Influence of cotton variety on compression and destructuration abilities under elevated pressure

Fourteen cotton samples of various strength, maturity and fineness were compressed in the same conditions at elevated pressure (2.0 GPa) and temperature (120 °C) in a home-made Bridgman anvil press designed to process samples of about 20 mm diameter. The influence of cotton properties to the abilities to be compacted into a solid 3D object was studied by mechanical measurements (nano-indentation and DMA) and scanning electron morphology observations. No influence of maturity ratio was observed. But strength and fineness were important parameters. It was shown that the lower are the mechanical properties of the cotton fibres (low strength or large fineness value), the easier it is to compact them. By observing the morphology of compacted samples, it was shown that compaction is linked to the destructuration of fibres under pressure down to the nanofibrillar level.     

Chemically modified cellulose micro- and nanofibrils as paper-strength additives

Chemically modified cellulose micro- and nanofibrils were successfully used as paper strength additives. Three different kinds of cellulose nanofibrils (CNFs) were studied: carboxymethylated CNFs, periodate-oxidised carboxymethylated CNFs and dopamine-grafted carboxymethylated CNFs, all prepared from bleached chemical fibres of dissolving grade, and one microfibrillated cellulose from unbleached kraft fibres. In addition to mechanical characterization of the final paper sheets the fibril retention, sheet density and sheet morphology were also studied as a function of addition of the four different cellulose fibrils. In general, the cellulose fibrils, when used as additives, significantly increased the tensile strength, Young’s modulus and strain-at-break of the paper sheets. The effects of the different fibrils on these properties were compared and evaluated and used to analyse the underlying mechanisms behind the strengthening effect. The strength-enhancing effect was most pronounced for the periodate-oxidised CNFs when they were added together with polyvinyl amine (PVAm) or poly(dimethyldiallylammonium chloride) (pDADMAC). The addition of periodate-oxidised CNFs, with pDADMAC as retention aid, resulted in a 37% increase in tensile strength at a 2 wt% addition and an 89% increase at a 15 wt% addition (from 67 to 92 and 125 kNm/kg, respectively) compared to a reference with only pDADMAC. Wet-strong sheets with a wet tensile index of 30 kNm/kg were also obtained when periodate-oxidised CNFs and PVAm were combined. This significant increase in wet strength is suggested to be the result of a formation of cross-links between the aldehyde groups, introduced by the periodate oxidation, and hydroxyl groups on the lignocellulosic fibres and the primary amines of PVAm. Even though less significant, there was also an increase in wet tensile strength when pDADMAC was used together with periodate-oxidised fibrils which shows that the aldehyde groups are able to increase the wet strength without the presence of the primary amines of the PVAm. As an alternative method to strengthen the fibre network, carboxymethylated CNFs grafted with dopamine, by an ethyl dimethylaminopropyl carbodiimide coupling, were used as a strength additive. When used as an additive, these CNFs showed a strong propensity to form films on and around the fibres and significantly increased the mechanical properties of the sheets. Their addition resulted in an increase in the Young´s modulus by 41%, from 5.1 to 7.2 GPa, and an increase in the tensile strength index of 98% (from 53 to 105 kNm/kg) with 5 wt% retained dopamine-grafted CNFs.     

Dynamic mechanical and crystal-strain measurements on ultrahigh modulus oriented polyoxymethylene: A revised value for the true crystal modulus

Dynamic mechanical measurements on ultrahigh modulus polyoxymethylene have been undertaken over the temperature range ?150 to 20°C. Measurements of the longitudinal crystal modulus have also been made by studying changes in the (009) reflection with load, over a similar range of temperatures. The dynamic Young's modulus at 5 Hz reaches a value at low temperatures of 64.5 GPa for the most highly oriented sample. The crystal modulus at low temperatures is 105 GPa, which is almost twice the previously reported room-temperature value.     

