Effect of Heat Treatment on Color Changes,Dimensional Stability,and Mechanical Properties of Wood

Abstract

Properties of fast-growing timbers with low durability can be improved by thermal modification. Thermal modification is an eco-friendly method of improving durability of wood. In this work, specimens of rubberwood (Hevea brasiliensis) and silver oak (Grevillea robusta) were thermally modified in vacuum between 210 to 240°C for 1 to 8 hours, and their weight loss, color, and chemical changes evaluated. Rate of thermal degradation was determined from weight loss data. The color of the modified wood darkened and was uniform throughout. CIE lightness color coordinate (L*) decreased with treatment severity, while chroma coordinates a* and b* increased initially, but later decreased with increased process severity. FTIR analysis showed degradation of cell wall polymers resulting in generation of structures which are responsible for color darkening of thermally modified wood. Mechanical properties (bending strength, MOR, and bending stiffness, MOE) of heat-treated wood decreased. A decrease in hydroxyl groups reduced the hygroscopic nature, resulting in increased dimensional stability of thermally modified wood.     

Polypropylene (PP)–Acacia mangiumcomposites: the effect of acetylation on mechanical and water absorption properties

Acacia mangiumwood flour (AMWF)–polypropylene (PP) composites were produced at different filler loading (20, 30, 40, and 50 w/w) and mesh no. (35, 60, 80, and 100 mesh). The AMWF–PP composites (using unmodified or modified wood flour) were compounded using a Haake Rheodrive 500 twin screw compounder. The mechanical and water absorption (WA) properties of modified (only at mesh no. 100) and unmodified AMWF–PP composites were investigated. Increase in the mesh number (35–100) of the unmodified AMWF showed increased flexural and impact properties. Flexural modulus exhibited higher properties as the filler loading increased (20–50). However, flexural and impact strength showed the opposite phenomenon. Water absorption and thickness swelling increased as the mesh number and filler loading increased. This has been attributed to the presence of hydrophilic hydroxyl groups of the filler. Modified AMWF–PP composites exhibited higher mechanical properties and good water resistance when compared to unmodified AMWF–PP composites at all values of filler loading. The evidence of the failure mechanism (from impact strength) of the filler–matrix interface was analyzed using scanning electron microscope.     

A Model of Drying Kinetics of Acacia mangium Wood at Different Temperatures

The objective of this study was to determine the isothermal drying kinetics of Acacia mangium wood blocks by employing a relative humidity-controlled drying chamber. A model was developed based on solution of Fick's second law and evaluated through the coefficient of determination (R ² ), sum of square error (SSE), root mean square error (RMSE), and reduced chi-square (χ ² ). This model was compared to semi-theoretical models which are commonly used to describe the drying behavior of biomass in previous studies. The porosity and shrinkage characteristics of dried specimens were also evaluated. Based on the findings in this work, it was determined that the proposed model resulted in an excellent fit with experimental data for all four drying temperature levels of 30, 35, 40, and 45 ^° C to describe the isothermal drying kinetics of Acacia mangium . It appears that volumetric shrinkage of the samples decreased quadratically with decreasing moisture ratio. The activation energy of the drying process was determined to be 41.07 kJ/mol.     

Thermogravimetric analysis and dynamic Young's modulus measurement of N,N‐dimethylacetamide‐impregnated wood polymer composites

Mercerized wood species were impregnated with N,N‐dimethylacetamide. Their Fourier transform infrared spectra then showed enhanced absorption at 1419 cm^?1 (? C? /CH3), and the 1267‐cm^?1 (? N? /CH3) stretching band confirmed the occurrence of a modification reaction. Thermogravimetric investigation of the resultant wood polymer composites (WPCs) indicated a better thermal stability in comparison with that of the raw wood. The dynamic Young's modulus of the WPCs was significantly increased compared with that of raw wood. After modification, analysis by scanning electron microscopy showed porous cells of raw wood filled with the polymer, which led to the better stability of WPCs. Analysis by XRD indicated that the crystallinity of WPCs increased because of an increase in the stiffness and the thermal stability of the composites. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Bond integrity of cross laminated timber from Acacia mangium wood as affected by adhesive types,pressing pressures and loading direction

