Research and application of composite stochastic resonance in enhancement detection

Aiming at the problem that the intermediate potential part of the traditional bistable stochastic resonance model cannot be adjusted independently, a new composite stochastic resonance(NCSR) model is proposed by combining the Woods–Saxon(WS) model and the improved piecewise bistable model. The model retains the characteristics of the independent parameters of WS model and the improved piecewise model has no output saturation, all the parameters in the new model have no coupling characteristics. Under α stable noise environment, the new model is used to detect periodic signal and aperiodic signal, the detection results indicate that the new model has higher noise utilization and better detection effect.Finally, the new model is applied to image denoising, the results showed that under the same conditions, the output peak signal-to-noise ratio(PSNR) and the correlation number of NCSR method is higher than that of other commonly used linear denoising methods and improved piecewise SR methods, the effectiveness of the new model is verified.

Development and Characterization of Eco-Friendly Non-Isocyanate Urethane Monomer from Jatropha curcas Oil for Wood Composite Applications

The aim of this research work was to evaluate the potential of using renewable natural feedstock,i.e.,Jatropha curcas oil(JCO)for the synthesis of non-isocyanate polyurethane(NIPU)resin for wood composite applications.Commercial polyurethane(PU)is synthesized through a polycondensation reaction between isocyanate and poly-ol.However,utilizing toxic and unsustainable isocyanates for obtaining PU could contribute to negative impacts on the environment and human health.Therefore,the development of PU from eco-friendly and sustainable resources without the isocyanate route is required.In this work,tetra-n-butyl ammonium bromide was used as the activator to open the epoxy ring with 3-Aminopropyltriethoxisylane as a catalyst to yield urethane of JCO(UJCO).The UJCO were characterized by Fourier Transform Infra-Red spectroscopy(FTIR)and their oxirane,and hydroxyl values were measured.The result showed that a decrease in oxirane value was found while the hydroxyl value was increased during the time,confirming that the urethane group was formed.The presence of functional groups in FTIR spectra at wave numbers 1732.08,1562.34,and 3348.42 cm^(−1) indicates the functional groups of C=O(urethane carbonyl),–NH,and–OH,respectively confirmed this finding.The potential applications of NIPU in the wood composite were also outlined.

Static Bending Creep Properties of Glass Fiber Surface Composite Wood

To study the static bending creep properties of glass fiber reinforced wood,glass fiber reinforced poplar(GFRP)specimens were obtained by pasting glass fiber on the upper and lower surfaces of Poplar(Populus euramevicana,P),the performance of Normal Creep(NC)and Mechanical Sorptive Creep(MSC)of GFRP and their influencing factors were tested and analyzed.The test results and analysis show that:(1)The MOE and MOR of Poplar were increased by 17.06%and 10.00%respectively by the glass fiber surface reinforced composite.(2)The surface reinforced P with glass fiber cloth only exhibits the NC pattern of wood and loses the MSC characteristics of wood,regardless of the constant or alternating changes in relative humidity.(3)The instantaneous elastic deformation,viscoelastic deformation,viscous deformation and total creep deflection of GFRP are positively correlated with the stress level of the external load applied to the specimen.Still,the specimen’s creep recovery rate is negatively correlated with the stress level of the external load applied to the specimen.The static creep deflection and viscous deformation of GFRP increase with the increase of the relative humidity of the environment.(4)The MSC maximum creep deflection of GFRP increased by only 7.41%over the NC maximum creep deflection,but the MSC maximum creep deflection of P increased by 199.25%over the NC maximum creep deflection.(5)The Burgers 4-factor model and the Weibull distribution equation can fit the NC and NC recovery processes of GFRP well.

