Wenhong Ruan

Studies on the transformation process of PVDF from α to β phase by stretching

Poly(vinylidene fluoride) (PVDF) has excellent pyro- and piezoelectric properties which are related to the β-crystal of PVDF. Most of the β-crystal of PVDF can be transformed from the α-crystal by mechanical stretching. The effects of stretching conditions on the transformation from α to β phase of PVDF were studied in this paper. In addition, changes of crystalline structure of PVDF during the stretching process were observed in situ under an optical tensile stress microscopy tester, and the samples after being stretched were investigated using a 3D digital microscope and an infrared microscope. The results show that stretching temperature (Ts) and drawing ratio (λ) are critical to the transformation from α-crystal to β-crystal of PVDF. The Ts around 100 °C and λ above 3 is recommended. The in situ observation indicates that the deformation of crystalline structure began from the middle of α-spherulite and extended to another spherulite, and caused the large-scale transformation. Scanning results of infrared microspectroscopic and 3D digital microscopy revealed that α phase of PVDF would change into β phase with the deformation of the spherulite, and the distribution of the different crystalline phase in PVDF after being stretched was also given. It is believed that this work is instructive and meaningful to studies on phase transformation and production of the piezoelectric film of PVDF.

High-water-content graphene oxide/polyvinyl alcohol hydrogel with excellent mechanical properties

In this study, high-water-content boron-cross-linked graphene oxide/polyvinyl alcohol (B-GO/PVA) hydrogels were prepared by a freeze/thaw method and immersion in boric acid solution for boron cross-linking. High-water-content B-GO/PVA hydrogels with a water/polymer mass ratio ranging from 19 : 1 to 49 : 1 (water content 95–98) could be obtained. It is found that a small addition of GO can lead to significant reinforcement of the tensile strength of B-GO/PVA hydrogels with an increase in elongation. Compared to B-PVA hydrogel, a 144% increase of fracture tensile strength is achieved when the content of GO is 0.1 wt% (∼0.609 MPa, water content ∼ 95%). Meanwhile, compression and shear strength (0.1 MPa and 0.201 MPa, water content ∼ 95%) of such hydrogels are increased by 26% and 35%, respectively. A method of acquiring high-water-content PVA hydrogels and the reinforcing mechanism of B-GO/PVA hydrogels are suggested. It is believed that such new high-water-content hydrogels are promising materials in the application of biomedical engineering and polymer electrolytes.

Application of solid-phase microextraction for the determination of organophosphorus pesticides in textiles by gas chromatography with mass spectrometry

A method based on solid-phase microextraction (SPME) and gas chromatography with mass spectrometry (GC/MS) for the determination of 18 organophosphorus pesticides (OPPs) in textiles is described. Commercially available SPME fibers, 100 microm PDMS and 85 microm PA, were compared and 85 microm PA exhibited better performance to the OPPs. Various parameters affecting SPME, including extraction and desorption time, extraction temperature, salinity and pH, were studied. The optimized conditions were: 35 min extraction at 25 degrees C, 5% NaSO4 content, pH 7.0, and 3.5 min desorption in GC injector port at 250 degrees C. The linear ranges of the SPME-GC/MS method were 0.1-500 microg L(-1) for most of the OPPs. The limits of detection (LODs) ranged from 0.01 microg L(-1) (for bromophos-ethyl) to 55 microg L(-1) (for azinphos-methyl) and the RSDs were between 0.66% and 9.22%. The optimized method was then used to analyze 18 OPPs in textile sample, and the determined recoveries were ranged from 76.7% to 126.8%. Moreover, the distribution coefficients of the OPPs between 85 microm PA fiber and simulative sweat solution (K(pa/s)) were determined. The determined K(pa/s) of the OPPs correlated well with their octanol-water partition coefficients (r=0.764 and 0.678) and water solubility (r=-0.892 and -0.863).

Effect of migration of layered nanoparticles during melt blending on the phase morphology of poly (ethylene terephthalate)/polyamide 6/montmorillonite ternary nanocomposites

To study the effect of migration and selective localization of layered nanoparticles during melt compounding on the phase morphology of polymer blends, poly (ethylene terephthalate) (PET)/polyamide 6 (PA6)/organic montmorillonite (OMMT) ternary nanocomposites were prepared. Three different blending sequences were adopted either by pre-compounding OMMT into PET or into PA6 or by mixing all three components together. The morphology and tensile properties of PET/PA6/OMMT nanocomposites were investigated. TEM observation showed that OMMT platelets exclusively localized within the PA6 phase independent of the blending sequences, suggesting OMMT platelets migrated from PET into the PA6 phase during both the one-step and two-step compounding processes with pre-mixed PET/OMMT, and this migration was attributed to interfacial effects. SEM results revealed that the migration and selective localization of OMMT platelets had great influence on the size of the dispersed phase due to the conjunct action of the migration cutting effect and viscosity effect. The morphology determines the final properties of the nanocomposites as indicated by tensile test. It is believed that this work provides a way to tune the morphology and performance of immiscible blends.

