Development of semitransparent wood‐polymer composites

A new material has been developed consisting of pieces of wood embedded within a matrix of acrylic polymer, resulting in a transparent or semitransparent wood‐based product. This material presents quite appealing aesthetic features, thereby opening new possibilities for decorative applications. Because acrylic and methacrylic monomers are in the liquid state at room temperature, it is possible to introduce wood (in the current case, walnut wood) into a mixture of acrylic (hydroxypropyl acrylate) and/or methacrylic monomers (methyl methacrylate and 2‐hydroxyethyl methacrylate) along with a plasticizer (dioctyl phthalate) in the presence of a chemical initiator (benzoyl peroxide). A transparent polymeric matrix with dispersed wood is then obtained through bulk free‐radical polymerization. Introducing this reaction mixture along with pieces of wood into a mold results in a wood‐polymer composite. A 2^4?1 experimental fractional factorial design was implemented to study the importance of the composition of these materials on several relevant properties. The sheets produced were characterized by tensile testing, dynamic mechanical thermal analysis, thermal gravimetric analysis, and heat deflection temperature. The models obtained for predicting each property pointed to valuable insights regarding the influential constituents. In particular, our results suggested that monomers to be used in future applications of this material should be selected in terms of their cost and the desired flexibility for the final product, not in terms of their polarity. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers     

Use of expanded‐EPDM as protecting layer for moderation of photo‐degradation in wood/NR composite for roofing applications

Changes in tensile properties, sample size, interfacial strength, and thermal conductivity of melt‐laminating layers of wood/ebonite natural rubber (NR) and expanded ethyelene–propylene diene rubber (EPDM) for polymeric roofing applications were monitored under a period of UV aging times for 60 days, the results being compared with single rubber layers of wood/NR and expanded‐EPDM. The experimental results suggested that the tensile modulus of the wood/NR‐EPDM melt‐laminating layer increased with increasing aging time. The tensile strength of the wood/NR layer decreased after prolonged UV aging, and positioned between that of the wood/NR and expanded‐EPDM layers. The sample size reduction of wood/NR layer with expanded‐EPDM top coating layer was lower than that for wood/NR single layer. The peel strength of the wood/NR‐EPDM melt‐laminating layer was found to decrease with increasing UV aging time as a result of delamination of the rubber layers. The thermal conductivity of the wood/NR‐EPDM melt‐laminating layer decreased from 0.085 to 0.070 W/m K with increasing aging times upto 40 days, but tended to increase to 0.080 W/m K at the aging time of 60 days. The experimental results in this work clearly suggested that expanded‐EPDM could be used as protecting layer, not only for moderation of photo‐oxidative degradations of wood/NR layer for roofing application, but also for minimization of dimension changes of the wood/NR‐EPDM melt‐laminating layer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The thermal conductivity of fir and beech wood heat treated at 170, 180, 190, 200, and 212°C

Heat treatment changes the chemical, physical, and mechanical properties of wood. The properties of heat‐treated wood have been researched considerably, but the thermal conductivity of heat‐treated wood in various conditions has not been reported. In this study, the thermal conductivity of heat‐treated fir and beech wood at temperatures 170, 180, 190, and 212°C for 2 h with ThermoWood method were investigated. The results were compared with industrially kiln‐dried reference samples. The results show that heat treatment caused an important reduction on thermal conductivity of wood, the extend of which is depend upon temperature and wood species. Considering all heat treating temperatures, generally by increasing heat treatment temperature the thermal conductivity of wood decreased. The effect of heat treating temperature on thermal conductivity was identical for fir and beech wood. The highest decrease in thermal conductivity occurred at 212°C for both wood species. When compared with untreated wood, the decreases in thermal conductivity at 170°C, and 212°C for fir and beech wood were 2%, 9 and 2%, 16% respectively. Depending on heat treatment temperature, the decrease found out beech in high temperature is higher than that of fir. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Wheat gluten fractions as wood adhesives—glutenins versus gliadins

