Hydrophobicity of fluorocarbon-finished electrospun poly (acrylonitrile) nanofibrous webs

This article reports the hydrophobicity of fluorocarbon-finished nanofibrous webs composed of electrospun poly (acrylonitrile) nanofibers with fiber diameter in the range of about 100–3000 nm. The results obtained from sliding angle and contact angle measurements tests are reported. It was found that the contact angle of unfinished samples with average fiber diameters of about 700, 980 , and 3050 nm lies between 132° and 134°, indicating a rather high and at the same time not much different hydrophobicity for the webs. However, after finishing the electrospun nano- and microfibrous webs, the contact angle increased by a considerable amount to 138°–157° for the webs with average fiber diameter in the range of about 100–3050 nm, respectively. Sliding angle test of the finished nanofibrous webs showed a minimum angle of about 3° for the web with average fiber diameter of 3055 nm. To the best of authors’ knowledge, the rolling angle of 3° is the smallest rolling angle ever reported in the literature. The result of this work showed also that sliding angle test may be more sensitive than contact angle test. It was also ascertained that none of the Wenzel model and Cassie–Baxter model can represent the superhydrophobicity of the fluorocarbon-finished nano- and microfibrous webs.     

多针头静电纺丝工艺过程探讨

借助于Maxwell电场仿真模拟软件和具体实验研究了针头间距和针头数量对静电纺运动射流所处电场分布以及纤维最终沉积形态的影响。结果表明,随着针头间距的增加,电场相互干扰程度减弱,得到的环形纤网会由椭圆形向圆形转变。在多针头静电纺丝工艺中,靠中排布的针头得到的纤网与边缘针头对应的纤网的外观存在明显差别。基于此结果,设计了钢带式多针头连续静电纺丝装置,此装置可以通过调整针头排布并配合钢带旋转制备出不同幅宽和不同规格的均匀纳米纤维网。     

非织造布结构特性的测试方法及其发展方向

论述了非织造布的几种主要结构特性，如孔隙大小分布、纤维排列方向分布、纤网的均匀性及瑕疵等的测试方法及其原理与各自的优缺点。通过对比，说明非织造布结构特性的测试方法的发展方向。     

静电纺再生丝素/明胶纳米纤维的结构与性能

 以质量分数为98%的甲酸为溶剂,将再生丝素与明胶以质量比70∶30进行共混静电纺丝。研究纺丝液质量分数及乙醇处理对纤维膜的结构及力学、溶解性能等的影响;测定不同纺丝液质量分数及不同厚度下纤维膜的孔隙率及孔径;在纤维膜上进行小鼠成纤维细胞(L929)和人脐静脉内皮细胞(HUVECs)培养实验。结果表明:随着纺丝液质量分数的提高或经乙醇处理后,丝素β化程度提高,纤维结晶度增大,溶失率减小,拉伸强度增大;随着纺丝液质量分数的提高,纤维膜的孔隙率减小,孔径增大,厚度增加时,纤维膜的孔隙率及孔径均减小;L929及HUVECs均能够在纳米纤维膜上黏附、生长和增殖。     

粉末粘结非织造布厚度方向上粉末粘结剂的分布研究

分析了粉末粒子在纤网厚度方向上的下落分布过程 ,并探讨了沿纤网厚度方向上粉末分布的确定方法。实验表明 ,当纤网条件一定时 ,一种粗细正好的粒子与纤网密度、纤维粗细相匹配 ,可使其达到在厚度方向上的均匀分布     

PORE SIZE DISTRIBUTION AND STRUCTURE OF A COOKED BEEF PRODUCT AS AFFECTED BY VACUUM COOLING

True density, apparent density, and pore size distribution were measured for a vacuum cooled cooked beef product using helium pycnometry and mercury porosimetry. Vacuum cooled samples resulted in the development of high porosity and lower density in comparison to more conventional cooling methods. Pore size distribution for vacuum cooled samples revealed the presence of random pore sizes with no distinct pore size but rather a pore size range of 10 μm to 0.02 μm. It was determined that the vast majority of porosity in vacuum cooled samples was composed of void space volume as distinct to regular pores. Analysis of estimated diffusion coefficients revealed that the efficiency of vacuum cooling is dependent on the development of porosity within the samples during cooling which leads to more efficient cooling times and higher diffusion rates in samples with higher porosity and larger pore size distributions.     

