Durability Of Resin Research Articles

Long-term durability of adhesive systems bonded to fresh amalgam

A strong durable resin bond to fresh amlgam is desired in composite-veneered amalgam restorations and in adhesive amalgam restorations. The purpose of this study was to evaluate the influence of long-term water storage on the durability of the shear bond strength of new adhesive systems bonded to fresh amalgam. Sixty cylindrical specimens composed of equal parts of amalgam and composite, with a layer of bonding material in between, were prepared for each adhesive system: All-Bond 2, Amalgambond Plus, High-Q-Bond, and Comspan. Specimens were divided into three subgroups and immersed in saline at 37°C for either 48 hours, 3 months, or 6 months. After the immersion period, specimens were thermocycled and subjected to shear bond strength testing. Shear bond strength of Comspan and High-Q-Bond adhesives did not deteriorate significantly during the 6-month experiment and maintained a mostly mixed mode of failure. All-Bond 2 and Amalgambond Plus adhesives exhibited deterioration of the shear bond strength as a function of immersion time and shifted from dominantly mixed mode of failure to totally adhesive (All-Bond 2) or mostly adhesive failure (Amalgambond Plus). Incubation in saline for long periods should be a standard test in evaluating the bond of new adhesive systems to fresh amalgam, whereas short exposure time to water might be misleading.

Mechanical Properties and Durability of Resins for Crown and Bridge

Mechanical Properties and Durability of Resins for Crown and Bridge

Studies of Fabric Wear

We have shown that it is possible to make fundamental studies of fabric/fabric self- abrasion using a simple laboratory cyclic abrader. Abrasive wear rate depends on the contact pressure between the fabrics and is also influenced by the direction of curvature in the abraded zone. A concave surface is abraded more than a convex one. The observed effect of curvature is attributed to the effective change in yam count for the yams that are perpendicular to the direction of the rubbing motion. We have also found that relaxation of tension between episodes of cyclic abrasion results in reduced wear. The results for three cotton fabrics, two of which had been treated with durable press resin formulations, were as we expected in that increased abrasion wear correlated with the level of treatment.

New Hydrolysis Method for Total Formaldehyde Analysis in Durable Press Resins or Resin-Treated Fabrics

Total formaldehyde was determined in durable press resins and resin-treated fabrics after hydrolysis in I N H2SO4 for one hour under reflux using chromotropic acid. This new hydrolysis technique gives total formaldehyde values that are closer to theoretical values and requires less time. The technique also results in higher formaldehyde values for THPOH-NH3-treated fabric and for THPS resin. Thus, the hydrolysis method may have wider applicability than durable press resins or resin- treated fabrics.

Fire Resistant Cotton Blends Without Fire Retardant Finish

Cotton, a modacrylic (SEF), and polyester fibers were ground, blended, and made into pads weighing the equivalent of 4.8 oz. per square yard. The pads were treated with a durable press resin (DMDHEU), Sb2O3 or a combination of the two. The purpose was to develop technology for producing fire resistant durable press cotton blend textiles without the use of fire retardant chemical finishes. The pads were analyzed with and without the finishes for ease of ignition, rate of burning in the horizontal position, and Oxygen Index (01). Cotton and cotton/PE blends easily ignited, readily burned and ex hibited low Ols. The presence of SEF had a highly significant effect on all of the fire resistant test results. DMDHEU, Sb2O3 or DMDHEU plus Sb2O3 increased fire resistance of cotton and all blends. Considerable fire resistance, as measured by ignition, rate of burning, and 01 was obtained by application of the durable press resin to cotton/SEF and cotton/SEF/PE blands.

