No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Fast realization of high-strength, repeatable, damp-heat resistant bamboo-strip scarf bonding joints via hot-melt adhesives
At present, most of the existing studies on bamboo nodes focus on the raw bamboo. There is still a lack of researches on the nodes in side press-laminated bamboo lumber (LBL). However, after processing, bamboo nodes in the laminated bamboo lumber are different from the raw bamboo nodes in terms of performance. Therefore, this paper carried out tests to analyze the influence of bamboo node on the tensile properties parallel to grain of side press-laminated bamboo lumber. A total of 180 specimens were divided into six groups, and the number and position of the bamboo nodes at the specimen in each group were different. The effects of these factors on the strength, elastic modulus, and Poisson’s ratio of the side press-laminated bamboo lumber under tension parallel to grain were obtained. The tensile failure of side press-laminated bamboo lumber was a brittle fracture, and the typical failure mode can be classified into three types. The mean value for tensile strength was 127.18 MPa when there was no bamboo node, while the mean value was 89.99–107.37 MPa when there were one to three bamboo nodes. The number of bamboo nodes would significantly affect the tensile properties parallel to grain of side press-laminated bamboo lumber, whereas the position of bamboo nodes has an insubstantial impact. Comparisons with other research results were also carried out. A series of formulas were proposed based on the test results to reflect how the node influenced the mechanical properties of side press LBL under tensile conditions.
In the present study, the adhesive strength of scarf joint is examined by using the stress intensity factor of the fictitious small interface crack. The stress intensity factor of small crack near the interface edge is dominated by the singular stress field of the interface corner. In this study, to evaluate the joint strength, small crack is assumed at the interface corner of the scarf joint. The stress intensity factor of the interfacial crack is calculated by changing the thickness of the adhesive layer and the scarf angle. By using the experimental fracture strength of the scarf adhesive joint specimens under tension, the values of the critical stress intensity factor are calculated. From the analysis result, when the combination of adhesive materials and the scarf angle are fixed, the critical stress intensity factors of the small interface crack are constant value irrespective of the adhesive layer thickness. Therefore, the adhesive joint strength can be evaluated as the constant stress intensity factor of small interface crack. In addition, it is possible to evaluate easily the stress intensity factor by using the dimensionless coefficients depending only on the material combination when the crack length is sufficiently smaller than the thickness of the adhesive layer. The effects of adhesive layer thickness and adhesion angle of scarf joint specimen were discussed and the effectiveness of the proposed method was indicated.
Adhesively bonded technology is now widely accepted as a valuable tool in mechanical design, allowing the production of connections with a very good strength-to-weight ratio. The bonding may be made between metal-metal, metal-composite or composite-composite. In the automotive industry, elastomeric adhesives such as polyurethanes are used in structural applications such as windshield bonding because they present important advantages in terms of damping, impact, fatigue and safety, which are critical factors. For efficient designs of adhesively bonded structures, the knowledge of the relationship between substrates and the adhesive layer is essential. The aim of this work, via an experimental study, is to carry out and quantify the various variables affecting the strength of single-lap joints (SLJs), especially the effect of the surface preparation and adhesive thickness. Aluminium SLJs were fabricated and tested to assess the adhesive performance in a joint. The effect of the bondline thickness on the lap-shear strength of the adhesives was studied. A decrease in surface roughness was found to increase the shear strength of the SLJs. Experimental results showed that rougher surfaces have less wettability which is coherent with shear strength tests. However, increasing the adhesive thickness decreased the shear strength of SLJs. Indeed, a numerical model was developed to search the impact of increasing adhesive thickness on the interface of the adherend.
