Transfer efficiency for airless painting systems

Spray transfer efficiency (TE) is defined as the mass fraction of sprayed paint which is deposited on the intended target, the remainder of the sprayed paint becomes undesirable overspray. The relationship between TE and gun supply pressure (or paint mass flow rate), gun-to-target distance, gun traverse speed, the angle of the spray gun relative to the target (gun-to-target angle), plus spray cone angle is reported herein for a typical fan spray system. Experimental results indicate that spray momentum rate (SMR) and droplet size dictate the TE for the various combinations of parameters considered here. The key finding is that TE correlates with SMR and spray mean drop size (Sauter mean diameter, or D₃₂) via an expression of the form TE=a+b SMR − c (SMR)²+d D₃₂, where a, b, c, and d are coefficients, determined by fitting the experimental data, and SMR is estimated via SMR=m²/ρA, where the paint mass flow rate m, the paint density is ρ, and the gun exit orifice effective tip cross sectional area is A. This expression accounts for physical phenomena that govern sprayed droplet deposition characteristics, such as entrainment, bounce-back, and drop size. Experimental results also show that, for the range of parameters studied, gun traverse speed has no effect on TE, but increasing the angle of the spray gun relative to the target (gun-to-target angle), increasing the spray cone angle, or increasing the gun-to-target distance will decrease TE.     

Wet‐spinning of biomedical polymers: from single‐fibre production to additive manufacturing of three‐dimensional scaffolds

Wet‐spinning of polymeric materials has been widely investigated for various biomedical applications, such as extracorporeal blood treatment, controlled drug release and tissue engineering. This review is aimed at summarizing and assessing current advances in wet‐spinning of biomedical polymers to manufacture single fibres and three‐dimensional scaffolds, as well as their functionalization through loading with bioactive agents. The theoretical principles and the main technological aspects of fibre production by wet‐spinning on either a laboratory or an industrial scale are outlined. The non‐solvent‐induced phase inversion determining polymer coagulation during the wet‐spinning process is discussed by highlighting its influence on the resulting fibre morphology and how it can be exploited to induce a nano/microporosity in the solidified polymeric matrix. The versatility of wet‐spinning in material selection, bioactive agent loading and fibre morphology tuning is underlined through an overview of significant literature reporting on the processing of various naturally derived and synthetic polymers. A special focus is given to cutting‐edge advancements in the application of additive manufacturing principles to wet‐spinning for enhanced control and reproducibility of three‐dimensional polymeric scaffold morphology at different scale levels (i.e. macrostructural to micro/nanostructural features). © 2017 Society of Chemical Industry     

Aligned core/shell electrospinning of poly(glycerol sebacate)/poly(l‐lactic acid) with tuneable structural and mechanical properties

In an earlier study, scaffolds of biodegradable poly(glycerol sebacate) (PGS)/poly(l ‐lactic acid) (PLLA) core/shell fibres had been fabricated using a core/shell electrospinning method, and the scaffolds were found to have mechanical properties similar to those of natural soft tissues, excellent cytocompatibility and slow degradation rate. In this paper, PGS/PLLA core/shell fibre mats with tuneable degrees of fibre alignment were fabricated using core/shell electrospinning with a rotating fibre collection mandrel. An increase in the rotational speed raised the degree of fibre alignment in the fibre mats. Single and cyclic tensile testing of the mats showed that an increase in the fibre alignment raised the modulus, resilience, ultimate tensile strength (UTS) and elongation up to a maximum at 1000 or 1500 rpm, but the resilience, UTS and elongation decreased when the rotational speed was further raised to 2000 rpm. Nonlinearly elastic biomaterials with a large range of mechanical properties were successfully fabricated using this method and the aligned fibre structure may be capable of guiding the growth of attached cells. © 2016 Society of Chemical Industry     

An investigation into the influence of electrospinning parameters on the diameter and alignment of poly(hydroxybutyrate‐co‐hydroxyvalerate) fibers