Cross laminated timber (CLT) was fabricated from Acacia mangium wood by using phenol resorcinol formaldehyde (PRF) and one component polyurethane (PUR) as binders. The purpose of the study was to evaluate the bond integrity of A. mangium CLT produced using different working parameters. The assemblies were pressed at 30 °C for 30 min using three pressing pressures (0.9 N/mm², 1.2 N/mm², and 1.5 N/mm²). Delamination and block shear tests were conducted on the CLT according to European Standards, EN 391 and EN 392, respectively. The results revealed that PRF-bonded CLT experienced lower percent delamination compared to that bonded with one component PUR. It appears that a higher clamping pressure i.e. 1.5 N/mm², is needed to sufficiently bond A. mangium lumbers as indicated by a marked increase in bond shear strength with an increase of pressing pressure. PRF was found to be a more superior adhesive than PUR irrespective of cramping pressure and loading direction. A. mangium wood is relatively dense thus requires quite high pressure, 1.5 N/mm², irrespective of adhesive used. PRF appears to bond A. mangium wood better compared to PUR with shear bond strength of 21% and wood failure percentage of 220% higher.     

Synthesis and properties of novel phenolic resins modified with nanosized copper particles

Phenol–formaldehyde (PF) resins modified with nanosized copper particles were synthesized by an in situ polymerization process. X‐ray diffraction analysis and transmission electron microscopy revealed that the copper particles in the resulting PF resins had a spherical geometry with a size of 30–60 nm in diameter, and there were about 5% of the particles which were agglomerated. The thermal properties of the resulting PF resins were investigated using TGA. It was found that the copper nanoparticles markedly improved the thermal stability of the PF resins at lower temperatures. The initial decomposition temperature of the modified PF resins could be increased by 47 °C compared to unmodified resins. However, the copper nanoparticles increased the rate of degradation of the PF resins at elevated temperatures. The effects of copper nanoparticles on the thermal properties of the PF resins when used as binders for friction materials are beneficial. The toughness of the resulting PF resins was also studied. The results revealed that copper nanoparticles obviously improved the brittleness of the PF resins. The impact strength of the modified PF resins was increased by 66.6% compared to unmodified resins. Copyright © 2006 Society of Chemical Industry     

Investigations of mechanical properties and chemical changes occurring during welding of thermally modified ash wood

Abstract

Heat treatment of wood appears as an ecological and environmentally friendly alternative in the field of wood treatment. Generally, thermal modification increase dimensional stability by reduces of hygroscopicity and water absorption but it makes it difficult to bonding in some application. During welding, changes in the morphological, chemical, and physical properties of the wood cell wall are observed due to the compression and high temperatures produced by welding. Also, the degradation of cell wall in the wood causes some mechanical properties are reduced. This modification appears without any effect on the linear welding of thermal-ash wood. Scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) were used for evaluation of properties of wood–welding systems and their interactions. The mass spectrometry (MS) analysis was used to identifying the organic degradation products emitted during welding of thermo-ash. The results of experiments show that the use of friction welding for the bonding of thermal ash wood in dry conditions was possible, and we had good results. The best combination was with a welding time of 3.5?s devised to 0.5?s and 3?s and welding pressure 2.5 and 4?MPa, respectively. The result obtained is comparable to the result obtained with EPI adhesives. Welding time greater than 3.5?MPa negatively affects the welding quality and gives low the mechanical strength.     

Synthesis and characterization of PLA nanocomposites containing nanosilica modified with different organosilanes II: Effect of the organosilanes on the properties of nanocomposites: Thermal characterization

Thermal behavior of polylactic acid (PLA)/nanosilica nanocomposites prepared via bulk ring opening polymerization from lactide was investigated by differential scanning calorimetry and thermogravimetric analysis (TGA). Both unmodified nanosilica and modified by surface treatments with different amounts of two distinct silanes were used. Samples containing pure silica show enhanced crystallization processes; with silane‐modified silica this effect is magnified, especially in the case of materials with high loadings of epoxy silane. Nonisothermal crystallization temperatures become higher and isothermal crystallization kinetics show a marked increase of Kinetic constant (K_c). TGA analyses show that, when pure nanosilica is present, nanocomposites have a thermal stability far greater than the one of standard PLA, starting their degradation at temperatures up to 70°C higher than the ones of pure PLA. When silanes are present, thermal stability lowers as silane content increases, but it is anyway higher than the one of the pure polymer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal stability and kinetics analysis of epoxy composites modified with reactive polyol diluent and multiwalled carbon nanotubes

