Preparation and properties of biocomposites composed of glycerol‐based epoxy resins,tannic acid,and wood flour

After polyglycerol polyglycidyl ether (PGPE) and glycerol polyglycidyl ether (GPE) were mixed with tannic acid (TA) in ethanol and without solvent at epoxy/hydroxyl ratio 1/1, the obtained GPE‐TA and PGPE‐TA solutions were mixed with wood flour (WF), prepolymerized at 50°C, and subsequently compressed at 160°C for 3 h to give GPE‐TA/WF and PGPE‐TA/WF biocomposites with WF content 50–70 wt %, respectively. The storage moduli of the biocomposites in the rubbery state at more than 80°C were much higher than that of the control cured resins. The PGPE‐TA/WF composites had higher tensile modulus and rather lower tensile strength than PGPE‐TA. On the other hand, both the tensile modulus and strength of GPE‐TA/WF were much higher than those of GPE‐TA (2.4 GPa and 37 MPa). Those values of GPE‐TA/WF increased with WF content, became maximal values (5.1 GPa and 51 MPa) at WF content 60 wt %, and were lowered at 70 wt %. FE‐SEM analysis of the fractured surface of the biocomposites revealed that WF is tightly incorporated into the crosslinked epoxy resins. As a result of optimization of the epoxy/hydroxyl molar ratio for GPE‐TA/WF composite with WF content 60 wt %, the composite prepared at the ratio of 1.0/0.8 showed the highest tensile modulus and strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of mold design on the mechanical properties of high-pressure injection—molded polyethylene

High-pressure injection molding (nominal pressure 500 MPa) is known to substantially improve the mechanical properties of high-density polyethylene of a high molecular weight (HMWPE). This work shows that if the mold is equipped with an exit cavity, the tensile modulus and strength of HMWPE-bars molded is further improved at high pressure levels. The maximum values of the stiffness and strength (thin bars, 1 mm) obtained with the exit chamber is about 12 GPa and 260 MPa, respectively. The improvement due to the exit cavity is of the order of 30 percent for the tensile strength for thicknesses lower than 4mm, while the modulus increases about 1 to 1.5 GPa for bars with thicknesses between 1 and 6 mm. The orientation of the melt during the filling of the mold was also found to have an influence on the mechanical properties of the HMWPE bars.     

Mechanical and physical properties of ultraoriented polyoxymethylene produced by microwave heating drawing

The properties of ultra-oriented polyoxymethylene tubes produced by drawing under microwave heating have been assessed by mechanical testing, optical microscopy, scanning electron microscopy, X-ray analysis, birefringence and differential scanning calorimetry. The highest Young's modulus of 58 GPa was obtained at room temperature (77 GPa at ?150°C) at a draw ratio of 33. The maximum tensile strength was 1.7 GPa at a draw ratio of 26. The nonuniformity of Young's modulus in a radial direction has been compared with the nonuniformity of the birefringence and heat of fusion.     

Ultra-high modulus isotactic polypropylene. I. The influence of orientation drawing and initial morphology on the structure and properties of oriented samples

The influence of a number of factors (temperature–speed regime and the quantity of draw stages, molecular weight of a polymer, etc.) on the deformability of initial isotropic IPP and on mechanical characteristics of highly-oriented samples, obtained in the process of a two-stages isothermal orientation drawing, was studied. It was shown that the maximum achievable values of elastic modulus and draw ratio depended not only on the molecular weight of a polymer and the sizes of spherulites, constituting initial IPP, but on the structural organization of inner-and interspherulite regions. Upon physical aging of initial isotropic films, irreversible structural changes take place, which result in the formation of microvoids while being drawn and in the reduction of mechanical properties of obtained material. An extremal dependence of elastic modulus and draw ratio of maximum drawn IPP samples on draw speed was discovered. A structural model, which is supposed to possesstie molecules with various degrees of tautness in amorphous layers, was proposed. Higher effectiveness of two-stage drawing in comparison with one-stage drawing was established. The optimum temperature–speed regime of orientation drawing, which permits the reception of highly oriented, ultra-high modulus IPP with maximum high mechanical characteristics (elastic modulus ～ 30–35 GPa and tensile strength ～ 1,1 GPa), was determined.     

