Surface Characterization of Chemically Modified Wood: Dynamic Wettability1

Dynamic wettability of chemically modified yellow-poplar veneer was investigated with sessile water droplets in this study. Dynamic contact angle, decay ratio, spreading ratio, and their changing rates (the wetting slope and K value) were used to illustrate the dynamic wetting process. Dynamic contact angle (α) and droplet height decay ratio (DRh) followed the first order exponential decay equation, whereas the droplet base-diameter spreading ratio (SRφ) fitted the Boltzmann sigmoid model. Wetting behavior of Epolene G-3015 [a maleated polypropylene (MAPP) copolymer with a high molecular weight]-treated wood surface was independent of the retention and wetting time. The retention effect on wetting slopes of >, DRh, and SRφ on poly(ethylene and maleic anhydride) (PEMA)-treated specimens was opposite to that on Epolene E-43 (a MAPP copolymer with a low molecular weight)-treated specimens. Based on these two models, the wetting slope and K value were used to interpret the kinetics of wetting. Therefore, these methods were helpful to characterize the dynamic wettability of wood surfaces modified with different coupling agents

Surface and Interfacial Characterization of Wood-PVC Composite: Imaging Morphology and Wetting Behavior1

An imaging technique was used to investigate wetting behavior of wood-PVC composites in this study. Two-dimensional and time-dependent profiles of water droplets on maleated wood surface and wood-PVC interface were observed. Experimental results indicated that coupling agents Epolene E-43 (a maleated polypropylene copolymer with low molecular weight)- and polyethylene-maleic anhydride (PEMA)- treated veneers had a hydrophilic surface, whereas the coupling agent Epolene G-3015 (a maleated polypropylene copolymer with high molecular weight)-treated veneer had a hydrophobic surface. For E-43- and PEMA-treated veneers, a water droplet had an elliptical shape after initial contact with the wood surface. However, a sessile droplet on G-3015-treated specimens was closer to a circular shape. During wetting, contact angle changes on E-43- and PEMA-treated specimens were larger than those on G-3015- treated specimens. Contact angles on maleated specimens with heat treatment and maleated interphases were almost independent of wetting time. Initial contact angle was influenced by coupling agent type, acid number, and retention and directions of wood grains. Initial contact angle decreased with increase of E-43 retention, but it was proportional to PEMA retention. However, it was independent of G-3015 retention. Wettability of fractured wood-PVC interface was similar to that of maleated wood surface with heat treatment. Thus, the interfacial characteristics of wood-PVC interface can be simulated with maleated wood surface with heat treatment

Selected Properties of Wood Strand and Oriented Strandboard From Small-Diameter Southern Pine Trees

Thermal and mechanical properties of southern pine and willow strands and properties of southern pine oriented strandboard (OSB) from small-diameter logs were investigated in this study. The effects of density and species group on tensile strength, dynamic moduli, and thermal stability of wood strands, and of strand quality (i.e., wood fines) on three-layer OSB properties were analyzed.Strand tensile strength and dynamic storage moduli (E') increased with the increase of strand density. A large variation in both tensile strength and E' values was observed for southern pine, while willow strands showed much smaller variability. The dynamic moduli (E") of strands decreased with increase of temperature in the range of 25° to 200°C. Small loss modulus (E") peaks were observed over the temperature range studied. The strands with higher densities had higher E". Thermogravimetric analysis results revealed that high-density strands were thermally more stable than low-density strands.Three-layer OSB made of small-diameter southern pine trees showed satisfactory strength and dimensional stability properties. As the fines loading levels increased, linear expansion (LE) along the parallel direction decreased, while the LE value along the perpendicular direction and thickness swelling increased. With increased fines levels, the internal bond strength showed an increasing trend up to the 20% fines level, and bending strength and modulus varied little in the parallel direction and slightly decreased in the perpendicular direction

Molecular characterization and expression of DgZFP1, a gene encoding a single zinc finger protein in chrysanthemum

A single zinc finger protein gene was isolated from chrysanthemum by rapid amplification of cDNA ends (RACE) approach and was designated as DgZFP1. The DgZFP1 encodes a protein of 168 amino acids residues with a calculated molecular mass of 18.1 kDa and theoretical isoelectric point is 4.71. DgZFP1 contains one single zinc finger motif and one ethylene-responsive element-binding factor (ERF)-associated amphiphilic repression (EAR) domain. The transcripts of DgZFP1 was enriched in nodes and ray petal than in disc petal, disc stamen, disc pistil and ray pistil, but not detected in other tissues. Subcellular localization revealed that DgZFP1 was preferentially distributed to nucleus. We argued that DgZFP1 is a new member of the single zinc finger protein genes and it may be the ortholog of LIF

