Foaming conditions of high density polyethylene–natural rubber blends

Abstract

Foams made from high density polyethylene (HDPE) and natural rubber (NR) blends, using azodicarbonamide as a chemical blowing agent, have been investigated to establish a relationship between the structure and physical properties. The blends of HDPE, NR, epolene wax, chemical blowing agent, and necessary ingredients were prepared on a two roll mill. Subsequently, foamed structures of the blends were obtained by a single stage compression moulding. Results indicate that foaming process variables, i.e. heating time, blowing agent loading, ratio of HDPE/NR, crosslinking agent loading, and ratio of HDPE/NR at a fixed crosslinking agent loading, affect the physical properties of the foams. Attempts were made to relate such properties as foam density, hardness, tensile strength, elongation at break, tear strength, flexural strength, elastic modulus, and gel content to the foam structure. The foam structure was investigated using optical microscopy, in terms of the average cell size and its distribution.     

Microwave processing of thermosets: non-contact cure monitoring and fibre optic temperature sensors

Abstract

Conventionally, curing thermosetting resins involves heating the sample in an autoclave or an oven where heat is transferred to the sample through conduction and convection involving long processing time. Microwave curing offers an efficient alternative to thermal processing as heating occurs directly inside the sample resulting in lower energy consumption and faster curing. However, it requires non-metallic cure monitoring systems. In this study, a non-contact fibre optic probe was constructed and deployed inside a custom-modified microwave oven to record near-infrared (NIR) spectra, in real-time, of a thermoset undergoing cure. Simultaneous spectroscopic and temperature data on the sample during cure have been obtained for a range of microwave power levels. Comparison is also made between a sample cured in the microwave oven with one cured conventionally. In the final part, two optical fibre temperature sensors were designed and evaluated with an aim to use them in the microwave oven for temperature metrology. The sensors were based on the Fabry-Perot interferometer. The first sensor was evaluated from ambient to 400°C with an accuracy of ± 1·0°C, while the second sensor was tested from ambient to 300°C. The accuracy of the second sensor was ± 0·5°C.     

Cure Characteristics of Phenol-Formaldehyde Resin Catalyzed with Ba(OH)2

Phenol-formaldehyde resins are high performance wood adhesives, and are also used to impregnate base papers which are manufactured high-pressure laminates applied in furniture and interior decoration. In this investigation, PF resins catalyzed with Ba(OH)₂ were studied. Both Ba(OH)₂ content and F/P molar ratio were found to influence the cure rate. The cure rate of the Ba(OH)₂ catalyzed PF resin was faster by 50% than that of ordinary PF resin at 150°C. The DSC results showed that the Ba(OH)₂ catalyzed PF resin was cured at a lower temperature than the ordinary PF resin. And the IR results showed that the Ba(OH)₂ catalyzed PF resin has higher degree of ortho-position coupling.     

In situ cure monitoring of adhesively bonded joints by dielectrometry

Since the reliability of adhesively bonded joints is much dependent on the curing status of thermosetting adhesives, the in situ cure monitoring during the cure of adhesive joints could improve the quality of adhesively bonded joints as it enables one to control the cure parameters. In this work, a dielectric method which measures the dissipation factor of the adhesive during the cure of joints and converts it into the degree of cure of the adhesive was devised. Steel adherends were used for the adhesively bonded joints because the steel adherends worked as the electrodes for the measurement of dissipation factor without additional electrodes. The relation between the dissipation factor and the degree of cure of adhesive was investigated, which could eliminate the temperature effect on the dissipation factor that is largely affected by the degree of cure and temperature of adhesive. Comparing the results obtained by the method developed with those by DSC (differential scanning calorimetry), it was found that the dissipation factor showed a trend similar to the cure rate of the adhesive.     