Environmentally Friendly Chitosan-Based Wood/Wood Composite Adhesive: Review

Due to the world’s energy issues and dependency on petroleum resources, focus has switched to finding new, sustainable raw material sources for wood adhesives. Renewable biopolymers would gradually replace petroleum and natural gas as the primary raw materials used in wood adhesives. Chitosan is a biomass substance having a lot of reserves. Chitosan is one of the most fascinating biopolymers in the adhesive sector because of its potential qualities for adhesive applications, such as biodegradability, biocompatibility, and non-toxicity. Chitosan and its derivatives have so garnered considerable interest in a wide range of adhesive applications. However, its adhesive strength is insufficient to glue wood under normal, humid conditions. There has been a lot of study done on how to make chitosan-based adhesives more cohesive and water resistant. In order to effectively use chitosan-based wood glue in wood/wood composite adhesive that gives comparable performance to synthetic adhesives, numerous new ways have been developed. It has been modified by the addition of various cross-linkers, including aldehydes like glyoxal glutaraldehyde etc., epoxy compounds, blended with other polymers, different acids and chitosan grafted onto vinyl acetate. In the production of wood composites, chitosan can also scavenge formaldehyde. This review of chitosan-based adhesives focuses on various cross-linkers for chitosan modification in order to improve the properties of chitosan-based wood adhesives.

Physicomechanical Properties of Sustainable Wood Plastic Composites of Tropical Sawdust and Thermoplastic Waste for Possible Utilization in the Wood Industry

This work investigated and quantified the physicomechanical properties of flat-pressed wood plastic composites produced with recycled polyethylene terephthalate, recycled polyethylene and sawdust derived from selected tropical timbers, namely, Nauclea diderrichii, Brachystegia eurycoma, Erythrophleum suaveolens and Prosopis africana, for possible utilization in the wood industry. The compounding of the polymer blends of the precursor plastics, namely recycled PET (rPET) and recycled PE (rPE) with the sawdust (SD) from the selected timbers to produce the desired wood rPET/rPE composites was carried out via the flat press method. The characterization of the physicomechanical properties of the wood plastic composites (WPCs) produced, such as the density, hardness, flexural strength, ultimate tensile strength, elongation %, thickness swelling and water absorption capacity was carried out using methods based mainly on the European Committee for Standardization (CEN) and the American Society for Testing Materials (ASTM) standards. The results of the investigation on the resultant composites indicated that changes in the SD content affected the density of flat-pressed WPCs in line with literature. Generally, it was observed that as wood dust increased and PET content decreased, the density of composites decreased with some deviations as expected probably due to the anisotropic nature of the wood fillers. The analysis of variance (ANOVA) revealed that there was a statistically significant variation in the wood composites of Nuclea diderichii based on the physicomechanical values as the p-value (0.020) obtained was less than the critical level of α = 0.05. It was also observed that the composite, Wood 1 Sample 5 (W1S5) which was composed of 40% rPE, 40% rPET and 20% SD (derived from Nuclea diderichii), had the highest percentage elongation (26.84%);the highest flexural strength (14.995 N/mm2) and possibly the least carbon footprint in the environment. These properties of W1S5 suggest that it could therefore be the best option for the production of building materials like ceiling boards or floor skirting in the wood plastic composite industry. The results of these investigations have therefore indicated that the fabrication of WPCs from sawdust and rPET/rPE was technically feasible and had prospects for large scale production in the wood industry.

Properties of paper mill sludge–wood fiber–HDPE composites after exposure to xenon-arc weathering

We used paper mill sludge（PMS） to substitute for part of the wood fibers（WF） used to reinforce high density polyethylene（HDPE）.The resulting composites were subjected to xenon-arc weathering.The composite filled with limited PMS（under 10 %） had mechanical properties and aging resistance similar to those without PMS.The composites containing more PMS faded and cracked more readily than those without PMS.Based on the carbonyl index,crystallinity,and wood index,PMS appeared to accelerate the degradation of composites during weathering.Adding PMS to WF–HDPE composites reduced the weathering resistance,and this reduction was not significant if the PMS content did not exceed 20 % of the wood fibers.Therefore,PMS could be used as a reinforcement in wood-plastic composites at levels less than20 % of the wood fiber content.

Impacts of freezing and thermal treatments on dimensional and mechanical properties of wood flour-HDPE composite

Wood plastic composite （WPC） of wood flour （WF）, high density polyethylene （HDPE）, maleic anhydride-grafted polyethylene （MAPE） and lubricant was prepared by extrusion, and then exposed to different temperatures to evaluate the effects of freezing and thermal treatment on its dimensional and mechanical properties. At elevated temperatures, WPC expanded rapidly initially, and then contracted slowly until reaching an equilibrium state. Treatment at 52°C and relative humidity of 50% for 16 days improved the mechanical properties of WPC： flexure, tensile strength, and izod unnotched impact strength increased by 8%, 10% and 15%, respectively. Wide-angle X-ray diffraction （XRD） tests showed that the degree of crystalization of HDPE in WPC declined with increasing treatment temperature.

