Zaidon Ashaari

Determination of polyphenolic content of bark extracts for wood adhesives

Summary The phenolic content of condensed tannins varies considerably, depending on the method of determination. Even though the Stiasny precipitation number has been commonly used to estimate the amount of reactive tannin towards formaldehyde, particularly in adhesive applications, this estimation alone is not sufficient. In this study two methods of determining the amount of reactive tannin towards formaldehyde were examined. These were (1) the reactivity towards formaldehyde or the Stiasny precipitation number, and (2) the formaldehyde uptake. Five different types of tannin were examined from Rhizophora mucronata, P. radiata, mimosa, quebracho and chestnut. The study indicates that the phenolic content in tannin can be better estimated by determining both the Stiasny number and the amount of formaldehyde uptake. High correlation (r2 = 0.905) was detected between the two methods. The study also revealed that hot water extracts of R. mucronata contain relatively small amounts of reactive polyphenols and are less reactive than sulfite extracts. The consumption of formaldehyde by this type of tannin was only 0.294 molecules per flavanoid unit. Similar to R. mucronata, the sulfite extracts of P. radiata contain relatively high amounts of reactive polyphenols and reacted with substantially higher amounts of formaldehyde per flavanoid unit, comparable to mimosa and quebracho tannins. Nonetheless, the reactivity towards formaldehyde (gel time) of the latter tannins is muchlower, despite their higher polyphenolic content. Of the two methods used to estimate the polyphenolic content of bark extracts, the Stiasny number had a relatively higher correlation (r2 = 0.518) with gel time than formaldehyde uptake (r2 = 0.345) did. The behaviour of these tannins in relation to their reactivity and chemical structures is discussed.

Influence of Resin Molecular Weight on Curing and Thermal Degradation of Plywood Made From Phenolic Prepreg Palm Veneers

The present work evaluates curing and the thermal behavior of different molecular weight phenol formaldehyde (PF) resins used to prepare PF prepreg oil palm stem veneers. The physical properties (solid contents, gelation time, pH, and viscosity) of PF resins were determined. The molecular weight of resins was characterized by gel permeation chromatography, whilst thermal properties were determined by differential scanning calorimetry and thermogravimetric analyses. The average molecular weight of PF resins were 526 g/mole (low), 1889 g/mole (medium), and 5178 g/mole (control - commercial). Among the resins, medium (MMwPF) gives better thermal stability with a retained weight of 48.9% at 300°C. High (Commercial PF) had a low decomposition temperature (109.3°C) which occurred within 11 min. Both low (LMwPF) and MMwPF started to melt at ≥120°C. Based on strength and shear values, phenolic prepreg palm veneers can be prepared using either low or medium molecular weight PF but with varying results. In all cases, the mechanical properties of palm plywood made from PF prepreg veneers were superior to those made from PF-bonded plywood using the commercial process.

Chemical, physico-mechanical properties and biological durability of rubberwood particleboards after post heat-treatment in palm oil

Abstract The chemical properties, dimensional stability, mechanical strength and termite resistance of urea formaldehyde (UF) bond rubberwood (RW) particleboard (PB) were assessed after a two-step oil heat treatment (OHT). The PB was immersed in palm oil before heating to 180, 200, and 220°C in a laboratory oven for 2 h. Anti-swelling efficiency (ASE) and water repellency efficiency (WRE) as well as bending (MOE, MOR) and internal bonding strength (IB) were determined. Resistance against a subterranean termite, Coptotermes curvignathus Holmgren, was tested. The degradation of hemicelluloses and cellulose, that are mainly responsible for wood wetting processes, was confirmed by Fourier transform infrared (FTIR) spectra. Formation of an elevated cross-linking density in lignin also contributed to the dimensional stability, where 93.6% ASE and 46.3% WRE were achieved in the samples treated at 220°C. Mechanical properties of treated samples were inferior to the control samples due to hemicelluloses degradation and breakage of the UF bonding network. A significant improvement in termite resistance has been found in the treated samples.

