Thermogravimetric study of high temperature treatment of aspen: effect of treatment parameters on weight loss and mechanical properties

Aspen was heat-treated at high temperature in a laboratory thermogravimetric analyzer. The high temperature wood treatment technology is new in North America and needs to be adapted to the North American species. The objective of this study is to understand how the treatment affects the mechanical properties of aspen such as hardness, modulus of elasticity and modulus of rupture, and, consequently, the quality of the product. The wood samples were heated in an inert gas environment under different operating conditions. The parameters studied are the final treatment temperature, heating rate, holding time, and the gas humidity. The weight loss and the temperature history of wood were monitored during the treatment. After the experiments, the properties of the samples were measured, and the effects of the above parameters on the properties were analyzed. The weight loss increased with increasing temperature, heating rate, holding time, and gas humidity. Increasing temperature caused an increase in MOE and a decrease in MOR. Overall hardness decreased with increasing temperature above 160 °C and it increased with increasing holding time and heating rate whereas it decreased with increasing gas humidity. Holding time and heating rate did not seem to affect MOE. Gas humidity increased MOE. MOR increased with holding time and decreased with heating rate and gas humidity.     

Changes of wood properties treated with aqueous amine solution,bending tests and X-ray analysis of wood after amine treatment

Bending tests were conducted on oven-dried wood samples (Picea jezoensis Carr.) following treatment with various concentrations of aqueous ethylenediamine (EDA) to investigate the influence of amine treatment on the mechanical properties of wood. Under oven-drying conditions following EDA treatment and a methanol rinse, the densities of wood samples increased at concentrations above 50%, and the Young’s modulus decreased at concentrations above 60%. The specific Young’s modulus of wood samples decreased at concentrations above 60%, and stress- and strain-at-yield changed slightly at EDA concentrations in the range of 60–70%. X-ray analysis showed that the structures of cellulose changed at concentrations above 60% EDA and confirmed the transformation into cellulose III_I at 70% EDA. These results indicate the possibility that changes in the structure of the cell wall, accompanied by changes in the structures of cellulose microfibrils, contributed to changes in the specific Young’s modulus of the treated wood samples. In the same concentration range, changes in the Young’s modulus of wood samples increased with increasing relative humidity (RH). This also suggests that changes in the cell wall structure during the treatment contributed to changes in the Young’s modulus of wood at different RHs.     

Moisture adsorption and desorption properties of some tropical woods

The sorption of moisture for ten species of tropical wood, in the density range 480–1120 kg m^–3 was investigated by measuring the moisture content (MC) and dimensions (DC) during relative humidity (RH) cycling. In general, it was found that there was an increase in dimensions as well as moisture content on increasing the RH, while there was a decrease in dimensions as well as MC on decreasing the RH. Hysteresis effects were observed both in the DC-RH and the MC-RH curves on RH cycling. The hysteresis properties were observed to be not only anisotropic but also species specific. In addition, an anomalous contraction was observed at moisture contents below 2%. The shell-core model is advanced to explain this anomalous behaviour of wood.     

A comparative study on the effects of Coriolus versicolor on properties of HDPE/wood flour/paper sludge composites

In this study, the effects of white-rot fungus (Coriolus versicolor) on the properties of high density polyethylene (HDPE)/wood flour/paper sludge composites were examined. In addition, the effectiveness of using coupling agent on the durability of decayed and undecayed WPCs was investigated. Two different types of sludge materials, namely paper making waste water sludge (PS) and ink-eliminated sludge (IES) were used. The mechanical properties, morphology, and water absorption of fabricated composites were investigated. At a similar wood flour loading, except for modulus of elasticity, the fungi treated composites showed lower mechanical properties (such as modulus of rupture and unnotched Izod impact strength), and higher water absorption compared to untreated composites. According to the results, addition of wood flour decreased the resistance of the composites to moisture and fungal environment. The exposure of the composites to a 4-cycle (2, 24, 48 and 72 h) water immersion caused serious damage to the interfacial adhesion between wood flour and polymer matrix due to contraction and swelling stresses developed during the cyclic exposure. The detrimental effect of fungal treatment on the water uptake of the composites could be explained by the degradation of lignin which made the cellulose content more accessible. Further, it makes chains of cavities that accelerate water absorption. However, the weight losses of all cases of treated composites were low (less than 2.5%), while PS filled composites were more susceptible to white-rot fungi. The addition of coupling agent during the compounding of wood flour and HDPE prevented the colonization and proliferation of fungus on the surface of the composites, and had an advantageous effect on the water uptake and mechanical properties of both treated and untreated composites.     

