact strength of HDPE first increased and then decreased with increasing the content of BaSO4 nanoparticles. The maximum impact strength of HDPE nanocomposites was achieved at a weight ratio of BaSO4/HDPE = 1/100. However, the tensile yield stress gradually increased with the content of BaSO4 nanoparticles. Dynamic mechanical analysis data showed an increase in the storage modulus of composites with increasing content of BaSO4 nanoparticles. The tan d value of nanocomposites decreased in comparison to the neat HDPE. It was demonstrated that the BaSO4 nanoparticles treated with sodium stearate had stronger effective interface interaction with HDPE matrix and adding 1.0 wt.% modified BaSO4 nanoparticles could effectively reinforce HDPE matrix.

Environmental Degradation of Starch/Poly(Lactic Acid) Composite in Seawater

In order to study the degradation property of starch/polylactic acid (PLA) composites in a briny environment, injection-moulded tensile bars of starch/PLA composites were investigated by immersion in static seawater controlled at 25 °C for 1 year. SEM micrographs showed that starch particles were lost from the bar because of microbial action. GPC results showed the number average molecular weight (Mn) of PLA decreased with degradation time. The glass transition temperature (Tg) and melting temperature (Tm) measured by DSC decreased slightly with degradation time. An increase of crystallinity calculated from the DSC data was attributed to the decrease of molecular weight. Weight losses were mainly due to loss of starch. The impact strength of the composites decreased monotonically with degradation time; tensile strength and elongation at break of the composites first decreased, then increased and at last decreased again with degradation time, and the water was acting as a plasticizer. The starch/PLA composites in seawater had degradability, but the degradation rate of composite bars studied in this paper was very slow.

Isothermal Crystallization Kinetics and Melting Behavior of a Luminescent Conjugated Polymer, Poly(9,9-Dihexylfluorene-Alt-2,5-Didodecyloxybenzene)

A study of the isothermal crystallization behaviors of poly(9,9-dihexylfluorene-alt-2,5-didodecyloxybenzene) (PF6OC12) was carried out using differential scanning calorimetry (DSC). The crystallization kinetics under isothermal conditions could be described by the Avrami equation. The Avrami exponent n ranges from 3.43 to 3.71 for PF6OC12 at crystallization temperatures between 100.0°C and 90.0°C, indicating a three-dimensional spherical crystal growth with homogeneous nucleation in the primary crystallization stage for the isothermal melt crystallization process. In the DSC scan, after the isothermal crystallization, multiple melting behavior was found. The multiple endotherms could be attributed to melting of recrystallized materials produced originally during different crystallization processes. According to the Arrhenius equation, the activation energy was determined to be 211.29 kJmol−1 for the isothermal melt crystallization of PF6OC12.