The effect of interfacial instabilities on the strength of the interface in two-layer plastic structures

We have experimentally investigated the coupling between interfacial instabilities and mechanical interlocking in polymeric films consisting of the incompatible polymer pair of polypropylene/high-density polyethylene and the compatible polymer pair of linear low-density polyethylene/high-density polyethylene. Our experimental results show that mechanical interlocking between the two phases can be achieved by controlling the extent of interfacial instabilities by properly selecting the initial disturbance frequency and amplitude as well as the layer depth ratio. Additionally, it has been shown that strength enhancement of the interface due to mechanical interlocking is directly proportional to the extent of wave bending in the processing apparatus. In fact, it has been demonstrated that in our test geometry maximum strength enhancement can be achieved at dimensionless wavenumbers near unity that correspond to disturbances with the largest growth rates. Overall, it has been shown that mechanical interlocking induced by a controlled amount of interfacial instabilities (i.e., based on knowledge of the stability of the interface and growth/decay rate of interfacial waves) can significantly increase the interfacial strength of two layer polymeric structures consisting of incompatible and compatible polymer pairs. Moreover, this effect is more pronounced in incompatible polymer pairs that possess negligible interfacial strength in absence of mechanical interlocking.     

Operability limits of slide coating

Slide coating is one of the pre-metered methods used for high precision single and multilayer coatings. The thickness of each liquid layers is set by the flow rate and web speed only and it is independent of other process parameters. The uniformity of the deposited layer, however, is affected by the operating conditions. In the design of coating processes, it is crucial to know the set of conditions at which the deposited layer is adequately uniform, i.e. to define the operability window of the process. We developed a theoretical model of slide coating flow by solving the full two-dimensional Navier–Stokes equations and used it to uncover the mechanisms of coating bead breakdown at low vacuum, high vacuum, and low flow limits. With full understanding of the bead breakup processes, we then constructed a theoretical coating window as a function of coating thickness, web speed, and applied vacuum. A simple stability criterion was used to predict the onset of ribbing instability and deployed to add the onset of ribbing limit inside the coating window.     

Rapid coating of millimeter-scale hydrogel capsules with interfacial polymerization

A rapid and mild coating strategy was applied on the millimeter scale calcium alginate capsules (Ca-SA caps) by in situ interfacial polymerization of ethyl cyanoacrylate (ECA). The generated poly(ethyl cyanoacrylate) (PECA) coating was initiated by trace water in the surface of the Ca-SA caps. The effects of ECA content, reaction time, and type of aromatic solvent on the morphology and control-release property of the resulting PECA-coated Ca-SA caps (Ca-SA caps@PECA) were investigated. The results demonstrated a white PECA layer successfully coated on the surface of Ca-SA caps. Notably, the Ca-SA caps@PECA remained consistently pleasing spherical shape as prepared in methylbenzene and ethylbenzene. When the ECA was 6 mL, the thickness of PECA layer of the Ca-SA caps@PECA was 43.52 μm. Compared with the Ca-SA caps, the weight retention ratio of water in the Ca-SA caps@PECA increased by 254.61%, indicating the effective delay of water diffusion from core of the Ca-SA caps@PECA. Moreover, the PECA coating improved the stability of the Ca-SA caps@PECA, which achieved release-controlling of dye at different pH. This method provides solution for surface modification of fragile hydrogel capsules to effectively control the releasing of liquid core, which is highly valuable in the field of food, cosmetic, and medical delivery.     

Transient rise velocity and mass transfer of a single drop with interfacial instabilities - experimental investigations

An experimental study of transient drop rise velocities and mass transfer rates was carried out in the system toluene/acetone/water which is known to show interfacial instabilities. The rise velocity of toluene drops was studied without added solute (acetone) in the diameter range 1-3 mm and with added solute for 2 mm drops. The initial concentration of the transferred solute was varied from 0 to 30 g/L. The transient drop rise velocities were used to quantify the Marangoni effect since the drag coefficient depends on the strength of the Marangoni convection patterns caused by interfacial tension gradients. In addition, mass transfer measurements were carried out in order to determine the modification of the mass transfer rate due to Marangoni convection. Velocity and mass transfer measurements were then correlated via the contact time. Results reveal the existence of a range in which a critical value for the solute concentration can be defined for Marangoni convection.     

