Understanding effects of drying methods on wood mechanical properties at ultra and cellular levels

Conventional kiln and vacuum drying are commonly used in industry to dry wood. In this research, an attempt was made to develop a better understanding of the effects of both drying methods on the mechanical properties of wood at the ultra-structure and cellular structure levels. Dynamic mechanical analysis (DMA) and nanoindentation (NI) were used together with standard static bending tests according to ASTM D143 to assess the respective effects of both drying methods on the performance of yellow birch (Betula alleghaniensis Brit.) wood, an important species in the Canadian wood industry. Measurements of equilibrium moisture content (EMC) at different relative humidity (RH) levels showed that vacuum drying consistently yielded higher EMC values. Vacuum-dried wood also exhibited superior MOE and MOR performance. Tests conducted by DMA demonstrated that the chemical structure of wood had undergone more changes during conventional kiln drying than during vacuum drying. The elastic modulus and hardness measured by the nanoindentation technique revealed that the impact of wood drying can be detected at the cell wall level as well. The results of this study showed that special attention should be paid to the effects of specific drying methods on the chemical structure of wood, as the chemical changes occurring in the kiln impact on the quality of the final products

Thermal Properties of Composites Made of Heat-treated Wood and Polypropylene

ABSTRACT: Exposure of wood to high temperatures improves thermal stability of wood and it has been used as a means to boost dimensional stability of wood for centuries. Inclusion of wood in thermoplastic matrix composites reduces the thermal stability of the composites considerably because of poor adhesion between wood and the matrix, and lower thermal stability of wood in comparison to the matrix. In order to invest natural fiber/thermoplastic composites with thermal stability, wood flour was heat treated under different temperatures and time. Thermal stability measurements conducted by thermogravimetric analysis (TGA) indicated that heat-treatment of wood increased thermal stability, ash content, and DTG max degradation temperature of wood. As the heat-treated wood flour used as filler for PP composites, thermal stability, ash content, and DTG max degradation temperatures of the composites were affected markedly as well. The higher the temperature and longer the time employed in heat-treatment, the more was the improvement gained. The melting point (T m ) of composites measured by differential scanning calorimetry (DSC) showed that wood content and preheat treatment had no effect on melting points (T m )

A Rapid Method to Assess Viscoelastic and Mechanosorptive Creep in Wood

This study presents an alternative method to measure the viscoelastic and mechanosorptive creep of wood using a dynamic mechanical analyzer (DMA). Measurements were made on sugar maple wood specimens in the radial and tangential directions in different RH conditions. Viscoelastic creep measurements showed that DMA can detect effects of time, RH, load level, and wood direction on wood creep. With the applied stress levels (5, 25, 35, and 45%), wood exhibited linear viscoelastic behavior. DMA also demonstrated its value in measuring mechanosorptive effect. The mechanosorptive effect was observed as RH changed during the loading period, resulting in very high deflections. In both viscoelastic and mechanosorptive creep measurements, creep proved to be greater in the tangential direction than in the radial direction. The results of this study demonstrated that a DMA can be a rapid and accurate tool to predict the time-dependent behavior of wood under load

The effects of material formulation and manufacturing process on mechanical and thermal properties of epoxy/clay nanocomposites

A holistic study was conducted to investigate the combined effect of three different pre-mixing processes, namely mechanical mixing, ultrasonication and centrifugation, on mechanical and thermal properties of epoxy/clay nanocomposites reinforced with different platelet-like montmorillonite (MMT) clays (Cloisite Na+, Cloisite 10A, Cloisite 15 or Cloisite 93A) at clay contents of 3–10 wt%. Furthermore, the effect of combined pre-mixing processes and material formulation on clay dispersion and corresponding material properties of resulting composites was investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), flexural and Charpy impact tests, Rockwell hardness tests and differential scanning calorimetry (DSC). A high level of clay agglomeration and partially intercalated/exfoliated clay structures were observed regardless of clay type and content. Epoxy/clay nanocomposites demonstrate an overall noticeable improvement of up to 10 % in the glass transition temperature (Tg) compared to that of neat epoxy, which is interpreted by the inclusion of MMT clays acting as rigid fillers to restrict the chain mobility of epoxy matrices. The impact strength of epoxy/clay nanocomposites was also found to increase by up to 24 % with the addition of 3 wt% Cloisite Na+ clays. However, their flexural strength and hardness diminished when compared to those of neat epoxy, arising from several effects including clay agglomeration, widely distributed microvoids and microcracks as well as weak interfacial bonding between clay particles and epoxy matrices, as confirmed from TEM and SEM results. Overall, it is suggested that an improved technique should be used for the combination of pre-mixing processes in order to achieve the optimal manufacturing condition of uniform clay dispersion and minimal void contents

