Influence of radiant exposure on degree of conversion,water sorption and solubility of self-etch adhesives

The purpose of this study was to investigate the influence of the radiant exposure on the degree of C=C conversion (DC), water sorption (WS), and solubility (S) of the Clearfil SE Bond (CSE) and Filtek LS (LS) self-etch adhesive systems. The primer of the LS (LSP), and bond agents of the CSE (CSEB) and LS (LSB) were tested. Specimens were light-cured using a light-emitting diode (LED) at different radiant exposures (6.1, 12.2, 13.9, and 27.8 J/cm²). DC (n=10) was measured using Fourier-transform infrared spectroscopy (FT-IR). WS and S were determined according to ISO 4049. Data were subjected to two-way ANOVA and Tukey's test at pre-set alpha of 0.05. The highest DC was exhibited by LSP, followed by CSEB and LSB, all with statistical difference (p<0.001). The DC was increased with higher radiant exposure and extended light-curing time (p<0.001). LSB and CSEB showed the lower WS followed by LSP, all with statistical difference (p<0.001). CSEB and LSB presented no significance difference on the S values (p>0.05) and were lower than LSP (p≤0.05). The WS and S were not influenced by the different radiant exposures evaluated (p=0.9548 and p>0.05, respectively). The monomer conversion is related to improvement on the mechanical properties of resinous material, but these properties also depend on the polymer network structure formed.     

Photopolymerization and structure formation of methacrylic acid based hydrogels in water/ethanol mixture

Hydrogels are a desired material for biomedical and pharmaceutical applications. To better control the synthesized hydrogels for various applications, it is necessary to have a thorough understanding of hydrogel structure and reaction mechanism. In this study, pH-sensitive hydrogel networks consisting of methacrylic acid (MAA) crosslinked with tri(ethylene glycol) dimethacrylate (TEGDMA) were synthesized by free-radical photopolymerization in the water/ethanol mixture. Reaction rate was measured using Photo-differential scanning calorimetry (PhotoDSC) with a modified sample pan designed for handling volatile reagents. A photo-rheometer and a dynamic light scattering (DLS) goniometer were used to follow the changes in viscosity and molecule size of the resin system during photopolymerization. It was found that the rate of polymerization increased and more compact and less swelling gels would form with a higher water fraction in 50 wt% solvent/reactant mixture. This is because the weaker interactions between the MAA and the solvent give a higher opportunity for propagation and a higher reaction rate. And the hydrophobic TEGDMA and initiator tend to form aggregates in the higher water solution, contributing to the inhomogeneous microgel formation. This mechanism is conformed by viscosity measurement, DLS analysis, scanning electron microscopy (SEM) observation, and kinetics analysis.     

Investigation on the effect of fiber wettability on water absorption kinetics of geopolymer composites

Fiber-reinforced geopolymer composites receive widespread attention due to their desirable mechanical properties but the effect of fiber wettability on the water transport properties is rarely investigated. This work aims to reveal the effect and mechanism of hydrophilic and hydrophobic fibers, represented by polyvinyl alcohol fiber (PVAF) and polypropylene fiber (PPF), on the water absorption kinetics of geopolymer composites. Results indicate that both fibers can slightly weaken the water absorption capacity due to increased micron-scale voids and capillary length. Moreover, waterproof composite with a water contact angle of ～120° can be fabricated by adding PPF and polydimethylsiloxane. PPF weakens the vaporization-condensation process of moisture, thereby extending the duration of the induction stage by 16.7 h, within which a low water absorption rate is maintained. In contrast, hydrophilic PVAF promotes the water absorption process. Therefore, hydrophobic fibers are more beneficial to improve the waterproof performance of geopolymer composites. The development of waterproof fiber-reinforced geopolymer composites is of great potential to improve the corrosion resistance and durability of buildings serving in high-humidity environments.     

