Enhanced airborne sound absorption effect in poly(vinylidene fluoride)/(K0.5Na0.5)NbO3-nanofiber composite foams

Introducing electrical conductive function to discharge local piezoelectric effect is found effective for improving airborne sound absorption performance. In this work, instead of conductive fillers, a composite with two piezoelectric materials with opposite piezoelectric responses was explored aiming at enhanced sound absorption effect. Open-cell poly(vinylidene fluoride)/(K_0.5Na_0.5)NbO₃ (PVDF/KNN)-nanofiber composite foams were proposed and investigated for airborne sound absorption purpose. Structural and thermal analyses showed that the KNN nanofibers were well dispersed in the PVDF matrix and enhanced the degree of crystallinity of polar phase of PVDF. Significantly enhanced airborne sound absorption over a broad frequency range was observed in the PVDF/KNN-nanofiber composite foams, with increasing KNN nanofibers. One possible mechanism for the improved sound absorption with the piezoelectric KNN nanofibers with positive piezoelectric coefficient added in the PVDF matrix with negative piezoelectric coefficient is that electrical discharge could be facilitated for energy dissipation with the opposite charges generated through the piezoelectric effects in the two phases with opposite polarity. The experimental results show that the open-cell PVDF/KNN-nanofiber composite foams are promising for broadband airborne sound absorption application, and our analysis shed a light on the strategy in designing piezoelectric composite foam with high sound absorption performance.     

A void surface flame retardant strategy for polymeric polyHIPEs

Effective flame retardant strategy for open-cell foam (e.g., polyHIPE) remains of a great challenge. Herein, a void surface flame retardant strategy for polyHIPE was presented. An open-cell polystyrene (PS) polyHIPE was fabricated through an emulsion-templating technique. Polyphosphazene (PSZ), a highly efficient flame retardant polymer, was then in situ fabricated and covalently attached to the void surface of the foam to be a uniform flame retardant protective layer, while the open-cell structure of the foam was perfectly preserved. Compared with the pristine PS polyHIPE, the PSZ modified one had significantly improved thermal stability (char residues yield at 800°C increased from 3.36 to 16.53 wt%) and mechanical properties (Young's modulus increased by 2.6 times); the values of average heat release rate and total heat release of combustion were reduced by 62.36% and 41.57%, respectively. While, the value of limiting oxygen index was increased from 17.39% to 19.75%, owing to the combined action of condensed phase flame retardant and gas phase flame retardant. These results indicate that the in situ surface modification strategy is effective for improving the flame retardancy of highly interconnected polymer foams.     

Particulate-filled glassy polymers

Glass beads, NaCl crystals, or other imperfections act as stress concentrators in glassy polymers causing early crazing upon stressing. Stress–strain curves of glassy thermoplastic polymers filled with uncoupled glass beads or NaCl crystals exhibit a knee, or a slope-discontinuity point. The characteristics of the slope change, related to crazing, are studied in the present work. Foams were produced from the polymer/salt samples by soaking them in water resulting in complete leaching of the salt. This preparation procedure gives open-cell foams and there are strong indications that these polymeric foams have a highly cracked structure formed during the extraction step.     

Mass-scale processing of open-cell metallic foams by pressurized casting method

Here, we report a simple and cost-effective technique for mass-scale processing of open-cell foams of metals and alloys with precise control over foam parameters (pore size, pore distribution, and strut thickness). The process involves pressurized infiltration of molten metals/alloys into salt preforms under 1.5–4 bar inert gas pressure. The preforms were fabricated from spherical particles of different salts, selected on the basis of the melting temperature of the metals/alloys. The porous metallic structures were recovered by leaching out the salt patterns. The working temperature and the applied pressure play the most vital role in determining the foam structure. The developed foams were studied with optical microscope, scanning electron microscope (SEM), and X-ray computed tomography (CT). Mechanical properties of the developed foams evaluated under quasi-static compressive loading are also reported.     