Surface modification of synthetic textiles

Due to their hydrophobic nature, textiles composed of polyester fibers are prone to accumulate electrostatic charges and to retain oily stains. Retention of oils may also be paralleled by increased redeposition of particulate soils. Ilydrophilic surface finishes are known to be capable of improving these static and soiling properties. Such durable topical finishes are generally attained by modifying the fiber surface chemically, by depositing preformed polymers, or by forming insoluble polymers from appropriate monomers in situ the fiber, by grafting. Interfacial polymerization tciTjues —— similar to those suggested earlier for wool shrink— proofing -have been investigated in the present work to deposit polyamide, polyurea and polyurethane coatings on texturized woven polyester. The effect of the coating on soiling characteristics was found to be highly dependent on the specific monomers employed. The most significant improvements in soiling characteristics were obtained with a polyamide coating formed via the polycondensation of piperazine and adipoyl chloride. Soil release problems are associated not only with 100% polyester textiles, but also with polyester/cellulosic blends, especially those treated with durable press resins. Anionic copolymers, perfluoroacrylates containing hydrophilic segments and topical finishes composed of combinations of these are the most effective in enhancing the soil release properties of such blends. INTRODUCTION With the continued increase in the use of synthetic fibers and the introduction of easy-care cellulose and synthetic fiber/cellulose blends in the last fifteen years, many investigations have been crried out with the objective of obtaining a better understanding of the soiling and soil release behavior of textiles. Soiling problems on textiles generally arise from the unwanted accumulation of oily and/or particulate materials on the surfaces or interior of fibrous structures. The degree of soil removal during cleaning is a function of the substrate, soil, cleaning method and interactions between these. To achieve soil removal from textiles, the oily and particulate matter must not only be separated from the fiber, but must also be carried away from it in the wash liquor with minimum reattachment to fiber surfaces. Complete soil removal is hardly ever achieved in commercial or home cleaning operations (1). As little as 0.1-0.2% (by weight) of an oily soil is probably sufficient to form a thin layer covering most of the fiber surfaces, particularly on the relatively smooth synthetic fibers.

Stress analysis of mandibular partial dentures with bounded and free-end saddles

Efforts towards achieving durable resin–dentin bonds have been made for decades, including the understanding of the mechanisms underlying hybrid layer (HL) degradation, manufacturing of improved adhesive systems, as well as developing strategies for the preservation of the HL.This study critically discusses the available peer-reviewed research concerning the formation and preservation of the HL, the mechanisms that lead to the degradation of the HL as well as the strategies to prevent it.The degradation of the HL occurs through two main mechanisms: the enzymatic degradation of its collagen fibrils, and the leaching of the resin from the HL. They are enabled by residual unbound water between the denuded collagen fibrils, trapped at the bottom of the HL. Consequently, endogenous dentinal enzymes, such as the matrix metalloproteinases (MMPs) and cysteine cathepsins are activated and can degrade the denuded collagen matrix. Strategies for the preservation of the HL over time have been developed, and they entail the removal of the unbound water from the gaps between the collagen fibrils as well as different modes of silencing endogenous enzymatic activity.Although there are many more hurdles to be crossed in the field of adhesive dentistry, impressive progress has been achieved so far, and the vast amount of available research on the topic is an indicator of the importance of this matter and of the great efforts of researchers and dental material companies to reach a new level in the quality and longevity of resin–dentin bonds.

Weathering Durability of Cotton Fabrics Treated with APO-THPC Flame Retardant

The influence of APO/THPC mole ratio on durability of flame retarclancy, resin retention, and strength retention of treated cotton fabric was determined by means of natural and artificial weathering tests. In both types of weathering, the use of photo active dyes as a means of accelerating the tests was studied. APO/THPC mole ratios of 2 : 1-8; 1 gave greater durability of APO-THPC resin and flame retardancy than did the standard I : 1 ratio. Photoactive dyes accelerated outdoor weathering by as much as fivefold, without obscuring the effect of mole ratio on resin durability. Predyeing was more effective than afterdyeing in causing accelerated weathering. Increased APO/ THPC mole ratios also gave increased breaking strength retention during weathering of undyed fabric, but produced no improvement on dyed fabric. These effects also occurred in Weather-Ometer tests made in the presence and absence of photoactive dyes. The APO-Zn(BF4)2 flame-resistant, wash-wear finish showed improved weathering durability comparable to that obtained from high-mole ratios 'of APO/THPC. The chlorine content of APO-THPC-treated fabric was 81% to 96% of theory at all mole ratios of APO THPC, indicating at least two modes of copolymer formation. The rate at which phosphorus was lost from APO-THPC during weathering was generally equal to the rate of nitrogen loss, expressed in percentage losses/time. The APO-Zn(BF 4)2 finish lost phosphorus more rapidly than nitrogen, indicating a different mode of resin breakdown.

COATING AND COATINGS

Protective coatings resistant to atmospheric corrosion are usually dependent to some degree on organic finishes, and it is interesting to note how current research appears to be concerned more with improved application characteristics rather than fundamental changes in polymer composition. An opinion I have heard expressed frequently during the past year is that, as far as durability is concerned, we have probably reached an adequate level; after all, under normal circumstances a paint system on steel can be expected to last for up to ten years. While more durable resins are known, and could be extended to industrial use, optimum performance could be obtained only by an almost surgical control of application conditions unattainable except in the laboratory, and an essential feature of any industrial paint is tolerance to a wide range of application conditions.