Fire retardancy of a reactively extruded intumescent flame retardant polyethylene system enhanced by metal chelates

A reactive extrusion technology was adopted to synthesize a flame retardant (ER), based on the esterification of melamine phosphate and pentaerythritol. The ER imparts good flame retardancy and non-dripping for polyethylene (PE) when combined with ammonium polyphosphate to yield an intumescent polyethylene (PE-IFR). The performance of this intumescent system has been enhanced by the addition of small amounts (0.2%) chelated copper(II)salicylaldehyde (CuSA) and salicylaldoxime, (CuSAO). The thermal stabilization and burning behaviour of the flame retardant PE system have been investigated by TGA, LOI, the UL-94 test and cone calorimetry. All formulations studied provide good flame retardant behaviour, with LOI ≥ 27.4 and UL-94 V-0 rating. The onset of decomposition in TGA for flame retarded PE (PE-IFR, PE-IFR-CuSA and PE-IFR-CuSAO) commences at lower temperature than that of PE with release of blowing agent, but continues to a higher temperature, leaving a greater residue. Significant differences have been observed in burning behaviour using cone calorimetry, between flame retarded PE (PE-IFR, PE-IFR-CuSA and PE-IFR-CuSAO) and PE, showing decreases in HRR, PHRR, MLR, FIGRA and CO emission.     

Preparation and flammability of a novel intumescent flame-retardant poly(ethylene-co-vinyl acetate) system

A phosphorus-containing flame retardant, 4-(5,5-dimethyl-2-oxo-1,3,2-dioxaphosphorinan-2-yloxymethyl)-2,6,7-trioxa-1-phospha-bicyclo[2.2.2]octane-1-oxide (MOPO), was synthesized successfully and characterized. The flame retardancy and thermal behavior of a new intumescent flame-retardant (IFR) system for EVA, which was made of MOPO and ammonium polyphosphate (APP), were investigated by limiting oxygen index (LOI) test, vertical burning test (UL-94), cone calorimeter, and thermogravimetric analysis (TGA). An LOI value of 28.4 and UL-94 V-0 rating can be achieved when the total loading of MOPO and APP was 30 wt.%. The results from cone calorimeter indicate that both the heat release rate (HRR) and the total heat release (THR) of IFR-EVA decreased significantly compared with those of neat EVA. TG curves showed that the amount of residues increased significantly when intumescent additives were added; it also could be found that the LOI values increased with the increase in char residues. Meanwhile, morphology of the residues obtained from burning IFR-EVA in LOI test was studied through the SEM observations and rich compact char layers could explain the excellent flame retardance.     

Synergistic effect of ammonium polyphosphate and layered double hydroxide on flame retardant properties of poly(vinyl alcohol)

A novel flame retardant system of poly(vinyl alcohol) (PVA) is prepared via using ammonium polyphosphate (APP) and layered double hydroxide (LDH). The flammability of PVA composites containing APP-based LDH at a 15 wt.% global percentage showed that the flame retardancy of all PVA/APP/LDH samples increase with the increase of LDH concentration in the range of 0.1-1.0 wt.%, and reach a LOI value of up to 33 and UL-94 V-0 rating for most composites. Thermo-gravimetric analysis reveals that PVA/APP/LDH samples show higher initial decomposition temperature in comparison with PVA/APP composite. The morphology and structures of residues generated during LOI test were investigated by scanning electronic microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the composition of the residue formed after thermo-oxidation to support a fundamental analysis for the mechanism of char formation. The test of mechanical properties demonstrated that LDH can enhance tensile strength, Young's modulus and elongation at break of PVA/APP composites.     

Synthesis and characterization of new flame-retardant microspheres by dispersion polymerization of pentabromobenzyl acrylate

New flame-retardant nano/micro particles of sizes ranging between 0.06 ± 0.01 and 1.70 ± 0.23 μm were formed by dispersion polymerization of the pentabromobenzyl acrylate monomer (PBBA) in methyl ethyl ketone as a continuous phase. The effect of various polymerization parameters, e.g., monomer concentration, initiator type and concentration, stabilizer concentration and crosslinker monomer concentration, on the size, size distribution and polymerization yield of the produced poly(pentabromobenzyl acrylate) particles has been elucidated. Poly(pentabromobenzyl acrylate)/polystyrene (PPBBA/PS) nano/micro blends of the contents of different PPBBA particles were prepared by mixing the PPBBA particles with a PS solution in methylene chloride, followed by evaporation of the methylene chloride from the mixture. The thermal stability of these blends was also studied.     