Theoretical and experimental analysis of interfacial instabilities in coextrusion flows

Interfacial instabilities developed during two‐layer flows of LDPE melts were investigated theoretically through viscoelastic FEM analysis as well as experimentally on a flat multi‐manifold coextrusion die. During continuous reduction of the minor layer, the wave type appears in the film first whereas the zig‐zag type is only visible later, at the much thinner minor layer, which is an opposite order compared to film blowing coextrusion. Moreover, extensional viscosity of the minor layer was found to play a significant role from the interfacial instability point of view. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 153–162, 2005     

Fluidized bed spray granulation: Investigation of the coating process on a single sphere

The coating and granulation of solid particles in a fluidized bed is a process which converts pumpable and atomizable liquids (solutions, slurries, melts) into granular solids in one step by means of drying. The solution to be processed is sprayed onto a fluidized bed. Particle growth can take place either via surface layering or agglomeration. In the case of surface layering the atomized droplets deposit a thin layer of liquid onto the seed particles. The solvent is then evaporated by the hot fluidizing, leaving behind the dissolved material on the surface. Although fluidized bed spray granulation and film coating have been applied in industry for several years, there is still a lack of understanding of the physical fundamentals and the mechanisms by which spherical granules are formed. Hence a new method was developed which allows the direct observation of the subsequent particle-forming mechanisms such as droplet deposition, spreading, wetting and drying. The authors present a laboratory scale apparatus in which a single freely suspended particle can be coated under well defined and constant coating and drying conditions. With this device, particle-growth-rate and the development of particle morphology were measured and investigated under various experimental conditions.     

滑板涂料的试制和使用

结合国外样品,选择适当成膜材料、基料等研制出低成本滑板涂料,在铜厂试用表明,该涂料具有快干、增强滑板润滑性、防止钢水粘附滑板的作用,提高了滑板的使用寿命。     

Effect of interfacial instabilities and hydrodynamic interaction on liquid-liquid mass transfer

Mass transfer rate between two liquid phases with a plane interface has been studied in a modified Lewis stirred cell. The time interval between the successive concentration determinations was reduced to thirty seconds by the use of a continuous flow refractometer. The mass transfer coefficients were found to correlate satisfactorily with the surface renewal model unless interfacial motion is opposed by the change in physical properties of the system or interfacial shear stresses. Under these conditions Levich-Davies model could successfully explain the experimental mass transfer coefficients found in this work.Due to the effect of the shear stresses and the changes in the physical properties, bulk Reynolds numbers were not sufficient alone to explain the hydrodynamics at the interface which control the mass transfer rate. Instead, another dimensionless quantity such as the ratio of interfacial stresses to kinetic energies of the eddies should be used as a criterion of the hydrodynamics at the interface.     

Controlling interfacial instabilities in PP/EVOH coextruded multilayer films through the surface density of interfacial copolymers

Coextruded polypropylene/tie/ethylene vinyl alcohol/tie/polypropylene (PP/tie/EVOH/tie/PP) films often exhibit optical defects which appear as randomly distributed scattering objects, in the submillimeter range. These defects may strongly affect the film transparency and prevent their practical use in packaging. Based on an objective optical test aimed at quantifying the film transparency, and on a systematic analysis, through optical microscopy, of transverse cuts of films obtained in various coextrusion conditions, the nature of the defects could be identified as resulting from a modulation of the thickness of the inner ethylene vinyl alcohol (EVOH) layer, with no variation in the overall thickness of the multilayer films. Thanks to a recently developed method to dose the surface density of interfacial copolymers, a clear correlation between the amplitude of the thickness modulation of the inner EVOH layer and the density of copolymer molecules formed in situ at the EVOH/tie layer interface during the coextrusion process was established. These results open the way to a better design of tie layers composition to avoid these kinds of defects.     

滑板工作面用耐火涂料的研制

介绍了涂料中复合填料、防氧化剂、悬浮剂、表面活性剂的选择过程及涂料密度与涂层厚度、渗透性的关系。该耐火涂料经过数千套滑板工作面上的喷涂应用,证明具有快干、耐磨蚀、防氧化等特性,提高了滑板的工作性能。     

一种含羧基表面活性剂HDXA界面特性研究

通过系统研究一种含羧基表面活性剂HDXA的界面张力特性,表明在一定条件下,该表面活性剂在0.05%~0.4%的范围内可形成10-3mN/m数量级的超低界面张力,添加剂的加入能使油水界面快速的达到最低界面张力,其中最低界面张力和稳定界面张力值均低于单一表面活性剂体系,活性剂HDXA浓度不同时,最佳添加剂浓度也随之改变。不同活性剂浓度达到最低界面张力及稳态界面张力的时间也不同,随着浓度的增大依次缩短。     