Plant proteins, such as wheat gluten, constitute attractive raw materials for sustainable wood adhesives. In this study, alkaline water dispersions of the protein classes of wheat gluten, glutenin, and gliadin were used as adhesives to bond together wood substrates of beech. The aim of the study is to measure the tensile shear strength of the wood substrates to compare the adhesive performance of glutenin and gliadin and to investigate the influence of application method and penetration of the dispersions into the wood material. A sodium hydroxide solution (0.1M) was used as dispersing and denaturing agent. Dispersions with different protein concentrations and viscosities were used, employing wheat gluten dispersions as references. Two different application methods, a press temperature of 110°C and a press time of 15 min, were employed. The tensile shear strength and water resistance of the wood substrates were compared, using a slightly modified version of the European Standard EN 204. The bond lines of the substrates were examined by optical microscopy to study the penetration and bond‐line thickness. The results reveal that the adhesive properties of gliadin are inferior to that of both glutenin and wheat gluten, especially in terms of water resistance. However, the tensile shear strength and the water resistance of gliadin are significantly improved when over‐penetration of the protein into the wood material is avoided, rendering the adhesive performance of gliadin equal to that of glutenin and wheat gluten. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Membrane inflation of polymeric materials: Experiments and finite element simulations

A high‐speed optical measurement system, which is capable of measuring transient surface shape, is used in the polymer membrane inflation experiments. The accurate measurement data, which is an array of points, with known Cartesian coordinates and with respect to a fixed coordinate system, provides a source for further bubble shape analysis. Inflation pressure is correlated with each bubble shape measurement. The measured results reveal the importance of the thermal warpage and temperature gradient in the bubble inflation tests. Potential errors in the material parameter calculation, which are caused by assuming uniform temperature and zero thermal warpage, are pointed out. Consequently, a finite element analysis has been carried out to simulate the membrane inflation with/without thermal warpage and the temperature gradient. The material parameters obtained considering the thermal warpage and temperature gradient yield improved agreement with the experimental data. Although in this paper the measurement data is mainly used for the determination of the material parameters in the bubble inflation tests, they are also a source of validating other computer‐aided simulations as well as in the study of the thermal shrinkage of polymer products.     

Dynamic mechanical properties of extruded nylon–wood composites

Dynamic mechanical properties determine the potential end use of a newly developed extruded nylon–wood composite in under‐the‐hood automobile applications. In this article, the dynamic mechanical properties of extruded nylon–wood composites were characterized using a dynamic mechanical thermal analyzer (DMTA) to determine storage modulus, glass transition temperature (T_g), physical aging effects, long‐term performance prediction, and comparisons to similar products. The storage modulus of the nylon–wood composite was found to be more temperature stable than pure nylon 66. The T_g range of the nylon–wood composite was found to be between 23 and 56°C, based on the decrease in storage modulus. A master curve was constructed based on the creep curves at various temperatures from 30 to 80°C. The results show that the relationship between shift factors and temperature follows Arrhenius behavior. Nylon–wood composites have good temperature‐dependent properties. Wood fillers reduced the physical aging effects on nylon in the wood composites. The comparison of the nylon–wood composite with other similar products shows that nylon–wood composites are a promising low cost material for industrial applications. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Influence of the filler material on the thermal stability of one‐component moisture‐curing polyurethane adhesives

Filler materials are part and parcel for the adjustment of adhesives, in particular, their rheological and mechanical properties. Furthermore, the thermal stability of adhesives can be positively influenced by the addition of an expedient filler, with inorganic types common practice in most cases. In this study, one‐component moisture‐curing polyurethane adhesives for engineered wood products based on isocyanate prepolymers with different polymer‐filled polyether polyols were investigated with regard to the filler's potential to increase the thermal stability of bonded wood joints. The property changes due to the addition of fillers were determined by means of mechanical tests on bonded wood joints and on pure adhesive films at different temperatures up to 200°C. Additional analyses by atomic force and environmental scanning electron microscopy advanced the understanding of the effects of the filler. The tested organic fillers, styrene acrylonitrile, a polyurea dispersion, and polyamide, caused increases in the cohesive strength and stiffness over the whole temperature range. However, the selected filler type was hardly important with regard to the tensile shear strength of the bonded wood joints at high temperatures, although the tensile strength and Young's modulus of the adhesive films differed over a wide range. Prepolymers with a lower initial strength and stiffness resulted in worse cohesion, in particular, at high temperatures. This disadvantage, however, could be compensated by means of the filler material. Ultimately, the addition of filler material resulted in optimized adhesive properties only in a well‐balanced combination with the prepolymer used. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