The failure of adhesive bondlines has been studied at the microscopic level
via tensile tests. Stable crack propagation could be generated by means of
samples with improved geometry, which made in-situ observations possible. The
interaction of cracks with adhesive bondlines under various angles to the crack
propagation was the focus of this study as well as the respective loading
situations for the adhesives UF, PUR, and PVAc, which have distinctly different
mechanical behaviors. It is shown how adhesive properties influence the
occurrence of certain failure mechanisms and determine their appearance and
order of magnitude. With the observed failure mechanisms, it becomes possible
to predict the propagation path of a crack through the specimen.
Adhesives are of pivotal importance in modern society as over 6 billion pounds of adhesives are used globally per annum. Among these, hot melt adhesives (HMAs) represent the most dynamically developing area, reaching 15 – 21 % of the global volume of production and usage of adhesives. The application of expanded high amylose corn starch (HACS) and its propionate derivatives with differing degrees of substitution (DS) in a formulation comprising polyvinyl alcohol (PVOH) and glycerol to afford 100% biodegradable HMAs is reported. Esterification of expanded starch was conducted to increase the stability and hydrophobicity of starch. The effects of amounts of esterifying reagent and reaction time on DS of starch propionates were investigated. Native starch was expanded (BET surface area, 176 m2 g-1; DS = 0) and derived propionate esters were studied by ATR-IR, TGA, 13C CPMAS NMR, 1H NMR and titrimetric methods. The HMAs, irrespective of DS, displayed a Tg at approximately 0 oC, melting (Tpeak) at approximately 160 oC and crystallisation (on cooling) at approximately 115 oC. The adhesive properties (tensile strength) with respect to DS of expanded high amylose corn starch and its propionate esters show a distinct structure-property relationship. Expanded high amylose corn starch (DS = 0) gives the strongest adhesion, outperforming native (non-expanded) starch. The expansion process is beneficial in promoting adhesion which may be linked to the increased availability of hydroxyl moieties promoting better non-covalent interactions and mixing with PVOH and glycerol. Adhesion decreases with increasing DS and the adhesive strength starch propionate with DS in the range 1.46 – 1.82 is comparable to that of native (non-expanded) starch. This is the first reported occurrence of the use of expanded starch and its propionate esters as HMAs.
Bamboo, an important natural resource claiming great significance in the socioeconomic, cultural, ecological and functional context. It grows rapidly, matures in a short period with high yield and sprouts new shoots after every harvest. It is easily manageable, long lasting and environment-enhancing versatile resource. Its high strength, elasticity, wear resisting and other mechanical characteristics establish certify it as a commercially viable raw material for industries. Apart from its traditional uses, Bamboo can substitute not only wood, but also other high-priced materials in structural and product applications. The paper presents an account of potential and opportunities of bamboo in scientific and engineering innovations for harnessing bamboo based technologies in modern industrial development.
The structure, composition, and mechanical response of Australian bamboo were investigated. The graded structure, composition, and mechanical properties were confirmed by depth profiles obtained using synchrotron radiation diffraction and Vickers indentation. The mechanical performance of bamboo was strongly dependent on age. Results indicated that young bamboo has a higher strength, elastic stiffness, and fracture toughness than its older counterpart does. In addition, the hardness of bamboo is both load dependent and time dependent as a result of an expanding interfacial damage zone and indentation creep, respectively. In addition to fiber debonding, crack deflection and crack-bridging are the major energy dissipative processes for imparting a high toughness in bamboo.
Bamboo is a typical natural fiber-reinforced composite material with superior mechanical properties. As the reinforce phase in bamboo composite, the vascular bundles were extracted from different height locations of a Moso bamboo with an alkali treatment method, and the mechanical properties were investigated via the tensile test. It is found that both the longitudinal Young’s modulus and strength of the vascular bundles are linearly increased from the inner to outer side. To study the variation of mechanical properties of bamboo culm along the radial direction, thin bamboo slices were also tested. Using a modified rule of mixtures, the longitudinal Young’s modulus of bamboo slices are analyzed and excellent agreement can be found between experimental and theoretical results, which indicates that the longitudinal Young’s modulus of bamboo culm is cubically increased in the radial direction.