Absorption and glass transition temperature of adhesives exposed to water and toluene

If adhesives are to be used in practical applications, such as for aerospace or marine components, it is essential that their long-term behaviour when exposed to aggressive environments, natural or man-made, should be known. The objective of this paper is to determine the liquid absorption behaviour of epoxy adhesives under complete immersion in two solvents (water and toluene) at two different temperatures (room temperature and 60 °C) and the effect on their glass transition temperature (T_g). The specimens were periodically removed from their environment for weighing and T_g measurement, the latter by using a rapid method which was developed previously by the authors. The rate of weight gain of the specimen (sorption) and the equilibrium level were higher for the higher temperature immersion than for the low temperature. The equilibrium level reached for toluene was higher than that of water. The values of T_g were significantly influenced by the liquid uptake. Finally, heating to a temperature above the T_g of the adhesive, even in a very short time, was found to significantly influence the results of the liquid uptake.     

Effects of phosphorus-containing additives on soy and cottonseed protein as wood adhesives

Soy and cottonseed proteins appear promising as sustainable and environment-friendly wood adhesives. Because of their higher cost relative to formaldehyde-based adhesives, improvement in the adhesive performance of proteins is needed. In this work, we evaluated the adhesive properties of soy and cottonseed protein formulations that included phosphorus-containing acids and esters. For cottonseed protein isolate, most of these additives improved dry adhesive strength, with methylphosphonic acid, phosphorous acid, and phosphoric acid increasing the dry strength by 47, 44, and 42%, respectively, at their optimal concentrations. For soy protein isolate, these additives did not show significant benefits. The phosphorus-containing additives also improved the hot water resistance of the cottonseed protein formulations but showed either no effect or a negative effect for the of soy protein formulations. Thus, the combination of cottonseed protein with phosphorus additives appears to be attractive as wood adhesives.     

Study and optimization of water repellence stability in fluoroacrylate photopolymers

Fluoropolymers have attracted a lot of attention in the past 20 years mainly due to their hydrophobic properties. Unfortunately, they have also shown some stability issues mainly in hot water due to the easy disorganization of the fluorine chains. In this paper Confocal Raman Microscopy (CRM) has been used as an indirect probe to optimize the fluoroacrylate content in an acrylic photocurable resin in order to reduce the effect of hot water. Advancing and receding contact angles have also been measured to characterize the surface repellence both before and after immersion in hot water. Results show that despite an improvement of the stability of the fluoroacrylate coating with a careful selection of the concentration range, water still has a negative effect on the surface properties of the coating. This effect can be partly counterbalanced by successive thermal annealings at 100 °C which help to stabilize the hydrophobicity of the coating.     

Studies on the toughness and water resistance of zein-based polymers by modification

To develop novel biodegradable materials, zein was modified using polycaprolactone (PCL)/hexamethylene diisocyanate (HDI) prepolymer. The modified zein polymers, containing various PCL-HDI components (PCLH) content and plasticized by Dibutyl l-tartrate (DBT), were compression-molded. Mechanical properties, water resistance, thermal properties and morphology of the molded zein-based sheets were investigated. The toughness was improved significantly by a small amount of PCLH due to the existence of micro-phase separation structure in the sheets. In particular, zein exhibited better mechanical properties when modified by 20-50 wt% PCLH, and when the corresponding sheets were immersed in water for 24 h than when stored in 75% relative humidity. This implies an excellent water resistance. Thermal analysis indicated that the formation of physical cross-linking from PCLH segment extension, and the plasticization of water to the zein matrix, improved the water resistance of modified zein sheets. DBT had a stronger interaction with zein than with PCLH, and was considered as a compatibilizer for zein matrix and PCLH component in modified zein sheets.     