加工因素对HDPE基木塑复合材料静曲强度的影响

为了研究木塑复合材料加工因素对复合材料力学性能的影响,采用正交实验法以静曲强度为评价标准,利用极差分析和方差分析法分析了螺杆转速、造粒温度、偶联剂质量分数和木粉含量等加工因素对力学指标静曲强度影响的顺序及各因素的最佳水平,确定了木塑复合材料静曲强度的各加工因素的最佳参数组合;系统地分析了各加工参数对木塑复合材料力学性能指标静曲强度的影响。结果表明,影响木塑复合材料静曲强度的主要加工因素由大到小依次为偶联剂质量分数>木粉含量>转速>造粒温度;得到最佳静曲强度的加工因素参数组合为转速150 r/min、造粒温度145℃、偶联剂质量分数为5%、木粉含量为60%;木粉含量及偶联剂质量分数对材料的静曲强度具有显著性影响,转速和造粒温度对材料静曲强度影响的显著性较低,其中,随着偶联剂含量的增加,静曲强度呈明显上升的趋势;当木粉含量从30%增大至70%时,材料的静曲强度呈先增加后减小的趋势。

Preparation of electromagnetic shielding wood-metal composite by electroless nickel plating

Electrical and electromagnetic shielding wood metal composite was prepared by using electroless nickel plating. The effects of solution amount, plating time and plating temperature on surface resistivity and electromagnetic shielding effectiveness were investigated. And P content, microstructure and surface feature of layers obtained at different temperatures were analyzed by energy dispersion spectrometer （EDS）, X-ray diffraction （XRI）） and scanning electron microscopy （SEM）. The results showed that layers with higher electro-conductivity and electromagnetic shielding effectiveness were obtained under the optimum conditions that plating solution was 500 mL, plating time was 30 min and plating temperature was 62℃. The results showed by EDS analysis; that P content increased gradually in a small extent with plating temperature increased. It was showed by XRD and SEM analysis that layers plated at different temperatures were all microcrystalline structure and uniform and successive, which had noticeable metal luster. Those indicated that plating temperature had little influence on microstructure and surface feature under pH value invariable.

Reinforcing effects of modified Kevlar~ fiber on the mechanical properties of wood-flour/polypropylene composites

Kevlar fiber （KF） is a synthesized product with strong mechanical properties. We used KF as a reinforcement to improve the mechanical properties of wood-flour/polypropylene （WF/PP） composites. KF was pretreated with NaOH to improve its compatibility with the thermoplastic matrix. Maleated polypropylene （MAPP） was used as a coupling agent to improve the interfacial adhesion between KF, WF, and PP. Incorporation of KF improved the mechanical properties of WF/PP composites. Treatment of KF with NaOH resulted in further improvement in mechanical strength. Addition of 3% MAPP and 2% hydrolyzed KF （HKF） led to an increment of 93.8% in unnotched impact strength, 17.7% in notched impact strength, 86.8% in flexure strength, 50.8% in flexure modulus, and 94.1% in tensile strength compared to traditional WF/PP composites. Scanning electron microscopy of the cryo-fractured section of WF/PP showed that the HKF surface was rougher than the virgin KF, and the KF was randomly distributed in the composites, which might cause a mechanical interlocking between KF and polypropylene molecules in the composites.

Creep Behaviour of Wood Flour/Poly(vinyl chloride) Composites

The experimental creep data were focused on wood-flour （WF）/poly vinyl chloride （PVC） composites with the variations in additive concentrations of wood flour, silane coupling agent, organomodified montmorillonite （OMMT） and nano-cacium carbonate （nano-CaCO3）. Their effects were analyzed using the Four-element Burger Model incorporating microscopic mechanisms. Total creep strain was low with increasing WF while elastic strain was high and plastic flow strain was low in modeling. Modification of WF with silane was beneficial to creep resistance, so did adding low ratio of OMMT （1.5 wt%） and nano-CaCO3 in composites. Thus, it was effective in reducing creep either by stiffening the PVC matrix using rigid nano-particles or by improving their adhesion with resin. However, superfluous quantity of any additament did not benefit the improvement owing to either earlier destruction of their agglomerates or stress-concentrated cracks in the over-incrassated interface.