Preparation of Poly(vinyl alcohol) Microspheres Based on Droplet Microfluidic Technology

A new method for preparing poly (vinyl alcohol) (PVA) microspheres was developed by using droplet microfluidic technology. In the microfluidic chip, a large number of uniform, monodispersed PVA droplets were prepared quickly and continuously by using droplet formation technology, and the droplet preparation speed reached 7 per second. The size of the PVA droplets could be controlled by changing the injection flow rate of the two-phase fluid and the width of microfluidic channel. Then the PVA microspheres were formed by physical crosslinking. This method has high preparation efficiency and good monodispersity of the obtained microspheres. Moreover, the process does not require the incorporation of chemical crosslinking agents, avoiding interference with the inclusion material, and is well suited for applications such as drug carrier.     

Multilayer poly(vinyl alcohol)-adsorbed coating on poly(dimethylsiloxane) microfluidic chips for biopolymer separation

A poly(dimethylsiloxane) (PDMS) microfluidic chip surface was modified by multilayer-adsorbed and heat-immobilized poly(vinyl alcohol) (PVA) after oxygen plasma treatment. The reflection absorption infrared spectrum (RAIRS) showed that 88% hydrolyzed PVA adsorbed more strongly than 100% hydrolyzed one on the oxygen plasma-pretreated PDMS surface, and they all had little adsorption on original PDMS surface. Repeating the coating procedure three times was found to produce the most robust and effective coating. PVA coating converted the original PDMS surface from a hydrophobic one into a hydrophilic surface, and suppressed electroosmotic flow (EOF) in the range of pH 3-11. More than 1,000,000 plates/m and baseline resolution were obtained for separation of fluorescently labeled basic proteins (lysozyme, ribonuclease B). Fluorescently labeled acidic proteins (bovine serum albumin, beta-lactoglobulin) and fragments of dsDNA phiX174 RF/HaeIII were also separated satisfactorily in the three-layer 88% PVA-coated PDMS microchip. Good separation of basic proteins was obtained for about 70 consecutive runs.     

A novel intumescent flame retardant: Synthesis and application in ABS copolymer

A novel phosphorous-nitrogen structure containing intumescent flame retardant, poly(4,4-diaminodiphenyl methane spirocyclic pentaerythritol bisphosphonate) (PDSPB) was synthesized and characterized. Thermal stability and flammability properties of ABS/PDSPB composites were investigated by thermogravimetric analysis (TGA) and cone calorimeter test, respectively. The results showed that the addition of PDSPB enhanced the thermal stability and flame retardancy of ABS significantly. The weight of residues improved greatly with the addition of PDSPB. FTIR and SEM investigations revealed that the residual chars contain polyphosphoric or phosphoric acid, which plays an important role in the process of carbonization. The intumescent chars formed from PDSPB and ABS/PDSPB composites were intact, multicellular and strong. It is confirmed that the char structure was a critical factor for flame retardancy of ABS resin.     

Flammability performance of poly(vinyl alcohol) nanocomposites with zirconium phosphate and layered silicates

Nanocomposites of poly(vinyl alcohol) with α-type zirconium phosphate (PVA/ZrP) and with layered silicates (montmorillonite and hectorite) were prepared by solution blending. Thermal properties and flame retardancy of the materials were characterized by thermogravimetric analysis and microscale combustion calorimetry. PVA/ZrP nanocomposite showed a faster charring process in temperature range between 200 and 350 °C but higher thermal stability and greater char yields above 350 °C and a different heat release rate feature, compared to clay-based samples. Observation of the micrographs of the chars from the nanocomposites present two distinct structures; one constituted by the stacked clay layers on the surface combined with clay-reinforced foams in the interior residue, and the other formed by carbon covered on the tightly curled ZrP nanoplatelets. The results indicated different flame retardant mechanisms of the two nanocomposites, which depend on the chemical/physical effects from the inherent properties of the nanofillers.     

Preparation of poly(vinyl pivalate) microspheres by dispersion polymerization in an ionic liquid and saponification for the preparation of poly(vinyl alcohol) with high syndiotacticity

We report here a successful free-radical dispersion polymerization of vinyl pivalate (VPi) in an ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][TFSI]) using poly(vinyl pyrrolidone) (PVP) as a stabilizer. Morphological analysis by FE-SEM revealed that poly(vinyl pivalate) (PVPi) obtained from dispersion polymerizations were in the form of spherical particles. Micron-sized, PVPi particles with a number-average molecular weight (M_n) of 166,400 g/mol could be obtained using 5% stabilizer (w/w to monomer) at 65 °C for 20 h. The effects of varying concentration of stabilizer, initiator and monomer upon polymer yield, molecular weight, and morphology of PVPi were also investigated. Analogous polymerizations in dimethyl sulfoxide (DMSO) and bulk served as references. In addition, the preparation of poly(vinyl alcohol) (PVA) by saponification of the resultant PVPi was described.     