低于液氮温度的泡沫塑料吸湿增重

为减少火箭上液氢/液氧燃料蒸发损失,要求绝热材料热导率小,附加质量轻,并有好的抗应力强度。泡沫塑料因其密度低、绝热性能及机械强度好等优点,是国内外最广泛使用的火箭上深低温系统绝热材料。但泡沫塑料长时间存在大温度梯度时,将强化吸湿增重,从而增加火箭起飞附加质量,也恶化绝热效果。因此,获得可靠的泡沫塑料吸湿增重数据对大推力火箭推力设计有重要意义。报告了用脉管制冷机冷却的泡沫塑料吸湿增值实验装置及实验结果。利用两台自行研制的GM型单级脉管制冷机提供冷量,样本一面被冷却到约45 K温度,同时另一面暴露在30℃恒温及>95%的相对湿度环境。设计了一种波纹管结构来减少环境对真空低温系统的漏热。总共测试了4组8个样本,测试时间为7 h。测试结果与液氮温度的测试结果进行对比和分析,结果发现两者吸湿增重相同,即温度梯度降低引起的低温泵增强效应在该温区可忽略不计。同时发现样本搭接结构对吸湿增重没有影响。     

Thermal decomposition behavior of silica‐phenolic composite exposed to one‐sided radiant heating

When polymer‐matrix composite reaches sufficiently high temperature, pyrolysis reactions of the polymer matrix occur. The thermal decomposition behavior of silica‐phenolic composite was investigated using solar radiant heating experiment with one‐sided heat flux. Thermogravimetric studies and combined thermal analysis techniques were performed to characterize the thermal decomposition kinetics of phenolic resin. Simultaneously a thermal response model was used to calculate the through‐thickness temperature distribution. The calculated time‐dependent temperature profile at different material depths were compared with the experimental results measured at the same location. The silica‐phenolic composite exhibited an excellent thermal insulation during thermal exposure. The postheating specimen was sectioned in millimeter segments to determine the density profile. On the basis of the density profile, the transition from char layer to pyrolysis zone to virgin material was estimated. Finally, the material morphology was analyzed for silica‐phenolic composite after thermal exposure. POLYM. COMPOS., 36:1557–1564, 2015. © 2014 Society of Plastics Engineers     

Three‐Dimensional Simulation of Moisture Diffusion in Polymer Composite Materials

Abstract

This article presents a three‐dimensional Galerkin finite element methodology (GFEM) for simulating Fickian diffusion with temperature‐dependent diffusion coefficients, with particular application to moisture diffusion in composite materials. The coupled thermal and moisture diffusion problems are solved by using three‐dimensional finite element method with orthotropic diffusion coefficients and an implicit time‐stepping procedure. Both Frontal and Jacobi conjugate gradient (JCG) solution techniques are used. Numerical examples are presented to illustrate the methodology and include orthotropic diffusivities and multiple material regions. Moisture diffusion within a periodic unit cell of a typical composite material is also considered. The results show that the iterative JCG method is effective and computationally inexpensive to analyze diffusion three‐dimensional diffusion problems with multiple materials.     

Experimental investigation on reprocessing of extruded wood flour/HDPE composites