低温下磁性载体强化MBBR硝化性能及微生物群落分析

为了增强生物膜耐寒性，提高低温环境下移动床生物膜反应器（MBBR）硝化性能，本文以投加磁性载体构建新型MBBR反应器（R2），同时以投加商用载体作为对照组（R1），在不同温度（14℃±1℃和9℃±1℃）下长期运行，考察了低温下磁性载体对反应器污染物去除性能和生物膜生长特性的影响，并利用高通量测序技术探究了生物膜微生物的响应关系。结果表明：在整个低温运行阶段（0~60天），R2对COD和氨氮去除效果均优于R1。特别在9℃±1℃时，R1和R2出水氨氮平均浓度分别为11.94mg/L、7.60mg/L，R2对氨氮平均去除率比R1提高了16.2%。低温下，磁性载体明显提高了生物膜硝化活性，并促进了胞外聚合物（EPS）分泌，维持和改善了生物膜的形貌结构。高通量测序结果显示，9℃±1℃下不同载体生物膜的微生物群落结构存在显著差异。两种载体的大多数优势属均能降解有机物；磁性载体富集了更多的硝化菌属，其氨氧化细菌（AOB）和亚硝酸盐氧化细菌（NOB）的相对丰度比商用载体分别提高了1.82倍和1.05倍，并且驯化富集了MND1和Candidatus_Nitrotoga 两种特有硝化菌属。从生物膜特性和硝化菌群丰度的角度解释了两个反应器氨氮去除效果的差异性，表明低温下磁性载体MBBR具有更好的硝化性能，可进一步开发应用。     

Young’s modulus and thermal conductivity of closed-cell,open-cell and inverse ceramic foams – model-based predictions,cross-property predictions and numerical calculations

Numerical calculations of relative Young’s modulus and thermal conductivity have been performed on computer-generated microstructures of wall-based (closed-cell) and strut-based (open-cell) cellular materials (foams) and inverse foams. The results are compared to rigorous upper bounds (Wiener-Paul, Hashin-Shtrikman), model-based predictions (power-law, exponential) and cross-property predictions (CPRs). It is shown that closed-cell foams exhibit higher property values than open-cell and inverse foams, Kelvin foams higher than random foams, and the difference between closed-cell and open-cell foams is larger than that between Kelvin and random foams. While the properties of closed-cell foams are higher than the power-law prediction, those of inverse and open-cell random foams are between the exponential and power-law predictions, and open-cell Kelvin foams follow the Gibson-Ashby power-law prediction for open-cell foams. The Pabst-Gregorová CPR is shown to predict Young’s modulus with accuracy better than ±0.02 relative property units (better than any model-based relation and any other CPR).     

Evaluation of the salt leaching method for the production of ethylene propylene diene monomer rubber foams

The thermomechanical behavior of ethylene propylene diene monomer (EPDM) foams produced with the salt leaching method has been investigated and compared with the behavior of EPDM foams obtained from conventional blowing agents. Moreover, the salt-leaching process has been optimized to minimize salt residues and the influence of different parameters (such as average particle size and particle size distribution) has been investigated. Scanning electron microscopy and density measurements highlighted that salt-leaching leads to the formation of open-cell porosity with cell dimensions of around 60 to 80 μm, while foams obtained with the two traditional foaming agents lead to closed-cell porosity. Compression set values indicate that the behavior of the foams produced with salt leaching are more similar to the unfoamed rubber, characterized by higher elasticity and low residual deformation. Two theoretical models were successfully applied to the compression curves (Mooney-Rivlin and Exponential-Logarithmic) and they highlighted the effect of foaming on the properties of EPDM rubber and in particular the higher chain extensibility obtained through the salt leaching foaming method.     

原位生物膜技术去除水源藻类研究

考察了原位生物膜技术对水源水中藻类的去除率。试验结果表明:原位生物膜技术对藻类具有较好的去除效果,去除率稳定在80%左右;随着水力停留时间的延长,藻类去除率显著增加。对于除藻而言,水力停留时间5h较为合适。生物膜+高锰酸钾联用技术对藻类的去除率进一步提高,当高锰酸钾投量为0.75mg/L时,藻类去除率可以达到90%。试验期间,原位生物膜技术对有机物、氨氮的去除率分别稳定在40%、80%左右。由此可见,在水源水中采用原位生物膜技术是解决水厂除藻问题的一个重要途径。     