The effect of polyether polyol and amino‐functionalized multiwalled carbon nanotubes (NH₂‐MWCNTs) on the thermal stability of three‐phase (epoxy/polyol/NH₂‐MWCNTs) epoxy composites was investigated. Thermal stability and degradation characteristics of polyol/MWCNTs modified epoxy composites was evaluated using thermogravimetric analysis. The kinetics of thermal degradation was assessed from data scanned at 5, 10, and 20°C/min. Activation energy for degradation of epoxy nanocomposites was calculated using different differential and integral methods, that is, Kissinger's, Flynn–Wall–Ozawa, Coats–Redfern, and Horowitz–Metzger methods. In addition, the integral procedure decomposition temperature was determined to evaluate the inherent thermal stability of the modified composite system. Rate of thermal degradation in MWCNT/Polyol samples was found to be reduced significantly while activation energy of degradation was increased compared to unmodified epoxy composite. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41558.     

Synthesis and characterization of linear low‐density polyethylene/sepiolite nanocomposites

Linear low‐density polyethylene (LLDPE)/sepiolite nanocomposites were prepared by melt blending using unmodified and silane‐modified sepiolite. Two methods were used to modify sepiolite: modification before heat mixing (ex situ) and modification during heat mixing (in situ). The X‐ray diffraction results showed that the position of the main peak of sepiolite remained unchanged during modification step. Infrared spectra showed new peaks confirming the development of new bonds in modified sepiolite and nanocomposites. SEM micrographs revealed the presence of sepiolite fibers embedded in polymer matrix. Thermogravimetric analysis showed that nanocomposites exhibited higher onset degradation temperature than LLDPE. In addition, in situ modified sepiolite nanocomposites exhibited higher thermal stability than ex situ modified sepiolite nanocomposites. The ultimate tensile strength and modulus of the nanocomposites were improved; whereas elongation at break was reduced. The higher crystallization temperature of some nanocomposite formulations revealed a heterogeneous nucleation effect of sepiolite. This can be exploited for the shortening of cycle time during processing. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Modification of wood flour/PLA composites by reactive extrusion with maleic anhydride

MA modified wood flour/PLA composites were prepared by one‐step reactive extrusion, in which wood flour and poly(lactic acid) (PLA) were used as raw material, maleic anhydride (MA) was used as modifier, and dicumyl peroxide (DCP) was used as initiator. The influences of MA concentration on the morphology, thermal stability, rheological, and mechanical properties of the composites were studied. The addition of MA improved the compatibility of the composites significantly. The thermal and rheological results showed that with the increase of the concentration of MA, the thermal stability of the composites decreased, the storage modulus and complex viscosity of the composites also decreased. The MA modified composites had an enhanced mechanical strength compared to the unmodified one. As the concentration of the MA increased, the tensile and flexural strength of the composites first increased and then decreased, and reached a maximum when the concentration of MA was 1 wt %. The MA modified composites showed a better water resistance than the unmodified ones. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43295.     

Use of N‐(N′‐arylamino)maleimides to improve the thermal properties of poly(vinyl chloride) through chemical modification and graft copolymerization

The reaction of poly(vinyl chloride) (PVC) with N‐(N′‐arylamino)maleimide derivatives was studied. The thermal stability of the modified polymer was improved markedly when compared with that of the unmodified polymer. The stability improvement was attributed to the replacement of the labile chlorine atoms by more stable organic groups. The modified polymer also showed a lower extent of discoloration when compared with that of unmodified PVC. In order to introduce a polymeric stabilizer into PVC, the dienophilic monomer was chemically grafted onto the polymeric chains. The mechanism of the chemical modification as well as that of the graft copolymerization are discussed. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.     

