Polyamide single polymer composites prepared via in situ anionic polymerization of ε-caprolactam

In order to prepare the polyamide single polymer composites (SPC_PA) comprised of polyamide 6 (PA6) fiber and PA6 matrix, a novel method based on the in situ anionic polymerization of ε-caprolactam was developed. The influence of a critical process parameter, molding temperature, on the structure of SPC_PA was investigated by thermogravimetric analysis (TGA) and scanning electron microscope (SEM). Mechanical properties of SPC_PA prepared at 140, 160, 180, and 200 °C were appraised by three-point bending and tensile test. An optimum molding temperature (160 °C) at which both the tensile and flexural strength reached a peak value was found in the studied molding temperature range. High reaction degree (>93%), low void fraction (<2.5%) and strong and stable fiber/matrix interface contributed to the obvious reinforcing effect of PA6 fibers on PA6 matrix.     

Poly (butylene terephthalate)/silica nanocomposites prepared from cyclic butylene terephthalate

Poly (butylene terephthalate) (PBT)/silica nanocomposites were compounded from cyclic butylene terephthalate (CBT) resin with very low melt viscosity via high-speed stirring and subsequent in situ polymerization. The effect of silica nanoparticles on the properties of CBT and its polymer composites has been studied. It was shown that the well-dispersed silica nanoparticles, even in small content (1–2 wt.%), result in the dramatic extension of the polymerization process of CBT resin. The flexural properties of polymerized PBT nanocomposites, including modulus, yield strength and failure strain, was improved significantly with the incorporation of silica nanoparticles.     

Thermal and rheological properties of highly concentrated PET composites with ferrite nanoparticles

Ferrite nanoparticles were introduced into poly(ethylene terephthalate) (PET) in a melt state at 270 °C upto 20 wt%, and the thermal and rheological properties of the nanocomposites were investigated. The introduction of ferrite nanoparticles increased a little the crystallization temperature (T_c) of PET by ca. 3 °C, while it had little effect on the melting temperature (T_m). In addition, it increased both heat of crystallization (ΔH_c) and heat of fusion (ΔH_m) with ferrite content. PET nanocomposites with ferrite 5 wt% and above exhibited an increased thermal stability and a two-stage degradation. The dynamic viscosity of PET nanocomposites was increased with ferrite content. However, ferrite loading of 5 wt% and above produced a high degree of shear thinning leading to even lower viscosity in a high frequency range than that of pure PET. The nanocomposites gave a non-zero positive value of yield stress, which was notably increased particularly from 5 wt% loading. In the Cole–Cole plot, at contents 1 wt% and above, ferrite nanoparticles caused the deviation from the master curve and a reduced slope. In addition, the relaxation time was increased with ferrite content and an increasing degree was more notable at a lower frequency.     

Ambient cure POSS–epoxy matrices for marine composites

A room-temperature cure epoxy consisting of diglycidyl ether of bisphenol-F (DGEBF) and diethylene triamine (DETA) was modified with 26.5 wt.% and 63.5 wt.% octaglycidyl polyhedral oligomeric silsesquioxane (POSS) to investigate elevated temperature thermomechanical performance. Composites fabricated using vacuum assist resin transfer molding (VARTM) were compared to vinylester and epoxy standards. POSS modified matrices were low viscosity of 0.25–0.40 Pa s. Although T_g was 20% lower than vinylester, we observed an increase of >300% in 150 °C storage modulus, >50% in tensile modulus, >35% in flexural modulus, and the complete elimination of a heat distortion temperature (HDT) up to 200 °C. The matrices demonstrated an excellent balance of flow, wetting, and pot-life behaviors making them attractive alternatives for ambient cure marine applications.     

Bonding strength of heat treated compressed Eastern redcedar wood

The objective of this study was to evaluate effect of heat treatment and compression on some properties of Eastern redcedar (Juniperus virginiana) including bonding strength, hardness and surface quality. Specimens were exposed to three temperature levels of 120 °C, 160 °C and 190 °C for 6 h before they were compressed using 2.5 MPa pressure for 5 min. Polyvinyl acetate (PVAc) bonded specimens showed 23.6% reduction in their shear strength when they were exposed to a temperature of 120 °C. Such strength reduction values were 44.4% and 64.1% for the specimens exposed to temperature levels of 160 °C and 190 °C, respectively. The lowest average Janka hardness value of 214.08 kg was determined for the samples exposed to a temperature of 190 °C while those treated with a temperature of 120 °C had the highest hardness value of 397.73 kg. It appears that combination of heat treatment and compression enchanced overall surface quality of the samples in the form of their roughness determined using stylus type equipment.     