Composite materials based on wood and nylon fibre

Nylon-wood fibre and polypropylene-wood fibre composite materials were manufactured without any additives to determine the effects of wood fibre on the mechanical properties of the different composites. The raw materials used were eucalypt hardwood fibre, Nylon fibre obtained from stockings, and polypropylene (PP) pellets. A hot press technique was used to manufacture the composite materials, and improvements in the manufacturing methods are suggested. Tests were carried out on the manufactured boards to determine tensile strength and modulus of elasticity. Fracture surfaces were examined using scanning electron microscopy to investigate failure mechanisms. An increase in tensile strength and modulus of elasticity was observed in wood fibre/Nylon matrix composites, indicating that interfacial bonding occurred between these two phases. Bundles of wood fibres with internal voids prevent achieving maximum mechanical properties. The tensile strength of the PP based composites decreased significantly with increasing wood fibre content.     

The effect of crosslinker on mechanical and morphological properties of tropical wood material composites

In this study, wood polymer composites (WPCs) based on five kinds of selected tropical wood species, namely Jelutong (Dyera costulata), Terbulan (Endospermum diadenum), Batai (Paraserianthes moluccana), Rubber (Hevea brasiliensis), and Pulai (Alstonia pneumatophora), were impregnated with methyl methacrylate (MMA) and hexamethylene diisocyanate (HMDIC) monomers mixture in the ratio of 1:1 for composite manufacturing. All these tropical wood reacted with hexamethylene diisocyanate and crosslinked with MMA which enhanced the hydrophobic (restrained water) nature of wood. The vacuum-pressure method was used to impregnate the samples with monomer mixture. The monomer mixture loading achievable was found to be dependent on the properties of wood species. Low loading was observed for the high density wood species. Mechanical strength of fabricated wood polymer composites (WPCs) in term of modulus of elasticity (MOE) and modulus of rupture (MOR) were found to be significantly improved. The wood–polymer interaction was confirmed by Fourier transform infrared (FTIR) spectroscopy. Morphological properties of raw wood and WPC samples were evaluated by scanning electron microscopy (SEM) and XRD analysis and an improvement in morphological properties was also observed for WPC.     

Assessment of wood load condition by Near Infrared (NIR) spectroscopy

The assessment of the mechanical properties of wood using non-destructive evaluation (NDE) tools has been widely developed and refined. These NDE tools mainly rely on vibrational, ultrasonic or stress-wave approaches. Vibrational techniques generally show higher correlations between the estimated modulus of elasticity (MOE), or modulus of rupture (MOR), and the measured MOE, or MOR, than stress-wave techniques. They are, however, relatively difficult to apply in the field due to boundary conditions common in many timber structures. Thus, improved tools for assessing timber structures are still needed. Recently, near infrared (NIR) spectroscopy (500–2400 nm) has shown promise for predicting the MOE and MOR of wood. This work focuses on extending the use of NIR for measuring the load applied to small wood beams. The reflectance NIR spectrum was measured as the applied load was increased. Good correlations (r > 0.96) between the measured load and the predicted load were obtained using spectra taken from both the tension and compression surfaces of the small wood beams.     

Hygroscopic properties of magnetic recording tape

Relative humidity has been recognized as an important environmental factor in many head-tape interface phenomena such as headwear, friction, staining, and tape shed. Accordingly, the relative humidity is usually specified in many applications of tape use, especially when tape recorders are enclosed in hermetically sealed cases. Normally, the relative humidity is believed regulated by humidification of the fill gas to the specification relative humidity. However, this study demonstrates that the internal relative humidity in a sealed case is completely controlled by the time-dependence of the hygroscopic properties of the pack of magnetic recording tape. Procedures for the humidity conditioning of sealed cases must be established on the basis of the tapes' hygroscopic properties, and not on humidification of the fill gas. Without taking the tape into account, the final, stabilized, relative humidity can be significantly different from the specification requirement. Additionally, this same study finds differences in the hygroscopic properties of the same brand of tape, which apparently results from aging, and which may have significance on the long-term humidity-regulating behavior in a sealed case, and on the occurrence of head-tape interface phenomena from the long-term use of the tape. This article presents results on the basic hygroscopic properties of tape, its humidity-regulating behavior in a sealed case, and includes a theoretical commentary on the relative humidity dependence of head-wear by tape.     

塑木复合材与木材主要力学性质的比较研究

分析了塑木复合材与木材的抗弯强度、抗弯弹性模量、抗压强度和抗剪强度之间的差异,结果表明,塑木复合材的抗弯性能远低于鹅掌楸(Liriodendron sp.)和速生杨木(Populussp.);纵向抗压强度也低于木材的顺纹抗压强度,横向抗压强度为木材横纹抗压强度的2.95倍(I-69杨)～3.74倍(鹅掌楸),纵向抗剪强度与木材的顺纹抗剪强度与木材相当.因此可采用降低密度、改进材料结构或改进材料成型方式来增加塑木复合材料的抗弯性能和纵向抗压性能,以扩大其应用范围.     

Changes in the properties of wood cell walls during the transformation from sapwood to heartwood

Changes in the chemical, viscoelastic and hygroscopic properties of wood cell walls in Chinese fir (Cunninghamia lanceolata) during the transition from sapwood to heartwood were studied to provide insights into the formation of heartwood. In situ imaging FTIR measurements indicated that the composition of the main components of cell walls remained almost unaltered, but more extractives were deposited in the wood cell walls during the sapwood–heartwood transition. Compared to the sapwood and transition wood, the heartwood had a higher softening temperature and greater activation energy, suggesting that the mobility restrictions of cell wall biopolymers were due to extractives obstructing the accessing of the plasticizer (ethylene glycol). The moisture sorption was the same from the sapwood to heartwood at a low relative humidity (RH), while the heartwood adsorbed less water at a high RH, probably caused by the extractives deposited in the matrix and mesopores of heartwood cell walls.     

摩擦力和样品厚度对压痕法测量生物试样弹性的影响

生物试样的弹性测量可为生物体疾病的早期诊断和治疗提供依据。利用压痕法对生物试样的弹性进行了测量,并用有限元软件对压痕过程进行了模拟。研究发现,试样厚度对弹性测量存在影响,试样厚度越大,测量结果越接近试样真实的杨氏模量。当试样厚度为压痕深度的75倍时,测量误差仅为0.74%。又研究了压头速度对弹性测量结果的影响。研究发现,当压头速度较大时,由于摩擦力的作用,测量结果与试样弹性的真实值之间存在一定的差异。在模拟过程中添加摩擦力可准确反演试样的弹性,误差在5%以下。     

Estimation of wood stiffness and strength properties of hybrid larch by near-infrared spectroscopy

This work was undertaken to investigate the feasibility of near-infrared (NIR) spectroscopy for estimating wood mechanical properties, i.e., modulus of elasticity (MOE) and modulus of rupture (MOR) in bending tests. Two sample sets having large and limited density variation were prepared to examine the effects of wood density on estimation of MOE and MOR by the NIR technique. Partial least squares (PLS) analysis was employed and it was found that the relationships between laboratory-measured and NIR-predicted values were good in the case of sample sets having large density variation. MOE could be estimated even when density variation in the sample set was limited. It was concluded that absorption bands due to the OH group in the semi-crystalline or crystalline regions of cellulose strongly influenced the calibrations for bending stiffness of hybrid larch. This was also suggested from the result that both alpha-cellulose content and cellulose crystallinity showed moderate positive correlation to wood stiffness.     

