表面改性对纳米SiO_2增强木纤维/PP复合材料微观结构及性能的影响

为研究经表面处理的纳米SiO_2在复合材料内的分散状态及其对复合材料性能的影响,选择硅烷偶联剂KH570对纳米SiO_2进行表面改性,分别通过激光粒度仪、傅里叶红外光谱分析仪、接触角测定仪表征纳米SiO_2的改性效果,采用XRD、SEM对经表面处理后的纳米SiO_2在木纤维/PP内的分散状态进行表征,测试并分析其力学性能、吸水膨胀率和吸水率。结果表明:当KH570的质量分数为5%时,纳米SiO_2的平均粒径为62nm,KH570可以成功接枝在纳米SiO_2表面。其对木纤维/PP复合材料的力学性能提高最优,吸水膨胀率与吸水率最低,弯曲强度达到52.6 MPa,拉伸强度为30MPa,冲击强度可以达到11.8kJ/m2;相比添加未经过表面改性的纳米SiO_2,分别提高了75%,20%和47.5%。     

Parameters Affecting the Cross-Flow Filtration of Dissolved LignoBoost Kraft Lignin

In the kraft pulping process, the lignin-containing by-product kraft black liquor is currently combusted as an energy source. LignoBoost is a technique that extracts lignin from kraft black liquor, resulting in a lignin-lean black liquor, which is returned to the process, and an extracted kraft lignin. To facilitate the use of the extracted kraft lignin in high-value applications, it can be refined via fractionation to produce a more homogeneous starting raw material. Hence, the aim of this study is to investigate the behavior of dissolved softwood kraft lignin during cross-flow filtration. The effects of the lignin concentration, pH, and ionic strength on the fractionation of the dissolved lignin during cross-flow filtration are investigated. The results indicate that large amounts of low-molecular-weight kraft lignin can be produced from solutions having a low lignin concentration. Furthermore, the effects of pH and ionic strength on the fractionation of low-molecular-weight lignin are identified within the studied ranges.     

Nanopaper membranes from chitin–protein composite nanofibers—structure and mechanical properties

Chitin nanofibers may be of interest as a component for nanocomposites. Composite nanofibers are therefore isolated from crab shells in order to characterize structure and analyze property potential. The mechanical properties of the porous nanopaper structures are much superior to regenerated chitin membranes. The nanofiber filtration‐processing route is much more environmentally friendly than for regenerated chitin. Minerals and extractives are removed using HCl and ethanol, respectively, followed by mild NaOH treatment and mechanical homogenization to maintain chitin–protein structure in the nanofibers produced. Atomic force microscope (AFM) and scanning transmission electron microscope (STEM) reveal the structure of chitin–protein composite nanofibers. The presence of protein is confirmed by colorimetric method. Porous nanopaper membranes are prepared by simple filtration in such a way that different nanofiber volume fractions are obtained: 43%, 52%, 68%, and 78%. Moisture sorption isotherms, structural properties, and mechanical properties of membranes are measured and analyzed. The current material is environmentally friendly, the techniques employed for both individualization and membrane preparation are simple and green, and the results are of interest for development of nanomaterials and biocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40121.     

Mathematical Modeling the Drying of Poplar Wood Particles in a Closed-Loop Triple Pass Rotary Dryer

Closed-loop drying systems are an attractive alternative to conventional drying systems because they provide a wide range of potential advantages. Consequently, type of drying process is attracting increased interest. Rotary drying of wood particles can be assumed as an incorporated process involving fluid–solid interactions and simultaneous heat and mass transfer within and between the particles. Understanding these mechanisms during rotary drying processes may result in determination of the optimum drying parameters and improved dryer design. In this study, due to the complexity and nonlinearity of the momentum, heat, and mass transfer equations, a computerized mathematical model of a closed-loop triple-pass concurrent rotary dryer was developed to simulate the drying behavior of poplar wood particles within the dryer drums. Wood particle moisture content and temperature, drying air temperature, and drying air humidity ratio along the drums lengths can be simulated using this model. The model presented in this work has been shown to successfully predict the steady-state behavior of a concurrent rotary dryer and can be used to analyze the effects of various drying process parameters on the performance of the closed-loop triple-pass rotary dryer to determine the optimum drying parameters. The model was also used to simulate the performance of industrial closed-loop rotary dryers under various operating conditions.     

