Instrumented indentation testing of an epoxy adhesive used in automobile body assembling

Instrumented indentation has been used to investigate the mechanical properties of BETAMATE 1496 (R) Epoxy adhesive. The properties of the adhesive were analyzed by measuring its hardness and its Young`s modulus in samples extracted from six different positions of the front door of a commercial passenger vehicle in two phases of processing: after application of the adhesive in the door assembling (""pre-cured"" state) and after final cure in the painting oven (""cured"" state). Special attention was given to setting the optimal parameters (""creep"" time and unloading time step) for the instrumented indentation testing for the present application. Young`s modulus values around 1.1 +/- 0.2 GPa and hardness values around 0.15 +/- 0.05 GPa were obtained for all samples, irrespective of the variation of the indentation parameters in the testing procedure and of the relative position of the adhesive in the door frame in both states. (C) 2008 Elsevier Ltd. All rights reserved.

FiltekTM Silorane and FiltekTM Supreme XT resins: tissue reaction after subcutaneous implantation in isogenic mice

The aim of this study was to evaluate the tissue compatibility of a silorane-based resin system (FiltekTM Silorane) and a methacrylate-based nanoparticle resin (FiltekTM Supreme XT) after implantation in the subcutaneous connective tissue of isogenic mice. One hundred and thirty five male isogenic BALB/c mice were randomly assigned to 12 experimental and 3 control groups, according to the implanted material and the experimental period of 7, 21 and 63 days. At the end of each period, the animals were killed and the tubes with the surrounding tissues were removed and processed for microscopic analysis. Samples were subjected to a descriptive and a semi-quantitative analyses using a 4-point scoring system (0-3) to evaluate the collagen fiber formation and inflammatory infiltrate. Data were statistically analyzed using the Kruskal Wallis test (?=0.05). The results showed that there was no significant difference between the experimental and control groups considering the three evaluation periods (p>0.05). The silorane-based and the methacrylate-based nanoparticle resins presented similar tissue response to that of the empty tube (control group) after subcutaneous implantation in isogenic mice.

Mass loss of four commercially available heat-polymerized acrylic resins after toothbrushing with three different dentifrices

The association between a toothbrush and a dentifrice is the most used denture cleaning method. The purpose of this study was to evaluate the abrasiveness of specific and non-specific denture cleaning dentifrices on different heat-polymerized acrylic resins. Sixteen specimens (90x30x3mm) of each acrylic resin (QC-20, Lucitone 550, Clássico, Vipi-Cril) were prepared and randomly assigned to 4 groups: 1: control (distilled water), 2: Colgate, 3: Bonyplus and 4: Dentu-Creme. The specimens were subjected to simulated toothbrushing in an automatic brushing machine using 35,600 brush strokes for each specimen. Brushing abrasion run at a 200-g load with the specimens immersed in 2:1 dentifrice/water slurry. Specimens were reconditioned to constant mass and the mass loss (mg) was evaluated. Data were analyzed by 2-way ANOVA and Tukey's test (a=0.05). Analysis of dentifrices' abrasive particles was made by scanning electron microscopy. Colgate produced the greatest mass reduction (42.44 mg, p<0.05), followed by Dentu-Creme (33.60 mg). Bonyplus was the less abrasive (19.91 mg), similar to the control group (19.69 mg) (p>0.05). The mass loss values indicated that QC-20 (33.13 mg) and Lucitone 550 (33.05 mg) resins were less (p<0.05) resistant to abrasion than Clássico (26.04 mg) and Vipi-Cril (23.43 mg). In conclusion, Colgate produced the greatest abrasion. Specific dentifrices for dentures tend to cause less damage to acrylic resins.