A recently developed three-dimensional eigenfunction expansion approach for prediction of the singular stress field in the neighborhood of the interfacial front of an adhesively bonded scarf joint is presented. The plate is subjected to extension/bending (mode I) and in-plane shear/twisting (mode II) far field loading. Each material is assumed to be isotropic and elastic, but with different material properties. Numerical results include the dependence of the lowest eigenvalue (or stress singularity) on the wedge aperture angle of the plate material. Variation of the same with respect to the shear moduli ratio of the component plate and adhesive layer materials is also an important part of the present investigation. Hitherto unobserved interesting and physically meaningful conclusions are also presented.
Bamboo is a natural biological composite with superior mechanical strength and toughness. What is the secret recipe that Mother Nature uses to fabricate bamboo? Here we report discovery of cobble-like polygonal cellulose nanograins with a diameter of 21–198 nm in the cell wall of bamboo fibers. These nanograins are basic building blocks that are used to construct individual bamboo fibers. Nanoscale mechanical tests were carried out on individual fiber cell walls by nanoindentation. The nanograin-structured bamboo fibers are not brittle in nature but somewhat ductile. The bamboo fiber reinforcing mechanisms are discussed with reference to the hierarchical structure and mechanical properties of individual bamboo components.
This paper presents the results of a series of multi-scale experiments and numerical models concerning the mechanical properties of moso culm functionally graded bamboo structures. On the nano- and microscales, nanoindentation techniques are used to study the local variations in the Young's moduli of moso culm bamboo cross-sections. These are then incorporated into finite element models in which the actual variations in Young's moduli are used to model the deformation and fracture of bamboo during fracture toughness experiments. Similarly, the measured gradations in moduli are incorporated into crack bridging models that predict the toughening observed during resistance curve tests. The implications of the results are discussed for the bio-inspired design of structures that mimic the layered, functionally graded structure of bamboo.
Bamboo is a fast growing and natural fiber-reinforced material with excellent flexural strength and ductility. While it has been increasingly used in many applications, flexural ductility of bamboo and methods to evaluate this property have not been fully investigated. This paper proposed an original approach to assess the flexural ductility of bamboo and presented a number of reasons why bamboo outperforms wood in this aspect. Results showed that bamboo had significantly higher flexural ductility, better strength properties but moderately lower elasticity than wood. At similar density, the flexural ductility and modulus of rupture of bamboo were 3.06 and 1.72 times that of wood, respectively. On the other hand, the modulus of elasticity was 0.84 times that of wood. The flexural strength of bamboo was positively correlated to the vascular bundle content, whereas the flexural ductility was directly correlated to the parenchyma content. There existed a conflicting relationship between the flexural strength and ductility in bamboo. This work contributes to critical knowledge surrounding the flexural strength and ductility of bamboo as a sustainable building construction material.
Urea-formaldehyde resin (UF) or phenolic resin (PF) is used widely as binder in the production of fiberboard, and formaldehyde emissions from UF or PF is seriously harmful for human health. Eco-friendly fiberboard was produced without binder using poplar wood shavings (PWS) bio-pretreated by white rot fungi Coriolus versicolor in this study, and the correlations between the metabolites and lignocellulose components and the bending strength (BS) of fiberboard were also studied. After PWS were pretreated by C. versicolor for 21 days, the BS and water swelling ratio of the fiberboard were reached to 22.7 MPa and 12.4%, respectively. The soluble polysaccharide and reduce sugar in PWS were detected very low, which had a weak effect on the fiberboard. Lower content of hemicellulose and higher content of lignin were detected and beneficial to the BS of fiberboard. Manganese peroxidase was detected and had a lag enzymolysis effect. Laccase, lignin peroxidase and cellulase were not detected but laccase or cellulase might have a weak influence on fiberboard. The fiberboard production with this bio-pretreatment should be eco-friendly and eliminate the potential formaldehyde emission.