Retention of mechanical performance of polymer matrix composites above the glass transition temperature by vascular cooling

An actively cooled vascular polymer matrix composite containing 3.0% channel volume fraction retains greater than 90% flexural stiffness when exposed continuously to 325 °C environmental temperature. Non-cooled controls suffered complete structural failure through thermal degradation under the same conditions. Glass–epoxy composites (T_g = 152 °C) manufactured by vacuum assisted resin transfer molding contain microchannel networks of two different architectures optimized for thermal and mechanical performance. Microchannels are fabricated by vaporization of poly(lactide) fibers treated with tin(II) oxalate catalyst that are incorporated into the fiber preform prior to resin infiltration. Flexural modulus, material temperature, and heat removal rates are measured during four-point bending testing as a function of environmental temperature and coolant flow rate. Simulations validate experimental measurements and provide insight into the thermal behavior. Vascular specimens with only 1.5% channel volume fraction centered at the neutral bending axis also retained over 80% flexural stiffness at 325 °C environmental temperature.     

Carbide-free bainite in medium carbon steel

Heat-treatment processes to obtain carbide-free upper bainite, low bainite and low-temperature bainite in the 34MnSiCrAlNiMo medium-carbon steel were explored. Results show that in the steel bainite transformation mainly goes through three stages: short incubation, explosive nucleation and slow growth. When transformation temperature, T > Ms + 75 °C, upper bainite consisted of catenary bainitic ferrite and blocky retained austenite is obtained in the steel. When Ms + 10 °C < T < Ms + 75 °C, lower bainite is the main morphology composed of lath-like bainitic ferrite and flake-like retained austenite. When T < Ms + 10 °C, the lower bainite, also known as low-temperature bainite, is obtained, which contains much thinner lath-like bainitic ferrite and film-like retained austenite. Mechanical testing results show that the lower the transformation temperature is, the better comprehensive performance is. The low-temperature bainite has the very high tensile strength and impact toughness simultaneously. The lower bainite has lower tensile strength and higher impact toughness. The upper bainite has higher tensile strength and lower impact toughness. The big difference of the mechanical performance between these kinds of bainite is mainly caused by interface morphology, size, and phase interface structure of the bainitic ferrite and the retained austenite. Additionally, when the bainite transformation temperature is decreased, the high-angle misorientation fraction in packets of bainite ferrite plates is increased. High-angle misorientation between phase interfaces can prevent crack propagation, and thus improves impact toughness.     

Effect of substrate temperature on the properties of pyrolytically deposited nitrogen-doped zinc oxide thin films

The effect of substrate temperature (T_s) on the properties of pyrolytically deposited nitrogen (N) doped zinc oxide (ZnO) thin films was investigated. The T_s was varied from 300 °C to 500 °C, with a step of 50 °C. The positive sign of Hall coefficient confirmed the p-type conductivity in the films deposited at 450 °C and 500 °C. X-ray diffraction studies confirmed the ZnO structure with a dominant peak from (1 0 0) crystal plane, irrespective of the variation in T_s. The presence of N in the ZnO structure was evidenced through X-ray photoelectron spectroscopy (XPS) analysis. The obtained high N concentration reveals that the 450 °C is the optimal T_s. Atomic force microscope (AFM) analysis showed that the surface roughness was increased with the increasing T_s until 400 °C but then decreased. It is found that the transmittance of the deposited films is increased with the increasing T_s. The optical band gap calculated from the absorption edge showed that the films deposited with T_s of 300 °C and 350 °C possess higher values than those deposited at higher T_s.     

Evaluation of hardness and surface quality of different wood species as function of heat treatment