Effect of repeated disinfections by microwave energy on the physical and mechanical properties of denture base acrylic resins

The present study evaluated the effect of repeated simulated microwave disinfection on physical and mechanical properties of Clássico, Onda-Cryl and QC-20 denture base acrylic resins. Aluminum patterns were included in metallic or plastic flasks with dental stone following the traditional packing method. The powder/liquid mixing ratio was established according to the manufacturer's instructions. After water-bath polymerization at 74ºC for 9 h, boiling water for 20 min or microwave energy at 900 W for 10 min, the specimens were deflasked after flask cooling and finished. Each specimen was immersed in 150 mL of distilled water and underwent 5 disinfection cycles in a microwave oven set at 650 W for 3 min. Non-disinfected and disinfected specimens were subjected to the following tets: Knoop hardness test was performed with 25 g load for 10 s, impact strength test was done using the Charpy system with 40 kpcm, and 3-point bending test (flexural strength) was performed at a crosshead speed of 0.5 mm/min until fracture. Data were analyzed statistically by ANOVA and Tukey's test (α= 0.05%). Repeated simulated microwave disinfections decreased the Knoop hardness of Clássico and Onda-Cryl resins and had no effect on the impact strength of QC-20. The flexural strength was similar for all tested resins.

Study of the surface hardness and modulus of elasticity of conventional and microwave-cured acrylic resins

The aim of this study was to evaluate the following acrylic resins: Clássico®, QC-20® and Lucitone®, recommended specifically for thermal polymerization, and Acron MC® and VIPI-WAVE®, made for polymerization by microwave energy. The resins were evaluated regarding their surface nanohardness and modulus of elasticity, while varying the polymerization time recommended by the manufacturer. They were also compared as to the presence of water absorbed by the samples. The technique used was nanoindentation, using the Nano Indenter XP®, MTS. According to an intra-group analysis, when using the polymerization time recommended by the manufacturer, a variation of 0.14 to 0.23 GPa for nanohardness and 2.61 to 3.73 GPa for modulus of elasticity was observed for the thermally polymerized resins. The variation for the resins made for polymerization by microwave energy was 0.15 to 0.22 GPa for nanohardness and 2.94 to 3.73 GPa for modulus of elasticity. The conclusion was that the Classico® resin presented higher nanohardness and higher modulus of elasticity values when compared to those of the same group, while Acron MC® presented the highest values for the same characteristics when compared to those of the same group. The water absorption evaluation showed that all the thermal polymerization resins, except for Lucitone®, presented significant nanohardness differences when submitted to dehydration or rehydration, while only Acron MC® presented no significant differences when submitted to a double polymerization time. Regarding the modulus of elasticity, it was observed that all the tested materials and products, except for Lucitone®, showed a significant increase in modulus of elasticity when submitted to a lack of hydration.

Flexural and diametral tensile strength of composite resins

This study evaluated the flexural strength (sf) and the diametral tensile strength (st) of light-cured composite resins, testing the hypothesis that there is a positive relation between these properties. Twenty specimens were fabricated for each material (Filtek Z250- 3M-Espe; AM- Amelogen, Ultradent; VE- Vit-l-escence, Ultradent; EX- Esthet-X, Dentsply/Caulk), following ISO 4049 and ANSI/ADA 27 specifications and the manufacturers’ instructions. For the st test, cylindrical shaped (4 mm x 6 mm) specimens (n = 10) were placed with their long axes perpendicular to the applied compressive load at a crosshead speed of 1.0 mm/min. The sf was measured using the 3-point bending test, in which bar shaped specimens (n = 10) were tested at a crosshead speed of 0.5 mm/min. Both tests were performed in a universal testing machine (EMIC 2000) recording the fracture load (N). Strength values (MPa) were calculated and statistically analyzed by ANOVA and Tukey (a = 0.05). The mean and standard deviation values (MPa) were Z250-45.06 ± 5.7; AM-35.61 ± 5.4; VE-34.45 ± 7.8; and EX-42.87 ± 6.6 for st; and Z250-126.52 ± 3.3; AM-87.75 ± 3.8; VE-104.66 ± 4.4; and EX-119.48 ± 2.1 for sf. EX and Z250 showed higher st and sf values than the other materials evaluated (p < 0.05), which followed a decreasing trend of mean values. The results confirmed the study hypothesis, showing a positive relation between the material properties examined.

