Effect of polymerization protocol on the degree of conversion of photo- and dual-polymerized self-etch adhesives

This study investigated the effect of different polymerization protocols on the degree of conversion (DC%) of various photo-polymerized and dual-polymerized self-etch adhesive resins. Five different photo-polymerized (All-Bond Universal, Bisco; G-ænial Bond, GC; Futurabond M+ LC, VOCO; Single Bond Universal LC, 3M ESPE and Peak Universal Bond, Ultradent) and four dual-polymerized self-etch adhesives (Futurabond U, VOCO; Gradia Core SE, GC; Futurabond M+ DC, VOCO and Single Bond Universal DC, 3 M ESPE) were tested. All adhesives were applied on potassium bromide pellets (KBr) following the manufacturer’s instructions. The KBr pellets were divided into 10 experimental groups for the photo-polymerized adhesives and 12 experimental groups for the dual-polymerized adhesives according to the two levels of the study, Level 1: polymerization protocol and Level 2: adhesive system. For the photo-polymerized adhesives, the adhesives were polymerized either at 1 or 10 mm from the KBr pellets. For the photo-polymerized adhesives, the adhesives were photo-polymerized either at 1 or 10 mm distance or polymerized chemically. The DC% of the unpolymerized and polymerized adhesives was assessed using Fourier transform infrared spectroscopy. Data were analyzed using two-way ANOVA to evaluate the effect of polymerization protocol, adhesive system, and their interaction on the DC% of the self-etch adhesives. For the photo-polymerized and dual-polymerized adhesives, one-way ANOVA and Tukey HSD post hoc test was used to evaluate the effect of adhesive system within each polymerization protocol and the effect of polymerization protocol within each adhesive for the dual-polymerized adhesives (p = 0.05). Student t-test was used to compare the effect of polymerization distances within each photo-polymerized adhesive. For both photo- and dual-polymerized adhesives, the polymerization protocol and adhesive system had a significant effect on the DC (p = 0.000). The interaction between the two factors (polymerization protocol and adhesive system) revealed also a significant effect on the DC% of the different adhesives (p = 0.000). Polymerization distance of 1 mm showed significantly higher DC% compared to 10 mm distance. When the dual-polymerized adhesives were left to set chemically, they showed the lowest DC% among all polymerization protocols. DC varied depending on the chemical composition of the self-etch adhesives. The tip of the polymerization device should be positioned as close as possible to the surface to achieve higher DC% of the tested adhesives. Photo-polymerization of the dual-polymerized self-etch adhesives is a mandatory step to improve their DC.     

Poly 2-ethyl-2-oxazoline/microcrystalline cellulose composites for cultural heritage conservation: Mechanical characterization in dry and wet state and application as lining adhesives of canvas

The aim of this work is the investigation of the stabilizing effect of microcrystalline cellulose powder (MCC) on the mechanical performance of two commercial thermoplastic resins (Aquazol® 200 and Aquazol® 500) used as adhesives in the conservation of artworks. The two polymers, having different molecular weights, were melt-compounded and compression molded with various amounts of MCC (5–30 wt%). The mechanical response of the microcomposites under dry and wet (equilibrium at 23 °C and a R.H. 55%) conditions, was investigated. DMTA analysis showed an increase of the dynamic moduli and the glass transition temperature with the microfiller content more pronounced for conditioned samples over the dried ones, and a concurrent decrease of the thermal expansion coefficient. Creep tests showed that MCC caused an improvement of the creep stability (i.e. a reduction of the creep compliance) for both dried and conditioned samples. For wet samples, the simultaneous enhancement of the elastic modulus and the stress at break limited the embrittling effect detected for dried composites. These materials were applied as lining adhesive for oil paintings between two kinds of canvas an English linen and a woven polyester under environmental conditions at temperature of 23 °C and a relative humidity of 55%. Single-lap shear tests both in quasi-static and creep conditions confirmed the improvement of the dimensional stability provided by MCC with a reduction of the joint displacement and an increase of the adhesive strength as the filler content increases. Additionally, post-fracture optical microscope observations of the cross-sections of the adhesive area proved how MCC introduction did not change the fracture behavior of the neat adhesives.     

