Pressure control system for electrospinning process

Electrospinning is used to produce micro‐ and nano‐sized synthetic fibers through the use of electrostatic forces. Commercially, viable production of fibers requires high throughput of uniform fibers that are free of defects. To achieve greater control over the process variables that affect the fiber formation, a scalable closed loop control system that can maintain a constant pressure at the capillary tip was designed and tested. Two sensing technologies, infrared and ultrasonic, were used and compared for their ability to detect the height of polymer solution in the electrospinning fluid container. The air pressure above the solution was measured with a pressure transducer and adjusted through a controllable syringe pump. The closed loop electrospinning system was successful at controlling and maintaining a constant pressure at the capillary tip to within 2% of the specified pressure continuously. The controlled pressure at the capillary tip showed a strong correlation to fiber diameter and uniformity for polydimethylsiloxane‐based polyurethane/DMF‐based fibers. However the control system was less effective to control fiber diameter for polyethylene oxide/Water‐based fibers. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Impact of electrospinning process parameters on the measured current and fiber diameter

In this article, polycaprolactone (PCL) nanofibres were processed by electrospinning using a 3:1 ratio of tetrahydrofuran to methanol as solvent. The solvent choice was motivated by the possibility of greener alternatives to the halogenated compounds most often used for electrospinning. The morphologies and fiber diameters resulting from the electrospinning of PCL solutions at room temperature under various conditions are presented in this article. The material morphology was characterized using scanning electron microscopy and a measuring software. The process was optimized for smaller fibers with a narrower fiber diameter distribution by studying parameters such as polymer concentration, applied voltage, the tip to collector distance (TCD), and the solution flow rate. A comparison analysis was used to separate the current resulting from whipping and that resulting from spraying at high voltage. The fiber diameters obtained under various processing conditions were effectively modeled using the terminal jet theory, referenced in several works. Process parameters were optimal for a 20% PCL concentration spun at a flow rate of 0.5 mL/h, with a TCD of 15 cm and an applied voltage of 8 kV. Fibers spun under these conditions displayed diameters of 546 ± 173 nm. POLYM. ENG. SCI., 55:2576–2582, 2015. © 2015 Society of Plastics Engineers     

静电纺丝技术的研究进展

介绍了静电纺丝工艺的历史发展背景;详细分析了静电纺丝工艺的影响因素,包括实验装置、聚合物及其溶液的性能以及加工艺条件等;指出静电纺丝是制备连续微/纳米纤维的最有效的方法,并有望应用于组织工程、人造血管、药物传递、创伤修复、病毒检测、微型传感器以及滤材等。     

Garland formation process in electrospinning

The electrospinning technique has become a widely used method to produce nanofibers. Much experimental and theoretical work has been done to investigate the electrospinning process. A typical path of a single jet of polymer solution begins with a straight segment, and then a bending instability generates coils inside a cone shaped envelope. The jet elongates and becomes thinner, and dries into a nanofiber.Polystyrene solutions with different salt concentrations were electrospun to investigate the effect of changing the electrical conductivity on the fibers that were formed. Salt increased the conductivity of the solution and smooth fibers formed. Electrospinning a polystyrene solution with salt, at relatively high voltage, caused the jet to first form bending coils with small and slowly increasing diameters. These small diameter coils were subsequently incorporated into a larger diameter bending instability coil. That is, a coil with a slender envelope cone developed first and this slender coil formed a larger bending coil with a more rapidly increasing diameter. This unusual situation produced a complicated jet path, which is called a “garland”. The coils entangled and conglutinated in flight to form a fluffy network of fibers. The conditions for the formation of garlands also provide examples of jet splitting and branching during the electrospinning process.     