Large-scaled laminated bamboo lumber (LBL) is manufactured from bamboo strips after lengthening with
joints. In this study, three types of joint shapes for lengthening bamboo strips were explored with threelayered
LBL, and the effects of quantities and locations on bending performance of the LBL were further
evaluated. The heat-treated (120 �C) moso bamboo strips with joints were used to produce the laminated
samples, comparing with the control group without joints. The results showed that the reduced rate of
bending strength of LBL with three types joints were all exceed 10%. However, the simpler and more efficient
process of machining and gluing made hook joint the most potential choice for bamboo strip lengthening.
Based on optimizing joint shape, the reduced rate of strength attained minimum (1.43%) when the
hook joint was located at the 1/4 length of the sample. As increasing the joint quantity from 1 to 3, the
bending strength decreased by 6.82–31.11%. It appeared that the parameters of joint had a great influence
on the strength of LBL and it is important to control the quantities and locations of the joint
Bending properties of bamboo laminates composed of two layers of unjointed bamboo strips and one layer of lengthwise jointed bamboo strips with 3 kinds of joint types under lateral pressing were tested. Then properties of bamboo laminates composed of different layers unjointed bamboo strips and one layer of lengthened bamboo strips with hook joints were further determined. The results showed that the bending strength of the bamboo laminates with jointed bamboo strips was slightly reduced without significant difference among joint types. When the jointed bamboo strip was laid in the middle of the bamboo laminates composed of more than 3 layers of bamboo strips, layer number of bamboo strips had little effects on bending properties of the bamboo laminates.
Bamboo is a typical agricultural and forestry biomass resource in China, which has the advantage of short growth cycle, high yield, abundant reserves. However, biomass has the disadvantages of high water content, high O/C ratio, poor grinding performance and low energy density. Torrefaction is a mild pre-pyrolysis process which operates at normal pressure, inert gas and lower temperature (200 to 300℃). Torrefaction pretreatment can effectively improve the properties of biomass, such as increasing the heating value or energy density, reducing the moisture content and O/C ratio, and improving the grinding and hydrophobicity. By these upgraded properties, the torrefaction pretreatment can also reduce the content of moisture and oxygen-containing compounds in the bio-oil, increase the heating value of bio-oil, and improve the quality and stability of bio-oil. In this paper, bamboo torrefaction was carried out in a furnace with programmed temperature controlling, Thermogravimetric analyzer coupled with Fourier transform infrared spectrometry (TGA-FTIR), pyrolyzer coupled with gas chromatography/mass spectrometer (Py-GC/MS) at different temperatures of 210, 240, 270 and 300℃. Then the effect of torrefaction temperature on the properties of the gas, solid, and liquid products was studied in order to reveal the torrefaction mechanism. The results showed that: (1) When the torrefaction temperature increased, the content of fixed carbon and C in the solid product increased significantly, resulting in an increasing of the calorific value and energy density from 18.85 MJ/kg to 23.12 MJ/kg. The oxygen content was significantly reduced, resulting in a decrease of the O/C ratio from 0.74 to 0.42. (2) Based on the FTIR analysis, the gas composition was mainly composed of H2O, CO2, CO, and CH4, and CO2 was the dominant gas, followed by H2O, CH4 and CO, and all gas content gradually increased as the torrefaction temperature increased; (3) Based on the Py-GC/MS analysis, the liquid products are mainly composed of acids, ketones, furans, phenols, aldehydes and other organic compounds. Acids, phenols and furans were the dominant components with the content of the 20.34%, 22.05% and 31.42% respectively. However, the contents of ketones and aldehydes were relatively lower, which are 10.43% and 8.26%, respectively. As the torrefaction temperature increases, the content of acid increases first and then decreases. The contents of furans, phenols, and ketones increase gradually, and the aldehyde content does not change significantly. (4) Based on the properties of gas, solid, and liquid products, the oxygen in the bamboo was mainly removed in the form of gas components (H2O, CO2 and CO, etc.) and oxygen-containing organic components (acids, phenols and furans, etc.). The torrefaction pretreatment can improve the content of C in the solid product and reduce the oxygen content, thereby increasing the energy density of bamboo. In addition, torrefaction can remove moisture and oxygen-containing compounds in bio-oil, and eventually increase the application value of biomass. This study provides basic data for the energy use of bamboo. © 2018, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.
