Junwen Pu

Impregnation of poplar wood (Populus euramericana) with methylolurea and sodium silicate sol and induction of in-situ gel polymerization by heating

Abstract Poplar wood (Populus euramericana cv. “I-214”) has been impregnated by pulse dipping at 0.7–0.8 MPa for 30 min with a mixture of methylolurea and sodium silicate, and the sol modifier has been cured within the wood micropores by in situ gel polymerization by kiln drying, so that a Si-O-Si framework was formed. The treated wood acquired higher mechanical strength and its hygroscopicity was lowered. It was demonstrated by X-ray diffraction that sodium silicate crystallized within the interfibrillar region of the cell wall. Fourier transform infrared spectra showed that reactions occurred between the wood-OH, Si-OH, and N-CH2-OH from methylolurea to form C-O-Si and C-O-C bonds. As visible by scanning electron microscopy (SEM), the Si-O-Si framework was embedded in the pretreated wood. Moreover, SEM-energy-dispersive X-ray spectroscopy analysis revealed that the modifier formed layers from various thicknesses ranging from a thin layer on the cell walls up to big amounts filling the lumen.

Particulate reinforcement and formaldehyde adsorption of modified nanocrystalline cellulose in urea-formaldehyde resin adhesive

In this study, nanocrystalline cellulose (NCC) was used for reinforcement and formaldehyde (HCHO) adsorption of urea-formaldehyde (UF) resin adhesive in fiberboard. The original NCC was modified by 3-aminopropyltriethoxysilane for improving the wetting property with UF resin adhesive. The UF resin adhesive with modified NCC was analyzed by X-ray powder diffraction, thermogravimetric analysis, and Fourier transform infrared. The HCHO emission and bending and bonding strength of the UF resin adhesive with modified NCC were tested according to Chinese National Standard GB/T 17657-1999. Compared with the original UF resin adhesive, modified NCC led to limited effects on the crystal structure, thermal stability, and characteristic absorption peaks of UF resin adhesive. The HCHO emission of the UF resin adhesive with 1.0% modified NCC decreased by 13.0%, while the bending and bonding strength increased by 40.5 and 158.3%, respectively. The improvements of modified UF resin adhesive were destroyed by the reunion of NCC when the content was more than 1.5%.

Optical and Mechanical Properties of Polyurethane/Surface-modified Nanocrystalline Cellulose Composites

In order to improve the optical and mechanical performances of waterborne polyurethane (WPU), nanocrystalline cellulose (NCC)/WPU composites were synthesized in this study. NCC (prepared by acid hydrolysis of cotton fiber) was modified by (3-aminopropyl)triethoxysilane (APTES) to enhance its compatibility with WPU, and the surface-modified NCC was characterized by grafting ratio, crystallinity and contact angle (CA). NCC/WPU composites were examined by scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and thermogravimetric analysis (TG). The anti-yellowing property, specular gloss, pencil hardness, and abrasion resistance of NCC/WPU composites were investigated by the methods of Chinese National Standards GB/T 23999-2009, GB/T 9754-2007, GB/T 6739-2006 and GB/T 1768-2006, respectively. The results showed that the grafting ratio of NCC modified by 6% APTES was 36.01% and the crystallinity of modified NCC was decreased with the enhancement of APTES. CA of the modified NCC was decreased by 28.8% and the nanoparticles were homogeneously dispersed in the WPU matrix. The XRD patterns of the NCC/WPU composites were relatively steady, while the thermal stability of the composites was enhanced by 6.7% with 1.0 wt% modified NCC. Modified NCC affected the specular gloss of NCC/WPU composites more obviously than the anti-yellowing property. The pencil hardness of NCC/WPU composites was increased from 2H to 4H by addition of NCC and the abrasion resistance of the composites was enhanced significantly. In general, NCC/WPU composites showed significant improvements in the optical and mechanical performances.