Shear strength and water resistance of modified soy protein adhesives

Soy protein polymers recently have been considered as alternatives to petroleum polymers to ease environmental pollution. The use of soy proteins as adhesives for plywood has been limited because of their low water resistance. The objective of this research was to test the water resistance of adhesives containing modified soy proteins in walnut, maple, poplar, and pine plywood applications. Gluing strength and water resistance of wood were tested by using two ASTM standard methods. Glues with modified soy proteins had stronger bond strength than those containing unmodified soy proteins. Plywood made with glue containing urea-modified proteins had higher water resistance than those bonded with glues containing alkali-modified and heat-treated proteins. After three 48-h cycles of water-soaking, followed by 48 h of air-drying, no delamination was observed for either walnut or pine specimens glued with the urea-modified soy protein adhesives. Gluing strength for wood species with smooth and oriented surface structure was lower than for those with rough, randomly oriented, surface structures. Wood species with greater expansion of dimensions during water-soaking had a higher delamination rate than those showing less expansion.     

纳尔科水处理技术在循环水冷却系统的应用

介绍了中国石油大庆石化分公司水气厂第一循环水冷却系统,通过采用纳尔科公司的A.Z.Lite水处理方案、HSP高效分散技术及Trasar技术,使循环水浓缩倍数从3倍提高到5倍以上,从而实现了较好的节水效益。     

Insight into the wetting and interfacial behavior of Cu-Ti/ZrB2 system: A combined experimental and DFT calculation

The wetting of ZrB₂ ceramic by molten pure Cu, Cu-(20, 30, 40, 50 at.%)Ti alloys were performed by the sessile drop method under vacuum of ∼4 × 10⁻⁴ Pa in the 1030−1070 °C temperature range. The wetting and interfacial behaviors of Cu-Ti/ZrB₂ systems were analyzed and discussed. Furthermore, the work of adhesion and electronic properties of the Cu(1 1 1)/ZrB₂(0 0 0 1) and Ti(0 0 0 1)/ZrB₂(0 0 0 1) atomic interfaces were quantitatively evaluated by first-principles method. The wettability is significantly improved with the Ti concentration or wetting temperature increasing as a result of the formation of (Ti) solid solution at interface. The calculated results show that the B-terminated ZrB₂ (0 0 0 1) surface is preferable to bond with Ti(0 0 0 1) surface, and the electronic structure reveals that the dominant interfacial bonding is the Ti-B ionic bond for the Ti/B-terminated ZrB₂ interface.     

Synthesis and photopolymerization kinetics of new flexible diacrylate and dimethacrylate crosslinkers based on C18 diacid

A series of new di(meth)acrylate monomers was synthesized from the reactions of methyl α-hydroxymethylacrylate (MHMA), ethyl α-hydroxymethylacrylate (EHMA), hydroxyethyl acrylate (HEA) and hydroxyethylmethacrylate (HEMA) with α,ω-C18 diacid chloride. The photopolymerization behavior and reaction kinetics of the synthesized monomers were investigated using photoinitiation with differential scanning calorimetry. The polymerization rates, conversions and kinetic constants for propagation and termination were determined for each of the monomers. The maximum rate of polymerizations of the diacrylate monomers was higher than that of the dimethacrylate monomers and followed the order: HDDA (1,6-hexanediol diacrylate)>HEA-C18>EHMA-C18∼HEMA-C18>MHMA-C18. The total conversions obtained were 78, 75, 72, 64 and 69% for MHMA-C18, EHMA-C18, HEMA-C18, HEA-C18 and HDDA, respectively, indicating comparable or higher conversions for methacrylates despite their lower rates of polymerization. Propagation and termination mechanisms of the monomers were investigated by plotting propagation and termination rate constants as a function of conversion.     

