CONTROL OF THE DRYING PROCESS THROUGH THE RELATIONSHIP OF WOOD AND WET-BULB TEMPERATURES

The ratio of wood temperature to wet-bulb temperature (WT/ WBT) with the wood moisture, aiming at its use in the control of the drying process in drying kilns, were correlated. Slash pine boards measuring 25 mm thick and 750 mm length were dried in an electric forced convection kiln, using four temperatures and two air velocities. The process was controlled through a computerized system comprising a microcomputer and data acquisition unit. The analyses indicated a good correlation (0.97 < r < 0.99) between the coefficient WT/WBT and the moisture content of the wood. The adjustment of polynomial models was satisfactory in the range from green condition to 10% moisture content, at the temperature range and air velocity studied. These results, variables, together with the ease and speed of measurement of the suggest that the coefficient WT/WBT can be used as an alternative for the control of the drying process. However, the practical application of this system still depends on further research and development.     

Adhesion Performance and UV-Curing Behaviors of Interpenetrated Structured Pressure Sensitive Adhesives with 3-MPTS for Si-Wafer Dicing Process

Abstract

As Si-wafers, as used in the electronic industry, become thinner and thinner, it is important to investigate the conditions which are suitable for easily peelable acrylic dicing tapes. In the ‘pick-up’ process, the adhesion strength decreased after UV irradiation as a result of polymer network formation. In this study, interpenetrating polymer network (IPN) structured acrylic pressure sensitive adhesives (PSAs) were investigated with two different types of UV irradiation — a steady UV irradiation and a pulsed UV irradiation of 100 mJ/cm². The PSAs binder contained 2-ethylhexyl acrylate (2-EHA), acrylic acid (AA) and 3-methacryloxypropyl trimethoxysilane (3-MPTS). The hexafunctional monomer, dipentaerythritol hexacrylate (DPHA) and 3-methacryloxypropyl trimethoxysilane (3-MPTS) were used as diluent monomers. The adhesion performance as related to the peel strength and the tack properties on the Si-wafer substrates, was examined with increasing UV dose. The effect of UV-curing on the behavior and viscoelastic properties of the ‘pick-up’ acrylic tapes was investigated using Fourier transform infrared — attenuated total reflectance spectroscopy (FTIR–ATR) and an advanced rheometric expansion system (ARES). It is also necessary to consider the contaminants on the Si-wafer substrates left behind after releasing the dicing tapes, because of possible damage to the Si-wafers and subsequent processes. Field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) analysis revealed little residue on the Si-wafer after removing the tapes and after more than the specific level of UV dose.     

Analysis of the Mechanical Behavior of Wood and Welded Wood under Tensile–Shear Loads Using a Modified Arcan Device

Abstract

The aim of this work was to analyze the possibility of using a modified Arcan device to characterize the mechanical behavior, under tensile–shear loads, of wood and of wood assemblies obtained using friction welding without any adhesive. This process is interesting as only friction energy is used to assemble the two pieces of wood; thus, the process is characterized by low environmental impact and by easier recycling at the end of the product’s life. For this assembly technique to become widespread in industry, it is necessary to develop numerical tools in order to predict the behavior of such assemblies under complex loads. Thus, it is also necessary to obtain a large data base of experimental results under various tensile–shear loads, in order to analyze the multi-axial mechanical behavior of such welded assemblies. However, few experimental devices have been proposed in the literature, and furthermore, very few papers in the literature analyze the complex mechanical behavior of wood. This paper describes the use of a modified Arcan test to analyze the behavior of wooden blocks and their welded assemblies. The stress state in the middle of the specimens used was not homogenous and, thus, finite element simulations were required to determine the stress distributions. These simulations were possible as the load transmitted by the tensile loading machine was known. Some experimental results are presented in the case of beech wood in a transversal direction.     

Initial evaluation of novel polyamide-imides and their copolymers as adhesives

—An adhesive screening study was performed at NASA Langley Research Center on two linear aromatic polyamide-imide (PAI) homopolymers and two linear aromatic PAI copolymers. The homopolymers were made with either of two amide diamines, 3,3'- or 4,4'-diaminobenzanilide (DABA), and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA). The two copolymers studied were prepared with a combination of 3,3'-DABP and amide diamines. These aromatic PAIs possess high thermal stability because of intermolecular hydrogen bonding and chain stiffness. Lap shear strength (LSS) tests, conducted at room temperature, 177, 204 and 232°C, were the primary criterion for evaluation of the polymers as adhesives. Included in the study were measurements of the glass transition temperature made on fractured specimens for each bonding condition and a visual determination of the type of bond failure for specimens at each test temperature. Of the four adhesive candidates investigated, the best LSS values were obtained with the PAI copolymer identified as LARC-TPI(25% 3,3'-DABA). However, the LSS values were higher for the LARC-TPI polyimide with which the adhesive strengths were compared. The combination of a high molecular weight and the increased interchain electronic interaction associated with the amide group appears to contribute to the poor flow properties observed.     

Effect of model fillers on the adhesive strength of pressure-sensitive tapes

—The effect of various model fillers, namely glass beads, 'Spheriglass', and PTFE powder, on the adhesive strength of natural rubber (NR) and poly(n-butyl acrylate) (PBA) tapes has been investigated. Glass fillers treated with alkyl chlorosilane were also used. The adhesive strength was measured over a range of rates and temperatures, and corrections for the thickness of the adhesive and volume fraction of the polymer were introduced into the rate term. It was observed that the adhesive strength of PBA tapes filled with 20% PTFE is comparable to that of the control sample without filler. The strength measured over a range of strain rates increased for both untreated and treated Spheriglass-filled adhesives. Filled NR adhesives showed an enhanced strength only at very high strain rates. With 40% PTFE, this increase was quite apparent. The mechanism of improvement of the strength of adhesion due to the incorporation of a filler is explained. The addition of a filler introduces an additional mechanism of energy dissipation during deformation of the adhesive and a higher energy will be expended due to debonding of the filler and hysteresis.     