The effect of using mixed initiator systems on the efficiency of photopolymerization of dental resins

A study was performed in order to determine the efficiency of the simultaneous use of the photoinitiators phenylpropanedione (PPD) and camphorquinone (CQ) in the polymerization of acrylic polymers and evaluate possible mechanisms leading to synergism or antagonism. It was found that efficiencies of both initiators taken individually are higher than that of their mixture, indicating that when both dyes are used simultaneously there will be an energy transfer from the more efficient initiator (CQ) to the less efficient one (PPD). Also, there was no proof of any reaction between the amine present in the CQ formulation and the PPD excited state.

Knoop microhardness and FT-Raman evaluation of composite resins: influence of opacity and photoactivation source

The aim of this study was to evaluate the degree of conversion by Knoop microhardness (KHN) and FT-Raman spectroscopy (FTIR) of one nanofilled (Filtek Supreme-3M-ESPE [FS]) and one microhybrid composite (Charisma-Heraeus-Kulzer [CH]), each with different opacities, namely enamel, dentin, and translucent, which were photo-activated by a quartz-tungsten-halogen lamp (QTH) and a light-emitting diode (LED). Resin was bulk inserted into a disc-shaped mold that was 2.0 mm thick and 4 mm in diameter, obtaining 10 samples per group. KHN and FTIR values were analyzed by two-way ANOVA and Tukey's tests (α = 0.05). Nanofilled resin activated by a LED presented higher microhardness values than samples activated by a QTH for dentin opacity (p < 0.05). The microhybrid resin showed no differences in KHN or FTIR values with different activation sources or opacity. The nanofilled dentin and enamel resins showed lower FTIR values than the translucent resin. The KHN values of the translucent resins were not influenced by the light source.

Clarification of a wheat straw-derived medium with ion-exchange resins for xylitol crystallization

BACKGROUND: Xylitol bioproduction from lignocellulosic residues comprises hydrolysis of the hemicellulose, detoxification of the hydrolysate, bioconversion of the xylose, and recovery of xylitol from the fermented hydrolysate. There are relatively few reports on xylitol recovery from fermented media. In the present study, ion-exchange resins were used to clarify a fermented wheat straw hemicellulosic hydrolysate, which was then vacuum-concentrated and submitted to cooling in the presence of ethanol for xylitol crystallization. RESULTS: Sequential adsorption into two anion-exchange resins (A-860S and A-500PS) promoted considerable reductions in the content of soluble by-products (up to 97.5%) and in medium coloration (99.5%). Vacuum concentration led to a dark-colored viscous solution that inhibited xylitol crystallization. This inhibition could be overcome by mixing the concentrated medium with a commercial xylitol solution. Such a strategy led to xylitol crystals with up to 95.9% purity. The crystallization yield (43.5%) was close to that observed when using commercial xylitol solution (51.4%). CONCLUSION: The experimental data demonstrate the feasibility of using ion-exchange resins followed by cooling in the presence of ethanol as a strategy to promote the fast recovery and purification of xylitol from hemicellulose-derived fermentation media. (c) 2008 Society of Chemical Industry.

Environment-friendly soy flour-based resins without formaldehyde

Glyoxalated soy flour adhesives for wood particleboard added with a much smaller proportion of glyoxalated lignin or tannin and without any addition of either formaldehyde or formaldehyde-based resin are shown to yield results satisfying the relevant standard specifications for interior wood boards. Adhesive resin formulations in which the total content of natural material is either 70 or 80% of the total resin solids content gave good results. The resins comprising 70% by weight of natural material can be used in a much lower proportion on wood chips and can afford pressing times fast enough to be significant under industrial panel pressing conditions. The best formulation of all the ones tried was the one based on glyoxalated precooked soy flour (SG), to which a condensed tannin was added in water solution and a polymeric isocyanate (pMDI), where the proportions of the components SG/T/pMDI was 54/16/30 by weight. (C) 2008 Wiley Periodicals, Inc.