Bamboo fiber possesses excellent innate properties such as fast growing, high tensile modulus, high wear resistance, biodegradability, and is a cheaper substitute for glass fiber and carbon fiber. To make full use of bamboo resources in China, research and development of bamboo powder (BP) reinforced plastic is a good way. As we know, bamboo plastic composite (BPC) has broad applications including building, decoration, packing, and automobile manufacturing. BP contains high content of starch, protein, carbohydrate, fat, and other nutrients and thus is vulnerable to microorganisms. Researches showed that the anti-mold performance of BPC was inferior to other wood plastic composite (WPC) and the anti-mildew performance of BPC became worse with the increase of the BP content. The proliferation of mold not only affects the appearance, mechanical properties, and service life of the BPC, but also raises human health issues. Therefore, study on the anti-mold performance of BPC is of great significance. Heat treatment is a good modification method to improve the water resistance, dimension stability, and durability of plant fiber-based materials. In this paper, BP/polypropylene composites with 60% BP were prepared by hot pressed molding and the BP was heat-treated at the temperature of 150, 170 and 190℃ respectively for 120 min. Three common types of mould i.e. Aspergillus niger, Penicillium citrinum, Trichoderma viride were used to conduct mildew test. The effects of heat treatment on the BP chemical content, mass loss, and hygroscopicity were studied. The influences of heat treatment on the composites surface color, mechanical properties, surface wettability, and anti-mold property were also investigated. The results showed that the BP chemical content did not vary much at the heat temperature of 150℃, and the BP cellulose and hemicellulose content gradually decreased and the lignin content accordingly increased with the increase of heat temperature. The heat-treated time of 60, 120, and 240 min had less influence on the BP chemical content than the temperature ranging from 150 to 190℃. The increase of mass loss and the reduction of equilibrium moist content (EMC) for the heat-treated BP were directly related to the change of chemical composition. After heat treatment at 190℃ for 120 min, the BP holocellulose dropped by 7.00 percentage points, the lignin enhanced by 2.92 percentage points, the mass loss was 4.41 percentage points, and EMC was 6.39%. Compared with the untreated composite, the heat treated composites possessed lower surface wettability, lower bending properties, but higher color stability during mold test and stronger anti-mold performance. The 190℃ heat-treated composite became darker and slightly turned green and blue; the lightness change was -5.47, and the color change was 7.54; the bending strength and bending modulus were reduced by 9.79% and 5.37%, respectively. Compared to composite without mildew test, the lightness change, redness change, and yellowness change of tested composite were 0.87, -0.30 and 0.20, respectively, and the color change was only 0.94; the mold resistance value was decreased from 3.75 to 2.25 and the anti-mold effectiveness was increased to 40%. This paper provides experimental data and theoretical reference for the development and application of mold-resistant BPC and WPC. © 2017, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.
This paper aimed to provide a closed-form solution for the stress distribution in adhesively bonded scarf joints under thermo-mechanical loads. Based on the elasticity theory, the present approach can accurately predict thermo-mechanical stress distributions on both adhesives and adherends layers taking into account the influences of the scarf angle and the adhesive thickness.
The accuracy of the present method is highlighted through comparison with finite element solutions of stress distribution under separated and simultaneous thermal and mechanical loads for two configurations of scarf joint. Analytical and numerical results of normal and shear stresses show a good agreement for both configurations. A parametric study is also conducted in order to examine the influence of adhesive thickness and scarf angle on stress distributions in the joints and the joint strength. The results should be relevant to the design and application of adhesive scarf joint.
