Microhardness Of Poly Research Articles

Removable partial or complete dentures exposed to beverages and mouthwashes: evaluation of microhardness and roughness

<title>Abstract</title><sec><title>Purpose</title><p>To evaluate microhardness and roughness of denture base polymethylmethacrylate resinn exposed to acid beverages and mouthwashes.</p></sec><sec><title>Material and method</title><p>Rectangular samples (n=80) were prepared from poly (methyl methacrylate) (PMMA). They were divided into 8 groups and had the initial microhardness and Knoop roughness measured. Samples of each group were immersed for 10 min into a test solution (coffee, lemon juice, chlorhexidine gluconate, red wine, cola-based soft drink, vinegar or antiseptic with and without alcohol) and after stored in artificial saliva for 23 h and 50 min, completing a period of 24 h. This procedure was performed for 14 consecutive days and after this period the microhardness and surface roughness measurements were made again. Data were statistically analyzed using ANOVA non parametric, Kruskal-Walis and the Dunn´s test for microhardness and the t-Student and ANOVA for roughness.</p></sec><sec><title>Result</title><p>For microhardness there were found statistically significant differences among the chlorhexidine gluconate solution, antiseptic without alcohol and cola-based soft drink. For roughness was observed that the mean values between the initial period and after immersion in the test products differed statistically in all groups, without difference among groups.</p></sec><sec><title>Conclusion</title><p>The microhardness of poly(methyl methacrylate) was affected by continue exposition to chlorhexidine gluconate, antiseptic without alcohol and cola-based soft drink. The roughness of poly(methyl methacrylate) is negatively influenced by the exposure to all tested products. It may be concluded that both, microhardness and roughness, were affected by the treatments.</p></sec>

Contribution of postpolymerization conditioning and storage environments to the mechanical properties of three interim restorative materials

Because polymer-based interim restorative materials are weak, even well-made restorations sometimes fail before the definitive restoration is ready for insertion. Therefore, knowing which fabrication procedures and service conditions affect mechanical properties is important, particularly over an extended period. The purpose of this study was to evaluate the effect of thermal treatment, surface sealing, thermocycling, storage media, storage temperature, and age on autopolymerizing poly(methylmethacrylate) and bis-acryl interim restorative materials. Outcome measures were flexural strength, Vickers surface microhardness, and impact strength. Flexural strength and microhardness of poly(methylmethacrylate) (Jet Acrylic) and 2 bis-acryl-composite resin (Protemp 3 Garant and Integrity) interim restorative materials were evaluated as affected by storage media, storage temperature, storage time, thermocycling, postpolymerization thermal treatment, or application of a surface sealer. In total, 2880 beam specimens (25×2×2 mm) were fabricated. Mechanical property analyses were made at 10 days, 30 days, 6 months, and 1 year after specimen preparation. Flexural strength was determined by using a 3-point bending test in a universal testing machine with a 1 kN load cell at a crosshead speed of 5.0 mm min(-1). Fracture specimens were recovered and used for determining Vickers microhardness. Measurements were made with a 0.1 N load and 15 second dwell time. Three microhardness measurements were made for each specimen, and the mean was used for reporting Vickers microhardness. Notched impact specimens (64×12.7×6.35 mm) were fabricated from Jet, Protemp 3 Garant, and Integrity interim restorative materials, yielding 288 impact specimens. Impact strengths were assessed at 10 days, 30 days, 6 months, and 1 year with a 2 J pendulum. The effects of the various experimental treatments were determined and rank ordered with analysis of variance, F ratios, and least square means differences Student t tests (α=.05). All experimental treatments investigated had significant effects on flexural strength, with material (P<.001) and thermocycling (P<.001) being dominant. Moreover, all experimental treatments investigated had a significant overall impact on Vickers microhardness with material (P<.001) and Palaseal glaze (P<.001) showing large effects. Material (P<.001) and age (P=.010) had a significant effect on impact strength. Mechanical properties of some interim polymeric materials can be improved by postpolymerization heat treatments or surface glazing. This procedure may extend the useful lifetime of some bis-acryl interim restorations.