甲基丙烯酸改性聚醋酸乙烯乳液胶粘剂研究

采用半连续种子乳液聚合法,以甲基丙烯酸（MAA）为功能性单体,考查MAA的加入量、加入方式和中和度对乳液耐水性能的影响,合成了醋酸乙烯／叔碳酸乙烯酯／甲基丙烯酸（VAc／Veova10／MAA）三元共聚乳液。改性共聚乳液干强度为951MPa,湿强度为377MPa,吸水性为47．0％。电导滴定法分析MAA共聚后,部分竣基基团分布于乳胶粒子表面。提高乳液的耐水性能;扫描电镜（SEM）观察乳胶颗粒分散均匀。合成的共聚乳液可用作木材胶粘剂。     

The effects of water soluble polymers on paper coating consolidation

The consolidation process of wet paper coating layers has been generally divided into several stages by the definitions of first critical concentration (FCC) and second critical concentration (SCC), however few works have been done on the kinetics of water expelled during drying and its influence on the critical concentrations. In this paper, the effects of three kinds of water soluble polymers, i.e., carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and modified coating starch, on the consolidation of model kaolin clay-latex coatings were investigated. On-line water evaporation loss rate, together with the level of FCC and time needed to reach FCC, was characterized. The results showed that water evaporation loss weight increased almost linearly with drying time during the initial wet coating layer consolidation stage. On-line water evaporation rate and the value of FCC decreased with water soluble polymers addition, while the time needed to reach FCC became longer. Among the three polymers studied, CMC was the most effective, then PVA and starch.     

Reactive wetting of amorphous silica by Sn0.3Ag0.7Cu-xTi (x = 1 and 3 wt.%) alloys at 800–900 °C

The wetting of SiO₂ by molten Sn_0.3Ag_0.7Cu(SAC)-xTi (x = 1 and 3 wt.%) was studied by using the modified sessile drop method at 800–900 °C under a high vacuum. The small addition of Ti into SAC alloy can improve wettability, significantly. Because the SnTi intermetallics with high melting point covered Ti addition and blocked further dissolution of Ti, and thus Ti cannot be dissolved completely when the nominal concentration of Ti was 3 wt.%. The reaction products at liquid/solid interface are Ti₅Si₃ and TiO. The spreading dynamics can be described by reaction product control model. The spreading may be coupled firstly with the precipitation of Ti₅Si₃ and TiO together meanwhile be affected by the dissolution of Ti addition, and then the precipitation of TiO alone. The final wettability was determined both by the wetting character of reaction products and also TiO adsorption at interface.     

Discussion on calculation of maximum water recovery in nanofiltration system

In desalination process, the effect of concentration factor (CF) and concentration polarization degree (CP degree) on water recovery in nanofiltration (NF) system displays a significant difference from that in reverse osmosis (RO) system due to their different salt rejections. In this work, the relationship between CF, salt rejection and water recovery was firstly discussed in a single NF element. In order to keep a stable performance, a spiral NF2 membrane was taken as an example, and water recovery for the single NF2 element should be about 25% instead of 15%, which is generally considered suitable for the single RO element. Then, the CP degree was calculated according to the theoretical model and experimental test, and the ultimate value was pointed out to be below 1.2. Thus, when calculating the scaling tendency of the sparingly soluble salts, the salt concentration near the membrane surface was recommended to be 1.15 times as high as that in bulk solution. Finally, a calculation method for maximum recovery was proposed for NF system. Because of the varied rejection with different NF membranes for the same feed water, which is significantly different from that in RO system, the pre-test is very necessary for NF system design.     

The effect of curing temperature on thermal,physical and mechanical characteristics of two types of adhesives for aerospace structures

The effects of cure temperatures on the thermal, physical and mechanical characteristics of two types of thermosetting structural epoxy film adhesives were determined in detail. The aim of this paper is to assess the effect of cure temperatures (82–121 °C) on the degree of cure of the two adhesives and the relevant void formations that need to be addressed in bonded part production and repair. Two thermal parameters were used to characterize the advancement of the reaction, such as degree of cure and glass transition temperature. The joint properties with respect to the cure temperatures were characterized by void content and bond-line thickness measurements and lap shear strength tests. Experimental results presented that all lap shear strengths were well within minimum shear strength (29 MPa) required by the specification of the film-type adhesive. However, the lap shear strength testing after aging at 82 °C and 95%R.H for 1000 h showed that the improved durability when the adhesive is cured at 121 °C did not occur for the 82 °C cure. Low curing conversion (75–77% degree of cure) combined with high voids (over 2 areal%) has a catastrophic effect on the bonding qualities at the metal-adhesive interface and due to lack of cohesion in the adhesive. The changes in the interface caused by the low temperature curing may contribute to an increased susceptibility of the bonded joint to moisture and consequent bond-line degradation.     

