Dynamic Mechanical Analysis of Amorphous-Phase Organization in Acrylic Polymers

Factors affecting polymer network organization were studied in highly crosslinked acrylics of the type used in dental adhesive resins. The variables tested were comonomer content and processing conditions. BisEMA (2,2,-bis[4-(2-methacryloyloxyethoxy)-phenyl]-propane) and BisEMA + TEGDMA (triethyleneglycol dimethacrylate) were cured with and without 25% comonomer. Comonomers had characteristics that are expected to influence intrachain organization in amorphous phases: TEGDMA, crosslinking; methyl methacrylate (MMA), monomer conversion; isobornyl methacrylate (IBM), low cure shrinkage; tetrahydrofurfuryl methacrylate (THFM), antiplasticization. Dynamic mechanical analysis temperature scans were run at 0.1 Hz 2h or 24h after ambient cure, or 24h postcure after heating at 75° or 125°C. After 24h, tan δ maxima occurred in ranges centering on approximately -30°, 75° and 150°C (T_g). Heating at 125°C nearly eliminated all peaks except T_g, reduced tan δ peaks and increased T_g by 0–14°. T_g increased in the order: TEGDMA>125°C>IBM>MMA>75°C>2h>24h>THFM. The ability to crosslink, and postcure heating at 125°C, were the more important factors found to increase intrachain organization in amine-promoted, unfilled BisEMA resins of the type used in dental sealants, luting cements and bulk-filling resin composite materials.     

An investigation of six- to eleven-year-old children with allergic disorders.

Compared 6-11 yr. old children with and without allergic reactions on their intellectual ability, academic performance, social interaction patterns, medical history, TAT responses, and scores on a number of other psychological tests. Placement in the allergic sample was determined by a medical history provided by the parents of each child. The allergic sample included 199 boys and 172 girls, while the nonallergic sample consisted of 419 boys and 400 girls. Results indicate that Ss who did not exhibit allergic reactions were otherwise healthier and were rated as superior on a number of academic, social, and emotional adjustment dimensions. Results are related to studies of psychosomatic children. (19 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of a difunctional oxirane and multifunctional acrylate interpenetrating polymer network composite system with antimicrobial properties

This research continued the development of a difunctional Oxirane and multifunctional Acrylate interpenetrating polymer network composite System (OASys) with antimicrobial properties. The effects of 4-Isopropyl-4′-methyldiphenyliodonium tetrakis (pentafluorophenyl) borate (Borate), hexamethylene diamine (HMDA) and N,N-dimethyl p-toluidine (DMPT) on OASys (Epalloy 5001:dipentaerythritol hexaacrylate) composite hardness, contact angle, monomer-to-polymer degree of conversion (DoC), mechanical properties, polymerization shrinkage, shrinkage stress, and antimicrobial properties were determined. Bis-GMA:TEGDMA composites were used as the control. OASys composites with 9 wt% Borate and 0.5 wt% DMPT or 1.5 wt% HMDA had comparable hardness, DoC's and polymerization shrinkages to controls, but had lower contact angles and mechanical properties. Additionally, OASys composites with 1.5 wt% HMDA had significantly less polymerization stress than controls and demonstrated significant antibacterial activity against Streptococcus mutans and Lactobacillus casei out to 3 months. With lower shrinkage stress and long-term antimicrobial activity, OASys composites look promising for increasing the clinical lifetime of dental composites, but improvements in mechanical properties are needed.     

Probabilistic prediction of minimum fatigue life behaviour in α + β titanium alloys

The objective of this work was to develop and demonstrate a probabilistic life prediction method for the prediction of minimum fatigue lives that are typically used in the design of fracture critical rotating turbine engine components. A Monte Carlo analysis was used to predict the variability in fatigue lives based on the distribution of microstructural features that lead to early crack initiation as well as the variability in small fatigue crack growth rates. Two titanium alloys, both with bimodal microstructures, were tested and analysed in this study. The distribution of critical microstructural features was calibrated based on test results and understanding of microstructure neighbourhood effects. Testing was conducted on both alloys and included both smooth and notched specimens. The predictions are presented and compared with the data for smooth and notch geometries for the various loading conditions. A parametric study was performed to identify the importance of several model inputs and to identify areas for future improvement.     

A comparison between robust z and 0.3-Logit Difference procedures in assessing stability of linking items for the Rasch model

There are at least two procedures to assess item difficulty stability in the Rasch model: robust z procedure and ".3 Logit Difference" procedure. The robust z procedure is a variation of the z statistic that reduces dependency on outliers. The ".3 Logit Difference" procedure is based on experiences in Rasch linking for tests developed by Harcourt. Both methods were applied to archival data from two large-scale South Carolina assessment programs: HSEE 1986/1987 and PACT 2004/2005.The results of the analysis showed the ".3 Logit Difference" procedure identifies slightly more stable items (2.6%) for all items under study. In addition, approximately 93% of all items under consideration were identically classified as stable or unstable for both procedures. This very high level of agreement between the two methods indicates that either procedure can be safely used to identify stable items for use in a common-item linking design. The advantage of the robust z procedure lies in its foundation of robust statistical inference. The procedure takes into account well-accepted models for identifying outliers and permits critical values set at a specified Type I error.     

