Qun Gao

Synthesis and properties of a millable polyurethane nanocomposite based on castor oil and halloysite nanotubes

The use of bio-based materials has recently attracted a lot of attention in the area of polymer synthesis. In this work, a bio-based millable polyurethane (MPU) based on castor oil and its nanocomposites containing a very low content of halloysite nanotubes have been successfully prepared. These MPU/HNT nanocomposites showed higher tensile strength and elongation at break compared with the pristine MPU material. The tensile strength and Young’s modulus of the MPU/HNT nanocomposites were improved by 35% and 63% by incorporating only 0.5 wt% of the HNTs, respectively, which was primarily attributed to the formation of covalent bonds between the OH groups of the HNTs and the NCO groups of 2,4-toluene diisocyanate (TDI). The nanostructure of these MPU nanocomposites was characterized by spectroscopy studies and direct microstructural analysis.

Influence of PNA012 on Crystallization and Mechanical Properties of Polybutylene Terephthalate

PNA012 is a new nucleating agent on polybutylene terephthalate. The effect of different dosage of PNA012 on crystallization and mechanical properties were investigated by means of differential scanning calorimetry, universal testing machine, melt flow indexer and vicat softening testing machine. It was revealed that the PNA012 could substantially accelerate the crystallization of PBT. Compared with the pure PBT,the crystallization temperature of PBT/PNA012 rises from 196.3 °C to 199.7 °C and crystallization degree from 34.2% to 39.9%. The tensile Strength of PBT/PNA012 is increased 9.7%. The Bending Strength has a rise of 9.3% and the heat distortion temperatures of PBT/PNA012 is increased from 115.07°C to 125.94°C.

Synthesis and properties of a millable polyurethane elastomer with low halloysite nanotube content

Nanocomposites comprised of millable polyurethane (MPU) and very low loadings of halloysite nanotubes (HNTs) have been prepared with high tensile strength and elongation at break, and cured using either toluene diisocyanate dimer or dicumyl peroxide as crosslinking agents to further enhance the mechanical performance of the nanocomposites and to reduce costs. A 1.17-fold increase in tensile strength and a 0.58-fold increase in elongation at break was achieved for synthetic linear polyurethane elastomer nanocomposites by incorporating only 1 wt% of HNTs, and these increases were primarily attributed to the formation of covalent bonds between the OH groups of HNTs and the NCO groups of 4,4′-diphenyl-methane diisocyanate (MDI). Remarkable improvements in Youngs modulus were further obtained after curing using the crosslinking agents. The nanostructure of these nanocomposites consisted of individual HNTs covalently bonded and specifically associated with hard MPU microdomains, and therefore affected the degree of phase separation, as characterized by spectroscopy studies and direct microstructural analysis. Moreover, an unprecedented environmental solvent-free prepolymer method has been proposed to compound the MPU/HNTs nanocomposites.

Nanoparticles vs. nanofibers: a comparison of two drug delivery systems on assessing drug release performance in vitro

In this study, the different encapsulation methods involving emulsification and coaxial electrospinning were both utilized to fabricate a series of core/sheath composite, nanoparticles (NPs) and Nanofibers (NFs) separately, for drug delivery on potential biological and therapeutic applications. Bovine serum albumin (BSA) was employed as an active pharmaceutical ingredient model for core; poly(L-lactic acid) (PLLA) and methoxy poly(ethyleneglycol)-Poly lactic acid (mPEG-PLA) were selected as the encapsulation matrix for sheath. Attributed to the optimized fabrication procedures, the obtained NPs and NFs had the small average diameters and narrow size distributions with uniform structures and smooth surface morphologies. Based on the drug release profiles, both the NPs provided a burst release process followed by a drug diffusion manner, while for the NFs, the drug diffusion was the predominant factor in drug release. In particular, the mPEG-PLA NFs were fabricated with excellent hydrophilicity and highly neutralized surface resulting in a sustained release of BSA over 10 days. In addition, mPEG-PLA NFs also provided a better zero-order drug release profiles during the release time from 8 to 72 h, and a one-dimensional Fickian diffusion pattern during the whole BSA release period. A cytotoxicity study suggested that the two drug delivery systems were both safe to cells. In conclusions, the synergism of PEGylation with coaxial electrospinning may be an effective way to retard the release of drugs in a more sustained manner.