Hydrogenation of C=C and C=O groups on ruthenium-tin catalysts

The effect of addition of tin on the catalytic activity of Ru/C catalysts has been investigated in the liquid phase hydrogenation of -methylstyrene and hydrocinnamaldehyde. On increasing the Sn content, the amount of CO chemisorbed decreases, indicating a decrease in the number of Ru surface atoms. In the hydrogenation of -methylstyrene the specific activity of Ru (calculated per Ru surface atom) remains constant regardless of the Sn/Ru ratio. An increase of specific activity is however observed in the hydrogenation of hydrocinnamaldehyde. It is suggested that tin, present mainly as Sn ions, enhances the reactivity of the C=O group.     

芳烃装置水系统优化操作的研究

对吉林石化公司芳烃装置抽提单元水系统的参数进行了优化,通过控制水洗比、降低回收塔真空度、回流比等操作,节约了溶剂,降低了消耗。     

Degree of conversion of a copolymer of an experimental monomer and methyl methacrylate for dental applications

The aim of this study was to determine the degree of double bond conversion of the copolymer of an experimental monomer and methyl methacrylate after photopolymerization. A mixture of an experimental monomer with four methacrylate groups and methyl methacrylate monomer (mass ratio 70 : 30) was polymerized by using various concentrations of light initiator system. The degree of conversion was determined with FTIR spectrometry. A photopolymerized 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloxypropoxy)‐ phenyl]propane/triethylene glycol dimethacrylate (mass ratio 40 : 60) copolymer was used as a control material for degree of conversion. The maximum degree of conversion for the experimental monomer/methyl methacrylate copolymer was 62% and was obtained with 2 wt % initiator concentration. It was comparable to that of the control polymer (64%). The results of this study suggest that the experimental monomer/methyl methacrylate system can be polymerized by light initiator system. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1908–1912, 2004     

Bonding effectiveness of different dentin conditions on etch-and-rinse mode of two universal adhesives: the confocal laser scanning and shear bond strength

The purpose of this study was to evaluate the shear bond strength and the morphological differences of adhesive/dentin interface of two one-step universal adhesives to dentin using different dentin-conditioning methods with etch-and-rinse mode. Ninety-six dentin specimens were randomly divided into two groups based on application of two adhesives and assigned to three subgroups according to different dentin conditioning (wet-bonding; air-dried; rewetting). After etching and rinsing, experimental dentin conditioning was conducted on the etched dentin specimens. All specimens were subjected to shear bond strength testing using a universal testing machine, and all data were statistically analyzed using two- way analysis of variance with Tukey’s post hoc test. All debonded specimens were examined for fracture pattern by scanning electron microscopy (SEM). Adjunctively, one specimen per group was prepared by the same processing and longitudinally sectioned. Then, the infiltration ability of adhesives into dentin was examined by observing the interface using confocal laser-scanning microscopy (CLSM). Wet and Rewet groups exhibited significantly higher shear bond strength than dry groups on the etch-and-rinse system, regardless of different adhesives. The bond strength between wet and rewet groups showed no significant difference in Tukey’s test. Analysis of failure surface using SEM showed that predominant failure patterns were mixed in both the wet-bonding group and dry-bonding group. CLSM presented that resin penetration into etched dentin was enhanced similarly in wet and rewet group. Application of rewetting agents on dried dentin increased the bonding performance of universal adhesives on etch-and-rinse mode.