Properties of glycerin‐thermally modified wood flour/polypropylene composites

This study aimed to investigate the combination effect of glycerin treatment and thermal modification of wood flour on the physical, mechanical, thermal dynamic mechanical properties of wood flour/polypropylene (PP) composite. The morphological aspect was also investigated. The wood flour was first impregnated in the aqueous solution of glycerin, followed by heat treatment at 200°C for 1 h. Then the unmodified or modified wood flour was blended with PP at a weight ratio of 4:6 to prepare composites. Moisture adsorption experiment and X‐ray photoelectron spectroscopy analysis of wood flour demonstrated that the hygroscopicity and the free surface hydroxyl groups of wood flour decreased after glycerin‐thermal modification. Thickness swelling of the 10% wt glycerin‐thermally modified wood flour/PP composite was reduced by 42.8% after 96 h immersion as compared to unmodified control. Evaluation of mechanical properties in impact and flexure modes indicated that glycerin treatment alone had no significant effect, but the combination of glycerin and thermal treatment slightly decreased the strength, with the exception of 10% glycerin and heat modified sample. Dynamic mechanical analysis and scanning electron microscope illustrated the improved interfacial bonding between PP and wood flour modified by 10% glycerin and heat treatment. POLYM. COMPOS., 35:201–207, 2014. © 2013 Society of Plastics Engineers     

Preparation and properties of novel phosphorus‐containing binaphthyl epoxy polymer

Novel phosphorus‐containing binaphthyl epoxy DGEBN (diglycidyl ether of 2,2′‐hydroxy‐1,1′‐binaphthalene) with high thermal performance was obtained from the addition reaction of DGEBN and diethyl phosphite. The modified binaphthyl epoxy was characterized by Fourier transform infrared (FTIR) and nuclear magnetic resonance spectroscopy. The dynamic mechanical property of the cured epoxy polymer was investigated by dynamic mechanical thermal analysis. The result revealed that the cured polymer with lower phosphorus content displayed higher value of the storage modulus when the networks reached rubbery state (above the glass transition temperature T_g). The T_gs decreased slightly with increasing phosphorous content. The thermal degradation was studied with thermogravimetric analysis and the evolved gas was analyzed using thermogravimetric analysis/Fourier transform infrared technique. The influence of phosphorus content and the chemical structure on the degradation behavior was discussed. The P‐modified binaphthyl epoxy polymers exhibited higher thermal stability than the P‐modified diglycidyl ether of bisphenol A polymer. Flammability measurements were performed by the examination of limited oxygen index and UL‐94 test. Compared with unmodified DGEBN, P‐containing epoxy polymers displayed higher limited oxygen index values and exhibited better flame retardance. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Mechanical,thermal, and burning properties of viscose fabric composites: Influence of epoxy resin modification

The influence of epoxy resin modification by 3‐aminopropyltriethoxysilane (APTES) on various properties of warp knitted viscose fabric is reported in this study. Dynamic mechanical, impact resistance, flexural, thermal properties, and burning behavior of the epoxy/viscose fabric composites are studied with respect to varying content of silane coupling agent. The results obtained for APTES‐modified epoxy resin based composites reinforced with unmodified viscose fabric composites are compared to unmodified epoxy resin based composites reinforced with APTES‐modified viscose fabric. The dynamic mechanical behavior of the APTES‐modified resin based composites indicates improved interfacial adhesion. The composites prepared from modified epoxy resin exhibited a twofold increase in impact resistance. The improved adhesion between the fiber and modified resin was also visible from the scanning electron microscope analysis of the impact fracture surface. There was less influence of resin modification on the flexural properties of the composites. The 5% APTES modification induced early degradation of composites compared to all other composites. The burning rate of all the composites under study is rated to be satisfactory for use in automotive interior applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46673.     

Surface treatment of eucalyptus wood for improved HDPE composites properties

In this study, the effect of Eucalyptus globulus wood (UE) used as a filler (5–20% w/w) on the physical and thermal properties of high-density polyethylene (HDPE) composites was evaluated. To improve the compatibility with HDPE, the wood was modified (TE) using crude glycerol derived from biodiesel production. The addition of 20% (w/w) of UE or TE led to more rigid and durable composite materials compared to neat HDPE (about 50 or 100% increase in tensile strength, respectively). Composites also revealed 55–75°C higher temperatures at maximal degradation rates. The advantageous behavior of TE over UE in composites was attributed to the improvement of surface morphology of modified wood and it is better compatibility with the HDPE as revealed by surface energy analysis. The changes in wetting behavior of HDPE and ensuing HDPE-TE composites (contact angles of ca 72 and 80°, respectively) explain the matrix-filler interactions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48619.     