The sampling apparatus of volatile organic compounds for wood composites

Terpenes, aldehydes, ketones, benzene, and toluene are the important volatileorganic compounds (VOCs) emitted from wood composites. A sampling apparatus of VOCs for woodcomposites was designed and manufactured by Northeast Forestry University in China. Theconcentration of VOCs derived from wood based materials, such as flooring, panel wall, finishing,and furniture can be sampled in a small stainless steel chambers. A protocol is also developed inthis study to sample and measure the new and representative specimens. Preliminary research showedthat the properties of the equipment have good stability. The sort and the amount of differentcomponents can be detected from it. The apparatus is practicable.

Microwave Irradiation Treatment of Wood Flour and Its Application in PVC-Wood Flour Composites

The technique of microwave irradiation induced free radical bulk- polyaddition reactions in porous wood flour was used to modify wood flour. The behaviors of the modified wood flour under microwave irradiation, such as thermal stability and moisture sorption properties, were studied. A kind of semiinterpenetrating polymer network wood four （Semi-IPN-WF） can be formed through polymerization of MMA in the porous wood flour by microwave irradiation, and the thermal decomposition temperature of the semi-IPN-WF is considerably increased. PVC/Semi-IPN-WF composites were prepared by melt mixing in double rolls, which exhibit improved rheological properties, lower water sorption properties and outstanding mechanical performances.

Optimum preparation technology for Chinese fir wood/Ca-montmorillonite (Ca-MMT) composite board

For this study, an intercalation compounding method was used to prepare Chinese fir wood/Ca-montmorillonite （Ca-MMT） composite board to improve its properties such as surface mechanical properties, flame retardance and dimensional stability. By virtue of water-soluble phenolic resin （PF）, Chinese fir wood and Ca-MMT were mixed by pressure and vacuum impregnation. The optimum impregnation technology of Chinese fir wood/Ca-MMT composite board was obtained by using an orthogonal design and a single factor design of pressure and vacuum impregnation, using weight percent gain （WPG） as the basic index. The results are as follows： 1） On the basis of the orthogonal design and an actual experiment, the optimum preparation technology of Chinese fir wood/Ca-MMT composite board is 20% PF resin dispersion concentration （wt%）, 1.0 CEC amount of organic intercalation agent, 0.098 MPa vacuum degree, 5% concentration of Ca-MMT and 1.0 MPa pressure. 2） The WPG of the composite board samples of 450 mm length was much larger than that of the samples of 600, 750 and 900 mm length. Warm water extraction contributed little to WPG

Research advance in wood composites in China

Wood composites can generally be classified in three parts: laminated composites, mixed composites and penetrated composites. Every part has its own characteristic and can be further divided. This paper introduces the history and the state of development of wood composites in China. The research about glue-laminated timber is rare and the industry hardly comes to being. A great of achievements have been obtained in mixed composites and it is well industrialized. Many studies on scrimber have been done and the Chinese researchers are looking for a feasible way to develop the scrimber industry in China. Chinese researchers also spent so much energy in studying wood plastic composites (WPC), but it has not been industrialized due to the high cost.

Preliminary study of viscoelastic properties of MAPP-modified wood flour/polypropylene composites

Viscoelastic properties of maleated polypropylene （MAPP）-modified wood flour/polypropylene composites （WPC） were investigated by both a compression stress relaxation method and dynamic mechanical analyses （DMA）. Three wood to polymer ratios （40：60, 60：40, and 80：20） and five MAPP loading levels （0, 1, 2, 4 and 8%） were used to study their effects on the viscoelastic prop- erties of MAPP-WPC. The results show that： 1） higher wood to polymer ratio corresponds to higher stress relaxation levels for unmodified WPC. The modification with MAPP has an obvious effect on the stress relaxation of MAPP-WPC at higher wood to polymer ratios （60：40 and 80：20）, but almost no effect at the 40：60 wood to polymer ratio. The optimal MAPP loading level for the wood to polymer ratio of 60：40 appears at 1%; 2） the storage modulus reaches its maximum at a MAPP loading level of 1% for wood to polymer ratios of 40：60 and 60：40, while for the 80：20 wood to polymer ratio, a higher storage modulus is observed at higher MAPP loading levels, which is quite consistent with the stress relaxation results. The results suggested that a suitable loading level of MAPP has a positive effect on the viscoelastic properties of WPC at higher wood to polymer ratios. Excessive MAPP loading would have resulted in adverse effects.