Measurement of the flexibility of wet cellulose fibres using atomic force microscopy

Flexibility and modulus of elasticity data for two types of wet cellulose fibres using a direct force–displacement method by means of AFM are reported for never dried wet fibres immersed in water. The flexibilities for the bleached softwood kraft pulp (BSW) fibres are in the range of 4–38 × 10¹² N^?1 m^?2 while the flexibilities for the thermomechanical pulp (TMP) fibres are about one order of magnitude lower. For BSW the modulus of elasticity ranges from 1 to 12 MPa and for TMP between 15–190 MPa. These data are lower than most other available pulp fibre data and comparable to a soft rubber band. Reasons for the difference can be that our measurements with a direct method were performed using never dried fibres immersed in water while other groups have employed indirect methods using pulp with different treatments.     

Tensile properties and structure of polypropylene fibres spun from a blend of different polymer grades

 The tensile behavior of fibres, spun from a blend of small percentage of plastic grade poly-propylene with fibre grade poly-propylene, was studied in relation to their structure. The spinning and drawing process was optimized in order to increase the elastic moduli of produced filament yarns. By such optimization of the process a tenacity of 0.7 GPa, an elastic modulus of 14.8 GPa and a dynamic modulus of 19 GPa were attained. From diffuse small-angle X-ray scattering the presence of voids, up to 11.5%, was established. Voidness of the fibrillar structure was confirmed with electron micrographs. In spite of the rather drastic changes in morphology the mechanical properties of high void fibrillar structures are good, indicating that the load bearing units of the filament have maintained their integrity. The improved mechanical behavior of highly drawn fibres spun from 10/90 plastic/fibre grade polymer blend is related to higher crystalline and above all to higher amorphous orientation. Received: 12 December 1996 Accepted: 28 February 1997     

Kapok/cotton fabric–polypropylene composites

Kapok/cotton fabric has been used as reinforcement for conventional polypropylene and maleic anhydride grafted polypropylene resins. Treating the reinforcement with acetic anhydride and sodium hydroxide has modified the fabric (fibres). Thermal and mechanical properties of the composites were investigated. Results show that fibre modification gives a significant improvement to the thermal properties of the plant fibres, whereas tests on the mechanical properties of the composites showed poor tensile strength. Mercerisation and weathering were found to impart toughness to the materials, with acetylation showing slightly less rigidity compared to other treatments on either the fibre or composites. The modified polypropylene improved the tensile modulus and had the least toughness of the kapok/cotton reinforced composites. MAiPP reinforced with the plant fibres gave better flexural strength and the same flexural modulus at lower fibre content compared with glass fibre reinforced MAiPP.     

The disproportionation reaction phase transition,mechanical, and lattice dynamical properties of the lanthanum dihydrides under high pressure: A first principles study

The pressure-induced disproportionation reaction phase transition, mechanical, and dynamical properties of LaH₂ with fluorite structure under high pressure are investigated by performing first-principles calculations using the projector augmented wave (PAW) method. The phase transition of 2LaH₂ → LaH + LaH₃ obtained from the usual condition of equal enthalpies occurs at the pressure of 10.38 GPa for Perdew–Wang (PW91) functional and 6.05 GPa for Ceperly–Adler (CA) functional, respectively. The result shows that the PW91 functional calculations agree excellently with the experimental finding of 11 GPa of synchrotron radiation (SR) X-ray diffraction (XRD) of Machida et al. and 10 GPa of their PBE functional theoretical result. Three independent single-crystal elastic constants, polycrystalline bulk modulus, shear modulus, Young's modulus, elastic anisotropy, Poisson's ratio, the brittle/ductile characteristics and elastic wave velocities over different directions dependences on pressure are also successfully obtained. Especially, the phonon dispersion curves and corresponding phonon density of states of LaH₂ under high pressure are determined systematically using a linear-response approach to density functional perturbation theory (DFPT). Our results demonstrate that LaH₂ in fluorite phase can be stable energetically up to 10.38 GPa, stabilized mechanically up to 17.98 GPa, and stabilized dynamically up to 29 GPa, so it may remain a metastable phase above 10.38 GPa up to 29 GPa, these calculated results accord with the recent X-Ray diffraction experimental finding and theoretical predictions of Machida et al.     