Thermodegradation of Poly(4-Vinylpyridine-co-Maleic Acid-co-Divinylbenzene) and N-oxide Derivatives: Modeling of TG and DTG Curves

Copolymer networks based on 4-vinylpyridine (4VPy)/maleic acid (MA)/divinylbenzene (DVB) and their N-oxide derivatives have been investigated by thermogravimetric analysis (TG) to evaluate their thermal stability in nitrogen atmosphere at fixed heating rate. Thermal stability was determined from TG curves to investigate the influence of 4VPy content and introduction of N-oxide groups. The TG and DTG curves of unmodified copolymers clearly show one thermodegradation stage and the same kinetic pathway. The decomposition temperatures do not depend on the 4VPy content. The copolymers modified by oxidation present lower thermostability than unmodified showing that the introduction of N-oxide groups modifies their kinetic pathways. A kinetic model Ozawa was used to determine the kinetic parameters. The apparent thermal decomposition activation energies (Δ E _d) of the unmodified copolymer under nitrogen was higher than that in modified copolymer.     

Properties and preparation of olefin block copolymer/thermoplastic polyurethane blends

The properties of olefin block copolymer (OBC)/thermoplastic polyurethane (TPU) blends with or without maleic anhydride (MA) modification were characterized and compared. Compared with the OBC/TPU blends, OBC‐g‐MA/TPU blends displayed finer morphology and reduced domain size in the dispersed phase. The crystallization temperatures of TPU decreased significantly from 155.9 °C (OBC/TPU) to 117.5 °C (OBC‐g‐MA/TPU) at low TPU composition in the blends, indicating the inhibition of crystallization through the sufficient interaction of modified OBC with TPU composition. The modified systems showed higher thermal stability than the unmodified systems over the investigated temperature range due to the enhanced interaction through inter‐bonding. The highest improvement in tensile strength was more than fivefold for OBC‐g‐MA/TPU (50/50) in comparison with its unmodified blend via the enhanced interfacial interaction between OBC‐g‐MA and TPU. This also led to the highest Young's modulus of 77.8 ± 3.9 MPa, about twofold increase, among the investigated blend systems. A corresponding improvement on the ductility was also observed for modified blends. The modification did not vary the glass transition temperature and crystalline structure much, thus the improvement in the mechanical properties was mainly attributed to the improved compatibility and interaction from the compatibilization effect as well as increased viscosity from the crosslinking effect for modified blends. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43703.     

Thermal Degradation of Condensed Tannins from Radiata Pine Bark

Abstract

In order to understand the influence of the inherent chemistry on the relative thermal stability of condensed tannins, the thermal degradation behaviors of various radiata pine bark extracts have been investigated using thermogravimetric analysis (TGA). Generally, results suggest pine bark extract fractions may be readily processed at temperatures below 200°C if co-extracted polysaccharides contents are minimized. Those extracts possessing greater carbohydrate content and lower tannin purity tend to have decreased thermal stability. The initial onset temperature for degradation of relatively crude extracts with high proportions of carbohydrate contents were relatively low (ca. 150°C), whereas extract purification to < 5% carbohydrate content gave increases in thermal stability of at least 50°C. The complicity of the carbohydrate content in the degradation of the tannin samples was also supported by calculated Ozawa activation energies and modulated TGA experiments. While no increase in the thermal stability was gained by acetylating the pendant hydroxyl groups of the pine bark tannin extract, chemical variations such as sulfonation have a large effect on thermal degradation, promoting lower degradation temperatures.     

In situ grown titania composition for optimal performance and durability of Nafion® fuel cell membranes

Nafion® membranes were modified via in situ, catalyzed sol–gel reactions of titanium isopropoxide to form titania particles in the polar acid domains. FTIR spectroscopy showed successful intraparticle chemical bond formation with incomplete condensation of TiOH groups. Although such modification can lower membrane fuel cell performance, this study was aimed at reducing membrane degradation without significantly altering performance in the sense of material optimization. These incorporated particles did not change membrane equivalent weight and the water uptake was similar to that of the unmodified Nafion® membrane. Membrane dimensional stability, mechanical properties, and ability to withstand contractile stresses associated with humidity change at 80°C and 100% RH were improved. An open circuit voltage (OCV) accelerated degradation test showed the titania modification held voltage better than the unmodified membrane. Performance deterioration of Nafion® after the OCV test was much higher than that of the modified membrane and the fluoride emission of the latter was lower. The degraded Nafion® membrane failed when subjected to creep, whereas the modified membrane remained intact with significantly low deformation. This inorganic modification offers a simple way to enhance membrane durability by reducing both physical and chemical degradation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011