Reducing the moisture sensitivity of linear friction welded birch (Betula pendula L.) wood through thermal modification

Linear friction welding of wood is a bonding process applied to wood and during which a stiff bond line is formed by the softening and rehardening of wood components to form a composite material composed mainly of wood fibres embedded in a modified lignin matrix. Unfortunately, the bonds tend to spontaneously delaminate or lose their strength when exposed to moist conditions. Some approaches were previously applied to overcome this problem, but so far a suitable solution has not been found. This paper presents results of applying post-welding thermal modification to reduce the moisture sensitivity of welded wood. The experiments included welding of birch wood, thermal modification under superheated steam at atmospheric pressure, internal bond (IB) and tensile-shear strength testing and soaking tests. As supposed, the non-modified reference specimens performed poorly after the seven days soaking test (on average 0.33 MPa IB strength), whereas the thermally modified specimens yielded almost the same IB strength in dry and wet condition (on average e.g. 1.15 and 0.93 MPa, respectively). Such a similar load bearing capacity in very different moisture conditions was previously reported only in the case of paduk wood. Similar to the reduction of IB strength occurred during the soaking test, also delamination was observed more clearly in non-modified reference specimens (e.g. 4 vs. 0 total delaminations after seven days soaking). Therefore, the authors suggest that post-welding thermal modification could provide a suitable bond-stabilisation method against moisture, although the process parameters must be optimised in further research, for instance, to ensure scalability.     

甲酸/盐酸胍DES温和高效分离毛竹木质素

以毛竹为原料,采用甲酸/盐酸胍酸性低共熔溶剂（DES）温和高效分离木质素,并对其结构、热稳定性和抗氧化性进行了表征。结果表明,甲酸/盐酸胍（摩尔比为4:1）DES实现了温和短时条件下（100 ℃,2 h）高效分离木质素（得率为59.31%）,当进一步升温至120 ℃时,得率可达73.98%,其原因是该酸性体系中氢质子使木质素中大量的β-O-4、β-β、β-5连接键断裂,促使木质素大分子解聚成小分子而溶出。分离的木质素纯度高于96.6%,分子量低（Mw=1040~2040 g/mol）,多分散系数小于1.5,结构均一,热稳定性好。同时,该木质素抗氧化活性强（IC50=0.016~0.045 mg/ml）,优于商业抗氧化剂丁基羟基茴香醚（IC50=0.056 mg/ml）。     

偶联剂对竹材表面润湿性及胶合强度的影响

利用3种硅烷偶联剂KH550、KH560及KH602和1种偶联剂HMR处理竹材表面,考查了偶联剂对竹材表面性能及粘接性能的影响。结果显示,偶联剂HMR、KH560及KH602可以提高竹片的表面自由能,改善竹片的表面润湿性能;而KH550处理竹片后降低了竹片的表面自由能,竹片的表面润湿性变差。但是4种偶联剂均能提高竹片的胶合强度。综合价格与性能因素,偶联剂HMR的使用效果最好。     

Prediction of the colorimetric parameters and mass loss of heat‐treated bamboo: Comparison of multiple linear regression and artificial neural network method

In this study, the colorimetric parameters (L*, a*, b*) and mass loss of heat‐treated bamboo were investigated, and the obtained results were modeled by using two methods: multiple linear regression (MLR) and artificial neural network (ANN). First, bamboo samples were exposed to heat treatment at different temperatures (110°C, 140°C, 170°C, and 200°C) and durations (15, 30, 45, 60, 75, 90, and 115 minutes) in a laboratory oven. Then, the colorimetric parameters (L*, a*, b*) and mass loss of each sample were measured after each period of heat treatment. All data were modeled by using two methods separately for each parameter and the performances of these proposed methods were compared. It was found that color change and mass loss increased with increasing temperature and duration of heat treatment. Mean absolute percentage error (MAPE) values of all obtained MLR ranged from 0.64% to 10.63%, while the all MAPE values of ANN were found to be lower than 1.5%. Based on these results, it can be said that MLR and ANN could be used to evaluate the changes on the selected properties of heat‐treated bamboo samples. On the other hand, it should be emphasized that the ANN gave more accurate results than the MLR method because of its learning capability.     

振动法测试涤纶原丝线密度及其不匀率

介绍用振动仪测试涤纶原丝线密度及其不匀率。通过振动法与烘箱法对比测试,证明振动法测试 涤纶原丝线密度满足准确性要求;对振动法测试的线密度不匀率与通常测试的断面不匀率数据相关性检验, 可证明其表征线密度不匀率的有效性。     

竹制品蒸煮废水的处理

结合工程实例,介绍了厌氧发酵与生物接触氧化工艺在处理竹制品蒸煮废水工程中的应用。工程运行表明,该工艺运行稳定、投资少、处理成本低,出水水质各项指标均达到《污水综合排放标准》GB8978-1996一级排放标准。     

Comparative study on the morphology and mechanical strength of induction welding joint of polyetheretherketone under different currents

