Hygroscopic Coatings Control Surface White Discoloration of Peeled (Minimally Processed) Carrots During Storage

White discoloration on peeled carrots is partially due to surface dehydration which can be controlled with hygroscopic coatings: e.g., polyhydric alcohols and salt solutions. This study was performed at 2.5, 7.5, 10, and 15°C, using a model system controlling relative humidity at 33, 75 or 98% or a commercial system with low-density polyethylene (LDPE) plastic film bags. The moisture sorption properties of propylene glycol, sorbitol, glycerol and calcium chloride enabled them to keep the carrot surface moist and maintain a transparent surface layer through which the underlying orange color was visible. This effect was only observed at high relative humidities (e.g., 98% RH). Similar effects were observed on treated peeled carrots stored in LDPE bags. The moisturized appearance provided by the hygroscopic coatings during storage was effective at several different temperatures.     

HVOF coatings for heavy-wear, high-impact applications

The aircraft hookpoint used for an arrested landing is exposed to various forms of heavy wear and impact. Nowhere is this more true than training field landings, where the hookpoint is subjected to drag along a concrete runway for possibly thousands of feet while flying at high speeds and heavy downloads. After extensive screening, a series of materials were subjected to special impact tests and concrete wear tests. Ten coatings, applied by thermal spray, were selected for future arrestment testing on the basis of these results.     

Characterization of Lead Scandium Tantalate Ceramics Prepared by Precipitation Method

Precipitation and coating techniques that proved successful for lead scandium niobate were tried with lead scandium tantalate. The Ta₂O₅ did not prove to be a useful substrate for the precipitating carbonates, but the resulting fine-particle-size powder lowered the sintering temperature to 1375° with only 0.4 wt% PbO loss. Annealed samples showed shifts in the dielectric response and sharpening of infrared and X-ray diffraction patterns, but little development of super lattice.     

Silicon Carbide-Coated Boron Fibers

A study of a silicon carbide-coated boron fiber showed that it retained its room-temperature strength after being heated to 1000°C for 24 h in air. This fiber was consolidated successfully in a titanium matrix at 930°C without degradation, although previous results with another silicon carbide-coated boron fiber indicated that there might be a reaction problem at this temperature.     

Powder coatings technology: new developments at the turn of the century

The growth of the powder coating business is affected by the toxicological effects of the raw materials used in the coating formulation and the saturation of the present market for powder coatings, being limited to general metal applications only. This has a strong influence on the long-term research programmes at both raw materials suppliers and powder paint producers. In the last decade of the 20th century, we witness appearance of several new types of toxicologically-safe powder coating systems on the commercial scale. At the same time, there is strong evidence of efforts to penetrate new market fields where powder coatings are not typically used. This includes the markets for automotive clear top coatings, can and coil coatings, coatings for industrial wood, plastics and paper. The new developments in the chemistry of powder coatings are followed by changes and improvements in the production technology for powder coatings as well as developments of new application techniques. This paper summarises the research work on chemistry, production and application technology of powder coatings and tries to extrapolate the tendencies in the years to come in order to predict the achievements and the impacts on the paint industry.     

Mikrostruktur und Eigenschaften lichtbogengespritzter Schichten auf Eisenbasis

Microstructure and properties of Fe‐based wire arc sprayed coatings Innovative iron based feedstocks for wire arc spraying are a promising alternative for conventional carbide reinforced feedstocks for wear applications. Recently the main area of research is focused on improving the properties of deposited functional coatings by varying the wire composition. The influence on the crystalline structure and the dimension of the hard phases in the resulting microstructure is of particular interest in this context. The objective of the investigation is to produce coatings with an amorphous phase, submicron and nanocrystalline structure. The forming of the amorphous phase is influenced by high cooling rates of the molten and partly molten particles impinging on the substrate. Thus, the achieved coatings are characterized by high hardness as well as high corrosion and wear resistance. The present paper introduces iron based coatings produced by wire arc spraying. Due to the application of cored wires with a modified alloy composition the forming of an amorphous phase as well as a submicron‐ and nanocrystalline structure is promoted. The filling of the cored wires are based on FeB with a eutectic composition and is varied by adding Cr₃C₂, FeSi, FeCrC and AlMg. The adding of further elements like Cr, C, Si, Al and Mg should improve the forming of the amorphous phase. The deposited coatings are analyzed regarding to the resulting coating properties and phase composition in connection with the composition of the cored wires. XRD‐analysis’ proved that the Fe‐based coatings contain an amorphous phase.     