聚乙烯醇-碘复合物在水溶液中的形成

聚乙烯醇(PVA)在碘-碘化钾混合水溶液中能形成蓝色复合物,该复合材料在人们日常生活中已广泛应用.本文综述了在稀溶液条件下聚乙烯醇-碘复合物的形成,并对其复合物形成的可能影响因素,如:PVA的分子量、链结构的规整度、1,2-羟基结构、支链以及浓度、添加其它物质和反应时间等,进行了系统论述.从聚集模型观点看,在复合物中,碘主要是以线性多聚碘负离子形式存在的,如:T3-和I5-等;而PVA链通过分子间氢键作用形成链间聚集将多聚碘负离子包裹在内而形成复合物.     

Poly(vinyl alcohol)/GO-MMT nanocomposites: Preparation,structure and properties

A facile, efficient and environment friendly method is established to prepare poly(vinyl alcohol)(PVA) based graphene oxide-montmorillonite(GO-MMT) nanocomposites in aqueous media. GO-MMT nanohybrid is obtained by the combination of GO and MMT in water without any reducing or stabilizing agents. The formation of GO-MMT nanohybrid is due to the hydrogen bonding and crosslinking effects. The sodium ions within MMT sheets act as crosslinkers between GO sheets and MMT platelets. The resultant nanocomposites are characterized by means of X-ray diffraction(XRD), scanning electron microscopy(SEM), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA) and mechanical testing. Compared to that of pure PVA, PVA nanocomposites show enhanced thermal stabilities and mechanical properties, which results from strong interfacial adhesion of the nanoadditives in PVA matrix. The further increase in the tensile strength and modulus results from strong interaction between PVA chains and layered GO-MMT as well as good mechanical properties of GO-MMT hybrid, compared to PVA/GO and PVA/MMT nanocompsoites.     

与基板间相互作用对聚乙烯醇水凝胶摩擦行为的影响

选择分别与聚乙烯醇(PVA)水凝胶具有较强和较弱相互作用的基板, 研究水介质中PVA水凝胶在其表面的摩擦行为. 结果表明, 与具有弱相互作用的凝胶-玻璃板体系相比, 具有强相互作用的凝胶-铝板体系的摩擦力(f)较高, 且其粘弹-流体润滑转变速率(vf)较大, 用吸附-排斥模型对其进行了分析. 当滑动速率v相似文献   

Transport of water in polyvinyl alcohol films: Effect of thermal treatment and chemical crosslinking

Data on sorption and transport of water in polyvinyl alcohol films, modified by thermal treatment above T_g, or by chemical crosslinking with glutaraldehyde at different crosslinking degrees, are presented. Equilibrium swelling is constrained by both treatments, except for low degrees of crosslinking where the said reduction is counterbalanced by the partial loss of crystallinity. Analysis of the resulting water uptake kinetics indicates that viscous relaxation effects are, at least partly, responsible for the observed non-Fickian kinetic behavior. Thermodynamic diffusion coefficients of water, D_W, and relaxation frequencies of the swelling polymer, β_W, are determined by application of a theoretical model accounting for relaxation-dependent sorption kinetics in glassy polymers. The results indicate that the effect of both heat-treatment and chemical crosslinking is more intense on the macromolecular relaxation process than on the diffusion coefficient of water. Comparison of the release kinetics of a model drug from as-prepared, non-crosslinked and from crosslinked matrices indicate that the retardation of macromolecular relaxations process induced by crosslinking results in a more uniform release rate.     

CE of poly(amidoamine) succinamic acid dendrimers using a poly(vinyl alcohol)-coated capillary

Various generations (G1-G8) of negatively charged poly(amidoamine) (PAMAM) succinamic acid dendrimers (PAMAM-SAH) were analyzed by CE using a poly(vinyl alcohol)-coated capillary. Due to its excellent stability and osmotic flow-shielding effect, highly reproducible migration times were achieved for all generations of dendrimer (e.g., RSD for the migration times of G5 dendrimer was 0.6%). We also observed a reverse trend in migration times for the PAMAM-SAH dendrimers (i.e., higher generations migrated faster than lower generation dendrimers) compared to amine-terminated PAMAM dendrimers reported in the literature. This reversal in migration times was attributed to the difference in counterion binding around these negatively charged dendrimers. This reverse trend allowed a generational separation for lower generation (G1-G3) dendrimers. However, a sufficient resolution for the migration peaks of higher generations (G4-G5) in a mixture could not be achieved. This could be due to their nearly identical charge/mass ratio and dense molecular conformations. In addition, we show that dye-functionalized PAMAM-SAH dendrimers can also be analyzed with high reproducibility using this method.     