Determination of organophosphorus pesticides in ecological textiles by solid-phase microextraction with a siloxane-modified polyurethane acrylic resin fiber

A novel solid-phase microextraction (SPME) fiber coating was prepared with siloxane-modified polyurethane acrylic resin by photo-cured technology. The ratio of two monomers was investigated to obtain good microphase separation structure and better extraction performance. The self-made fiber was then applied to organophosphorus pesticides (OPPs) analysis and several factors, such as extraction/desorption time, extraction temperature, salinity, and pH, were studied. The optimized conditions were: 15 min extraction at 25 °C, 5% Na(2)SO(4) content, pH 7.0 and 4 min desorption in GC inlet. The self-made fiber coating exhibited better extraction efficiency for OPPs, compared with three commercial fiber coatings. Under the optimized conditions, the detection limits of 11 OPPs were from 0.03 μg L(-1) to 0.5 μg L(-1). Good recoveries and repeatabilities were obtained when the method was used to determine OPPs in ecological textile.

A TiO2/PEO composite incorporated with in situ synthesized hyper-branched poly(amine-ester) and its application as a polymer electrolyte

This paper has reported a new polymer nanocomposite of nano-titanium dioxide/polyethylene oxide (TiO2/PEO) incorporated with in situ synthesized hyper-branched poly(amine-ester) (HBPAE) and its application as a polymer electrolyte. Firstly, the HBPAE/HBPAE-g-TiO2/PEO is obtained by synthesizing HBPAE in methyl acrylic acid methyl ester grafted TiO2 (MMA-g-TiO2)/PEO, to simultaneously form the hypergrafted polymer on the nano inclusions (HBPAE-g-TiO2) and hyperbranched particles dispersed in the PEO. Then the Li2SO4 is introduced to prepare the polymer electrolyte, and the relevant structure and properties are studied. It is found that the incorporation of HBPAE into TiO2/PEO can benefit the ionic transportation of the composite electrolyte, and can bridge the nano inclusions which further improves ionic conductivity. The best ionic conductivity of the HBPAE/HBPAE-g-TiO2/PEO polymer electrolyte with 15 wt% TiO2 content can reach as high as 3.2 mS cm−1, which is ∼10 times of that of the PEO electrolyte and ∼28% of that of the HBPAE-g-TiO2/PEO electrolyte without homopolymer component. Furthermore, the optimized polymer electrolyte is assembled into a LiTi2(PO4)3//LiMn2O4 lithium-ion battery, with better excellent cell performance compared with the PEO electrolyte. This study shows that the new polymer nanocomposite has great potential for the assembly of high performance solid electrochemical devices.

A graphene oxide-based polymer composite coating for highly-efficient solid phase microextraction of phenols

Sensitivity and selectivity of the solid phase microextraction (SPME) in analysis are mostly determined by the coating material of the fiber used. Graphene oxide (GO) has attracted great attention because of its large specific surface area, rich oxygen functional groups, good dispersibility in aqueous solution and high reactivity. However, the low thermal stability of the functional groups limits the wide application of GO in SPME coating design. Highly cross-linked polyoxyethylene (POE) is a substrate widely used for composite material construction, which could significantly improve the thermal stability, water resistance as well as biocompatibility of the functional materials. In this study, we incorporated GO with highly cross-linked POE as a novel fiber coating material for SPME through the gluing approach. The obtained fiber possessed a wrinkled shape surface, which could increase the accessible surface area. In addition, the thermal and chemical stability of the fiber coating were also improved, rendering the fiber rigid enough for more than 100 repetitive extraction cycles. The performance of this developed SPME method for phenols was evaluated by headspace extraction of phenols in aqueous samples. Compared with three commercial fibers, the home-made fiber showed excellent extraction efficiencies towards phenols. Under the optimized conditions, it showed low detection limits (0.12-1.36 ng· L-1), good precision (<8.4%), good fiber-to-fiber repeatability (3.1%-8.1%), wide linear range (almost 5-1000 ng·L-1and correlation coefficients (R2) >99%), as well as good enrichment efficiencies (enrichment factors (EFs), 172-1752). Furthermore, the method was successfully applied in simultaneous analyses of five phenols for real water samples with satisfactory recoveries (81-113% for the Pearl River samples).