不同填料的厌氧氨氧化污泥挂膜性能比较

向厌氧氨氧化反应器内投加填料形成生物膜有利于污泥的持留,然而有关填料本身的不同特点对厌氧氨氧化生物膜生长影响的报道较少。将两种不同密度的悬浮塑料填料和两种不同密度的海绵填料置于同一反应器内,进行厌氧氨氧化污泥的挂膜,结果发现海绵填料的单个填料氨氮平均去除速率和亚硝态氮平均去除速率整体高于悬浮塑料填料,所挂污泥的EPS含量整体也高于悬浮塑料填料,并且挂膜速度也相对较快。在挂膜30 d后,单个小密度海绵填料便可检测出氨氮和亚硝态氮去除速率,且Δ（NO₂^--N）/（NH₄⁺-N）值接近1.32。在挂膜105 d后,单个小密度海绵填料的氨氮平均去除速率为0.123 mg·L^-1·h^-1,亚硝态氮平均去除速率为0.160 mg·L^-1·h^-1,值为1.30,最为接近理论值1.32,厌氧氨氧化活性为最佳,并且其所挂污泥的厌氧氨氧化菌丰度值在4种填料中最大,为1.73×10¹⁰ copies·（g dry sludge）^-1,总体来看小密度海绵填料的挂膜效果更好。     

活性炭生物转盘的制备及处理有机模拟废水

为了寻找一种质轻高效的新型生物转盘盘片材料,实验以活性炭作为生物膜附着的载体,聚丙烯塑料板为基体,采用化学氧化-铁离子覆盖技术制备了活性炭生物转盘盘片。使用该活性炭生物转盘处理有机模拟废水,以COD和NH3—N质量浓度变化为评价指标,借助微生物显微镜观察了挂膜期间微生物的生长过程。结果表明,该盘片具有独特的微生物吸附能力,微生物量达到2.60×109个/g,生物膜干质量为16.909 6 g/m2;在进水初始COD质量浓度为1 000 mg/L、NH3—N质量浓度为100 mg/L左右时,当HRT为12 h时,盘片的有机去除负荷为5.61 g/m2;当循环进水3 d时,COD和NH3—N去除率均在80%以上,该三级生物转盘反应器各级污染物去除率均较高,第1级去除效果最显著,处理后水质达到了国家污水综合排放标准(GB8978-96)的二级标准。     

膜材料对膜曝气生物膜反应器性能影响的比较

选择聚偏氟乙烯(PVDF)和聚丙烯(PP)中空纤维曝气膜作为膜曝气生物膜反应器(MABR)的膜组件材料,比较两种膜材料由于亲疏水性能、表面形态、生物相容性等性质的差别,对MABR挂膜启动速度、生物附着量、脱氮除碳及膜污染等性能的影响。研究显示,运行末期PVDF和PP膜纤维生物附着量分别为35.62 g·m^-2和30.63 g·m^-2。通过场发射扫描电子显微镜观察两种膜表面生物污染情况,PVDF膜纤维表面呈鱼鳞状结构,有效保护了膜孔不被微生物完全堵塞。在90 d的运行周期内以PVDF为曝气膜材料的MABR获得了90%以上的COD去除率和78%的TN去除率;而以PP为曝气膜的MABR由于运行后期曝气膜纤维污染严重仅得到了76.5%的COD去除率和49.1%的TN去除率。因此,PVDF曝气纤维更适于作膜曝气生物膜反应器的曝气膜。     

轻质生物膜陶瓷载体的研制及在废水处理中的应用

选用轻质粘土、硅藻土和蛭石等陶瓷原料,按一定比例进行配方和制作,研制成一种轻质生物膜陶瓷载体,比重仅有1.47g/cm^3,将其用于流化床生物反应器来处理有机废水,在较小的曝气量条件下即可呈现出良好的流态化.本研究重点考察了该载体挂膜特性,并和橡胶材料作对比研究,发现陶瓷载体上的生物膜仅经过一个批次的试验后对COD的去除率就达到80%以上,而橡胶载体上的生物膜却需要5个批次后才达到同样的去除率,同时发现两种载体的表面生成的生物膜群落有差异.经过连续试验发现,陶瓷载体表面的生物膜具有比较好的生物活性.     

