Evaluation of furfurylamines as curing agents for epoxy resins

Epoxy resin adhesives are widely used because of their strength, versatility, and ability to bond a variety of substrates. Furfurylamines represent a potential, new class of epoxy curing agents. Furfuryl amine (FA), tetrahydrofurfuryl amine (THFA), and 5,5′-methylenebis-2-furanmethanamine (DFA) were studied as possible epoxy curing agents. The utility of FA and THFA are limited by their volatility at the temperatures needed to effect cure of diglycidyl-ether of bisphenol A (DGEBA) based epoxy resins. DFA is a very effective epoxy curing agent with the ability to cure DGEBA at rates similar to that of standard epoxy curing agents such as liethylenetriamine.     

Fracture behavior of triglyceride‐based adhesives

The use of natural plant oils in the production of adhesives has been the focus of much research because natural oils are a renewable resource which have environmental and economic advantages over the petroleum‐derived chemicals used in traditional adhesives. The network formation and the stress–strain behavior of these plant oil–based adhesives is studied using a combination of simulation techniques. An off‐lattice Monte Carlo simulation has been developed to model the formation of these networks via the free‐radical copolymerization of the triglycerides present in natural oils. Networks of systems representing the triglycerides found in soybean oil, linseed oil, and olive oil are generated, as are networks made from other “theoretical” natural oils. The structure of the networks is characterized by percolation analysis. The stress–strain behavior of these networks is studied using large‐scale molecular dynamics simulations. Tensile strains are applied to the networks and it is observed that with increasing n the failure stress increases but the failure strain decreases. Also, for systems with low values of n, large voids form while the system is strained and then the system fails cohesively. However, for large n, no significant voiding is observed and the system fails close to the interface. The simulation results are shown to be consistent with the vector percolation theoretical prediction for how the failure stress relates to n. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3333–3343, 2004     

种植牙周围颌骨的骨重建模拟

研究的目的是通过骨重建模拟来预测种植牙植入后周围颌骨的密度分布情况.基于两种成熟且得到广泛应用的骨重建理论,提出了一种新的模拟骨重建的算法,该算法既包含了"死区效应",同时又是基于自组织控制过程.建立了包含种植体和颌骨在内的二维有限元模型,并用文中提出的算法对种植牙周围骨骼组织的密度分布情况进行了骨重建模拟,同时讨论了...     

Water‐Based Adhesives with Tailored Hydrophobic Association: Dilution Resistance and Improved Setting Behavior

Hydrophobic association and stimuli‐responsiveness is a powerful tool towards water‐based adhesives with strongly improved properties, which is demonstrated based on the example of hydrophobically modified alkali‐soluble latexes (HASE) with modulated association. Their rheological properties are highly tunable due to the hydrophobic domains that act as physical crosslinking sites of adjustable interaction strength. Ethanol, propanol, and butanol are used as water‐soluble model additives with different hydrophobicity in order to specifically target the association sites and impact the viscoelastic properties and stimuli‐responsiveness. The rheological and mechanical property response upon dilution with water can be tailored, and dilution‐resistant or even dilution‐thickening systems are obtained. The investigations are of high importance for water‐based adhesives, as our findings provide insight into general structure–property relationships to improve their setting behavior, especially upon contact with wet substrates.

     

Fast local reconstruction by selective backprojection for low dose in dental computed tomography

The high radiation dose in computed tomography (CT) scans increases the lifetime risk of cancer, which becomes a major clinical concern. The backprojection-filtration (BPF) algorithm could reduce the radiation dose by reconstructing the images from truncated data in a short scan. In a dental CT, it could reduce the radiation dose for the teeth by using the projection acquired in a short scan, and could avoid irradiation to the other part by using truncated projection. However, the limit of integration for backprojection varies per PI-line, resulting in low calculation efficiency and poor parallel performance. Recently, a tent BPF has been proposed to improve the calculation efficiency by rearranging the projection. However, the memory-consuming data rebinning process is included. Accordingly, the selective BPF (S-BPF) algorithm is proposed in this paper. In this algorithm, the derivative of the projection is backprojected to the points whose x coordinate is less than that of the source focal spot to obtain the differentiated backprojection. The finite Hilbert inverse is then applied to each PI-line segment. S-BPF avoids the influence of the variable limit of integration by selective backprojection without additional time cost or memory cost. The simulation experiment and the real experiment demonstrated the higher reconstruction efficiency of S-BPF.     