This experimental study investigates the effect of environmental loading and joining methods on the static and dynamic performance of lightweight multimaterial single-lap joints (SLJ). Joint adherend material combinations are divided into two groups; namely, composite-based and steel-based materials that include glass fiber reinforced polymer (GFRP), steel (St), aluminum (Al), and magnesium (Mg). A commercially available adhesive is selected for the study. Investigated joining methods include bonding-only, bolting-only, and hybrid bonding-and-bolting. Static performance is assessed by the load transfer capacity (LTC) of SLJ after they have been subjected to heat cycling at ambient level of relative humidity, or after heat cycling at high relative humidity. Dynamic performance is measured by durability life (in cycles) of SLJ test samples under a fixed dynamic load ratio in a tensile-tensile fatigue test, after they have been subjected to heat cycling and humidity. The cyclic test load fluctuated between 67.5% and 75% of the static LTC at ambient condition. Sample finding includes the significant effect of heat cycling at an ambient humidity level; it has tripled the LTC of bonded-only composite-to-composite SLJ, relative to their baseline LTC at ambient conditions. Detailed discussion of the results, observations, and conclusions are presented in this paper.
With the increasing scarcity of wood as a natural resource, bamboo has become a popular substitute for wood. The present work developed a high-strength original state multi-reorganization material (GPEHB), without the use of a hot press or traditional assembly. The original bamboo units were polygonized into outer contours and milled into finger-joints on each ending. The GPEHB was organized and assembled under an external press, using industrial adhesives. The mechanical properties and thermal insulation of GPEHB were characterized. Moreover, the overall GPEHB unit bending strength was 73.15 MPa, and the parallel-to-grain compression was 55.22 MPa (higher than that of Pinus sylvestris lumber, though less than that of glued laminated bamboo). The GPEHB unit overall density was 0.24 g/cm3, 76% lower than that of glued laminated bamboo, and 50% lower than Pinus sylvestris lumber. The compressive strength of GPEHB (7 units) was 170.5 kN, while the compressive strength of GPEHB for 14 units was 493.5 kN, which meet the requirements of GB 50005 (2003). The bending strength of GPEHB 7 units was 12 kN, while that of 14 units was 37 kN. The heat conductivity coefficient for GPEHB was 0.25 W/mK, which is better than concrete and steel. The GPEHB has taken full advantage of its honeycomb-structured material, which allows it to avoid stress concentration in the regular polygonal corners.
The structural performance of finger-jointed laminated bamboo was investigated for two bamboo species by considering the finger length, profile orientation, lamination direction, culm growth height, and mechanical properties of bamboo materials. Based on the growth height variation and bamboo species, the best finger-jointed laminated bamboo was found for the lamina processed from the middle growth height of a moso bamboo culm with the finger profile shown on the width face of the beam. It was 38.7% higher in bending strength than the lowest group, with the lamina from the lower ma bamboo culm showing the finger profile on the thickness face of the beam. When considering the finger length and lamination orientation, the strongest finger-jointed laminated bamboo joined with an 18-mm finger, showing the finger profile on the width face of a vertically laminated beam was 50.1% higher in bending strength than the lowest group having a 12-mm finger showing the finger profile on the thickness face of a vertically laminated beam. The laminated ma bamboo showed higher finger-joint efficiency, 11.6%, than moso bamboo, and the members showing the finger profile on the width surface was 12.3% better in joint efficiency than that showing on the thickness surface of the beam.
The shear and peel stress distributions in a scarf joint made of two isotropic adherends with blunt adherend tips are analysed using a linear elastic analysis. The limits of the analysis with respect to adherend tip thickness have been investigated. A finite difference method is used to solve the differential equations for the shear and peel stress distributions over the joint. The boundary conditions used limit the analysis to the two adherends having the same thicknesses, lengths, and material properties. The adherends are modelled as plates with extensional and bending stiffnesses bonded together with an elastic interlayer. The stresses across the adhesive layer are assumed to be constant. The current analysis applied to cases known from the literature shows good agreement with the shear stresses but the peel stresses are overestimated.