There is an increasing need for joining technologies of polyetheretherketone (PEEK), in which induction welding technique is one of the most promising methods. The induction welding experiment of PEEK thin plates was conducted under different input currents in this research, while metal meshes were selected as induction components. The analysis of morphology, microstructure, and elemental composition of welding joints was performed by optical microscope (OM), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Moreover, the mechanical strength of the induction-welding joint was investigated by tensile test. The results indicate that the PEEK can be joined effectively when the metal mesh is selected as an induction component, and the welding joints with good appearance are formed under the appropriate process parameters. The more induced joule heat produced by the higher input current promotes the resin fusion at the interface, which is propitious to reduce the generation of defects. However, the excessive heat input results in the extreme melting and thermal decomposition of PEEK resin, which will deteriorate the morphology and property of the welding joints. When the input current is 5.2A, the induction-welding joint can reach a maximum mechanical strength of 125.63 MPa, which increases by almost 60.55% through the optimization of welding parameters.     

热塑性塑料激光透射焊接研究

针对混合20%玻纤的丙烯腈-苯乙烯共聚物(AGS)热塑性塑料,进行激光透射焊接试验,得到了线能量对AGS焊接质量的影响规律。在线能量为0.75~1J/mm之间时,剪切强度可达18MPa以上,焊接质量最优。     

线密度测试方法应用分析

介绍振动法及称量法测试线密度的原理,对其优劣性进行了比较,并对如何改进振动法的不足提出了解决方法。     

LLDPE电缆料TJDL-9270的开发

介绍了线型低密度聚乙烯(LLDPE)电缆料TJDL-9270的性能特点和开发过程。根据电线电缆应用对树脂加工和机械性能的要求,确定了产品指标和生产技术路线及反应条件。分析了F催化剂产品的生产难点。提出了产品切换过程的关键控制要素。研制的TJDL-9270相对分子质量分布宽,易于加工,产品质量稳定,表面光洁度高,并具有优异的机械性能和耐环境应力开裂性能,完全适应高速电缆料的挤出应用。     

Effect of curing temperature on properties and solvent welding strength of ovalbumin

Effect of curing temperature on properties of ovalbumin has been investigated. Functional basis, crosslinking degree, tensile strength, and hardness increases with rising curing temperature. The increase of visible transmittance and the decrease of absorption accompany with increasing wavelength. The absorptive peak shows at 440–450 nm and the wavelength of the absorptive peak increases with the rising curing temperature. The relationship of joint strength with solvent welded joints of ovalbumin to their microstructure is also investigated. Ovalbumin can promote joint strength after the treatment of distilled water and curing. Comparing joint strength with fracture morphology, the smoother fracture surface morphology is related to the maximum tensile and shear joint strength, respectively. The joint strength is increasing with curing temperature and compressive stress, and the joint strength of treatment with 150°C curing temperature and 0.12 kgf/mm² compressive stresses are larger than its original tensile fracture strength of cured ovalbumin at same curing temperature. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Laser welding of niobium to AISI 304 steel using a copper interlayer

Abstract

Cu interlayers with thicknesses of 1, 1.5, and 2?mm were used to join niobium and AISI 304 steel. Fractures occurred in the weld, the Nb base metal, and the unmelted Cu interlayer when the Cu interlayer thickness was 1, 1.5, and 2?mm, respectively. When the thickness of the Cu interlayer was 1?mm, the weld microstructure consisted of austenite with Cu-rich particles along the austenitic grain boundaries and within the austenitic grains, a composite-like structure (the Fe₂Nb lamellae and particles in a γ matrix) embedded with coarse Cu globules, and a mixture of bulk Fe₇Nb₆, Nb-rich dendrites, and Cu matrix. The bulk brittle Fe₇Nb₆ phase embrittled the joint. However, when the thickness of the Cu interlayer was 1.5?mm, the weld microstructure consisted of austenite with Cu-rich precipitates along the austenitic grain boundaries and a Cu-rich phase embedded with Nb-rich particles and dendrites. Solid-solution strengthening of Cu by Fe was responsible for the improved mechanical properties of the joint. The mixture of Nb-rich particles and dendrites in the Cu matrix was also helpful in enhancing the joint strength. Furthermore, when the thickness of the Cu interlayer was 2?mm, the weld microstructure consisted of austenite with Cu-rich precipitates along the austenitic grain boundaries and within the austenitic grains, an unmelted Cu interlayer, and Nb-rich particles and dendrites embedded in a Cu matrix. The unmelted Cu interlayer reduced the joint strength.     

涤纶短纤维线密度不匀率的影响因素探析

阐述了涤纶短纤维线密度不匀率对质量的影响 ,分析了影响线密度不匀率的因素。结果表明减小熔体粘度波动、提高拉伸倍数、加大环吹滤网进风面积和调整集束丝束转角可降低线密度不匀率     

开口剂在LLDPE中的应用

通过无机、有机、复配开口剂对线型低密度聚乙烯(LLDPE)爽滑、开口性能的改进研究发现,添加复配开口剂可使LLDPE薄膜获得理想的爽滑、开口性能,并在LLDPE装置上成功实现工业化生产,且生产平稳可控.工业化产品测试结果表明:LLDPE产品PE-l的熔体流动速率为2.0 g/10 min,拉伸屈服应力为10.20 MPa;薄膜雾度为28.1%,动摩擦系数为0.342,静摩擦系数为0.307,薄膜爽滑、开口性能得到大幅改进,满足质量指标要求.     