The objective of this study was to evaluate the effect of heat treatment on surface roughness and hardness of four wood species, namely black alder (Alnus glutinosa L.), red oak (Quercus falcata Michx.), Southern pine (Pinus taeda L.) and yellow poplar (Liriodendron tulipifera). Samples were exposed to heat treatment schedules having two temperature and exposure levels of 120 °C and 190 °C for 3 and 6 h, respectively. Average hardness value of red oak samples exposed to a temperature of 190 °C for 6 h was 41.7% lower than that recorded before the heat treatment. Temperature of 190 °C produced 7.9% lower hardness values for black alder with the increased exposure time from 3 h to 6 h. No significant differences were found between same type of Southern pine and yellow poplar specimens before and after the heat treatment in terms of their hardness values. Among the four species considered in this study red oak having the most porous anatomical structure showed the roughest surface. An improvement in surface quality (R_a) with 7.46% with extending exposure time from 3 h to 6 h at the temperature level of 190 °C was noticed. However all four types of wood species kept in the oven at 190° for 6 h presented smoother surface quality. It was found that increased temperature from 120 °C to 190 °C for both exposure times showed significant differences from the surface quality of nontreated samples at 95% confidence level. The anatomical structure of samples was also observed by scanning electron microscope (SEM) and some damage of the cell wall was determined due to heat treatment. The findings of this study demonstrated that heat treatment resulted in adverse effect on hardness characteristics of the samples. It appears that strength losses can be limited through alternative modified heat treatment techniques. On the other hand, surface quality of the samples from all species was enhanced as a result of heat treatment. Therefore such heat treatment would be considered to improve surface quality of the sample for furniture applications where smooth surfaces are ideal adding potential value on wood material to be used more effectively in furniture manufacturing.     

Effect of fiber morphology on rheological properties of plant fiber reinforced poly(butylene succinate) composites

Sisal fibers (SFs), steam exploded sisal fibers (SESFs) and steam exploded bagasse fibers (SEBFs) which have different fiber morphologies, were mixed with poly(butylene succinate) (PBS) using a torque rheometer. The rheological properties of these plant fiber-reinforced PBS composites were evaluated. Results show that the fiber morphology has a large effect on rheological behavior. At the same fiber content (e.g., 10 wt% and 30 wt%), the non-Newtonian index n of composites reinforced by flexible fibers with a higher aspect ratio and larger contact area with the matrix is smaller. In general, n decreases with increasing fiber content but when the fiber content is too high (e.g., 50 wt%), the aggregation of fibers is too extensive so that the actual contact area between fibers and matrix becomes much lower, n increase instead. At the same fiber content (e.g., 10 wt% and 30 wt%), the consistency indices of fibrous filler-reinforced composites are larger than those of powder-filled composites; the larger the actual contact area between the matrix and the fibers, the greater the consistency index of the composite.     

Hygrothermal effect on henequen or silk fiber reinforced poly(butylene succinate) biocomposites

The hygrothermal effect of poly(butylene succinate) biocomposites reinforced with silk or henequen fibers was investigated. The biocomposites were fabricated using a compression molding method. The biocomposites were maintained in the chamber at 60 °C and 85% RH for 1000 h. The results show that the degradation of PBS matrix is the main cause for the deterioration of biocomposites performance and the biocomposites degraded much slowly than PBS matrix did. The storage modulus for the biocomposites exposed at 60 °C and 85% RH for 1000 h was decreased 20% and 50% with the silk and henequen fibers comparing to the original specimens, respectively.     

Ice adhesion to pristine and eroded polymer matrix composites reinforced with carbon nanotubes for potential usage on future aircraft

In aircraft icing conditions, the accretion of super-cooled liquid droplets on to the surface of an aircraft is dependent on numerous factors. In particular the temperature, liquid water concentration and material properties are of crucial importance in this context. This article features results obtained upon accretion of impact ice on pristine and eroded polymeric matrix composites with and without carbon nanotube reinforcement, for potential use in aeronautical applications. Results are shown for ice shear strength of a selection of advanced materials at T = − 5 °C and T = − 10 °C for a liquid water concentration LWC ≅ 0.3 g·m^− 3, actualized in an icing tunnel. The effect of surface roughness is further examined on the considered specimens in relation to their ice shear strength characteristics.     

Hot tensile behavior of an extruded Al–Zn–Mg–Cu alloy in the solid and in the semi-solid state

This is the first reported research into the tensile behavior of as-deformed Al–Zn–Mg–Cu alloy in the semi-solid state. Tensile tests of extruded 7075 aluminium alloy were carried out in the high temperature solid and semi-solid states. Based on the tensile results and microstructural examination, the tensile behavior can be divided into three stages according to the effect of liquid: one behaves in predominantly ductile character between 400 and about 520 °C (f_l ∼ 0.31%), one is governed by both of solid and liquid between 520 and 550 °C (f_l ∼ 2%), and almost completely dominated by liquid above ∼550 °C. A brittle temperature range (519–550 °C) is proposed, in which the as-deformed Al–Zn–Mg–Cu alloy exhibits large crack probability. An equation based on ultimate tensile stress and temperature is proposed.     

