Surface Mechanical Properties of the Spore Adhesive of the Green Alga Ulva

The mechanical properties of the adhesive produced by spores of the green, marine, fouling alga Ulva linza are reported. Atomic force microscopy studies were performed and nanoindentation data were analyzed using a model for an asymmetric indenter. Freshly secreted adhesive is characterized by multiple layers. We found that the modulus of the outer ～600-nm thick layer was about 0.2 ± 0.1 MPa, whereas the modulus of the inner layer was about 3 ± 1 MPa. Older adhesive showed the formation of a “crust” of harder material with a yield strength of ～20 MPa at a loading rate of 2.5 × 10^?6 N · s^?1. Mechanical properties under tension are also described, and extension profiles that showed either constant or nonlinear force changes with tip-sample separation were observed. Models for both kinds of behavior are described. The work of adhesion between poly-dimethylsiloxane (PDMS)-coated AFM tips and the adhesive was determined to be less than 1.5 mJ · m^?2.     

Surface Mechanical Properties of the Spore Adhesive of the Green Alga Ulva

The mechanical properties of the adhesive produced by spores of the green, marine, fouling alga Ulva linza are reported. Atomic force microscopy studies were performed and nanoindentation data were analyzed using a model for an asymmetric indenter. Freshly secreted adhesive is characterized by multiple layers. We found that the modulus of the outer ∼600-nm thick layer was about 0.2 ± 0.1 MPa, whereas the modulus of the inner layer was about 3 ± 1 MPa. Older adhesive showed the formation of a “crust” of harder material with a yield strength of ∼20 MPa at a loading rate of 2.5 × 10^-6 N · s^-1. Mechanical properties under tension are also described, and extension profiles that showed either constant or nonlinear force changes with tip-sample separation were observed. Models for both kinds of behavior are described. The work of adhesion between poly-dimethylsiloxane (PDMS)-coated AFM tips and the adhesive was determined to be less than 1.5 mJ · m^-2.     

Chemistry of the reduction of Ellman's reagent by ascorbic acid

Ellman's reagent is reduced in two stages by ascorbic acid in the presence of copper ions. The first stage involves some reversible steps and is associated with the formation of dehydroascorbic acid. In this stage, the disulphide compound probably accepts electrons in place of oxygen. The reducing power of 2,3-diketogulonic acid, formed by delactonisation of dehydroascorbic acid, probably effects the second stage of reduction. This is only observed upon addition of EDTA at specified intervals. Two moles of sulphydryl anions are formed per mole of disulphide. The reaction is useful for following the copper catalysed oxidation of low concentrations of ascorbic acid, but is complicated by the effects of copper ion and the hydrogen peroxide formed on the coloured anion.     

环氧树脂低温固化剂在建筑胶黏剂中的应用

用抗压强度、剪切强度、不同温度下的固化时间研究环氧树脂低温固化剂的性能 ,从多种固化剂中选择适合需要的品种 ,配成建筑胶黏剂解决环氧树脂低温固化难的问题。随着温度的进一步降低 ,环氧树脂的固化更趋缓慢。     

固化剂对酚醛树脂灌封胶性能的影响

为满足灌封胶黏剂中温固化耐高温的要求,研制新型耐高温灌封胶黏剂体系是十分重要的。研究了酚醛树脂固化剂对酚醛树脂挥发份、粘接强度、玻璃化转温度、固化温度等的影响,确定了固化剂和酚醛树脂最佳固化比例。表明采用的酚醛树脂固化剂可以显著降低酚醛树脂的挥发份,降低酚醛树脂固化温度,提高常温粘接强度,缺点是使酚醛树脂的玻璃化转变温度和高温剪切强度稍有下降,显示了固化剂的优异性能。该胶黏剂作为中温固化耐高温灌封胶黏剂可以满足航空工业耐高温的技术要求。     

预聚物对UV固化胶黏剂性能的研究

预聚物作为胶黏剂的主要成膜物质,它的性能基本决定了固化后胶黏剂的主要性能.采用不同类型的丙烯酸酯共混聚合的方法研究了预聚物对紫外光固化胶黏剂性能的影响.主要讨论了预聚物的种类、含量及复配对胶黏剂的固化速率、黏附力及粘接强度的影响.实验发现预聚物的种类和含量是胶黏剂的主要影响因素,脂肪族聚氨酯丙烯酸酯6148J和改性脂肪族聚氨酯丙烯酸酯6079性能较好,且二者比列为3:7,含量为50%时胶黏剂综合性能较好.     

