Structures and mechanical properties of plied and twisted polyacrylonitrile nanofiber yarns fabricated by a multi-needle electrospinning device

Polyacrylonitrile (PAN) nanofiber filaments were manufactured continuously for several hours by a homemade multi-needle electrospinning device. The yarns were continuously obtained by plying and twisting nanofiber filaments using a self-made twisting device. The structures and mechanical properties of yarns were investigated. The influences of twist setting temperatures and periods of time on morphology and mechanical properties were discussed. The results showed that the alignment degree of nanofibers along the filament axis could reach 70.9 %. The twist angle increased with increasing twists and the number of filaments. With increasing twists, the breaking stress and strain increased initially and then decreased; the maximum breaking stress and strain were 34.7 MPa and 26.1 %, respectively; the initial modulus decreased with increasing twists and plies, the maximum modulus was 391.3 MPa. Both the breaking stress and strain increased with the increase of twist setting temperatures and times. The optimal setting temperature and time were 90 °C and 30 min, respectively, the maximum breaking stress and strain were 32.8 MPa and 20.8 %, meanwhile, the crystallinity improved from 34.5 % to 39.9 %. This study demonstrates the possibility of continuously and stably manufacturing PAN nanofiber yarns.     

Investigation of mechanical and fracture behavior of plane weave glass fiber/polymer composite with inclined through thickness cracks

The aim of this study is to investigate mechanical and fracture behavior of plane weave glass fiber reinforced high density polyethylene (HDPE) thermoplastic composite using a middle tension (MT) specimen with inclined through-thickness cracks under static tension. In this study, crack growth, crack opening displacement (COD), stress intensity factors and fracture toughness are studied. Crack growth and crack opening displacement values are taken as a damage parameter factor for crack geometry calculations. Experimental results are evaluates using both J-integraland stress intensity factormethods.     

Investigations on mechanical characteristics of glass fiber reinforced epoxy composite modified with amino-terminated hyperbranched polymer

Glass fiber, GF, which was first hydroxylated and silanized, was incorporated into epoxy resin modified with amino-terminated hyperbranched polymer (ATHBP) to obtain high performance composite. The effects of GFs content on the mechanical properties of composites were investigated, discussing the results from flexural, tensile, and impact tests. The composites revealed noticeable improvement in flexural strength, tensile strength as well as impact strength but slow decrease in elongation at break, compared to the epoxy/ATHBP thermoset. FESEM morphology results indicated the good compatibility between epoxy matrix and GF in the appearance of ATHBP and showed that the toughening mechanism was mainly attributed to the stress transfer mechanism.     

Effect of polypropylene fiber cross sectional shapes on some structural/mechanical fiber properties and compressibility behaviour of plain knitted fabrics

Synthetic fibers are generally produced with circular cross sectional shapes. Other cross sectional shaped fibers such as trilobal, triangular, hollow and pentagonal fibers are also produced to improve some properties of fibers and fabrics such as lustre, handle, wicking rate, strength, stiffness and bulkiness. In this research we aimed to investigate compressional behaviours of fabrics knitted from polypropylene fibers having three different cross sectional shapes; namely circular, trilobal and triangular. Morphological, structural and mechanical properties of produced fibers were evaluated by using scanning electron microscopy, X-ray diffractometry, differential scanning calorimetry and tensile tester, respectively. In terms of structural and mechanical properties, no significant differences were found related to fiber cross sectional shapes. Then, plain knitted farbrics were produced and compressional properties of these fabrics were investigated. Fabrics knitted from trilobal fibers showed the highest compressibility properties and it is followed by fabrics which are produced from triangular and circular fibers.     

Effect of the low and radio frequency oxygen plasma treatment of jute fiber on mechanical properties of jute fiber/polyester composite

We investigated the surface modification of jute fiber by oxygen plasma treatments. Jute fibers were treated in different plasma reactors (radio frequency “RF” and low frequency “LF” plasma reactors) using O₂ for different plasma powers to increase the interface adhesion between jute fiber and polyester matrix. The influence of various plasma reactors on mechanical properties of jute fiber-reinforced polyester composites was reported. Tensile, flexure, short beam shear tests were used to determine the mechanical properties of the composites. The interlaminar shear strength increased from 11.5 MPa for the untreated jute fiber/polyester composite to 19.8 and 26.3 MPa for LF and RF oxygen plasma treated jute fiber/polyester composites, respectively. O₂ plasma treatment also improved the tensile and flexural strengths of jute fiber/ polyester composites for both plasma systems. It is clear that O₂ plasma treatment of jute fibers by using RF plasma system instead of using LF plasma system brings about greater improvement on the mechanical properties of jute/polyester composites.     

An experimental investigation on the response of woven natural silk fiber/epoxy sandwich composite panels under low velocity impact

This paper presents results of dynamic deformation behavior of woven natural silk/epoxy sandwich composite panels. The specimens were prepared in configurations of reinforced woven natural silk fiber (RWNSF)/Epoxy/Foam, RWNSF/Epoxy/Coremat; RWNSF/Epoxy/Honeycomb and reinforced RWNSF/Epoxy (control material) using hand-lay-up method. Each of the three core material was sandwiched between reinforced woven natural silk fiber/Epoxy composite facesheet. Drop weight impact test was carried out under 32 J impact energy. Degree of damages inflicted on the contact surface, through thickness and rear surface were analyzed, sandwich composites performed better than the reinforced (control material). Failure mechanism involved interlaminar matrix cracking, layer debonding, delamination and fibre breakage.     

乌龙红碎茶香气组成研究

红碎茶兴起于20世纪30年代，目前已发展成为世界茶叶生产和贸易最大宗的茶类，占世界茶叶贸易量的70％以上。我国红碎茶随着1964年转子机的研制成功，开始大量生产出口。我国出口的以云南大叶种鲜叶加工而成的红碎茶，浓强鲜突出，品质优良，国内外享有盛誉，但香气稍逊于印度、斯里兰卡高山红碎茶，总体品质受到制约，中高档茶不足40％，在国际市场上竞争力弱。为了改变这种状况，提高我国红碎茶品质，扩大出口，广东省农业科学院茶叶研究所在总结红碎茶加工工艺的基础上，导入乌龙茶的部分加工工艺，     

霞浦县茶场推广"元宵茶"速生栽培效果与技术的调查报告

福建省农业厅将“霞浦元宵茶”列为21世纪茶园更新换代新品种之一。我县茶场于九十年代末引种“霞浦元宵茶”获得成功后,从2001年开始逐年引种推广至2005年,全场推广“霞浦元宵茶”15hm2,建成高香特种绿茶生产示范园区。近年来,茶场职工应用茶树速生栽培技术,采用科学管理方法,使幼龄“元宵茶”达到速生成园的效果,成为茶场职工增收的新亮点。1速生栽培效果调查表明,特早高香新品种“霞浦元宵茶”在我县大京茶场坡地红、黄壤茶园栽植,经科学栽培管理,能快速成园,形成丰产型树冠,达到提早收益的效果,尤其是发挥特早开采、品质优异的优良特性,…