Melting cellulose

Cellulose has been deformed plastically by the use of mechanical shear, uniaxial pressure, and laser radiation. Felty specimens either from wood pulp or cotton wool were converted to thin compact transparent disks. Afterwards, the disks were examined by IR-spectroscopy, light microscopy, and scanning electron microscopy. This novel approach may pave the way for a new method to convert natural cellulose to plastic products (fibres, films), thus widening the use of natures most frequent polymer.     

Mechanical properties of hybrid glass/sugar palm fibre reinforced unsaturated polyester composites

A research has been carried out to investigate the mechanical properties of composites made by hybridizing sugar palm fibre (Arenga pinnata) with glass fibre into an unsaturated polyester matrix. Hybrid composites of glass/sugar palm fibre were fabricated in different weight ratios of strand mat glass fibres: sugar palm fibres 4:0, 4:1, 4:2, 4:3, 4:4, and 0:4. The hybrid effects of glass and sugar palm fibre on tensile, flexural and impact properties of the composites were evaluated according to ASTM D5083, ASTM D790 and ASTM D256 respectively. Results have been established that properties of hybrid glass/sugar palm composites such as tensile strength, tensile modulus, elongation at break, toughness, flexural strength, flexural modulus and impact strength are a function of fibre content. The failure mechanism and the adhesion between fibres/matrix were studied by observing the scanning electron micrographs of impact fracture samples. In general, the incorporation of both fibres into unsaturated polyester matrix shows a regular trend of increase in the mechanical properties.     

Mechanical and optical properties of SiO<Subscript>2</Subscript> thin films deposited on glass

The optical and mechanical properties of amorphous SiO₂ films deposited on soda-lime silicate float glass by reactive RF magnetron sputtering at room temperature were investigated in dependence of the process pressure. The densities of the films are strongly influenced by the process pressure and vary between 2.38 and 1.91 g cm^?3 as the pressure changes from 0.27 to 1.33 Pa. The refractive indices of the films shift between 1.52 and 1.37, while the residual compressive stresses in the deposited films vary in the range from 440 to 1 MPa. Hardness and reduced elastic modulus values follow the same trend and decline with the increase of process pressure from 8.5 to 2.2 GPa and from 73.7 to 30.9 GPa, respectively. The abrasive wear resistance decreases with the density of the films.     

First-principles investigations on structural,electronic and elastic properties of BeSe under high pressure

The structural, electronic and elastic properties of BeSe in both B3 and B8 structures have been studied by first-principles calculations within the generalized gradient approximation (GGA). The calculated lattice parameters and bulk modulus of BeSe are in reasonable agreement with previous results. The predicted value of phase transition pressure from B3 to B8 is 50.24 GPa, which is well in line with the experimental data (56 ± 5 GPa). The calculation of the electronic band structure shows that the energy gap is indirect for B3 and B8 phases. Especially, the elastic constants of B8 BeSe under high pressure were studied for the first time. The bulk modulus, shear modulus, compressional and shear wave velocities of B8 BeSe evaluated from elastic constants as a function of pressure were investigated. In addition, Poisson's radio, elastic anisotropy and Debye temperature were analyzed successfully.     

Electrical and mechanical properties of the zone-drawn polypyrrole films

The zone-drawing method (ZD) was applied to electrochemically synthesized polypyrrole films containing tosylate (PPy/TsO) and the mechanical and electrical properties of the resulting films were investigated. It was found that the electrical conductivity of the zone-drawn film reached 365 S cm⁻¹ in the drawing direction, which was 4.7 times that of the original film. The tensile properties of the zone-drawn film were improved and Young's modulus and strength at break increased to 4.32 GPa and 90.1 MPa from 0.53 GPa and 40.4 MPa of the as-synthesized film, respectively. The dynamic storage modulus (E) increased by the zone-drawing over a whole experimental temperature range and attained 7.0 GPa at room temperature and 4.0 GPa even at 200°C. © 1996 John Wiley & Sons, Inc.     