Electrospinning is an effective technology for the fabrication of ultrafine fibers, which can be the basic component of a tissue engineering scaffold. In tissue engineering, because cells seeded on fibrous scaffolds with varying fiber diameters and morphologies exhibit different responses, it is critical to control these characteristics of electrospun fibers. The diameter and morphology of electrospun fibers can be influenced by many processing parameters (e.g., electrospinning voltage, needle inner diameter, solution feeding rate, rotational speed of the fiber‐collecting cylinder, and working distance) and solution properties (polymer solution concentration and conductivity). In this study, a factorial design approach was used to systematically investigate the degree of influence of each of these parameters on fiber diameter, degree of fiber alignment, and their possible synergetic effects, using a natural biodegradable polymer, poly(hydroxybutyrate‐co‐hydroxyvalerate), for the electrospinning experiments. It was found that the solution concentration invoked the highest main effect on fiber diameter, whereas both rotational speed of the fiber‐collecting cylinder and addition of a conductivity‐enhancing salt could significantly affect the degree of fiber alignment. By carefully controlling the electrospinning parameters and solution properties, fibrous scaffolds of desired characteristics could be made to meet the requirements of different tissue engineering applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Some features of spinning hollow fibres from polycarbonatesiloxane melts

Conclusions The following parameters have been determined as a result of calculations: fibre tension, solidification path length, and the change along the spinning path of the following: stretching stresses, speed, radius, wall thickness, and fibre temperature.It has been shown that, with increase in take-up speed, the length of the section of fibre deformation is reduced, varying practically proportionally to the flow rate of the polymer system.Stability of the process of spinning hollow fibres from polycarbonatesiloxane melts is assured within a narrow range of stretching force.Translated from Khimicheskie Volokna, No. 3, pp. 41–43, May–June, 1989.     

Solution blowing of thermoplastic polyurethane nanofibers: A facile method to produce flexible porous materials

Solution blowing (SB) is a promising and scalable approach for the production of nanofibers. Air pressure, solution flow‐rate, and nozzle‐collector distance were determined as effective process parameters, while solution concentration was also reported as a material parameter. Here we performed a parametric study on thermoplastic polyurethane/dimethyl formamide (TPU/DMF) solutions to examine the effect of such parameters on the resultant properties such as fiber diameter, diameter distribution, porosity, and air permeability of the nanofibrous webs. The obtained solution blown thermoplastic polyurethane (TPU) nanofibers had average diameter down to 170 ± 112 nm, which is similar to that observed in electrospinning. However, the production rate per nozzle can be 20 times larger, which is primarily dependent on air pressure and solution flow rate (20 mL/h). Moreover, it was even possible to produce nanofibers polymer concentrations of 20%; however, this increased the average nanofiber diameter. The fibers produced from the TPU/DMF solutions at concentrations of 20% and 10% had average diameters of 671 ± 136 nm and 170 ± 112 nm, respectively. SB can potentially be used for the industrial‐scale production of products such as nanofibrous filters, protective textiles, scaffolds, wound dressings, and battery components. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43025.     

静电纺丝SF/PLGA纤维支架用于血管组织工程的研究

将丝素蛋白（SF）和乳酸-羟基乙酸共聚物（PLGA）溶解在六氟异丙醇中配制成溶液,采用静电纺丝技术制备了SF/PLGA纳米纤维支架,使用扫描电子显微镜（SEM）对纤维支架进行表征,研究了聚合物溶液浓度、纺丝电压、接收距离以及体积流率对纳米纤维形态的影响,从而得到纺丝的最适宜工艺参数。考察了纤维支架表面对HUVECs细胞的相容性。结果表明：HUVECs可以在SF/PLGA纤维支架表面很好的黏附和增殖,支架具有良好的细胞相容性,在组织工程领域有良好的应用前景。     

Investigation on the effect of spinning conditions on the properties of hollow fiber membrane for hemodialysis application