Wood-fiber/high-density-polyethylene composites: Coupling agent performance

The coupling efficiency of seven coupling agents in wood-polymer composites (WPC) was investigated in this study. The improvement on the interfacial bonding strength, flexural modulus, and other mechanical properties of the resultant wood fiber/high-density polyethylene (HDPE) composites was mainly related to the coupling agent type, function groups, molecular weight, concentration, and chain structure. As a coupling agent, maleated polyethylene (MAPE) had a better performance in WPC than oxidized polyethylene (OPE) and pure polyethylene (PPE) because of its stronger interfacial bonding. A combination of the acid number, molecular weight, and concentration of coupling agents had a significant effect on the interfacial bonding in WPC. The coupling agents with a high molecular weight, moderate acid number, and low concentration level were preferred to improve interfacial adhesion in WPC. The backbone structure of coupling agents also affected the interfacial bonding strength. Compared with the untreated composites, modified composites improved the interfacial bonding strength by 140% on maximum and the flexural storage modulus by 29%. According to the statistical analysis, 226D and 100D were the best of the seven coupling agents. The coupling agent performance was illustrated with the brush, switch, and amorphous structures. © 2005 Wiley Periodicals, Inc

The Influence of Maleation on Polymer Adsorption and Fixation, Wood Surface Wettability, and Interfacial Bonding Strength in Wood-PVC Composites1

The influence of maleation on polymer adsorption and fixation, surface wettability of maleated wood specimens, and interfacial bonding strength of wood-PVC composites was investigated in this study. Two maleated polypropylenes (MAPPs), Epolene E-43 and Epolene G-3015, were used to treat yellow-poplar veneer samples. Retention of coupling agent, graft rate, graft efficiency, static contact angle on treated samples, and shear strength of resultant wood-PVC laminates manufactured under hot-pressing were measured. It was shown that the relationship among graft rate, coupling agent retention, and treating solution concentration for MAPP-treated wood specimens followed a three-dimensional paraboloid model. Graft efficiency decreased with the increase of concentration and retention. The relationship between retention and concentration was linear for G-3015 and polynomial for E-43. Maleation treatment greatly improved the compatibility and interfacial adhesion. The veneer samples treated with these two MAPPs presented different wetting behaviors. For G-3015-treated samples, measured contact angles varied from 115° to 130° independent of retention, graft rate, and wetting time. For E-43-treated samples, retention, graft rate, and wetting time had a significant influence on the contact angle. Compared with controls made of untreated wood and PVC, shear strength of the maleated wood-PVC laminates increased over 20% on average. There was no direct correlation between measured contact angle and shear strength. Extractives had negative effects on retention. However, they did not significantly influence contact angles and interfacial bonding strength. Monolayer models were proposed to illustrate the bonding structure at the interface

Chemical Coupling in Wood Fiber and Polymer Composites: A Review of Coupling Agents and Treatments

Coupling agents in wood fiber and polymer composites (WFPC) play a very important role in improving the compatibility and adhesion between polar wood fibers and non-polar polymeric matrices. In this paper, we review coupling agents, pretrcatment, and mixing technology for wood fiber and polymer currently used in the manufacture of WFPC. So far, over forty coupling agents have been used in production and research. These agents are classified as organic, inorganic, and organic-inorganic groups, among which organic agents are better than inorganic agents because of stronger interfacial adhesion. The most popular coupling agents currently being used include isocyanates, anhydrides, silanes, and anhydride-modified copolymers. Coupling agents are usually coated on the surface of wood fiber, polymer or both by compounding, blending, soaking, spraying, or other methods. Three basic processes suitable for coupling treatment are discussed: directly coating during mixing and fully or partly pretreating before mixing. The pretreatment of wood fiber and polymer by coating or grafting is the preferred method to improve the mechanical properties of WFPC.

Fitting Weibull and Lognormal Distributions to Medium-Density Fiberboard Fiber and Wood Particle Length

Fiber lengths were analyzed for random samples of medium-density fiberboard (MDF) fibers and wood particles taken from eleven different populations. For six of the samples, the lognormal distribution fit the data, while the Weibull distribution did not. For three of the samples, the Weibull fit the data, while the lognormal did not. For two of the samples, both the lognormal and Weibull fit the data. Conclusions were based on hypothesis tests imposing a bound of 0.05 on the probability of making a Type I error for each test. Tests were based on large sample 95% nonparametric simultaneous confidence bands for the underlying cumulative distribution functions of the data

Isolation and molecular characterization of RcSERK1: A Rosa canina gene transcriptionally induced during initiation of protocorm-like bodies

A somatic embryogensis receptor-like kinase (SERK) gene was isolated from protocorm-like bodies (PLBs) of Rosa canina by a rapid amplification of cDNA ends (RACE) approach and was designated as RcSERK1. The RcSERK1 encodes a protein of 626 amino acid residues with a calculated molecular mass of 68.79 kDa and theoretical isoelectric point of 5.65. The amino acid sequence of RcSERK1 shares all the characteristic features of a SERK protein, including the signal peptide (SP), the leucine zipper (LZ), the five leucine-rich repeats (LRRs), the pro-rich domain containing the so-called Ser-Pro- Pro (SPP) motif, the transmembrane domain (TM), the kinase domain and the C-terminal domain. The transcripts of RcSERK1 were more enriched in PLBs than in rhizoids and callus, but not detected in leaflets (incubated under dark and before producing callus) and the regenerated shoots. Subcellular localization indicated that the fluorescence of RcSERK1-GFP was recorded in the plasma membrane. We argue that RcSERK1 is a Leu-rich repeat receptor-like kinase (LRR-RLK) and plasma  membrane localization protein.Keywords: somatic embryogensis receptor-like kinase (SERK)1, protocorm-like bodies (PLBs), Rosa canina, RACE, RcSERK1