High modulus semi-crystalline polymers by solid state rolling

Solid state rolling of semi-crystalline polymers is shown to be an effective method of producing high strength, high modulus tape at acceptable production rates. High density polyethylene tape was produced having a tensile strength exceeding 300 MPa and a tensile modulus of 8.7 GPa at production rates exceeding 8 m/min. A significant factor in producing highly oriented tape by the rolling process is roll temperature. Increasing the roll temperature from 25°C to 125°C not only increases the maximum extent of orientation achievable, but increases the mechanical properties at a given degree of thickness reduction. Internal frictional heat development limited the maximum thickness reduction ratio of polypropylene to 6.6:1. This reduction was reached by rolling at 150°C. The resultant tape had a tensile modulus of 5.1 GPa and a tensile strength of 300 MPa.     

Biaxial orientation of linear polyethylenes using the compressive deformation process

The tensile properties of three grades of linear polyethylene were enhanced by a factor of as much as 15 using a melt/solid phase compressive deformation process that produced equi-biaxial planar orientation in the sheet. Ultra high molecular weight polyethylene with planar isotropy and an in-plane modulus of 10 GPa and a tensile strength of 330 MPa was produced using this method. It was found that the molecular weight had a significant influence on the optimum processing temperature, the ultimate biaxial deformation ratio and hence the ultimate tensile properties. High density polyethylene processed under ideal conditions had a tensile modulus of 2.3 GPa and a tensile strength of 250 MPa. The tensile strength increased linearly with increasing biaxial deformation ratio and the tensile modulus increased non-linearly with increasing biaxial deformation ratio. The deformation rate and the dwell time did not have a significant effect on the tensile properties. Shrinkage tests showed that biaxial deformation was less effective than uniaxial deformation in inducing orientation of the polymer chains, however differential scanning calorimetry results were consistent with the presence of extended chain crystals in very highly oriented ultra high molecular weight polyethylene sheets.     

Preparation and characterization of syndiotacticity-rich ultra-high molecular weight poly(vinyl alcohol)/imogolite blend film

To enhance the physical properties of syndiotacticity-rich (syndiotactic diad content 63·4%) ultra-high molecular weight (UHMW) (number-average degree of polymerization 12300) poly(vinyl alcohol) (PVA) film, it was solution blended with rigid-rod imogolite in dimethyl sulphoxide. In addition, the blend film prepared was stretched using a high-temperature zone drawing technique for effective orientation of the film. Through a series of experiments, it was found that imogolite caused significant changes in the structure and properties of syndiotacticity-rich UHMW PVA film, i.e. imogolite acted as an important agent which increased crystal orientation of syndiotacticity-rich UHMW PVA, resulting in enhanced tensile strength of the film. However, imogolite played a hindering role in raising the amorphous orientation of syndiotacticity-rich UHMW PVA. The maximum tensile modulus of 19·8GPa and maximum tensile strength of 1·8GPa could be obtained at the maximum draw ratio of 7·45 for PVA/imogolite blend film. In the case of PVA homo film, the highest tensile modulus and strength were 25·2GPa and 1·4GPa, respectively. © 1998 Society of Chemical Industry     

Mechanical properties and microstructure of poly(ethylene terephthalate) microfiber prepared by carbon dioxide laser heating

We determined that a poly(ethylene terephthalate) microfiber was easily obtained by irradiating a carbon dioxide laser to an annealed fiber. The annealed fiber was prepared by zone drawing and zone annealing. First, an original fiber was zone drawn at a drawing temperature of 90°C under an applied tension of 4.9 MPa, and the zone‐drawn fiber was subsequently zone annealed at 150°C under 50.9 MPa. The zone‐annealed fiber had a degree of crystallinity of 48%, a birefringence of 218.9 × 10^?3, tensile modulus of 18.8 GPa, and tensile strength of 0.88 GPa. The microfiber prepared by laser heating the zone‐annealed fiber had a diameter of 1.5 μm, birefringence of 172.8 × 10^?3, tensile modulus of 17.6 GPa, and tensile strength of 1.01 GPa. The draw ratio estimated from the diameter was 9165 times; such a high draw ratio has thus far not been achievable by any conventional drawing method. Microfibers may be made more easily by laser heating than by conventional technologies such as conjugate spinning. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1955–1958, 2003     