Environmental effects on the mechanical and thermomechanical properties of aspen fiber–polypropylene composites

The mechanical properties of newly developed aspen fiber–polypropylene composites (APC) were experimentally explored and numerically predicted at the temperatures and humidity that are typical for domestic housing applications. The mechanical properties of APCs with five different fiber-loadings were evaluated at the room temperature, 4 °C, and 40 °C. Environmental effects on the mechanical properties of APCS were experimentally quantified after conditioning the APCs with two different fiber-loadings in the following temperature and humidity for over 7000 h: (1) hot/dry at 40 °C and 30% relative humidity (RH), (2) hot/wet at 40 °C and 82% RH, (3) cold/dry at 4 °C and 30% RH, and (4) cold/wet at 4 °C and 82% RH. The tensile moduli, flexural moduli, and the flexural strength increased as the woodfiber content increased in the composites. However, the tensile strength decreased as the fiber content increased. The tensile strength was shown to slightly improve with an addition of a coupling agent between the aspen fibers and polypropylene. The simple empirical micromechanics Halpin–Tsai model for randomly distributed short fiber reinforced composites was employed to predict the homogenized elastic moduli of APC, by optimizing the interfacial model parameter. Scanning electron microscopy (SEM) micrographs confirmed that an addition of the adhesion promoter maleated anhydride polypropylene (MAPP) between the aspen fibers and polymeric matrix improved the interfacial bonding.     

Effects of the sulfidation temperature on the structure,composition and optical properties of ZnS films prepared by sulfurizing ZnO films

Nanocrystalline ZnS films have been prepared by sulfidation of the reactive magnetron sputtered ZnO films. The structure, composition and optical properties of the sulfurized ZnO films as a function of the sulfidation temperature (T_S) have been systematically studied. It is found that at T_S ⩾ 400 °C ZnO is completely converted to ZnS with the hexagonal structure. The ZnS films have a strongly (0 0 2) preferred orientation and an optical transparency of about 80% in the visible region. In addition, at T_S < 444.6 °C (boiling point of sulfur), some residual sulfur decomposed from H₂S gas can adhere to the sulfurized film surface while at T_S = 580 °C a S/Zn ratio much higher than the ideal stoichiometric proportion of ZnS is obtained for the ZnS films. ZnS films with a minimum XRD FWHM value of 0.165° and a good S/Zn ratio of 0.99 are obtained at a temperature of 500 °C indicating the ZnS films to be suitable for use in the thin film solar cells.     

Fabrication and characterization of three-dimensional PMR polyimide composites reinforced with woven basalt fabric

A PMR polyimide composite reinforced with three-dimensional (3D) woven basalt fabric is fabricated for medium high temperature applications. The PMR polyimide matrix resin is derived from 4,4′-methylenediamine (MDA), diethyl ester of 3,3′,4,4′-oxydiphthalic (ODPE) and monoethyl ester of Cis-5-norbornene-endo-2,3-dicarboxylic acid (NE). The rheological properties of the PMR polyimide matrix resin are investigated. Based on the curing reaction of the PMR type polyimide and the rheological properties, an optimum two-step fabrication method is proposed. The three dimensional fabric preforms are impregnated with the polyimide resin in a vacuum oven at 70 °C for 1 h followed by removing the solvent and pre-imidization. The composites are then consolidated by an optimized molding procedure. Scanning electron microscopy analysis shows that needle shaped voids are generated in yarns and the void volume fraction is 4.27%. The decomposition temperature and the temperature at 5% weight loss of the composite post-cured at 320 °C for 24 h are 440 °C and 577 °C, respectively. The dielectric constant and the dielectric loss of the composite are measured by circular cavity method at 7–12 GHz. The tensile strength and the modulus in the warp direction of the composite are 436 MPa and 22.7 GPa. The composite shows a layer-by-layer fracture mode in three-point bending test. The flexure strength and modulus in the warp direction of the composite are 673 MPa and 27.1 GPa, respectively.     