Lead ion removal characteristics of poly(lactic acid)/hydroxyapatite composite foams prepared by supercritical CO2 process

We have prepared a series of poly(lactic acid)/hydroxyapatite (PLA/HAp) composite foams by a supercritical CO₂ foaming process and investigated the lead ion (Pb²⁺) removal performances of the foam samples in batch aqueous solutions (foam sample of 5 g, aqueous solution of 500 ml, initial Pb²⁺ ion concentration of 275 mg/l, pH values of 2.0–6.0) at 25°C. It is characterized that the porosity of the foams decreases from 96.3% to 50.3% as the HAp content increases from 0 to 40 wt%, although all the foam samples exhibit well‐developed open porous structures. The maximum capacity of Pb²⁺ ions removed by the composite foams increases from 81.2 to 140.5 mg/g with increasing the HAp content from 10 to 40 wt%, due to the increased adsorption sites of HAp for Pb²⁺ ions. However, the removal kinetic analysis based on the pseudo‐second order model demonstrates that the Pb²⁺ ion removal rate is slightly faster for the composite foams with higher porosity (i.e., lower HAp content). The maximum Pb²⁺ ion removal capacity of a given composite foam increases from 20.2 to 140.5 mg/g with increasing the initial pH value from 2.0 to 5.0 but it decreases slightly to 111.7 mg/g at the initial pH value of 6.0. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Characterization of triple electrospun layers of PVDF for direct contact membrane distillation process

Recently, electrospinning technique was applied successfully to fabricate porous hydrophobic membranes for MD applications. In this work, a novel triple layer configuration with diameter gradient for PVDF nanofiber membranes is proposed, with the objective of to minimize mass transfer resistance and heat loss. In outer layers of these membranes, the minimum concentration of PVDF (20 wt%) was used to produce bead-free nanofibers with thinner diameters and middle layers were composed of thicker nanofibers formed at higher polymer concentrations (21.5-26 wt%). Characterization of prepared membranes was conducted by the measurement of porosity, thickness, liquid entry pressure (LEP), scanning electron microscopy (SEM), contact angle, thermal and mechanical properties. Direct contact membrane distillation performance of fabricated membranes was tested using 42 g/L NaCl as feed solution. Water permeate flux of triple layer membranes (27.8-31.5 kg/m² h) was found to be considerably higher than that obtained from single layer membrane (15.4 kg/m² h), indicating the proposed configuration can effectively improve evaporation efficiency.     

Polyvinylpyrrolidone modified barium zirconate titanate /polyvinylidene fluoride nanocomposites as self-powered sensor

Highly flexible biocompatible nanocomposites comprising of Polyvinylpyrrolidone (PVP) modified Barium Calcium Zirconate Titanate (BCT-BZT) /Polyvinylidene fluoride (PVDF) were fabricated. The crystalline BCT-BZT powders were synthesized by a simple sol-gel method. Rietveld refinement analysis confirmed the coexistence of orthorhombic and tetragonal phase in the synthesized powders. The structural, dielectric and ferroelectric properties of the composites were analysed. Addition of PVP modified BCT-BZT powders was observed to enhance the polar phase in PVDF matrix. The piezoelectric output response as a function of different weight percentage of ceramic powders in the PVDF matrix was investigated. The optimal device with 60?wt% PVP modified BCT-BZT powders exhibited maximum peak to peak voltage of 23?V when tested for harnessing waste biomechanical energy (human hand palm force). The nanogenerator was easily scaled up to 4?×?4?cm and the stored power was utilized for powering fifty five LEDs. The fabricated device is flexible, light- weight and eco-friendly. Therefore, it can be explored as a potential candidate for application as self powered sensor.     

Comparative study of nitrification performances of immobilized cell fluidized bed reactor and contact oxidation biofilm reactor in treating high strength ammonia wastewater

BACKGROUND: The immobilized cell fluidized bed reactor and contact oxidation biofilm reactor are two common choices for high strength ammonia wastewater treatment, however, comparative study of the nitrification performance of the two reactors has not been thoroughly studied. The nitrification performance of the two bioreactors when treating strong synthetic ammonia wastewater was investigated and compared. RESULTS: Results demonstrated that the immobilized cell fluidized bed reactor had a shorter acclimation period, and possessed several advantages over the contact oxidation biofilm reactor, in the form of complete oxidation of 150–360 mg L^?1 ammonia wastewater in a shorter time, higher ammonia removal rates (from 9.6 to 4.32 × 10² mgN L^?1 d^?1) over the temperature range 8 to 32 °C, irrespective of organic load. In contrast, a large reduction in ammonia removal was found in the contact oxidation biofilm reactor with chemical oxygen demand (COD) load. The immobilized cell fluidized bed reactor exhibited stable and high rates of nitrification in the long term. CONCLUSION: These facts demonstrated that the immobilized cell fluidized bed reactor is a suitable selection for high strength ammonia wastewater treatment. Copyright © 2007 Society of Chemical Industry     