Methods for predicting the quality of nylon 612 filament for use as a bristle material

Splaying and curling of bristles is a very important performance characteristic of nylon toothbrushes. For this reason, analytical methods are needed that correlate fundamental physical–chemical properties with the eventural development of bristle splaying. Differential scanning calorimetry, thermogravimetric analysis, and wide-angle X-ray diffraction were each found to identify subtle differences in nylon 612 filament that had been subjected to varying processing conditions during manufacture. These differences were found to be related to water absorption and crystalline perfection and could be correlated with the characteristics of toothbrush wear. From the results, it was concluded that these three methods can be used for quality control and research purposes to predict and to study end-use performance factors such as bristle splaying. © 1992 John Wiley & Sons, Inc.     

cis-5-Monoenoic fatty acids in some chenopodiaceae seed oils

Methyl esters from seed oils of four Chenopodiaceae species are unusual in that they contain methylcis-5-hexadecenoate (4.6–12%) and methyl 5-octadecenoate (1.1–1.2%). There are indications of small amounts of 18∶2^5,9 and 18∶3^{5, 9, 12} along with unsaturated acids commonly found in seed oils-oleic (14–21%), linoleic (53–57%) and linolenic (3.5–7.8%). Fatty acid composition of the oils was determined by gas chromatography, and positions of the double bonds were established by application of gas chromatography-mass spectrometry to the methoxylated methyl esters. N. Market. Nutr. Res. Div., ARS, USDA.     

Fracture toughness of zirconia nanoparticle-filled dental composites

The fracture toughness of dental composites containing zirconia nanoparticles dispersed in a bisphenol A glycol dimethacrylate-based monomer blend (GTE) was studied for several yttria contents. Three-point bend test bars with and without a notch were tested at ambient temperature to determine elastic modulus, flexure strength, and fracture toughness. The ZrO₂ nanoparticles increased the fracture toughness of the nanocomposites compared to previous results for the matrix and Schott glass-filled nanocomposites. X-ray diffraction analyses revealed mostly tetragonal ZrO₂ in the nanocomposites before and after testing, in agreement with a theoretical analysis. The enhancement in fracture toughness in ZrO₂-filled nanocomposites was caused mainly by the higher values of particle toughness and interface toughness in GTE/ZrO₂ compared to those of GTE/Schott glass nanocomposites.     

Pre-positioning planning for emergency response with service quality constraints

Pre-positioning of emergency supplies is a means for increasing preparedness for natural disasters. Key decisions in pre-positioning are the locations and capacities of emergency distribution centers, as well as allocations of inventories of multiple relief commodities to those distribution locations. The location and allocation decisions are complicated by uncertainty about if, or where, a natural disaster will occur. An earlier paper (Rawls and Turnquist 44:521–534, 2010) describes a stochastic mixed integer programming formulation to minimize expected costs (including penalties for unmet demand) in such a situation. This paper extends that model with additional service quality constraints. The added constraints ensure that the probability of meeting all demand is at least α, and that the demand is met with supplies whose average shipment distance is no greater than a specific limit. A case study using hurricane threats is used to illustrate the model and how the additional constraints modify the pre-positioning strategy.     

Structural and mechanical behavior of layered zirconium phosphonate as a distributed phase in polycaprolactone

Mixed‐surface octyl/methoxyundecyl α‐zirconium phosphonates (ZrPs) were investigated as distributed nanoscale fillers, in concentrations up to 50% w/w, for the purpose of increasing the elastic modulus and yield strength of polycaprolactone (PCL) without a meaningful reduction of its ductility. The volumetric nanoparticle loadings were estimated to be over 70% higher than those in nanocomposites with comparable weight fractions of nanoclay. The mechanical properties of the ZrP/PCL nanocomposite were evaluated with tensile, flexural, and dynamic mechanical testing methods. Nanocomposites containing 5% w/w ZrP showed significant increases in both the tensile yield stress and elastic modulus without any loss of ductility versus the unfilled polymer. Layer delamination from the ZrP tactoids was minimal. Kinetic barriers and the strong interlayer attraction between the ZrP surfaces limited intercalative penetration of the ZrP tactoids. ZrP loadings of 20% w/w or more resulted in the agglomeration of tactoids, leading to defect structures with a loss of strength and, at the highest loading, ductility. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009