Reducing Benzo(a)pyrene Content of Coal-Tar-Pitch Modified by Styrene-Butadiene Rubber through Dynamic Vulcanization

Coal tar pitch (CTP) mainly consists of polycyclic aromatic hydrocarbons (PAHs), some of which are carcinogenic. Among PAHs, benzo (a) pyrene (BAP) as one of the most prominently reported carcinogens which present in CTP causes the concerns of environmentalists. In this work, CTP was modified by styrene-butadiene rubber (SBR) through dynamic vulcanization. Ultraviolet-visible spectrophotometry (UV-VIS) was used to measure the content of BAP. After SBR modification through dynamic vulcanization, the BAP content have been reduced to 50%. With increasing the content of SBR,the content of BAP further reduced. The light component of the modified CTP decreased by the SBR modifier,verified by Headspace gas chromatography-mass spectrometry (GC-MS). Meanwhile, the SBR modifier has improved physical properties of the CTP, such as softening point, ductility, flowing property at high temperature. When the SBR content reached to 6 from 5.5, the softening point increased dramatically to 99 from 50.5. Thus, the modified CTP has various potential applications such as road pavement and carbon binder.

Formation of Orientation Adhesion and Dendritic Crystal of ZnO Nanocrystallites

In this contribution, the orientation adhesion and dendritic crystals of ZnO nanocrystallites were synthesized by the method of ultrasonic spray pyrolysis. The microstructure was characterized by X-ray diffraction (XRD) and Raman Spectroscopy, the morphological analyses were carried out by Scanning Electron Microscopy (SEM). The growth process and formation mechanism of this unique ZnO nanostructure were theoretically supported by the growth units model of anion coordination-polyhedra (ACP).

Influence of Nucleating Agent on PLLA Crystalline and Mechanical Properties

This paper mainly concerned the effect of nucleating agents CAV101 on PLLA crystalline property. CAV101 was mixed with poly (L-lactic acid) (PLLA) to make PLLA/CAV101 blends, with CAV101 contents of 0, 0.1%, 0.3%, 0.5%, 0.7%, respectively. Mechanical performances, morphology and crystalline properties were investigated by tensile test, WAXD, SEM. The results demonstrated that the tensile strength and elongation of PLLA increased with the increase of CAV101 content and the maximum value at CAV101 of 0.3% and 0.5%, respectively. The crystallinity of PLLA blends CAV101 of 0.1%, 0.3%, 0.5%, 0.7% were 86.58%, 82.43%, 49.01%, 64.00% respectively.The SEM investigation found that the agglomeration of PLLA with the increasing of nucleating agents CAV101 content.

Study on Toughening of the Epoxy

Abstract. The effect of styrene-The effect of hydroxy-terminated polybutadiene liquid rubber (HTPB) and softened agent on the performance of epoxy resin are studied. The mechanical properties of the composites investigated and the toughening mechanism were studied trough the SEM. In the HTPB/epoxy resin composites, the hardness is reduced but the elongation and the shear strength increased . Added 20wt%HTPB, the breaking elongation can be up to 16.19% and the shear strength rise to 13.74MPa. From the images of the SEM, the globular and trumpet-like hole and shear zone can hinder the development of the cracks, thus increasing the toughness of the epoxy resint. In the softened agent/epoxy resin composites, The addition of the softened agent, the breaking elongation and the impact strength have increased. From the images of SEM,we found that ,with the addition of the softened agent ,the single phase structure turns to two-phase structure and the bicontinuous phase and the brittle fracture turns to ductile fracture.

Effect of CTBN on properties of oxide graphene/epoxy resin composites

The effect of liquid carboxyl terminated butadiene acrylonitrile copolymer (CTBN) on the properties of oxide graphene (OG) /epoxy resin (EP) composite has been studied. The results show that oscillations process can greatly increase the tensile strength, shear strength and hardness of the composites, for the compatibility between the EP and the OG can be greatly improved after oscillations. Infra-red analysis shows that CTBN reacts with EP to form ester group. The tensile strength of the EP decrease, and the elongation at break increase, as more and more CTBN added. The tensile strength of the OG/EP composite is 14.37 MPa, while that of CTBN/OG/EP (15/0.001/100) composite is 4.84 MPa.