High‐performance poly(ethylene‐2,6‐naphthalate) fiber prepared by high‐tension annealing

A high‐tension annealing (HTA) method has been applied to zone‐annealed poly(ethylene‐2,6‐naphthalate) (PEN) fibers in order to further improve their mechanical properties. The HTA treatment was carried out under an applied tension of 428 MPa at a treating temperature of 175 °C. The applied tension was close to the tensile strength at 175 °C. The resulting HTA fiber had a birefringence of 0.492 and degree of crystallinity of 57%. Wide‐angle X‐ray diffraction (WAXD) photographs of the HTA fibers showed three reflections (010, 100, and 1 10) attributed to an α form crystal, but no (020) reflection attributed to a β form was observed in the equator. The tensile modulus and tensile strength increased with processing, and the HTA fiber had a maximum modulus of 33 GPa, a tensile strength of 1.1 GPa, and a storage modulus of 33 GPa at 25 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 61–67, 2000     

Preparation and characterization of fibres from a thermotropic liquid crystal polyester with non-coplanar biphenylene units

Abstract

Fibres were prepared from the nematic melt of poly(2,2′-dimethyl-4,4′-biphenylene phenylterephthalate). The phenyl substitution in the terephthalic acid moiety in combination with the non-coplanar biphenyl moiety prevent crystallization of this thermotropic polyester. Oriented fibres were prepared by two different methods. Similarly to other thermotropic liquid crystal polymer fibres, chain orientation can be achieved by an elongational flow in a down draw process. This polyester also allows tensile deformation of the spun fibres around the glass transition temperature. In both routes similar degrees of orientation and mechanical properties were obtained. Tensile moduli in the order of 40–45 GPa and tensile strengths up to 550–650 MPa were obtained. The orientation function values were determined to be in the order of 0·8–0·9. A comparison with other unsubstituted thermotropic liquid crystal polyesters at the same level of orientation revealed that the moduli are the same, although the substituents increase the chain diameter. This result may be attributed to an increase of the apparent shear modulus due to an interlocking mechanism of the rigid lateral substituents.     

Effect of annealing on the structure and properties of poly(vinylidene fluoride) β‐form films

Oriented poly(vinylidene fluoride) (PVDF) films consisting of β crystals were prepared by the solid‐state coextrusion (SC) of a gel film near the melting temperature (T_m) and by conventional cold tensile drawing (TD) of a melt‐quenched film. These films were annealed over the temperature range of 75–190 °C (below and above the static T_m) while the sample length was kept constant or constant loads were applied. After annealing with the sample length kept constant, the dynamic Young's modulus markedly decreased because of the relaxation of oriented amorphous chains, as shown by infrared spectroscopy. In contrast, annealing under a constant load improved the chain orientation in both the crystalline and amorphous regions, resulting in an increase in the modulus from an initial 10.5 to 14.3 GPa for the SC and from an initial 3.3 to 4.8 GPa for the TD. The SC, annealed at 190 °C with a constant load corresponding to an initial tension of 200 MPa, exhibited an extreme crystalline‐chain orientation of 0.998 and a modulus of 14.3 GPa, among the highest values ever reported for PVDF. Although the remanent polarization (P_r) of the TD increased slightly from the initial 62 to 68 mC/m², P_r of the SC stayed constant at 100 mC/m² independently of the annealing conditions. This suggests that the P_r value of 100 mC/m² approached the equilibrium value for this PVDF sample containing 3.5 mol % structural defects. Therefore, although the modulus and P_r of the TD increased slightly with annealing, the maximum values achieved by annealing were markedly lower than those of the SC and annealed SC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1701–1712, 2003     

Stishovite's Relative: A Post‐Coesite Form of Phosphorus Oxonitride

Phosphorus oxonitride (PON) is isoelectronic with SiO₂ and may exhibit a similar broad spectrum of intriguing properties as silica. However, PON has only been sparsely investigated under high‐pressure conditions and there has been no evidence on a PON polymorph with a coordination number of P greater than 4. Herein, we report a post‐coesite (pc) PON polymorph exhibiting a stishovite‐related structure with P in a (5+1) coordination. The pc‐PON was synthesized using the multianvil technique and characterized by powder X‐ray diffraction, solid‐state NMR spectroscopy, TEM measurements and in situ synchrotron X‐ray diffraction in diamond anvil cells. The structure model was verified by single‐crystal X‐ray diffraction at 1.8 GPa and the isothermal bulk modulus of pc‐PON was determined to K₀=163(2) GPa. Moreover, an orthorhombic PON polymorph (o‐PON) was observed under high‐pressure conditions and corroborated as the stable modification at pressures above 17 GPa by DFT calculations.     