Negative oxygen ion (NOI) production by enhanced photocatalytic TiO2/GO composites anchored on wooden substrates

Abstract Titanium dioxide (TiO2)/graphene oxide (GO)-treated wood was fabricated through a one-step hydrothermal-vacuum dipping technique, in which silica sol serves as a dispersant and linker owing to its good stability and high surface area, while the visible light activates TiO2/GO and negative oxygen ions (NOI) arise. This approach exhibits a super dye adsorption capacity and enhanced photocatalytic efficiency. In focus was the effect of the three-dimensional (3D) GO dopant on the NOI production, which was very high in this system. Namely, the concentration of NOI is up to 1710 ions cm−3 after 60 min visible light irradiation. Moreover, recycling experiments show that the properties of a TiO2/GO-wood system are stable. The TiO2/GO-treated wood is a healthy, environmentally friendly material which is promising for indoor decoration.

Improved wood properties via two-step grafting with itaconic acid (IA) and nano-SiO2

Abstract Itaconic acid (IA) with its trifunctional structure was first introduced into the wood cell lumen and cell wall, which functions as a grafting anchor for fixing various polymers via strong chemical bonds. Then nano-SiO2 was grafted to the IA-modified wood. Field-emission scanning electron microscope revealed that the grafting experiment was successful and that the modified cell wall thickness increased by 65%. The incorporated hydrophobic nano-SiO2 substructure reduced the wood’s hygroscopicity and improved its dimensional stability. The thermal stability of the new composite was also excellent. The presented approach is simple and efficient and the probability is high that it can be up-scaled to a level of a large-scale engineering material.

Fire retardancy of graphene oxide/wood composite (GOW) prepared by a vacuum-pulse dipping technique

Abstract Graphene oxide/wood (GOW) composite was fabricated by a vacuum-pulse dipping technique, and the resulting composites were characterized by scanning electron microscope (SEM), Raman spectroscopy and thermogravimetric analysis (TGA). As demonstrated, the wood matrix became filled by the dense multilayer graphene oxide (GO) membrane structure, which was formed by the layer-by-layer self-assembly of GO nano-sheets. X-ray diffraction (XRD) revealed that the amorphous GO decreased the composite’s relative degree of crystallinity. Additionally, the filled GO generated improvement in the thermal stability of GOW composites in comparison with that of the natural wood (NW).

Characterization of hot-pressed poplar wood with chemical pretreatment

The aim of this research is to study the characterization of modified poplar wood. A chemical impregnation was utilized before the poplar wood was dried and compressed in a multilayer hot-press drying kiln. The results showed that with the compression rate of 31.7%, the basic density, the over dried density and air-dried density of treated wood increased 25%, 75% and 74%, respectively. The bending strength and compressive strength parallel to grain improved 72% and 47%. The water uptake rate of treated wood was lower compared with the untreated wood. The results of XRD curves indicated that the degree of crystallinity for treated wood increased from 37.88% to 39.01%. The FT-IR analysis showed that the intensity of hydroxyl (-OH) absorption decreased, which due to the reaction between the wood hydroxyl and the impegnated chemicals. The morphologic models of the poplar wood were examined by SEM.

Study on Urea-Formaldehyde Prepolymer and Hot-Press Treatment of Italian Poplar Wood

Abstract The purpose of this study was to modify Italian poplar (Populus euramevicana cv. ‘I-214’) wood with urea-formaldehyde prepolymer followed by hot pressing. The timbers were impregnated with urea-formaldehyde prepolymer using a pulsed-dipping machine and cured in a hot press. The results showed that the timbers could be easily compressed and cured at temperatures between 90°C and 120°C. The characteristics and quality of the modified wood were up to A grade according to Chinese Standard GB/T 6491‐1999. The air-dried density of modified wood was improved by 58 percent, and the hardness in the transverse, tangential, and radial directions was increased by 67, 210, and 160 percent, respectively. The bending strength was improved by 78 percent; the bend elastic modulus was improved by 66 percent. The water absorption of treated wood decreased relative to that of the untreated timbers. Fourier transform infrared spectroscopy of the modified wood showed a significant reduction in the C=O absorbance at 1,...