Threshold crack growth behavior of shear and tensile cracks

Crack-face interference-free mode I and mode II crack-growth data was combined with smooth axial (λ = ε_xy/ε_xx = 0) and torsional (λ = ∞) endurance limit data to develop unified crack growth models that incorporate both shear and tensile cracking. The crack growth models incorporated growth from a slip band (including short crack behavior) size crack until the final failure of a long crack, and the ability to switch between crack growth on shear planes to growth on tensile planes. The models successfully predicted smooth specimen crack-face interference-free fatigue lives and gave reasonable estimates of the smooth specimen endurance limits of crack-face interference free tubular tests run at intermediate strain ratios (λ = 3/4, 3/2, and 3). The series of Kitigawa–Takahashi (threshold fatigue) diagrams developed from the models help illustrate the competition between shear and tensile cracking at the fatigue limit under crack-face interference-free crack growth.     

Influence of interface microstructure on the mechanical properties of titanium/17-4 PH stainless steel solid state diffusion bonded joints

In the present study, titanium was diffusion bonded to a type 17-4 precipitation hardening stainless steel in vacuum at different temperatures and times. Bonded samples were characterized using light microscopy, scanning electron microscopy (SEM) and X-ray diffraction technique (XRD). The inter-diffusion of the chemical species across the diffusion interface was evaluated by electron probe microanalysis (EPMA). Up to 850 °C for 60 min, FeTi phase was formed at the diffusion interface; however, α-Fe + λ, χ, Fe₂Ti and FeTi phases and their phase mixtures were formed above 850 °C for 60 min and at 900 °C for all bonding times. The maximum tensile strength of ∼342.4 MPa and shear strength of ∼260.3 MPa along with 12.8% elongation were obtained for the diffusion couple processed at 950 °C. The thicknesses of different reaction products at the bond interface play an important role in determining the mechanical properties of the joints. The residual stress of the bonded joints increases with the increases in bonding temperatures and times.     

Investigation of the effect of nanoclay and processing parameters on the tensile strength and hardness of injection molded Acrylonitrile Butadiene Styrene–organoclay nanocomposites

Polymer–clay nanocomposites have attracted considerable interest over recent years due to their dramatic improved mechanical properties. In the present study, compatibility of Acrylonitrile Butadiene Styrene (ABS) and organically modified montmorillonite nanoclay (Cloisite 30B) and composition capability of them are investigated. Polymethylmethacrylate (PMMA) in varying amount (0, 2, and 4 wt%) is used as the compatibilizer. In order to produce nanocomposite parts, the material is first compounded using a twin-screw extruder and then injected into a mold. The effect of the nanoclay percentage and processing parameters on the tensile strength and hardness of nanocomposite parts is also explored using Taguchi Design of Experiments method. Nanoclay content (in three levels: 0, 2 and 4 wt%), melt temperature (in three levels: 190, 200 and 210 °C), holding pressure (in three levels: 80, 105 and 130 MPa) and holding pressure time (in three levels: 1, 2.5 and 4 s) are considered as the variable parameters. Moreover, distribution of nanoclay layers is analyzed using Wide Angle X-ray Diffraction (XRD) test. XRD results displayed that with the presence of PMMA, nanoclay in ABS matrix is compounded in more exfoliated and less intercalated dispersion mode. Adding PMMA also leads to a remarkable increase in the fluidity of the melt during injection molding process. Results also illustrated that nanocomposites with medium loading level (i.e. 2%) of nanoclay have the highest tensile strength, while the highest hardness number belongs to nanocomposites with 4 wt% nanoclay. Obtained results also indicated that injection temperature has the most important effect on tensile strength and hardness of ABS–clay nanocomposites.     

Grafting of nano-TiO2 onto flax fibers and the enhancement of the mechanical properties of the flax fiber and flax fiber/epoxy composite

In this article, a flax fiber yarn was grafted with nanometer sized TiO₂, and the effects on the tensile and bonding properties of the single fibers and unidirectional fiber reinforced epoxy plates were studied. The flax fiber yarn was grafted with nanometer sized TiO₂ through immersion in nano-TiO₂/KH560 suspensions under sonification. The measured grafting content of the nano-TiO₂ ranged from 0.89 wt.% to 7.14 wt.%, dependent on the suspension concentration. With the optimized nano-TiO₂ grafting content (∼2.34 wt.%), the tensile strength of the flax fibers and the interfacial shear strength to an epoxy resin were enhanced by 23.1% and 40.5%, respectively. The formation of Si–O–Ti and C–O–Si bonds and the presence of the nano-TiO₂ particles on the fiber surfaces contributed to the property enhancements. Unidirectional flax fiber reinforced epoxy composite (V_f = 35.4%) plates prepared manually showed significantly enhanced flexural properties with the grafting of nano-TiO₂.