Crosslinking of poly(vinyl alcohol) using functionalized gold nanoparticles

We report on the preparation of a new class of polymer hydrogels obtained through the chemical crosslinking reaction of poly(vinyl alcohol) (PVA) and functionalized gold nanoparticles. Carboxylic group functionalized gold nanoparticles were synthesized, dispersed in a PVA matrix and allow to react with the hydroxyl groups of PVA at high temperature. FT-IR and swelling experiments carried out on the cross-linked samples confirmed that the crosslinking reaction took place. This is the first time, to our knowledge, that functionalized nanoparticles are used as chemical crosslinking agents.     

Electrospinning and characterization of medium-molecular-weight poly(vinyl alcohol)/high-molecular-weight poly(vinyl alcohol)/montmorillonite nanofibers

Submicron fibers of medium-molecular-weight poly(vinyl alcohol) (MMW-PVA), high-molecular-weight poly(vinyl alcohol) (HMW-PVA), and montmorillonite clay (MMT) in aqueous solutions were prepared by electrospinning technique. The effect of HMW-PVA and MMT on the morphology and mechanical properties of the MMW-PVA/HMW-PVA/MMT nanofibers were investigated for the first time. Scanning electron microscopy, viscometer, tensile strength testing machine, thermal gravimetric analyzer (TGA), and transmission electron microscopy (TEM) were utilized to characterize the PVA/MMT nanofibers morphology and properties. The MMW-PVA/HMW-PVA ratios and MMT concentration played important roles in nanofiber's properties. TEM data demonstrated that exfoliated MMT layers were well distributed within nanofibers. It was also found that the mechanical property and thermal stability were increased with HMW-PVA and MMT contents.     

Morphology assessment of chemically modified cryostructured poly(vinyl alcohol) hydrogel

The morphology of hydrogels based on poly(vinyl alcohol) (PVA) in their frozen hydrated state, modified with biologically active di- and multifunctional molecules was studied by scanning electron microscopy (SEM) with cryo-attachment. The porosity of samples was found to be more regular and ordered in the case of samples containing difunctional, and especially multifunctional carboxylic acids as compared to the neat PVA hydrogel. The morphology is dependent not only from the hydrogel composition but also the number of freezing-thawing cycles. Resulted highly porous and oriented structure has significant influence on materials properties, such as compressive stress and crosslinking density.     

Morphology and structure of highly elastic poly(vinyl alcohol) hydrogel prepared by repeated freezing-and-melting

Morphology and structure of poly(vinyl alcohol) (PVA) hydrogel prepared by the repeated freezing-and-melting method have been investigated by X-ray diffraction, scanning electron microscopy, light-optical microscopy, and simple tension test. The PVA aqueous solution gelled highly by using this method to show rubber-like elasticity, reflecting the gel network in which the amorphous chains are physically cross-linked by the crystallites. The gel morphology was characterized by the porous structure, which was originated from the gelation of continuous PVA-rich solution phase segregated around copious ice crystal phases formed upon freezing. The high gelling ability involved in this method was closely related to the segregation mechanism.     

DNA capillary electrophoresis using poly(vinyl alcohol). I. Inner capillary coating

Two new methods of inner capillary coating with poly(vinyl alcohol) (PVAL) have been investigated and evaluated by performing DNA capillary electrophoresis (CE) using PVAL as a separation medium and by measuring the electroosmotic flow (EOF) mobility. The treatment of capillaries with a silanol-group modified PVAL (PVAL-Si) has been found to give good coating effects for improving the resolution of DNA CE and for reducing the EOF. This coating must be effectively achieved by combining the adsorptive property of PVAL chains onto silica with the reaction between the silanol groups of PVAL-Si and the silica surface. The adsorption of PVAL onto silica has been observed by using atomic force microscopy (AFM) for PVAL-Si as well as for a nonmodified PVAL as a control. The coating with PVAL that links to the capillary wall surface with more hydrolytically stable bonding, -Si-C-, has been formed by performing the Grignard reaction, followed by in-capillary polymerization of vinyl acetate (VAc) and hydrolysis. This coating has been found to be effective for improving the resolution of DNA CE and for reducing the EOF.