Creep performance of glued-in rod joints in controlled and variable climate conditions

Presented in this study are the results of creep tests on joints with single glued-in rods performed in controlled and variable climate conditions. The joints were prepared using steel threaded rods of 8 mm in diameter, wood of two species: Black spruce (Picea mariana Mill) and Norway spruce (Picea Abies L.), and two adhesives: polyurethane (PUR) and epoxy (EXP). The first test campaign was performed under two constant climate conditions: 20 °C / 65% relative humidity (RH) and at 50 °C / 72% RH. The applied load corresponded to a stress level of 50% of the static breaking load. The moisture content of wood remained constant during the experiments. Results revealed that the joints were subject to creep with major differences between the adhesives. Low data variability was observed for specimens with the EPX and strong correlations were found between the initial stiffness and the stiffness at 10 days and 25 days. The EPX joints developed lower creep than the PUR joints at 20 °C. At the temperature of 50 °C, the creep of the EPX joints increased but there were no failures observed within 60 days, whereas all PUR joints reached failure at the same stress level within days. The second test campaign was launched using the EPX to study the creep of the joints in variable climate conditions at the stress ratios between 60% and 78% of the static strength. The variation in ambient conditions appeared to affect the creep: humidification phase preceded by drying generated significantly higher creep. The humid and dry cycles may govern the load duration and cause the rupture. In addition, this study revealed that the wood drying from 18% to 10% created some damaging cracks at the wood-adhesive interface. The propagation of stable cracks induced an increase of the slippage in the joints and reduction of the residual strength.     

The morphology,rheological, and mechanical properties of wood flour/starch/poly(lactic acid) blends

An entirely biosourced blend composed of poly(lactic acid) (PLA), starch, and wood flour (WF) was prepared by a co‐extruder with glycerol as a plasticizer. The morphology, rheological properties, and mechanical properties of the WF/starch/PLA blends were comprehensively analyzed. The results showed that with the decrease of the starch/WF ratio, the morphology experienced a large transformation, and the compatibility of the blends was found to be superior to other blends, with a starch/wood flour ratio of 7/3. The dynamic mechanical thermal analysis (DMA) results demonstrated the incompatibility of the components in WF/starch/PLA blends. Following the decrease of the starch/WF ratio, the storage modulus (G″) and the complex viscosity (η*) of the blends increased. The mechanical strength first increased, and then decreased with the increase of the WF concentration. The water absorption results showed that the water resistance of the blends was reduced with the lower starch/WF ratio. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44743.     

Mechanical properties of individual fiber segments of electrospun lignocellulose‐reinforced poly(vinyl alcohol)

The influence of lignocellulosic nanofibers (LCNF) additive on the inherent mechanical properties of submicron electrospun poly(vinyl alcohol) (PVA) fibers is reported. LCNF with a diameter of 25 ± 15 nm and a length of 220 ± 90 nm obtained from hemp shives were dispersed in aqueous PVA solutions to produce homogeneous nanocomposite fibers with 0, 5, and 10 w/w % LCNF loads in solid PVA. Tensile tests on mats show that LCNF additive causes up to sevenfold increase in stiffness and significant decrease in elongation at yield. AFM‐based 3‐point bending tests on single LCNF‐doped fibers reveal up to 11.4 GPa Young's modulus in the diameter range of 300 to 500 nm, indicating a 2.4 times increase compared to neat PVA fibers. Mechanical properties of both neat and LCNF‐doped PVA fibers are found to be strongly size‐dependent at lower fiber diameters, with Young's modulus values exceeding 100 GPa at below 100 nm diameters. The results can be explained by extensive restructuration of hydrogen bonding network due to the LCNF additive. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44361.     