Adhesive bonded joints are exposed to a range of different environments in aerospace applications. This paper reports dielectric and mechanical analysis of aluminium–epoxy bonded adhesives joints exposed to de-ionized water, aqueous urea solution and salt water at 65°C. The changes observed are the results of plasticization and corrosion. In the case of the aqueous urea solution, passivation of the oxide by the urea reduced the rate of corrosion. Sea water contains mobile ions and a new feature is detected associated with filiform corrosion. The non-polar media aviation fuel and hydraulic fluid are able to plasticize the adhesive and there is a consequent reduction in the strength of the joint. Propylene glycol, although it is polar solvent, produces limited plasticization and degradation of the joints. Dichloromethane was very aggressive and produced a rapid loss of strength of the joints.
A series of ethylene vinyl acetate copolymers (EVAs) were blended with aromatic hydrocarbon resins for use as hot-melt adhesives. The glass transition temperature, viscoelastic properties, melt viscosity, crystallinity and adhesion properties of the EVA/aromatic hydrocarbon resin system were determined as a function of the softening point of the aromatic hydrocarbon resin, the blend ratio of the two components and the vinyl acetate content of EVAs. Most blends showed a glass transition temperature at about −25°C and a melting peak between 30°C and 100°C. The peaks of loss modulus increased with increasing softening point of the aromatic hydrocarbon resin. The melt viscosity of the blends decreased with increasing temperature. Also, the melt viscosity increased with increasing softening point, but decreased with increasing aromatic hydrocarbon resin and vinyl acetate content. Increasing the softening point of the aromatic hydrocarbon resins, in cases of the same blend ratio, increased the crystallinity, while the addition of aromatic hydrocarbon resin decreased the crystallinity. Also, increasing the vinyl acetate content decreased the crystallinity of the blend, due to a decrease in the crystalline region of ethylene. The lap-shear strength increased with increasing softening point of the aromatic hydrocarbon resin. The lap-shear strength also increased with increasing concentration of aromatic hydrocarbon resin, until it reaches a maximum value.
The cyclic-fatigue behaviour of adhesive joints, which consisted of an aerospace-grade epoxy-adhesive bonding aluminium-alloy substrates, has been investigated. Fracture-mechanics tests were used to obtain the relationship between the rate of fatigue crack growth per cycle, da/dN, and the maximum strain-energy release rate, Gmax, applied during the fatigue cycle. These cyclic-fatigue tests were conducted in both a “dry” environment of 23±1°C and 55% relative humidity and a “wet” environment of immersion in distilled water at 28±1°C. In particular, the effect of using various surface pretreatments for the aluminium-alloy substrates, prior to forming the adhesive joint, has been investigated. X-ray photoelectron spectroscopy and electron microscopy techniques have been used to identify the locus of joint failure and the mechanisms of environmental attack.
Bamboo plays an essential role in the daily life of millions of people in subtropical and tropical regions. Increased research during the recent years has contributed considerably to the understanding of these important arborescent grasses as well as to an improved processing for wider uses. The treatise gives an overview on aspects of biology, properties and utilization of bamboos with emphasis on further research directions.
A series of poly(ethylene-co-vinyl acetate) (EVA)-based hot melt adhesives containing either a rosin or a hydrocarbon (C5–C9) tackifier have been prepared to investigate viscoelastic properties and peel adhesion. Fracture energies were determined by the use of a T-Peel geometry (two polypropylene films bonded with model EVA adhesives). The rosin has only one glass transition temperature, but the C5–C9 resin has two glass transition temperatures, indicating phase separation. The rosin has better compatibility with EVA than does the C5–C9 resin. The bond strength of tackified EVA to polypropylene depends not only on compatibility, but also on viscoelastic properties. A higher storage modulus results in a higher T-Peel strength. Under certain test conditions, glassy C5–C9-rich domains act as reinforcing filler, resulting in a higher storage modulus. Here, a C5–C9-tackified EVA adhesive has higher T-Peel strength than does one containing rosin. © 1997 John Wiley & Sons, Inc.