Cross-linking of ultra-high strength polyethylene fibres by means of electron beam irradiation

Summary Ultra-high strength polyethylene fibres, with a tensile strength at break of 3.0 and 3.4 GPa, were irradiated, at various temperatures in a hydrogen atmosphere, by means of high energy electrons.When the fibres were not annealed, the tensile strength at break was found to decrease upon irradiation, while the Young's modulus remained unchanged. A maximal obtainable tensile strength of 22 GPa was calculated from the decrease in tensile strength and the gel-sol measurements. Gel contents upto 100% were obtained for fibres irradiated in the hexagonal phase.     

Young modulus and degree of crystallization of highly‐elongated polyoxymethylene

The physical structure of polyoxymethylene (POM) drawn into two steps by a press and a simultaneous biaxial drawing machine was studied and the drawing dependency on the degree of the crystallization, the orientation, and the modulus were analyzed. The stretching ratio by the press reached 6.0 and the tensile modulus of elasticity increased from 2.5 to 4.5 GPa. However, the degree of crystallization decreased slightly. The rupture elongation increased in the lower drawing region and it peaked when the drawing ratio was 1.7. The film stretched by 2 times was drawn by the biaxial drawing machine. The high tensile modulus of elasticity was obtained and the maximum value was 11.5 GPa at 14 times of the drawing ratio. The lamella structure of POM was supposed to loosen and become oriented to the drawing axis ambiguously by the first drawing. The lamella was highly oriented by the second stretching procedure. The tensile strength and the elongation as well as the modulus were analyzed as a function of the degree of the stretching and the crystallization. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1223–1227, 2006     

Molecular Orientation and Mechanical Properties of Poly(Vinyl Alcohol) Fibers

Abstract

A number of poly(vinyl alcohol) fibers with different draw ratios was characterized by measuring the birefringence, crystalline orientational order, crystallinity, tensile strength, and modulus. The birefringence, tensile strength and modulus increased with increasing draw ratio whereas the crystallinity and crystalline order parameters remained constant within narrow limits. The increase in birefringence has to be attributed solely to an increase in chain orientation in the amorphous phase of the semicrystalline fiber. The tensile strength and modulus are therefore directly related to the chain orientation in the amorphous phase. With the aid of a simple two-phase model it was found that the modulus of the amorphous phase in its disordered conformation was 4.8 GPa. The intrinsic birefringence of the amorphous phase was found to be 79 × 10^?3, i.e. much higher than the value obtained for the crystalline phase (52 × 10^?3). When this value was used in calculations, it was found that the order parameter of the amorphous phase increased from around 0.1 for a draw ratio of 1 to approximately 0.6 for a draw ratio of 5, whereas the order parameter of the crystalline phase was close to 1 for all draw ratios.     

High strength and high modulus carbon fibers

Carbon fibers have been processed from gel spun polyacrylonitrile copolymer on a continuous carbonization line at Georgia Tech (GT) with a tensile strength in the range of 5.5–5.8 GPa, and tensile modulus in the range of 354–375 GPa. This combination of strength and modulus is the highest for any continuous fiber reported to date, and the gel spinning route provides a pathway for further improvements in strength and modulus for mass production of carbon fibers. At short gauge length, fiber tensile strength was as high as 12.1 GPa, which is the highest value ever reported for a PAN based carbon fiber. Structure analysis shows random flaws of about 2 nm size, which results in limiting tensile strength of higher than 20 GPa. Inter-planar turbostratic graphite shear modulus in high strength carbon fibers is 30 GPa, while in graphite the corresponding value is only 4 GPa.     