Macro and nano dimensional plant fiber reinforcements for Cementitious Composites

uncorrected proofNowadays, the use of plant fibers in the civil construction industry is growing rapidly due to their low cost, light weight and good specific mechanical properties, lower health hazard, and environmental benefits. Nanodimensional fibers derived from plants such as nanocellulose are also getting considerable attention due to their excellent mechanical properties. This chapter discusses these different types of plant fibers and their derivatives which have huge application potential in the civil construction sector. The influence of plant fibers on microstructure as well as on physical–mechanical properties of cementitious composites are discussed in detail. The challenges regarding plant fiber processing and dispersion, the fiber/matrix interface, and the durability of plant fiber-cement composites are also addressed. The application of nanocellulose in polymer composites has been included in this chapter just to provide the readers sufficient background information and techniques to inspire engineered cement-based composites. Finally, the chapter concludes with the current application of plant fibers in civil construction and the future trends(undefined)info:eu-repo/semantics/publishedVersio

UNDERSTANDING THE EFFECTS OF DRYING METHODS ON WOOD MECHANICAL PROPERTIES AT ULTRA AND CELLULAR LEVELS

Conventional kiln and vacuum drying are commonly used in industry to dry wood. In this research, an attempt was made to develop a better understanding of the effects of both drying methods on the mechanical properties of wood at the ultra-structure and cellular structure levels. Dynamic mechanical analysis (DMA) and nanoindentation (NI) were used together with standard static bending tests according to ASTM D143 to assess the respective effects of both drying methods on the performance of yellow birch (Betula alleghaniensis Brit.) wood, an important species in the Canadian wood industry. Measurements of equilibrium moisture content (EMC) at different relative humidity (RH) levels showed that vacuum drying consistently yielded higher EMC values.  Vacuum-dried wood also exhibited superior MOE and MOR performance. Tests conducted by DMA demonstrated that the chemical structure of wood had undergone more changes during conventional kiln drying than during vacuum drying. The elastic modulus and hardness measured by the nanoindentation technique revealed that the impact of wood drying can be detected at the cell wall level as well. The results of this study showed that special attention should be paid to the effects of specific drying methods on the chemical structure of wood, as the chemical changes occurring in the kiln impact on the quality of the final products. 

Determining the Linear Viscoelastic Region of Sugar Maple Wood by Dynamic Mechanical Analysis

Dynamic mechanical analysis (DMA) is a powerful analytical technique to study wood structure and properties. In order to draw firm conclusions from results obtained by DMA, strain rate of tests conducted by DMA should be within the linear viscoelastic region (LVR) of the tested material. In this study, the LVR limit of sugar maple (Acer saccharum Marsh.) wood specimens was determined in the three directions under a range of temperature and relative humidity (RH) conditions. The results demonstrated that wood had very different LVR limits in the different directions. The longitudinal direction had much lower LVR limits than the radial and tangential directions. While LVR limits were not strongly affected by changes in temperature and RH in the longitudinal direction, they proved very sensitive to these factors in the tangential direction. The results of this study showed the importance of determining LVR limits before running any test by DMA

Ultrasonication Technique: A Method for Dispersing Nanoclay in Wood Adhesives

The efficiency of ultrasonication technique to disperse nanoclay in polyvinyl acetate (PVA) was examined. A hydrophilic nanoclay was added to PVA, and its effects on bond strength of wood joints were determined. The results of bond strength measured on block shear tests showed that nanoclay increased the bond strength of wood joints, especially in humid conditions. Atomic force microscopy (AFM) proved that it can be used to examine the quality of nanoclay dispersion in a matrix very precisely. The results of this study showed that ultrasonication technique is efficient in mixing nanoclay with the PVA matrix