Surface modification of microcrystalline cellulose (MCC) and its application in LDPE‐based composites

Microcrystalline cellulose (MCC) was modified by grafting onto its surface ferulic acid, methacryloyl chloride and oleoyl chloride. The efficacy of the chemical modification was confirmed by X‐ray photoelectron spectroscopy. In addition, the size distribution of the cellulosic particles was investigated by optical microscopy and laser granulometry and its hydrophobicity was evaluated using a contact angle method. Finally, to investigate the affinity of modified MCC with a nonpolar polymer and to assess its potential as a biobased reinforcing filler, the modified MCC was compounded into low‐density polyethylene. An organic peroxide, dicumyl peroxide, was added at selected formulations to see if it could further enhance mechanical bonding between the polymer and the particulates. The dispersion was assessed by scanning electron microscopy. Mechanical properties were investigated through tensile testing while the melt rheology of the composites was monitored by small angle oscillatory shear rheology. The acylation modification of the MCC improved the dispersion within LDPE and enhanced the mechanical properties of the composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44348.     

木塑复合材料制备及其在建筑中应用进展

综述了木塑复合材料的生产工艺,分析了影响木塑复合材料力学性能和耐久性的因素,阐述了木塑复合材料在建筑工程中的应用,展望了未来木塑复合材料的研究方向。指出今后木塑复合材料的研究应主要集中在耐久性机理的进一步探索以及提高木塑复合材料耐久性的改性和结构设计方法。     

Design and UV-curable behaviour of boron based reactive diluent for epoxy acrylate oligomer used for flame retardant wood coating

Difunctional boron-containing reactive flame retardant for UV-curable epoxy acrylate oligomer was synthesized from phenyl boronic acid and glycidyl methacrylate. The synthesized reactive diluent was utilized to formulate ultraviolet (UV)-curable wood coatings. The weight fractions of reactive diluent in coatings formulation was varied from 5 to 25 wt % with constant photoinitiator concentration. The molecular structure of reactive flame retardant was confirmed by Fourier-transform infrared, Nuclear magnetic resonance (NMR) and ¹¹B NMR spectral analysis. Further, the efficacy of flame retardant behaviour of coatings was evaluated using limiting oxygen index and UL-94 vertical burning test. Thermal stability of cured coatings films were estimated from thermogravimetric and differential scanning calorimetry analysis. The effects of varying concentration of reactive diluent on the viscosity of coatings formulation along with optical, mechanical and chemical resistance properties of coatings were also evaluated. The coatings gel content, water absorption behaviour, contact angle analysis and stain resistance were also studied.     

CNT基木塑复合材料的力学性能、电磁屏蔽性能

采用碳纤维(CF)和碳纳米管(CNT)通过模压工艺制备出具有电磁屏蔽功能的丙烯酸酯木塑复合材料。借助材料试验机、动态热机械分析仪、微欧计和电磁屏蔽测量仪等详细研究CNT质量分数对丙烯酸酯木塑复合材料弯曲性能、动态力学性能、电阻率和电磁屏蔽效能的影响。结果表明,添加质量分数为2%的CNT,使得复合材料的弯曲强度和弯曲弹性模量分别增加了10%和16%。复合材料的储能模量也在CNT质量分数为2%时达到最大值,之后储能模量随着CNT的增加而逐渐下降,损耗因子在CNT质量分数多于2%时也逐渐增加。复合材料的吸水率和导电性能随着CNT含量的增加而增加。同时复合材料的电磁屏蔽效能也随着CNT含量增加而递增。在30~1 500 MHz范围内,电磁屏蔽效能从27 d B增加到40 d B。结果证明,当CNT质量分数在2%时,丙烯酸酯木塑复合材料具有较佳的力学性能和较好的电磁屏蔽效能(30 d B),能满足商业要求。     

Chemical characterization of Cedrus deodara wood extracts using water and molybdenum catalysts