国产高强高模芳纶Ⅲ纤维的拉伸性能测定

对11批次国产高强高模芳纶Ⅲ纤维进行了拉伸性能检测,结果表明:9批次的芳纶单束纱拉伸强度在4.78~5.32 GPa之间,拉伸弹性模量在123.71~129.26 GPa之间,断裂延伸率在3.87%~4.20%之间,离散系数均小于5%;2批次的合股束纱拉伸强度在4.96~5.02 GPa之间,拉伸弹性模量在106.7~107.7 GPa之间,断裂延伸率为4.60%,离散系数均小于5%,证明国产芳纶Ⅲ纤维已经具备了较好的力学性能。     

Rolling and roll-drawing of ultrahigh molecular weight polyethylene reactor powders

Ultrahigh molecular weight polyethylene (UHMWPE) reactor powders have been found to be processable in the solid state by the techniques of rolling and roll-drawing. Plates of compacted UHMWPE reactor powder were prepared below their melting points. These plates were then rolled at 124°C. The maximum uniaxial draw ratio (DR) obtained by multiple rolling was about 10. In additional experiments, rolled plates of a DR of 6 were further drawn by tensile stretching at a temperature of 135°C. The specimens prepared by rolling and by the two-stage draw were characterized by tensile measurements, differential scanning calorimetry (DSC), and X-ray diffraction. Results show that, on rolling alone, the tensile modulus and tensile strength achieved were 3 GPa and 42 MPa, respectively, at a DR of 9.6. The rolled plates were effectively drawn further to a total DR of 86. Such highly drawn films exhibited tensile moduli and tensile strength up to 81 and 1.3 GPa, respectively. A high crystallinity and high crystal orientation were also obtained by the two-stage draw.     

Strong carbon nanofibers from electrospun polyacrylonitrile

Strong carbon nanofibers with diameters between 150 nm and 500 nm and lengths of the order of centimeters were realized from electrospun polyacrylonitrile (PAN). Their tensile strength reached a maximum at 1400 °C carbonization temperature, while the elastic modulus increased monotonically until 1700 °C. For most carbonization temperatures, both properties increased with reduced nanofiber diameter. The tensile strength and the elastic modulus, measured from individual nanofibers carbonized at 1400 °C, averaged 3.5 ± 0.6 GPa and 172 ± 40 GPa, respectively, while some nanofibers reached 2% ultimate strain and strengths over 4.5 GPa. The average tensile strength and elastic modulus of carbon nanofibers produced at 1400 °C were six and three times higher than in previous reports, respectively. These high mechanical property values were achieved for optimum electrospinning parameters yielding strong PAN nanofibers, and optimum stabilization and carbonization temperatures, which resulted in smooth carbon nanofiber surfaces and homogeneous nanofiber cross-sections, as opposed to a previously reported core–shell structure. Turbostratic carbon crystallites with average thickness increasing from 3 to 8 layers between 800 °C and 1700 °C improved the elastic modulus and the tensile strength but their large size, discontinuous form, and random orientation reduced the tensile strength at carbonization temperatures higher than 1400 °C.     

Mechanical properties of LDPE/granular starch composites

The mechanical properties of composites of granular starch and low density polyethylene (PE) have been studied as functions of starch volume fraction ?, granule size, and presence of compatibilizer. Property–volume fraction relationships were interpreted using various theories of composite properties. The dependence of elongation (? ～ ?^1/3) and tensile strength (σ ～ ?^2/3) agree with theoretical predictions, although the proportionality constants are less negative than theoretical values. The addition of compatibilzer (ethylene-co-acrylic acid copolymer, EAA) did not significantly affect the elongation or tensile strength, but significantly increased the composite tensile modulus. The cornstarch/PE moduli could be described by the Kerner or Halpin-Tsai equations. Analysis of the composite moduli data using the Halpin-Tsai equation allowed the estimation of the modulus of granular starch. The value obtained, 15 GPa, is considerably greater than most unfilled synthetic polymers of commercial importance, but significantly lower than the modulus of cellulose. It is also greater than a previously reported value of 2.7 GPa. © 1994 John Wiley & Sons, Inc.     

Ultra-drawing of High Molecular Weight Polyethylene

The effective drawability of solution-cast or -spun high molecular weight polyethylene is enhanced significantly in comparison with an identical polymer sample that is crystallised from the melt. The maximum attainable draw ratio, which primarily determines the final mechanical properties, increases continuously with decreasing initial polymer concentration in solution. A tensile strength of 3.2 GPa and an axial Young's modulus of 120 GPa could be obtained by drawing high molecular weight polyethylene cast from a 1% polymer solution. This phenomenon of increased drawability is discussed in terms of a reduced number of entanglements per macromolecule in solution-cast polyethylene.     