Study of the influence of reaction conditions on the degree of substitution,intrinsic viscosity,and yield of oxidized cellulose acetate by factorial experimental design

A half‐fraction, two‐level, four‐factor factorial experimental design was used to study the effects of the acetic anhydride concentration, reaction temperature, reaction time, and sulfuric acid concentration on the degree of substitution, intrinsic viscosity, and yield of oxidized cellulose acetate (OCA). Oxidized cellulose containing 20% (w/w) carboxylic acid was used as the starting material. The data were fitted by multiple regression analysis with SAS software. The correlation coefficients obtained from plots of the predicted and observed values for the degree of substitution, intrinsic viscosity, and yield were 0.985, 0.993, and 0.991, respectively. Residual normal plots of the regression models showed a linear relationship. Lenth and main‐factor‐effect plots revealed an increase in the degree of substitution of OCA with an increasing concentration of acetic anhydride. The latter had no effect on the intrinsic viscosity and yield of OCA. An increase in the reaction temperature led to an increase in the degree of substitution and a decrease in the intrinsic viscosity and yield of OCA. The influence of the reaction time on the degree of substitution and intrinsic viscosity followed a trend similar to that observed with the reaction temperature, but the yield of OCA was unaffected. Increasing the concentration of sulfuric acid reduced the degree of substitution, intrinsic viscosity, and yield of OCA. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 696–705, 2005     

The effect of degree of polymerization on the structure and properties of polyvinyl alcohol fibers with high strength and high modulus

Polyvinyl alcohol (PVA) fibers were prepared using PVA with different degree of polymerization (DP) under the same wet spinning process. The effect of the DP of PVA on the structures and properties of PVA and PVA fibers were studied by using nuclear magnetic resonance hydrogen spectroscopy (¹H-NMR), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimeter (DSC), thermo gravimetric analysis (TGA), and environmental scanning electron microscope (ESEM). The results showed that DP had little effect on the crystallinity and tacticity of PVA, but had a positive effect on melting temperature, and initial decomposition temperature of PVAs. The hot drawing ratio determined by the spinning process where the PVA fibers could be continuously collected without breaking. The drawing ratio was decreased with an increase of DP, resulting in an increase of the final fiber diameter. The PVA fibers with medium DP and medium size demonstrated high strength and high modulus, but relatively low breaking elongation. It suggested that high DP of PVA was not a guarantee of high strength and high modulus PVA fibers, but rather a primary structure factor. The fiber performance was determined by a comprehensive effect combining a variety of factors including polymer properties and spinning conditions. It provided a guideline for PVA fiber manufacture that the PVAs with different DP require different spinning processes to obtain optimal fiber performance.     

Radiation-induced cationic polymerization of vinyl ethers in solution: 3. The influence of monomer and solvent concentrations on the rate of polymerization of ethyl vinyl ether in ether solvent

The influence of the monomer concentration on the rate of propagation of the radiation-induced polymerization of super-dry ethyl vinyl ether has been examined in detail in two ether solvents, diethyl ether and diglyme, chosen for their different dielectric constants and their different abilities to solvate ions. Estimations of the rate of initiation and of the rate of termination have made possible the evaluation of the rate constants of polymerization. Very similar values were obtained in both ethers. Experiments were also performed in benzene-diglyme and diglyme-methylene chloride mixtures. The results are in good agreement with the previous studies, made in benzene and methylene dichloride, and confirm the important role of the solvation of the free propagating species concerning the reactivities observed in the radiation-induced polymerization of EVE in solution.     

The influence of conditioning and regeneration on the separation behaviour of rigid surface filters for the separation of particles from gases

Rigid ceramic filter media can be used for the separation of particles from gas streams at elevated temperatures. In order to characterize comparatively the separation behaviour of differently structured filter media over a multitude of filtration cycles, experiments were performed in a filter test rig. The filter test rig used is built in accordance with VDI guideline 3926 and equipped with a special type of optical particle counter, which has the advantage of measuring both the particle size and the particle concentration simultaneously and in situ on the clean gas side.