Starch as a Pore‐forming and Body‐forming Agent in Ceramic Technology

Wheat and corn starch can be used for the preparation of porous alumina ceramics via the SCC (starch consolidation casting) process, resulting in porosities ranging from > 20% to approx. 50% (using nominal starch contents of 10 – 50%, v/v), with open porosity dominating (closed porosity < 6.5%). The character of porosity and the shape of the pores corresponds to the starch granules used, but the pore size is determined by a complex interplay between starch swelling (during the body‐forming step) and pore shrinkage (during sintering of the ceramic). Typically, for low starch contents (e.g. nominal starch contents of around 10%, v/v) starch swelling is a significant effect, and the pores after sintering are larger than the size of the starch granules. For higher starch contents swelling is constrained (by limited space and/ or water availability), and the matrix shrinkage during sintering overcompensates the swelling effect, so that the final pores in the ceramic can be significantly smaller than the original starch granule size. In this paper it is shown how porosity is related to pore size. In particular, it is demonstrated that the porosity indirectly determined from image analysis (via the median pore size) is closely related to the porosity directly measured via the Archimedes method. On the other hand, mercury porosimetry measures the distribution of pore throat sizes. With increasing starch content in the suspension, the pore throat size in the as‐fired ceramic materials increases, resulting in a more open microstructure.     

Characteristics of pores in native and hydrolyzed starch granules

Low‐temperature nitrogen adsorption and mercury porosimetry were applied for analyzing effect of α‐amylolysis upon the porosity of granules of native corn, wheat, rice, and potato starches. Specific surface area (S_BET), porosity, pore size distribution, total pore area, and mean pore radius were determined for native and digested granules. It was found that native starch granules are macroporous materials with a small participation of mesopores. In the case of native starches, the highest value of S_BET was obtained for rice starch (1.27 m²/g) and the lowest – for potato starch (0.14 m²/g). Pore size distribution curves obtained by nitrogen adsorption showed peaks in the range of diameters 2–3 nm (for all starches) and 100–200 nm (for corn and rice starches). After 60 min of enzyme action, surface area of all starches doubled in comparison to native ones. Arising of the new pores was also noted. The results of mercury porosimetry measurements showed that rice starch had the highest total area of pores and porosity but the lowest mean pore radius among all native starches. The pore size distribution curves for all starches exhibited solely one peak corresponding to the dominant group of pores of the radii in the range 0.5–8 µm, dependent on the starch source. There were also much smaller peaks situated within the range of 3–30 µm. After α‐amylolysis of corn and rice starches, the average radius of the dominant group of pores diminished. No substantial changes in the pore radii could be noted for potato starch.     

Porosity and pore size distribution of different wood types as?determined by mercury intrusion porosimetry

In this work, densities and porosity parameters are determined on domestic and overseas soft- and hardwoods by application of pycnometric methods and mercury intrusion porosimetry (MIP). Great variability was found in bulk density, porosity and in the specific surface area. According to the pore size distribution, four pore size classes could be distinguished: macropores (radius 58?C2???m and 2?C0.5???m), mesopores (500?C80?nm), and micropores (80?C1.8?nm). The pore size distribution can vary even in the case of comparable pore volumes. The hardwoods, particularly the European diffuse-porous ones, show a higher amount of micropores, which represent the microvoids or cell wall capillaries. A?high cumulative pore volume can also be the result of a high content of micropores with poorer accessibility. The value of the total specific surface area from MIP measurements is, generally, below those values obtained by the water vapour adsorption technique. These results can provide information for further investigations on the sorption behaviour and the fluid intake as technological characteristics in industrial processes of impregnation and penetration of coating materials or adhesives.     