Polyethersulfone (PES) hollow fiber membranes were fabricated via the dry‐wet phase inversion spinning technique, aiming to produce an asymmetric, micro porous ultrafiltration hollow‐fiber specifically for hemodialysis membrane. The objective of this study is to investigate the effect of spinning conditions on the morphological and permeation properties of the fabricated membrane. Among the parameters that were studied in this work are air gap distance, dope extrusion rate, bore fluid flow rate, and the take‐up speed. The contact angle was measured to determine the hydrophilicity of the fibers. Membrane with sufficient hydrophilicity properties is desired for hemodialysis application to avoid fouling and increase its biocompatibility. The influences of the hollow fiber's morphology (i.e., diameter and wall thickness) on the performance of the membranes were evaluated by pure water flux and BSA rejection. The experimental results showed that the dope extrusion rate to bore fluid flow rate ratio should be maintained at 1:1 ratio to produce a perfectly rounded asymmetric hollow fiber membrane. Moreover, the flux of the hollow fiber spun at higher air gap distance had better flux than the one spun at lower air gap distance. Furthermore, spinning asymmetric hollow fiber membranes at high air gap distance helps to produce a thin and porous skin layer, leading to a better flux but a relatively low percentage of rejection for BSA separation. Findings from this study would serve as primary data which will be a useful guide for fabricating a high performance hemodialysis hollow fiber membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43633.     

航天行业筒段产品表面涂层的自动喷涂工艺

通过考察产品转速、喷枪移动速率、喷涂距离、喷涂压力和涂料流量对"环氧锌黄底漆+环氧硝基磁漆"体系喷涂效果的影响,确定了IRB 580-12型立式喷涂机器人在喷涂航天行业用筒段产品时的最佳工艺参数。     

Melt electrospinning writing of three‐dimensional star poly(ϵ‐caprolactone) scaffolds

In the last decade, the melt‐electrospinning technique has gained attention for the production of highly porous microfibrous tissue engineering scaffolds. The possibility of processing polymers without the use of organic solvents is one of the main advantages over solution electrospinning. In this study, computer‐controlled melt‐electrospinning of a commercial poly(?‐caprolactone) and of two batches with different molecular weights of a three‐arm star poly(?‐caprolactone) by means of a screw‐extruder‐based additive manufacturing system is reported. Experimental parameters such as processing temperature, extrusion flow rate and applied voltage were studied and optimized in order to obtain non‐woven meshes with uniform fibre morphology. Applying the optimized parameters, three‐dimensional scaffolds were produced using a layer‐by‐layer approach (0 ? 90° lay‐down pattern). © 2013 Society of Chemical Industry     

Experimental investigation of the governing parameters in the electrospinning of poly(3‐hydroxybutyrate) scaffolds: Structural characteristics of the pores

We sought to determine the impact of electrospinning parameters on a trustworthy criterion that could evidently improve the maximum applicability of fibrous scaffolds for tissue regeneration. We used an image analysis technique to elucidate the web permeability index (WPI) by modeling the formation of electrospun scaffolds. Poly(3‐hydroxybutyrate) (P3HB) scaffolds were fabricated according to predetermined conditions of levels in a Taguchi orthogonal design. The material parameters were the polymer concentration, conductivity, and volatility of the solution. The processing parameters were the applied voltage and nozzle‐to‐collector distance. With a law to monitor the WPI values when the polymer concentration or the applied voltage was increased, the pore interconnectivity was decreased. The quality of the jet instability altered the pore numbers, areas, and other structural characteristics, all of which determined the scaffold porosity and aperture interconnectivity. An initial drastic increase was observed in the WPI values because of the chain entanglement phenomenon above a 6 wt % P3HB content. Although the solution mixture significantly (p < 0.05) changed the scaffold architectural characteristics as a function of the solution viscosity and surface tension, it had a minor impact on the WPI values. The solution mixture gained the third place of significance, and the distance was approved as the least important factor. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanism of Cf/SiC hole making with high shape precision using abrasive waterjet based on response surface method

This paper aims to explore the accurate control of hole shape for AWJ hole-making of C_f/SiC based on experimental and mathematical analysis methods, and the influence mechanism involved is emphatically analyzed. The results reveal that D_difference is most influenced by the standoff distance, followed by the traverse speed, while it is less influenced by the pressure and the abrasive flow rate. The traverse speed, pressure and abrasive flow rate affect the D_difference by changing the total energy of the jet; while the standoff distance mainly affects the D_difference by changing the effective impact area, which is fundamentally different from other process parameters. In terms of interaction effects, decreasing the traverse speed and increasing the waterjet pressure can amplify the effect of interaction with the involvement of the standoff distance on the D_difference. Based on the established D_difference model and D_offset model, a control method that can gain acquired hole shape is finally obtained for selecting the process parameters of AWJ machining.     