静电纺丝的研究进展

简述了国内外静电纺丝的研究现状;介绍了静电纺丝的制备原理、静电纺丝装置的改进、影响纤维成形的主要工艺参数及纤维形态;叙述了静电纺丝纳米纤维在过滤材料、生物医学和传感器等方面的应用;展望了静电纺丝的发展方向。指出静电纺丝是纳米纤维的新型生产技术,今后应进一步调整静电纺丝工艺,开发绿色溶剂,以尽早实现静电纺丝的工业化。     

静电纺丝过程中的非稳定性研究

通过静电纺聚丙烯腈纳米纤维,研究了静电纺丝过程中的非稳定性。结果表明:静电纺丝电压和接受距离是影响静电纺丝过程中的非稳定性因素,电压和接受距离增大,纳米纤维摆动加大,电压增加到一定量后,纳米纤维的摆幅在一定范围内,不会无限扩大,趋于一个固定值,接收距离超过一定范围后,纳米纤维出现不规则扰动,出现彼此缠绕。     

干喷湿法静电纺丝研究进展

介绍了干喷湿法静电纺丝原理;分析了干喷湿法静电纺丝与干法静电纺丝的区别;综述了干喷湿法静电纺丝在制备纤维素、聚苯胺、聚己内酯等超细纤维中的应用研究进展。指出干喷湿法静电纺丝主要适用于不易挥发性溶剂;干喷湿法静电纺丝应进一步改进静电纺丝收集方法或设备,控制适宜的工艺参数,可得到纳米纤维。同时,要加强产业化方面的研发工作。     

离子液体在静电纺丝中的应用

概述了室温离子液体的特性;介绍了离子液体在静电纺丝及其他方面的应用,详述了纤维素和聚间苯二甲酰间苯二胺的离子液体的静电纺丝;指出离子液体将成为静电纺丝非常重要的溶剂,开发能够溶解各种高聚物的离子液体,探索其溶解的高聚物的静电纺丝条件是今后的研究方向。     

Allometric scaling for voltage and current in electrospinning

Electrospinning is a simple method used in the preparation of polymer fibers, the diameter of the electrospun fibers, varying in large from micrometer to nanometer, mainly depends upon the electrical field applied. The non-linear relation between the current of charged jet and the applied voltage is an intriguing and enduring problem. An allometric scaling relation between the current and voltage is obtained. He Chengtian's inequality, which has millennia history, is applied.     

Optimizing the process of forest fertilization as a control system

We propose a new method for determining optimal fertilization strategies for tree plantations. The method is based on principles of Control Theory and basically consists in evaluating approximately the equations governing the dynamics of the system fertilizer-tree, and then applying optimization techniques adapted to additive cost functions. We describe the procedure as used in a real experiment withEucalyptus rostrata. The main advantage of the method lies in the possibility of taking into account sequences of potentially different amounts of fertilizer added at different times. The results are interpreted as recommendations about when and how much fertilizer should be applied to a similar plantation in order to maximize profit.

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Resumen Proponemos un método nuevo para encontrar estrategias óptimas de fertilización en bosques implantados. El método se funda en principios de Teoría de Control, y básicamente consiste en determinar aproximadamente las ecuaciones que gobiernan la dinámica del sistema árbol-fertilizante, y luego aplicar técnicas usuales de optimización para costos aditivos. Describimos el procedimiento mediante un experimento real con ejemplares deEucalyptus rostrata. La ventaja principal del método consiste en la posibilidad de tomar en cuenta sucesiones de aplicaciones de fertilizantes que puedan ser distintas en magnitud y también efectivizadas en momentos distintos. Los resultados producen recomendaciones sobre cuándo y cuánto fertilizante debería aplicarse en una plantación similar para maximizar las ganancias globales.

     

熔体静电纺丝技术及其在生物医学中的应用

熔体静电纺丝技术不使用溶剂,可制备连续的超细纤维,在生物医学领域有着广泛的应用。从流体黏度、射流特点、纤维直径、纺丝效果方面比较了熔体静电纺丝与溶液静电纺丝的差异;介绍了近年来熔体静电纺丝的技术进展,如激光加热熔体静电纺丝技术、同轴熔体静电纺丝技术,以及熔体静电纺丝直写技术等;综述了熔体静电纺丝技术在组织工程、伤口敷料和药物释放方面的应用;指出熔体静电纺丝应进一步优化加工工艺,获得具有适度自粘结结构的支架,从而提高其应用性。     

Evaluation of optimisation techniques and control variable formulations for a batch cooling crystallization process