Dimensional stability of heat oil-cured particleboard made with oil palm trunk and rubberwood

Dimensional stability of heat oil-cured particleboard made with admixture of oil palm trunk and rubberwood was evaluated. Particleboard made with oil palm trunk had better dimensional stability due to better compact ratio and lower hygroscopicity than rubberwood. Combination of repellent properties of oil and application of heat had greatly reduced the hygroscopicity of particleboard by decreasing its equilibrium moisture content, thickness swelling and water absorption.

Performance of compreg laminated bamboo/wood hybrid using phenolic-resin-treated strips as core layer

Physical and mechanical properties of compreg laminated bamboo/wood hybrid using phenolic-resin-treated strips as core layer were investigated. Compreg laminates made from treated core layer revealed better properties than the untreated control samples. Compreg laminated wood showed lower properties compared to compreg laminated bamboo and bamboo/wood hybrid. Assembly orientation exerted great influence on the properties as parallel laminated samples showed better strength and dimensional stability.

Development and Characterization of Wood and Non-wood Particle Based Green Composites

Production of green composites involve a manufacturing process that combining both renewable plant-based particles and green polymers. Characteristics of wood and non-wood particles are one of the main factors that influencing the properties of green composite, particularly particle based composite i.e., particleboard and wood plastic composite (WPC). Characterization of wood and non-wood particles are vital for properties determination of the resulting particleboard and WPC. The present work reviewed some characterization studies of particles including the size (length, width, and thickness, aspect ratio, and slenderness ratio) and geometry of the particles. This paper also highlighted the effects of particle size and geometry of wood and non-wood particle on the mechanical and physical properties of particleboard and WPC. Findings revealed that particle size exerted significant effect on the mechanical and physical properties of both particleboard and WPC. On the other hand, types of materials (wood or non-wood) are crucial factor that affects the performance of particleboard, but not a critical factor on the performance of WPC as it contained lesser amount of particles.

Physico-mechanical properties of particleboard made from heat-treated rubberwood particles

Physico-mechanical properties of particleboard fabricated from heat-treated rubberwood particles were investigated. Reduction in water absorption and mass loss were observed in heat-treated rubberwood particles, and it was associated with the properties of particleboard. The density and moisture content of the particleboard decreased with increasing treatment temperature and time. Heat treatment of particles improved the dimensional stability of the particleboard, but the mechanical properties were adversely affected.

Light Organic Solvent Preservative Behavior on Bending Strength of Mengkulang (Heritiera spp.) Glulam

The purpose of this study was to determine the behavior of LOSP on the bending strength of glulam manufactured using Malaysian tropical timber namely Mengkulang. Timber preservatives are used to prevent from degradation which can be due to some extend weathering, fungi, or insects. Therefore, the use of quality preservatives is essential in determining the performance of timber under such conditions. An experiment was carried out to determine the effect of using preservative to the performance of Mengkulang (Heritiera spp.) glued laminated timber (glulam) treated using light organic solvent preservative (LOSP). LOSP was chosen due to its more environmental friendly chemical ingredient. Ten specimens of Mengkulang manufactured at a factory in Selangor, Malaysia which followed the Malaysian Standard, MS 758 were divided into one group of five timber beams treated with LOSP prior to gluing and another group of five untreated timber beams. This paper only reported the effect of LOSP on the bending strength properties. The static bending test under four-point loading was carried out based on American Standard for Testing and Material, ASTM D 198. The results showed that LOSP-treated Mengkulang glulam had higher values of modulus of rupture (MOR) and modulus of elasticity (MOE) compared with untreated Mengkulang glulam by 4 % and 6 %, respectively. Since most researches have so far focused on temperate softwood species, the findings of this study are significant as the specimens were from tropical timber species and the study employed experimental design. It can be concluded that LOSP has the quality to improve the bending strength of Mengkulang glulam thus increasing its performance.