Thermoplastic polyurethane elastomers (TPUs) are now widely used because of their excellent properties that include high tensile and tear strength, and good abrasion, impact and chemical resistance. TPUs are multiblock copolymers with alternating sequences of hard segments composed of diisocyanates and simple diols (chain extenders) and soft segments formed by polymer diols. Commonly used hard segments for TPUs are derived from 4,4′-diphenylmethane diisocyanate (MDI) and aliphatic diols. The aim of our research was to examine the possibility of obtaining TPUs with good tensile properties and thermal stability by using an unconventional aliphatic-aromatic chain extender, containing sulfide linkages. Three series of novel TPUs were synthesized by melt polymerization from poly(oxytetramethylene) diol, poly(ε-caprolactone) diol or poly(hexane-1,6-diyl carbonate) diol of number-average molecular weight of 2000 g mol−1 as soft segments, MDI and 3,3′-[methylenebis(1,4-phenylenemethylenethio)]dipropan-1-ol as a chain extender. The structure and basic properties of the polymers were examined using Fourier transfer infrared spectroscopy, X-ray diffraction, atomic force microscopy, differential scanning calorimetry, thermogravimetric analysis, Shore hardness and tensile tests. It is possible to synthesize TPUs from the aliphatic-aromatic chain extender with good tensile properties (strength up to 42.6 MPa and elongation at break up to 750%) and thermal stability. Because the structure of the newly obtained TPUs incorporates sulfur atoms, the TPUs can exhibit improved antibacterial activity and adhesive properties. Copyright © 2011 Society of Chemical Industry
Thermoplastic polyurethane elastomers were prepared from 4,4-diphenylmethane diisocyanate (MDI)/1,4-butanediol (BD)/poly(propylene glycol) (PPG) and MDI/BD/poly(oxytetramethylene glycol) (PTMG). The MDI/BD-based hard-segment content of polyurethane prepared in this study was of 39–65 wt %. These polyurethane elastomers had a constant soft-segment molecular weight (Mn, 2000), but a variable hard-segment block length (n, 3.0–10.1; Mn, 1020–3434). The effects of the hard-segment content on the thermal properties and elastic behavior were investigated. These properties of the PPG-based MPP samples and the PTMG-based MPT samples were compared. The polyurethane prepared in this study had a hard-segment crystalline melting temperature in the range of 185.5–236.5°C. With increasing hard-segment content, the dynamic storage modulus and glass transition temperature increased in both the MPP and MPT samples. The permanent set (%) increased with increasing hard-segment content and successive maximum elongation. The permanent set (%) of the MPP samples was higher than that of MPT samples at the same hard-segment content. The value of K (area of the hydrogen-bonded carbonyl group/area of the free carbonyl group) increased with increasing hard-segment content in both the MPP and MPT samples, and the K value of the MPT samples was higher than that of the MPP samples at the same hard-segment content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 345–352, 1999
Bamboo Shoot Growth Model Based on the Stochastic Process and Its Application
- Yongjun
Eexperimental Study on the Heat-transfer Characteristics of New Bamboo Structure Building
- Nianping
Research progress of moisture curing PUR hot melt adhesive
- Liu
Bamboo scarf mechanical properties of jointed samples
- Wang
Polymer Matrix Composite using Natural Fiber Lantana-Camara
- C R Deo
Green Industry Path of Rural Revitalization-Based on Jingxian County of Anhui Province
- Zhang
The Influence of Connecting and Laminating on the Performance of Flattened Bamboo Board
- Zhu
Study on slip joint for poplar veneer
- Tang