The effect of the presence of some molybdenum catalysts on the amount of extractives in cedar wood has been studied. Autoclave treatment of cedar wood in the presence of some molybdenum catalysts can increase the amount of extracts. While autoclave treatment of cedar wood in water gave 2.85% extractives, the same treatment in the presence of H₃PMo₁₂O₄₀ gave 7.51% extractives. In the presence of silica-supported MoO₃, the amount of extractives was 5.50%. The extractives obtained using water were partially soluble in chloroform (40.7%). Only 27.6% of the extractives obtained using H₃PMo₁₂O₄₀ was soluble in the same organic solvent. When cedar was treated with silica-supported MoO₃, 56.4% of the extractives was soluble in chloroform. The extracts can be a source of fatty acids for biodiesel production and simple carbohydrates. The analysis of the chloroform-soluble fraction showed that the autoclave treatment of cedar wood gave 49.7% of a mixture of 2-hydroxy-1-(hydroxymethyl)ethyl hexadecanoate, 2-hydroxy-1-(hydroxymethyl)ethyl octadecanoate, and 2,3-dihydroxypropyl octadecanoate. The extractives obtained in the presence of the polyoxometalate molybdenum derivative gave 95% of the same esters of fatty acids, while those obtained in the presence of silica supported MoO₃ showed the presence of 93% of the same esters. Gas chromatography–mass spectrometry (GC-MS) of water-soluble fraction showed the presence of some simple carbohydrates, mainly ribose, xylose, and arabinose.     

Alkyne cellulose for Huisgen [3 + 2] cycloaddition with azido‐terminated targets

Azido‐grafted cellulose has been reported widely applied for further functionalization by click chemistry. As an alternative method, we proposed alkyne‐grafted cellulose as a prototype molecule for Huisgen [3 + 2] cycloaddition with azido‐terminated target compounds. Alkyne cellulose was synthesized by acylation with prop‐2‐ynyl 5‐chloro‐5‐oxopentanoate and, subsequently cycloaddition with 4‐aminophenylazide, ethyl 2‐azidoacetate, and (S)‐2‐(Azidomethyl)‐1‐(tert‐butoxycarbonyl)pyrrolidine (Boc‐pyrrolidine azide) to form triazole cellulose in a click manner. The reactions were confirmed qualitatively by Fourier transform infrared and NMR spectroscopy and analyzed quantitatively with elemental analysis data. The results show that a degree of substitution of up to 1.91 was obtained for esterification and, in most cases, was preferred completely in a selective way for the primary hydroxyl groups at the O‐6 position and partially at the O‐2 and O‐3 positions. Cycloaddition conversions were found as high as 0.95, 0.99, and 0.99 for aniline–triazole cellulose, acetate–triazole cellulose, and Boc‐pyrrolidine‐triazole cellulose, respectively. Both esterification and cycloaddition were undertaken under mild conditions without additional heating. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44410.     

Layer‐by‐layer self‐assembly of a lignin–poly(vinyl alcohol) based polyelectrolyte with a conductivity method

In this study, we made a new attempt to examine the relationship between the conductivity and the concentration of a polyelectrolyte solution and to prepare multilayer films with cationic lignin and polyanions through layer‐by‐layer self‐assembly. The nitrogen content of trimethyl lignin quaternary amine salt (TLQA) was 3.56%, and the carboxyl content of carboxymethylated poly (vinyl alcohol) (CMPVA) was 0.62 mmol/g. Attenuated total reflectance spectra confirmed that TLQA and CMPVA were fabricated and assembled successfully. The concentration of TLQA had a polynomial correlation with the conductivity [correlation coefficient (R²) = 0.9953], and the concentration of CMPVA was linear with the conductivity (R² = 0.9819). The electrostatic sequential adsorption process was monitored with a UV–visible spectrophotometer, and the morphology of the (TLQA/CMPVA)_n (where n is the number of double membranes) multilayer film was observed by atomic force microscopy and scanning electron microscopy. When the absorbance of the (TLQA/CMPVA)_n multilayer film increased linearly, the linear equation was y = 0.0267x + 0.07453 and R² was 0.9735. When five layers of TLQA and CMPVA were assembled, the surface root mean square roughness of TLQA and CMPVA were 21.07 and 65.28 nm, respectively. When the number of layers increased, the film surface roughness increased. The stability of the multilayer films in aqueous solution was determined by a conductivity meter. The (TLQA/CMPVA)_n multilayer film was stable in water. The results of the research demonstrate for the first time that TLQA and CMPVA could be assembled and successfully driven by electrostatic forces. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44416.