液晶芳香族聚苯唑纤维的性能

论述了液晶态芳香族聚苯唑的干喷湿纺纤维的纺丝工艺条件、热处理条件等对其力学性能的影响,并提出了几种有效的改善其抗压力学性能的途径,指出多数芳香族聚苯唑纤维的抗张强度高于３．１ＧＰａ,抗张模量高于２００ＧＰａ,其中以聚对苯撑苯并二唑纤维性能最佳,其最高抗张强度和抗张模量分别可达６．９ＧＰａ和     

高模量碳纤维的现状及发展(3)

主要介绍了国内外聚丙烯腈基和沥青基高模量碳纤维的研究现状及发展趋势。⑴高模量碳纤维的发展方向:1980年代,两大高模量碳纤维都朝着高强高模方向发展,以满足飞机主承力结构件高强高模并重的需要,因而促使高模量碳纤维的性能从单一高模化向高强高模化方向迈进,如东丽公司的M50J和M60J的抗拉伸强度(σ)分别为4.12 GPa和3.92 GPa,抗拉伸模量(E)分别为475 GPa和588 GPa,与M50(σ:2.45 GPa,E:490 GPa)相比均大幅度提高;1990年代率先研制出XN-70(σ:3.3 GPa,E:690 GPa)和FT-700(σ:3.3 GPa,E:700 GPa)沥青基高强高模碳纤维产品不久,美国AMOCO公司也生产出Thorne K-1000(σ:3.1 GPa,E:956 GPa)商品,满足了工业界的需求。⑵原丝的品质是提升高强高模碳纤维性能的关键:人们特别关注聚合物单体、溶剂、环境等的净化,以及聚合纺丝工艺参数的选择和调整,目的是如何能生产出低灰份杂质,细直径,高碳收率,高取向度和结晶度,毛丝少,柔韧性好,均匀稳定的优质原纤维。优质原纤维是制备高强高模的物质基础。⑶热处理制备工序、设备选型及工艺参数的调控也是提高高强高模碳纤维性能不可或缺的条件:人们在热处理过程用DSC-TG(热分析仪)、EA(元素分析仪)、FE-SEM(场发射扫描电镜)、HRTEM(高分辨透射电镜)、XES(X-射线能谱仪)、XRD(X-射线衍射仪)、Raman(拉曼光谱)、NMR(核磁共振仪)、STM(原子力显微镜)和AAS(原子吸收光谱)等先进的测试分析方法以及万能材料试验机等,研究各工序的工艺参数对产品性能和结构的影响,并详细的用图表阐述之。前人研究的成果加速了世界高强高模碳纤维性能的提升。进而提出了提高我国高强高模碳纤维的关键技术(例如研制非硅系新油剂,加强各工序的净化度和设备加工精度,强化工艺参数调控精度和加强灵活可变性,分析测试的准确度和测试方法的统一性等)。同时简介了高模量碳纤维的应用领域和前景。     

Effect of the dissolution time on the structure and properties of lyocell‐fabric‐based all‐cellulose composite laminates

In this study, all‐cellulose composite laminates were prepared from lyocell fabric with ionic liquid (1‐butyl‐3‐methyl imidazolium chloride), a conventional hand layup method, and compression molding. Eight layers of lyocell fabric, which were impregnated with ionic liquid, were stacked symmetrically and hot‐pressed under compression molding for various times; this resulted in the partial dissolution of the surface of the lyocell fibers. The dissolved cellulose held the laminas together and resulted in a consolidated laminate. Finally, the prepared laminate was impregnated in water to remove the ionic liquid and to regenerate a matrix phase in situ; this was followed by hot‐press drying. Optical microscopy and scanning electron microscopy studies were used to analyze composite structures. With increasing dissolution time, the void content in the composites decreased, and the interlaminar adhesion improved. For LC‐2h and LC‐3h, the highest tensile strength and modulus values obtained were 48.2 MPa and 1.78 GPa, respectively. For LC‐4h, the highest flexural strength and modulus values obtained were 53.96 MPa and 1.2 GPa, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43398.