紫外光(UV)固化胶黏剂收缩率与强度的研究

UV胶黏剂的固化收缩率与固化后的残留应力乃至粘接强度有着密切关系。对比UV胶黏剂中不同丙烯酸单体、几种低聚物和阳离子单体的收缩率和相应的粘接强度。讨论了单体和树脂类型对收缩率和粘接强度的影响。介绍了以低收缩丙烯酸酯树脂和阳离子树脂为主体树脂,以低收缩单体为稀释剂、配合填料和适当增强剂制备出混合型UV胶黏剂。该胶黏剂粘接强度和耐久性好,其固化收缩率为3．5％,远低于普通自由基型UV胶黏剂。经湿热老化试验后,粘接强度保持率仍保持在80％。     

The Effect of Adherends on the Curing of an Epoxy Adhesive

The effect of E-glass, cured vinyl ester resin, and silica gel on the curing of an epoxy-anhydride adhesive was examined. The techniques used were calorimetry in both isothermal and scanning modes and Fourier transform infrared spectroscopy in the attenuated total reflectance (ATR-FTIR) mode. Isothermal calorimetry was used to obtain the exotherm, conversion rate, and curing kinetic parameters, and scanning calorimetry was used to obtain the glass transition temperature. ATR-FTIR was used to study the curing kinetics and chemistry of the adhesive. The results suggest either the immobilization of a layer of the epoxy adhesive adjacent to inert solid surfaces or selective adsorption of the accelerator or both, each of which suppresses the cure reaction. This was reversed by the presence of adsorbed water. At least for this epoxy-anhydride system, adsorbed water seems to have had the beneficial effect of increasing the crosslink density in the interfacial region between the adhesive and adherend. Water seems also to change the overall cure reaction, causing more ether formation and less ester formation than without water. An additional finding was that the cured vinyl ester surface appeared to have a catalytic effect on the reaction, perhaps in conjunction with the accelerator, benzyldimethylamine.     

Influence of Dynamic Loading and Different Adhesive Systems on the Microleakage in Root Canals

Abstract

The objective of this study was to evaluate the influence of dynamic loading and different adhesive systems on the microleakage in root canals.

80 human premolars were used in this study. The crowns of the teeth were sectioned at the cemento-enamel junction using a low speed diamond saw. After post space preparation, the roots were randomly assigned to 4 groups (n = 20) and restored with different adhesive systems. Group 1: Rely X ARC (RA) + Single Bond (SA), Group 2: Clearfil SA Cement (CL), Group 3: Panavia F 2.0 (PAN), Group 4: Rely X Unicem (RU). All the teeth were restored with the same type of glass fiber post and coronal cores built up with light-polymerizing hybrid composite resin. Half of the specimens of each group (n = 10) were subjected to additional dynamic loading in a universal testing machine. Apical parts of the roots were attached to computerized fluid filtration device for leakage measurement.

The two-way ANOVA test was used first to detect overall significance, followed by two-sample t-test to identify which pairs of groups had significant differences. For each outcome statistical significance was set at p < 0.05. Dynamic loading significantly increased the microleakage values for Rely X ARC (p = 0.005), Clearfil SA Cement (p = 0.002) and Rely X Unicem groups (p = 0.001) but Panavia F 2.0 group was not affected by the dynamic loading (p = 0.111). One-way ANOVA test was applied to detect any significant differences in microleakage values for the adhesive systems. In the unloaded groups, there is no difference between the adhesive systems (p = 0.13). For the dynamically loaded groups, there is only significant difference between PAN and RA groups (p = 0.010). Post-hoc pairwise comparisons were done using Tukey’s multiple comparisons. Differences between Rely X ARC-Clearfil SA Cement and Rely X ARC-Panavia F 2.0 are statistically significant (p = 0.009, 0.013).     

耐高温丙烯酸酯乳液压敏胶的固化及性能研究

将环氧有机硅固化剂9301以及异氰酸固化剂2102加入到增黏丙烯酸酯乳液中,成功制备出耐高温丙烯酸酯压敏胶。研究压敏胶的固化行为,探讨固化剂的种类和用量对压敏胶粘接性能及耐温性的影响。结果表明:固化剂与复合物发生了交联反应,9301和2102固化体系的适宜固化条件分别为150℃/5min和110℃/3min。随着固化剂用量增加,压敏胶的凝胶率和玻璃化转变温度提高,剥离时由内聚破坏转变为界面破坏,初黏力与剥离强度降低,耐高温性能得到改善。当9301与2102用量为2wt%时,压敏胶的剥离强度分别为11.6N/25mm与10.2N/25mm,可耐180℃高温。     

Effect of Synthesis Conditions on the Structure and Curing Characteristics of High-Urea Content PUF Resin

Phenol-urea-formaldehyde (PUF) resins of high urea content were prepared at different hydroxyl/phenol (OH/P) mole ratios and formaldehyde/(phenol + urea) [F/(P + U)] mole ratios. The effect of synthesis parameters including OH/P and F/(P + U) mole ratios on the structure, composition, and curing characteristics of PUF resins were investigated by using both liquid ¹³C nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC). The NMR analysis indicated that an increase in the OH/P mole ratio and/or F/(P + U) mole ratio decreased the amount of unreacted urea and monosubstituted urea, and promoted the formation of polysubstituted urea. The DSC results showed that the higher OH/P mole ratio and/or F/(P + U) mole ratio of PUF resins resulted in a lower curing temperature. The F/(P + U) mole ratio of PUF resins seemed to have a more significant accelerating effect on the curing reaction than the OH/P mole ratio.     