Applications of Raman spectroscopy in dentistry part II: Soft tissue analysis

Raman spectroscopy is rapidly moving from an experimental technique for the analysis of biological molecules to a tool for the real-time clinical diagnosis and in situ evaluation of the oral tissue in medical and dental research. The purpose of this study is to identify various applications of Raman spectroscopy, to evaluate the contemporary status, and to explore future directions in the field of dentistry. Several in-depth applications are presented to illustrate Raman spectroscopy in early diagnosis of soft tissue abnormalities. Raman spectroscopy allows researchers to analyze histological and biochemical composition of biological tissues. The technique not only demonstrates its role in the disclosure of dysplasia and malignancy, but also in performing guided biopsies, diagnosing sialoliths, and assessment of surgical margins. Raman spectroscopy is used to identify the molecular structures and their components to give substantial information about the chemical structure properties of these molecules. In this article, we acquaint the utilization of Raman spectroscopy in analyzing the soft tissues in relation to dentistry.     

Effect of Polymer Degree of Conversion on Streptococcus mutans Biofilms

Biofilm–material interactions are increasingly recognized as critical to success of some materials/devices and failure of others. We use a model system of dental monomers, salivary pellicles, and oral biofilms to demonstrate for the first time that degree of conversion of cross‐linked dimethacrylate polymers alters biofilm metabolic activity. This response is due primarily to leachable release (not surface chemistry) and is complex, with no changes in some biofilm measurements (i.e., biomass), and time‐ and leachable‐dependent responses in others (i.e., metabolic activity). These results highlight the need for considering biofilm‐material interactions when designing/evaluating new materials.

     

Development and thermo‐mechanical behavior of nanocomposite epoxy adhesives

Two kinds of organo‐modified (OM) clays were dispersed in an epoxy resin for the preparation of nanocomposite adhesives at various filler amounts. XRD tests evidenced the formation of intercalated structures, increasing the intercalation degree with the clay hydrophilicity. The original transparency of the samples was retained up to a filler content of 3 wt%, and then decreased due to filler agglomeration. The glass transition temperature of nanocomposites filled with the more hydrophilic clay (30B) raised up to a filler content of 3 wt% and then decreased, probably because of the concurrent and contrasting effects of the physical chain blocking and reduction of the cross‐linking degree. Also elastic modulus, stress at break, and fracture toughness were sensibly improved by nanoclay addition up to filler loadings of 0.5–1 wt%. For higher concentrations the positive contribution of clay nanoplatelets was counterbalanced by the presence of agglomerated tactoids in the matrix. Mechanical tests on single‐lap composite (epoxy/glass) bonded joints evidenced an enhancement of the shear strength by about 25% for an optimal filler content of 1 wt%. Therefore, it was concluded that the addition of a proper amount of OM clay to epoxy adhesives could represent an effective way to improve the shear resistance of adhesively bonded composite structures. Copyright © 2011 John Wiley & Sons, Ltd.     

Bis-GMA复合牙科材料的合成和抗菌改性

以甲基丙烯酸缩水甘油酯（GMA）修饰聚六亚甲基胍盐酸盐（PHMG）,制备端基具有甲基丙烯酸酯基的抗菌改性剂PHMG-GMA。将PHMG-GMA与树脂双酚A-甲基丙烯酸缩水甘油酯（Bis-GMA）、稀释剂二甲基丙烯酸二缩三乙二醇酯（TEGDMA）、填料纳米SiO2、光引发剂樟脑醌（CQ）混合均匀,经紫外灯固化后得到了具有抗菌性能的复合牙科材料。测试了该材料的抗菌性能,研究了SiO2、PHMG-GMA的加入对紫外透过率的影响。结果表明：随着SiO2含量的增加,材料的紫外透过率下降。当PHMG-GMA的质量分数为1.0%时,复合牙科材料对变形链球菌的抑菌率达到99.99%。     

气相色谱法测定胶粘剂中的游离甲醛

采用超声波萃取胶粘剂中游离甲醛,经2,4-二硝基苯肼衍生后用气相色谱一电子捕获检测器法测定．对提取方法、衍生化条件及色谱条件进行了研究,确定了甲醛检测的最佳条件．研究数据显示,该方法对甲醛的检出限为0．175μLg／g,在0．1～60．0μg／mL浓度范围内,线性相关系数R^2=0．9999;在1、2和8μg／mL3个添加水平下的添加回收率在98．97％-102．24％之间,5个实验室对同一样品中甲醛含量测定值的相对标准偏差为4．0％．结果表明本方法简便、快速、检测限低、回收率高、重现性好．