This article presents an experimental study on the change in the properties of wood–plastic composites (WPCs) when reprocessed. The degree of properties degradation upon reprocessing, for recycling purpose, can be considered as a key factor to choose an alternative against discarding into the environment. A material which retains its properties when recycled, or at least exhibits insignificant reduction in its properties, is favorable in environmental point of view. To investigate the reprocessing effect on the WPC properties, in this study, cylindrical profiles of WPC, with 60 wt% of wood content, were produced using a twin screw extruder, at first stage (virgin WPC). These profiles were then chopped into granules and used in the reproduction of the same shaped product (recycled WPC). For the measurement of mechanical properties, tensile and three‐point bending tests were conducted. Differential scanning calorimetry (DSC) test was performed to compare thermal behavior of the neat HDPE, virgin and recycled composites. Scanning electron microscopy (SEM) images were also produced to observe the adhesion quality of the components and changes in wood particles size. Physical properties such as density and water uptake were also measured. A reduction in strength was observed upon recycling which was accompanied with the decrease in density, while an increase in the flexural modulus was noticed. The results also indicate that the recycled samples exhibit a higher water uptake. Analysis of thermal behavior showed a slight increase in the melting temperature of the reprocessed composite and decrease in the degree of crystallinity especially at the first stage of the HDPE process. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Production of Al2O3‐Stabilized Tetragonal ZrO2 Nanoparticles for Thermal Barrier Coating

Al₂O₃‐stabilized tetragonal ZrO₂ nanoparticles were obtained through hot‐air spray pyrolysis and characterized after postsynthesized treatments. The produced nanoparticles were 26 nm in size with surface area of 59 m²/g. A multilayer thermal barrier coating of nanostructured Al₂O₃‐ZrO₂‐embedded silicate was applied to the mild steel (EN3) specimen using spin‐coating technique and characterized comprehensively employing X‐ray diffraction and scanning electron microscope. The Al₂O₃‐stabilized ZrO₂ with silicate matrix facilitates the formation of zirconium silicate nanostructured surface‐protective coating on EN3 specimen. The Al₂O₃‐ZrO₂/SiO₂ matrix‐based hybrid inorganic coating shows effective thermal barrier for EN3 after firing at a high temperature of 600°C.     

Compressive strength of lumber at high temperatures

A model was developed to predict the residual strength in compression parallel to grain for dimension lumber subjected to axial loads at elevated temperatures while braced to prevent buckling. Prediction of the time‐dependent temperature profile within the cross‐section of a lumber member was achieved by adapting a two‐dimensional heat transfer model. An extensive literature review examined seven models proposed by various authors to predict residual strength under various temperature regimes. With knowledge of the temperature‐history and material properties, it was possible to predict the time to failure by crushing of axially loaded members exposed to elevated temperatures. Initially, predicted times to failure did not show as good an agreement with those measured in an experimental programme as had been hoped. However, when a new residual strength‐temperature model was developed and used to simulate the axial load capacity of nominal 38 mm × 89 mm studs exposed to fire, the results obtained showed good agreement with experimental results. Copyright © 2004 John Wiley & Sons, Ltd.     

聚乙烯基木塑复合材料蠕变量影响因素分析

在室温恒定的情况下,主要研究了原材料配比、材料制备工艺参数在不同载荷条件下对木塑复合材料24 h蠕变性能的影响。结果表明,在24 h蠕变试验中各载荷下影响蠕变量的优势因素各不相同,但木塑比都为第一显著因素;载荷为30 % 弯曲强度时,木塑比与螺杆转速为显著因素;载荷为50 %弯曲强度时,木塑比为显著因素;载荷为70 %弯曲强度时,只有木塑比为极显著因素。     

Modeling Microwave Heating and Moisture Redistribution in Wood

A finite element model was developed to describe and explain microwave heating of wood and the following moisture redistribution in wood. Dielectric and thermal properties are of great importance, since they are continuously affected during the process by moisture content, density, grain direction, temperature, and more. Computer tomography was used to detect wood density and moisture content. Heat distribution was verified by fiber-optic temperature sensors. The tests were performed in a designed microwave dryer based on 1-kW generators, 2.45 GHz. The results show that finite element modeling is a powerful tool to simulate heat and mass transfer in wood, providing the material is well described.     

Modeling Microwave Heating and Moisture Redistribution in Wood

A finite element model was developed to describe and explain microwave heating of wood and the following moisture redistribution in wood. Dielectric and thermal properties are of great importance, since they are continuously affected during the process by moisture content, density, grain direction, temperature, and more. Computer tomography was used to detect wood density and moisture content. Heat distribution was verified by fiber-optic temperature sensors. The tests were performed in a designed microwave dryer based on 1-kW generators, 2.45 GHz. The results show that finite element modeling is a powerful tool to simulate heat and mass transfer in wood, providing the material is well described.     