抗焦剂对粘胶基碳纤维碳化收率及抗拉强度影响因素的研究

通过实验研究了抗焦剂在粘胶基碳纤维生产过程中对碳化收率、抗拉强度的影响。实验表明:经浓度为5%的磷酸氢二铵处理后的粘胶原丝,其碳化收率最高,抗拉强度最大。     

PET薄膜表面性能及其与紫外光固化涂层粘接性能相关性研究

通过粘结性能实验研究了表面处理方法对PET薄膜/紫外光固化涂层体系粘接性能的影响,结果表明:表面处理提高了PET薄膜/涂层体系粘接强度。研究了PET表面处理对PET表面性能如表面形貌、光泽度(粗糙度)、表面张力、表面官能团含量的影响,结果表明:PET薄膜经电晕处理后,其表面粗糙度有增大的倾向,而涂层处理对PET薄膜表面粗糙度无影响;经电晕处理和底涂处理后,PET薄膜表面张力均有增加,底涂处理提高PET薄膜表面张力的幅度更大。研究了PET薄膜表面性能与剪切强度的关系,发现PET薄膜/涂层粘接体系剪切强度τ与PET薄膜表面张力γ具有线性关系。     

The Effect of Hyperbranched Polyester Epoxy Resin on the Curing Kinetics and Thermal Degradation Kinetics of the Diglycidyl Ether of Bisphenol-A Epoxy Resin

Hyperbranched poly(trimellitic anhydride butylene glycol)ester epoxy (HTBE) has relatively low viscosity and high molecular mass and holds great promise as a functional additive for enhancing the strength and toughness of thermosetting resins. The effect of molecular mass or generation and content of HTBE on the activation energy, reaction order, and curing time was discussed using DSC and TG techniques. The results indicated that HTBE could accelerate the curing speed and reduce the activation energy and reaction order of the curing reaction, and the thermal degradation activation energy (Ea ₂) of HTBE/DGEBA hybrid resin also decreased remarkably in high temperature section.     

纸塑复膜胶粘接性的影响因素及改善粘接性的对策

通过各组分用量对纸塑复膜胶粘接力影响的讨论,提出了改良粘接性方面的对策.     

The Effect of Ageing and Environment on the Static and Fatigue Strength of Adhesive Joints

This paper describes the results of a durability programme designed to test the effects of ageing and environment on the performance of adhesive joints. Specimens were kept under a variety of loading and environmental conditions and the paper reports results of static and fatigue tests after 8-9 years storage. Some adhesive joints showed excellent durability performance, while others were adversely affected by the environment, particularly high humidity and natural exposure. It was found that the effect of ageing on static and fatigue performance is not necessarily the same.     

氟橡胶配方硬度、硫化体系及焦烧特性对其与金属粘接性能的影响

以氟橡胶与丁字铁粘接为例,研究了氟橡胶与金属铁粘接的课题,发现粘接效果与橡胶配方的硬度、焦烧特性以及硫化体系都有着密切的关系。研究表明,氟橡胶的邵尔A硬度为65时,其与基材的粘接强度优于其他硬度时;在硫化体系方面,双酚AF/BPP硫化体系优于3#硫化剂体系和过氧化物硫化体系;随着t10、t90时间差的延长,粘接性能提高。     

化学试剂重铬酸盐对过滤材质腐蚀分析及滤材的选择

分析了在化学试剂重铬酸钾、重铬酸铵生产中,它们对纤维素滤纸以及聚丙烯PP微孔折叠滤芯的腐蚀的机理。选择了适用于化学试剂重铬酸盐生产的砂芯滤器,解决了在化学试剂重铬酸盐生产中由于滤材选择不当导致水不溶物难以符合GR级规格的问题。     

增黏树脂差异性对热熔压敏胶外观及性能的影响

热熔压敏胶是一类集热熔和压敏双重特性的胶黏剂。松香树脂、萜烯树脂及石油树脂作为增黏剂较为广泛地应用于热熔压敏胶中。研究发现,由于生产原料及生产工艺的细小差别,不同厂家生产的同类型增黏树脂在空间结构和相对分子质量上均有差异,所制备的热熔压敏胶性能也明显不同。这种差异性对控制热熔压敏胶的产品质量是非常不利的,对我国松香树脂及萜烯树脂产品的出口有很大影响。因此,研究生产原料的组成、生产工艺、分子结构对松香树脂、萜烯树脂的应用性能的影响是非常有意义的。