Starch-Based Adhesives for Wood/Wood Composite Bonding: Review

Increasing global energy crisis and scarcity of petroleum resources has shifted focus of chemical industries to look for alternative raw material resources. The main focus of raw materials in wood adhesives, such as petroleum and natural gas [1] [2], would be gradually replaced by renewable biopolymers. Starch is a relatively inexpensive and renewable product from abundant plants, easy processing and it has been extensively used as binders, sizing materials, glues and pastes [3], but its bonding capacity is not strong enough to glue wood [4]. Extensive research has been carried out on improving the cohesive properties, especially water resistance, of starch-based adhesives. In starch-based wood adhesive many new approaches have come forward for effective use it in wood/wood composite adhesive giving comparable performance as synthetic adhesives. This review of starch-based adhesives is made with the focus on starch modification methods for improving properties of starch-based adhesives.

Production of mahogany sawdust reinforced LDPE wood–plastic composites using statistical response surface methodology

We produced wood–plastic composite board by using sawmill wastage of mahogany（Swietenia macrophylla） wood and low density polyethylene.We used multi-response optimization to optimize the process parameters of composite board production including mixing ratio,fire retardant（%） and pressing time（min）.We investigated the effects of these three process parameters in the mechanical and physical properties of the composite board.Afterwards,Box–Behnken design was performed as response surface methodology with desirability functions to attain the optimal level of mixing ratio,fire retardant and pressing time（min）.The maximum modulus of elasticity（MOE） and modulus of rupture（MOR） were achieved at the optimal conditions of wood plastic mixing ratio of60：40,pressing time of 9 min and zero fire retardant percentage.The optimized MOR and MOE were 13.12 and1,781.0 N mm-2,respectively.

Dielectric properties of Simon poplar wood flour/polypropylene composite at oven-dry state

Interfacial compatibility is a crucial factor to the performance of wood-plastic composites （WPCs）. Yet, so far, the coupling mechanisms of WPC have not been completely understood. In order to further clarify the interfacial coupling mechanism, the dielectric constant and dielectric loss factor of Simon poplar wood flour/polypropylene composites without additives at different wood contents were measured at oven-dry state, and parameters and thermodynamic quantities of the relaxation process were also analyzed and calculated. Consequently, an obvious relaxation process based on the reorientation of methanol groups in amorphous region of wood cell wall was observed exactly that its dielectric loss factor peak decreased with the decreasing wood content within the measured range of 50%-100%. With the trend of dielectric relaxation strength, the two changing trends both revealed that the existence of polypropylene could hinder reorientation of methanol groups. Following the decreasing wood contents, the effect of the hindrance on the dielectric properties turned obvious gradually. It elucidated that introduction of polypropylene caused the quantities of hydrogen bonds formed between each methanol group and the groups around it change. The same conclusion could be drawn from the analysis of thermodynamic quantities during the dielectric relaxation progress.

The Accelerated Thermo-Oxidative Aging Characteristics of Wood Fiber/Polycaprolactone Composite:Effect of Temperature,Humidity and Time

This study investigated the characteristics of wood fiber/polycaprolactone composite after an artificial accelerated thermo-oxidative aging treatment.The effect of time,temperature and humidity during the treatment on their mechanical,chemical and morphology properties were evaluated.The composite was prepared from melted wood fibers and modified polycaprolactone by a molding process.A temperature and humidity controllable test chamber was used for the thermo-oxidative aging of the composite.The thermo-oxidative aging caused surface of the composite to be much more rougher and even a few cracks and holes appeared on it.According to the spectra of Fourier Transform Infrared(FTIR)and Gel Permeation Chromatography(GPC),C=O in the molecular chain of polycaprolactone was hydrolyzed and C–O was broken after the aging treatment,which resulted in a reduction in average molecular weight of the composite.Moreover,results showed that the mechanical strength decreased a lot with the increase in time,temperature and humidity,and the effect of temperature and humidity was more significant compared with that of time.Controlling the temperature and humidity during thermo-oxidative aging treatment could accelerate the aging of composite,which provided a quick and effective method for evaluating the aging resistance of the composite.