Effect of temperature on the sorption curves of earthen materials

Unfired earth is a sustainable construction material with low embodied energy, but its development requires a better evaluation of its moisture–thermal buffering abilities and its mechanical behavior. Both of them are known to strongly depend on the amount of water contained in its porous network and its evolution with external conditions (temperature, humidity), which can be assessed through several sorption–desorption curves at different temperature. However, the direct measurement of these curves is particularly time consuming (up to 2 month per curve) and thus, indirect means of their determination appear of main importance for evident time saving and economical reasons. In this context, this paper focuses on the prediction of the evolution of sorption curves with temperature on earth plasters and compacted earth samples. For that purpose, two methods are proposed. The first one is an adaptation of the isosteric method, which gives the variation of relative humidity with temperature at constant water content. The second one, based on the liquid–gas interface equilibrium, gives the variation of water content with temperature at constant relative humidity. These two methods lead to quite consistent and complementary results. It underlines their capability to predict the sorption curves of the tested materials at several temperatures from the sole knowledge of one sorption curve at a given temperature. Finally, these predictions are used to scan the range of temperature variation within which the evolution of water content with temperature at constant humidity could be neglected or should be taken into account.     

Mechanical properties of cork: Effect of hydration

Cork is known to exhibit low permeability to liquids and gases, imputrescibility and good mechanical properties, with a remarkable elasticity. These properties make this material particularly interesting for sealing wine. We focused in this study on the compression properties of cork along the radial and tangential direction at 25 °C under atmospheric pressure when cork is stored in various relative humidity environments, from 0% to 100%.The direction of compression significantly affected the Young’s modulus, with a higher value for the radial direction. This corresponds to the orientation of the lenticels which reinforce the rigidity of the material when the strain is applied along their growth direction. More surprising is the effect of water sorption in cork on its mechanical property. Both radial and tangential directions exhibit the same behavior when the relative humidity is increasing. First the Young’s modulus is constant up to 50% relative humidity (RH) with mean values around 37 MPa and 22 MPa for radial and tangential directions, respectively. Then, above this point, the increase in water content leads to a decrease in material rigidity which is attributed to water clusters formations. For high moisture contents, the anisotropy of cork is reduced: Young’s moduli are of 10.5 MPa and 6.6 MPa for radial and tangential orientations, respectively.Differential scanning calorimetry and dynamic mechanical thermal analysis (DMTA) allowed to identify a glass transition temperature (T_g) in cork over a broad range of temperatures, depending on the moisture content and giving a T_g-midpoint from −8 °C to 3 °C. Moreover, a secondary transition was observed by DMTA at approximately −80 °C, for 50% RH.     

Using almond (Prunus amygdalus L.) shell as a bio-waste resource in wood based composite

In this research, the suitability of almond shell as a bio-waste resource in wood based composite manufacturing was investigated. Particleboards containing different almond shell particle rations were made using urea–formaldehyde (UF) resin. Some chemical properties of almond shell (holocellulose, α cellulose, lignin and ash contents, alcohol–benzene solubility, 1% NaOH solubility, hot and cold water solubility), mechanical (modulus of rupture, modulus of elasticity and internal bond strength) and physical properties (thickness swelling and water absorption) of the particleboards were determined. The addition of almond shell particles greatly improved the water resistance of the panels. However, flexural properties and internal bond strength decreased with increasing almond shell particle content. The amount of almond shell particles at most should be 30% in the mixture to meet the standard required for mechanical properties. Conclusively, almond shell, an annual agricultural residue, could be utilized with mixture of wood particles in the particleboard manufacturing.     

纳米 ZrO_2固体的内耗和力学性能

通过 X 射线,透射电子显微镜和内耗测量等手段,研究了水热法制备纳米 ZrO_2固体的界面行为和烧结性能。结果表明在一定温区纳米 ZrO_2固体的内耗和模量同时大于传统多晶 ZrO_2由于晶粒细化,界面结构特殊,使得纳米 ZrO_2材料的烧结性能得到提高。400℃以下退火主要影响内耗,600℃以上遇火主要表现为模量的增大。     

高性能防静电瓦楞纸板及其影响因素的研究

目的研制一种高性能的防静电瓦楞纸板、纸箱,并研究涂布量,运输环境的温度、相对湿度及机械摩擦对其防静电性能的影响。方法采用定量涂布的方式将防静电涂料均匀涂覆在原纸表面,通过改变涂布量研究其与纸板防静电等级的关系;通过改变环境温度、相对湿度、摩擦参数(次数和强度)来模拟研究实际运输途中温度、相对湿度及摩擦参数(振动、冲击等机械力造成的)对瓦楞纸箱防静电性能的影响。结果在研究的范围内,随着温度、相对湿度的增加,防静电纸板表面电阻率也增加,但是材料的防静电等级未发生变化,仍为导静电材料,其中相对湿度对防静电的影响较温度的影响更为明显;摩擦对防静电性能的影响比相对温湿度明显。结论温度、相对湿度及摩擦参数对瓦楞纸板的防静电性能均有不同程度的影响,但仍为静电防护型材料,能够有效保护内装物不受静电的危害。     

Effects of hardener type,urea usage and conditioning period on the quality properties of particleboard

The effects of hardener type (ammonium chloride, ammonium sulphate and aluminium sulphate), urea usage (with urea and without urea), and conditioning period (one day and one month) of the particleboard on the physical (thickness swelling), mechanical (modulus of rupture, modulus of elasticity and internal bond strength), surface properties, and formaldehyde emission of particleboard and acidity of the wood particles were investigated. The hardener type was found to be effective all of the properties of particleboard. The pH of the wood particle with the urea was slightly higher than that of particles without urea.The lowest pH value for the resinated wood particles was obtained from ammonium chloride, followed by ammonium sulphate and aluminium sulphate, respectively. The best quality properties were obtained from the particleboards manufactured with ammonium chloride, followed by particleboard made with the ammonium sulphate and aluminium sulphate, respectively. The urea usage significantly decreased the formaldehyde emission of the particleboards while it slightly decreased the mechanical properties and increased thickness swelling. Increasing conditioning period of the particleboards from one day to one month improved the quality properties.     

Modeling the effects of yarn material properties and friction on the ballistic impact of a plain-weave fabric

Impact of a rigid sphere onto a high-strength plain-weave Kevlar KM2^® fabric was modeled using LS–DYNA^® focusing on the influence of friction and material properties on ballistic performance. Quasi-static friction was experimentally determined and incorporated into the model. Two clamped edges and two free edges were used as boundary conditions to correlate the model to an experimental test providing yarn–yarn movement. Yarns were modeled as continua with modulus and strength dominating along the length. Parametric studies incorporating different yarn material properties and initial projectile velocities were then performed with the above set of boundary conditions. Results indicate that ballistic performance depends upon friction, elastic modulus and strength of the yarns. While friction improves ballistic performance by maintaining the integrity of the weave pattern, material properties of the yarns have a significant influence on the effect of friction. It is shown that fabrics comprised of yarns characterized by higher stiffness and strength relative to the baseline Kevlar KM2^®, exhibited a stronger influence on ballistic performance. Therefore all three parameters viz., friction, elastic modulus and strength along with other variables (fabric architecture, boundary conditions, and projectile parameters) are needed to examine ballistic performance of high-strength fabric structures.     

纳米铜润滑油添加剂的摩擦学特性及其自修复机理

为了评价纳米铜添加剂对摩擦副的减摩和自修复性能,采用液相化学还原法合成了二烷基二硫代磷酸(HDDP)修饰纳米铜微粒,利用四球摩擦磨损试验机分析了不同载荷条件下纳米铜添加量对摩擦系数、磨斑直径等摩擦学性能影响,采用扫描电镜(SEM)和X射线光电子能谱仪(XPS)分析了磨痕形貌及其化学成分组成,并通过纳米压痕测试技术测量铜膜硬度及弹性模量。结果表明:纳米铜添加量为0.4%(质量分数)时减摩效果最佳,磨斑直径和摩擦系数明显下降,比未添加纳米铜的降低了23.0%~27.2%和15.1%~24.9%。摩擦过程中纳米铜微粒在摩擦表面形成化学沉积膜,铜膜的纳米硬度为1.63 GPa,弹性模量为78.08 GPa,表现出优良的抗磨减摩性能。