Poly‐left‐lactic acid tubular scaffolds via diffusion induced phase separation: Control of morphology

In this work, tubular poly‐left‐lactic acid scaffolds for vascular tissue engineering applications were produced by an innovative two‐step method. The scaffolds were obtained by performing a dip‐coating around a nylon fiber, followed by a diffusion induced phase separation process. Morphological analysis revealed that the internal lumen of the as‐obtained scaffold is equal to the diameter of the fiber utilized; the internal surface is homogeneous with micropores 1–2 μm large. Moreover, a porous open structure was detected across the thickness of the walls of the scaffold. An accurate analysis of the preparation process revealed that it is possible to tune up the morphology of the scaffold (wall thickness, porosity, and average pore dimension), simply by varying some experimental parameters. Preliminary in vitro cell culture tests were carried out inside the scaffold. The results showed that cells are able to grow within the internal surface of the scaffolds and after 3 weeks they begin to form a “primordial” vessel‐like structure. Modeling predictions of the dip‐coating process display always an underestimate of experimental data (dependence of wall thickness upon extraction rate). POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Formability of Fe-doped bioglass scaffold via selective laser sintering

Because of its outstanding characteristics, bioglass is considered a potential bone substitute; however, it is difficult to be fabricated into a scaffold because of insufficient strength. Although there are several methods for producing a three-dimensional ceramic scaffold, most of these methods cannot completely mimic the bone structure. In this study, a bioglass scaffold was fabricated through selective laser sintering (SLS) with the addition of the iron element that could ascend the laser absorption rate with the improvement of the formability and mechanical strength of scaffolds. As a result, the laser absorption proficiency improved with an increase in the amount of iron added; a competent bioglass scaffold could be successfully manufactured with a 5% iron element addition at the energy density of 2.5 cal/cm² (3-W power and 120 mm/s scan speed). In a comparison of scaffolds sintered with various parameters of the heat treatment, scaffolds that had favourable mechanical strength and cell survival rate could be acquired after sintering at 1100 °C. According to the result of the present study, a competent biocompatible bioglass scaffold could be obtained using the SLS process with the addition of the iron element and suitable post-processing parameters.     

Electroless Palladium-Coated Polymer Scaffolds for Electrical Stimulation of Osteoblast-Like Saos-2 Cells

Three-dimensional porous scaffolds offer some advantages over conventional treatments for bone tissue engineering. Amongst all non-bioresorbable scaffolds, biocompatible metallic scaffolds are preferred over ceramic and polymeric scaffolds, as they can be used as electrodes with different electric field intensities (or voltages) for electric stimulation (ES). In the present work we have used a palladium-coated polymeric scaffold, generated by electroless deposition, as a bipolar electrode to electrically stimulate human osteoblast-like Saos-2 cells. Cells grown on palladium-coated polyurethane foams under ES presented higher proliferation than cells grown on foams without ES for up to 14 days. In addition, cells grown in both conditions were well adhered, with a flat appearance and a typical actin cytoskeleton distribution. However, after 28 days in culture, cells without ES were filling the entire structure, while cells under ES appeared rounded and not well adhered, a sign of cell death onset. Regarding osteoblast differentiation, ES seems to enhance the expression of early expressed genes. The results suggest that palladium-coated polyurethane foams may be good candidates for osteoblast scaffolds and demonstrate that ES enhances osteoblast proliferation up to 14 days and upregulate expression genes related to extracellular matrix formation.     