First principles investigation on the ultra‐incompressible and hard TaN

The structural, electronic, and mechanical properties of TaN were investigated by use of the density functional theory (DFT). Eight structures were considered, i.e., hexagonal WC, TaN, NiAs, wurtzite, and CoSn structures, cubic NaCl, zinc‐blende and CsCl structures. The results indicate that TaN in TaN‐type structure is the most stable at ambient conditions among the considered structures. Above 5 GPa, TaN in WC‐type structure becomes energetically the most stable phase. They are also stable both thermodynamically and mechanically. TaN in WC‐type has the largest shear modulus 243 GPa and large bulk modulus 337 GPa among the considered structures. The volume compressibility is slightly larger than diamond, but smaller than c‐BN at pressures from 0 to 100 GPa. The compressibility along the c axis is smaller than the linear compressibility of both diamond and c‐BN. The estimated hardness is 34 GPa. Thus, TaN in WC‐type structure is a potential candidate to be ultra‐incompressible and hard. The unique mechanical properties of TaN in WC‐type structure would make it suitable for applications under extreme conditions. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Mechanical properties of the novel organometallic polymer poly(ferrocenyldimethylsilane)

A study of the mechanical properties of poly(ferrocenyldimethylsilane) [Fe(η‐C₅H₄)₂SiMe₂]_n, 3 , a novel organometallic polymer, has been performed on thin films of this material. The Young's modulus and Poisson's ratio of film samples (15 × 1 × 1 mm) of 3 were measured in quasi‐static tension using a video extensometer. For 3 , the values of the Young's moduli (E) and Poisson's ratios (ν) were similar between axes in the plane and independent of the splicing direction used during sample preparation. The mean and standard deviation of the Young's modulus and Poisson's ratio were 0.78 ± 0.08 GPa and 0.37 ± 0.06 GPa, respectively. Thermomechanical analysis of 3 revealed a steady decrease of E from a room temperature value of approximately 0.70 GPa. Additionally, it was found that at 150 °C, 3 was unable to support even small stresses, consistent with the onset of a melt transition (ca. 135 °C). A mathematical model based on molecular geometry is developed to describe the results. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2280–2288, 2005     

Preparation and characterization of poly(m-xylylene oxamide) and its copolymer

New polyoxamides, poly(m-xylylene oxamide) (PMXD2) and its copolymer with 2-methyl-1,5- pentanediamine (P(MXD2/M52)) with relative viscosity up to 4.6 were synthesized via spray/solid state polymerization. The obtained polyoxamides were characterized by FTIR, NMR, WAXD, DSC and TGA. The T_m of the copolymers decreased with increasing percentage of poly(2-methyl-1,5- pentaneoxamide) (PM52) in the copolymer from 346°C for 100% poly(meta-xylyleneoxamide) (PMXD2) to 277°C for copolymers of PMXD/PM52 (60/40). TGA analysis revealed that the thermal stability of the copolymers compared well with commercial PA6 and XRD studies suggested the copolymers possessed high crystallinity. DMA profile of the PMXD/PM52 (70/30) copolymer showed better mechanical performance with a storage modulus of about 7.2 GPa as compared to 1.8 GPa of PA6 at 25°C.     

Nanocrystalline Fe - 1 wt. %C compacts obtained by high pressure torsion of mechanically alloyed powder

Powders of a nanocrystalline Fe - 1 wt.% C alloy produced by mechanical alloying were consolidated to form a bulk nanocrystalline sample by means of high pressure torsion at 540°C. The density of the compacts reached 96 % of the theoretical density. The fracture stress of the material was 1 GPa and the microhardness 7.5 GPa, respectively. The grain size was approximately 70 nm and remained stable up to 700°C. The material contained fine particles of oxides and carbides.