Comparison of Canola and Soy Flour with Added Isocyanate as Wood Adhesives

Canola is widely grown in the northern latitudes for its vegetable oil, generating large quantities of residual, low value canola flour used as animal feed. The common wood adhesive poly(diphenylmethylene diisocyanate) (pMDI) should react with the wide variety of functional groups in proteins. Therefore, it would seem that canola flour with added pMDI could be an effective adhesive. Two main questions are addressed in this study: How do the wood adhesive properties of canola flour compare to the better-studied soy flour? How well do proteins, which contain an abundance of functional groups, cure with the very reactive pMDI? These questions were addressed using the small-scale adhesive strength test ASTM D-7998, with various adhesive formulations and bonding conditions for canola flour plus pMDI compared to soy adhesives. The more challenging wet cohesive bond strength was emphasized because the dry strengths were usually very good. Generally, soy adhesives were better than canola ones, as was the polyamidoamine-epichlorohydrin cross-linker compared to pMDI, but these generalizations can be altered by the conditions selected. Three-ply plywood tests supported the small-scale test results.     

Moisture transfer and stress development during high-temperature drying of Chinese fir

Abstract

The knowledge of moisture content (MC) and drying stress are crucial parameters to control the drying process and maintain the quality of dried wood. Herein, we investigated the pattern of moisture transfer and stress development in Chinese fir during the high-temperature drying process. The MC in each layer of lumber was separated into bound water and free water via nuclear magnetic resonance (NMR), and the drying and residual stress were measured using prong test method. There was different MC in each layer along the thickness, resulting in an MC gradient that initially increased and then decreased, which is consistent with the trend of drying stress. The T₂₁ peak indicating bound water shifted to the left especially when MC was below the fiber saturation point, signifying that the discharge of moisture became difficult with prolonged drying time. The ratio of bound water to free water was different in each layer, indicating that the moisture transfer was different along the thickness. Furthermore, the residual stress was greater than the corresponding drying stress though the disparity reduced gradually, which suggests that the MC gradient was the largest affecting factor for drying stress at high MC stages but decreased to some extent as the drying process continued.     

热分析技术在胶合板／木材阻燃性能评价中的应用

主要介绍了常用的几种热分析技术（热重法、差热分析、差示扫描量热法、动态热机械分析和微商热重法）、胶合板及木材的阻燃机理,以及热分析技术在胶合板及木材阻燃性能评价中的应用情况。     

磨削木竹材表面粗糙度对胶合强度的影响

采用探针法测定了水曲柳、毛竹和落叶松砂带磨削表面的粗糙度,分析了影响表面粗糙度的因素,并采用心理分析方法讨论了的粗糙感与表面粗糙度关系;还分析了木材表面粗糙度对胶合强度的影响.为获得不同树种及不同粒度砂带磨削对工件表面粗糙度和粗糙感的影响,实验测量了磨削工件表面的粗糙度和粗糙感触觉心理量、视觉心理量.研究结果表明,材种和表面组织构造影响表面粗糙度;表面粗糙度值因为材种不同而不同,随着加工精度的提高而降低;水曲柳、毛竹和落叶松表面粗糙感的触觉心理量与视觉心理量呈正相关;阔叶材、竹材、针叶材表面粗糙感的触觉心理量与视觉心理量的相关性逐渐增大;触觉心理量与表面粗糙度参数的相关性要高于视觉心理量.砂带磨削木竹材表面的胶合强度在磨削砂带柱度为100～150目时达到最大值.