Enzymatic synthesis of monoglycerides by esterification reaction using Penicillium camembertii lipase immobilized on epoxy SiO(2)-PVA composite

Glycerol-fatty acid esterification has been conducted with lipase from Penicillium camembertii lipase immobilized on epoxy SiO(2)-PVA in solvent-free media, with the major product being 1-monoglyceride, a useful food emulsifier. For a given set of initial conditions, the influence of reaction was measured in terms of product formation and selectivity using different fatty acids as acyl donors. Results were found to be relatively dependent of the chain length of the fatty acids, showing high specificity for both myristic and palmytic acids attaining final mixture that fulfills the requirements established by the World Health Organization to be used as food emulsifiers. (C) 2010 Elsevier B.V. All rights reserved.

Application of the essential work of fracture method in ranking the performance in service of high-density polyethylene resins employed in pressure pipes

High-density polyethylene resins have increasingly been used in the production of pipes for water- and gas-pressurized distribution systems and are expected to remain in service for several years, but they eventually fail prematurely by creep fracture. Usual standard methods used to rank resins in terms of their resistance to fracture are expensive and non-practical for quality control purposes, justifying the search for alternative methods. Essential work of fracture (EWF) method provides a relatively simple procedure to characterize the fracture behavior of ductile polymers, such as polyethylene resins. In the present work, six resins were analyzed using the EWF methodology. The results show that the plastic work dissipation factor, beta w(p), is the most reliable parameter to evaluate the performance. Attention must be given to specimen preparation that might result in excessive dispersion in the results, especially for the essential work of fracture w(e).

Synthesis, characterization, and bactericidal properties of composites based on crosslinked resins containing silver

Two different commercial crosslinked resins (Amberlite GT73 and Amberlite IRC748) were employed for anchoring silver. The -SH and -N(CH2COOH)2 groups, respectively, present on these resins were used for Ag+ chelation from an aqueous solution. The Ag+ ions were reduced with three different reductants: hydrazine, hydroxylamine, and formaldehyde (under an alkaline pH). The produced composites were characterized with thermogravimetry/differential thermogravimetry and scanning electron microscopy combined with a backscattered scanning electron detector. Energy-dispersive X-ray spectroscopy coupled to scanning electron microscopy allowed the observation of submicrometer particles of silver, and chemical microanalysis of emitted X-rays revealed the presence of metal on the internal and external surfaces of the composite microspheres. The amount of incorporated silver was determined by titration. The antibacterial activity of the silver/resin composites was determined toward 10(3)-10(7) cells/mL dilutions of the auxotrophic AB1157 Escherichia coli strain; the networks containing anchored submicrometer silver particles were completely bactericidal within a few minutes because of the combined action of silver and functional groups of the resins. (c) 2007 Wiley Periodicals, Inc.

Preparation and characterization of crosslinked resins containing ferrite particles

Micrometer-sized magnetic particles hosted on network material were successfully prepared by a simple chemical process (ion exchange followed by co-precipitation) from commercial styrene-divinylbenzene copolymers. Energy dispersive X-ray spectroscopy (EDS) coupled to scanning electron microscopy (SEM) allowed the observation of submicron particles. All the produced spherical beads have presented metallic particles (NiFe2O4, CuFe2O4, CoFe2O4, or MnFe2O4), either as isolated particles or agglomerates, located on their external and internal (within pores) The thermal stability of the composites, evaluated by thermogravimetric techniques, were found to be dependent on the amount of ferrite particles incorporated into them.

Synthesis, characterization and evaluation of phosphorylated resins in the removal of Pb(2+) from aqueous solutions

Phosphinic-derivative poly(styrene-co-divinylbenzene)-based on PS-DVB copolymers with different porosity degrees have been prepared by aromatic electrophilic substitution reaction using PCl(3)/AlCl(3) followed by base-promoted hydrolysis. The phosphorylation reaction was analyzed by infra-red spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetry (TG/DTG). In addition, the phosphorous content of the phosphorylated copolymers was determined by spectrophotometry using the method based on sodium molybdate reactant so that the extension of that modification could be assessed. The performance of the phosphorylated resins in the extraction of Pb(2+) from aqueous solutions in a batch system was also evaluated. The Pb(2+) content was determined by atomic absorption spectrometry (AAS). These materials presented excellent extraction capacity under the contact time of 30 min and pH 6.