A model for the two-layer blown film process with flow-enhanced crystallization

A 2-D model for non-isothermal bi-layer film blowing is developed based on the 1-D film blowing model of Henrichsen and McHugh [2007a. Analysis of film blowing with flow-enhanced crystallization: part 1. Steady-state behavior. International Polymer Processing XXII (2), 179-189] that accounts for viscoelasticity and flow-enhanced crystallization. Numerical results demonstrate the role of rheological, thermal, and crystallization properties on the development of crystallinity and stresses in a bi-layer system consisting of two crystallizable polymers. For a two-layer film consisting of the same materials, the evolution of the stress in an individual layer can be significantly different due to the temperature difference. Varying the material properties in a given layer, such as the plateau modulus and the maximum crystallization rate, not only leads to the corresponding responses in its own layer, but also influences stresses and crystallinity in the other layer through heat transfer between two layers. Results further demonstrate that stresses in the film after the frost line will be borne primarily by the layer that solidifies first, while the second, molten component will have a tendency to relax. The layer arrangement is also shown to have direct impact on the stresses and semi-crystalline phase orientation at the freeze point which will impact the final properties of the film.     

汽车涂装工艺优化

传统的汽车涂装工艺存在能耗高、生产时间长和污染严重等问题.对汽车涂装工艺进行了优化——将“电泳漆+中涂+面漆”的涂装工艺优化为“电泳漆+面漆”,并在轻型车上进行了验证.试验表明,优化后涂装成本降低,能耗减少,缩短了生产时间,使单台车涂装成本和能耗由原来的242元降到41元,涂膜常规性能满足生产要求.     

Biological treatment of wastewater from a polymer coating process

Wastewater containing propylene glycol methyl ether from a powder and E‐coating plant was treated biologically. The wastewater was circulated through a packed column at rates of 0.014, 0.028, and 0.042 m³ m^?2 s^?1 (14, 28, and 42 kg m^?2 s^?1) with an airflow in a countercurrent direction. Various air flowrates from 0.034 to 0.10 m³ m^?2 s^?1 (0.041–0.12 kg m^?2 s^?1) were used. The removal of the biological oxygen demand (BOD) of the wastewater did not change significantly with the air flowrate. After 4 days of treatment in the packed column the BOD was reduced by about 70% while a BOD reduction of 10% was observed with the wastewater in a stagnant tank. BOD removal with aeration in the packed column was about 40% higher than that without aeration. At the air flowrate of 0.068 m³ m^?2 s^?1 and the liquid flowrate of 0.028 m³ m^?2 s^?1, BOD removal for the wastewater seeded with Polyseed® increased by about 25% compared with that of the unseeded wastewater. In order to minimize the power consumption, cyclic pumping of the liquid to the packed column with aeration was also tested. For the liquid‐pumping cycle of 2‐h on and 4‐h off, BOD removal was about the same as that with a continuously pumping operation. © 2002 Society of Chemical Industry     

双层配碳烧结过程的传热传质分析

为了研究双层配碳下的铁矿石烧结过程及其节能效益,建立了铁矿石烧结过程的二维非稳态数学模型。模型基于多孔介质理论,考虑了烧结过程中的主要物理变化和化学反应,以烧结杯为求解对象,利用FLUENT软件及C语言自定义编程对烧结过程进行了数值模拟,并利用烧结杯实验数据对模型进行了验证。通过对常规均匀配碳和双层非均匀配碳烧结的传热传质过程进行仿真计算,分析了两种烧结方式下床层温度和物料熔化分数分布,并通过熔化分数对烧结矿成品率进行判定。研究结果表明：在不改变整个床层配碳量的条件下,相对于单层均匀配碳,双层配碳条件下热效率更高,床层温度和物料熔化分数沿料层高度分布更加均匀;上下层物料配碳分别为5%和3.4%且料层厚度相同时,烧结成品率提高10%;降低上层高配碳区料层厚度,即当上下层厚度比为5：9,配碳为5%和3.756%时,成品率能够进一步提高。     

Monte Carlo simulations to determine coating uniformity in a Wurster fluidized bed coating process