静电纺PLGA管状支架的构建及其生物力学性能

以具有良好生物相容性、生物可降解性的聚丙交乙交酯(PLGA)为原料,以高速旋转的滚轴为收集装置,通过静电纺丝法,制备PLGA管状支架(d=6mm)。研究不同工艺及乙醇处理对PLGA管状支架形貌结构、微细结构和生物力学性能的影响。结果表明:当纺丝液质量分数为7%,滚轴转速为1500r/min时,可制得纤维形貌规整、分布均匀,直径为(1660±218)nm,孔隙率为80.6%的PLGA管状支架;经乙醇处理后,其孔隙率减小,玻璃化温度和热分解温度提高,热稳定性增强;断裂强度、爆破强度及缝合强力均显著提高。     

静电纺丝制备聚醚酮酮超细纤维

用溶液静电纺丝方法制备了聚醚酮酮超细纤维,用扫描电子显微镜研究了实验过程中纺丝电压、纺丝距离、流量、纺丝液浓度对于聚醚酮酮纤维直径和形貌的影响,并对多个纺丝参数的影响规律进行了分析。实验结果表明,在一定条件下纺丝电压和纺丝距离对纤维直径影响较小,而流量和纺丝液浓度能显著影响纤维直径,在小流量、低浓度容易得到较细的纤维,并且纤维直径分布集中。     

Morphology of ultrafine polysulfone fibers prepared by electrospinning

Ultrafine fibers of bisphenol‐A polysulfone (PSF) were prepared by electrospinning of PSF solutions in mixtures of N,N‐dimethylacetamide (DMAC) and acetone at high voltages. The morphology of the electrospun PSF fibers was investigated by scanning electron microscopy. Results showed that the concentration of polymer solutions and the acetone amount in the mixed solvents influenced the morphology and the diameter of the electrospun fibers. The processing parameters, including the applied voltage, the flow rate, and the distance between capillary and collection screen, were also important for control of the morphology of electrospun PSF fibers. It was suggested that uniform ultrafine PSF fibers with diameter of 300–400 nm could be obtained by electrospinning of a 20 % (wt/v) PSF/DMAC/acetone (DMAC:acetone = 9:1) solution at 10–20 kV voltages when the flow rate was 0.66 ml h^?1 and capillary–screen distance was 10 cm. Copyright © 2004 Society of Chemical Industry     

Evaporation of clearcoat solvents from a rotary bell atomizer and its relationship with bell speed,flow rate,and electrostatic potential

The relations between evaporation of clearcoat solvents and various operating parameters of the spray from a rotary bell atomizer were measured using a particle dynamic anemometer (PDA). The robot arm holding the spray applicator was moved relative to the PDA so that the volume flux at different parts of the spray could be measured. The difference in total flux between two planes, perpendicular to the spray axis, was considered to be equal to the evaporation. Evaporation was found to increase with increasing bell speed. Evaporation also increased with increasing coatings flow rate from 100 to 200 cm³/s flow rate, but not for a further increase to 300 cm³/s. Higher electrostatic potential, bell speed, and lower flow rate decrease the mean particle diameter. Particle mean velocity increases with increasing bell speed and flow rate. Coatings flow rate, bell speed, electrostatic potential, and the interaction between flow rate and bell speed were significant factors affecting evaporation rate. Of the former three, coatings flow rate was the most influential.     

Spray winding,a novel one-step spray-technology to perform CMCs from preceramic polymers

A novel spray-technology to perform CMC tubes has been developed in order to establish an one-step process which enables shorter process times along with the saving of costs. The manufacturing route combines the textile fibre technique with both matrix polymer spraying and IR heated curing/pyrolysis which transfers the preceramic polymers into an inorganic amorphous SiOC matrix.The applied metalorganic polymer as a commercial polysiloxane precursors which can be easily handled in air. The use of an organic solvent and WC-filler particles enables a low viscous suspension. Carbon fibres were wound onto a rotating tapered mandrel and simultaneously spray-coated with the polymer suspension, i.e. fibre winding and matrix spraying occurred at the same time to build up the CMC tube layer by layer. A heatable two flux nozzle is positioned perpendicular over the rotating mandrel and coats the surface continuously. An ellipsoid IR-mirror furnace which cures and pyrolyses the matrix (up to about 900 °C) was in 180° orientation displaced, focusing its radiation onto the surface. Rotation and traverse speed of the mandrel were computer controlled to facilitate a variability in fibre architecture. In a circular ring-test small winding angles leads to a maximum strength of 45 MPa. Because the shrinkage of the matrix polymer occur at a free surface only very limited strain hindrance arises.