Hongfu Zhou

Preparation of Multi-walled Carbon Nanotube/Polyaniline/Fe3O4 Composites

A method to prepare multi-walled carbon nanotube/polyaniline/Fe3O4 nanocomposites was developed. Acid-treated multi-walled carbon nanotubes (MWCNTs) were first encapsulated with polyaniline (PANI) by an in-situ micro-emulsion polymerization and then reacted with Fe3O4 modified with aniline dimer (ADM-Fe3O4). Fourier transform infrared spectrometry demonstrated that there existed chemical linkages between the MWCNTs and the PANI as well as between the MWCNTs and the ADM-Fe3O4 nanoparticles. The morphology of the nanocomposites was examined using transmission electron microscopy. The bulk structure of the nanocomposites was investigated with X-ray diffraction. The resulting products could be separated from the deionized water under an external magnetic field within about several seconds.

Reactive Modification of Poly(ethylene terephthalate) and its Foaming Behavior

A methodology for the preparation of chain extended poly (ethylene terephthalate) (PET) and its foams by autoclave batching foaming method was proposed. First, PET was mixed with tetraglycidyl diamino diphenyl methane (TGDDM) as chain extender to generate the branching/crosslinking molecular structure and improve the viscoelasticity of PET. Then, PET foams were prepared using supercritical CO2 as physical blowing agent. The molecular structures of various PET samples were characterized by the nuclear magnetic resonance, gelation degree and crosslinking density test. The results showed that with the introduction of TGDDM, the branching/crosslinking structure of PET appeared. The influences of various molecular structures on the thermal property and rheology of PET were also studied. The results showed that the crystallization temperature, crystallization rate, and crystallinity of various PET samples decreased with the content of TGDDM, but the modified PET had higher melt elasticity than that of pure PET. PET foam with the addition of 0.4% TGDDM had finer cellular morphology and the highest expansion ratio.

The Preparation and Characterization of Branching Poly(ethylene terephthalate) and its Foaming Behavior

Chain extension was an effective method for increasing the molecular weight, the melt strength and the foaming property of linear polymer. In this paper, pyromellitic dianhydride (PMDA) was used as chain extender to improve these properties of linear poly (ethylene terephthalate) (PET). The intrinsic viscosity, rheological and thermal characterizations of various PET samples was investigated. The results demonstrated that the increasement of the viscoelasticity at low frequencies was correlated to the raise of the intrinsic viscosity and the formation of long chain branching. These structural changes resulted in the decreasement of the crystallization temperature and melt temperature as well as the increase in the cold crystallization values with the increasing content of PMDA. The cellular morphology and expansion ratio of CEPET foams were also obviously improved by the introduction of PMDA. The expansion ratio of CEPET foam with the PMDA content of 1.0 phr would reach 31.78. In addition, the effect of the chain extension reaction time on the intrinsic viscosity, the rheological behavior, and foaming properties of PET were also studied. The results showed that the intrinsic viscosity, the rheological behavior, and the foamability of CEPET also decreased gradually with increasing chain extension reaction time, which should be attributed to the occurrence of more and more intense thermal degradation.

The Effect of Compatibilization on the Properties and Foaming Behavior of Poly(ethylene terephthalate)/Poly(ethylene-octene) Blends

The methodology for improving the properties and foaming behavior of poly (ethylene terephthalate) (PET)/poly(ethylene-octene) (POE) blends through compatibilization was proposed. In this paper, PET/POE blends were prepared through a melt blending method, POE was employed as elastomer toughener, maleic anhydride grafted POE (mPOE) was selected as compatibilizer, and pyromellitic dianhydride (PMDA) was used as chain extender. The content of mPOE was changeable to study the effect of compatibility on crystallization behavior, toughness, dispersion morphology, and rheological behavior of PET/ POE blends. The results demonstrated that the crystallization peak of PET/POE blends shifted towards high temperatures from 196.97°C to 201.24°C with the content of mPOE increasing. The brittle-ductile transition for PET/POE blends occurred at the mPOE content in the range of 4–5 phr. The particle size of POE dispersed phase decline firstly and then was almost unchanged with an increasing content of mPOE. The storage modulus and complex viscosity of compatibilized PET/POE blends were obviously higher than that of uncompatibilized PET/POE blends. Then PET/POE blends were foamed using supercritical CO2 as physical blowing agent. The results showed that the cell size, cell density, and tensile properties of the PET/POE blending foams were affected by the content of mPOE strongly. With the content of mPOE, the cell size decreased and then kept stable as well as the cell density the trend of cell size increased then remained unchanged. In addition, the elongation at break of PET/POE blending foams was higher than that of the uncompatibilized PET/POE blending foam. PET/POE blending foams with fine cell morphology and good ductility could be achieved with a proper content of compatibilizer in the blends.

Multiple actions of poly(ethylene octene) grafted with glycidyl methacrylate on the performance of poly(lactic acid)

Poly(ethylene octene) grafted with glycidyl methacrylate (POE-g-GMA) was employed to improve the rheological and thermal properties, toughness, and foaming behaviors of poly(lactic acid) (PLA) through a chain extension effect. The dynamic rheological properties of PLA were improved significantly with increasing content of POE-g-GMA, due to the chain extension reaction between PLA and POE-g-GMA. As the content of POE-g-GMA increased, the cold crystallization temperature of PLA decreased by more than 10 °C and the crystallinity of PLA increased slightly from 1.2% to 4.7%, respectively. The impact strength of PLA with a POE-g-GMA content of 10 wt% increased by more than 4 times, compared with that of pure PLA. A sea-island structure could be observed in the PLA/POE-g-GMA blends and the distribution of POE-g-GMA was uniform. PLA foams with various POE-g-GMA contents were prepared in a stainless-steel autoclave using supercritical CO2 as a physical blowing agent. The cellular morphology of PLA foam was obviously improved when the concentration of POE-g-GMA increased from 5 wt% to 10 wt%.

The Effect of Composite Nucleating Agent on the Crystallization Behavior of Branched Poly (Lactic Acid)

Composite nucleating agent (CNA) consisting of zinc oxide as a crystallization promoter and phenylphosphonic acid zinc salt (PPZn) as an heterogeneous nucleation agent was employed to improve the crystallization behaviors of branched poly (lactic acid) (B-PLA) which was prepared by use of multi-functional epoxy-based chain extender (CE). The differential scanning calorimeter results showed that the crystallinity and crystallization temperature of prepared B-PLA/CNA were higher than that of linear poly (lactic acid) (L-PLA) and B-PLA at a high cooling rate. The corresponding phenomena of heterogeneous nucleation of B-PLA/CNA were observed by means of polarized optical microscope. The crystalline mechanism research results show that the degradation reaction and chain extending reaction were occurred simultaneously after the addition of CE and CNA into the PLA, PPZn as an effective nucleation points could increase the nucleation density and the degraded short molecular chains with higher chain mobility would improve crystal growth during the crystallization of the branched PLA. Non-isothermal cold crystallization kinetics of various B-PLA with different content of CNA was studied. The corresponding result showed that the crystallinity and crystallization rate increased obviously with the CNA content greater than or equal to 5phr, as well as the crystallization time decreased. The similar experimental results of non-isothermal and isothermal melt crystallization kinetics also showed that CNA had a significant impact on crystallization behavior of B-PLA.