This paper presents a coating model to predict the mass coating uniformity in a Wurster fluid bed coater using a Monte Carlo method. The velocity and voidage data obtained using imaging techniques on the same Wurster coater are used as inputs to the model. The semi-circular Wurster fluid bed used in this work was 22.9 cm in diameter. A batch of 3.6 kg tablets was used to conduct coating experiments and the coating weight gain distribution results were compared to predictions from the simulation. The model rigorously considers the sheltering effect of particles as they move in the spray zone. Good agreement was obtained when comparing the results with an analytical model.Spray shape and orientation of discretization were found to play an important role in predicting the coating uniformity. A simple spray experiment in a particle-free bed showed that the direction of spray material, in general, was vertically upward. Simulation results confirmed that an upward cylindrical spray model gives better agreement with experimental results compared to a solid cone spray model. Finally, the model was used to predict the changes in coating uniformity with bed operating conditions such as gas velocity and gap height. A wider coating distribution was found for the case with the lower gas velocity and gap height.     

Viscocapillary model of slide coating: Effect of operating parameters and range of validity

Slide coating is one of the premetered high‐precision coating methods. The layer thickness is set by the flow rate and web speed. The uniformity of the layer, however, can be affected by other operating conditions. Modeling the flow in the coating bead is necessary in developing the range of operability conditions where the layer is adequately uniform. Lubrication and viscocapillary models have been used to describe the flow and some of the operability limits of different coating processes. However, the available models of slide coating were developed with adhoc hypotheses that compromise their accuracy. We present a critical review of the available viscocapillary models and proposed changes to improve its range of applicability. The accuracy of the model is tested by comparing its predictions to the solution of the full two‐dimensional Navier‐Stokes equation. The model is valid at low capillary and Reynolds number regime and at low gap‐to‐wet thickness ratio. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

涂装双色车生产工艺

双色车属于特殊颜色车身,其外表面颜色通常在2种以上.精益的双色车生产工艺不仅能提高车身外观质量,而且能降低能耗及单车成本.本文对双色车生产工艺作了详细的介绍,包括色漆和清漆的第一、第二遍喷涂以及中涂遮蔽打磨等工艺流程.     

Experimental investigation of a new type of interfacial instability in a reactive coextrusion process

This paper deals with the study of new interfacial instabilities, called “grainy” defects, in coextrusion process of reactive multilayer polymers. The main objective was to better understand this phenomenon since no help can be found in the literature. The fundamental approach from a micro‐scale to a macro‐scale involves the study of relationships between polymer structure, processing, and interfacial properties. The influence of these parameters on the generation of “grainy” defects during coextrusion has been assessed in correlation with physicochemical properties. Through this work, rheological properties and the interfacial morphology between tie and barrier layers have been investigated by shear stress relaxation experiments and transmission electronic microscopy, respectively. Depending on the reactive polymers, the interfacial coupling was found to significantly alter the stress relaxation behavior by extending the relaxation time and generating an interfacial roughness. Hence, relations between the copolymer architecture, the relaxation process, and the interfacial morphology were established in correlation with the generation of grainy defects in coextrusion process. POLYM. ENG. SCI., 55:2542–2552, 2015. © 2015 Society of Plastics Engineers     

Transposition from a batch to a continuous process for microencapsulation by interfacial polycondensation

A novel continuous process is proposed and investigated to produce microcapsules by interfacial polycondensation. Polymeric microcapsules are obtained via a two-step process including an initial emulsification of two immiscible fluids in static mixers and a subsequent interfacial polycondensation reaction performed in two different continuous reactors, the Deanhex heat exchanger/reactor or a classical coiled-tube. This study is carried out through a step by step approach. A model system involving polyurea as the polymeric membrane and cyclohexane as the encapsulated species is chosen. A semi-batch reaction kinetic study is first performed in order to obtain kinetics data of the polycondensation reaction and to highlight hydrodynamic issues that can happen when running the encapsulation reaction in classical stirred tank. Parameters influencing droplets size obtained when carrying out emulsification in static mixers are then investigated. The hydrodynamic of the Deanhex reactor used is also characterized in terms of mixing time and residence time distribution. To validate the innovative continuous process, the emulsion droplets obtained at the static mixer outlet are encapsulated firstly in the Deanhex reactor and secondly in the coiled-tube. The apparent reaction kinetics and microcapsules characteristics corresponding to different operating conditions are discussed.