It is demonstrated that by far largest share of the particles reaches the clean gas as a result of the filter regeneration process. During the subsequent formation of the dust cake, the particle penetration is almost zero. The regeneration parameters, actually in essence only the tank pressure, possess the decisive influence on the separation behaviour. In the course of a filtration experiment, the number of particles reaching the clean gas reduces with the increasing number of filtration cycles due to the filter conditioning. The particles arriving in the clean gas during regeneration are extremely fine. The mean particle size is almost entirely independent of the regeneration conditions and the filter cycle number. The fine particulate emissions measured here are an anthropogenic source of particulate matter in ambient air. They have to be considered as relevant with respect to the new standards of ambient air quality (PM 10 and PM 2.5).

It is shown that membrane-coated ceramic filter media at identical operating conditions exhibit, as expected, a better separation and regeneration behaviour than fibrous ceramic, open-pored filter media. However, the advantages are at the expense of a 10 times higher pressure loss, which is essentially attributed to the membrane layer.     

Metal-free isotactic-specific radical polymerization of N-isopropylacrylamide with pyridine N-oxide derivatives: The effect of methyl substituents of pyridine N-oxide on the isotactic specificity and the proposed mechanism for the isotactic-specific radical polymerization

The radical polymerizations of N-isopropylacrylamide (NIPAAm) in chloroform at low temperatures in the presence of pyridine N-oxide (PNO) derivatives were investigated. It was found that the methylation at meta-positions of PNO improved the isotactic specificity induced by PNO, whereas the methylation at ortho-positions prevented the induction of the isotactic specificity. NMR analysis revealed that NIPAAm and PNO derivatives formed predominantly 2:1 complex through a hydrogen-bonding interaction. Furthermore, the induction of the isotactic specificity was attributed to the conformationally limited propagating radicals. Based on these findings, the mechanism of the isotactic-specific radical polymerization was discussed.     

The effect of non‐ideal mixing on the number of steady states and dynamic behaviour for autocatalytical reactions in a CSTR

In this paper, we analyze the concentration multiplicity and dynamic behavior for an autocatalytical reaction, A + R → (n + 1)R + products with an overall rate expression given by – γ_a= kc_a^pc_r^r(p > 0 and r > 0) in a imperfectly mixed (Cholette's model) CSTR. We proved that non‐ideal mixing had an effect on the number of steady states and dynamic behavior for the reaction orders r > 1 and r = 1. However, the above‐mentioned effect does not happen for the reaction order r < 1. Furthermore, a simulated example was used to demonstrate our results.     

The effect of kaolin properties on their behaviour in ceramic processing as illustrated by a range of kaolins from the Santa Cruz and Chubut Provinces, Patagonia (Argentina)

The Patagonian kaolins offer a wide set of origin of deposits, composition, mineral processing and ceramic properties, giving a rare opportunity for investigating the interdependence of mineralogy, chemical composition, particle size distribution, texture, and surface activity with their technological behaviour in sanitaryware and porcelain stoneware production. Plasticity is strictly dependent on surface activity, < 2 μm fraction and expandable clay minerals; slip rheology is affected by soluble salts and expandable clay minerals, but also by high specific surface or tubular halloysite. Kaolinite/halloysite play an opposite role versus smectite/interstratified I/S in slip casting and tile pressing: the former allow faster casting rates, while the latter improve powder flowability and mechanical strength. Kaolinite and quartz are beneficial for drying behaviour while high surface activity or expandable clay minerals increase significantly drying sensitivity. Firing behaviour is mainly affected by minor components supplying “fluxing” (i.e. iron, alkali and alkaline-earth) oxides. A great deal of technological parameters seem to be reasonably predicted by the surface activity of clays and especially the Methylene Blue index, which is the most reliable, simple and economic method to predict and control the ceramic response of kaolins and ball clays.     