塑化度与焊接条件对PVC-U型材焊角强度的影响

通过正交试验对比PVC—U型材塑化度和焊接条件对焊角强度的影响试验得知：焊接温度、加热时间及型材塑化度对焊角强度的影响较大,焊接时间与进给压力对焊角强度影响相对较小。型材塑化度在70％左右时具有较好的可焊性,适当提高焊接温度及延长加热时间有利于提高型材的焊角强度,焊接时间超过一定时间后则对焊角强度影响不大,根据型材截面不同进给压力有一最佳值。     

化学镀镍316不锈钢激光焊接裂纹研究

通过调整镀液中磷酸钠的质量浓度,在316不锈钢表面化学镀得到P质量分数分别为1.2％、2.3％和3.4％的镍镀层.对镀镍316不锈钢进行激光焊接实验,得到较佳的工艺参数为:激光功率50 W,脉冲宽度60 ns,焊接速率200 mm/s.当镀层中磷的质量分数为1.2％时,焊缝中无裂纹,剪切强度为242 MPa.随镀层中磷...     

On the melting behavior of isothermally crystallized 1‐octene linear low‐density polyethylene copolymers

The melting behavior of two 1‐octene linear low‐density polyethylene (LLDPE) copolymers is investigated. One made using Dow′s INSITE constrained geometry catalyst technology (LLDPE‐A) and the other using titanium‐based Ziegler–Natta catalysts (LLDPE‐B). Both have similar comonomer content as well as melt flow index. Differential scanning calorimetry (DSC) was used throughout the work. Isothermal crystallizations in the DSC for several times were carried out at various temperatures between 90 and 100°C for LLDPE‐A and between 105 and 112.5°C for LLDPE‐B. As a result of the isothermal crystallizations for both copolymers, multiple melting peaks are found in the DSC traces on subsequent heating. The melting behavior was also examined as a function of heating rate (1, 2.5, 5, 10, and 20°C/min). The multiple melting behavior indicates that they are inhomogeneous. In addition, a melting–recrystallization process was shown to be responsible for the appearance of one of the melting peaks in LLDPE‐B. A lowering in heating rate from the crystallization temperature favors the occurrence of melting–recrystallization during the dynamic experiment. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2022–2028, 2001     

茂金属线型低密度聚乙烯的结构与性能

利用傅里叶变换红外光谱、凝胶渗透色谱、差式扫描量热法和力学性能测量等手段表征了茂金属线型低密度聚乙烯(mLLDPE)和传统线型低密度聚乙烯(LLDPE)的结构及性能,用热分级法表征了LLDPE的片晶厚度多散性,测试了mLDPE薄膜的相关性能。结果发现,mLLDPE的片晶厚度分布指数为1.1347,小于传统LLDPE,表明其具有更好的支化均匀性,但其相对分子质量分布窄;mLLDPE薄膜具有较高的落镖冲击强度、撕裂强度、热封强度和突出的光学性能。     

线性低密度聚乙烯/有机蒙脱土纳米复合材料的制备及性能研究

通过熔融共混法制备了线性低密度聚乙烯／有机蒙脱土（LLDPEtOMMT）纳米复合材料,采用X-射线衍射分析（XRD）和透射电镜（TEM）对材料的结构进行表征,研究了OMMT的用量对LLDPE／OMMT纳米复合材料力学性能及阻燃性能的影响。结果表明,当OMMT的用量为30％（重量百分比）8寸,材料的极限氧指数（LOI）从180％提高到23．8％,热释放速率峰值（PHRR）从LLDPE的771．9kW／m2下降到5113kW／m2,下降幅度高达33．8％,表现出较好的阻燃性能;同时材料也呈现出良好的力学性能。     

The charring rate and charring depth of bamboo scrimber exposed to a standard fire

To better understand the charring properties of bamboo scrimber, a standard fire test was conducted to examine the effect of moisture content, exposure time, and grain direction on the charring rate of bamboo scrimber. The bamboo scrimber specimens were exposed to fire on one side with furnace temperatures following the requirements of ISO 834. The experimental results indicated the charring depth decreased as moisture content increased from 6% to 18%. Due to the thermal insulation of the char layer of bamboo scrimber, the charring rate decreased non‐linearly as the fire exposure time increased from 10 to 40 minutes. The charring rate of bamboo scrimber parallel to grain was approximately 1.23 times that perpendicular to grain. The non‐linear equation to express the charring rate of bamboo scrimber with moisture content, exposure time, and grain direction was established by regression analysis of the test data. The temperature of the char front was approximately 280°C, determined by heat transfer analysis of the 3‐dimensional finite element method model. Compared with different timber species in the literature and in standards, bamboo scrimber has better fire performance and a lower charring rate.