Extrusion of polystyrene nanocomposite foams with supercritical CO2

Intercalated and exfoliated polystyrene/nano‐clay composites were prepared by mechanical blending and in situ polymerization respectively. The composites were then foamed by using CO₂ as the foaming agent in an extrusion foaming process. The resulting foam structure is compared with that of pure polystyrene and polystyrene/talc composite. At a screw rotation speed of 10 rpm and a die temperature of 200°C, the addition of a small amount (i.e., 5 wt%) of intercalated nano‐clay greatly reduces cell size from 25.3 to 11.1 μm and increases cell density from 2.7 × 10⁷ to 2.8 × 10⁸ cells/cm³. Once exfoliated, the nanocomposite exhibits the highest cell density (1.5 × 10⁹ cells/cm³) and smallest cell size (4.9 μm) at the same particle concentration. Compared with polystyrene foams, the nanocomposite foams exhibit higher tensile modulus, improved fire retardance, and better barrier property. Combining nanocomposites and the extrusion foaming process provides a new technique for the design and control of cell structure in microcellular foams.     

Nitrification of fertilizer wastewaters in a biofilm reactor

The nitrification characteristics of fertilizer wastes were investigated in a biofilm system using a submerged aerated filter. The attachment of biomass on packing media was studied. Supplement of organic carbon in the form of glucose and yeast extract enhanced biofilm formation although the nitrifiers did not require organic carbon for growth. After an attachment period, continuous operation of the reactor at different loading rates and dissolved oxygen levels was investigated. The maximum achievable nitrification rate was strongly dependent on the dissolved oxygen. In the dissolved oxygen range of 3·2–3·5 mg dm⁻³, the maximum ammonia removal rate was about 0·17 kg NH₄ N m⁻³ day⁻¹. When the dissolved oxygen was increased to 4·9 mg dm⁻³, removal rates as high as 0·41 kg NH₄ N m⁻³ day⁻¹ could be obtained. Nitrite accumulation depended on the bulk nitrogen and dissolved oxygen concentrations.     

Synthesis and characterization of open‐cell foams for sound absorption with rotational molding method

Foams with open‐cell structures have improved sound absorption abilities over conventional closed‐cell foams. One technique to optimize the acoustic abilities of open‐cell foams is to control their cellular properties through the manipulation of processing parameters. This article presents a novel process to synthesize open‐cell polymeric foams for acoustic applications. The process combined rotational foam molding and particulate leaching to produce foams with open‐cell networks that are desirable for acoustic absorption. Open‐cell foams with open‐porosity of about 0.90 were successfully fabricated with this combined foaming process. Effects of processing parameters on the cellular and acoustic properties of the foam samples were examined and discussed. On the basis of the results from the study, the cellular and acoustic properties of the foam fabricated from the proposed method can be controlled through the use of different salt particle sizes in the process. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

双系统曝气生物滤池处理玉米青贮渗出液

采用双系统改性沸石曝气生物滤池(BAF)反应器对玉米青贮渗出液进行除碳脱氮处理,研究了对COD、氨氮、总氮(TN)的去除效果及其影响因素气水比(流量比)、水力停留时间、有机负荷和回流比。结果表明:挂膜成熟后,沸石生物膜反应器对COD和氨氮有较好的去除效果;挂膜23 d后,COD的去除率可以稳定在70%,氨氮去除率可以稳定在80%以上;当气水比为2∶1,水力停留时间为12 h,生物膜活性达到最高,COD去除率达到83.4%;有机负荷对氨氮去除效果影响较大,有机物质量浓度从160 mg/L提高到280 mg/L时,NH4+-N的去除率由88.6%降为32.7%;回流比对COD、氨氮去除率影响不大,但对TN的去除影响显著,回流比从50%提高到300%,TN去除率从42.3%上升到81.3%。双系统改性沸石BAF反应器明显地改善了玉米青贮渗出液的出水水质。