Template removal in MCM-41 type materials by solvent extraction: Influence of the treatment on the textural properties of the material and the effect on its behaviour as catalyst for reducing tobacco smoking toxicity

In this work a series of MCM-41 catalysts have been prepared by eliminating the template by calcination and by different extraction treatments. The extracted samples were also calcined and aluminium ion exchanged. A hydrothermal stability test of the final materials has also been performed. N₂ adsorption isotherms, NH₃ thermal desorption, X-ray fluorescence, X-ray diffraction, ²⁷Al NMR and thermogravimetry of each material have been determined in order to establish the influence of the procedure used for template elimination on the physicochemical and textural properties of the material. Moreover, the ability of the different catalysts prepared for reducing the toxicity of the mainstream smoke evolved when cigarettes are smoked has been checked too. The results obtained show that the final properties of the catalyst depend noticeably on the experimental conditions used in the template extraction process (i.e., the solvent selected, the solvent:catalyst ratio, the temperature, the contact time and the number of successive extraction steps). Thus, the adequate selection of such conditions permits a material to be obtained with properties very similar to that of the calcined MCM-41 material. As a conclusion, the material showing the best properties, among the catalysts studied in this work, produces a mean reduction of the yield of the different compounds analyzed in the gases and in the condensed products retained in the filters and in the traps of around 35%, 75% and 45%, respectively, which are slightly higher than the values corresponding to the calcined MCM-41 used as reference (i.e., 25%, 56% and 40%, respectively). These reductions results in an increase of the amount of ashes of around 2 mg/cigarette due to the presence of the catalyst.     

Preparation and characterization of poly(o‐anisidine) with the influence of surfactants on stainless steel by electrochemical polymerization as a counter electrode for dye‐sensitized solar cells

Efficient fast electron transfer from counter electrode to an electrolyte is a key process during the operation of dye‐sensitized solar cells (DSSCs). We introduce a surfactants assisted electro‐polymerized poly(o‐anisidine) (POA) counter electrodes (CE) for DSSCs. Commencing the electrochemical impedance spectroscopy, the POA/sodium dodecyl sulphate (SDS) CE exhibited very low series and charge‐transfer resistance. This is due to high electrocatalytic activity confirmed by cyclic voltammetry, surface area and the conductivity of the stainless steel film. The photovoltaic performance of POA/SDS counter electrode shows an energy conversion efficiency of 2.5% under 1 sun illumination. Short‐term stability test for POA/SDS point out that CE have almost uphold its initial performance. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42310.     

The effect of Nb2O5 and ZrO2 additions on the behaviour of Li/MgO and Li/Na/MgO catalysts for the oxidative coupling of methane

Incorporation of Nb₂O₅ or ZrO₂ into both Li/MgO and Li/Na/MgO systems produced ternary and quaternary catalysts, respectively, capable of attaining optimal C₂ yields and selectivities at lower temperatures relative to the unpromoted materials. The degree of enhancement effected by these metal oxide additives was compared to that produced by Li/MgO and Li/Na/MgO catalysts promoted with SnO₂ or Co₃O₄. At reaction temperatures < 700°C, the Li/Co/MgO ternary system showed marked differences in behaviour compared to the other ternary catalysts tested. This was particularly evident in the variation in C₂ selectivity with time on stream during ageing studies of (i) untreated materials, (ii) materials pretreated in CO₂, and (iii) materials dosed periodically with CHCI₃.     

The role of particle size on the electrochemical properties at 25 and at 55 °C of the LiCr0.2Ni0.4Mn1.4O4 spinel as 5 V-cathode materials for lithium-ion batteries

The role of the particle size on the electrochemical properties at 25 and at 55 °C of the LiCr_0.2Ni_0.4Mn_1.4O₄ spinel synthesized by combustion method has been determined. Samples with different particle size were obtained by heating the raw spinel from 700 to 1100 °C, for 1 h in air. X-ray diffraction patterns revealed that all the prepared materials are single-phase spinels. The main effect of the thermal treatment is the remarkable increase of the particles size from 60 to 3000 nm as determined by transmission electron microscopy. The electrochemical properties were determined at high discharge currents (1C rate) in two-electrode Li-cells. At 25 and at 55 °C, in spite of the great differences in particle size, the discharge capacity drained by all samples is similar (Q_dch ≈ 135 mAh g⁻¹). Instead, the cycling performances strongly change with the particle size. The spinels with Φ > 500 nm show better cycling stability at 25 and at 55 °C than those with Φ < 500 nm. The samples heated at 1000 and 1100 °C, with high potential (E ≈ 4.7 V), elevate capacity (Q ≈ 135 mAh g⁻¹), and remarkable cycling performances (capacity retention after 250 cycles >96%) are very attractive materials as 5V-cathodes for high-energy Li-ion batteries.