Jinzhen Cao

Improvement of dimensional stability of wood by in situ synthesis of organo-montmorillonite: preparation and properties of modified Southern pine wood

Abstract Southern pine (Pinus spp.) wood was impregnated sequentially with sodium montmorillonite (Na-MMT; in concentrations of 1%, 2%, and 4%) and didecyldimethylammonium chloride (in a concentration of 2%) in a two-step method to form organo-montmorillonite (OMMT) inside the wood. The impregnated samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy analyses. Moreover, the water absorption, anti-swelling efficiency, compression strength, and surface hardness of the modified samples were investigated. In the first step, wood is impregnated with Na-MMT, and in the second step, Na-MMT is transformed to OMMT by in situ synthesis and the silicate layers of the clay are intercalated into the cell wall. As a result, the dimensional stability of the modified wood was improved as a function of increased clay concentration. The compression strength and surface hardness of OMMT-modified wood were also improved greatly compared with the untreated control.

Effects of Modifier Type on Properties of in Situ Organo-Montmorillonite Modified Wood Flour/Poly(lactic acid) Composites

Wood flour (WF) was modified with sodium-montmorillonite (Na-MMT) and two types of surfactant modifiers, namely, didecyl dimethylammonium chloride (DDAC) and sodium dodecyl sulfonate (SDS) though a two-step process inside WF. The thus-modified WFs were characterized, and the effects of MMT type on physical, mechanical, and thermal properties of their composites with poly(lactic acid) (PLA) were investigated. The results showed: (1) either DDAC or SDS could modified Na-MMT into OMMT, and then uniformly distributed in WF cell walls; (2) OMMT improved the physical properties, most mechanical properties, and thermal properties of the composites except for the impact strength; and (3) compared with SDS, DDAC seemed to perform better in properties of composites. However, DDAC showed some negative effect on the early stage of composite thermal decomposition.

Thermal modification of Southern pine combined with wax emulsion preimpregnation: effect on hydrophobicity and dimensional stability

Abstract The aim of this study was to enhance the water repellency and dimensional stability of thermally modified wood by combining the preimpregnation of paraffin wax emulsion. To achieve this, Southern pine (SP; Pinus spp.) samples were first impregnated with paraffin wax emulsion (with 2.0% solid content) and then subjected to thermal modification (TM) in an oven at 180°C and 220°C for 4 and 8 h. The contact angle (CA), surface free energy, water absorption rate (WAR), anti-swelling efficiency (ASE), and bending properties of the control and modified samples were investigated. Moreover, the chemical and morphological alterations were analyzed by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Both the wax impregnation and TM decreased the surface wettability, water absorption, and tangential swelling, while the combination of wax and thermal treatment exhibited the best water repellency and dimensional stability, indicating the synergism between the two procedures. However, the wax preimpregnation did not affect the mechanical properties of thermally modified wood. The FTIR, SEM, and XPS analyses confirmed that the synergistic effect is mainly due to the redistribution of the paraffin wax during TM rather than its impact on the chemical changes caused by thermal degradation.

Effects of a layered double hydroxide (LDH) on the photostability of wood flour/polypropylene composites during UV weathering

In this study, a kind of layered double hydroxide, MgAl–CO3-LDH, was synthesised and its effects on the photostability of wood flour/polypropylene (WF/PP) composites during weathering were investigated. WF/PP composites with different LDH loading levels were prepared and tested in a QUV accelerated weathering tester for a total 960 h. The surface color, surface gloss, and flexural properties of the composites were tested, accompanied by characterizations using SEM, ATR-FTIR, and TG. The results indicated that (1) the flexural properties of the LDH-loaded composites were improved; (2) the composites containing LDH showed less discoloration, fewer surface cracks, and less loss of flexural strength and modulus than the control group; (3) LDH played a positive effect on alleviating the photo-oxidation process of WF/PP composites, confirming its UV-shielding effect; (4) LDH enhanced the thermal stability of the composites before and after weathering.

Characterization and properties of organo-montmorillonite modified lignocellulosic fibers and their interaction mechanisms

In this study, lignocellulosic natural fibers (NFs), namely, cellulose fiber/flour (CF) and lignin flour (LF) separated from poplar wood flour (WF) as well as xylan as a representative of hemicellulose flour (HF), were modified with organo-montmorillonite (OMMT) through a two-step method. Some physical and mechanical properties of the thus-modified materials were investigated. Besides this, the interaction mechanisms between OMMT and these NFs were studied. The results showed that OMMT partly intercalated with HF and completely exfoliated in LF. However, it hardly penetrated into CF. Owing to that, OMMT reduced the moisture content of HF and LF and improved their mechanical properties. But for CF, OMMT showed negative/little effect on its physical/mechanical properties. No reaction was found between OMMT and CF. It mainly reacted with the amorphous constituents of the NFs by basically forming links with the carboxyl/phenolic hydroxyl end groups of the HF/LF molecular chains.