Silver coating of spindle- and filament-type magnetic particles for conductive adhesive applications

Spindle-type hematite and magnetite particles and nickel filaments have been coated uniformly with silver by using chemical reduction. The effects of the reaction time and the concentration and nature of the reducing agent on the particle coatings were investigated at constant temperature. The reaction time had a pronounced effect on the nature of the coated surface layer. Coated and core particles were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDAX). The electrical properties of the particles were also characterized. The conductivity of nickel filaments which can be oriented under a magnetic field for anisotropic electric conduction increased from 302 to 877 S/cm at 3.5 kPa pressure when coated with silver.     

Experimental Investigation and Practical Application of Superheated Steam Drying Technology for Softwood Timber

Abstract

Due to several advantages, superheated steam drying of timber has attracted great attention. However, the technology is still restricted to some special cases, partly due to the lack of fully understanding of the drying process. In this work, experiments were conducted to dry radiata pine timber using superheated steam under vacuum and at pressure. In the first part of the experiments, softwood timber was dried in a superheated steam kiln with drying rates, steam temperature across the stack and wood temperature being measured during drying. In the second part of the work, experimental studies were performed to investigate potential applications of the superheated steam drying at ultra-high temperatures (UHT) and pressurized steam conditioning of kiln dried timber. Compared to normal drying temperatures, the UHT drying can reduce the drying time by a factor of 5 to 10 and it is also more energy efficient. The pressurized steam conditioning has been proven to be a promising technology to relieve drying stresses and to reduce twist of the dried timer.

     

POLYSTYRENE-BENZOYLATED EFB REINFORCED COMPOSITES

Reinforced thermoplastics generally are produced by incorporation of reinforcement agents or fillers into thermoplastic resins. The utilization of lignocellulosic material as filler with reinforcement in polymer matrix has received much interest due to its lower price and other properties. A composite of polystyrene reinforced with oil palm empty fruit bunches (EFB) and chemically treated EFB with benzoyl chloride (EFB-benzoylated) as a function of loading and fiber surface modification were prepared. The chemically treated fibers were analyzed with FT-IR to observe the extent of chemical reaction with EFB fiber. The sharp peak at 710 cm^?1 appeared on the spectra, which indicated that the mono-substituted benzene ring has taken place. The strong peak at 1720 cm^?1 has indicated the presence of ester group treated fiber. The flexural test was performed using Instron 4301 testing machine to study flexural properties of the composites with various fiber sizes. The results showed that the flexural properties increased with particle size. The flexural strength of EFB-benzoylated composites was observed to be stronger than untreated EFB fiber. Scanning electron microscope was used to investigate the morphological structure of the fiber surface, fiber pull out, fracture surface, and fiber–matrix interface. The untreated EFB composites showed hole and fiber end, which indicated that most of the fiber have pulled out breaking during the fracture of composites; however, the treated EFB-benzoylated showed a good adhesion between fiber and matrix.     

Studies on conductivity of nitrile rubber and its blends with NR,EPDM, and PVC

Abstract

Nitrile/butadiene rubber has been made electrically conducting by the incorporation of acetylene black. The change in conductivity and mechanical properties with varying amounts of acetylene black was studied. Nitrile rubber was blended with NR, PVC, and EPDM and their conductivity and mechanical properties were determined after incorporation of acetylene black. On comparison it was found that NBR-NR blends are more conducting than NBR-PVC and NBR-EPDM blends. Blends of NBR-NR containing varying amounts of NR and NBR were prepared with the same amount of acetylene black, and their properties were also studied. A blend of 80:20 NBR/NR was studied in detail by varying the concentration of acetylene black. It was found that electrical conductivity depends on the degree of dispersion of acetylene black in the polymer matrix.     

Enhanced thermal stability and flame retarding properties of recycled polyethylene based wood composites via addition of polyethylene/nanoclay masterbatch

Abstract

Barrier and mechanical properties of wood powder composites based on recycled polyethylene (RPE) were modified using a commercial nanoclay masterbatch. X-ray diffraction, dynamic rheology and thermogravimetric analysis measurements showed that nanoclay from the selected masterbatch was well dispersed and formed a percolation network in both virgin and RPEs. The resulting nanocomposites promoted the thermal stability of matrix significantly. Modification efficiency of nanoclay, however, was evidently influenced by the type of matrix, where the strongest effect was achieved in a low viscosity virgin high density PE. The masterbatch was incorporated into an industrial formula designed extrusion quality RPE/wood flour composite. Processing procedures, mainly compounding cycles, and material composition, mainly clay content and type of coupling agent, were optimised. Two extrusion cycles led to higher uniformity of resulting composites than one cycle. Addition of a coupling agent, which has medium viscosity and plenty functional groups, led to enhanced tensile strength. The twice compounded composites were well stiffened and strengthened via combination of 6 wt-% clay and medium viscosity coupling agent. All composites without the addition of nanoclay burned faster after ignition and dripped much earlier and more compared to the composites containing nanoclay even with as small amount as 3 wt-% and being compounded once. The material with 6 wt-% clay showed the best sample integrity and burned slowest of all the tested composites. Furthermore, no dripping during combustion was seen for this material. This study shows that the incorporation of nanoclay using the selected masterbatch can effectively improve the flame retarding properties of RPE based wood composites.