Nanostructure of atmospheric and high-pressure crystallized poly(ethylene-2,6-naphthalate). Part II: structure–microhardness correlations

The microhardness of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN), with a detailed characterized nanostructure has been investigated. PEN samples were crystallized from the glassy state at atmospheric pressure and from the melt at high pressure and were characterized using small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC). Results show that the degree of crystallinity derived from WAXS, for both atmospheric and high-pressure crystallized PEN, is smaller than that obtained by density and calorimetry. For high-pressure crystallized samples, both, crystallinity and microhardness values are larger than those found for the material crystallized under atmospheric pressure. In the latter case, the hardness values depend on the volume fraction of lamellar stacks within spherulites X L that depends on the crystallization temperature T c. For T c<200 °C, X L is found to be less than 50%. Thus, for T c<200 °C a linear relationship between H and T c is observed provided a sufficiently long crystallization time is used. Results are discussed in terms of the rigid amorphous fraction that appears as a consequence of the molecular mobility restrictions due to the crystal stacks.

Structure development in poly(ethylene terephthalate) quenched from the melt at high cooling rates: X-ray scattering and microhardness study

The structure and microhardness of poly(ethylene terephthalate) (PET) cooled from the melt, using a wide range of cooling rates, was studied. PET thin films rapidly cooled from the melt (cooling rates larger than 5°C/s) show a continuous variation of structure and properties depending on cooling rate. Results highlight differences in the micro-mechanical properties of the glass suggesting the occurrence of amorphous structures with different degrees of internal chain ordering. The comparative X-ray scattering study of two glassy PET samples (7500 and 17°C/s) reveals the occurrence of frozen-in electron density states giving rise to an excess of scattering for the amorphous sample solidified at a lower cooling rate. The initial glassy structure and its evolution, during isothermal cold crystallization at 117°C of these two samples can be interpreted by assuming an improvement in the state of internal order. The differences in the incipient molecular ordering, which are detected by SAXS but not by WAXS, could be responsible for the hardening observed in the glassy PET samples.

Effect of sulfur mustard on microhardness of poly(ethylene terephthalate) films

The effect of sulfur mustard (SM), a well-known chemical warfare agent on the microhardness of two poly(ethylene terephthalate) (PET) films was investigated at different loads. SM induces hardness in PET films, perhaps due to an antiplasticizing effect. Heat treatment of the films enhanced their microhardness. The heat-set films show a further increase in their microhardness after exposure to SM. These results were supported by physicochemical techniques like plasma and amine etching, which revealed complex etching phenomena giving rise to a structure-specific pattern. The film having a higher weight loss due to plasma and amine etching showed lower microhardness. © 1996 John Wiley & Sons, Inc.

Effect of sulfur mustard on microhardness of poly(ethylene terephthalate) films

Effect of sulfur mustard on microhardness of poly(ethylene terephthalate) films

Radiation effects of an electron beam on the microhardness of poly(methyl methacrylate): Poly(chlorotrifluoroethylene) polyblends

AbstractSpecimens of poly(methyl methacrylate) (PMMA): poly(chlorotrifluoroethylene) (PCTFE) polyblends with different weight percentage ratios were subjected to electron beam irradiation (1–10 Mrad). The effect of irradiation on the strength of the blend specimens was studied by measuring the surface microhardness using a Vicker's microhardness tester attached to a Carl Zeiss NU 2 Universal research microscope. Significant changes were observed in the Vicker's hardness number, Hv. An irradiation dose of 3 Mrad was found to enhance greatly the microhardness level of the specimens. An increase of approximately 78% in microhardness was observed as the radiation dose was increased from 1 to 3 Mrad. Electron irradiation was also found to induce crosslinking and degradation in the material. The degree of crosslinking was found to be maximum at a dose of 3 Mrad. Specimens incorporating 10 wt% PCTFE were found to exhibit the highest level of microhardness at all radiation doses.

Optical absorption and microhardness of gamma irradiated poly(vinyl alcohol) doped with CuCl 2 and CrCl 3

The effect of γ-irradiation on the optical absorption and microhardness of poly(vinyl alcohol) (PVA) doped with different concentrations of copper chloride and chromium chloride were studied. The salts were added such that the total concentration was kept constant. For unirradiated samples, it was found that microhardness decreases as the copper content is increased. The samples were subjected to various doses of γ-rays (2, 4, 6, 8 and 10 MR), when it was found that the absorption spectra and microhardness are dependent on the radiation dose and the concentration of the two additives.

Influence of composition and molecular weights on the microhardness of poly(ethylene oxide)-isotactic poly(methyl methacrylate) blends

We show that Vickers micro-indentation is an experimental method that can reveal information about some structural features and the degree of intermixing in these systems