Influence of internal stress and extensibility on the exterior durability of wood coatings

Different types of coatings were characterised for: swelling by moisture, moisture permeability, elastic modulus and extensibility. These data were used to calculate maximum internal stress. Internal stress was also measured directly whilst changing temperature and humidity. The stress data were compared to cracking and flaking results in both natural and accelerated weathering tests. Results showed that high levels of stress occur if there is a difference in swelling between coating and wood. In most cases stress relaxation took place rapidly. Comparing maximum stress, extensibility and cracking, a good correlation between these data was found. The ratio between maximum stress and extensibility appeared to be a very good predictor for crack formation.     

Studies on the chemical, physical and mechanical properties of high-solids clearcoats prepared from hydroxyl-terminated isophthalate-based oligoesters and a melamine resin

A series of high-solids (solvent-free) clearcoats was prepared from hydroxyl-terminated isophthalate-based oligoesters and the hexakis(methoxymethylol)melamine resin (HMMM). The oligoesters, which were used as binders, were prepared via a transesterification reaction of dimethyl isophthalate (DI) under various molar ratios R (=mol ratio diols/diester) with a mixture of 1,6-hexanediol (HD) and 2-methyl-1,3-propanediol (MP). Mixtures of the two diols of different composition R_d (=mol ratio HD/MP), were used as well. An attempt was made to investigate and correlate the chemical, physical and mechanical properties of the formulated solvent-free clearcoats to: (a) the amount of the cross-linker (melamine resin); (b) the curing conditions (time and temperature); (c) the synthetic parameters applied in the preparation (via transesterification) of the oligoesters (e.g. excess of the diols in reaction with the DI and the molar ratio between the two diols, the species of the Lewis acid catalyst). The properties of all the new formulated high-solids clearcoats were compared to those of a reference clearcoat and their cross-linking was correlated to their chemical structure and composition as well as to their T_g values. It was found that the R and R_d values applied in the synthesis of the oligoesters (binders) significantly affected the performance of their corresponding clearcoats. More specifically, the clearcoats obtained from binders where 3<R<4, combined an enhanced processability, higher values of non-volatiles (80%) (lower VOC content) and better or comparable chemical, physical and mechanical properties (e.g. impact resistance, gasoline resistance, mar resistance, flexibility and pencil hardness) upon comparison to those of the reference clearcoat.     

Characterization of the wear behavior of thermal sprayed coatings

Friction and wear cause a reduction in quality and properties of materials, especially their surfaces. A wear test is a good method for estimating the wear of components and their durability. This article discusses some wear test methods and results of wear tests on thermal spray composite coatings (particle-and fiber-reinforced).     

Effects of polyvinylchloride films and edible starch coatings on quality aspects of refrigerated Brussels sprouts

To extend shelf life, the effects of polyvinylchloride film (PVC) and edible coatings on quality aspects of refrigerated Brussels sprouts were studied. Starch-based coatings were formulated using glycerol (G), sorbitol (S) or glycerol plus sunflower oil (O). Sprouts so treated as well as uncoated ones were placed on expanded polystyrene trays. Combinations of PVC and coatings (treatments named G-PVC, S-PVC and O-PVC) were also tested. Uncovered trays were maintained as controls. All packages were stored at 0 °C for 42 days and samples were removed every 14 days to determine commercial acceptability, weight loss, surface colour (of sprouts’ heads and bases) and texture. Sprouts in all treatments maintained optimum quality conditions over the first 14 days. At the end of storage, browning of cut zones and losses in weight and firmness were minimised in PVC-packaged sprouts, particularly in G-PVC. Therefore, PVC and G-PVC treatments were selected to evaluate some nutritional quality components. Ascorbic acid and total flavonoid contents remained almost constant while radical scavenging activity increased after 42 days of storage. Thus, PVC and G-PVC treatments showed the best performance for long-term refrigerated storage of Brussels sprouts.