Properties of electrospun PVA/nanoclay composites

Laponite^® nanoclay was added to poly(vinyl alcohol) (PVA) solution which was electrospun to make PVA/Laponite^® nanocomposites. After adding Laponite^® nanoclay, fibers were observed to be warped, making their surface rougher. The addition of Laponite^® resulted in less water solubility of electrospun PVA web. PVA/Laponite^® nanocomposite disintegrated after exposure to heat and agitation in water reducing its filtration capability. PVA/Laponite^® nanocomposites showed lower air permeability than electrospun PVA webs probably because of more resistance to air stream caused by rougher and less uniform fiber surface. Tensile and tear strength were weakened by Laponite^® nanoclay due to several reasons: random orientation of nanoclay along fiber axial direction, and fiber discontinuity caused by nanoclay and inhomogeneous distribution of nanoclay.     

Investigation of pore parameters of woven fabrics by theoretical and image analysis methods

Fluid permeability property is an important performance feature of fabrics and must be considered during the designing processes of products. Since the rate of fluid flow through a textile is a function of viscosity, density, pressure gradient of fluid, and the pore properties of fabric, it is necessary to define pore properties by controlling the structural parameters of fabric for a certain area of use. Due to the complexity of fabric structure, modeling of pore structure and predicting the pore parameters are difficult. In this study, the interyarn porosity, pore size, and pore-size distribution of cotton woven fabrics were calculated by using two-dimensional (2D) and three-dimensional (3D) geometrical pore models and image analysis method. The effect of weave types and weft settings on the pore parameters and air permeability of fabrics were investigated, and the advantages of 2D, 3D geometrical pore models and image analysis method were compared.     

非织造材料孔隙结构的定量表述

利用计算机图像处理技术,提取了孔隙尺寸、孔隙形状和纤维取向分布等直观表达非织造纤维材料结 构的参数;利用新的几何学———分形几何,对非织造纤维材料的孔径分布情况进行分析,获得孔径分 布分形维数。在此基础上研究纤维网单位面积质量和特征长度对纤维网结构的影响,以及孔径分布 分形维数与通透性能之间的关系。     

Physical Properties of Air-Dried and Freeze-Dried Chicken White Meat

Cooked, diced chicken meat was dehydrated by various air- and freeze-drying techniques. The dried material was evaluated to determine shear strength, friability, color, rehydration, surface area, porosity, density and pore size distribution. A Scanning Electron Microscope was employed to study effects of the drying process on meat fiber structure. We found that freeze-drying produced a porous material with excellent rehydration properties. Air-drying produced samples with less porosity and poorer rehydration. We concluded that porosity was the primary factor in rehydration potential and surface area and pore size distribution was less important.     

Porosity Evaluation of Ginseng Roots from Real-Time Imaging and Mass Measurements

Real-time imaging and mass measurements were used for evaluation of instantaneous porosity in convective drying of ginseng roots. Porosity changes were evaluated from moisture–shrinkage–porosity correlation. It was found that any deviation of shrinkage–moisture relationship from linearity was due to the changes of porosity. The impact of temperature on porosity development was evaluated from drying experiments at moderate (38 °C) and high (50 °C) temperatures. Drying at 38 °C resulted in gradual increasing of porosity to 20–25% with the next quick decreasing of porosity to 10–15% at the end of drying due to intensive shrinkage. In contrast, drying at 50 °C resulted in constant porosity (0–5%) for most of the drying period, with the next increasing to 30% at the end of drying due to the case hardening. The method of porosity evaluation was verified with direct microscopic measurements at different stages of drying.     

甘蔗混合汁粒径分布及陶瓷微滤膜过滤阻力研究

建立了甘蔗混合汁中颗粒粒径分布测定和分析方法;研究了0．1μm、0．2μm和0．45μm陶瓷微滤膜分析甘蔗混合汁时的阻力分布,探讨了不同膜元件主要阻力形式,确定了阻力分析方法。结果表明：致密性膜的制造精度越高,过滤料液时总阻力相对较小,孔隙率高的膜元件堵塞阻力随膜孔径减小而降低,利于膜通量的恢复和延长使用时间。     

防羽面料孔径及分布特征与透气性和防钻绒性的关系

为开发优质防羽面料,探明孔径及其分布特征对防羽面料性能的影响机制,借助多功能孔径测定仪、透气量仪和防钻绒性能测试仪获取10种不同规格防羽面料的孔径、透气率和钻绒根数,分析了孔径及其分布特征与透气性和防钻绒性之间的关系。结果表明:防羽面料的孔径分布符合正态分布的规律,且孔径均值和标准差的相关系数为0.99;在原料和组织结构相同的情况下,防羽面料透气率随着孔径均值的减小而减小;钻绒根数与孔径均值拟合方程的判定系数为0.94,当孔径均值小于8 μm时,面料的钻绒根数低于23根;提出采用透钻比(透气率和钻绒根数的比值)综合评价防羽面料的防钻绒性和透气性发现,透钻比与孔径变异系数呈显著负相关,即孔径变异系数越小,透钻比越大,面料的综合性能越好。     

Beitrag zur Porositätsanalyse von Holz mit dem Quecksilber-Porosimeter

As a contribution to the determination of the pore structure of wood with the mercury porosimeter, the effect of the size, form and structure of the wood specimens, which is of particular bearing on the results of porosity, was investigated in detail; furthermore, the pore size distribution in 30 domestic and overseas wood species was determined. Particular attention was given to the fact in how far the “bottle-neck effect”, occurring as a source of error in connection with wood cells with very narrow openings (pits) as compared with the wide lumina, may falsify the results of pore size distribution; beyond this the problem of how diminishing considerably the effect of this source of error was investigated. In further studies the characteristic differences between the pore size distribution in heartwood and sapwood, in normal wood and reaction wood as well as in untreated and heat treated wood was elucidated qualitatively and quantitatively.     

织物毛细孔径分布与其组织结构及组分的关系

由于织物组织结构及组分对织物毛细孔半径及其分布有影响,采用质量分级法,测定5种组织结构的棉和涤/棉机织物的毛细孔半径分布。分别考察纱线线密度、织物经纬密和组分对织物毛细孔径分布曲线的影响。结果表明：这些织物的孔径分布曲线大都由4个区段构成;随着纱线线密度的减小,整个孔径范围明显扩展,其中最小孔径略有增加,最大孔径显著增加,最大比例孔径显著减小;随着经纬密的降低,分布曲线的部分区段被压缩甚至和其他区段归并,织物孔径分布趋于简单化和均匀化;织物的组分并不影响其孔径分布曲线的特征形状,只是在不同区段曲线略有压缩和伸展变形。     

静电纺高效防尘复合滤料的制备及其性能

为获得无毒无害高效防尘口罩的过滤材料,采用静电纺丝技术制备直径为（0.088±0.01）μm的锦纶6∕ 壳聚糖（PA6/CS）共混纳米纤维,与丙纶熔喷非织造布复合形成高效防尘复合滤料,研究了静电纺丝时间对复合滤料表面形貌、孔径及其分布、过滤性能和透气透湿性能的影响。结果表明,静电纺（PA6/CS）纳米纤维层可显著提高丙纶熔喷非织造布的过滤效率,静电纺丝 90 min 后复合滤料对 NaCl 气溶胶的过滤效率达到99%以上,明显高于丙纶熔喷非织造布的过滤效率（29%）,但是随着静电纺丝时间的延长,复合滤料的孔径、过滤阻力和透气性能明显下降,而透湿性能变化不明显。     

Liquid sorption behaviour of nonwovens

In this paper, spunbond, meltblown and spunbond–meltblown–spunbond (SMS) nonwovens made from polypropylene are analysed for liquid transport behaviour. The thickness, grams per square metre (GSM), porosity, fibre diameter, fibre orientation distribution and water contact angles of these nonwovens are measured. Vertical wicking with decane using tensiometry and water absorbency and spreading using gravimetric absorbency tester are reported. The equivalent pore radii of the nonwovens are deduced from the vertical sorption experiments using tensiometry. The sorption rate under vertical wicking and water spreading rates are faster along machine direction compared with that in cross‐direction due to preferential fibre orientation. The thickness of the nonwoven, fibre diameter and porosity play a vital role in transporting liquid. Thin nonwovens have poor vertical wicking and spreading rate. SMS web has poor absorbency behaviour mainly due to the inability of its top S‐layer to pull the liquid from the middle M‐layer. The measured water spreading lengths with respect to time are compared to the theoretical ones using a model developed by earlier researchers. This model reasonably predicts the spreading behaviour of nonwovens.