聚类算法在木材缺陷图像分割中的应用

数据聚类是数据挖掘、模式识别、图像处理和数据压缩等领域的一个重要方法。针对不同的数据对象类型，不同的聚类目的和应用，有多种聚类算法可供选择。分别用K-means，BIRCH，CURE对原木CT图像数据进行聚类，分析三者在聚类时间、聚类质量以及对参数的敏感程度的特征。     

Moisture durability of four moisture cure urethane adhesives

Moisture durability of four low modulus adhesives was examined. The four low modulus adhesives all had the same basic moisture cure polymer but contained different fillers and additives. Hot-dipped galvanized steel was bonded to random fiber-reinforced unsaturated polyester and aged in two moisture environments for various durations. Adherend surface wipes included acetone, isopropyl alcohol and a typical surface contamination for galvanized steel (an organic lubricant). Diffusion coefficients, moisture uptake and modulus changes due to moisture environment were determined for the adhesives and the fiber-reinforced plastic (FRP). The moisture cure adhesive with clay and poly(vinyl chloride) (PVC) as fillers (adhesive 252) had the highest retained lap joint strengths. Initially, adhesive 252 had single lap joint strengths of 1.47 ± 0.08 MPa for acetone-wiped joints and 1.39 ± 0.33 MPa for organic lubricant-wiped joints. After accelerated aging in a cataplasma environment for 9 weeks, lap joint strengths fell to 0.61 ± 0.08 MPa for acetone-wiped joints and to 0.65 ± 0.11 MPa for organic lubricant-wiped joints. Environmental scanning electron microscopy (ESEM) and energy-dispersive spectrometry (EDS) showed that the actual failure locus was through a corroded zinc layer and between the adhesive and the zinc surface after aging. Dynamic mechanical analysis (DMA) showed that the modulus for adhesive 252 dropped from 21.7 to 13.9 MPa after cataplasma aging. From finite element analysis (FEA), this modulus drop corresponded to a drop in normal stress concentration from 0.75 to 0.57, and a drop in shear stress concentration from 1.41 to 1.36 at a point 0.5 mm from the end of the single lap joint overlap.     

应用聚类算法的WebGIS对象预获取策略的研究

WebGIS利用Internet技术在Web上发布空间数据提供给用户浏览和使用,但在进行远程访问时常会产生严重的响应延迟。本文针对这一问题,将改进后的CURE算法应用于WebGIS的对象预获取过程。保证了预测的准确率,同时减少了用户访问的响应时间。     

基于马氏距离的双层聚类电力远动异常检测

通过对电力远动监测系统和数据挖掘技术的讨论,提出一种基于马氏距离的双层聚类异常检测算法。针对远动系统数据非球面分布的特点,该算法通过K-means聚类改进算法对数据进行初始分类,然后使用基于马氏距离的Clustering Using Representatives(CURE)聚类改进算法对初始分类结果进行优化,以较少的计算成本去除K值设定的影响,达到预期的检测结果。同时,基于马氏距离的CURE聚类改进算法对球面和非球面分布的数据有非常好的适应能力。     

基于CURE聚类算法改进的原型选择算法

针对传统K近邻分类器在大规模数据集中存在时间和空间复杂度过高的问题,可采取原型选择的方法进行处理,即从原始数据集中挑选出代表原型（样例）进行K近邻分类而不降低其分类准确率.本文在CURE聚类算法的基础上,针对CURE的噪声点不易确定及代表点分散性差的特点,利用共享邻居密度度量给出了一种去噪方法和使用最大最小距离选取代表点进行改进,从而提出了一种新的原型选择算法PSCURE （improved prototype selection algorithm based on CURE algorithm）.基于UCI数据集进行实验,结果表明：提出的PSCURE原型选择算法与相关原型算法相比,不仅能筛选出较少的原型,而且可获得较高的分类准确率.     

引入信息熵的CURE聚类算法

为了提高传统CURE(Clustering Using REpresentatives) 聚类算法的质量,引入信息熵对其进行改进。该算法使用K-means算法对样本数据集进行预聚类;采用基于信息熵的相似性度量,利用簇中的元素提供的信息度量不同簇之间的相互关系,并描述数据的分布;在高层、低层聚类阶段,采取不同的选取策略,分别选取相应的代表点。在UCI数据集和人造数据集上的实验结果表明,提出的算法在一定程度上提高了聚类的准确率,且在大型数据集上比传统CURE算法有着更高的聚类效率。