Effects of vitamin E combined with antioxidants on wood flour/polypropylene composites during accelerated weathering

Abstract The aim of this research was to investigate the influence of different antioxidant systems containing vitamin E (VE) and antioxidant 168 (AO) on the photodegradation of wood flour/polypropylene (WF/PP) composites, as well as to provide insight into the processes taking place in these systems during weathering. Five groups of composites were treated in a QUV accelerated weathering tester for a total of 960 h. The surface color and the flexural properties of the weathered samples were tested. Additionally, the weathered surface was characterized by SEM, ATR-FTIR, and XPS. The results were: (1) composites with VE and AO showed less loss of flexural strength and modulus, as well as less color fading and fewer cracks on weathered surfaces than surfaces without antioxidants; (2) AO reacted with hydroperoxide and quinones and showed a synergistic effect with VE to further improve the anti-weathering ability of the composites; (3) 0.2% VE and 1.0% AO was the optimal formulation, yielding the best anti-weathering properties among all.

Improved properties of thermally modified wood (TMW) by combined treatment with disodium octoborate tetrahydrate (DOT) and wax emulsion (WE)

Abstract The aim of this study was to investigate the effect of preimpregnation of thermally modified wood (TMW) with paraffin wax emulsion (WE), which was loaded with disodium octoborate tetrahydrate (DOT). The improvements of physical, mechanical, and biological properties of WEDOT-TMW was in focus. The thermal modification (TM) was conducted at 220°C for 4 h. The equilibrium moisture content (EMC), water absorption, volumetric swelling, bending strength, mold and termite resistance of WEDOT-TMW were determined. The boron leaching data were also determined, while the borate was analyzed by Inductively coupled plasma atomic emission spectroscopy (ICP-AES), followed by the model fitting according to a pseudo-second order differential model. The results indicate that WEDOT improved water repellency, dimensional stability, bending strength as well as the mold and termite resistance of WEDOT-TMW. The boron leaching of WEDOT-TMW was reduced compared with DOT-TMW due to the hydrophobic effect of WE. The pseudo-second order differential model describes accurately the boron leaching process from WEDOT-TMW.

Penetration and distribution of paraffin wax in wood of loblolly pine and Scots pine studied by time domain NMR spectroscopy

Abstract Impregnation of wood with paraffin wax emulsion (PWE) is a common eco-friendly approach for improving water repellency. In this study, loblolly pine (Pinus taeda) and Scots pine (Pinus sylvesteris) samples were impregnated with PWEs with different solid contents and particle sizes, and the influence of the impregnation parameters on wax penetration and distribution in treated wood was elucidated by time domain nuclear magnetic resonance (TD-NMR). A good linear correlation (R2=0.981) between wax content determined by TD-NMR and weight percent gain (WPG) of the impregnated wood was established. According to wax loading and distribution data, loblolly pine has a much better permeability than Scots pine. With decreasing solid content and particle size, the penetration of PWE increases in both species. The water contact angles (CA) on the surface at different depths of wood were also determined, and the CA results were consistent with the wax distribution found by the TD-NMR analysis.

Mechanical properties of wood flour/poly (lactic acid) composites coupled with waterborne silane-polyacrylate copolymer emulsion

Abstract Wood flour/polylactic acid (WF/PLA) composites were produced with a WF content of 50% based on three types of waterborne polyacrylate (PA) emulsions including a PA homopolymer emulsion and two types of silane-PA copolymer emulsions as coupling agents. Two silanes were in focus, namely, γ-methacryloxypropyl- trimethoxysilane (silane-1) and vinyltrimethoxysilane (silane-2). The emulsions and the modified WFs were characterized, and the effects were investigated in terms of emulsion type and their loading levels on the mechanical properties of WF/PLA composites. (1) Both types of silanes could be successfully copolymerized with PA to form stable emulsions. (2) With increasing PA loading, the mechanical properties (except for flexural modulus) of the composites increased at first before reaching the maximum values at 4% PA loading and then the properties worsened. However, these values were larger than those of pure composites, especially in cases when PA-silane emulsions were applied. (3) PA modified with silane-1 showed the best coupling effect among all the three PA emulsions. The results can be interpreted that PA emulsions are effective coupling agents for the preparation of high-performance WPCs.

Properties of wood treated with compound systems of paraffin wax emulsion and copper azole

Wood is a natural and renewable material used extensively. However, it is generally susceptible to biological attacks caused by fungi and termites. Studies showed that copper azole (CA) could effectively inhibit the growth of such organisms. CA belongs to water-borne preservatives and CA-treated wood inevitably suffers from poor dimensional stability. In order to improve the water repellency of CA-treated wood, a paraffin wax emulsion was added to the CA preservative system at different ratios. The compound systems were then used to treat Southern pine (Pinus spp.) samples. The basic properties of the compound systems, such as stability (storage stability and centrifugal stability), particle size and pH value, as well as the weight percent gains, contact angles, water repellency (water absorption, shrinkage and swelling) of treated samples were investigated. The results are as follows: (1) the compound systems of CA and paraffin wax emulsion had a favorable miscibility, and their stabilities all reached level one (good stability); (2) compared with untreated wood, CA-treated samples showed poor water repellency, whereas samples treated with the compound systems indicated an obvious reduction in water absorption, and improved dimensional stability as well.