Piloted ignition of wood: A review

The physical phenomenon of piloted ignition of a material is described. A number of mathematical models of this phenomenon are presented in order of decreasing complexity. The most sophisticated models include gas-phase phenomena. Simple models neglect all chemical effects and are purely thermal. The most commonly used criteria for piloted ignition are discussed. Correlations used in piloted ignition studies from the past 40–50 years are summarized. Many investigators have been successful in correlating piloted ignition data of wood using a simplified thermal model in combination with a critical surface temperature criterion. Emphasis of this review is therefore on this approach. The paper concludes with a detailed analysis of various factors affecting piloted ignition of wood. Some of the factors are related to the experimental conditions, others are associated with the characteristics of the material.     

Experimental and numerical investigations of the interlaminar shear properties of carbon/carbon composites

Experimental tests and numerical simulations were implemented to investigate the interlaminar shear properties of carbon/carbon composites (C/Cs). A unit‐cell model, according to the microstructure of the C/Cs, was used to predict material properties of the C/Cs. A three‐dimensional finite element model was established to investigate the damage behavior of C/Cs on the basis of Linde failure criterion and damage evolution. Good agreement, in terms of the load force history and failure modes, was observed between the experimental and numerical results; this provided the applicability of the numerical simulation. The test results show that the interlaminar shear strength of the C/Cs was 10.52 MPa and the value of the simulation result was 10.89 MPa, with the relative error being less than 4%. Damage contours and stress distribution analysis of the simulation results are discussed. Fiber damage occurred at the bottom of the specimen, and matrix damage was found in the upper half of the specimen; this was similar to the appearance of the tested specimens. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44783.     

Repeated thermal shock behavior of ZrB2-SiC-graphite composite under prestress

The thermal shock resistance of ZrB₂-SiC-graphite composite under nominal prestress of 0, 20, 30, 40 or 50 MPa after subjected to 10 and 30 cycles of thermal shock was evaluated by measuring the residual flexural strength of the tested specimen. In each test the applied prestress kept constant and in each cycle the specimen center was heated to 2000 °C within 5 s through electrical resistance heating method and cooled down naturally to room temperature. A lot of broken SiO₂ bubbles in the tested specimens were observed with a SEM. For the specimen subjected to 10 cycles of thermal shock, the residual flexural strength does not show big change under different levels of prestress, although the thickness of oxide layer increases at larger prestress, which is presumably attributed to the effect of the oxide layer that heals the cracks and the pores and enhances the strength. For the specimen subjected to 30 cycles of thermal shock, the residual strength decreases, in general, with the increase of prestress level. The thermal shock fatigue under different levels of prestress was also tested, and it was found that the increase of prestress may speed the failure of the specimen, indicating that the level of prestress may fatally affect the failure of the material.     

Full scale experiments for evaluating theoretical fire wall models

The aim of the research described in this paper was to provide experimental results for the evaluation of theoretical models for predicting the behaviour and time‐to‐failure of loadbearing and non‐loadbearing wood framed walls in fire. References for thermal and mechanical properties of wood and gypsum board are given to provide comprehensive input for the evaluation of theoretical wall models. The scope of the research involved full‐scale uninsulated cavity walls with well‐controlled clearly known conditions including initial ambient vertical load capacity for benchmarking the reduction in capacity and stiffness, rotational stiffness of supports, eccentricity of vertical load, elastic moduli of wood and gypsum board in compression, stiffness of slip between gypsum board and studs and end stud effects. The experiments were repeated and they demonstrated that the controls led to high consistency in the results despite the inherent large variability of the mechanical properties of wood. The results include temperature distributions, initial vertical load capacity, load‐deflection plots and times‐to‐failure. The results show that the temperatures in the studs are approximately uniform until all the moisture is vaporized. Thermal properties of wood will not vary significantly for consistent density, moisture content and species of wood. The main structural actions that should be modelled for different loading regimes are deduced. Copyright © 2004 John Wiley & Sons, Ltd.