The mathematical optimisation of a batch cooling crystallization process is considered in this work. The objective is to minimize the standard deviation of the final crystal size distribution (CSD), which is an important feature in many industrial processes. The results with the problem written as a nonlinear programming and solved with the successive quadratic programming (SQP) coupled with the discretization of the control variable are compared with those obtained when SQP coupled with the parameterisation of the control variable is applied. Also it is proposed the implementation of the genetic algorithm (GA) coupled with parameterisation of the control variable. Extensive evaluations show that the SQP method is sensitive both to the parameterisation formulation and to the initial estimate. The solution with GA provided the control variable profile that leads to the minimum standard deviation of the final CSD. Nevertheless, it is a very time-consuming technique, which hampers its utilization in real time applications. However, its feature of global searching suggests its suitability in solving offline problems, in order to provide initial setup profiles. Bearing this in mind, it is proposed an algorithm which allows for the implementation of GA solution in a real time fashion, taking advantage of its robustness to find out the optimal solution.     

Profitability as a criterion of batch process control design

Batch processes have in some cases many advantages in comparison with continuous processes even though continuous processes are becoming common.

The main disadvantages of batch processes are the discontinuous usage of raw materials and energy as well as the discontinuous production thus causing difficulties in power plant and other continuous processes connected with the batch process in question. If there are several parallel process units, difficulties can arise with parallel process unit sequencing and product quality equalization. However, with the aid of computer control these and other disadvantages are eliminated or minimized so that total automation of batch processes is possible.

In this paper the basic principles of batch process control design are considered, with particular emphasis on the economic justification criterion. As an example, a computer control design of sulphate batch digesters is considered. This approach is based on more than 20 implementations of batch process automation.     

强化生产过程控制降低直流电消耗

通过对隔膜法烧碱生产过程各项工艺指标控制和加强管理,延长电解槽使用周期,提高隔膜法烧碱生产的电流效率,降低直流电耗,以达到节能降耗的目的。     

An applicable electrospinning process for fabricating a mechanically improved nanofiber mat

Engineered polymer scaffolds play an important role in tissue engineering. An ideal scaffold should have good mechanical properties and provide a biologically functional implant site. Considering their large surface area and high porosity, nanofibers have good potential as biomimetic scaffolds. However, the main shortcomings of scaffolds consisting of nanofibers are their mechanical inability to sustain a stress environment for neotissues and shape‐ability to form a variety of shapes and sizes. In this study, we produced design‐based poly (ε‐carprolactone) (PCL) nanofiber mats using an electrospinning method with various auxiliary electrodes and an x‐y moving system. To achieve stable initial solution at a nozzle tip of the electrospinning, various types of auxiliary electrodes were introduced. To characterize the effect of the electrodes in the electric‐field distribution near the nozzle tip, we calculated the electric field concentration factor and compared it with the experimental results. The nanofiber mat produced using the moving x‐y target system demonstrated orthotropic mechanical properties due to the fiber orientation, and human dermal fibroblasts seeded on the structure tended to grow according to nanofiber orientation. POLYM. ENG. SCI., 47:707–712, 2007. © 2007 Society of Plastics Engineers.     

流动电流检测仪在混凝过程控制中的应用

采用流动电流检测法就能准确反映混凝效果。经过实践应用比较,以此建立的混凝投加自动控制系统能做到检测、投加量调节与原水水量、水质变化同步,并取得满意效果。     

Chitin and chitosan: Transformations due to the electrospinning process

Electrospinning is a complex process that requires numerous interacting physical instabilities. Assuming that a chosen polymer and solvent system can be spun, the chosen polymer exists in various states, which have variable crystallinities starting with the highest degree of crystallinity (when in bulk form) and ultimately being transformed into a non‐woven mat. In an effort to better understand the effects that the electrospinning process has on the biopolymers chitin [practical grade (PG)] and chitosan [PG and medium molecular weight (MMW)], including post‐production neutralization and cross‐linking steps, field emission scanning electron microscopy (FESEM) and solubility studies were performed. An evaluation of diffraction peaks of the bulk, solution, and fibrous forms of chitin and chitosan were evaluated by X‐ray diffraction (XRD) and determined that the formation of chitosan chains is influenced by the addition of solvent and cross‐linking agent. This study is of importance since the crystallinity of chitin and chitosan directly relate to the ability of the biopolymers to chelate metals, and the chemical stability of non‐woven mats aid in the creation of functional filtration membranes. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers