【作者】 张素风；

【导师】 张美云； 李可成；

【作者基本信息】 陕西科技大学 ， 制浆造纸工程， 2010， 博士

【摘要】 高性能芳纶纸是全球公认的最佳绝缘纸和结构材料纸,我国长期依赖进口。与Nomex纸相比,国产芳纶纸在匀度、厚度均一性和强度等技术性能上还有明显差距,根本原因是缺乏相关交叉学科的基础理论和关键技术研究。从理论上揭示纤维结构、性能与成纸的相关性,是突破技术瓶颈,提升芳纶纸质量的当务之急。物质的各种宏观性质源出于本身的微观结构,探索芳纶纤维的结构与性质之间的关系,是凝聚态物理、结构化学的一个重要研究内容。本文从材料学和物理化学角度出发,研究纤维分子间化学力和纤维表面能、成纸体系电化学性等,揭示芳纶纤维/浆粕表面和界面的粘结成纸特性；研究芳纶纤维和浆粕的耐热性能,科学评价芳纶纸匀度、紧度、耐热性能的主要影响因素；研究芳纶纤维/浆粕的晶体结构特征,为芳纶纸强度性能差异性的评价提供理论依据。在此基础上解析芳纶纤维和浆粕的表面性能、结构特点和热性能与复合成纸特性的相关性规律。芳纶纤维的结构与其干纺或湿纺工艺有密切联系,且对纤维表面及结构影响较明显。采用光学显微、SEM、AFM等,对纤维表面进行显微分析,并对短切纤维横截面进行TEM观察。结果显示采用湿纺工艺生产的芳纶短切纤维(F1-纤),表面略带纺丝过程中的线条状痕迹,无明显的皮芯结构；SEM下观察其线条状痕迹为表面的微纤维,与纤维轴向平行,呈现出皱褶状,是成型过程中凝聚态急骤变化形成超分子结构在纤维表面的形态特征,是原丝的一种表面缺陷。浆粕柔软呈飘带状,平均长度是0.2～1mm。厚度不超过1或2μm,有利于湿法成形过程中的互相搭接和均匀分散。F2-纤颜色较深,为综褐色,形状不规则,中间有一条凹陷的细带,皮层呈膨胀状态,也与其纺丝工艺相关。F3-纤整体匀称,表面光滑。短切纤维横截面TEM图显示,三个不同制造工艺的纤维,其微细纤维的精细程度也有较大差异,Nomex工艺的F3-纤中的微细纤维很细小且排列很密实。芳纶成纸热压后进行一定时间的保温或者冷处理,研究其对纸张各项性能指标的影响。经过1～3min的保温时间,芳纶热压纸的抗张指数可提高8%～10%；撕裂指数也随着保温和冷浸渍条件而有所波动,纸张伸长率提高10%左右。冷浸渍处理后纸张的抗张指数降低4%以上,伸长率提高10%以上,可能是冷浸渍过程中纸张吸收了大量水分所致。冷浸渍的纸样重新经过热压和保温处理后其各项强度指标可以大幅度的恢复。证明温度对芳纶纤维成纸的影响是很大的,冷浸渍后的吸湿水也可以在再热压时排除掉,而不影响纸张的性能。因此纸张热压后逐渐冷却对芳纶纸的性能提高是很重要的工艺过程。纸张抄造方式上应用分层次多比例成纸形式,对所得纸张的性能指标与单一比例相比,发现有利于构造良好的纸张结构。与中间层相比,面层和底层中的沉析纤维含量较多,纤维间有良好的粘结基材,利于形成匀度较好的材料,纸张在压光后纸张表面不至于粗糙。中间层高强度的短切纤维含量较多,保证了纸张的机械强度性能。各层采用同样的湿法抄造,经复合过程,使三层结合并形成统一结构,充分利用不同芳纶纤维各自的粘接、绝缘和增强优势。对芳纶纸热压工艺进行了正交试验优化,分析了影响纸张性能的相关因素及水平。结果表明,热压温度、保温时间和热压力为F1-纸性能的主要影响因素,热压次数及压辊的转速为次要因素,F1-纸热压工艺优化结果为：热压温度240℃、保温时间3min,热压力14MPa,压辊转速1.5r/min,热压次数3次。热压温度、热压力和压辊转速为F2-纸性能的主要影响因素,热压次数及保温时间为次要因素；F2-纸热压工艺为热压温度240℃、保温时间2min,热压力14MPa,压辊转速1.5r/min,热压次数4次。采用图像份分析技术和SEM、TEM、AFM、共焦激光扫描显微镜(CLSM)等手段,对纸张表面进行XY和Z向研究,对纸页的内部结构与组成及其对成纸性能的影响进行分析。研究结果表明,热压过程能够显著提高芳纶纸的抗张强度、伸长率和纸张紧度等机械性能。当热压温度为130℃时,芳纶纸的抗张强度、伸长率和纸张紧度分别提升5、7和4倍。纸张横截面SEM图显示,热压后芳纶纸的内部结构变得密实,表面也变得光滑平整,纸张紧度得到提高。在热压过程中,芳纶浆粕以粘合剂和填充物的形式在纸页结构中存在,纤维受到挤压而产生形变。匀度分析结果表明,当芳纶纸定量大于60g/m2时,随着定量的增大,纸张中匀度较好的小尺寸匀度分量范围逐渐扩大,而大尺寸分量的匀度始终较定量35g/m2差。即定量的增大有利于提高纸张中细小组分的匀度。如果影响纸张性能的因素主要来自于组成纸张的细小组分,则可以通过提高纸张的定量来实现性能的改善。定量对纸张性能的影响与匀度分量相关。不同定量的纸张,其强度性能主要由短切纤维来承担,而沉析纤维主要承担芳纶纸的电气性能,耐压强度性能的提高主要依赖于两种纤维的比例。纸张横截面TEM观察结果表明,表明热压过程并没有使得芳纶微纤维间熔融为一体,或在纤维与基体间界面形成一个相互交叉的过渡区界面。不同工艺来源的芳纶纤维和浆粕原料对界面粘结性能的影响不同。F3-浆粕基体部分的微纤维像指纹一样,呈现出一种条纹和旋涡状结构。F1-浆和F2-浆粘合区域的指纹特征不突出,浆粕微纤维间层次较混浊,基体与纤维间的界面有明显的界限；纤维表面的沟槽明显,与浆粕形成镶嵌的“钉扎型”界面结构；部分区域的纤维与浆粕基体间界面甚至形成“间隙型”界面,相互间距离很大,这种现象可能与纤维和浆粕的热收缩性差异有关。在液滴形状法的理论基础上,根据Young-Laplace方程,利用矢量化技术,测定和计算的单根芳纶纤维的表面接触角为53.3。化学试剂表面处理对芳纶纤维接触角有较大影响,DMAc、DMF、甲苯、三氯甲烷、二氯丙烷等可以使芳纶纤维表面接触角变小,最小降低到44.9,提高了纤维在水相中的分散效果,改善芳纶纤维湿法成纸匀度。界面是芳纶纸基材料极为重要的微结构,它作为短切纤维与浆粕基体连接的“纽带”,对芳纶纸基的物理、化学及力学性能有着至关重要的影响。从原料、制造工艺、热压过程产生的热应力等界面性能影响因素方面,围绕芳纶纤维和浆粕形成的界面表征、界面微观结构与芳纶纸基材料综合性能的联系,探讨了芳纶纸基材料界面的基本情况,包括表面能、热压粘结行为和粘附力分析等。用水和乙二醇作为接触角测试液体时,芳纶纤维及浆粕的表面能在35～45mJ·m-2。其中,芳纶短纤维表面能稍高于芳纶浆粕,芳纶纤维及浆粕的极性分量大于色散分量；且纤维表面能越高越有利于表面可润湿性、粘附功及粘接强度的提高。芳纶短纤维与浆粕之间的色散分量和极性分量越匹配,表面能之差及界面张力越小,而复合纸抗张指数越高。芳纶纸热压后表面能的下降而具备优良的抗湿性能,但表面能下降过快对纤维间热压粘接过程及成纸性能不利。纸页断面分析和FTIR的检测结果显示,热压过程中,芳纶纸结构中纤维表面游离羰基减少,而缔合羰基增加,表明热压后芳纶纤维浆粕之间的粘结主要是物理粘结作用。采用原子力显微镜(AFM)探针修饰技术,对芳纶纤维间粘附作用力研究结果标明,聚芳酰胺浆粕薄膜修饰的探针与芳纶纤维和浆粕之间的粘附力(Pull-off adhesion forces, Fadh)分别为1.71nN和9.20nN。浆粕分子间粘附作用力大于其与纤维间的粘附力,可能是由于浆粕为无定型形态,分子之间接触面积会更大,而且能够提供更多的极性末端基,以形成分子链间的结合力。采用Derjaguin-Muller-Toporov(DMT)理论,借助纤维表面自由能,计算理论作用力,可以验证分子间粘附力的AFM测定。碱性环境对芳纶纤维成纸强度有不利的作用,酸性环境或者硫酸铝等可以改善芳纶纤维成纸状况,pH值控制在6.0左右为好,对应的Zeta电位为-4～-8.6mV(硫酸铝体系)或-18～-19 mV(盐酸和磷酸体系)。从高分子聚合物的凝聚态结构方面着手,对芳纶纤维和浆粕在加工过程中形成的,是由微观结构向宏观结构过渡的状态进行研究,主要分析其大分子之间的几何排列包括晶态结构、非晶态、取向态和织态等结构,以及纤维分子量、结晶度、内聚能密度(cohesive energy density,简称CED)等主要结构参数；采用热分析手段,研究纤维或浆粕受热时温度、热应力等对其结构的影响；并重点对影响热压效果的芳纶浆粕,在受热时结晶速率和结晶度大小的变化进行分析,以探讨芳纶纸热压加工过程中,纤维分子量与结晶度等主要结构特征；分析芳纶短纤维及浆粕的结构是如何影响成纸的热性能,了解结构特点与耐热性能、纸张性能之间的相关性,为改善芳纶热压纸性能的提出改善途径。研究结果显示,芳纶纤维平均分子量大小为10万左右,短纤维平均分子量稍高于浆粕,多分散系数在1～2之间。短纤维与浆粕分子量大小差异,表明两者在热压过程中对界面粘接、纸张结构与性能的不同贡献。不同来源芳纶短纤维与浆粕的内聚能密度CED均在530～540 J·cm-3,F1-纤和F2-浆分别较F2-纤和F1-浆的内聚能稍强。CED越高,说明分子链间的以氢键为主的宏观次价键作用力越大,有利于纤维维持稳定的凝聚态结构。良好的熔融流动性能、独特的黏度行为、容易结膜等,与F1-浆独特的细微丝晶结构有关,也是芳纶纸成形过程中纤维与浆粕间相容为一体的必要条件。树枝形晶体结构的F1-浆,其分子链段过于细碎,虽然具有较好的相对分子质量分布,但其高浓度的末端氨基基团结构,使得纤维受热后易返黄,在高压下挺度和刚度性能有所欠缺。F3-纤维在偏光下色彩更加鲜艳,为第二级干涉色,条带间界线也不十分清楚,表示纤维晶体在高取向过程中规整性更好。带状微丝晶结构较F1-浆大,可能是聚合物链段间相互作用力较大而形成强有力的取向结晶,也可能是由于芳纶聚合过程中晶体形成方式不同引起的,F3芳纶聚合物中有大量液晶的形成。纤维TEM观察结果显示,F1-纤中,微纤维晶体是具有一定规整形状的薄片晶,尺寸在纳米级别,约100nm长相互镶嵌堆积。F2-纤中,微纤维晶体颗粒也有一定规整性,但尺寸较大,长约500nm；F3-纤中颗粒细小,分布均匀。片晶组成颗粒大小的区别,主要是因为芳纶聚合条件的差异,形成不同密度的分子链,使得纤维受到热拉伸时聚集态急骤变化引起晶体结构尺度的不同。结合纤维的成纸性能及其形貌特征可知,细化晶粒可以提高纤维的强度性能。纤维和浆粕的衍射峰具有37%～65%的Cauchy分布和34%～62%的Gauss分布特点,表明芳纶产品既受到温度作用的影响产生了粒度的变化,又受到应力作用的影响产生了应变。这与芳纶短切纤维和浆粕生产过程中既受应力场作用又受温度场作用的工艺相一致。热压光导致芳纶纤维CED、结晶度上升,粘度及粘均分子量下降,且Tg与CED、结晶度之间具有一定对应关系。芳纶热压纸结晶度提高主要来自芳纶浆粕的贡献,因为芳纶浆粕初始结晶度较低,具有比短纤维强的冷结晶性能。芳纶纤维和浆粕的DSC曲线,在整个升温过程中即使发生裂解,也不融化而出现熔融吸热峰,这突显芳纶纤维分子链刚性的特征,使其能够保持优异的耐热性能。芳纶浆粕分子量比短切纤维小、初始结晶度也低得多,故玻璃化温度转变更容易,在高于玻化温度时的结晶性能也比短纤维强,两者结构上的差异决定了各自对芳纶纸热压过程机械性能、耐热性能的贡献不尽相同。从浆粕的冷结晶与热裂解过程可以看出,两者均受温度影响显著且敏感,若温度低于300℃,甚至玻化温度270℃以下,不会发生冷结晶现象；如果温度太高则将发生热裂解。故在芳纶纸的热压光中需要控制适当的加工温度,这对芳纶纤维尤其是浆粕的影响非常大。对于同一分子量大小及其分布的浆粕,温度太低则不能很好软化浆粕致使其对短纤维形成粘接,热压纸机械性能不佳,若温度太高则可能导致浆粕低分子量级分的迅速热裂解,影响热压成纸外观颜色及其耐热性能。热压光前后F1-浆和F2-浆的热分析结果表明,成纸用的芳纶短切纤维与浆粕两种纤维的热性能有差异。芳纶浆粕包含较多的非晶态结构,且分子量小于短纤维,分子量分散系数也普遍高于短纤维,故随着温度升高至玻璃化温度以上300℃左右,F1-浆与F2-浆均发生冷结晶现象,表现出较短纤维优良的结晶性能,这恰好说明了芳纶纸热压光过程中芳纶短纤维与浆粕不同性能的发挥。更多还原

【Abstract】 High performance aramid paper is generally acknowledged to be the superior sheet for electrical insulation and structural materials. In China, the great demand of aramid paper almost depends on import for a very long time; since the aramid paper made in China had not well meet the demand of the market and customs. There is a distinct differential between the properties of Chinese paper and Nomex in Du Pont. The properties of paper formation, thickness uniformity, and the physical strengths still need to be improved. The essential reason of the quality defect is due to the lacking of researches on basic theories and key techniques of the correlated cross-discipline.The key point of improving the paper properties is to determine the relationship between the fiber structures, which correlated to the fiber properties, and properties of the papermaking. To determine this, a series of questions will be dealt with from the perspective of material science and physical chemistry in this project.The adhesion properties of aramid fiber and fibrids will be revealed by study on their interfiber chemical forces, fiber surface energy, and electrochemical properties. The main factors of influence the aramid sheet formation, density and thermal resistance properties should be scientifically evaluated via investigating of the thermal resistance of aramid fiber and fibrids. In addition, study on the characteristic of fiber crystalline structure and dynamic viscoelastic properties were expected to support a theoretical analysis on the special difference of aramid sheet strength. With this foundation, more information of correlations between the surface properties, structure feature, and thermal properties with papermaking characteristics were studied. Thus, we can adjust the process of sheet forming and hot press, and further improve the techniques of fiber interfacial adhesion.The structure and surface properties of aramid fiber depends mainly on process it undergone in dry-spinning or wet spinning. Optical microscopy, scanning electric microscopy (SEM) and atomic force microscopy (AFM) were used for the microstructure analysis of aramid fibre/fibrids, and the cross sectional structure of aramid short fibre were observed by transmitting electric microscopy (TEM).The SEM observation showed the linear coverage of F1-fibres with discontinuous pleats, which are fairly uniformly distributed and run parallel to the fibre axis direction, no obvious skin-core structure. The surface pleats traces are fibrillar structure, which formed in the wet spinning process and caused by the steep change in the molecular structure. It is a precursor of a surface defects. Fibrids are soft like handkerchief with a few hundred microns or less in both length and width. They are non-rigid filmy, ribbon-like particles with irregular shape. Fibrids have an average length of 0.2 to 1 mm. These morphology characteristics of fibrids are beneficial to get well-dispersion and lap together in wet forming process.F2-fiber was brown, irregular shape with a thin groove in the middle of fibre surface, the cortex was in expanded state, which was also associated with spinning process. F3-fiber has a uniformity morphology and smooth surface. Cross-sectional TEM image of aramid fibers showed large differences in micro-fine degree between fibers of the various manufacturing processes. Nomex process F3-fiber had a very tiny micro-fiber and dense array.Heat preservation and cold impregnating process were conducted to the hot pressed aramid sheet, and the effects on sheet properties were studied. After the warm keeping time of 1- 3min, the tensile strength can be increased by 8%～10%, the paper elongation increased by 10%. After cold soaking the paper tensile strength index decreased by 4%, elongation increased by 10% or more, may due to water absorbing in the process of cold soaking. Tear index showed a fluctuate trend in both of the cold impregnating and heat preserving. Cold-impregnated samples were retreated by hot-pressing and warm keeping process. It was found that the strength parameters were significantly restored, which suggested significance of temperature for aramid fiber into paper. Therefore, a gradual cooling of sheet after hot pressing on the performance of aramid paper is a very important process.Sheet forming by laminating different layers with various furnish compounds was applied for better sheet structures. The sheet consists of three layers or more. In which, more fibrids were arranged in the surface and bottom layers of sheet, and more fibres in the middle layers than that of single layer sheet, so advantages of the two aramid fibre and fibrids were fully used, and a good formation and high strength aramid papers obtained.The hot-pressing process with warm keeping of aramid sheet was optimized by orthogonal experiment; the relevant factors affecting the performance of paper and level were analyzed. The results showed that the pressing temperature, warm keeping time and pressure were the main factors of F1-paper properties. F1-paper hot-pressing process was improved as follows: pressing temperature 240℃and holding time of 3min, thermal pressure 14MPa, pressure roller speed 1.5r/min,3-time pressing.main factors of F2-paper properties were hot-pressing temperature, heat stress and pressure roller, hot-pressing holding time was the secondary factors; F2-paper hot-pressing process were hot-pressing temperature of 240℃, holding time of 2min, thermal pressure 14MPa, roller speed 1.5r/min, pressing 4 times.Paper surface in XY and Z dimensions were investigated by image analysis techniques and SEM, TEM, AFM and confocal laser scanning microscope (CLSM). Internal structure and composition of sheet and its effect on sheet properties were also researched. The response of mechanical properties and the microstructure of an aramid sheet to the hot pressing process were present in this paper. It showed that hot pressing in aramid sheet manufacturing greatly improved the total properties of the sheets. Temperatures of calendering from 130-240℃were conducted in our experiment.Sheet density, tensile, and elongation were improved considerately by factors of 4,5 and 7 times, respectively in the hot calendering process at 240℃. Scanning electron microscopy (SEM) observation showed that the surface of the sheet becomes much smoother due to the melting of some of the fibrids in the sheet, which also contributed to a stronger adhesion between the fibres and fibrids. Fibres were deformed more than 20% by calendaring and the surfaces of fibres pulled out from the sheets were clean. Fibrids acted as binder and filler for the floc in the sheet structure. The increased tensile strength combined with the increased elongation suggested that the binding between the fibres and fibrids is mainly due to physical adhesion, rather than a chemical bonding, and this is verified to be hydrogen bond by FTIR.The relationship between formation and grammages of aramid sheets were analyzed. Grammage also strongly influences the relation between formation and properties of aramid paper. The effects of formation components on properties of sheets with various grammages were discussed in detail. The results showed that the increase of grammage was benefit for improving the small scales of formation. The analysis of. components of formation theoretically demonstrated that the staple fibers mainly provide mechanical strength, while fibrids particles provide the dielectric strength for the aramid paper structure; furthermore, it can be inferred that improving of the full wave impulse are mainly depend on the furnish ratios of the two kinds of aramid fibers.Cross-sectional TEM observation of sheet showed that aramid microfibers were not melted together by hot-pressing process or a transition zone interface were formed between fiber and matrix. Different process raw materials present different interface bonding properties. Micro-fibers from F3-pulp-based matrix like fingerprints, showing a stripe and spiral-like structure. While the fingerprint features in bonding region of F1-and F2-pulp are not prominent; fiber surface of the groove marked with the pulp to form "pinning-type" interface structure; some regions of the fiber and pulp interface even form a "gap-type" interface with a great distance from each other, this phenomenon may be related to differences in heat shrinkable nature of fiber and pulp. Based on theory of droplet shape and the Young-Laplace equation, surface contact angle of a single aramid fiber were measured by using vector technology. Chemical reagents for aramid fiber surface treatment had significant impact on contact angle. DMAc, DMF, toluene, chloroform, dichloro-propane may make Kevlar fiber surface contact angle smaller, the minimum contact angle reduced to 44.9, which increase the fiber dispersion in water and improve the sheet formation.Surface energy, hot press bonding behavior and adhesion properties of aramid sheet materials were discussed. Interface microstructure characteristics and properties of aramid sheet were analyzed. Raw materials factor, manufacturing processes, thermal stresses generated by hot-pressing process of interfacial properties were comprehensive considered. The surface contact angles of several meta-aramid fibres and meta-aramid pulps as well as their sheets were measured, the surface energy of aramid fibre, aramid pulp and sheet were determined according to harmonic mean-based Wu equation. The relationship between surface energy and sheet properties in sheet processing were discussed according to surface energy as well as interfacial tension and work of adhesion of the aramid fibre and pulp. The results show that surface energy of aramid fibres is in the range of 35-45mJ/m2, the surface energy of fibres is slightly higher than pulps, polar component of surface energy is larger than dispersion one, wettability and work of adhesion are enhanced with increase of the surface energy of aramid fibres and pulp, when water and glycol are employed as the testing liquids,. The surface energy of aramid sheet decreases during hot-press process, and compared to Nomex sheet, the surface energy of self-made aramid sheet decreases sharply after hot-press process. The better matching of polar component and dispersion component, and the smaller the difference of surface energy and the smaller interfacial tension, the stronger adhesion between fibres and pulp with the improved strength of aramid sheet. Understanding the interactive force and bonding force between aramid fibres and fibrids is important in design wet-forming and hot pressing technologies for manufacturing aramid paper sheet and in producing the paper sheets of desirable properties. In this study, the morphology of both aramid fibres and fibrids were observed with SEM and AFM. The adhesion force between aramid fibres and fibrids were measured by AFM with a small piece of fibrid attached to a regular AFM tip. The results show that the adhesion force between aramid fibrid and fibrid is 9.20±0.86nN and that between fibrid and fibres is 1.71±0.42nN. This explains the importance of the fibrids in the aramid paper sheet in helping bonding between the aramid fibres and gives the resulting sheet a strong physical structure. The adhesion force measured by AFM was confirmed by a theoretical calculation with the Derjaguin-Muller-Toporov (DMT) theory.A relationship between fibre structure and thermal property has been found. Firstly, the structure of aramid fibre during the hot-calendering process have altered notably, the viscosity and viscosity-average molecular weight of aramid fibre decreades with increase of fibre ohesive energy density, crystallinity and glass transition temperature. Additionally, GPC-MALLS testing results show the average molecular weight and molecular weight distribution coefficient of aramid fibre and pulp are 100～150 thousand and 1～2 respectively. XRD testing results indicate that the crystallinity of aramid fibre is higher than that of aramid pulp with non-crystal structure thereof. And it is concluded from DSC-TG that the pyrolysis peaks can only be found within the aramid fibre, in contrast, the glass transition temperature (start at 270℃) and re-crystallinity (start at 300℃) happens in aramid pulp with increased temperature. The pyrolysis temperature of aramid fibres can heighten with increase of average molecular weight, decrease of molecular weight distribution coefficient and improved re-crystallinity, and re-crystallinity ability depends on primal structure of the aramid fibre. Pyrolysis causes increased low molecular weight and deepened color of aramid fibre, and the integral intensity of DSC pyrolysis peak and heat-resistant ability can be enhanced with increased crystallinity at the start of pyrolysis process.The relationship between surface energy and paper properties in paper processing were discussed according to the surface energy, interfacial tension and work of adhesion of the aramid fibre and pulp. The results show that surface energy of aramid fibres and pulps is in the range of 35～45mJ/m2, the surface energy of fibres is slightly higher than that of pulps, and the polar component of surface energy is larger than the dispersion one, the wettability and work of adhesion are enhanced with increase of the surface energy of aramid fibres and pulp, when water and glycol are employed as the testing liquids,. The surface energy of aramid paper decreases during hot-press process, and compared to Nomex paper, the surface energy of self-made aramid paper decreases sharply after hot-press process. The better matching of polar component and dispersion component, and the smaller the difference of surface energy and the smaller interfacial tension, the stronger adhesion between fibres and pulp with the improved strength of aramid paper but left unclear laws upon tear strength of aramid paper.更多还原